Minutes and Summary

Main purpose of the meeting: Data taking progress (including plan for increased intensity); First look towards PbPb; 2026 questions, pPb configuration and prediction

LPC minutes 20 October 2025

Present (P = in person): Chris Young ({), Chiara Zampolli (P), Roderik Bruce (P), Andrej Gorisek (P), Giulia Negro (P), Archie Sharma (P), Filip Moortgat (P), Robert Muenzer, Jorg Wenninger (P), Riccardo Longo, Dragoslav Lazic, Roderik Bruce (P), Flavio Pisani, Ivan Calì, David Stickland (P), Natalia Triantafyllou, Andres Dellanoy, Witold Kozanecki, Vladislav Balagura, Giulia Ripellino, Matthew Nguyen, Stephane Willocq, Michi Hostletter (P), Anna Sfyrla

Introduction (Chris Young)

Filip Moortgat: would the test with 8b4e at the end of this year be with high pileup?

Jorg Wenninger: t would not be with collisions since we are at the end of the ion run when we are not supposed to irradiate. This would be a test for heating reasons.

Rodeik Bruce: we should also see when to fit it in the schedule.

Paula Collins: what is the combined “check-list” [mentioned in the description of the intensity ramp up for PbPb]? And when would it happen?

Chris Young: it is the check list from the different equipment groups on the LHC side. 

Roderik Bruce: It would be before the 800b fill. One option would be to do the VdM at that moment, since for this you don’t need more than 450 bunches. 

Chris Young: this is what we indeed did last year.

Paula Collins: going back to the intensity ramp up: will it have INDIVs?

Chris Young: we have schemes with and without, but we usually use those with INDIVs, which can be considered the default.

Jorg Wenninger: there was a discussion today with Rodri and Mike and we agree that from the next fill we can go to 1.75, and we’ll stay there for the moment; then at the LMC we will discuss what we do or do not observe for a possible further increase in B2.

Chris Young: is it confirmed B1 at 1.4?

Jorg Wenninger: yes, although the vacuum expert presses to try again at higher intensity, but there is nothing to learn. 

Robert Muenzer: for the ramp up in PbPb, when will be the VdM?

Chris Young: it is most efficient to do at least one of the two VdM during the checklist. Last year we did LHCb and ALICE in the same fill, and then ATLAS and CMS in separate ones. Is this still required? Or could they be in the same?

David Stickland: since the fills are short, it is probably better to plan to have two separate ones. 

Chris Young: I thought we separated the two since we had lost the beam.

David Stickland: if you want to have a reasonable lumi, it is better to foresee to have them in separate fills. 

Chris Young: then we’d have one during the check list and the other ones would be later if desired, but it is better to have them all done as soon as possible.

Robert Muenzer: we have some constraints from our experts side, I will let you know.

Chris Young: thanks. As soon as one is during the check list, we have more flexibility.

David Stickland: is the 450b to be used for the VdM?

Chris Young: we have a specific scheme, with ~200 bunches and 100 ns spacing. So we do the 2 450 fills and while they are being analyzed by the LHC experts, the VdM scan with the special settings can be done.

Roderik Bruce: looking at the schedule, if we think optimistically, and we go in SB on Sat week 46, then we have 3 fills before the check list step, then we could end on Sunday. Would it be an issue to do VdM on Sunday?

Everyone: we will check.

David Stickland: from CMS side we don’t have constraints.

Performance projections for pPb 2026 (Natalia Triantafyllou)

Roderik Bruce: the commissioning is based on the PbPb 2024 and the pPb from 2016, so it might be overestimated. In addition the VdM could also be shortened - are 1.5 days needed for both directions? But the margin is not so large.

Jorg Wenninger: why 2.5 days of re-commissioning? There are loss maps, cogging, but the ion setup is done.

Roderik Bruce: one shift for the cogging, then we need to realign the crystals. Some of this overhead comes from the fact that we use the crystals. When you reverse the beams you are off momentum in the other direction, so the crystal angle will most likely not be correct. You then need to retune. Then probably some recommissioning of the transfer line. So we might reduce the duration a bit, but for sure it will not be 1 day. 

Witold Kozanecki: a personal comment (even before we discuss this matter in ATLAS), about shortening the VdM: considering that the magnetic configuration should be symmetric, maybe the LSC could be done only 1x, but this is maybe less than 2h of beam time per experiment. The rest, I don’t think we can reduce since the luminometers are asymmetric, especially in ALICE and LHCb, and since the dominant systematic is non-factorization, and since there is no way to control the reproducibility of the beams in that respect, I find it difficult to think at something that could bring down the VdM time in case of beam reversal. 

