Minutes and Summary

Main purpose of the meeting: Data taking feedback, FASER/SND tests, pp ref config (inc. vdM)

LPC minutes 2nd September

Introduction (Federico Alessio)

(Catrin Bernius) It was asked and clarified that the decision from management not to increase the intensity this year is new since the last LPC.

(Matteo Solfaroli Camillocci) The request to anticipate the ppRef commisioning is strongly supported from the LHC side so that any issues discovered can be studied in the time between the two commissioning days. Additionally the final day of the cryo intervention cannot have beam so it will be lost unless the whole intervention is quicker which we cannot guarentee.

(Catrin Bernius, Matteo Solfaroli Camillocci) When would the this ppRef commisioning occur. It isn't urgent but in the next weeks prior to MD4 is likely. Additionally it could be split into shifts during the daytime. In the next weeks it will be scheduled and

(Georges Trad) Are the dates of MD5 still fixed. Yes, as this needs to act as a cooldown for the TS.

(Witold Kozanecki) It was clarified that all the ppRef physics data will be taken after the TS.

(Giovanni Cavallero, Matteo Solfaroli Camillocci) Currently LHCb is in the up polarity and this is the same as what the pp reference run will be done in. However, LHCb will switch to down soon, should the commissioning be done with the same magnet configuration as will be done in the ppRef. It isn't necessary from the machine point of view to do the commisioining with the same magnet configuration. ALICE will run with both polarities during the pp reference run.

(Reyes Alemany Fernandez, Matteo Solfaroli Camillocci) It is requested that ALICE starts with the -183 urad crossing at the start of the run and commissioning. For the first day of commissioning this isn't important but it will be important for the second day.

There were no objections to making the lost day for cryo. repairs in the pp run (by moving a pp reference setup day) rather than from HI.

(Witold Kozanecki) In the slides the pp reference and PbPb Vdm filling schemes are switched. This was due to the last minute re-production of the slides after the power cut.

(Roderik Bruce) For the FASER background test Bjorn has prepared an orbit bump that might be able reduce the FASER/SND backgrounds. This will be presented next.

Orbit bump for FASER and SND background mitigation (Bjorn Lindstrom)

(Federico Alessio, Filip Moortgat) We propose that when this is ready it will be tested in the machine. Is it worth it still? It is for validating a configuration that will probably be tested in simulation for running next year. It isn't for this year but for next year so it is definitely worth it.

(Roderik Bruce) It should be noted that this one could give a significant improvement, unlike the previous tests that were just validating the simulation. If we kept the same optics next year then this could be a potential solution. Also if the machine has an issue and only low intensity is possible would it be possible to put it on a list of things that would be done in such a case? Yes.

(Federico Alessio, Matteo Solfaroli Camillocci) If we were to put it in operation would this require machine validation? Yes, this would require a full re-validation that would lose a lot of time so this is only considered for next year.

(Chris Young, Matteo Solfaroli Camillocci, Federico Alessio) This is based on the current optics? Yes. For next year, depending on the outcome of the discussion on 2026 we might be forced to rotate the crossing planes and be horizontal in IP1. Would it be possible to prepare a similar bump in horizontal (with the crossing angle sign that works with trains: +) such that both can be tested in the same test/MD fill. Yes, this could be prepared, but are there thoughts on doing non-RP horizontal? This is on the table, as with everything else, but it isn't possible to test. The non-RP was the configuration last year and this wasn't a problem? With flipped planes we haven't tested it. The configurations will need to be discussed with the relevant experts and there is a zoo of possible configurations. Firstly this will need to be discussed to determine what is feasible from the machine side in eg. an LBOC and then we will come back to LPC for further discussions.

(Federico Alessio, Chris Young) Can we test the horizontal RP setup in MD? Would the same bump work in that configuration? It could be different so we would need to look at where to put the bump by looking at the tracks in simulation. It would be efficient to test as many things at once at possible. It could be that we put it on a list of things to be done if there is a problem with high intensity injection, but otherwise postpone to near the MD so as many ideas that can be tested as possible can be tested at once.

Configuration and plans for the pp reference run (Reyes Alemany Fernandez)

(Robert Helmut Munzer, Federico Alessio) The number agreed with PC in ALICE is 1.5e31 to achieve mu<0.05. This needs to be adjusted for the increased number of collisions in IP2 with the new filling scheme and we need to make sure that the cross-section is agreed between the machine and the experiments. This we need to take offline.

