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STFC-RAL-CR03  R61: Not at Varna, I'm not Jonty, you may have noticed, but yeah, they are away at the moment, so it's myself and Deborah hosting today. We are very lucky to have Ben with us, Ben's an associate professor at the University of Plymouth in theoretical physics.

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STFC-RAL-CR03  R61: And is working on, laser particle stuff, and is here to talk to us today about that. So, yeah.

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STFC-RAL-CR03  R61: I have a seat.

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STFC-RAL-CR03  R61: So, hello, everybody. Thanks to the organizers for inviting me here. Although I've been…

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STFC-RAL-CR03  R61: kind of, associated with the Central Asia Facility for a long time. The theories have never actually been around before, so this is very exciting to me, for me to be in this place. I'm very happy to speak here today.

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STFC-RAL-CR03  R61: So I'm going to talk about science goals in laser particle interaction. So this is a bit of a synergy between particle physics and laser physics.

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STFC-RAL-CR03  R61: And I noticed, we're just sitting in the cafe. The cafe sits between the particle physics building, which is attached to the, central laser facility, so…

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STFC-RAL-CR03  R61: This is a perfect place to begin this kind of talk.

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STFC-RAL-CR03  R61: Okay, so begin with some

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STFC-RAL-CR03  R61: sort of kind of some key concepts in strong field Qvd quantum electrodynamics. That's going to be the fundamental theory that's going to describe what's happening in those interactions between charges and laser pulses.

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STFC-RAL-CR03  R61: And I want to spend a little bit of time talking about charge field coupling and intense electromagnetic backgrounds. I think that's something kind of unique to both particle physics that we haven't encountered before, so it might be interesting.

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STFC-RAL-CR03  R61: And then the second half, well, a little bit about, kind of…

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STFC-RAL-CR03  R61: measurements that you want to make at in different experiments and science goals of these. And then finally, talk about problem.

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STFC-RAL-CR03  R61: Okay, so just starting with some very basics, then. So we have a scattering paradigm of particle physics of having 2 bunches of particles in our in stage, which is well defined and understood.

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STFC-RAL-CR03  R61: We collide them, and we infer from measurements of the scattered particles that physics that occur during that potential.

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STFC-RAL-CR03  R61: Now, what we consider is a paradigm where we replace one of these beams of particles with an intense laser pulse.

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STFC-RAL-CR03  R61: So we have a probe beam, the electrons or positrons or photons, and we have a intense laser cost.

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STFC-RAL-CR03  R61: and we can perform the same kind of scattering experiments where what we tend to measure is what's happened to the protein.

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STFC-RAL-CR03  R61: infer from that the physics that occurred during that collision as the charges propagated through the membranes.

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STFC-RAL-CR03  R61: different to the particles. We don't normally, tend to measure what happens to the laser pulse because, we're interested in high intensities. High intensities, laser pulses are highly focused, which means that the shot-to-shot reproducibility is quite low. Instead, it's mainly the probability of the laser pulse. It's slightly different, but there's some

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STFC-RAL-CR03  R61: So talks about intense electromagnetic fields by saying that electromagnetic fields intense and

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STFC-RAL-CR03  R61: I'm intrinsically saying that the field is coherent.

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STFC-RAL-CR03  R61: So interesting coherence electromagnetic fields, that's quite important. So some examples are slowly varying magnetic fields, so in cavity experiments.

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STFC-RAL-CR03  R61: Pv. Mass or else we've got coherent fields the fields inside crystals with a high degree of symmetry. Well, in that case you've essentially got lots of Coulomb centers. But if you have a charge which is colliding with that, all those cool centers in the rest frame of the charge appear as a coherent field.

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STFC-RAL-CR03  R61: So the structure of QDL I'll talk about can be used to describe biphasic physics.

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STFC-RAL-CR03  R61: Beam beam scattering, so beam scrolling, at high plasma energies, for example, we'll look at heavy field. And what I'll talk about mainly from this point is laser pulses, so this could be optical laser pulses or x-ray free electrical

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STFC-RAL-CR03  R61: Coherence implies that the average expectation value of the electric field is zero. A counter example would be incoherent fields like black body radiation and strong or radiating gas jets where there's not a well-defined phase relationship between photons produced at different space time points. So incoherent fields like this, we expect that the

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STFC-RAL-CR03  R61: The expected filtering is up to 0.

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STFC-RAL-CR03  R61: So I mentioned strong field QED, what do we mean by stronger fields? We can come up with a, a QED field strength scale by taking some of the fundamental parameters from QED, so maybe electron mass, the constant charge, speed of light, and reduced bias constant.

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STFC-RAL-CR03  R61: Put them all together, using dimension analysis, come up with a field strength, and you get this form of FPM.

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STFC-RAL-CR03  R61: So this is sometimes referred to as the Schwinger limits, or crystal field. These are really bad names, because first of all, it wasn't Schwinger who first came up with this like this.

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STFC-RAL-CR03  R61: more than a decade before. I think we're already talking about this. Technically, it's not a limit. As you can see, we can go beyond this. Crystal field is also a bad name. There's no crystal phase transition that happens here, but people use these names, so I'm going to refer to the steel strength as the strength of the crystal field.

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STFC-RAL-CR03  R61: What's the kind of physics that can occur in a field of this strength? Imagine you've got a, a constant homogeneous electric field of this strength.

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STFC-RAL-CR03  R61: You can work out the work done by the seal at home and lateral, same in the seal.

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STFC-RAL-CR03  R61: You just take the charge of the electron field strength, and for the dimension of the electron, we take its contact wavelength.

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STFC-RAL-CR03  R61: And the work done by a few advocates.

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STFC-RAL-CR03  R61: and make one that was this intense would be the rest energy of the electrons. We expect that when we have field strengths of this order, we'll see Qd. Effects like creation of electron.

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STFC-RAL-CR03  R61: Can we see this in nature? Do you have this strong in astrophysics? It seems like we can. So this is just a part from this review of strongly magnified neutron stars, and what magnetic field strength they have.

