CERN

LPC meeting summary 01-07-2024 - final

Minutes overview      LPC home


Minutes and Summary

Main purpose of the meeting: Feedback on data taking and HI planning

LPC minutes 1st July

Introduction (Federico Alessio)

(Mirko Pojer) The BCMS with lower tails will be tested in the next fill.

(Matteo Solfaroli Camillocci) The reason that the injector faults has many faults with an average short duration is that there were several small ones as well as the two long faults which moves the bubble to this place.

(Matteo Solfaroli Camillocci) The reason the leveling time is different between these fills is due to different bunch intensity which is being increased slowly after the TS.

(Witold Kozanecki) There are uncertainties at the level of 2% per experiment so the uncertainty on the difference is larger. Additionally at the current stage of the calibration the uncertainty online is not at this level yet. There are several technical differences between the current stages of the online calibration between the experiments. This should be kept in mind so we don't chase down differences that are well within the uncertainties.

(Catrin Bernius) How long will the FASER/SND access be? This will be about 3.5 hours from when they are granted access by RP.

(Catrin Bernius) As ATLAS separated while the magnet was down they will have lost some lumi with respect to CMS. However ATLAS were ahead of CMS prior so CMS caught up. It will be followed up which luminosity the LHC statistics page is using.

(Chris Young, Matteo Solfaroli Camillocci) Is the lifetime worse after the TS as it looks worse on slide 9? The beta* is different so lumi is higher and protons will be burnt off quicker meaning the curves will cross. The beam lifetime is difficult to estimate by eye from this plot.

(Federico Alessio) Establishing the PbPb leveling at 6.4e27 cm-2 s-1 is dependent on the R2E upgrades of the QPS system.

(Roderik Bruce, Catrin Bernius) Is it the case that that the other experiments use ZDC in pp reference. ATLAS says yes. They will check the tolerence of the ZDC. Situation is the same for CMS.

(Roderik Bruce) During the pp Ref vdM could ALICE take data? We would hope to do all 4 vdM in one fill so it will not have many colliding bunches.

(Roderik Bruce) The 5.3 nb-1 target assumes that we achieve 0.15 nb-1 per day, which was the max that we could get for 2 days in 2023, for every day in 2024 and 2025. This is therefore extremely challenging but not ruled out. The experiments should be aware of this.

(Federico Alessio, Roderik Bruce) For 2025 the setup will depend on the successes of 2024. For example in MD reducing beta* will be investigated in IP8. For this year the numbers are to be close to 2023 such that we understand the setup better. For 2025 there is aperature margin in several places which could be used to gain in beta* or crossing angle, but before studies are done nothing concrete can be proposed/promised.

(Catrin Bernius, Roderik Bruce) With the revered polarity should we expect higher backgrounds in ATLAS in PbPb. There could be surprises but for the Pb-207 that was the primary cause last year this should miss the detectors and impact the collimators.

ATLAS (Catrin Bernius)

(Matteo Solfaroli Camillocci, Chris Young) It is being studied from the LHC side how to make things more robust by providing some signal in the absence of signal from the experiments however this is not trivial and cannot be fixed quickly. However the LHC is aware that this is not robust enough. It was asked if all operators know to separate the IP if the lumi signal is missing. They are all now aware and there is an operator alarm as well as the cryo shifter will see alarms.

(Roderik Bruce) It is not expected that large changes in the background levels on the TAN will be caused by the change in TCT setttings. The reason for the change is a difference in the observed aperature after TS1 which is currently under study.

(Mirko Pojer, Matteo Solfaroli Camillocci, Roderik Bruce) The change to the pot incertion position can be done now as we are still injecting. There is no problem from the collimation group changing this. There will be a quick check with Stefano and then this will be implemented.

(Federico Alessio, David Stickland, Witold Kozanecki) Did sigma_vis also decrease for CMS. There are multiple look-up tables, calibration/efficiency/etc., that change so this is not long-term aging and this is also the case for ATLAS.

(Andrea Massironi, Witold Kozanecki, David Stickland) Is the ATLAS update based on the same data-taking as the CMS downward update? No, it is the full analysis of 2023 including all effects such as non-factorization. The CMS one uses 2024 data but doesn't include non-factorization and length scale calibrations. In 2023 these two effects largely cancelled but this won't necessarily be the case in 2024. We should not over-interpret the differences between the choices of the experiments and the differences observed.

(Andrea Massironi) Will this be updated from now on or also past fills? This applies to all the data so it will be applied from now on and also the MASSI files for previous fills will be updated.

CMS (Andrea Massironi)

(Chris Young) Based on the ATLAS request we won't make the 12 non-colliding bunches to be colliding. If the machine requests a single test fill then we will give the experiments notice before such a fill. However, there is no strong desire to do this from the machine side at the moment.

(Catrin Bernius, Andres Delannoy) The normalization is to the Z rate of the 2022 calibrated luminosity. This is also efficiency corrected for the 2024 detector conditions.

(Matteo Solfaroli Camillocci) I can find out how far you were separated when the problems occurred and get back to you.

(Roderik Bruce, Mirko Pojer) For PbPb it depends a bit on the conditions (injectors, emmitance, QPS upgrade - which is expected to be completed in TS2) and how well we are doing but maybe 5-6 hours. The numbers in the Ion Sharer on the LPC upgrade are not quite up to date but they will be updated. For the QPS upgrade, some boards are already installed in IP1 and things are going to plan so the QPS upgrade is expected to be completed. We can look at a good fill from last year as a template for what could be achieved in a default scenario. There is an interest in a default scenario and a best that could be achieved for trigger setup. The interest is more on the PbPb conditions rather than the pp Ref conditions.

LHCb (Elena Dall'Occo)

(Federico Alessio, Matteo Solfaroli Camillocci) Moving very quickly could be challenging from the machine side if there are other things going on. Prior to the TS the leveling was higher in ADJUST. This is lower to be safer based on the variability. It is more when the leveling procedure is launched which can be prioritised that determines how quickly the target is achieved. This will be followed up by the LHC and LHCb.

(Matteo Solfaroli Camillocci) We can run with the LHCb magnet off, and did it in the 75b fill. However, it isn't transparent and there would need to be checks and potential e-cloud issues.

(Federico Alessio) Was technical coordination informed of this cooling tower being off. No they weren't.

(Matteo Solfaroli Camillocci) Is the water temperature situation back to normal now? Yes, we are now back to the normal level.

(Federico Alessio) What is the trip threshold? It is 54 on the plot.

(Roderik Bruce) Excellent that the ion team are happy with the reversed polarity. It might not be easy to implement the lower beta* optics after the MD as some time might be needed to analyse the data and then there would also need to be some comissioning eg. loss maps. There is a small possibility this could be combined with the switch of ALICE polarity mid-way through the ion run which also requires loss maps, but this is more targetting next year.

ALICE (Andrea Ferrero)

(Roderik Bruce) Do you re-align the ZDC after the polarity switch? Yes, this is done and it is on a movable platform and therefore can be moved without an access.

(Roderik Bruce, Chris Young) Keeping the crossing angle the same for both polarities results in less commissioning. We just need to be sure it is ok for beam-beam and aperature. This means that the switch will not result in any more commissioning. It isn't essential in the pp Ref dataset that exactly equal datasets are taken with both polarities.