Minutes and Summary

Main purpose of the meeting: Commissioning, VdM, bug fix in filling scheme export (and old ones on git)

LPC minutes 12 May 2025

Present (P = in person): Chris Young (P), Chiara Zampolli (P), Robert Münzer (P), Andrej Gorisek (P), Filip Moortgat (P), Paula Collins (P), Eric Torrence (P), Rosen Matev (P), Flavio Pisani (P), Andrea Massironi, Gerardo Vasquez, Ivan Cali, Lorenzo Bonechi, Stefano Redaelli, Witold Kozanecki, Silvia Pisano (P), Joanna Wanczyk (P), Dragoslav Lazic (P), Michi Hostletter (P), Jorg Wenninger (P), Jaime Boyd, Peter Steinberg, Andres Dellanoy, Roderik Bruce, Gabriella Pasztor, Maciej Trzebinzki, Matteo Solfaroli Camillocci, Tomasz Bold, Geroges Trad, Klaus Monig, Riccardo Longo, Richard Hawkings, Anna Sfyrla

Introduction (Chris Young)

Chris Young: is the spiral scan final?

Michi Hostletter: we should try it with stable beam, possibly tonight. But the full program is shaky, because of the dump kicker issue.

Jorg Wenninger: note that not everybody can do it and not at any time. It is a special operation.

Chris Young: speaking to Michi, it sounded like if the experiments analyzed the data and found it to be the way they want to do things in the future, it could be adapted to become a more regular operation. 

Michi Hostletter: yes, the way it is implemented at the moment is not as a standard operation. In general it will not replace the old one, it could become another option though. It makes sense to make a few in this prototype way, analyze the data, make sure that this makes sense and is actually correctly analyzable, then we can implement in a more standard way. We should avoid that it becomes dead code in the future.

Witold Kozanecki: the new filling scheme that you propose for the VdM, would they have the issue if I take them from the git area?

Chris Young: they are not yet in the git area. In general, even for old schemes, you have no issue if you press “Download” from the website. The issue affects old schemes if you take them from git. But like said, these are not in git yet.

Jorg Wenninger: I have some news. It might be that the ABT team wants us to do an energy or voltage scan of the kickers after every scrubbing period, and this would take 2 hours. So it’d be better to take one long scrubbing instead of multiple small ones. This is still under discussion, but it might mean reshuffling of the plan. 

Chris Young: this might mean reshuffling in the delaying direction.

People are not sure.

Robert Münzer: last time it was mentioned that there were simulation in preparation for the transmutation of Ne to O which could have an impact, even if small, on the Ne contamination. Are these results going to be discussed here or somewhere else?

Chris Young: it would be nice to have them reported here. They are more used in the analysis of the physics data rather than in the operation of the data taking.

Roderik Bruce: I was in touch with John this morning about it but he said that he is close, but he does not have the results yet, but it should not be too long. 

Chris Young: it would be good to have it discussed here, but I don’t think it is critical to have it before the data taking because you’re subtracting this in the data analysis. 

Filip Moortgat: we’d like to have some ideas before, it can also be at the beginning of June.

Robert Münzer: same for ALICE.

Roderik Bruce: what could influence something is that if we see that this is a problem, we might choose to go for a fewer fills, to dump earlier before the contamination is too high and we’d re-inject. Of course this would make us lose time but if it is critical for the experiments, we have to do it anyway. This we need to know before the run.

Chris Young: this is a good point, as it can impact the operations.

Robert Münzer: as I understood, the plan is to move the MD between O and Ne to profit for the time and have lower contamination?

Chris Young: I don’t believe it was announced which MDs were approved, so we cannot arrange that yet, but assuming the collimation MD is approved, we could put it between the source switch and taking Ne data to make the physics data have the least contamination. 

 

Summary of Oxygen lumi projections (Natalia Triantafyllou)

S5:

Chris Young: you are assuming that the emittance scans after we have taken the whole physics and reached the targets? Because you added 4 hours of emittance scan. But you cannot do it at the beginning or you’d lose the best data. It is even a better idea to do like this.

Peter: The 100 urad is positive crossing angle?

