Minutes and Summary

Main purpose of the meeting: Data taking progress Leak in collimator Other news

LPC minutes 08 September 2025

Present (P = in person): Chris Young (P), Chiara Zampolli (P), Robert Münzer (P), Filip Moorgat (P), Andrej Gorisek (P), Eric Torrence (P), Paula Collins (P), Roderik Brice (P), Witold Kozanecki, Stephane Willocq, Michi Hostletter (P), John Jowett (P), Andres Guillermo, Richard Hawkings, Anna Sfyrla, Georges Trad (P), Jorg Wenninger (P), Matthew Nguyen, Giulia Ripellino, Joanna Wanczyk, Matteo Solfaroli Camillocci, Daniele Mirarchi

Introduction (Chris Young)

Robert Muenzer: is the TCSG.A6R7.B2 that is affected by the leak any relevant collimator for HI?

Roderik Bruce: no, it is not needed for ions since it is upstream of the crystals which in ions are the primaries, so it does not intercept much of the beam for ions.

Stephane Willocq: it is not yet confirmed that ATLAS will make the low mu request, we’re still discussing with the physics groups, so I would not characterize it as a likely request.

Chris Young: that is not quite what Gautier (CMS spokesperson) said at the LHCC.

Stephane Willocq: it is possible, I am not saying no, but we are collecting physics justification from the groups this month. We’ll probably know next month.

Filip Moortgat: the discussion was indeed among the physics coordinators who seemed to be converging but this does not mean that it is supported by the management.

 

Beam-beam transmutation in the OO and NeNe run (John Jowett)

Chris Young: since it seems that we are very much dominated by He, could we just consider that one?

John Jowett: yes, except for Ne. 

Chris Young: most of the times we see that the EMD contribution is smaller than the hadronic one. Do you have the Ne hadronic contamination plots?

John Jowett: it is included. I used the AAMCC simulation. I could also show FLUKA hadronic. Some other people have other simulations.
[The slides show both contributions when they are labeled with EMD and a clustering percentage which is used for the hadronic part.]

Chris Young: oxygen does not seem very different from Ne, other than the uncertainties being larger. Then it means that the data are good. 

Roderik Bruce: it would be interesting to know what the experiments see in OO and NeNe.

Chris Young: before the LHCC we got a couple of plots from ATLAS and CMS. They show very little in the O fills particularly, indeterminable basically. In the Ne fill there is a hint of something changing over time in the ATLAS plot. CMS only gave us O. 

Paula Collins: for LHCb SMOG, we’re still looking. 

Chiara Zampolli: in general, from the experiments, there is a bit more in Ne than in O. And I think it is larger than what reported here. Here we don’t get to the percent level. 

Roderik Bruce: we could get to the percent level due to the O contamination in the Ne beam, but not because of transmutation. 

Eric Torrence: but if there is contamination at the start, we would not be able to see it over time.

John Jowett: and I think that an O-Ne collision is not much different from a NeNe one. So it is probably hard to distinguish. 

Chiara Zampolli: it is also difficult to translate what we see in observables over time in terms of contamination percentages. 

Roderick Bruce: what observable are you looking at?

Chiara Zampolli: the number of tracks per primary vertex.

Robert Muenzer: in ALICE, as we showed here, we also use an asymmetry in the ZDC. A change in the symmetry would mean an asymmetric collision. And here we saw a change over time, and the same question of whether this comes from contamination arises. 

John Jowett: there might also be asymmetric beams. 

Chiara Zampolli: it seems that there is no agreement between what I see in ALICE Ne QC plots and here. According to these results, we should see nothing. 

Chris Young: in ATLAS and CMS there seems to be nothing seen in O. 

Chiara Zampolli: same in ALICE. It is only Ne showing something. In ALICE the different fills in O also tended to behave a bit differently, but these were not official ALICE plots. 

John Jowett: there is more uncertainty about the physics of the reaction in Ne, where the structure of the nucleus is different. 

Chiara Zampolli: I thought that Ne would have behaved similarly to O, but if what we see in the experiments is true, then it is now. 

John Jowett: naively thinking about the skittle model of the Ne, you could imagine that an alpha particle can get separated from the Ne nucleus more easily than in O. Just naively. But I don’t know. I am surprised that these results turn out so low. 

Roderik Bruce: i think that the biggest uncertainty is the cross section and the momentum distribution after the fragmentation, because we know the integrated lumi from data, we know the momentum cut which was confirmed with tracking, it is basic physics. On these things there is no uncertainty. But then the contamination means the number of contaminated particles divided by intensity. Intensity we know very well. So we’re left with the number of contaminated particles, which is the cross-section times integrated lumi. And the x-section is the x-section of creating something within the momentum cut of the ring which is very tight. So maybe those x-sections are not fully correct. 

John Jowett: it depends on the total x-section in the two cases (EMD and hadronic). If the momentum distributions are much narrower than this simulation predicts, then there might be more particles in the momentum acceptance. 

Chiara Zampolli: it would also be interesting if the experiments can do simulation with certain amount of contamination and see how that translates into the observables that they are using. 

John Jowett: I find it hard to believe that any observable is sensitive to these levels of contamination. 

Chiara Zampolli: not to this, but maybe we could find which contamination could explain what is seen, if any. 

Filip Moortgat: there might be other effects that can explain what is seen. 

