STFC-RAL-CR03 R61: the feasibility study reported 31st of March of this year, that the background, which we had encountered at, SLD in the, in the vertex detector, was actually kind of not mentioned. I'm not saying I should have mentioned, because it's a very long time ago.
STFC-RAL-CR03 R61: And with the help of my SLD colleagues, we looked into that and concluded that that background is probably going to scale with gymnasty, in which case that's going to be, obviously, quite a big issue at FCC.E.
STFC-RAL-CR03 R61: So, the particular from SLD, people of the company of Sugar, Fred Wickens, and Rodney Broidenberg, and then there are many other experts, as you see listed here, who have provided advice as we've gone along with this study. So, let's start with the almost forgotten story of SLD. We get stepping a little bit further back.
STFC-RAL-CR03 R61: The proof of principle that these,
STFC-RAL-CR03 R61: CCDs could be used for particle tracking was done in the C6P at the BS, 93 to 96, and then they had more collaboration that, Ivan already mentioned, where we looked at hydroproduction of CHOM.
STFC-RAL-CR03 R61: So that was the world's first pixel-based vertex detector with just two CCDs covering the entire spectrometer aperture, because it was forward spectrometer, and you didn't need much area if you put it right after the target, one or two centimeters after the target.
STFC-RAL-CR03 R61: This detector, this famous detector, has actually spent most of his time at Manchester University, because Steve Walsh was our postdoc, and, he's now retired, and he's a bit worried that it may not be revered as much as he did, and therefore, it's better to bring it here, which is where it was built. And, so I'll be coming here just within the coming days, and you'll be able to see it easily.
STFC-RAL-CR03 R61: in the BPD exhibition area, so that's the world's first
STFC-RAL-CR03 R61: a pixel-based vertex detector. All this was going on with ACMOR, but then in 1981, there was a workshop at Fermila, where I met Marty Meideenbach for the first time, and he said, what about,
STFC-RAL-CR03 R61: using these detectors at SLC, so I knew nothing about SLC. I said, do you ever watched SLC? What beam pipe radius do you need? He said, oh, Bert did the calculation.
STFC-RAL-CR03 R61: about the size of a drinking straw. So that was obviously, you know, very seductive, and we said, great, that's what we're going to do. So, we only needed 10 milliliters of the drinking straw beyond what we needed.
STFC-RAL-CR03 R61: At that time, there was a Villar workshop at Follett, and they said they needed 10 centimeter radius, and so I was sort of grumbling about that.
STFC-RAL-CR03 R61: But, colleagues said, you know, shut up and let them do what they feel can be safe. Eventually, they did reduce the inside railings, but only by a bit, so SLD was always in a far more compact scale, and that was very helpful from a point of view of emergency sectors and getting the precision you need at the, at the surface.
STFC-RAL-CR03 R61: So, Mark II were the first detectors in at, SLD, and they started their run, in 1989, and they discovered that there was a background that was not anticipated from, and that we're going to worry about.
STFC-RAL-CR03 R61: And, during that time, I'm not sure to assist a graduate student of UMD, and he wrote Guinea Pig, which everybody knows as the simulation program to tell you what's going to happen in these situations. Not many people know what the acronym means, so I put it on the
STFC-RAL-CR03 R61: on the thing here, generated unwanted interactions from numerical experiment analysis, program interface, and general. So that was, that was, a done and wonderful contribution.
STFC-RAL-CR03 R61: The R2 system, which had microscript detectors, was actually, as long as they stood beyond this, this, firewall, which they found by wire scans, was, virtually free of background. And so, when we were preparing our pixel-based detector, we thought, great, we've got a nice, clean environment, as we had in a fixed target experiment.
STFC-RAL-CR03 R61: However, this, turned out not to be the case, as you'll see. So here we are, with a concept, with a 10mm screen pipe, and, and a nice compact detector, which only had 120ccs, which was a lot compared to the two that we've had.
STFC-RAL-CR03 R61: At, CERN, but nevertheless, a handible. But what happened was that the, the studies, both at SLC and
STFC-RAL-CR03 R61: when Mark II went in, these wire scans showed that this was an unsafe situation, and eventually, in 1989, we had to pack up all these thoughts and go to 25 millimeters, so that's before we'd actually built
STFC-RAL-CR03 R61: But then we made prototypes, but we hadn't actually built the small detector. So, now we had to face that, and that was a… that was a huge challenge. How are we going to do that?
STFC-RAL-CR03 R61: Well, the, the, all right, so what I wanted to say here was just to explain the nature of the background. So, this is sort of jumping ahead historically, because what are these incremental repairs?
STFC-RAL-CR03 R61: Well, you all know about cyclone radiation, and and if you don't, there's going to be a talk in two weeks' time from the head of Diamond, which will give you great details on that.
STFC-RAL-CR03 R61: As well as that, when you go into a beam situation, the two bunches focus each other, and so you get the pinch effect, which actually is good for the physics, because it gives you an enhancement in luminosity.
STFC-RAL-CR03 R61: But as well as that, there's associated secret drug radiation because of the bending of the beams in the fields of each other, and so that gives you a particular type of secret frog radiation, which John Reese, the great accelerated scientist of SAC, called Beamstrog.
STFC-RAL-CR03 R61: And so that then produces a highly collinear beam of high-energy photons, which exit the beam pipe.
STFC-RAL-CR03 R61: And, and it's extremely intense, needs a carefully designed beampl, it's about 400 kilowatts at FCEE. So that's, that's a major thing. But it does disappear down the beam pipe, and it doesn't cause any problems with detectors.
STFC-RAL-CR03 R61: But as well as that, once you've got that, then you get incoherent pair creation. Now, that
STFC-RAL-CR03 R61: There are 3 purposes.
STFC-RAL-CR03 R61: I don't lift shits.
STFC-RAL-CR03 R61: Beta Hyper and Bright Muller, and, and as you've seen, okay, so, so the, the external legs are the Leanstrom podons, so the first one, Landau Richard, that dates from 1934.
STFC-RAL-CR03 R61: the prediction, and so that doesn't require any beamstromen at all. So you actually get that independently of the beamstromen, but with one or two beamstrom photons, you can get these other processes. And, there's a certain little trick that I learned at Stack.
STFC-RAL-CR03 R61: at lunch one day, how do you know which is… how do you remember which is which? Just keep track of the number of R's. So here there's no Rs, so there's no means strong. Here there's one, the R here, and here there's 2 in the name, and so that's how you can remember which is which.
