Minutes and Summary

Main purpose of the meeting: Physics production, feedback and VdM planning

LPC minutes 6th May

Introduction (Federico Alessio)

(David Nisbett) The message from cryo is that they are not done with the tuning but already it is looking more promising so they are looking to improve it further, and then hopefully remove the 2 hour limit. It is certainly the case that if we are running at high luminosity with the full machine and lose the beam near the start of the fill it is the worst case for cryo. stability particularly when running above 2e34. This is something we maybe want to think about in terms of mitigation.

(Chris Young) Both experiments (ATLAS & CMS) use a convention for z opposite to that which should be in the MASSI files so both should be reversing the sign of the z coordinate. Both experiments believe that they are doing this correctly.

(Witold Kozanecki, Jorg Wenninger) In ALICE there are parasitic crossings in the filling scheme for ATLAS/CMS VdM so it is desired to separate the beams in ALICE. It isn't possible to separate the beams fully in ALICE with this setup as that is not what was commissioned. In VdM everything is collapsed from the beginning so the beams are not separated at the beginning of data taking. It could be possible to do a 2-3 sigma separation but not a full separation. To reduce the parasitic collisions it is usually the crossing angle that is used. 3 sigma in each plane would be sufficient to limit this if this is possible from the LHC side. We should make sure that we are clear when describing things what is meants by "no collisions in a given IP", and if this is just that there are no colliding bunches or if the beams are separated.

(Andrea Ferrero) It was asked if during the VdM factorization MD if ALICE doesn't need to provide lumi. That is correct.

(Roderik Bruce, Catrin Bernius) There are 3 conflicting requirements. AFP desire it to be opened more to reduce the radiation dose, R2E need to keep it tighter to protect downstream electronics, and FASER/SND desire to keep the tighter settings to reduce the background. The plan is to open one side such that the benefits/disadvantages can be evaluated for the first two concerns. As there isn't an access planned in the next weeks the new plan is to do this test slightly later; just before the next planned access. If no significant benefit is seen for AFP then the situation is clear and both will move back to 1.6 mm. Otherwise this would need to be discussed at the LMC as the whole machine is affected. This makes sense for AFP/ATLAS.

vdM and Calibration Transfer Planning from ATLAS (Witold Kozanecki)

(Jorg Wenninger) 6 sigma separation is not an issue and this is similar to what was done in the past.

(Chris Young) So the aim is to keep the fill around 25 hours -> Yes. If it is lost then the part of the scan in question will need to be repeated in the next fill.

(Jorg Wenninger) To answer the question on the slide, it should also be ok to do the 6 sigma separation with physics optics.

(Jorg Wenninger) We should avoid 30 and 33cm in beta* but this is far from where you want to operate, so this proceedure should be fine in principle.

(Jorg Wenninger) It should be ok, but we should check the 6 sigma at 120 cm before the vdM program begins just to make sure.

(Chris Young) The maximum target mu; do I understand that this is to extrapolate as far as possible so this is not directly related to the value that the experiments level at. Yes, that is the case.

(Federico Alessio) What do you want IP2/8 to be doing during the length scale calibration. CMS should be head-on and not changing the leveling. For IP2/8 they should not change anything during the scan but between scans they can change what they are doing. The key is to not change the conditions during the scan.

(Federico Alessio) For the calibration transfer are the requirements similar? Yes.

(Federico Alessio) For the length scale calibration if it is done during the ALICE/LHCb fill is there are particular time it should occur. No it doesn't matter, but the relevant experts need to be awake/following.

(Catrin Bernius, Federico Alessio) Can it be specified which of the MDs have collisions as well as if lumi is required. This can be found out and fed back to the experiments.

ATLAS (Catrin Bernius)

(Federico Alessio) For the lumi imbalance we want to monitor this over the next week when we expect to have many production fills.

(Chris Young, Matteo Solfaroli Camillocci) Are the BSRT numbers trustable/calibrated yet? Not yet. They can be trusted bunch-by-bunch and run-by-run, but not H vs V and beam 1 vs beam 2, or year-by-year.

CMS (Andrea Massironi)

(Jorg Wenninger, Matteo Solfaroli Camillocci, Federico Alessio, Witold Kozanecki) This could be separation plane related, or some feed forward issue. Does it happen in every fill? It happened in the last 5 fills, and also a similar effect is seen in ATLAS. When we go head on we re-optimize both planes so this might be the cause. If you did an optimization in one of the planes and then waited before doing the other then we could see the effect from each plane separately. This can also be investigated from the size of the two corrections from the previous fills. These effects are pretty reproducible, but the shape of the changes in ATLAS and CMS are different. The LHC experts will check the sizes of the corrections and how much this is meant to change the average z position. All the features, including the increase at the beginning of the fill are reproduced each fill.

(Catrin Bernius) Last year ATLAS ran at mu of 65 for the calibration transfer. From the machine there is specific limitation (within reason).

(Witold Kozanecki, David Stickland) What is SS in the list? This is super-separation. Separating the beams as far apart as possible - probably 5 or 6 sigma. It is to try to measure nothing.

LHCb (Elena Dall'Occo)

(Witold Kozanecki) Is this 3.1 sigma the total separation or the separation per beam. It is thought to be total separation but this can be checked.

(Chris Young) In the last fills you leveled at around 1.2e33 rather than 2e33 which you were doing before - is there a particular problem. This is just to commission the UT and trigger and it will revert later.

ALICE (Andrea Ferrero)

(Federico Alessio) The gaps in the plots are between the fills. Yes, the larger gaps are the different fills. Some smaller gaps are when data-taking was interupted.

(Chris Young, Andrea Massironi, Elena Dall'Occo) ATLAS said that moving by 3 mm would not affect their physics. Is this also the case for CMS? For CMS it appears this will move the beamspot closer to 0 so this is also beneficial for CMS. For LHCb they will try to follow-up but currently there is a lot of movements between fills and within a fill which is not repeated. This will be followed up.

(Federico Alessio) How is progress going on DIP publication. There has been a meeting on the technicalities but it could take a little time. The MASSI files will come first. From the LPC side we will also think if there is a way of making the fills appear separately rather than all on top of each other to understand more.