Minutes and Summary

Main purpose of the meeting: Updates on 2024 data taking. Experiments feedback. Open points on ion / ppref runs.

LPC minutes 16th September

Introduction (Federico Alessio)

(Matteo Solfaroli Camillocci) Next year the VIP visits will be a different colour in the schedule from the TS such that people are aware that accesses might not be possible.

(Jamie Boyd, Gerardo Vasquez) The Friday is actually the 4th rather than the 5th. The exchange will be on the Friday. It was confirmed that both experiments emulsions will be removed during TS2.

(Matteo Solfaroli Camillocci) We shouldn't consider that the technical stop is extended as the intervention could be quicker. The experiments shouldn't consider the full day as free for access. The official stop of the technical stop should still be considered as the end of Wednesday afternoon.

(Catrin Bernius) For next year will the bunch intensity be discussed at JAPW? Yes, this will definitely be on the table.

(Jorg Wenninger) The 8th of November is likely another VIP visit which will require a stop.

(Catrin Bernius, Jorg Wenninger) Will the 4 bunches in the PbPb ramp-up be with stable beams or without? It can be decided near the time but there is not problem declaring stable beams.

(Chris Young, Roderik Bruce) If we decide to do pPb in 2026 this means that there is the possibility of taking all the reference pp data for PbPb this year, and saving the days in 2025. However, we would need a pPb reference run in 2026. If we are doing PbPb in 2026 then again we could take enough reference data this year, but it would require more than is currently planned so this is unlikely. This means that some thoughts on whether PbPb or pPb could be valuable before the pp reference run this year. It was clarified that the pPb reference data would be taken alongside the pPb data in 2026 if it is desired to do this rather than PbPb.

CMS (Andrea Massironi)

(David Stickland, Chris Young, Michi Hostettler) We have been trying to optimize the vdM program for CMS. Is the plan during the PbPb vdM run to separate the other experiment to reduce burn-off? This makes the time less useful for that experiment for head-on so there is a trade-off. It should be taken into account that ALICE will also contribute to the burn-off, but they could also be separated if this is desired. LHCb contributes less.

(Roderik Bruce) For this year in the pp reference run we have the standard crossing configuration. Does this mean that you want the same for pO/OO/PbPb next year? It doesn't need to be the same as this year, although that is presumably beneficial for the machine. The request is more that all the ion/special runs next year have crossing plane.

(Michi Hostettler) In the last PbPb vdM scans we separated the non-scanning IPs to about 25% of the head-on lumi. It is the baseline plan to do the same this year.

ATLAS (Catrin Bernius)

(Matteo Solfaroli Camillocci, Michi Hostettler) We could try to "reset position" to move it outwards until the end switch is triggered. But it is not clear that this will solve the issue with the system. In mode BEAM DUMP the devices are still allowed in by default. We can send them home, but this is not to do with the override key normally. We might need the override key to move them at all in this mode though, it will need to be looked at. Another solution could be to leave the STABLE BEAMS flag, retract them fully and then move on with the cycle. This would cause a delay and the other experiments would also see 5 mins or so with STABLE BEAMS but no beams in the machine which is not ideal. It might be that they continue to move after they have started which would reduce the 5 mins. This will need to be followed up offline.

(Michi Hostettler) Does this depend on which empty bunches you are looking at? We think it considers all empty bunches without a gap behind trains. Do you also include the 12 at the beginning which are non-colliding in IP1? No - these are completely empty crossings. It isn't thought to be a issue for data-taking/quality at the moment. Looking in the abort gap could be interesting where the beam is actively cleaned.

(Jorg Wenninger, Maciej Trzebinski, Roderik Bruce) It was thought to try to do the BBA of AFP before the TS, but not this week. The problem is that the time-of-flight (ToF) needs to be re-installed in TS2 so this cannot be anticipated. Therefore it is requested and agreed to do it after TS2. We shouldn't do it in the same fill as the loss maps for collimation reasons.

ALICE (Andrea Ferrero)

(Jorg Wenninger, Chris Young, Matteo Solfaroli Camillocci, Federico Alessio, Roderik Bruce) To do a test of the possible crossing angles the full commissioning would need to be done. This was a request from the LHC rather than ALICE. This would require further time prior to the TS. It would not be a problem for ALICE to have either of the crossing angles. For the larger crossing angle an aperature measurement would be required which is why this is an issue. For 340 it should be that an aperature measurement is not required such that this would simplify things and this should also be good for beam-beam. For ALICE it would be ideal if any test was after the VIP visit to minimise magnet cycles. This will need to be discussed offline.

(Federico Alessio) The ZDC high-voltage module replacement can happen on the 4th October in the shadow of FASER/SND.

(Federico Alessio) For the schedule date of the vdM. Ideally this will happen just after the intensity ramp-up for both of pp reference and PbPb.

(Chris Young, Michi Hostettler) In the pp reference run the cross-section is lower than in 13.6 TeV. Will the luminosity tool can be updated to use a different cross-section. When the experiments level on pile-up, like ATLAS/CMS, then the LHC uses the pile-up provided by the experiments so they will need to update their reference cross-sections. It might be less error prone if people level on lumi rather than pile-up. Each experiment is able to decide which they use to level on. DIP receives both a luminosity and a pile-up from each experiment.

(Michi Hostettler, Jorg Wenninger) When testing different lumi settings during the intensity ramp-up, be careful that the BLM thresholds will be different for pp reference such that it isn't the same interaction rate which will trigger a dump. The tool also does have some protection against dumps by preventing very bad settings.

LHCb (Giovanni Cavallero)

(Chris Young, Federico Alessio, Jorg Wenninger) For the 2nd half of the pp reference commissioning will this need to be after LHCb switch their magnet to the polarity that will be used in the pp reference commissioning? For the commissioning it doesn't matter what the LHCb magnet polarity is.