Minutes and Summary

Main purpose of the meeting: - The final PbPb data-taking - Total luminosity delivered! - Lessons learnt during Ions in MD & Operation - 2026 questions

LPC minutes 08 December 2025

Present (P = in person) ***meeting on Zoom only***: Chris Young, Chiara Zampolli, Martijn Mulders, Andrej Gorisek, Eric Torrence, Archie Sharma, Dragoslav Lazic, Giulia Negro, John Jowett, Maciej Trzebinski, Silvia Pisano, witold Kozanecki, Robert Muenzer, Ivan Calì, Richard Hawkings, Tomasz Bold, Gerardo Vasquez, Roderik Bruce, David Stickland, Andres Delannoy, Reyes Alemany

Introduction (Chris Young)

Tomasz Bolt: could one have the 25/50 with pPb?

Chris Young: the 25/50 ns scheme would be a PbPb scheme. If we run pPb, there are a couple of different things that can be done. We can try to put the full 25 ns scheme on the proton beam and the 50 ns scheme on the proton beam, which is something we discussed before. Technically we could put the 25/50 ns on the Pb beam and the 25 ns on the proton beam. I don’t think we can use the 25/50 ns on the proton beam. 

Roderik Bruce: we cannot produce the p beam with the 25/50 ns structure. The basic idea in case of pPb would be to have the 50ns Pb beam and the 25 ns p beam. We could also use the 25/50 ns Pb beam, but we should look how it would work with the 25 ns p beam.

David Stickland: the change in xing angle may be not consistent with the 25 ns scheme?

Chris Young: it can be that we have a better spacing so we could probably have 100 urad instead of 150 for example and you might still not get the long range effects.

Roderik Bruce: I think that it is clear that the beam beam effects will be a bit worse with this scheme, and we have to study it. We did now the beam beam MD with the 50 ns scheme, and we should study with the 25/50 ns. However, the 50 ns did not show limitation, and also I think the 25/50 ns should not, but it should be studied, considering also that the bunch intensity would be a bit higher with the 25/50 ns scheme.

Chris Young: in general, for the xing angle, we are not looking to go to zero. When we ran with the O scheme for example, we had xing angles of 100 urad instead of 100. So this is the kind of  range of operation that we’re looking at.

Roderik Bruce: if the experiments can give feedback on which xing angle is feasible for the ZDCs or if there are constraints, it would be useful. Usually we give you the xing angle in advance so that when you install the ZDCs, you can align around that, we would like to know if there is anything more. 

Tomasz Bolt: what is the timeline for the decision between pPb and PbPb in 2026?

Chris Young: we’re waiting for ALICE to see how much data were taken so that they could make up their preference. If this matches the one of everybody else, then it is trivial. If they say that in the next 7 days, then we’ll know in 7 days. If they argue for pPb, then we might need to go to the Research director to explain that there is this conflict, and it might take a bit longer. We thought to know certainly before the Chamonix workshop. 

Robert Muenzer: the decision for ALICE will be taken this week, then we’ll let you know.

ATLAS (Andrej Gorisek)

No comments. Discussion about organizing a visit at P1 (and the other experiments) not reported in the minutes.

 

CMS (Archie Sharma)

No comments. 

 

ALICE (Robert Muenzer)

No comment.

 

LHCb (Paula Collins)

Could not attend due to LHCb week in parallel.