Paula Collins: maybe it is obvious, but is there any reason to not use the 25ns for p in case of pPb?

Roderik Bruce: I think it should be studied; I am pretty sure it can be done, but we never collided this way. You waste many p bunches, and you have a different beam beam pattern in this situation than in standard. I don’t strictly expect issues, it should even be better than standard proton running, but we should verify that nothing funny happens beam dynamics wise. This is mostly offline analysis. To play it safe, we could start with a 50 ns scheme, do an MD with the 25ns, or do the intensity ramp up with the 25ns and see if we spot issues. We could also increase the intensity for the p to 1.6-1.8e11, but this is even more uncharted territory with one beam that is very weak and the other very strong, and we should think about this not just for beam dynamics but also for instrumentation etc. I would not try this in operation but in MD, then it could be considered for the next pPb run, whenever that happens. 

Chris Young: this would be a very interesting MD for Run 4 when ALICE will have a FoCAL, and ATLAS and CMS have extended trackers.

Filip Moortgat: it will be very interesting for CMS in Run 4.

Robert Muenzer: we need to check with our ZDC if it is feasible to run with 25 ns.

Roderik Bruce: only the p would be 25 ns, so the collision product will still have the 50 ns pattern. 

Chris Young: you said you used the PbPb configuration. Which b* you used in IP8?

Natalia Triantafyllou: 1m in IP8 and 71 urad in xing angle. This is the 2025 configuration. 

ATLAS (Andrej Gorisek)

No comments.

CMS (Giulia Negro)

Chris Young: for running something other than Pb, there could be a problem in the fact that they have a Pb program in the SPS at the end of next year, and there are 7 weeks between us stopping the ion operations and the North Area expecting the Pb. It is unclear if we can switch source in that period of time.

Roderik Bruce: from a preliminary discussion, it seems to be not impossible. But to be seen.

Filip Moortgat: for CMS, the 7 nb-1 is the most solid goal.

Chris Young: for the low pileup, you can do it any time, just organize with the CCC. 

Filip Moortgat: maybe one on Monday and one of Friday of that week. 

Roderik Bruce: for the collisions setup will hopefully be done in the first two days of commissioning, before the technical stop. There would probably be less collisions after the TS. To be seen. After the TS we have the transfer line steering, train injection tests, LM… and not necessarily with collisions. LM are with collisions, but they are usually quite short. 

Filip Moorgat: we will check with the experts. It should be rather fast.

 

ALICE (Silvia Pisano)

Roderik Bruce: the background test should happen on Sunday if everything goes well. If there are issues, it could be later in that day, or in the night, or in the worst case of a big delay, even after the TS. 

Silvia Pisano: this should not be a problem, the experts are coming on the 7th. And they usually stay for at least the first part of the data taking.

Jorg Wenninger: [about the ALICE concern to go to 1.8] for HI, only if something stick into the beam, there should be no problem for HI, due to the low intensity. But nobody would know how something could block the beam. Unless the concern is for the protons. If we discover that the TCLD has a kind of systematic problem, this might be a big thing, we’d need to discuss what to run in ALICE in Run 4, or consider to redesign the TCLD. 

Chris Young: considering that most of the things take 10 days to change, if we go to 1.8 this week, ions should still be safe from incidents.

Jorg Wenninger: we could also increase to 1.8 at the end of this week and in case go down next Mon/Tue, and see if there is anything that happens on a short timescale. 

Roderik Bruce: we should just not do such an increase the week before ions.

Jorg Wenninger: this is why I want to move on this week, then there is MD and TS also.

Roderik Bruce: I assume you need ½ statistics per polarity.

Silvia Pisano: yes.

Roderik Bruce: The ++ cycle is the one that we worked on till now, so it is safe to start with that.

 

LHCb (Paula Collins)

Discussion on when to swap the polarity: agreed that it can be done on Thu (to be checked in detail), even in case we decide to run at 1.8 in B2 on that same day.

Jorg Wenninger: [concerning the issue with the missing train in the filling scheme] the shifter was probably not aware that there was a discrepancy since we did not get any warning. 

David Stickland: on a formal level, we did send the information via DIP that there was a problem but neither we nor the LHC looked at it. 

Jorg Wenninger: this flag is probably digested nowhere. Now we have the check at the start of the ramp. This issue should not happen again, at least not in this form.

 

AOB

VdM scan in HI

David Stickland: I think that during the VdM scan last year, there were 2 6h fills, and probably you are right and the ATLAS one was dropped, I don’t see a LSC. So they did not complete the scan, the lumi dropped in their scan.

Chris Young: so we need 3 VdM fills, one ATLAS, one CMS, one ALICE + LHCb.