Minutes and Summary

Main purpose of the meeting: Data taking, discussions on PbPb/ppRef and 2025+2026 schedule

LPC minutes 14th October

Introduction (Federico Alessio)

(Chris Young, Catrin Bernius, Matteo Solfaroli Camillocci) We are waiting on the VIP visit timescales. For the 25th October there is a request to do it at midday. For the 8th November it is apparently in the afternoon. Both the 25th October and 8th November visits are ATLAS only and not the tunnel so should be quicker. In general due to the uncertainty in the visit time and when the cryo will be back after the TS there is some uncertainty in when the final pp ref setup and ion cycle will happen. We will keep the experiments informed as soon as more is known.

(Catrin Bernius) ATLAS reached pile-up 69, just short of 70, during the high pile-up test.

(Matteo Solfaroli Camillocci, Catrin Bernius) It might be that we need to do a ppRef intensity ramp-up fill as the PbPb commissioning is over the weekend. The ATLAS magnets will only come back on Saturday and can't profit without them for the pp ref program. It may be a problem filling the time with expert availability over the weekend. It will be clarified when the ATLAS magnets are back next week. The AFP alignment and the loss maps could be done, but both of these are pretty short as only about 3 hours of loss maps are still needed. It is both magnets so we can't do any part of the luminosity program and the small number of bunch fills are needed for validation before the vdM run.

(Andrea Ferrero) How do you define physics? It is the total of the first 3 columns so it excludes MD but includes PbPb setup and special runs.

(Chris Young) The vdM will come after the pO and OO runs and all are included in the same block of dark red.

(Catrin Bernius) In the previous version you didn't have a TS in Scenario A is it needed? This is to make the two equivalent as there is a TS prior to the HI run in Scenario B. It could be that it is not necessary and can be removed.

(Rende Steerenberg, Chris Young, Roderik Bruce) It is the preferred scenario of the LS3 committee to have a long cool-down - ie. scenario B, but they, with RP, are investigating the possibility of Scenario A. A pPb run, as opposed to a PbPb run, will provide a different cool-down. The previous run is probably not representative of what could be achieved now. Additionally it could involve a high intensity proton beam with similar numbers of bunches to normal running such that the cool-down at Point 7 would be minimal.

(Federico Alessio) There is the possibility of following a pPb run with some MDs to provide further cool-down if needed. Maybe particularly risky MDs depending on the interest in these and the beam conditions.

(Andrea Ferrero, Chris Young, Rende Steerenberg) It was mentioned the possibility of a Ne-Ne run last week. The injectors have not set this up yet, but Reyes is chairing a task-force looking at this. This would likely be a special run as it is not technically ion physics. It certainly wouldn't fit in the 2026 run as Pb ions will be needed in north area during the year and significant time is needed to switch between species such that with a short year like 2026 this is not possible.

(Robert Helmut Munzer, Roderik Bruce, Chris Young) Is it possible to have PbPb and pPb in the same period? Yes, this is possible as the injectors can keep protons in the injectors, but we would still need a second setup period. The second setup period would actually be a little shorter as the Pb beam would already be setup. There is a lot of discussion surrounding these runs so this would be doubled so we would need to be very organized. Therefore in principle with it all in one year it would still be possible to have PbPb and pPb. Yes, but this does mean that we would lose some of the gain from optimizing to have the least possible setup such that at this point the cool-down arguments would probably dominate. On the experimental side you would also need to be setup for both species in the same year in term of trigger etc. You would gain flexibility of when to start pPb depending on how the PbPb is going, assuming they are in that order.

(Andrea Ferrero) For the YETS duration do you know when this will be decided? There is a discussion at the LS3 committee on Wednesday. This might not make a decision but will hopefully move towards a decision. We are working on a baseline of 9 weeks with the end of the run near Christmas.

(Catrin Bernius, Andrea Ferrero) The question on the splitting is a dangerous question to ask? Should it be re-phrased as do you believe it is in agreement with the previous agreed sharing? It is based on the splitting agreed by the research board in the past, in December 2021, but obviously the schedule has changed multiple times since. Obviously your management can re-discuss this decision if they want.

(Andrea Ferrero) Are the numbers on slide 10 what has been realized in 2024. Yes, it is meant to be the realized schedule including anticipating HI commissioning, removal of cryo-re-config, VIP visits etc. The schedule is updated with the VIP visits, etc. each year.