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STFC-RAL-CR03  R61: So you can see on the top right there, the QED field time scale is showing a limit for magnetic fields around 10 to 13 gauss, and we see lots of data points beyond 10 to 13 gauss go up to 10 to 14, 10 to 15. This tends to be things like anomalous x-ray pulsars or sock and ray repeaters. So in nature we can see

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STFC-RAL-CR03  R61: fields which exceed the showing limits in the lab frame, albeit some magnetic fields not allowing it.

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STFC-RAL-CR03  R61: Can we see in the lab? Fortunately, with high-power lasers, we're not quite at the… the…

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STFC-RAL-CR03  R61: a level where we can produce these in the lab about 3 orders of magnitude away from, material limits with lasers.

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STFC-RAL-CR03  R61: So why, why are we talking about QED with lasers? Well, we use the standard trick, which is we consider gliding charges like electrons or positrons with a laser.

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STFC-RAL-CR03  R61: Then, in the rest frame of those charges, the field scene is noise boosted by the light scale factor.

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STFC-RAL-CR03  R61: So the faster the electron is that you can light the laser, the larger the field strength in the respirator. And this is just a nice cartoon from

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STFC-RAL-CR03  R61: from Jackson. This is the Coulomb field lines on an isolated charge, and this is what happens when you're in the horizontal direction. You have a bunching of the field lines to indicate the enhancing of the fields.

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STFC-RAL-CR03  R61: So how do we quantify this? I'm going to introduce a parameter, chi. It's going to occur quite a lot in the talk, so I'll spend some time defining it properly. So chi is the Stromfield parameter.

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STFC-RAL-CR03  R61: Well, it's just the projection of the…

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STFC-RAL-CR03  R61: Vertical momentum on the field strength tensor, normalized by the rest energy and the cubic field strength scale.

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STFC-RAL-CR03  R61: So what does that mean, physically? Well, if we choose our fields, our background field to be a plane wave, so we're going to be interested in lasers, so it makes sense to model our lasers in a plane wave.

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STFC-RAL-CR03  R61: Then this parameter is exactly the field seen in an electron rest frame in units of natural limits.

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STFC-RAL-CR03  R61: So,

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STFC-RAL-CR03  R61: we can come. We can again say, Oh, what kind of physics does that occur to? Does that correspond to?

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STFC-RAL-CR03  R61: we calculate the work done by this plane wave field in the rest of the electron, and what we get is that this is chi times MC squared, so obviously when chi is in order 1, we've got the

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STFC-RAL-CR03  R61: top of the Qd. Scale. That reason gold card.

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STFC-RAL-CR03  R61: focus on.

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STFC-RAL-CR03  R61: So getting to kind of order one experiment would be great. So I'll be kind of taking the odds in a later part of the experiment.

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STFC-RAL-CR03  R61: There are suggestions for getting to much higher values of this software parameter.

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STFC-RAL-CR03  R61: I'll just an example. So this is a few years ago, where they did a simulation of

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STFC-RAL-CR03  R61: beam scrolling for, two cerebral electron beams colliding with 125GB, and from their simulation, you can see here on the right, these regions of, I think, red, correspond to chi being the order of thousands, which, as we'll see later in the talk, is a significant value.

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STFC-RAL-CR03  R61: So next generation linear colliders. You could have

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STFC-RAL-CR03  R61: strong Qd. Effects, or whatever process.

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STFC-RAL-CR03  R61: Okay, so that's a little bit about what we mean by strong fields. I want to talk a little bit about the interaction between a charge and laser.

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STFC-RAL-CR03  R61: I'm going to specify for plain way, just for it's easier to explain.

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STFC-RAL-CR03  R61: So there's a little bit theory. Hopefully, it's it's

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STFC-RAL-CR03  R61: So this is the gate potential for the electronic background.

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STFC-RAL-CR03  R61: Alright, so it's…

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STFC-RAL-CR03  R61: the only important thing is psi. So M is the electron mass. This is the polarization background. This is just the shape of the laser pulse. Psi is something called the intensity character. The more intensely the laser pulse is that the higher the value of psi.

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STFC-RAL-CR03  R61: So what is science? It corresponds to physical.

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STFC-RAL-CR03  R61: So we consider a standard 2D process. I picked up the example of a photon colliding with a laser to use electron positron pair, and we can calculate the interaction of the pair with the background with the laser.

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STFC-RAL-CR03  R61: for example, having one interaction with the laser, represented by dashed lines, or having two interactions with the laser, n interactions, etc. We find that the amplitude scales with the size of the power n

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STFC-RAL-CR03  R61: That's kind of interesting, because normally in QED, N vertices scales with the standard QED coupling, the ultimate charge.

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STFC-RAL-CR03  R61: But here…

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STFC-RAL-CR03  R61: coupling is being replaced with the laser intensity. So the more intense we make the laser, the stronger, in some ways, we're binding the electron volatiles to the laser force. So actually, it looks like making more intense laser is actually changing the nature of the interaction.

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STFC-RAL-CR03  R61: There are other ways to understand this parameter. If we would look at, yeah, processes…

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STFC-RAL-CR03  R61: with n tracking to the laser. The probability scales like this square, so it would scale psi to n for n laser photons. Or in other words, psi squared to the power n.

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STFC-RAL-CR03  R61: So what is psi squared? Well, we can write it in terms of Alpha Qvd.

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STFC-RAL-CR03  R61: times a 3 volume to do with the laser wavelength and the quantum wavelength, and a total number density in the laser.

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STFC-RAL-CR03  R61: So in a very hand-waved way, the square of intensity parameter.

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STFC-RAL-CR03  R61: is… you need to find the number of interacting photons.

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STFC-RAL-CR03  R61: So the more intentionate the laser, the higher the number of photons in the laser interacting with the electron at any given time.

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STFC-RAL-CR03  R61: And it's going to be the next slide, number one.

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STFC-RAL-CR03  R61: And then you can't, truncate this perturbation series anymore. And you have to include all orders of interactions between the, the laser and the background. And so you would have this, you have to resum this.

