Minutes and Summary

Main purpose of the meeting: Almost Final Data taking progress; Planning PbPb and recent news; 2026 questions

LPC minutes 10 November 2025

Present (P = in person): Chris Young (P), Chiara Zampolli (P), Roderik Bruce (P), Andrej Gorisek (P), Eric Torrence (P), Robert Muenzer (P), Martijn Mulders (P), Paula Collins (P), Joanna Wanczyk (P), Gerardo Vasquez, Tomasz Bold, Giulia Negro, Detfle Kuchler, Filip Moortgat, Flavio Pisani, Natalia Triantafyllou, Reyes Alemany, Silvia Pisano, Witold Kozanecki, Anna Sfyrla, Jorg Wenninger (P), Andres Dellanoy, Aleksas Mazeliauskas, Archie Sharma, Peter Steinberg, Riccardo Longo, Wei Li, Matteo Solfaroli Camillocci (P), Juan Esteban (P), MIchi Hostletter (P), Ivan Calì, Matthew Nguyen

Introduction (Chris Young)

Roderik Bruce: if everything goes smoothly, the VdM could be on Saturday already. 

Andrej Gorisek: can we have the details of the schedule for the PbPb in the planning spreadsheet?

Roderik Bruce: yes, we can add our best guess. It now also includes the commissioning for the ALICE polarity switch, but for now it is a placeholder to have it on Saturday. 

Paula Collins: what is the intensity of the beam that was used for the estimates [for the 1 TeV run]?

Chris Young: 1.7 or 1.8e11 (not remembered exactly), the nominal bunch intensity, which is why we need the ramp up.

Paula Collins: going head on with 400b, the mu should then be higher.

Chris Young: the reason why we have a small mu comes from the b* that is 3.1m, plus a very large crossing angle of about 1000 murad from the LHCb magnet, then you lose a factor 7 from the beam energy gamma, then the x-section which is 60 mbarn instead of 80.

Jorg Wenninger: at this low energy, we need that your spectrometer adds to the external crossing or we’ll have too high parasitic collisions in the triplet. This is why you’ll have 1000 mrad. So one given polarity only.

Paula Collins: for the emittance scan during the special run, we should be sure that with the aperture that is quite close we get a signal. 

Constraints on Light Ion Running (Roderik Bruce)

Andrej Gorisek: when would the second source be available?

Reyes Alemany: the proposal will be presented again at the beginning of 2026 for the upgrade with a second source connected to the same LINAC, and we’d need 2-3 years to have all implemented (design, study, procurement, installation, commissioning), so by 2031. If it is approved.

Chris Young: the motivation in the proposal comes from the fixed target expts in the NA?
Reyes Alemany: it is a combination of motivations. One is that our capacity to test and deliver operation beams is very much reduced as discussed today; because we have a facility for R2E facility that is being built at CERN and that requires a second source (without it, it is not possible), and also because if NA61++ is approved in Run 4 and we have to deliver 2 operational beams per year (light ions for NA61++ and Pb for the NA60+ and LHC) then we are committed to deliver operational beams and we have no possibility to have the light ion test (pilot run) anymore. The second source would allow to serve a large community (LHC fixed target and R2E).

Reyes Alemany: concerning Ar: another possibility is Ar40 (more abundant) for which we could use the same Q/A ratio till PS (included) to use the O settings, then it would change in the SPS, but here it is not an issue. This could increase the chances for Ar. 

Roderik Bruce: it is a good idea, but for the LHC then it would be difficult, since we’d need a new cycle for the Ar40. It would be something in between in the end in terms of commissioning time. We’d need less in LEIR and PS, but then long in LHC and SPS. This in case the experiments want to run at the same energy as the pp reference (a different Z/A of 18/40 at the same energy would imply the need for a new cycle). 

Reyes Alemany: for the fixed SPS NA experiments in August, we don’t need nominal beam, but early beam and this can be commissioned in a very short time in the injectors. It is true that that 6 weeks still holds for source commissioning and stabilization, but one injection only is seen in the rest of teh complex, not like the 7 injections needed for the nominal, high performance beam of the LHC; and there is no slip-stacking in the NA. 