STFC-RAL-CR03 R61: And, so, so all of those, contribute. It's interesting to know what actually is the cross-section for these things, because, these are the things which are going to give us the background that we hadn't anticipated at,
STFC-RAL-CR03 R61: at, SLD. So here you see, I've actually, just from, from, the thesis, calculated this, because I haven't found it probably anywhere, because, mostly people put some sort of energy cutoff or something like that on the.
STFC-RAL-CR03 R61: On the pair production, but, if you… you shouldn't put any, threshold at all if you're concerned about the process we're going to talk about, because the positron is a positron, and, and, it annihilates, and it produces a little explosion when it annihilates, so that's our theory. So here's the, the, the, the,
STFC-RAL-CR03 R61: Brightwheeler is very low, landownerships and Beta Heika are the big ones, and so you've got a total, a very large total cross-section of about, 50-odd,
STFC-RAL-CR03 R61: Little ponds, which, which, is, creating this, this, bear, pear production within
STFC-RAL-CR03 R61: the, within the area of the B-pipe. Now, those, those pairs are mostly rather low energy, and so they tend to get trapped by the field, so it's just like many small energy, low energy particles which get produced
STFC-RAL-CR03 R61: at an interaction point, they don't get into the detector because the solenoid field tends to sweep and forward. So that's what's going on there.
STFC-RAL-CR03 R61: So here you see, for example,
STFC-RAL-CR03 R61: what we were just talking about. this is a, a simulation
STFC-RAL-CR03 R61: for, the, SID detector, for a linear collide, it doesn't make any difference in terms of what we're talking about. The solenoid field of pipe Tesla, which is very nice, because that tends to confine these pairs. This is… this is… this is the hard edge that you get. The beam pipe is shown in red.
STFC-RAL-CR03 R61: And the, by the way, there's a five times the standard scale here, so this is actually along this cylinder. And, so, so you get the,
STFC-RAL-CR03 R61: the pairs well contained within the beam pipe, and so to a first approximation, you don't have to worry about them from a point of view of background. There is a tail, which comes out at, larger angles, and which does then penetrate
STFC-RAL-CR03 R61: the detector, so you get, in your vertex detector, some, electrons and positrons, which traverse the detector, and, but they're very low level and never cause any problems. So that's not a major thing. The thing which is serious is… is much, is different than that.
STFC-RAL-CR03 R61: So, so, so, so far, so good. You, you designed your, your beam pipe and your detector, to be, in our case, 35 millimeters, to be free, because we had a lower field. See, this was, this is for a 5 tester at,
STFC-RAL-CR03 R61: At, SL, Mark Mach, 2 had only 0.5 Tesla, and we had only 0.6 Tesla, so that's why we needed the larger beam pipe. But it's all the same physics, and, and provided that you are aware of what's going on and you run the API, then you can design your beam pipe, and everything is safe.
STFC-RAL-CR03 R61: And, so first, first approximates, you think, okay, those are the background.
STFC-RAL-CR03 R61: But that's not the whole story. So, the situation for us was that we had to go from that beautiful little design detector, the 10mm, to 25mm, and this is the way we did it. We had,
STFC-RAL-CR03 R61: We had,
STFC-RAL-CR03 R61: 60, 60 ladders, in four, in four, cylinders are all very close to one another, which is not what you want to do. We'd rather have a bigger, a bigger lever on for the vertexing, but that's what we had. And, and so each of these have got eight CCDs, one on four on one side and four on the other, so there's no gaps along the ladder, but you see, between each ladder, you've got a gap.
STFC-RAL-CR03 R61: And so the second layer is more or less filling the gap in the first, and so on. So even though we had four layers, we only had something like 2.5 hits
STFC-RAL-CR03 R61: per track, going through that. So it was a difficult way to build a vertex detector, and that's all we could do with the available CCDs at the time. In fact, there was an advisory group meeting at Slack.
STFC-RAL-CR03 R61: when Marty Breidenback went round the table and asked, should we continue with these CCDs, or should we drop them and go to microstress, which are much easier to make in a big area?
STFC-RAL-CR03 R61: And the first speaker on this right, mentioning names, said 400 maybe CCDs is ridiculous, so we better go to microchips. And of course, that, us CCD people have been, you know.
STFC-RAL-CR03 R61: Excited, and so in the end, that's what we did, and Slack was incredibly supportive in terms of that, and also the ongoing R&D, which led to a better detector later on. So that was, so that's the XD2. Now,
STFC-RAL-CR03 R61: in 92, SLD moved in. It was supposedly a push-pull operation, as they also talk about for the linear collider. In fact, it only went in and never came back out again, because the Mark II was then out of action. And, so this was not only an excellent vertex detector.
STFC-RAL-CR03 R61: But he did very good physics, thanks to topological vertexing, that is to say, software in which you actually find the secondary and tertiary interaction points, because we had the lead production and child production, and, so, this was all devised by our, our wonderful former graduate student from Arthur Jackson.
STFC-RAL-CR03 R61: And, so he was a postdoc, and his program was called Xena Top, and that's, continued, over all these years. 30 years later, it was taken over by the IRC group of Tokyo University, and it continues to be IWU.
STFC-RAL-CR03 R61: And so, SLD played a very special role in running all the Z0, as well as the LEP detectors, because we had a combination of the longitudinally polarized electron beam B, which was not possible at depth when it's tried, pixel-based vertex detector, excellent drift chamber, rich-based particle ID,
STFC-RAL-CR03 R61: Liquid all got weak out, and the mass of aaked up, so it was hard to detect them, and it did a lot of very nice physics.
STFC-RAL-CR03 R61: However, of course, the big problem there was not the detector, it was the fact that SLC wasn't working. It took several years to get SLC to work, and there was a DOE
STFC-RAL-CR03 R61: panel, pushed actually by Fermilab, which was wanting to shut down the whole thing, because the mythology and the SLC never didn't work. And, I remember bumping into Bert
STFC-RAL-CR03 R61: in the corridor. It's a two-day meeting, and and you know, I just said to him, but it's really tough, the time you're having with these guys and so on, because they were very aggressive about the whole thing.