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STFC-RAL-CR03  R61: So we refer to this as a non-perturbative interaction between the laser and the charge. This is a prediction of field theory, which we can test in experiments.

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STFC-RAL-CR03  R61: So we made the comparison with, non-saturation, small building X.

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STFC-RAL-CR03  R61: the analogy is because essentially estimating density higher, the number of charge characters getting sorry number of photons, essentially number of targets that the electron has when it interacts with the laser force gets larger and larger.

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STFC-RAL-CR03  R61: Yes, I mean, it's important calculations. We have to resolve this. And

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STFC-RAL-CR03  R61: So my background is as a theorist. I think most of your backgrounds is maybe an experimental simulation. So I have one slide of theory to explain how we do the calculation. So if you have any questions, then just drop me.

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STFC-RAL-CR03  R61: So how do we do this? This? Okay?

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STFC-RAL-CR03  R61: calculation for all of this. What we're gonna do is,

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STFC-RAL-CR03  R61: you know, calculate each order and then sum it up. That's too complicated. Instead, what we do is we, we split our, left potential for the laser into two parts. Well, not so laser, for the left and the left field into two parts.

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STFC-RAL-CR03  R61: One part is the laser. It's going to be a classical field because the laser is supposed to be in a coherent state. And the other part is the radiated field. So electron radiates photons, or maybe there's a loop effect to do with the electromagnetic field. That's the quantized part.

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STFC-RAL-CR03  R61: We take the standard.

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STFC-RAL-CR03  R61: the function of QED. So it's the three parts. This is, the three fields, this is the electromagnetic field, this is the three fermions, and this is the interaction. And now we split into two parts. We've got an interaction between

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STFC-RAL-CR03  R61: fermions on the laser, and between the fermions and the quantized field, the radiation field.

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STFC-RAL-CR03  R61: I would just rearrange this.

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STFC-RAL-CR03  R61: We move the interaction of the laser into the free part of the theory, and the consequence of that is that the equation of motion that we have to solve for the electrical potholes, i.e. the equation is modified by placing the potential of the laser inside the direct equation.

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STFC-RAL-CR03  R61: And that's the thing I could solve, or in order to include this interaction with the next tool.

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STFC-RAL-CR03  R61: orders. Now, we don't have many closed form solutions of the Dirk equation in a given algebraic background, but one of them

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STFC-RAL-CR03  R61: likewise we can solve for the recreation. Cool is playing life.

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STFC-RAL-CR03  R61: I'm using a plain way to model a laser. You might argue that a laser focus laser

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STFC-RAL-CR03  R61: That's right, but we're gonna use these solutions in a circular way, and then we'll have to describe what happens in

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STFC-RAL-CR03  R61: Okay, so the leading process that we'd have is just that single vertex. This is an example, not only a contents capturing, the electrode comes in, collides with the laser, produces a hard protocol.

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STFC-RAL-CR03  R61: The double line represents the fact that we're using this solution to the Dirk equation with the plane wave. It's a Volkov state. It's a Volkov electron.

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STFC-RAL-CR03  R61: And if we wanted to, we could expand this double line in interaction with the laser and look at what happened to it.

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STFC-RAL-CR03  R61: what interaction related to interaction related, etc. But we don't typically do that, because, first of all, size all at once, we need all orders, and secondly, we have the all-order solution, so there's no reason to be able to define it.

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STFC-RAL-CR03  R61: So this is, normal content scattering.

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STFC-RAL-CR03  R61: Oh, okay.

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STFC-RAL-CR03  R61: It might seem strange that the leading order process is this 3 byte function. So normally in Qd.

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STFC-RAL-CR03  R61: A vertex like this is kinematically suppressed, so it can't take place. The leading ordering queue needs one of the 2 vertices here, because you've got a laser field interacting with the electrons.

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STFC-RAL-CR03  R61: That's able to donate energy, momentum, or absorb energy momentum from this interaction. So that changes the usual kinematics. So that means there's a region of phase space for this collider.

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STFC-RAL-CR03  R61: That's why I leave all the presses just a single vertex

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STFC-RAL-CR03  R61: So this is a lot of content scattering. We already saw hand creation.

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STFC-RAL-CR03  R61: Typically, people use the word nonlinear to describe these to differentiate them from the standard Qd processes because of the nonlinear interaction between the laser background and the charge.

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STFC-RAL-CR03  R61: before we also have at leading order absorption processes like one photon annihilation or photon absorption. But we don't. We don't enter

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STFC-RAL-CR03  R61: I don't know that much, mainly because it's difficult in a laser port to bring electrical annihilates or to absorb photons, and the outgoing phase space is much smaller for these than it is for these.

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STFC-RAL-CR03  R61: So typically, these are the ones most interesting experiments.

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STFC-RAL-CR03  R61: We also have signals from loop processes, something like a mass operator. You can use your QED and just, contribute to the mass renormalization of the electron, but now people

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STFC-RAL-CR03  R61: the laser there, there's an experimental signal, so one of the signals of this, this interaction, for example, is the spin of the electron as it, as it collides with the laser can flip in a non-radiated way, so there's no virtual photon here, so it can flip. That's something that can be measured in…

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STFC-RAL-CR03  R61: Experiments, polarization operator, another example of a loop process where we have an experimental signal, here the signal is very similar, so it's a photon interacting with a virtual electron-photon pair, which is polarized by the laser, and the signal there is a change in the polarization of the photon.

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STFC-RAL-CR03  R61: So you might have heard of the vacuum birefringence. That's essentially the process that they're trying to measure in experiments like Pblas or high Beth, or what helps. And then we have vertex operator, which is less worth study because it's got 3 vertices. So it's a higher order.

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STFC-RAL-CR03  R61: But the principle we do have. So we'll see what's in that as

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STFC-RAL-CR03  R61: Okay, so that's a little bit about the background. I wanted to talk a bit about what people are looking for in experiments, because that's more accessible.

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STFC-RAL-CR03  R61: Okay.

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STFC-RAL-CR03  R61: So 2 instruments refer to this picture again.

