Minutes and Summary

Main purpose of the meeting: Experiment feedback on full machine data taking and planning

LPC minutes 22nd April

Introduction (Federico Alessio)

(Catrin Bernius, Jorg Wenninger) Do we have a precise time for the start of the access. This comes from the protocall office, but we should start between 8am and 9am for FASER.

(Jorg Wenninger) For the cryo numbers we need to be very careful with the number of Watts per half-cell as there are different displays eg. online/offline, giving numbers that differ by 10 W/hc. Relative numbers do make sense though. Sources of the differences are under study by the cryo team.

(Jorg Wenninger) These other activities which are being moved to this week will only happen during the day due to people's availability.

(Jorg Wenninger, Michi Hostettler, Catrin Bernius) To explain the increase in the beamspot width it could be the emmitance growth and when the BSRT is complete more reliable numbers will be available. It can't be explained by the luminosity calibration. It was asked if it be possible to do something before TS1 about this difference as it will be 8 weeks so there will be a large imbalance. If the slope is due to emmitance then this is not possible to change. The overall offset could be altered but changing ATLAS's crossing angle to compensate will increase the hierarchy problem, and we need to understand this first. Understanding the hierarchy problem needs to be the priority. It could also be possible to increase the crossing angle in CMS to reduce their luminosity but this is also controversial and didn't improve the hierarchy situation. To be followed up after the hierarchy issue is understood, and will also be discussed in ATLAS's talk.

CMS (Andrea Massironi)

(Jorg Wenninger, Michi Hostettler, Georges Trad, Andres Delannoy) For the emmitance scan proposal this is non-ideal from the machine's side as it will be difficult to remember to do it. It would be better for the nth fill or in the next fill after n hours. The driving factor for having it not every fill is to have more beam-time. Why not do it like previous years where the experiments just ask before the fill for the next fill to have one. ATLAS and CMS will follow-up together to find a strategy that is efficient. The experiments prefer to have 15 points rather than 9 point fills. It was asked if the LHC need a 9 point one every fill, and this is useful until the BSRT is fully calibrated to have a cross-check of the emmitance.

ATLAS (Catrin Bernius)

(Jorg Wenninger) Which side is the increased background? It is mainly coming from beam 2 background as it is in the direction towards LHCb.

(Federico Alessio) R2E have said that increasing beyond 2 mm for TCL6 would not be good from their side. This will be discussed further in the collimation group. There is also a request to check this from the FASER background side at the end of a fill.

(Michi Hostettler, Witold Kozanecki) What is meant by "wrong way" diagonal. This is to do with the magnetic historisis. It refers to the scan where only one sign is wrong and we only have to do the y-direction twice.

ALICE (Andrea Ferrero)

(Chris Young) Have you changed your sign as this was opposite to what was in the MASSI files for comparing with the other experiments. For these plots the sign hasn't been changed but for the MASSI files they will be.

(Michi Hostettler) It is possible to move ALICE only through having not optimized crossing planes. ALICE could provide feedback on the 5min timescale, however, this is too long for a realistic operation. It isn't possible for the LHC to do an offset without feedback as they find the minimum and would not know how far to move away from this.

(Andrea Ferrero, Federico Alessio) Will it be possible for LPC to provide comparisons of the z-positions. Federico will try to display either 2D scatter plots or summed 1D plots of the z-positions from the MASSI files such that we have better comparisons as the data is too noisy to tell anything currently.

(Federico Alessio, Chris Young) Other experiments are to check if a shift of 3mm clockwise would be noticable to them as most runs in ALICE have a shift in the same direction.

LHCb (Elena Dall'Occo)

(Michi Hostettler) It is also possible to do this optimisation in the separation in the non-colliding plane which for LHCb is tilted in one of the decay periods as it only takes a few minutes to check if it is moving during the fill. This could then be put into a feed-forward correction.

(Federico Alessio) Do you only want one fill with INDIVs? Yes. LPC will create a filling scheme with more bunches and only 1 INDIV colliding per IP. ATLAS request INDIVs once per week and CMS request is once per month (so are in the shadow of the other requests).

AOB

(Witold Kozanecki, Elena Dall'Occo, Andrea Ferrero) Previous the VdM program did ATLAS 1, CMS 1, ATLAS 2, CMS 2 etc. then the ALICE/LHCb scans after a re-fill. Is there a preference if ALICE or LHCb goes first and if they want it in several sub-sessions? Last year ALICE did everything in one go, and LHCb did one of their scans very early in the program. It is possible to do some of the ATLAS/CMS length scale calibrations during the ALICE scans in case the beam is lost during the first fills. The early scan from LHCb last year was because their main program was later in the year which is not the case this time so this is not needed. The ordering of LHCb and ALICE will be clarified with the experts and communicated with the wider luminosity community. It is likely LHCb will want to go first such that they can provide SMOG for ALICE. Federico will fix the ordering on the website such that the physics optics runs occur after all the VdM scans.