STFC-RAL-CR03 R61: And he just shrugged his shoulders, and he said, oh, he says, they don't know how to run a lab. And that's interesting, because Bert was spending a lot of his time in Washington, and he had
STFC-RAL-CR03 R61: friends like, you know, Senator Feinstein and people like that, so actually, I mean, Slack kept going, and thank goodness, because the fact that SLC finally did work, and got very close to its design luminosity, is the reason why we've got international media guides, and we've talked about ever since. Otherwise, that would have been a
STFC-RAL-CR03 R61: That would have been, you know, dead, dead at birth. So,
STFC-RAL-CR03 R61: So, when we switched on VXD2 at the start of the SLD running, we were astonished to find that we had a high density of background bits, compact clusters which were far beyond what you expected from
STFC-RAL-CR03 R61: So what's going on? And, what is clear is that what was happening was we were getting soft x-rays coming through the beam pipe of 1 millimeter of beryllium lined with a thin layer of titanium. It's pretty transparent to low-energy X-rays, and so they were being picked up, and they were giving signals
STFC-RAL-CR03 R61: all the way from below Mini to many times Mini, and, indeed in the Sulika. So, so that was,
STFC-RAL-CR03 R61: Some of them even come through higher energy, for example, like 30K eV, and then they can excite the back plane of the CCD as a thin film gold, and they can excite, the, the…
STFC-RAL-CR03 R61: gold L-alpha line, and, and produce, and produce signals from those. The CC was even used for calibration purposes. That's quite, actually quite useful from that point.
STFC-RAL-CR03 R61: Right, so this is what we saw. So, here you see VXT2, as it was turned on in 1992, the beginning of the running.
STFC-RAL-CR03 R61: And, it was running with SLD at the considerably reduced luminosity. That's about a fifth of the luminosity that was finally achieved, and yet we had this rather high rate. It's not enormous. I mean, it's actually something that we… the data we don't occupying 19 boat crossings.
STFC-RAL-CR03 R61: And, and so it was something like a couple thousand hits in the detector. It's a… it's a tiny occupancy, 0.01%, because this is 120 megapixels. And, the, and and the other thing, which is a little bit misleading when you look at this, you see some quite large blobs. They actually… the event which was triggering this was actually a very clean new pair event.
STFC-RAL-CR03 R61: And you see the hits on those are very compact. Well, so are the hits here, physically compact. They're typically, sort of.
STFC-RAL-CR03 R61: 2x2 pixels in size, but the, but, the scale here of the block is showing you the charge, and so some of those are X-rays which are much more than a mini, and so they give you a larger, you know, parent signal there. So,
STFC-RAL-CR03 R61: the running situation there was that, that if you then scale this to FCCEE, at the design luminosity.
STFC-RAL-CR03 R61: SNLC,
STFC-RAL-CR03 R61: had about the same, luminosity per bunch crossing as FCCEE. It's just the fact that it was 120Hz, whereas at FCCEE, it's 50 MHz. So that's… it's mainly in the… in the bunch rate, and so if you could read out,
STFC-RAL-CR03 R61: at FCCE, for example, in… in 20 bunch crossings, but that's a very short time in terms of, of microseconds, then, you'd have the same background. So, if you say that, and it's been discussed that maybe you could come up with
STFC-RAL-CR03 R61: with, map space readouts, which could go in 1 microsecond, I really doubt the kind of occupancy we're talking about, but that would give you something like, you know.
STFC-RAL-CR03 R61: 6,000, times the, times the 50, bounce crossing.
STFC-RAL-CR03 R61: 300,000 hits, so the occupancy is still only 1.5%, it's not…
STFC-RAL-CR03 R61: obviously fatal, but it's a very challenging thing in terms of an air-cooled detector, which, if it's not air-cooled, you've got a lot more harmful material than you want. So this is a dangerous kind of background, I would say, certainly something which needs to be paid attention.
STFC-RAL-CR03 R61: So, continuing, we then, with the help of Slack, enormous funding going to, E2V,
STFC-RAL-CR03 R61: now ETD Teledyne, and, so by 96, we were able to, build this VXT3, which is a same 25mm inner radius, but more extended between the layers, and, and so what you've got here is one CCD, which is the stitched CCD, that's a, this is about,
STFC-RAL-CR03 R61: 8cm in length, and then another one on the other side, so you get 16cm length, and they actually overlap in, in, in, along the ladders, and so for 307 megapixels, you can make a very nice detector, but that's where most of the, of the,
STFC-RAL-CR03 R61: SLD physics was done.
STFC-RAL-CR03 R61: So,
STFC-RAL-CR03 R61: The background there… okay, well, just to say a bit about VXC3, this is… this is… these are the three, layers, shown double because one is, you know, north and the other is south, so they don't overlap only to the millimeter in the middle, but they would… the whole thing would have been comfortably inside
STFC-RAL-CR03 R61: the, Opal Micro Verdicts, for example. So having a compact verdicts detected was a big plus.
STFC-RAL-CR03 R61: from the point of view of physics. The background that we saw there was, was very similar for soft X-rays. There are details here, so if you look at the track associated.
STFC-RAL-CR03 R61: signal. Here you see it, so it's a broadened Lando, just as you expect from it. It's about 20 micron active thickness of silicon, and and so that's the, the expected Lando distribution, but the, but the X-rays, I'll show you in a minute, extend from below that to far above that.
STFC-RAL-CR03 R61: And, so, here you see some details. I mean, this is the Azimuthal Dependence, which
STFC-RAL-CR03 R61: There's some there. This is the three layers getting weaker because of the absorption of the X-rays as you go through, and and this is along the length, and the reason for these sort of humps is to do with details in the readout. But basically, all of these things were pointing very clearly to this X-ray-dominated background, and very little coming from charged particles. So that was the… that was the lesson from
STFC-RAL-CR03 R61: SLV, that that's where most of the, of the, background is coming from.
STFC-RAL-CR03 R61: And…
STFC-RAL-CR03 R61: would probably be the same also. So here you are. These are some signals that have been recovered from Sudon, Slack, unpublished work that he did with Ben Crawford. And so what you hear is a cluster signal.
STFC-RAL-CR03 R61: from the threshold, to 20 keV here, you see. So it's fairly flat, up to 20 keV, and by then, the silicon is becoming transparent, so it has to fall off. There are some oddities, little, things at the, at the low level, below.
STFC-RAL-CR03 R61: the MINI, so this is… this is the peak of the mini distribution. So, the point is simply, as I said before, that the bulk of the, the signal is X-rays of, relatively much higher energy than the particles. This is a plot of the, cluster signals of unlinked hits, which means hits that were not linked to tracks, and so that we know that they are,
STFC-RAL-CR03 R61: Intrinsically unlikely to be in charge bodies.