Roderik Bruce: we have only one week only, and the SPS commissioning is anyway after the 6 weeks of source commissioning. For this we have 1 week in the timetable, and I don’t think we can get much faster, because the week after we already start the NA run. So there is no time for 1 week of source maintenance.

Robert Muenzer: is there a chance to declare this as a special run?

Chris Young: the Research Board (RB) stated that the pp time should not be touched by any other activity. 

Roderik Bruce: what about the LHCb 1 TeV run?

Chris Young: this was agreed some time ago, in 2022.

Chris Young: are people interested in a long O run?

all: it needs internal discussions. 

Roderik Bruce: keep in mind that with full trains you would get much more lumi than the few days of this year. From a fast simulation we are looking at 200 nb-1, so it seems you can get a factor 20 more lumi than you got this year. Up to the experiments to say if it is interesting.

Chris Young: about the last slide: if we go for something at the start: if e.g. we go with He, because e.g. LEIR cannot cool it down, you can go back to pp commissioning, and you would realize this early enough to not lose any time because the injector commissioning is done early. This could be a strategy, it could be risky, but if it is not working in the injectors, you could get the time back at the end of the year (not super trivial because it means to keep the timetable flexible). 

Robert Muenzer: the timeline for the decision is very close. When do we need a decision? 

Chris Young: LHCC is next week, so if this is on the table, we should consult with them at least to know if they would support it. The RB is in 18 days, and we should finalize the timetable for next year. At least on paper one should say something that if PbPb this year is successful, we might do this. 

Roderik Bruce: for the machines it is also complicated to change the schedule too late. It is not a showstopper but it complicates life. 

Chris Young: [check!]

Robert: what is the decision making process? We can discuss in the collaboration to have an official statement, but what are the further steps?

Chris: we need a kind of consensus built around one single program and to show that this has physics motivation at the LHCC. So you should show why you motivate this choice in the LHCC experiments closed sessions. You could tell us which options are likely and we could share among the experiments so that we see if people are considering the same options. There are many options, so it would be useful to narrow them down with any statement. 

Roderik Bruce: maybe short O at the beginning of the year is not very interesting, to just have 2x the statistics of this year.

SND (Gerardo Vasquez)

Chris Young: a comment about why we did the second test: the first test had some lifetime issues, so we wanted to test it again and have it on both sides. Bump 3 was done in case of problems with radiation in the dispersion suppression, so we tried in the opposite direction. I think that also FLUKA studies are ongoing.

Roderik Bruce: there was a radiation monitoring working group meeting last Friday. They presented some first results. Radiation studies showed that we should have the similar radiation levels in 13 and 15 as we have now in cell 11 with the bump, however the electronics is not the same, and there are some QPS boards which are not radiation hard in cell 13 and 15 while they are in cell 11, so we need to check what type of radiation can be tolerated. So, with the ion run in memory, we probably don’t want to just do nothing and put the 9 mm bump, which might have issues in the QPS cards that were not updated. They are looking if they can upgrade those, maybe even only on the SND side. 

Chris Young: yes, for FASER this is an invisible background.

Roderik Bruce: I made the point that this is a useful bump for the machine, but it should not give R2E problems. We cannot move the radiation hard cards from cell 11 to cell 15 because in cell 11 there are all the losses that come from Pb. 

Chris Young: yes, the ion run should have no availability issue. 

Roderik Bruce: we can also have some FLUKA simulation of bump 3 which brings the losses to cell 9, which is not as good but would get rid of some radiation. 

Jorg Wenninger: bump 3 was a bit invasive for the machine while bump 1 was less invasive, which is going in the right direction.

Gerardo Vasquez: do you expect to have asymmetric configuration? I thought one always wants to be symmetric.

Chris Young: If we only have certain number of radiation cards, then we can consider an asymmetric configuration.

ATLAS (Andrej Gorisek)

Chris Young: [for the low mu run] a “normal” way to do this, is to do this is 3-3.5 weeks before the end. You could have VdM, then you switch to low mu till the end, potentially for both experiments. At this point, if you don’t reach the target, you just don’t reach it. Would you be happy with 3 weeks scheduled and then we stop such that you can’t keep running. To be seen if one can increase beyond mu = 3. 

Michi Hostletter: would you prefer to swap VdM and the low mu for cool down of your calorimeter?

Andrej Gorisek: related to this, is it important to know when we do the low mu run?