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STFC-RAL-CR03  R61: it's obviously going to differentiate themselves by a different source for the strong field or a different source for the strong field.

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STFC-RAL-CR03  R61: Sorry for high violation of these.

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STFC-RAL-CR03  R61: my optical focus beam. So energy to the few Ev at the interaction point.

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STFC-RAL-CR03  R61: Actually, for electrolytes and presses in these row fields.

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STFC-RAL-CR03  R61: studies around kev or into crystals. So the Na. 63 experiment 7, for example, takes 2 Gv. Electrons from the Sps, lies them with orange crystals, and they enter crystalline field there.

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STFC-RAL-CR03  R61: also Coulomb fields. So splitting photons in Coulomb fields will change the scattering of photons in Coulomb fields.

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STFC-RAL-CR03  R61: It's an example. We talked about as well. And so that's a bit of context. So that's kind of the different strong fields that we could consider in terms of the probe beams.

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STFC-RAL-CR03  R61: doing experiments at high-power laser facilities, you… you want to have some particle beam. Unfortunately, typically a LINAC is not co-located with a high-power laser facility, so, acceleration of electrons needs to happen on-site, and so that's normally done by laser wakefield acceleration

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STFC-RAL-CR03  R61: Just jets.

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STFC-RAL-CR03  R61: That's for an electron probe. For a photon probe, you might combine them with a target to give a ramstone source of photons, or use a secondary weak laser to produce a helmet scatter source, or use crystal, or even thermal emission.

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STFC-RAL-CR03  R61: if you've not seen the… well, if you've seen LaserPoint before, you would have definitely seen a plot like this. Every LaserPoint has to have one in, which is explaining why we were interested in using lasers to produce the sound field. So on the horizontal axis, we've got the decade, and then on the vertical axis, we've got the…

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STFC-RAL-CR03  R61: The maximum intensity produced in a laser in that decade, so obviously lasers were invented around the 1960s, and various inventions have allowed to get to higher intensities. Higher intensities allow us to grow QED, more and more of these lasers.

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STFC-RAL-CR03  R61: Opcpa was the invention that led to the Nobel Prize in 2018. And this is this was actually slightly outdated now. But there'll be other data points here. So the point is that a lot of

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STFC-RAL-CR03  R61: money and investment is going into high power load facilities, because to be able to reach higher intensities allows us to do more interesting experiments. And so I was trying to make the argument in talks like this, that high power load facilities are a great place to do fundamental physics.

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STFC-RAL-CR03  R61: Okay, this is another plot which is similar of different laser facilities by decade. The only thing I want to point out here is the most recent laser facilities around here are accessing intensities where QED is a dominant effect in experiments. So you've got dynamics which are dominated by initial hot photons.

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STFC-RAL-CR03  R61: Here we've got avalanche type cascades, acuity cascades of producing photons.

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STFC-RAL-CR03  R61: Okay, I want to give an example of an all optical experiment before I talk about the particle physics side of things. I realized being here, I should really have talked about Gemini, since it's not very far away, but when I made the slides, I chose different later, so…

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STFC-RAL-CR03  R61: If you're doing that, so…

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STFC-RAL-CR03  R61: The one example of a lot to experiment is a recent coral flake facility. So it's the center for relative laser science in Gwangju in South Korea.

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STFC-RAL-CR03  R61: So, this is kind of a typical setup. You have, your main laser beam collides with a gas jet or a gas cell to ionize particles to deliver rate of electrons, which are then accelerated higher. There's a rate of acceleration apart from that main beam is then, peeled off and refocused through an interaction point.

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STFC-RAL-CR03  R61: After the acceleration.

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STFC-RAL-CR03  R61: And so here, this is the gliding laser. This is the tiny wave that was on the previous slide, and you have the electron beam coming in, and this is in this case they measured on the Compton scattering. They image the electron beam downstream using linux screens, and they separate the products of the reaction using magnets, and later the

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STFC-RAL-CR03  R61: For the photons, there is the LISO screen, which is a bit like,

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STFC-RAL-CR03  R61: I feel like that like tolerance.

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STFC-RAL-CR03  R61: This is an example of a laser wavefield spectrum. So typically, it has a narrow peak at energy.

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STFC-RAL-CR03  R61: Which is, of course, very, very good. The problem is there's quite a tail here, so the, if you want to do anything with precision, with laser waveguide, sorry, the beam is white, you have to take into account the fact that you've got this long tail, and that's not just a matter of oscilloscope.

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STFC-RAL-CR03  R61: The advantage of using isolated acceleration is that you can do acceleration on a very small scale. So you don't need to do much.

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STFC-RAL-CR03  R61: Sorry, sorry, I shouldn't bring it to the

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STFC-RAL-CR03  R61: But the shot to shot reproducibility is quite poor in general, though it's getting better. So if you want to build up statistics with collisions, it's difficult. Instead, simply you, you choose collisions which

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STFC-RAL-CR03  R61: where the electromagnetic overlap really well, and then you have a wire space.

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STFC-RAL-CR03  R61: So the corals experiment. Then they measured the total spectrum. So that's kind of the idea.

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STFC-RAL-CR03  R61: So it's good, agreement with, production from QED, just by way of…

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STFC-RAL-CR03  R61: referring to the parameters. So the intensity problem is 10.

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STFC-RAL-CR03  R61: And the strong QED parameter is not 1, but it's… it's 0.1, 0.3, I think the best that they got is 0.4

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STFC-RAL-CR03  R61: So it's good agreement spectrum down the tail. The agreement gets a little bit more difficult.

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STFC-RAL-CR03  R61: So…

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STFC-RAL-CR03  R61: This is a some parameter space for different experiments. And on the accounting scattering in the virus complexes, we've got the intensity. So that's the charge.

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STFC-RAL-CR03  R61: Yeah.

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STFC-RAL-CR03  R61: the kind towards the strong field project towards the diagonal line, and we get to higher strong field effects to get over here.

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STFC-RAL-CR03  R61: The vertical axis is the energy parameter. So it's to do with the center mass energy. It's only of the order of about point 1 point 0 1 for these experiments.