(Catrin Bernius, Chris Young, Roderik Bruce) For luminosity expectations can these be provided? Yes, we can make proton ones very quickly, with a scenario close to this year and one more realistic of what is expected for next year given the hope to increase the intensity. For PbPb we will chat with Roderik about what numbers to use but they will have large uncertainties. Before the LHCC we should get a better idea as we will have taken some PbPb data. For pPb it is more difficult so if people can say what they would need in terms of luminosity and if they are interested at all that is useful. We can then try to estimate the number of days. For pPb there are different options for example we could have low ppb proton beam matching Pb filling, like 2016, or a high intensity beam, or a high intensity 25ns beam. This dramatically changes the picture. In the yellow report there are targets for pPb that people should look at to check their requests are reasonable. This was based on two 4-week runs of pPb and did include slip-stacking but there are some things that will have changed since then such as the proton beam emittance. The number of collisions in LHCb is also very low. There are also some more up to date notes on the topic.

CMS (Andrea Massironi)

No comments.

ATLAS (Catrin Bernius)

(Federico Alessio, Maciej Trzebinski) For AFP is there any problem doing the BBA with the magnets off. No this is not a problem.

(Roderik Bruce) Is the 300 pb-1 sufficient even with the additional days that have been presented today. This was calculated before the additional days were added. It therefore still needs to be checked.

(Matteo Solfaroli Camillocci) Just to clarify it is just the schedule you want to post-pone and not the optics decision? The optics can still be decided quickly and from ATLAS an early decision would be appreciated.

(Federico Alessio) What was the Run 2 luminosity for PbPb? It was 1.9 nb-1 in 2018. We did the same as 2018 in 2023. There was another small amount in 2015. The goal is still to get to the stated targets for Run 3. It still needs to be discussed if once this is reached what is done in terms of more PbPb, more pp data, etc.

(Filip Moortgat, Roderik Bruce) Would it affect anything other than the burn-off if both ATLAS and CMS were head-on. It would affect the burn-off but ALICE's leveling time is very long such that it is likely problems are encountered before we hit the ALICE limit.

ALICE (Andrea Ferrero)

(Roderik Bruce) In answer to; would it be possible to try colliding in the other IPs but separate in ALICE to observe the background in this configuration. Yes, this should be possible from the machine side.

(Roderik Bruce) We should certainly start data-taking with the same polarity as the setup. Yes, this is the plan.

(Chris Young, Roderik Bruce) Why is there such overhead needed, in pp ALICE polarity changes are usually transparent. This is because the crossing angle and collimator settings have to change. For a second polarity switch we will need to check with MPP.

(Federico Alessio, Chris Young) Note that the decision will be after the PbPb data-taking, as it is at the RB, but the LMC presentation is before but this does not cast things in stone. At the LMC we could present if the HI goes well it is favored to do different plans. It is understood that from ALICE the priority is to have ions in 2025 in all scenarios. Internally it will be discussed if it is desired in ALICE to split 2025 into PbPb and pPb in the scenario that all the ions are in 2025.

(Chris Young, Federico Alessio) Does the extra day of pp reference come from the expectations for the total PbPb for the rest of the year. It would be good to get some agreement of what we do if there are long-ish stops during the pp reference run or what happens if it goes extremely well. Please provide feedback next week. From ALICE only a stop longer than 2 days would make it favorable to have a pp reference run in 2026. The extra day in the slides is calculated to account for the difference in the targets from ALICE.

LHCb (Elena Dall'Occo)

(Chris Young, Federico Alessio) It would be good if all experiments could provide a statement if they were going to run out of disk if we run until the 15th December 2025. We also want to give it a weight, and also where this should be brought up, for example at the LHCC such that the problem can be solved. As disk is relatively inexpensive with sufficient pressure we hope that these problems can be solved.

(Chris Young) In the next day or so we can produce lumi projections for pp, with an optimistic and baseline scenario.

(Stephane Fartoukh, Chris Young, Catrin Bernius) For next year would it be assumed that leveling at mu=64-65 will be the target for ATLAS and CMS. Yes, this is expected, presumably 64 if we have ~100 more bunches with a different filling scheme, otherwise maybe 65. There have been requests for the optics for next year but this depends on the configuration. Additionally it would be the first time since I've been doing the optics that they are delivered before the end of the previous year's data-taking. The configuration will have to be discussed and approved. For CMS it is a bit clearer than for ATLAS as at IP1 we have conflicting requirements for the radiation to the magnets and for the forward physics experiments. This will need to be discussed at the LBOC and at the LMC on 6th November. Therefore an optics can be provided in the coming days, but this might not be the one that is decided on. The one that will be provided is the nominal polarity with horizontal crossing? Yes. We will follow the LBOC discussions tomorrow and bring this information to the experiments in this forum. The important date is the 6th November for the decision. For ATLAS it is also being discussed with regard to AFP as there is quite a bit of money involved to keep it running or it ends and there is a loss of physics.