Roderik Bruce/Chris Young: for ATLAS we can choose, for CMS we cannot choose, it has to be horizontal, because otherwise there is no acceptance for the ZDC. 

Eric: in fact we want to have it positive or we won’t have acceptance in the ZDC.

Roderik Bruce: for pO you might also wanted positive, but then we put negative for AFP.

Peter Steinberg: how do we characterize the risk associated with running above the setup beam limit?

Roderik Bruce: safety wise for the machine, there is not really a risk. The risk is that we lose in efficiency, since we cannot mask any interlock, and we run with the same interlocks as with full beams, so if we hit any interlock, we might then dump and lose time, and the time is very tight here. So the risk is that it takes too much time because we forget some interlock.

Chris Young: it is a “beam-loss-monitor-dumping-the-beam” risk, rather than “blowing-up-the-LHC” risk.

Robert Münzer: concerning the emittance or VdM scan, can they be done in parallel for the experiments? Meaning not all VdM at the same time.

Chris Young: you never want to be scanning one experiment while the other is also scanning or you won’t have constant conditions at the other IP.

Reyes Alemany: for the intensity of the beam we need to do some calculations from the injectors, what we expect from extraction at the SPS is an intensity of 4e10 charges. If we need to reduce these intensity, for one single injection from LINAC, because you need less, we’ll need to scrape in the SPS, which should not be an issue for OO because you require 3 which is within uncertainty; while for pO you require 1e10 which is quite lower, and we’d need to scrape quite a lot and we’d need to find a way to lower the intensity. We would need to find a solution from the injector side. The other question is why the intensity per bunch in pO, especially for O, is so low? 1e10 and not 3e10.

Roderik Bruce: the reason is that we want to keep the intensity reasonably low, with as many bunches as possible to have a low pileup target at ATLAS. So we need many collisions, only by doing that we can get to reach the lumi target in the allocated time. One could have a higher bunch intensity and the same number of bunches, and this should be checked with collimation and MP. We tried here to reach the target with the lowest intensity possible. If we can increase and go to 3e10 charges per bunch also for pO, there is no showstopper, but we might need more validation, and this would take more time, and we’d not gain. The only showstopper is if you need more validation fills, which takes time. For OO, 3e10 is not absolute, if we get 4e10 we’re happy. For OO we’d take as much as we can. For pO we would be much higher than the setup beam flag limit up to a factor 8 above.

 

LHCb (Paula Collins)

Chris Young: for the 0 field fill, you said you only needed an hour of data, but we’ll keep the fill, we have to [for MPP].

Paula Collins: we’ll profit from the fill and we’ll see what happens. 

Chris Young: if the fill is cut short, we’ll switch on the magnet at the next one?

Paula Collins: yes.

Michi Hostletter: concerning all the activities for the scan, in particular the Length Scale Calibration (LSC): do you care if the magnet is on or off? Otherwise this is an activity which you could potentially do in the next fill [the one with B off] to save some data for physics. For us, since we want the spiral scan at the end, we’d also save some time. 

Rosen Matev: for the most part, probably yes, but there are some detectors that are sensitive to magnet on so it would be nice to do it with magnet on. We anyway have some activities that are compatible with magnet off, so we will try to fill it. 

Michi Hostletter: in the end it is a matter of 1 hour or so.

Rosen Matev: maybe it is useful to repeat one of these with magnet off. 

Chris Young: this should fit in the time, since ATLAS will go to low mu in the first 400b fill for some of the time, so the levelling will last ~9h. 

Paula Collins: we thought the fill would have lasted ~10h

Chris Young: when nobody was at low mu, we got to the end in ~8.5h

Paula Collins: we have several activities, not all in these slides, which were planned relying on 10h, so this is not reliable?

Chris Young: we have to see. This one will probably be 10h since when ATLAS goes to low mu for a while (we saw the same with CMS), the time is longer.

Paula Collins: for us, any fill could be 10 hours.

Michi Hostletter: for these scans at 400b, do you have any restriction to go head-on? I guess  you rather want it with less intensity which will burn off slower with ATLAS low mu, so it is probably still good to do it only when we reach 18 cm because otherwise it may go a bit high for you. 

Rosen Matev: we can go head-on, but the fill has to be representative of the nominal conditions.