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STFC-RAL-CR03  R61: So you've got these series of experiments that we performed for the lasers where you're going to iron ion nonlinearity.

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STFC-RAL-CR03  R61: and then various experiments being various states are being commissioned, which will really push this to much higher bounds of the synthesis. So really look at really highly nonlinear interactions at the background. In contrast.

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STFC-RAL-CR03  R61: What about these experiments here? So, these guys here start at the bottom from the other side. They don't start with high power latency, they start with reaction.

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STFC-RAL-CR03  R61: Then they use a moderate laser in order to What's that?

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STFC-RAL-CR03  R61: Measure something through the effects. If it's something from the,

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STFC-RAL-CR03  R61: Slack, and Luxy is proposed that days, and I'll talk a bit more about Luxy in

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STFC-RAL-CR03  R61: So they have the advantage that they can go to higher energy. But they the so they can't probe this as much. But I'm going to make the argument that's fine also, because they've got a narrow band source of.

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STFC-RAL-CR03  R61: Electronics, so they can… The reproducibility of collisions is good, so you can know statistics in these

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STFC-RAL-CR03  R61: Just by way of interest, this kind of overlap between particle physics and laser physics, I think, is something that's attracting more and more people. Last year, we, participated in this exercise run by CERN every five years to,

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STFC-RAL-CR03  R61: So so there's an input to the European International Particle physics. We run such an example of

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STFC-RAL-CR03  R61: heads of groups of different places in Europe, and we had some some guest authors from outside of Europe. So these hypothesis.

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STFC-RAL-CR03  R61: But, you're not… laser physics is not quite as established as particle physics. Obviously, laser is much later than colliders, but…

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STFC-RAL-CR03  R61: it's slowly starting to consolidate, I think, into larger, larger groups.

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STFC-RAL-CR03  R61: So I want to talk about this looks experiment, because.

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STFC-RAL-CR03  R61: it's maybe more interesting for the part of this side. Also, you guys quite well represented. So looksy stands for laser on hexaphone experiment. And it's lazy.

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STFC-RAL-CR03  R61: and collaboration around other people at different institutions from the Uk. We've got Qb. Ucm, Manchester, and and the idea here is to use the electron beam that drives the Euxfl. So that's a 16.5 Gb. Electron beam.

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STFC-RAL-CR03  R61: and collide it with a laser. It currently has a 40 terawatt laser, but plans on a petrol laser before the end of the decade, and it's a similar kind of setup to what we saw in Carlos' experiment.

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STFC-RAL-CR03  R61: Downstream. Yeah, magnets just separate parts of the reaction. And

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STFC-RAL-CR03  R61: Separate them from the hygiene projects.

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STFC-RAL-CR03  R61: I'll give an example of what I think can bring to this field.

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STFC-RAL-CR03  R61: And that's, illustrated by this, this plot of the photon spectrum from one linear culture schedule.

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STFC-RAL-CR03  R61: By having a Linux, writing this, we have,

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STFC-RAL-CR03  R61: much narrower energy spread in our probe beam, which means that we can measure what's happening in our scatter total spectrum.

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STFC-RAL-CR03  R61: to a higher precision, just by being in statistics, but also by knowing what's the nature of the collision. Here's an example. So this is a log plot of the number of photons produced by crossing of the electron beam and the laser, mostly.

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STFC-RAL-CR03  R61: These are different intensity parameters.

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STFC-RAL-CR03  R61: What we see is for side order one, we see a harmonic edge here. This is due to the edge of the 1st harmonic interaction with laser. As we increase intensity, this harmonic edge gets washed out and it's redshifted.

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STFC-RAL-CR03  R61: Now, a lot of values are precise, it's high water volume, we see a very strong signal. By having a higher precision

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STFC-RAL-CR03  R61: probing, we can measure the position of this edge, which is much better access to what's going on in the physics than just how to do yields.

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STFC-RAL-CR03  R61: The position of this Compton edge, as it's called, is in both formulas. It's basically just a fraction of the photon energy.

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STFC-RAL-CR03  R61: by the electron amplitude. So 60.5 GB. Was the electron energy. So here it's around 3 GB.

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STFC-RAL-CR03  R61: He chose this energy parameter. It's not simple. It's not point 2.

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STFC-RAL-CR03  R61: Interesting thing is where the intensity comes. Remember, the excitement is the charge for your cup.

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STFC-RAL-CR03  R61: we can compare this with linear qvd. Within your qvd. We factor out positions where a lot of edges that's just given by Klein machine formula. That's kind of the textbook calculation.

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STFC-RAL-CR03  R61: the presence of the lasers introducing this, these nonlinear corrections.

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STFC-RAL-CR03  R61: And as we increase the intensity parameter, we're picking up more of the interaction related time and order.

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STFC-RAL-CR03  R61: So weight size in order one, then, we can't truncate this series anymore.

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STFC-RAL-CR03  R61: And instead, we have to include this interaction to all orders. So measuring the position of this edge as we change the intensity uses an experimental probe into this all order interaction predicted by our field theory.

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STFC-RAL-CR03  R61: An introduction to instructions will be, placed.

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STFC-RAL-CR03  R61: We could instead say, oh, okay, let's not look at the production of QED, let's look at the production of classical electrodynam

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STFC-RAL-CR03  R61: So I'll be normally at Thompson'

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STFC-RAL-CR03  R61: And again, we see a prediction of where this commodity change is and how it changes as we change the intensity.

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STFC-RAL-CR03  R61: So it's a leading order, which is up here. I factorized out a factor of H bar from this ether parameter to show that as we change the intensity, we're picking up factors of H bar. You're going more and more quantum, if you like.

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STFC-RAL-CR03  R61: And…

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STFC-RAL-CR03  R61: So one of the things I discovered is people really care about the difference between classical and quantum physics. So as you change intensity, you'll get more and more quantum corrections.

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STFC-RAL-CR03  R61: And so you can plot whether it comes to the edges as you change it, what the energy is as a function.

