Minutes and Summary

Main purpose of the meeting: pp data-taking, preparing for PbPb, and 2026 plans

LPC minutes 3rd November

Introduction (Chris Young)

(Martijn Mulders) Why is it that the most squeezed point is not always where the beams cross. This would give the best results.
(Michi Hostettler) In an ideal machine it is but due to imperfections in the machine a shift can be introduced that then results in lower luminosity.
(Chris Young) It can also happen in both plane which can be in opposite directions.
(Jorg Wenninger) All the magnets are correlated and as there are both planes to consider it isn't trivial to get it to work perfectly.

(Roderik Bruce) The numbers shown assume 6h fill times.
(Filip Moortgat) Is it worth investing time to fix the waist in ALICE rather than just taking more physics data?
(Roderik Bruce) It should only be 2h of measurements +2h turn-around, so only half a shift which is why it is justified.

(Roderik Bruce) Could ATLAS & CMS do their VdM directly after ALICE & LHCb through the Sunday night?
(Chris Young) It could be possible. 
(David Stickland) It isn't ideal to do things all through Sunday night.
(Roderik Bruce) We then rely that the checklist can be done on a Sunday. Note that the timeline has been updated this morning following a discussion on experts availability.

(Roderik Bruce) Note that we planned to have the IP angle scan in the fill when we find collisions. Do you still want this for this year, and would Saturday suit.
(Brian Cole) We expect it will be quite repeatable (based on last data), so maybe we won't need to do as extensive a scan as last year, but we will want something. Will will be available.
(Jorg Wenninger) Be careful, quite a lot changed so it might not be that repeatable.
(Roderik Bruce) Note that this is required before the TCTs are aligned at point 1.

(Roderik Bruce) I have heard suggestions of Helium, Argon, Krypton, and possibly more Oxygen. If there are others that we should look into potential possibilities, please let me know. Also if you know integrated luminosities that would be interesting that is also good input. Also, if we can eliminate any of these suggested ions then it would simplify the discussions.

ATLAS (Eric Torrence)

(Roderik Bruce) Yes, the IR7 optics MD will also require luminosity.
(Michi Hostettler) For the first fill in this MD they will also need BCM masked.
(Eric Torrence) Ok, it is important, particularly for those in the night that the lumi and BCM labels are correct.

(Jorg Wenninger) There is no need to AFP in the high lumi MD.

(Chris Young) For the schedule the length of the low-mu is important as we presumably want the vdM near it, and it can also be used as radiation cool-down. 

(Roderik Bruce) Rough luminosity estimates for any light ion suggestions would be good as while it will be difficult to promise anything it may be possible to rule out some requests as unrealistic.

(Jamie Boyd) Low-mu in ATLAS does have implications for FASER as it determines how many emulsions are needed so a decision relatively quickly would be appreciated.

(Michi Hostettler) Removing the calibration transfer fills makes it a lot simpler on the machine side as well.
(Witold Kozanecki) While we can remove the CT fill, we still need low Tile activation for the vdM, and it will be more important without the CT fill.
(Chris Young) Yes, we can consider this when creating the timetable for 2026.

(Chris Young) Who is following up the 18kV supply issues?
(Eric Torrence) This is being filled up by EN-EL.
(Chris Young) It would be good to have some post-mortem, particularly if it isn't discussed at the LMC as an agenda item.

CMS (Filip Moortgat)

(Chris Young) I presume as it is short you will wait for the x-angle leveling to finish and then level to low values?
(Filip Moortgat) Yes, this is the plan, and we will wait until the pile-up head-on is around 40.

(Chris Young) Would this be the same steps as ATLAS?
(Filip Moortgat) Yes, that would be the idea.
(Michi Hostettler) It is probably better to separate ATLAS and CMS one at a time for beam stability.

(Martijn Mulders) Do you mean that you don't want PPS inserted?
(Filip Moortgat) Yes.

(Roderik Bruce) How much more time in collision would you need?
(Filip Moortgat) Likely around 2 hours, and it needs to be after the TS.
(Roderik Bruce) It is better to insert a couple of hours of collisions rather than moving for example the background test.
(Filip Moortgat) We would prefer not to introduce delays and can commission during the intensity ramp-up.

(Roderik Bruce) Is the 7 nb-1 recorded or delivered?
(Filip Moortgat) We can probably compromise to make it delivered, which means we are potentially interested in light ions in 2026, but discussions are on-going.

(Chris Young) Will FSC also stay for the high intensity test, and will it survive?
(Filip Moortgat) Yes, it will stay. Due to the RP limitations it might also be ok.

(Martijn Mulders) Do you have any statement on the low energy run?
(Filip Moortgat) It has not really been discussed, but we are not interested. But note we aren't blocking it.

ALICE (Robert Munzer)

(Chris Young) There is a fill after the magnet reversal with 450b. Would you use this for low-field?
(Robert Munzer) We would want one with the full machine, I think. It is only the solonoid that is at low field.
(Jorg Wenninger) Do you want to do it in stable beams or between fills?
(Robert Munzer) We would prefer to do it between fills.

(Chris Young) When I did some rough projections of the low-E run it made very little difference to the LHCb delivered luminosity if there were collisions in IP1/5/2 as the main effect is emittance blow-up rather than burn-off.

LHCb (Flavio Pisani)

(Jorg Wenninger) A regeneration has been requested during the TS so this will be done.

(Chris Young) BGI measurements will be much appreciated by all the other experiments so thanks in advance.

(Chris Young) Similar to ATLAS on the 18kV it would be good it the TC and the ATLAS TC could follow-up if the events are linked with EN-EL.
(Flavio Pisani) Yes, we will, the signal seemed to go through several layers of UPS protection.
(Michi Hostettler) Big events like this can cause ripples 

(Roderik Bruce) One of the planned MDs with very high likelihood is the new beams from the injectors. This will have slip-stacked 75ns beams giving alternate 25ns/50ns spacing. It would be good to know how interested the experiments are.
(Chris Young) Some bunches will have a bunch 25ns before and some a bunch 25ns after but they won't have a bunch either side 25ns apart.
(Roderik Bruce) There is also a possibility of a pure 25ns beam. This could also motivate an upgrade of the PS RF for pure 25ns long trains which would likely have to be in LS4.
(Eric Torrance) Currently ATLAS struggles with 50ns spacing to trigger both central and UPC collisions. For next year definitely no, but looking further into the future, particularly Run 5 this could be possible. We will certainly study the data to see how to approach the problem. 
(Martijn Mulders) Is the reason to do this to double the luminosity?
(Roderik Bruce) It would result in a significant increase but not quite double the luminosity.
(Robert Munzer) This is likely limiting for the ALICE ZDC but for Run 4 onwards it could be possible.
(Flavio Pisani) It is likely Ok for us but there could be complications so testing it would definitely be nice for LHCb.
(Filip Moortgat) Similarly it is probably not possible for the ZDC but for Run 4 something could maybe be cooked up. Certainly interested in taking the data to study the issues.
(Eric Torrence) Having a filling scheme as soon as possible would be appreciated.
(Roderik Bruce) It depends on when the injectors know what will be ready, but as soon as they know we can circulate a scheme.