STFC-RAL-CR03 R61: So, There's, there's some mystery about these, plots, because, the records
STFC-RAL-CR03 R61: the computer on which all this stuff is stored at Slack is broken, and, Sue Bombay is doing a… so all the SLD records have been lost, but he's doing a grand job of trying to get back
STFC-RAL-CR03 R61: signals from the, the disk, which it may well be still, legible, if you can find the right software. So, we're still trying to get back to the record on the list. But, there even might be one or two people who are still around that who may have some, some memory of this, so we're working to try to get that. But it's all, you know, at the very edge of,
STFC-RAL-CR03 R61: What's, What's been, Lost to memory.
STFC-RAL-CR03 R61: A study of this is indicated by… this is the thing called the R20 module. This is the, the part of the detector which is inside the drift chamber, this is the wall of the drift chamber, and so this is the primostat of the vertex detector, there's the XC3, and so that's all in the area where the PIN
STFC-RAL-CR03 R61: beam pipe of only 1 millimeter perilium, but as soon as you get beyond that, you get into a region where you've got tungsten. So this is basically a tungsten box, there's a tungsten calorimeter at the end here, and we call that beam volume, and that is the volume in which the action is taking place, and which is, we now understand, generating this background.
STFC-RAL-CR03 R61: Which was, going far beyond what was expected from Guinea pig.
STFC-RAL-CR03 R61: So, so what we believe happens, and we're now, by now, quite remiss about it, is that, so you, you break your pairs, the electropositon pairs, with small moments in one or the other direction, symmetrically, and, so they then drift along
STFC-RAL-CR03 R61: small llama, most of the small llama radius around the, soluble, within the solenoid, and when they come here. Now, this is the end of the,
STFC-RAL-CR03 R61: of the quadrupole, first quadrupole. And, so around here, the field is no longer, doing, doing what it does at a most of the length, and the field lines are starting to bent, and so you get these
STFC-RAL-CR03 R61: electrons and positrons, dumping themselves in the material here. Now, the, if they're electrons, they range out, you actually, to help that process, there's a thin layer of graphite put here, so most of them end up in the graphite, and they stop, and that's the end of the story.
STFC-RAL-CR03 R61: And as opposed to the tungsten, where there's a bit of backscattery, but it's not very much for the electrons.
STFC-RAL-CR03 R61: The big danger is coming from the positrons, because every positron, even of zero energy, eventually ends up in this region, and and it annihilates.
STFC-RAL-CR03 R61: And so what you get is basically a sort of a fireworks of, of, gammas from the 500KV-ish gammas from the positron
STFC-RAL-CR03 R61: Annihilation in the tungsten, even
STFC-RAL-CR03 R61: if, they don't annihilate immediately, occasionally they form positronium, but within a nanosecond, they then are going to annihilate. So that's… so that's more or less what's happening all the time. So you've got, after the bunch crossing, you've got the, the positrons, making their way, guided by the field to… to… to either end of this, B volume, and then
STFC-RAL-CR03 R61: You're my lucky.
STFC-RAL-CR03 R61: And at that point, what happens? Well, we're just beginning to get simulations that are showing that, and I'll show you an example of those. And so what happens is that they are now flying around, of course, many of them just burying themselves in the tungsten of products, but, this content scattering and so on, so it's very easy for some of this energy. It's about a GEV of energy.
STFC-RAL-CR03 R61: the total, from the positron annihilation, and this… you only need to produce that background that you saw in the vertex, it'd be about 1 MeV.
STFC-RAL-CR03 R61: So it's a tiny fraction that needs to get delivered with all those hits.
STFC-RAL-CR03 R61: And so… but how do they come in? Well, of course, the cultural scattered things have to work their way along, so it's like the tail end of an electromagnetic shower in a calorimeter, except for an effect there's a calorimeter with a hole in it.
STFC-RAL-CR03 R61: And the hole in it provides a very easy path, so, you know, one of those, one of those gammas from the annihilation could immediately make its way to this region of the time, and then it would get into the detector. So it's intuitively
STFC-RAL-CR03 R61: Not surprising that that happens, but it was certainly not anticipated, and it was VXC2, and then followed that, VXC3, which actually showed us that, and that there's this by far, dominant, background coming from the, coming from the XAs. So,
STFC-RAL-CR03 R61: So,
STFC-RAL-CR03 R61: So, I think I've…
STFC-RAL-CR03 R61: actually said, my dear, you can learn quite a bit from PET scanners, because, of course, there you rely on positron violation, and
STFC-RAL-CR03 R61: And, there's actually some software which Zotivys use, which is quite good about seeing how these things develop in homogeneous material and so on. So that may mean the use of simulation. But we believe you can do most of it with Xiaom 4.
STFC-RAL-CR03 R61: And, you've actually now shown that. So, we've got these rather messy electromagnetic showers, and, you know, the only question is how much of that gets into your detector through the… through the B-pipe.
STFC-RAL-CR03 R61: So, of course.
STFC-RAL-CR03 R61: this is all hand waving, right? I mean, in principle, those, those showers could die down and not reach the thin area, as long as they're within the main volume of the, of the, the,
STFC-RAL-CR03 R61: B volume, then, they're, they're, innocuous. But the question is how… so it's a delicate question that needs a careful simulation, and that's what's, finally coming out of all this discussion. So, we, we, we actually can look at, at,
STFC-RAL-CR03 R61: what's been done there. So, yeah, so this is… this is the paper on which the, feasibility study is based, and so they… these are… these are not vertices. Yes, here's the vertex detective. This is the time
STFC-RAL-CR03 R61: the time of arrival of signals at the vertex detector, and so you see they're all, basically instantaneous. I mean, these are the, these are the, the,
STFC-RAL-CR03 R61: the pair of electrons and posture that fly through the detector, and they give you a prompt signal. We've now got recent results from, the, the CFO CQ,
STFC-RAL-CR03 R61: Which is a linear glide, but I don't think makes a difference at all. And so here you see the results, so the blue, the blue is the one from the… this is hydraulic, so we don't look at that. So… so here you've got a big spike, which is actually because the radius, the B5 radius, has been put a bit too close, but so if you move that out by a millimeter, then that will diminish greatly. So that's… and that's actually minor.
STFC-RAL-CR03 R61: The main thing, which you see, is this
STFC-RAL-CR03 R61: Back, back, splash. And, so, that is,
STFC-RAL-CR03 R61: at the moment, that the, the simulation, we've been looking over these results, and, the simulation doesn't actually tell you whether these are charged or gammas, but if they're charged, then there's something very strange going on. So I think that's, that's what's, you know, that.