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STFC-RAL-CR03  R61: If size is small, it's really, really small. It's just linear. If size is too large, as you can see, size too large is just nonlinear classical physics. The interesting thing is happening around time order plan.

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STFC-RAL-CR03  R61: that's happening around here where we can differentiate some fields. Ud prediction from standard linear community.

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STFC-RAL-CR03  R61: So my message for stuff like this is, we really want higher precision over power.

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STFC-RAL-CR03  R61: It's great to have really powerful, but using magnets and particle physics, higher precision.

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STFC-RAL-CR03  R61: Building up statistics allows us to actually have a much better probe of dictionary statistics.

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STFC-RAL-CR03  R61: So we don't just want to measure electron laser collisions, we also want to measure photon laser collisions. So we generate a photon beam neutralizing an electron

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STFC-RAL-CR03  R61: being at a solid target, there's rents wrong, phone calls.

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STFC-RAL-CR03  R61: Or we could also peel off part of the laser to have a conference-scattered source of photons, which has the advantage that we have quite a high polarization grade, which allows us to do more studies of the theory.

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STFC-RAL-CR03  R61: We'll be at the cost that we have much more energy.

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STFC-RAL-CR03  R61: I'm also considering using a crystal radiator.

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STFC-RAL-CR03  R61: So, like, structure target. Essentially, you can go here and grab a strong one, and it

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STFC-RAL-CR03  R61: kind of narrow bandish source photons.

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STFC-RAL-CR03  R61: So what's the signal for collision? So we've seen already. It's a pair creation.

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STFC-RAL-CR03  R61: So the thing about this process of pair creation, is if you take a single laser photon, and you take the hydrogen photons that we produce from that source, the center of mass energy is too low to create a pair.

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STFC-RAL-CR03  R61: You have to consider quite, a large number of those kind of things before you get to the threshold where you create a pair.

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STFC-RAL-CR03  R61: So if it looks like that comes to you, I'm

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STFC-RAL-CR03  R61: That means that alternative signal leading order and the example scales with size of power. 23.

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STFC-RAL-CR03  R61: the yield of pairs. The folks are obviously colliding with the laser. If we just had

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STFC-RAL-CR03  R61: mainly Qvd. But leading order. Qvd, this is currently now.

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STFC-RAL-CR03  R61: But as we increase time, we have to include higher and higher orders, because obviously, this is a series of size more than one. We have to include more orders.

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STFC-RAL-CR03  R61: And the result of that is actually suppression preparation.

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STFC-RAL-CR03  R61: and this curve here, and this turning of the curve away from the the interpretive, but highly nonlinear prediction is our signal of this one forward interaction between the charge in the background will be now preparation, which is a fully quantum process.

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STFC-RAL-CR03  R61: We're a former company, so we'll talk more.

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STFC-RAL-CR03  R61: Okay, so these are just legal processes. We also want to look at higher order processes. For example, Compton showers, you can imagine your electron being close to the laser, and you can get more than one photon.

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STFC-RAL-CR03  R61: Now, something's a bit different in interaction with laser pulses than in particle beams. In particle beams, if you have two energetic beams colliding, from a rest frame of one beam, it looks like the other beam is relativistically concave, right? The longitudinal direction will get relatively contracted.

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STFC-RAL-CR03  R61: But here, we don't have a hyperlink that we're riding with, we're riding against a focus license, which doesn't run through a city contract.

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STFC-RAL-CR03  R61: So the consequence of that is that the longitudinal scale of the laser pulse allows for much higher orders of emission.

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STFC-RAL-CR03  R61: And so you consider a high order process like this. The propagator has a virtual virtual parts and real parts.

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STFC-RAL-CR03  R61: Just like in terms of relation with virtual power, can't propagate very far.

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STFC-RAL-CR03  R61: So that means that high order processes like this are dominated by the propagated unreal. So here, for example, electron make a photon, then the unreal propagates like a normal electron.

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STFC-RAL-CR03  R61: This is kind of a standard approximation that we use to calculate higher order processes.

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STFC-RAL-CR03  R61: So here's just an example of…

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STFC-RAL-CR03  R61: simulation. This is for 80 electrons a cylinder, or we could have it. And this is using the Tarnigan open source simulation code which has been developed by Tom Blackburn at the University of Gothenburg.

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STFC-RAL-CR03  R61: So what we see is Type II. I'm able to use my different groups of people doing the same thing. Type II for our electrons on Earth.

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STFC-RAL-CR03  R61: average. The most expected thing to happen is that they don't make any kind of money.

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STFC-RAL-CR03  R61: as we increase time. So, for example, 7.5, it's most likely that each electron emits an average 2 phases.

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STFC-RAL-CR03  R61: So even though the second order process here is more probable than the leading order process, it's still preserved.

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STFC-RAL-CR03  R61: However, it's been known for a while that there's an exception to this, and this happens if we

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STFC-RAL-CR03  R61: Imagine that we have this swing through prototype. Imagine we can make it really large.

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STFC-RAL-CR03  R61: And what happens to these three-level processes, like one with the comp and one with the right wheeler, is that, in the large time limit, they scale as other community postcodes to two-thirds.

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STFC-RAL-CR03  R61: Now, this is significant, because you can ask the question, well, what if we could reduce 5 order of 1,000? We saw the poses for doing that already in the lab. What would that mean about this unique function?

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STFC-RAL-CR03  R61: Well, if I were order 1,000, I'm counting as order one.

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STFC-RAL-CR03  R61: What that means is that this kind of conservative series here is not something that we could truncate. We could have the situation where we could just say, Oh, we just stop our 6 phones or whatever.

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STFC-RAL-CR03  R61: Instead, if we had such an intense background of time so large, that would mean we'd have to include all orders of interaction, not just the laser, but also all orders of emission.

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STFC-RAL-CR03  R61: And so some people say that Judy.

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STFC-RAL-CR03  R61: I'm strongly troubled when we have such an intense field.

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STFC-RAL-CR03  R61: Now, it's not just the tree level diagrams. It's also loops. So polarization operator and electron bus operators go like Alpha Chi 2 slice.

