Minutes and Summary

Main purpose of the meeting: Start of 2024 data taking, experiment feedback and plans for upcoming data-taking.

LPC minutes 8th April

Introduction (Federico Alessio)

No questions

Luminosity Checks (Tobias Persson, Michi Hostettler)

(Federico Alessio) What is the step up in the geometrical factor? this is because we switch to 160 then back to 150

(Witold Kozanecki) Why is the label on the emmitance effect on lumi. ratio IP1/IP5 if this is meant to favor CMS. The label is wrong it should be IP5/IP1. For the beta* plot it is correct and this favors IP1.

(Catrin Bernius) Was this different before the half-RP change. Last year it was within 1% so it is a bit larger now, but it is always something that is corrected for each year.

(Witold Kozanecki) Does slide 4 assume equal emmitances in x,y. Yes, this is only the beta* effect. On slide 5 we add the emmitance difference.

(David Stickland) On the increase in noise; thinking of afterglow effects these shouldn't be very sensitive to long term effects fill to fill so this can't explain it. The source luminometer didn't change between the fills. However, there does appear to be an increase in the noise in the CMS internal plots too that will be investigated.

(Chris Young) Can you check if the most discrepant lines are from the INDIVs on the bunch-by-bunch plot. Yes, this can be checked.

(Federico Alessio) Is there a machine method of measureing bunch-by-bunch emmitances. Yes, the BSRT can measure this but it still needs to be commissioned for this year.

(Chris Young) Could we add the crossing angle to these plots. bpt plotting only lets you put 2 scales on plots, but maybe a solution can be found.

(Witold Kozanecki) Why can't the wire scanners be used. This is because we are above the intensity limitation for the wire scanners. For the dedicated run these will be available.

(Georges Trad) When will there be measurements of the luminous regions? The experiments will give some preliminary results today and they will be more detailed in the future with offline tracking. The results will be produced for all the runs that stable beams were declared, not just future fills.

(Catrin Bernius) What do you mean by the local coupling. This is something that is measured and then corrected for. The corrections have now been derived but weren't implemented in the fills so far. This will make a difference of around 1% and this effect is not included in the previous plots.

(Catrin Bernius) The blow-up of the beam at the end-of-fill, will this be done in stable beams or adjust. This will be in stable beams.

ATLAS (Catrin Bernius)

(Michi Hostettler) I can confirm that the leveling values set by ATLAS are being recieved properly.

(Witold Kozanecki, Tobias Persson) The higher the mu the stronger the underestimation of the luminosity of INDIVs. For mu of 50 this will be 3-5%. For 12b trains this will still be underestimated but the effect gets smaller as the trains get longer.

(Tobias Persson, Michi Hostettler) The leveling of CMS being higher is a result of the imbalance rather than a cause so this can't contribute to the explaination.

(Federico Alessio) The feature that is seen in 9473 - is this real. This is when a timing scan was being carried out so it is likely to be instrumental.

(Georges Trad, Witold Kozanecki) Is the online value sent over DIP or in the MASSI files. The online ones are generally not reliable for analysis as they are the trigger tracking. Offline reconstruction ones are what are in the MASSI files and are what should be used for analysis.

(Michi Hostettler, Matteo Solfaroli Camillocci) Since the collimation is already done and loss maps are done moving the IP transversely is tricky. During the TS this could be possible if we did a thorough validation afterwards. From ATLAS there isn't a strong request to do this. It will be followed up whether any change is needed in TS1.

(Matteo Solfaroli Camillocci) If the BSRT fill is seen as a priority then we can try to do this earlier, for example this week, but we would prefer this to be next week. From ATLAS there is no rush, just wanting to know when it will be.

(Chris Young) The online vs offline in sigma_z is greater than 1mm which is around the magnitude of a 5urad change in crossing angle. We need to do offline tracking, and in the same lumi block between ATLAS and CMS to get the correct ratio. These values should be sent in the MASSI files such that these kind of analysis can be done.

(Witold Kozanecki) A difference in luminous regions can be induced by non-round beams so we should be careful with ATLAS vs CMS comparisons particularly in x,y widths. However, longitudinal lengths will give the geometric factors with some reliability.

CMS (Giulia Negro)

(Michi Hostettler, Chris Young) The z-widths are similar to ATLAS but clearly this needs to be done numerically rather than read off plots for the precision needed.

(Federico Alessio) For the HCAL/ECAL scans how long is needed. A full run is needed for HCAL for example. It is not ideal to do this later in the ramp up so the aim is to do this in the 400b fills.

(Federico Alessio) By "no break" in the VdM program do you mean no dump. It is no dump and no ATLAS scan, but this only gives a gain of 40mins over the full program which is very small.

(Catrin Bernius, Witold Kozanecki, Matteo Solfaroli Camillocci, David Stickland) ATLAS would like the 1 bunch run to have stable beams. This run shouldn't be with the VdM optics. It was discussed when this could occur and if it could use the last fill of the MD period for example. Additionally it was asked it if could this be done tomorrow morning. In principle yes, this will be discussed offline, and it would be for CMS only as the ATLAS requirements of measuring across different luminosity values don't fit with doing it tomorrow.

(Georges Trad) Emmitance scans. Do you want this at 1.2m or at target. This would be at 1.2m

(Witold Kozanecki, Georges Trad) When will the factorization MD timing be confirmed? The MD program in MD1 will be confirmed on Wednesday afternoon.

(Witold Kozanecki) When is a table like the one CMS showed from ATLAS be needed. The end of April is fine from the LPC side.

ALICE (Andrea Ferrero)

(Tobias Persson) What is the scale of the shift in z. It is up to 0.5cm in the fill shown, slightly more in some other fills.

(Federico Alessio) How can the beams move longitudinally. This can happen if the path length is different.

(Chris Young) This should be the same for all experiments. Checking the 2nd 75b fill everyone sees some similar effects with some small differences in magnitude.

(Tobias Persson, Chris Young) The change across the run is strange but for a general shift for all experiments this can be done, providing all experiments agree. The experiments will measure the postion in the upcomming 75b fill and from the 400b fills (longer, with trains, and good stats, offline tracking) and will come up with a consensus on how far to move it (and the direction).

LHCb (Elena Dall'Occo)

(Chris Young, Federico Alessio) Does it do this through the full run or only in 15min bursts. It is when the lumi changes the LHCb lumi changes in several steps to the correct value. The trigger rates agree with the BRAN so this is what is believed to be correct.

FASER (Brian Peterson)

(Federico Alessio) When you say additional acceses, will it not be the same number as you have the same number of boxes. There will need to be one before TS1 while before it was hoped that this could be done in the TS1 shadow. It is also under discussion whether an additional box can be produced.

(Chris Young) Was it asked to the FLUKA team to put a energy cut on the muons to try to pin down the source more precisely. The files were passed to the FASER team and the muons are produced in the first 150m, so before all the collimators which is why they are then unable to stop the TeV muons. This means the fact the background varies little with the collimator settings makes sense.

SND (Gerardo Vasquez)

(Federico Alessio) It is not possible to revert the optics at this stage. We will continue to work with the machine teams to try to improve the situation but currently it appears to be difficult to improve things significantly.

(Chris Young) For the shoulder these could be the same as the TCL6 ones that are seen in negative muons in FASER plot. It would be good to have the same momentum signed plot from SND. This could be done in simulation but not in data as there isn't a magnet.

(Brian Peterson) The high momentum ones seen in FASER point towards the IP, while the negative ones come at an angle which possibly matches the shoulder seen in SND. The majority of the increase is the high momentum ones which also matches what is seen in SND.