STFC-RAL-CR03 R61: So, the,
STFC-RAL-CR03 R61: the software that's used for that is a beautiful pipeline that has been developed under the leadership of Lindsay Gray from Fermilab, and, so…
STFC-RAL-CR03 R61: You won't go through all the details, but basically, these are the things which come out at the end, and that's really what is currently providing the, the observation of, finally a simulation which is catching up
STFC-RAL-CR03 R61: with what we observed experimentally. And, the, and what, of course, to point out is that this pipeline is, well-suited
STFC-RAL-CR03 R61: To, to, any other, glider, and, so what the… probably the next step will be to actually
STFC-RAL-CR03 R61: to replicate what we've seen at SLD, and that would be lovely to really see that for the first time, and then to move on to FCCEE. So those are… those are the, the plans in terms of pushing this forward. And, the other thing which I found very interesting, I kept saying.
STFC-RAL-CR03 R61: You know, can't you do some sort of,
STFC-RAL-CR03 R61: sanity checks on these things, and of course you can, and the people who are most informative to me are two wonderful experts, Alberto, Rivant, and Vitaly Noah of CERN, and, they have, you know, you can run, I didn't know this, you can run jail in the so-called stepping actions, in which you can see
STFC-RAL-CR03 R61: you know.
STFC-RAL-CR03 R61: nanosecond by nanosecond, or 5 nanoseconds at a time, whatever you like, you can see the evolution, and so that would be most interesting to see whether this thing really does replicate what, what we got experimentally, but I mean, we're obviously led by the experimental results, and hopefully this will all, this will all come out with the, with some more advanced, simulations going on at the moment. So that's between
STFC-RAL-CR03 R61: I'm familiar with Slack people now.
STFC-RAL-CR03 R61: Alright, so,
STFC-RAL-CR03 R61: Now, there's an awful all this, of course, because even if we do reach this happy point of replicating the backgrounds that have been observed, there are other things, that can go on at Calibis, and we can't shut our eyes to those.
STFC-RAL-CR03 R61: Dramatic example was the VXD3 after installation, before, it was even tabled up.
STFC-RAL-CR03 R61: with a fire in one of the damping rooms, it sat. And, so they couldn't run it in. And, it took months to actually fix the damping.
STFC-RAL-CR03 R61: clean it up. But in the meantime, one of the accelerating buyers, won't mention any names, had the brightest idea, oh, he could do some studies with an undone people.
STFC-RAL-CR03 R61: So I put an undamped beam through, and, and, so while we were even, you know, cabling up, unknown to us, this beam was running through, and obviously being undamped, it was generating a huge amount of
STFC-RAL-CR03 R61: quadrupole synchron radiation, those final parts. And, so, so actually what happened was that that, that detector was damaged even before it was turned on. When we turned it on, the inner CCDs were dead, but, but we were running at, something like 200, yeah, 220 Kelvin.
STFC-RAL-CR03 R61: operating temperature. Fortunately, our cooling system, cold nitrogen, would go pretty well as low as you wanted. And, and so we just, we just pushed on that.
STFC-RAL-CR03 R61: And we got it down, and by 185 Kelvin, the famous Lazarus effect had taken over, and the detector was alive again. So we had a very lucky escape there with the, with VXT3. But the point
STFC-RAL-CR03 R61: from all of that, is to say that, as long as you're… now I'm talking about single beam effects, not the only colliding beams at all, so there's just every beam can generate background in that beam volume, which can… these are… these are X-rays, by the way, and we know that because it's mainly on layer 1. By the time you got to layer two, there was much less damage, and none at all on layer 2. So,
STFC-RAL-CR03 R61: So it's clear that, that soft X-rays are easily produced by various means, not only this, positrons in the pairs, but other needs as well. So here, there's no question of any positrons, this is just the polypole centrum radiation.
STFC-RAL-CR03 R61: And, so, that, of course, can be a second source of background during normal running as well, because, I, I was naive about this. I thought these tails on the beams I knew for damping rings and all the rest of it, you shouldn't have them.
STFC-RAL-CR03 R61: But, veto across the nettle is, is, integrated a lot along on this, and there is,
STFC-RAL-CR03 R61: the possibilities of, of, phase back, of the repopulation of these, these tails during running, and, I mean, this experience with SLC death, SuperKP, and, so this is always dangerous, and, I think what, he told me was that, at FCCEE, they… the machine guys have done some studies of these effects, but most of them have sort of got
STFC-RAL-CR03 R61: bond into, you know, a sort of retirement, and, but that really hasn't been picked up from the point of the detector as to how much, that is going to also come in. So there's a, there's just a concern there that this is something that does need to be, to be explored, and, there may well be other things, but… so,
STFC-RAL-CR03 R61: this issue of wide-angle protocols singular duration in the beam volume, is, it's… we've got a, we've got sort of Achilles heel in the form of this thin heat pipe, and, you know, we're not sure,
STFC-RAL-CR03 R61: What else there may be going on in the store. So, in summary, I think the study of these backgrounds is pretty much in its infancy.
STFC-RAL-CR03 R61: whatever the future holds, there is… now, with modern simulation tools, there's great, great means for optimism. These things can be, can be, tackled in time, because in time, the earliest is 2045, and,
STFC-RAL-CR03 R61: I mean, there are many things. For example, if it turns out that the main diagram is out of time with respect to the, to the primary beam, then, you can, with,
STFC-RAL-CR03 R61: modern maps devices, you can introduce gating, so that you gate off between the bunches, and so that can be helpful. But of course, if it's as broad as what we're seeing in that simulation that I showed recently, you know, it may not be so easy. So, there needs to be a, you know, a big effort on all aspects of this thing to, to take it forward.
STFC-RAL-CR03 R61: A final example that I just want to mention from, SLB was that,
STFC-RAL-CR03 R61: we had… that Christ hat that I showed you, was laid in two halves with a gasket. It's making a gas leak, and God help you if that leaks, because you have the cold gas going to the drift chamber, which would make us extremely unpopular. And, so while all that was, under development, Bob English, a wonderful
STFC-RAL-CR03 R61: technician, engineer working here, said, well, why don't we just install some heater wires, running around the gasket, heat the gasket warm, which is what we did, and that's why we never, you know, were…
STFC-RAL-CR03 R61: shut down by the drift chamber people, because we'd solve that particular problem. But it's tragic to just mention it, that while we were testing these, 1986,
STFC-RAL-CR03 R61: It was a tragic exposure to the Shuttle Challenger because of the O-rings that stiffened up, and we remember that Feynman was on… chaired the committee that investigated that and so on. If they had some
STFC-RAL-CR03 R61: who were Bob English's heater wire, they probably have avoided the problem of those cold O-rings, you know, through such a… such a tragic thing. So, that's just a sort of random example. So,
STFC-RAL-CR03 R61: I'm pretty much out of time. No, no, no, no. So, what I want to do is to just add
STFC-RAL-CR03 R61: something which is, nothing to do with what we were just talking about, but, we had an office just at home, Chan Hong Mo, one of our most wonderful theorists, and, left over, I mean, the theory group was shut down here for
STFC-RAL-CR03 R61: crazy reasons. Oh, no, hang on. And, you know, he had his theory of, sort of, you know, final theory. And, which, was, I think it was,
STFC-RAL-CR03 R61: C. Weinberg said that, that Holmo's theory, which is… oh, all these boxes are papers that I've rescued, in our house, they're tiny at the moment, but they will be delivered to the family who have agreed to accept them, and the point is that, that that's systematic, the box files within those, which is from 1961 on, really, the whole, the whole of Holmo's theory.
