Minutes and Summary

Main purpose of the meeting: 2024+2025 Schedule and Chamonix planning

15th January 2024 Topic: Schedule for 2024/2025 + Input for Chamonix

Federico Alessio (Introduction)

Slide 3 - it was asked if for the 2 days of ppRef setup schedule is potentially relaxed and could be quicker. It is potentially going to be quicker if there are no problems in which case we will start earlier, but not by a large margin.

Slide 3 - the 1st October is potentially a VIP visit for CERN's birthday so this might be a stop. When this is confirmed it will be added and the schedule adjusted.

Slide 3 - it was clarified that the hope is to be efficient enough that enough ppRef data will be taken in 2024 such that the 2025 reference run can be removed saving 2+2 (setup and running) days which would become PbPb data taking days.

Slide 3 - in principle it is agreed that an MD day can be donated to HI from pp. However, this needs to be discussed within the LHC community about the priorities of the pp and PbPb MD requests.

Slide 3 - for Wednesday it is decided that we will add one ppRef day in exchange of one PbPb day, and still keep the 2025 2-day run for now in the schedule.

Slide 3 - (Gianni Masetti) CMS raised that they could want a ppRef run in 2025 for measuring detector aging. They will follow-up to find out if this is a strong request as it would mean that the total HI luminosity would be reduced (by approximately 0.6nb-1). For now the 6+2 day scheme for 2024+2025 will be the default but it is known that this is still up for discussion.

Slide 5 - (Witold Kozanecki) It was raised that the JSON file doesn't contain the BCID collision information and only the injection pattern. This will be followed up with Delphine.

Slide 7 - (Jamie Boyd) There are on-going FLUKA simulations to estimate the changes in the background for FASER for partial RP. However, these are delicate and potentially unreliable. Therefore FASER will not be able to make a strong statement for/against the change to partial RP. They will carefully monitor the levels of background and iterate with the collimation team in case of observed problems with the first data during intensity ramp up.

Slide 7 - (Witold Kozanecki) It was asked if the optics would also be different for vdM scans as well. The optics for these also have to be re-done. This is built in to the commissioning with beam time (it is 1 week longer). This week is then saved in 2025 assuming that we go to full RP.

Slide 8 - For the 75ns vs 50ns slip-stacking there were some out-of-time effects but the charge leakage was at the % level, such that further understanding of the effects seen is needed.

Slide 9 - (Witold Kozanecki) It was pointed out that the non-factorization affects all four experiments, not just ATLAS/CMS who are the most affected/vocal. The desire from the experiments is that the machine studies how to reduce or understand the non-factorization in general.

Slide 9 - (Andrea Ferrero) ALICE pointed out that they want the TDIS open during their vdM scans for the acceptance of ZDC.

Slide 10 - it was clarified in the last steps to squeeze to b*=20cm the beam is only squeezed in the non-crossing plane such that the beams are then no longer round, but are round for the rest of the leveling period.

(Stephane Fartoukh & Jorg Wenninger) It was pointed out that as time is short for the commisioning of the optics for partial RP it could be that the optics for the final step of 30cm->20cm in the non-crossing plane is not available. Therefore it might not be there at the beginning, although it could become available later in the year.

(Jamie Boyd) It was asked if for the acceptance for neutrinos which depends on the field in the triplets there are available optics configurations. The current working model is still being modified but Stephane will pass it on as soon as it is ready.

Catrin Bernius (ATLAS)

Slide 3 - ATLAS will look into whether the out-of-time events are from the next colliding-pair, empty crossings within trains, or at the start of trains, etc.

Slide 3 (Roderik Bruce) It was pointed out that due to the differences in LEIR it is not fair to compare 75ns in 2018 vs 50ns in 2023, and we did in fact benefit from slip-stacking. The degree of loss due to out-of-time pile-up was thought to be in the range of 5-10% so this is what we should compare against.

Slide 4 It was clarified that the fast b* ramp-up has a larger benefit at 1.6e11 ppb vs 1.8e11 ppb, but it still gains performance so will be there as the standard approach.

Giulia Negro (CMS)

[No questions]

Andrea Ferrero (ALICE)

Slide 6 (Roderik Bruce) It was clarified that the first objective for the simulations is to try to simulate the known source to try to re-produce what was seen in ALICE. Iterating on trying to find other sources, and creating new optics to mitigate the new currently unknown source will take time. Therefore we should not be too optimistic that new optics will be ready for the 2024 run. ALICE clarified that they are still able to take good data with the current conditions, although they would prefer a lower background level.

Slide 6 - (Roderik Bruce) One of the proposed MDs is directly to try to see the impact of opening the TCTs on both ALICE and the other detectors.

Slide 6 - (Andrea Ferrero) ALICE clarified that from their side they are approaching the limit of how to mitigate the high background.

Niels Tuning (LHCb)

Slide 1 - It was clarified that until the last step (above 1800 bunches) adding INDIV is relatively free.

Slide 1 - It is requested from LHCb for the LHC to look into the optimal combination of crossing angle and magnet polarity.

AOB

(Mario Deile) In the case the flat beams are implemented will DIP publish the separate values for the two planes. This is not intended and DIP will publish the lower of the two values. Therefore if we see a value below 30cm then it will be squeezed in one plane and the other will be 30cm. Even with telescopic optics it is good to have a record of this in reconstruction to test dependencies.