Minutes and Summary

Main purpose of the meeting: Feedback and final VdM plans

LPC minutes 13th May

Introduction (Federico Alessio)

(Andrea Ferrero) As we won't have collisions I presume that we don't need to provide luminosity during the VdM MD. No, this is not required.

(Witold Kozanecki) When was the VdM program webpage last modified? Sunday morning.

(Witold Kozanecki) There is no difference in the performance from the bunch pattern for the length-scale-calibration so it is fine for this to go in the LHCb/ALICE fill. It is also ok for it to go after their VdM scans. However, it is preferred to do it in the stated order unless there are problems.

(Catrin Bernius, Witold Kozanecki) For the crossing-angle scan that is after the VdM what happens if the beam is lost during this? This is also lower priority so we would not refill just to do this but it could go at the end instead. However, it is prefered to do it in the long VdM fill.

(David Stickland) CMS also prefer to do everything in the one long fill, but also have the same flexibility as ATLAS.

(David Stickland) In the calibration transfer fill CMS would like to do a mu-scan during the last part when ATLAS is head-on.

(Michi Hostettler) We need to be careful that the separation leveling automatic configurations are not running for these specific leveling scenarios. You will need to rely on the other experiment to give pile-up values for the experiment doing its scans.

(Andrea Ferrero, Witold Kozanecki) Inbetween each "block" the leveled luminosity can be altered in IP2, but during the scans it is appreciated if changes are not done. This is equivalent to be every approximately 4 hours. The experiments should stay in contact with each other.

(Catrin Bernius, Gianni Masetti) Both AFP and CMS pots should only be inserted for the calibration transfer fill with trains - the very last part of the program.

(Witold Kozanecki, Catrin Bernius, David Stickland) For the last fill it is preferable to have 3 INDIVs rather than 2 INDIVs. This will be updated in the plan.

(Michi Hostettler) Is there a preference when to retract the BRANS. If there is no preference it is better to do it in collision as then their position is more testable. This will be discussed offline.

(Joanna Wanczyk) The instrumentation that is used on the LHC side for the VdM has been recalibrated this year and this should be in the best possible configuration. Additionally the BSRL data will also be present and the BPMs are also operational and ready to go.

LHCb (Giovanni Cavallero)

(Witold Kozanecki) Clarified that LHCb is asking that the status is ADJUST during the scraping at the end of the fill for detector safety. This will certainly be done.

(Michi Hostettler) I will check offline but the shift in the position might be when the feed-forward was implemented.

(Chris Young, Andrea Ferrero) For the z position is there a physics impact eg. tracking inefficiency, if the z is shifted by 3mm. This should be checked offline but it is thought not. ALICE can provide live-feedback if we do do the shift after the VdM.

(Federico Alessio) Is it known when the magnet polarity switch will happen. This is still being discussed.

ALICE (Andrea Ferrero)

(Federico Alessio) This week LPC will try to make the same plots as slide 2 for ATLAS and CMS.

(Chris Young) There is uncertainty in when the ALICE scans will start. Will your expert for the CCC be in the local area the whole time. Yes, they will be there from Thursday and LPC will try to keep the ALICE RCs up to date with the progress through the program.

ATLAS (Catrin Bernius)

(Chris Young, Mirko Pojer, Federico Alessio) The list of MDs, although it might change, is defined and details are in the LMC presentation, but the timetable is not yet defined. For ramping down the magnet it might be possible to arrange the MDs such that this can be done one of the latter days in the MD period after any that require information from ATLAS.

(Federico Alessio) What is the additional loss from offline data quality. This depends a bit on the analysis, eg. which triggers they use, but there have been less issues this year than last year. A typical number can be shared in a future LPC but the offline DQ takes longer to come in general.

(Gianni Masetti, Witold Kozanecki) For the maximum luminosity during the calibration transfer CMS should be able to do similar numbers to ATLAS but will check the details and communicate with ATLAS to make sure they are equivalent. From the machine side there should be an issue going very high in the run without trains.

(Federico Alessio) Similarly in LHCb we see more re-syncs/recoveries when running at higher rates so it is a common issue that the experiments need to optimize the precise point which is most efficient overall.

CMS (Gianni Masetti)

(Federico Alessio) Can you also give a summary of the efficiency similar to what has been shown by ATLAS to justify the higher leveled mu values.

(Federico Alessio, Witold Kozanecki, Michi Hostettler) For the overall imbalance it is a bit unclear what the source is. All the beam parameters are known reasonably well but all have some uncertainty. It should be noted that a 3% uncertainty in online luminosity is very difficult to achieve. The luminous size in z does point to a difference in the geometrical factor. It is also the case that horizontal emmitance will grow quicker than the vertical emmitance. LPC will have a discussion with the experts to see what small adjustments could be made to try to make things more similar but need to be careful about beam-beam. Also there is the hierarchy issue that also needs to be addressed which would allow beta* leveling down to 30cm in both experiments. It is also possible that the BCMS beams lead to different differences between IP1/5.

Summary/Wrap-up (Federico Alessio)
-- check webpage for VdM program which has been updated during the meeting
-- we will shift the beamspot 3mm in the positive direction in LHC coordinate system after the VdM provided the same offsets are still seen
-- BCMS will come possibly next week as agreed at a previous LMC -- we will keep people informed
-- LPC will try to coordinate a meeting of LHC experts on possible mitigations of the difference in luminosity between IP1/5
-- LHCC; please send requests of things to discuss