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STFC-RAL-CR03  R61: Typically, in calculations, we don't really include,

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STFC-RAL-CR03  R61: Related to corrections, because, as we saw, things are dominated by things being real.

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STFC-RAL-CR03  R61: So if we had alpha kinds of 2 thirds, not only would we have to include them, but again, we'd have to include loops

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STFC-RAL-CR03  R61: There's a nice series of papers in the 70s and 80s, where they calculated loops of higher order, and they go all the way up to 3 loop, and they found that the divergence with Kai's strongest 4 chains of

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STFC-RAL-CR03  R61: Organization operates on several global diagrams.

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STFC-RAL-CR03  R61: And so there's a conjecture called the conjecture that if we have a very intense field. So if the field is locally constant and it's playing away in nature.

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STFC-RAL-CR03  R61: The true expansion price of duty isn't up to community, but it's held by county

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STFC-RAL-CR03  R61: Okay, so just to kind of underline that fact, because I think it's kind of interesting, maybe not so well known.

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STFC-RAL-CR03  R61: It's not a community. We've got a process of N vertices that goes like other community to our ends and probability.

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STFC-RAL-CR03  R61: To get more and more accurate tests, we include radiative corrections, so loops, a high value, high-pass alpha, and this particular series is the thing that's being tested really well, and people say that QED is the best

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STFC-RAL-CR03  R61: test. It's one of my theory of of nudge. It's things like G minus 2 experiments.

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STFC-RAL-CR03  R61: What I've mainly been talking about is when we have an intense labels, these functions that have been functions of the intensity parameter. And as the load is made more intense.

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STFC-RAL-CR03  R61: This shifts the importance of those. The leading process that's going to be dominant.

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STFC-RAL-CR03  R61: What we're saying now with this is the high value regime. We don't know what we can't expand like this. We have to include all orders of this. So we won't be able to write down. So I think it's quite compelling that

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STFC-RAL-CR03  R61: There's a region of Qd. Where we get absolute calculations. So we really need input for expiring.

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STFC-RAL-CR03  R61: That brings us to the final topic of regulation reaction.

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STFC-RAL-CR03  R61: So radiation reaction is a very old topic, going all the way back to people like Lawrence and Abraham, and

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STFC-RAL-CR03  R61: But it's a general question of what do you do when the field is so intense that the radiation affects the trajectory of your charges.

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STFC-RAL-CR03  R61: So I'm gonna talk about it classically first, st and then put a little bit back in the week.

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STFC-RAL-CR03  R61: So if I ask you to calculate the radiation produced by electron when it arrives from laser.

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STFC-RAL-CR03  R61: How do you do that? Well, in undergraduate at some point, we know you can solve the Lorenz equation. This is the Lorenz equation by random variables.

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STFC-RAL-CR03  R61: But…

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STFC-RAL-CR03  R61: we use that to get trajectory, and then using trajectory that produces a current which we use the wave motion to get that radiation.

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STFC-RAL-CR03  R61: But immediately we see a problem that to solve the 1st line for the trajectory, we need to know the radiation to solve the radiation in the trajectory.

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STFC-RAL-CR03  R61: So it's really hard to solve this coupled set of higher order nonlinearity groups. They want to be learned in undergraduate physics, but we do it for them.

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STFC-RAL-CR03  R61: suppose we use the potential against 2 parts. The intensifier is the laser or the radiation field can use classically as well.

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STFC-RAL-CR03  R61: The laser interaction isn't E, so this factor of E is being absorbed there, in case you think I forgot the factor of E there.

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STFC-RAL-CR03  R61: Then you say, Oh, that's very intense. The radiation is going weak. So

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STFC-RAL-CR03  R61: And I also think that's on Zoom Excuse me, by this time.

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STFC-RAL-CR03  R61: we put the laser into the wave equation, we solve for the trajectory of the electron and laser, and we use that trajectory in the wave equation to calculate what radiation the electron uses.

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STFC-RAL-CR03  R61: Hopefully you have time to get our meeting in 5 min. So it just rolls over.

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STFC-RAL-CR03  R61: I was too confused with my computer, and that's gonna be up. So I'll tell you that I

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STFC-RAL-CR03  R61: Okay, thanks for the explanation. So,

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STFC-RAL-CR03  R61: Yeah, so imagine we do that, fine, but imagine now that the radiation reduces intense or there's a lot of it or this interaction happens for a very long time. Then you need to get the higher order, so you need to take that radiated field and then you need to plug it back into the equation of motion for the Lawrence equation. I need to solve for the early trajectory, take into account the fact that the radiated

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STFC-RAL-CR03  R61: Oh, we do.

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STFC-RAL-CR03  R61: field has effects on the direction of the electron.

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STFC-RAL-CR03  R61: So you solve that for a new trajectory, and then you put that into your weight equation and get a density correction for the radiation, and you continue doing this until you have a pair of equations. And if this effect was very strong, you'd have to include all of these, and we've solved them.

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STFC-RAL-CR03  R61: Now,

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STFC-RAL-CR03  R61: I'm gonna go through that. If you if you do that resummation procedure, you end up with something called the Lawrence Hayden-Hamburg equation. And

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STFC-RAL-CR03  R61: just easier to talk about an approximation to that that we use describe what happens with electrons.

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STFC-RAL-CR03  R61: plugging with, Microsoft Lambda versus Cohesion.

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STFC-RAL-CR03  R61: So here we have the lowest equation gain over in F. And this is a powerless plasma radiation reactor. So we see it's nonlinear in the laser field. That's normally involved. And it's got our radiation reaction parameter.

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STFC-RAL-CR03  R61: You slow down, sir.

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STFC-RAL-CR03  R61: Okay, so we solved this something close to all, not always, but we can solve in a family background. And that's great, because we want to look at lasers.

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STFC-RAL-CR03  R61: And one of the predictions of that is the following. If you calculate the

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STFC-RAL-CR03  R61: the momentum of the electron after it scatters with the laser in the same way.

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STFC-RAL-CR03  R61: as a fraction of the incoming momentum. If it's a plane wave, that ratio is exactly one. That's the Lawson-Woodward theorem. Plane waves can't accelerate electrons.