Chris Young: potentially for cool down this might be important. E.g. for the VdM cool down (for the tile activation), or the TS cool down. And we have several activities that can be used for cool down, like the low mu, the VdM, the 1 TeV. Then there are MDs, but it would put strong constraints on the MD, so it would be better to use the low mu.

Eric Torrence: we might still need 24h after the low mu if we want to do VdM after it.

Chris Young: it would be good to have CMS and ATLAS do the low mu at the same time, so that we can have very long fills. 

Andrej Gorisek: even if one is at high mu and the other low, you get slightly longer fills, and the one at high, will have a bit more time at higher mu.

Roderik Bruce: is there any issue in terms of beam-beam with low mu in one experiment and not the other?

Jorg Wenninger: We already did it in the past.

Michi Hostletter: if you do it at the same time for both, it is probably better to not fill with the max possible intensity.

Chris: do you need to put the VdM after the low mu, or close to it?

Eric: in our case, we don’t need that for the W mass.

Chris: it was a request by CMS to have it next to the VdM. 

Andrej Gorisek: then it will be after the TS or whatever is there, the MD block.

Chris Young: for heavy ion this year, in the nominal plan, we think that ALICE and LHCb will be done after the 400b during the check list, so then we’d have the 800b fill, and we’d be on Monday for the CMS and ATLAS.

Andrej Gorisek: can we do the VdM after the first 800b fill?

Roderik Bruce: yes.

Chris Young: the PS and SPS can switch easily.

Eric Torrence: so for sure we won’t do it before the 800b?

Chris Young: no, after that it is easier.

Michi Hostletter: note that I miss the scan files for the VdM from ALICE and CMS. 

 

CMS (Giulia Negro)

Roderik Bruce: how many hours do you need for the FSC?

Giulia Negro: I think at least 4 hours. But we don’t want to interfere, so in case we’ll make it with what we have.

Chris Young: we could also use the time in collision from the loss map fill.

Roderik Bruce: we won’t have much time in collision during the loss map fill. Maybe just 10 minutes. But it is a high chance that you get 4h during the night.

Chris Young: for the below mu run, we’ll check if it is better from the machine point of view and from an optimization point of view if it is better to have one high and one low, or both low. Probably better to have them both low considering the number of turn-arounds you’ll have to do.

Michi Hostletter: if both are low, the fills will be very long. 

Chris: LHCb should be aware that if we have both low, we’ll have very long fill, then short turnaround, then another long. These buffers that you have need to be able to cope with that. If it does not work, we might want to do one low and one high. 

Flavio Pisani: how long will it last?

Chris Young: probably 3 weeks with potentially 24h long fills. It might even be longer, but I imagine there will be some trips.

Flavio Pisani: thanks, we have some simulation tools that we can use.

 

ALICE (Silvia Pisano)

Roderik Bruce: [about the plot on s3] it looks like the spike in the red curve in the left plot is out of scale, so maybe the situation in 2025 is worse than 2024?

Robert Muenzer: this should just come from some fluctuations. 

Michi Hostletter: the y-scales of the plots are also different.

Roderik Bruce: then things are even worse. 

Robert Muenzer: we should prepare a ratio plot. 

Roderik Bruce: [about the collimator settings] the default is 14 because we open as much as we could to reduce the background. With the previous background source the more open they were the better, now it seems to not be the case any longer.

Chris Young: for the ion BPT, do you want that we put 1.85 as target [which is the 5.8 nb-1 on s7 minus what was already delivered till now in Run 3] instead of 2.25?

Robert Muenzer: this is our minimum, the target should be higher.

Chris Young: but not as high as 2.25…

Roderik Bruce: with lower leveling, it will be more difficult to reach.

Robert Muenzer: I think the target should be ~2.1.

Michi Hostletter: we can make a little prediction of what you would reach with your lower target, then we agree to put the target for this year something like 10-20% below that value. Then this should be comfortably reachable. It will not be your minimum minimum, but something reachable also in case of issues.

Robert Muenzer: with the simulation with the lower leveling we should end up with 2 nb-1, if we have a similar performance from the machine as last year.

 

LHCb (Paula Collins)

Roderik Bruce: following the results on the bkg test, we will continue like this, with 1m b* and no change on the on-disp bump.