(Catrin Bernius, Roderik Bruce) What are the implications of the aperature limit on IR1? The implication is that there would need to be a local measurement which would take time. This is why we avoid this configuration as it would make the commissioning longer and we would get less physics. It is only if the aperature in IR2 is low that there is a request from the machine for an aperature measurement. If there are beam-beam issues then we might need to go to 350 urad which would then imply that an aperature measurement will need to be done.

(Roderik Bruce) Here there is no assumed down-time and perfect turn-around (with the times assumed in the legend). Therefore this is very optimistic. Also this assumes the the leveling value from the 2nd slide such that if ALICE levels lower than this it will take a lot longer.

(Chris Young, Robert Helmut Munzer) If we look at the three fill scenario then if we have a first fill of 24h which is then dumped we need to decide whether to change the magnet polarity or not, having not yet taken half of the data. How flexible are you not to have exactly half of the dataset in each configuration? Would it be ok to take eg. 1/3 vs 2/3. The exact fraction needs to be checked but it shouldn't need to be exact. Something like 1/3 to 2/3 should be acceptable, but we can iterate this before the run.

(Catrin Bernius) This year the beam based alignment will need to be added to the commissioning. Yes, this is also mentioned at the end of the slides.

(Federico Alessio) We will check that the filling schemes for the ramp-up don't have bunches near the abort gap.

(Catrin Bernius) The head-on pile-up - what would that be. The maximum is expected to be around 7. If the emmitance is 2.5 then it is lower, around 6.

(Federico Alessio, Roderik Bruce) Can you explain the comment on the TCL? If we use the TCLs then we will need a bit more comissioning time. The hope is that at least most of them are not required at these low luminosities such that we can save setup time. There are on-going discussions if they will be needed or not.

CMS (Giulia Negro)

(Federico Alessio) Are the ones which are red and not bold are the ones we intend on removing - ie. remove 1 diagonal and both offset scans. We realize this is still pushing the limit. The general rule is to get it all done for all 4 IPs in 1 day which is 6h per experiment but there is overhead which brings it down to 4 hours.

(Catrin Bernius) Is the 1% lumi correction in addition to the one done in the last MD? Yes.

ATLAS (Catrin Bernius)

(Federico Alessio, Giulia Negro) For the 75b and 400b there are different train lengths so please make sure that it is fine for the purpose of the INDIVs. Ok, it will be checked but we think this is ok. From CMS they are also fine with only INDIVs for the first couple of fills.

ATLAS pp reference Lumi program (Witold Kozanecki)

(Reyes Alemany Fernandez) Can you explain the pile-up comment. Ideally we would calibrate at mu=0.5-1 but this would put the intensity in the region where the BPMs will complain so this is what drives the intensity numbers on the slides.

(Chris Young) For the total time on the first line I presume that the items that are done head-on are not included. Yes, this is correct.

(Chris Young, David Stickland) To CMS do you also intend on doing the length-scale calibrations in fills other than the vdM. Yes, it is usually done during the intensity ramp-up.

LHCb (Giovanni Cavallero)

(Witold Kozanecki, Federico Alessio) What does SMOG have to do with the gain of DOROS. It is thought that this is to help calibrate DOROS. The idea is to try to have DOROS unchanged in the SMOG off/on times. Therefore it is desired to have the scans in a single period. It will be investigated if the automatic DOROS calibration changes can be turned off to remove the restriction on these having to be together. We could do some inter-leaving with ALICE but it was pointed out that they also need the ghost charge information. If it evolves smoothy this is fine, but we have seen strange shapes in the ghost charge changing over time. LHCb can do some ghost charge measurements without SMOG but the signal is about a factor 20 smaller. Unless LHCb goes first then there will be a 2h period without precise ghost charge. Providing BSRL works better then that 2h could be during the scans at one of the other IPs and during that time the interpolation is taken from BSRL.

(Witold Kozanecki, Federico Alessio) How quickly does the intensity drop over the vdM? There is no burn-off but there are other sources of losses. This can be looked at in past vdM fills. From a past fill it appears there is a drop from 3.7e30 to 2.7e30 in luminosity over 10 hours. Therefore maybe it is better if there is 2 fills. This would solve the issue of the 2 hour gap. This would also help with emitance growth where the bunches can grow to over the scan range.

ALICE (Robert Helmut Munzer)

(Federico Alessio) Is it possible for you to have some alarm if there is an issue with the harmonic filters. This isn't trivial it seems but it is being looked into.