STFC-RAL-CR03 R61: And as Steve Weinberg said, of course, the Homo theory was completely rejected.
STFC-RAL-CR03 R61: By the, the worldwide, community, and then he said, but it's never been proved to be wrong.
STFC-RAL-CR03 R61: So I'm thinking, what if in 10 years, or 100 years, it's proved to be right, those papers are going to be worth millions, and be poured over by academics for, forever, like, you know, liens papers and things like that. So, and, and this is an interesting thing.
STFC-RAL-CR03 R61: On the side is Hong Mo, a wonderful company I only found out about. So often you find out only after… it's terrible.
STFC-RAL-CR03 R61: the birth of China seemed to… poetry.
STFC-RAL-CR03 R61: And he points out from nearly 3000 that the, the time of the Taoists, leadership, that, you know, there's been so much poetry which has told the history of China of the ordinary people, as opposed to the emperors and all the rest of it and so on, and it's an absolutely marvellous book.
STFC-RAL-CR03 R61: And what you see there are, at the back of the book, there's some seals.
STFC-RAL-CR03 R61: And, which are in that box… in those boxes, you can actually find some of this sealing material and steel things and so on. And, I'll just read to you, read you… so, so he describes those on the left. Seals carved my father in his lifetime, by my brother Ronfat.
STFC-RAL-CR03 R61: The pair on the extreme right and left say loosely.
STFC-RAL-CR03 R61: The sage puts himself behind, hence ends up in front. The scant regard for himself, hence is left with a greater self, which is a quotation from Nelson.
STFC-RAL-CR03 R61: The second, on the right, is also a quotation of nature that says, the highest virtue is like water, which benefits all living things, but strives not for itself, seeking only the low position that others hate. But how can…
STFC-RAL-CR03 R61: such compact things, tell such a story. I mean, to me, it's really amazing, so I'm just amazed by it. But Homo, I shared an office with him for years, and so on, and he would always come to all these seminars.
STFC-RAL-CR03 R61: And frequently, you know, oftentimes I didn't get, like, it was an experimental setting, I haven't worked out, but he was always so respectful, and, of experimenting and other things, and he's just a wonderful guy, so, oh, because this,
STFC-RAL-CR03 R61: worth of trying to see through poetry. I only just bought a copy, and well, that's totally off of context. Anyway, so thank you for your time.
STFC-RAL-CR03 R61: Can I just add one thing to this last point? The Steelized standard model that I'm holding on about. We had a talk on that at the Atlas Week this week, which, mentioned six other references, but not it. Oh, right!
STFC-RAL-CR03 R61: Yeah, no.
STFC-RAL-CR03 R61: Maybe we can't sit down.
STFC-RAL-CR03 R61: So…
STFC-RAL-CR03 R61: Yes? Yeah, I mean, I guess, Chris, that you've brought some thoughts to the attention of a quite wide community thinking about these issues, and they have
STFC-RAL-CR03 R61: explained the status of where they are in terms of the simulation and so on. So, can you comment on where you see this now? I think that the…
STFC-RAL-CR03 R61: you know, they do… they are able to quantify why it is that they don't see this as being as big an issue as perhaps it… it may be. Can you comment on your current thoughts on your discussions with them? Yeah, well, I mean, I think… I think that, it's… it's very contentious. I mean.
STFC-RAL-CR03 R61: I, I think it's actually…
STFC-RAL-CR03 R61: correct, say that, this background had been forgotten. I don't think that's any
STFC-RAL-CR03 R61: you know, criticism of anybody that had been forgotten, but now that it's back up again, I think that this, possibility of, soft x-rays… Oh, and the other thing I didn't mention… well, no, I did mention it, the fact that any… if you… if you've got this, this sort of, fireworks of, 511kED,
STFC-RAL-CR03 R61: then whatever electrons you produce are, by definition, going to be contained, right? I mean, so that… many people use a… the solid wood field to keep the rubbish inside, and that works very effectively. The fact that it is totally ineffective with respect to soft X-rays
STFC-RAL-CR03 R61: introduces a possible background. The reason you don't see it in microchip detectors, for example, is that they are 10 to 20 times thicker, and therefore your threshold is that much higher. So if you put in maps, and it might worry me.
STFC-RAL-CR03 R61: I mean, I'm just… I'm not going to be around in 2045, but my worry is that the people that are, and they put these things in, if they get a surprise like us in, in, in SLD,
STFC-RAL-CR03 R61: and find a large background from soft X-rays with a MAPS detector, then they have to keep a low threshold in order to, in order to get a signal. So, I mean, they're talking about now even 15 micron of active silicon, so I think it's a danger.
STFC-RAL-CR03 R61: And so I think it just needs to be taken… which is being taken seriously, and people investigate, and hopefully… but I don't think anybody can say
STFC-RAL-CR03 R61: We've already done it. That's not the case.
STFC-RAL-CR03 R61: I think we've got some of those experts online, so Fabrizio, I think, maybe. Yes, Fabrizio. Yes. Yes.
Fabrizio Palla: So, thank you for your.
Fabrizio Palla: told, but I need to make some, let's say, statements.
Fabrizio Palla: As you well know, that,
Fabrizio Palla: We have been, studying in quite details with Gerard
Fabrizio Palla: All the processes that you were describing, so we have a full simulation of all the…
Fabrizio Palla: Geometry of the beam pipes.
Fabrizio Palla: cut geometries. I mean, we really need to be sure here we didn't forgot anything, and even all the processes that you were mentioning, from the positron annihilation down to the low-energy X-rays, were inside the simulation.
Fabrizio Palla: So, since SLD times, fortunately enough.