Michi Hostletter: so we should wait anyway till we finish the fill. In general, if any of these activities go wrong, the fill will anyway count for MPP.

 

FASER (Jaime Boyd)

Eric Torrence: [concerning the behavior of the 75b which shows more mu rate than the 12b] this should come from the luminosity online that was not correct.

Jaime Boyd: ok, thanks, I did not know. Which fills are not good?

Eric Torrence: I will let you know. 

Stefano Redaelli: Do you think it makes sense to do some tests with other configurations or local bumps, or we can leave it like this this year?

Jaime: from the physics perspective, we can leave it like this this year, but if there is something that we could improve, and we can think of clever things that we could try, and it was cheap to do so, this would be an interesting option. But I had the feeling that end of last year we kind of ran out of things to try. Maybe this is not the care.

Stefano Redaelli: I would need to check. I think there were some cases with small improvements that might not be enough to justify the overhead, but maybe we can put something in the MDs. Let’s take it offline. 

Jaime: just to say that any increase in understanding that could lead to improvements, of course could be beneficial also for future years even potentially for the full physics facility, so it could be interesting to try to reduce the background rate, and see if it is validated in data.

Stefano Redaelli: indeed one of the big benefits last year was to increase our confidence on the tools. 

Chris: the bump on the top left plot, is it more due to the TCL6 rather than the polarity of the magnet?

Jaime: this would be my guess. Usually a change in TCL6 settings in the past showed more or less tracks in this area. So this might be quite possible, but of course we have never run with horizontal crossing angle before, so the effect of that I am not completely sure of. My guess is that this comes from tra arc and not the straight section.

Chris: Eric, can Jaime pick up the right lumi from your Massi file?

Eric: yes.

Jaime: I will try to pick it up.

 

SND (Gerardo Vasquez)

Chris Young: the different bricks show similar flux levels. So if we assume that we’re doing all the four bricks the whole year, it is better to have the distribution of muons homogeneous. So it is not necessarily a bad thing. You had the trick last year when you had a better signal over background, but if you’re doing all four, then it is better to have it levelled.
Gerardo Vasquez: the difference is that we have 5 targets this year, but if we expect 100 fb-1, the bricks with the current muon background can sustain only 15-16 fb-1, so we’ll not cope with the entire luminosity with 5 targets. 

Chris Young: indeed. You cannot make the momentum plot as FASER, but you can do a pointing one, right? You can measure the theta value, so that we see if also for you it comes from the arc?

Roderik Bruce: it seems like we hear for the first time ever a difference between the two sides of ATLAS (FASER vs SND): for FASER it seems that there is an increase by ~10%, while here we have ~80% more than 2023, but to my knowledge there is no fundamental difference between the two sides that should have appeared this year. Does anybody have an idea why we see this difference?

Jaime Boyd: one thing is that the angular acceptance is not the same between FASER and SND. SND is more off the line of sight than FASER. So the muons can be spread in a different way.

Gerardo Vasquez: even though we are at the same location in z, we don’t cover the same angle.

Jaime Boyd: For me it is not hugely surprising that there is no agreement with simulation since what we learnt from the last time is that it is difficult for simulation to give very precise results, but it is more the trends that we saw in the simulations. You do see a significant decrease in the muon rate compared to 2024, if I understand the table, and that is what the simulation says. If you think that you can take the simulation exactly at phase value, it is a bit optimistic. 

Chris Young: yes, but they still see 50% higher than 2023. 

Jaime Boyd: that, I think, is a more valid comparison. I guess that this is most likely because of the different angular region that SND covers compared to FASER. I think my last slide which was probably using the more correct luminosity value, FASER saw something like 20% higher that 2023, probably it was 18%. So it is definitely not the same, but it is not as different as saying that FASER sees exactly the same [as 2023].

Chris Young: if we know where they’re coming from, then maybe this gives the collimation teams more insight into maybe what could be thought about could be doen with TCL6.