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STFC-RAL-CR03  R61: But I think with radiation reaction, that's not the case

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STFC-RAL-CR03  R61: And so it's radiation reaction parameter here, which has a non-linear way on the intensity of building plates.

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STFC-RAL-CR03  R61: Okay, so that's the classical case, but we're obviously interested in Q&D.

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STFC-RAL-CR03  R61: Quantum radiation reactions. It's a general question about what happens. It's not because in QD, obviously, we don't make photons. That's why you have to create pairs. Maybe there are loops. It's much broader question in general.

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STFC-RAL-CR03  R61: I don't think you can make a connection between Qd and classical prediction by calculating things, the meeting order and the radiated field.

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STFC-RAL-CR03  R61: And what diagrams are important. Well, of course, constant scattering, you know, goes in, emits a photon, you know, recalling the electron that's clearly a effect of radiation reaction, but also in order to recover the classical prediction, you need to

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STFC-RAL-CR03  R61: It's kind of interesting that, you know, looks to be associated with quantum stuff. But actually, that's the limit. We've got this. So it's really important.

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STFC-RAL-CR03  R61: So we understand how to calculate a list for leading order and QED, but the general problem is unsolved.

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STFC-RAL-CR03  R61: So there were experiments like Gemini, not far from here, very successful. That shows a method of radiation reaction and a recent paper showing that there's a differentiate the QD radiation reaction from classical radiation reactions.

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STFC-RAL-CR03  R61: But I,

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STFC-RAL-CR03  R61: I think that we can do better. And one example of where we might be able to do better is in the following setup. So that's the Clarix accelerate and Dares 3.

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STFC-RAL-CR03  R61: It's on 1500 units.

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STFC-RAL-CR03  R61: So again, as I've been trying to extol the virtues of Linux and the properties of electron beams in this talk, which is our energy standard around 1%.

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STFC-RAL-CR03  R61: And it's also a… I have an optical laser, and there's very much to do.

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STFC-RAL-CR03  R61: reach high values around 10 in the nonlinear regime.

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STFC-RAL-CR03  R61: The strong food parameter is small, but the radiation reaction parameter is a few percent.

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STFC-RAL-CR03  R61: And the claim here is that by using the precision that you get from aligning methods from particle physics and accelerated physics, we can find signals of radiation action, not in the total yield, but in the spectrum.

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STFC-RAL-CR03  R61: I'll give some examples of… Simulation survey before. So…

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STFC-RAL-CR03  R61: This is an example of what happens to the electron beam energies after the collision. So there's no radiation reaction to the meb. We get this purple dash line here. Nothing happens.

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STFC-RAL-CR03  R61: If all the radiation reaction were classical, then what happens to this? The electron beam energies, they all get shifted down in this case by about 10 mev. All the electrons interact with the laser classically, and they all radiate continuously.

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STFC-RAL-CR03  R61: Contrast that with the prediction from Qd.

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STFC-RAL-CR03  R61: We've not seen, but the expectation value of this 3D code is about the same, but the variance on the 3D code is very spread out against Hale.

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STFC-RAL-CR03  R61: And that's because one of the features of radiation emission in QD is it's stochastic. So you could have an electron pass through the laser without missing once.

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STFC-RAL-CR03  R61: It's another name that's, crunchy.

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STFC-RAL-CR03  R61: or it might the electron and quantum theory might get to higher regions of the intensity of the data being because it only makes stochastically than it does classically.

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STFC-RAL-CR03  R61: Let's go straggling. So we have

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STFC-RAL-CR03  R61: quantum effects which contribute to potentially the spreading of the electron and emissions.

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STFC-RAL-CR03  R61: Where does that spreading occur? So this this is kind of transverse momentum distribution along the electric field direction for laser.

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STFC-RAL-CR03  R61: And you'll see, like, in the…

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STFC-RAL-CR03  R61: That's the no radiation reaction case. That's the most readily written quantum case there is.

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STFC-RAL-CR03  R61: 2 dimensions like this. So this you can see. Obviously, the amplitude goes down in the quantification center. Spread and the transversement distribution. So the idea would be to be able to measure what's happening in the tails.

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STFC-RAL-CR03  R61: to differentiate quantum from classical radiation reaction. You could also rotate the polarization plane of the laser. So

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STFC-RAL-CR03  R61: Scale should be around, depending on what colorization plan you prefer.

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STFC-RAL-CR03  R61: Sorry. So there's a collaboration form at the moment, obviously in difficult times between

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STFC-RAL-CR03  R61: So hopefully, we'll have more to report on that in the future. I thought it was a nice demonstration of collaboration between partners.

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STFC-RAL-CR03  R61: Okay, so… That's my summary,

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STFC-RAL-CR03  R61: I recommend to you that you can do some really nice things with some metaphysics on high power lasers. I only talked about QEDs because I think there's a lot of interesting things happening there. We can do things with lasers and lateral reprocesses on DSM, but I decided to focus on QEDs for this talk.

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STFC-RAL-CR03  R61: the interaction between the charging fields. It's a non-preservative prediction of home field theory, which we could test an experiment. We don't have many of those particularly non-preservative

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STFC-RAL-CR03  R61: The conditions that we have, require…

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STFC-RAL-CR03  R61: Large colliders are not difficult to get at, but in the interaction between lasers and electrons, it should be easy to access.

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STFC-RAL-CR03  R61: I'm…

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STFC-RAL-CR03  R61: I think it's a kind of growing synergy between particles and native physics, which is leading to new experimental prospects and definitely developments in simulation theory.

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STFC-RAL-CR03  R61: And this is including regime at high.

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STFC-RAL-CR03  R61: I have no methods to calculate this at the moment, so we definitely need input from experiments. And I think that using precision, increasing precision, rather than going to a high latency, I don't see this. So thanks for your attention.

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STFC-RAL-CR03  R61: Okay.

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STFC-RAL-CR03  R61: Thank you.

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STFC-RAL-CR03  R61: That's really interesting. Has anybody got any questions?