Chris Young: ALICE, ATLAS and CMS should have put out results from the light ion runs this morning, which is great in such a short time!

 

ATLAS (Eric Torrence)

Chris Young: for the VdM optics in 2026: we will probably have the VdM optics, as the overhead is not that large.

CMS (Filip Moortgat)

Roderik Bruce: can you confirm that the installation of the FSC fits in the TS?

Filip Moortgat: maybe that comment referred to next year, not sure. It is probably something true for this year and the next. 

Chris Young: I spoke to Angelo about ZDC installation: there are movable shields that can be used, and ATLAS and CMS were quite efficient to install their ZDCs, so he was looking for only 24h without collisions beforehand as a suitable cooldown, which is easy if we have the first day of Pb commissioning the day before the TS, for example. 

Filip Moortgat: we can get back to this when the ZDC expert (Lazla) is back. 

Roderik Bruce: now we have two days of Pb commissioning before the TS and before there is MDs; we could even reshuffle the MDs to have the low intensity ones at the end.

Chris Young: let’s see if it is needed, we probably have 8h of MDs after your commissioning if they're doing a quench test. 

Andrej Gorisek: the low-mu run might have an impact on the duration of the VdM. 

Chris Young: we could put the low-mu before the VdM such to use this for the low activation for the VdM. It would still put the low mu before the VdM.

Filip Moortgat: if it is next to it, it should be ok.

Chris Young: it is not sure that the ZDC will be really cooked during the HL tests. It is only 1.1 fb-1 in 2 weeks or something, 2x what you took in the pp ref run with it in.

Andrej Gorisek: will it be used again?

Chris Young: not in the LHC, there will be no TAN anymore.

Filip Moortgat: maybe they want to put in the test beams. If there is an opportunistic slot of ~6 hours, we might remove it. If it is not possible, it won’t be the end of the world. 

Chris Young: in the LMC they said they would not do cryo reconfiguration, so there would be no natural downtime. 

Filip Moorgat: maybe it will not be a problem to find 6 hours.

 

ALICE (Robert Muenzer)

Chris Young: how much acceptance is affected due to the ITS issue for which you’d need access?

Robert Muenzer: it is not large, no large impact on the data quality. I can find the number. 

Jorg Wenninger: how much will you go down with magnetic field?

Robert Muenzer: about ⅓ (10 kA).

 

LHCb (Paula Collins)

Jorg Wenninger: [concerning going down in pileup following the issue with the LHCb cooling] I would not consider 0.1 to do the feed-forward and go then back to 6. It is then better to do nothing till you’re back. 3 could be ok, but 0.1 is too low.

Chris Young: would the 0.1 be solely for the purpose of defining the feed-forward or also to take data?

Paula Collins: only for the feed-forward, we’d then separate.

Chris Young: then we should go separated completely.

Michi Hostletter: we cannot go fully separated. We cannot go beyond the ~2.5-3 sigma per beam which is what is agreed in scans. We cannot go full separation since we don’t move the TCTs around.

Paula Collins: In the on-going fill we will decrease to low pile-up after the end of the leveling when feed-forward is not being improved.

Michi Hostletter: [after the idea that at end of fills LHCb could go at pileup of 1-2 if requested and possible in that specific moment] for the feed-forward, for the tracking of the first fills, it is surely once you reach 60/18 when the LHC is no longer improving the feed forward, not before, so that then at least you have some check there. And you should not change at once by a factor more than 100. If you want to go up, maybe go up by a factor of 10. If the actual lumi you have is a factor 100 larger than what you request as target, then it can actually fail. It is something not expected

Jorg Wenninger: for the correction in y, it is a pity that we just did the Loss Maps without it.

Chiara Zampolli: but when it was presented the other time, it was said that this amount should not be an issue.

Paula Collins: we can also do just 50 um.

Michi Hostletter: 50 um is of the order of the lumi scan, so we could just put that in.

Paula Collins: if that is straightforward, let’s just do 50 um.

Chris Young: it would be good to do it when your tracker is fully back.

Michi Hostletter: yes, we’d need a feedback to know that we are moving in the right direction. If 50 um is enough, then there would be no change in the collimators. This would be 1-1.5 sigma displacement.

Roderik Bruce: will you do this with a normal lumi scan bump?

Michi Hosteltter: we’ll do it with one that can use the MCBX then it takes less excursions outside.

Roderik Bruce: it would be good to do is to check the excursions we get at different points including at the TCT. 

Michi Hostletter: sure, but with another knob it is for sure less than in a lumi scan where we have checked that we can move to 2.5 sigma per beam without issues. 

Jorg Wenninger: the request for 1 TeV does not say which type of beam: 3 bunches of 2000? It will make a big difference. If you ask for full machine, we will need a ramp up. If you ask for 2000 bunches, we’ll have to do it in steps, so it will be more fills. If you ask for 50, you might get one fill, or let’s say O(100) bunches. It is also special mode, we never did collisions at this energy, so we anyway would not go to 2000 immediately, but we’d step up progressively.

Rodeirk Bruce: we’d then need to validate, check the collimators also do LM. 

Michi Hosteletter: in collisions we’ll need to check the cleaning, and the leakage. 

Chris Young: if you could give us a luminosity, then we can work out what we can do, similar to what we did for oxygen.