Gerardo Velasquez: for us, what is important is to understand why do we see the mu uniformity across the entire target. It is important to look at the 400 bunches. We can also look at the track slope, to see if there are any changes. And we know from previous years we know that there is always a shoulder on x, and it is still there but we need to compare it with the 2023, to see if it is the same or not. In addition, one factor that could change the total density is that we need to get the correct luminosity for ATLAS, and more precise. So getting more luminosity will surely help. 

 

ALICE (Robert Münzer)

Michi Hostletter: [about changing the field in ALICE during the 2nd fill at 800b]: it would be good to ramp it down in stable beams gently, because depending on the scrubbing state you may or may not get trouble with the electron cloud. Therefore if you do it gently with beam in, if at some point you reach losses that are too high, we can stop. If we do it directly before we fill and then we ramp, if we get losses during the ramp, then we dump on those. So it would be better to define this as a baseline, to ramp it down in stable beams. 

Chris Young: this would be done in the CCC?

Michi Hostletter: yes.

Robert Muenzer / Silvia Pisano: so the procedure can be stopped in the middle? And you can control the velocity?

Michi Hostletter: yes, both. 

Michi Hostletter: [about the issue with the lumi steps] one option if you need more time, and we want to avoid it, you could send zero, so that then we determine the optimal step size, as done in ATLAS, CMS, LHCb.

Robert Muenzer: I thought that now you’re forcing a step size.

Michi Hostletter: yes, we can force it, but it is a manual action,and if you force it all the time, in particular at the very beginning, it takes a long time to reach. We can do it but like said, it is a manual action and it might be that we notice too late, if it happens at the beginning of the fill it could be fine because people are monitoring, but later, it might escape. 

 

CMS (Filip Moortgat)

Filip: PPS is fine with 60 urad for pO.

Chris: for BSRT we think that the filling scheme will be the same, we will confirm

 

ATLAS (Andrej Gorisek)

[Concerning about the beamline shift that is reported to be >1mm]

Jorg Wenninger: we should see if we can move by 1 mm.

Chris Young: this is vertical, rather than horizontal.

Andrej Gorisek: it s diagonal.

Roderik Bruce: if we move something, we will for sure to re-align the collimators in IP1. 

Jorg Wenninger: the TCL.

Roderik Bruce: maybe not the TCL, but we’d re-need loss maps revalidation and some intensity ramp up. Maybe if you could wait till TS1, then we could do it, because we’d need all that in any case.

Andrej Gorisek: if in TS1, probably it’d come in the shadow of the short intensity ramp up.

Roderick Bruce: yes.

Jorg Wenning: I hope AFP is beyond.

Andrej Gorisek: in AFP they can do it easily in one direction.

Maciej Trzebinzki: if we move the beam, it is pretty safe to move in y, while in x it should be compensated by the location of AFP.

Jorg: another concern will be extra dispersion. A bump will make dispersion, and we should look at that.

Chris: will this imply a new alignment of AFP?

Jorg: probably not but to be seen. 

Andrej: we’d like to know the possibilities and how much impact it would have on the program. 

Chris: we’ll let you know.

Jorg: once you start moving, whether to choose by 200 um or 400, it will cost the same.

 

LHC (Michi Hostletter)

[Concerning the ratio of lumi between ATLAS and CMS]

Michi Hostletter: At the moment CMS target is 60, ATLAS is 62. If you look at the ratio after the leveling, ATLAS seems to see 8% lower than CMS. The practical issue is that CMS levels almost 1 hour longer than ATLAS because the target is lower and their apparent luminosity is higher when head-on. This is the last fill with 12b trains.

Eric Torrence: part of that will go away with trains, because the luminosity we report is lower with single bunches.

Filip Moorgat: we will go up in pileup too.

Chris Young: it’d be useful if you are close by one unit, so that levelling finishes at the same time.

Michi Hostletter: but it depends also on what is the ratio afterwards. It is not a bit problem, but a consequence of this is that if you do xing angle antilevelling at the end, and CMS is still in levelling, or just out of levelling, you will exceed your target during the x-ing angle decrease by some amount. In this fill you don’t see it because it was compensated by adding a little bit of separation, but that is not a standard procedure. So, what we see is still within the uncertainty of your calibration?

Eric Torrence / Filip Moorgat: yes.

Michi Hostletter: ok, if CMS moves a bit up with pileup, that is good.