Fabrizio Palla: These giant simulation, has been evolved.
Fabrizio Palla: And since then, we have been able to make all possible simulations of these processes. Let me also…
Fabrizio Palla: comment about, two other things. So the… first of all, the computation that you hand-waved on the number of, hits that, we were
Fabrizio Palla: supposed to see inside the detectors are wrong, because we actually made our simulations using exactly the same
Fabrizio Palla: tools that you are referring to, so, Gineappig and, other things, and, we end up with completely different numbers and, with respect to those that you hand-waved.
Fabrizio Palla: We also demonstrated in our talk to you, and that was publicly available, if you want, I can even give a talk to Raoul in some of these days.
Fabrizio Palla: that if you were at SLD, at SLC, using a crossing angle, then the amount of IPC, of incoherent per creation, would be smaller.
Fabrizio Palla: Secondly, we also demonstrated that in the second version of the vertex determined in SLD,
Fabrizio Palla: you had a calorimeter just in face of the vertex detector that most probably was the cause of the splashing inside the vertex detector. That was disappearing to make room for the third version of the vertex detector. Nevertheless, the tungsten…
STFC-RAL-CR03 R61: luminometer that you had in SLs.
Fabrizio Palla: Was, in fact, giving much more noise.
Fabrizio Palla: Thirdly, the integration time that you had, which is… which was several micro milliseconds.
Fabrizio Palla: even if you scale down to microseconds, we'll end up with a negligible fraction of hits inside the vertex detector for
Fabrizio Palla: For us, whereas it was astonishingly higher for you.
Fabrizio Palla: Finally, let me also comment on two points. First is that the detector thickness that they were considering has a depletion layer of 50 microns, instead of your
Fabrizio Palla: less than 10 micron. So, the fact that the vertex detector would not be able, to see, such a small,
Fabrizio Palla: let's say, small energy X-rays, that is compensated by the fact that we can work with higher thresholds, and therefore be less visible. And finally, the…
Fabrizio Palla: the beams that we are using, I mean, is not Gaussian beams, but also have tails. So, in all our simulations, we make all these,
STFC-RAL-CR03 R61: Simulations quite well understood.
Fabrizio Palla: Whatever it lacks, in our… in my opinion, is that there is not yet a demonstration that SLC backgrounds have been…
Fabrizio Palla: totally understood, and presumably also the fact that at SLC, other kind of backgrounds might have been contributing, to, your,
Fabrizio Palla: your occupancies. And finally, as we know, we can deal with much more hits in the reconstruction, as Atlas and CMS have demonstrated
Fabrizio Palla: Offline. Thanks.
STFC-RAL-CR03 R61: Thank you very much, Fabricia, for your comment.
STFC-RAL-CR03 R61: I think we're moving forward. Basically, you know, I showed those two plots which showed the,
STFC-RAL-CR03 R61: the time of arrival of the vertex hits, and with two different simulations, one of which were prompt, and the other one has this big
STFC-RAL-CR03 R61: backsplash of the 20 nanoseconds.
STFC-RAL-CR03 R61: That is with the Lindsay Gray, etc. team. As I'm sure you know, that team includes Katerina Bernieri, and having spoken with Patrick Giano about all this, Katerina is now also joining in with your efforts and so on, so I think we've got these sort of two teams, and I'm in no position to make any judgment about it, but I think there are two teams
STFC-RAL-CR03 R61: And both of which presumably, can, you know, independently replicate backgrounds in SLD,
STFC-RAL-CR03 R61: CQ and FCCEE, and hopefully it'll come together, and I'm just really looking forward to that, but I have absolutely no confidence to make judgments about that, but thank you for your comments, I think that's all.
STFC-RAL-CR03 R61: It just shows how complex the situation is.
Fabrizio Palla: Let me reply that, I mean, it's quite,
Fabrizio Palla: strange that you do not believe that we are not based our studies on those plots. I mean, we made full simulation. Those plots are, let's say, quite late. The plots that you were showing at slide 8, please.
Fabrizio Palla: If you can go back. So we are not basing our studies on plots. We are just making a full,
Fabrizio Palla: fledge.
Fabrizio Palla: Exactly. These are not being used… this… on the left, these have not been used for our estimates. So we base our estimates exactly on the flow that Lynn Say Gray from Fermilab, which I know very well, is also,
Fabrizio Palla: making. We made very much similar things, and Lindsay is, of course, very welcome, together with Katerina, to make whatever simulations and present, but I think the way it has been presented, that we were not able to make it, is
Fabrizio Palla: Frankly speaking, not that much acceptable.
STFC-RAL-CR03 R61: Okay.
STFC-RAL-CR03 R61: Okay, thank you.
STFC-RAL-CR03 R61: More questions on Zoom?
STFC-RAL-CR03 R61: Or, you know what I'm saying? On Zoom.
STFC-RAL-CR03 R61: There's just a comment, maybe, I don't know if Patrick's able to speak, but I think there's been a very, open collaboration. You've been invited to many of the meetings, Chris, and had the opportunity to discuss this and, and discuss any, any, any,
STFC-RAL-CR03 R61: misinterpretations, misunderstandings, and work together on it. I think that this sounds… this sounds positive. It's always good to… to learn lessons and to… to expose the next steps.
STFC-RAL-CR03 R61: Is there… but, Patrick, I don't know if he was not able to speak, but I just wanted to sort of speak to the message he had written in the chat, here. I don't see further hands.
Patrick Janot: No, it was just to say that I had a… it's Patrick here. I had a one-to-one meeting with Chris, and I thought he had understood what I told him. I mean, all what he presented today is a repetition of the mistakes that he presented to us, and we showed…
Patrick Janot: that we were able to, with the same simulation applied to FCCEE, reproduce the background in SLD.
Patrick Janot: and show that the backgrounds with that same simulation, that the backgrounds in FCCE would be actually smaller.
Patrick Janot: that he does not believe is one thing. I have the fullest respect for your work on vertex Detector, Chris, but at one point, we should rather collaborate rather than miscommunicate.
Patrick Janot: Thank you.
STFC-RAL-CR03 R61: We're not going to solve them over in a discussion, I don't.
STFC-RAL-CR03 R61: I mean, basically, the results that you guys showed… I mean, what happened was on the 8th of September, I was given 20 minutes.
STFC-RAL-CR03 R61: to present all this. I did my best.
STFC-RAL-CR03 R61: There was no time for discussion. There was then a 20-minute presentation proving me wrong, which I had no idea that anybody was going to prove me wrong, and the results from there were, in my opinion, everybody's just giving their opinion incorrect, in the sense that all the background that you guys came up with
STFC-RAL-CR03 R61: supposedly explaining the SLD background, which are particles, not soft entries.
STFC-RAL-CR03 R61: So, I think there was some basic, strange thing going on there. So, but honestly.
STFC-RAL-CR03 R61: It's a long time ago, and I think we just moved forward with Katarina, hopefully we can work together and sort this all out. You see two here, complete contrast, one of which has no backsplash, and the other one a huge backsplash. So, we just need to get to work on that and understand what's the truth.
Fabrizio Palla: Well, we do see backsplashes, and we also showed you that there was a peak at exactly the positronium photon energy, and that was shown.
Fabrizio Palla: The other thing is that we gave 20 minutes to you, 20 minutes to my presentation, plus 10-20 minutes for discussion. The fact that there was no discussion
Fabrizio Palla: that you claimed there was no discussion is not simply true. Sorry about that. You can look… have a look at the agenda.
STFC-RAL-CR03 R61: Yeah, I can have a look at the agenda. I think… and I'm looking at, you know, Fabrizio's slides here. I think,
STFC-RAL-CR03 R61: you know, it's good to have a good scientific debate, right? There's no harm in this at all. It's exactly… it's exactly, you know, a good conversation to have, but I guess that there are still…
STFC-RAL-CR03 R61: some, you know, further understandings to… to establish across the two approaches. But it… but it is true, isn't it, that,
STFC-RAL-CR03 R61: FCCEE really does have these very, you know, very significant differences, such that you would expect that things could be under control. It's a different beam structure.
STFC-RAL-CR03 R61: the sensor technology is different, and the solenoid is different, and the Lumical has quite a different position with respect to the beam. So, I guess at least, you know, the work that Abrizio has done, and these slides I've been looking at from his
STFC-RAL-CR03 R61: contribution, there's certainly a lot of answer, perhaps, to… to some of these, concerns. So how does it go from here? Because I guess we don't want to leave the room with just a… how does it go from here? Are you still in discussion? We have the 5th November slot empty, if Fabrizio wants to… Oh, there you go! Well, if we want to continue this, Fabrizio, there's certainly an invitation to you to be a seminar speaker of ours.
STFC-RAL-CR03 R61: if people have appetite for more of this, it's certainly very welcome. We welcome, you know, scientific discussion on these points. If you want to take that up for a bit, too, you don't need to be put on the spot now, but that's…
Fabrizio Palla: I would be glad to come if you would like to hear.
STFC-RAL-CR03 R61: We'll get in touch with you. But in terms of your kind of, you know, business-as-usual way of dealing with this, I think, I mean, you have a…
STFC-RAL-CR03 R61: Fabricio, there's the working group where this is pursued very actively, I think, and these simulations are done, and Chris, you've been invited along to these in… I've joined it. You've joined it, yes. So, I mean, a seminar would be great here, but I just want to understand how this, you know, really moves forward in a…
STFC-RAL-CR03 R61: in a constructive way. So, Patrik, I think you said that Chris has been joining in full, sort of.
STFC-RAL-CR03 R61: open spirit and so on. Are you… are you, well, I guess you're all doing that, and so we can have another seminar here, but in the… in the wider world, this conversation is… is happening.
STFC-RAL-CR03 R61: I mean, sorry, I'm sort of… but Patrik, if you wanted a further… a further right to reply on that, please go for it.
Patrick Janot: No, no, that's fine, thank you. If Fabrizio goes for it in Rale, I'm very happy.
STFC-RAL-CR03 R61: Okay, wonderful, wonderful.
STFC-RAL-CR03 R61: Maybe there are other questions. More questions yet for Bill? Yeah, could I ask an orthogonal question? It was on your, sort of, second-last point. The, the,
STFC-RAL-CR03 R61: The background that kept left beam size beam size at being quite large was the scattered off the collabators, which I assumed was driven by Bremschildren in the accelerator. FCCE is talking about a 1cm beam pipe.
STFC-RAL-CR03 R61: Is that because there's less bone structure in the larger machine? And the consequent question is, if somebody built T-Net, would they be back at 5cm again, or do they see ways to do it 1cm?
STFC-RAL-CR03 R61: well, my opinion, just my opinion, having spoken with Frank Zimmerman, who's been very excellent at educating us in particle experimenters on these issues, is that, the,
STFC-RAL-CR03 R61: non-Gaussian tails are a threat in any machine. I mean, there are all sorts of problems that affect supervac B and so on, and, so it is by no means a closed issue. They can be…
STFC-RAL-CR03 R61: the tails can be repopulated after dampening rings, due to various things, resonances, and then you've got very closely spaced bunches, that's more dangerous, and there have been, as he explained to me, studies done, but they're by no means complete on the accelerator side. And of course, what we then need to do is to take those, and what do they do in terms of non-Gaussian tails inside that beam volume.
STFC-RAL-CR03 R61: And how much of that gets out. And as far as I'm aware, I haven't… I may well be corrected by this, there hasn't been a study of that as yet, so I think this is all work in progress, but we've got 20 years, so I don't think we should…
Fabrizio Palla: Oh my god.
STFC-RAL-CR03 R61: No questions.
Fabrizio Palla: I can say that, the… at, linear colliders,
Fabrizio Palla: The beam's strong is much, much higher because of the optics, and basically, in a nutshell, you do not reuse the beams, so you do not expect to have
Fabrizio Palla: let's say, the optics such that you can reuse the beam. The beams are lost, whereas in our cases are being reused, otherwise this is not a circular collider. So the smaller beam pipe drives from the fact that the beam's traveling
Fabrizio Palla: is much smaller at, at the SQLA colliders.
STFC-RAL-CR03 R61: Further questions in the room, or do you see any on Zoom?
STFC-RAL-CR03 R61: I see it in the chat.
STFC-RAL-CR03 R61: If you could read that.
STFC-RAL-CR03 R61: Bye.
STFC-RAL-CR03 R61: We will have smaller glamstrom, big, strong, than have linear colliders.
STFC-RAL-CR03 R61: The fact is that at sea, The beam is lost.
STFC-RAL-CR03 R61: We need to reuse, so we update CS3.
STFC-RAL-CR03 R61: Yeah, that's from Fabrizio, so just the comment that the circular collider has to be used, and so the optics have to be different.
STFC-RAL-CR03 R61: Any last-minute questions?
STFC-RAL-CR03 R61: Nope, that's fine. Please say again?
STFC-RAL-CR03 R61: I could see there was some… I mean, I don't think I did something.