Minutes and Summary

Main purpose of the meeting: Summary of p-O, O-O and Ne-Ne; VdM period data-taking

LPC minutes 14 July 2025

Present (P = in person): Chris Young (P), Chiara Zampolli (P), Robert Münzer (P), Andrea Massironi, Giulia Negro, Eric Torrence (P), Paula Collins (P), Rosen Matev (P), Jorg Wenninger (P), Roderik Brice (PO), Filip Moortgat (P), Hiroaki Menjo, Brian Cole (P), Andres Delannoy, Tomasz Bold, Witold Kozanecki (P), John Jowett, Qipeng Hu, Georges Trad (P), Ivan Calì, Anna Sfyrla, Richard Hawkings, Gerardo Vasquez, Lucia Silvestris, Dragoslav Lazic, Joanna Wanczyk, Lorenzo Rossini

Introduction (Chris Young)

Robert Muenzer: [concerning the LHC planning spreadsheet] does it mean that the ramp up is part of the light green boxes?

Chris Young: the 1200 will be counting as pink but the 400b and 75b should be included in the green boxes, even if they do not fit.

Filip Moortgat: [regarding the delay that we have accumulated and the fact that the VdM took a bit longer than expected] most of the delays were machine availability, and the delay is then 2 days, it is not the 1-2 hours of the experiments that matter. So maybe in the previous years we were more lucky to have nothing that was breaking during the VdM.

Chris Young: yes, last year ATLAS and CMS went perfectly while LHCb and ALICE were interrupted once.

Filip Moortgat: I also don’t remember the 16h of Loss Maps validation in the past.

Jorg Wenninger: they were always there after a technical stop. They should actually be 20h, because we have 4 hours per cycle, with 5 cycles, we have to readjust all the offsets for LHCb, go step by step etc. So at least 20h. By the way, the booster will have a 24h intervention this week, when we will have no beam. It should be on friday.

Chris Young: we should try to do it when we have a long fill. Even if it is a 400b, but it is long.

Jorg Wenninger: at that time, we should be at the ATLAS calibration transfer fill, or we have to see.

Chris Young: Friday is definitely useful, if they had said tomorrow, I would have pushed it later.

Jorg Wenninger: this also means that we don’t plan any programmed access for the moment. We have to see how we handle the CMS request [that was brought forward in the morning meeting].

Chris Young/Filip Moortgat: this is not urgent, it can be taken when there is anything else. 

Paula Collins: the delay in the restart of pp does not include the currently ongoing fill [BB MD].

Chris Young: yes. 

Paula Collins: I also support the comment that the 1h more from the experiments’ scans does not matter much.

Chris Young: yes, the accounting in the hours for the VdM is more for passing to the next experiment, to plan for the different stages of the VdM. Not so much for the overall physics program.

Paula Collins: more seriously, there will be a request for access from LHCb, which might change the discussion. There is an issue with the VELO movement, there seems to be a mismath between the resolver and the potentiomenter measurements which vary quite a lot, we would really appreciate the chance to go and inspect it. If 1h access is possible, we would bery much appreciate that, before going into next period, when it becomes even more complicated. It would be an access for inspection.

Jorg Wenninger: the best would be at the end of this fill, or tomorrow morning, before the CMS 3b fill. Let’s wait to see how the situation evolves, to see between which fills you can jump in.

Robert Muenzer: after this fill we also change the ALICE polarity, so there might be some down time.

Jorg Wenninger: we’ll definitely change it before we do the LMs. 

Filip Moortgat: now the VELO is out due to the BB MD, right? And it will stay out, so you could do the access at any time before it goes back in.

Paula Collins: yes, of course we are anxious to inspect it as soon as possible. 

Chris Young: for this kind of access, where there is just 1h in the experimental cavern, and does not require RP etc, we don’t try to pair it with the 24h access, we try to put it sooner rather than waiting for the 24h access for the booster. I think that after this fill is maybe the easiest opportunity.

Jorg: the target curve should be updated, since it makes no sense to base the target to something that is impossible. So we need to shift a bit the curve.

Paula Collins: can we take the opportunity to harmonize LHCb with CMS and ATLAS?

Jorg Wenninger: it is very delicate, since for you it depends basically on stable beam time essentially, while there are many more factors for the others. It is hard to make it equal. I would not insist on this.

Paula Collins: but the effect is smaller than the discrepancy that we see.

Chris Young: The curves were basically done by hand such that we hit the 120 and 12 fb-1 targets.

Paula Collins: which explains why these discrepancies are probably larger than those that come from the variation in fill length compared to what is expected.

Chris Young: it could be.

Paula Collins: we can calculate the length of the fills and show that this is the reason of the discrepancy, this would be very interesting. If not, then I suggest to harmonize them.

Paula Collins: we hope that at the restart the radiation levels measured to which cryo was sensitive will be suppressed. 

Eric Torrence: now there is a denser wall.

Jorg Wenninger: but the wall won’t help for the pressure guages.

Chris Young: for the pressure gauges, there is the sw fix by Benjamin that was proven to work well.

Chiara Zampolli: they also wanted to replace the one that was repeatedly giving problems.

Filip Moortgat: was it done in TS1?

Chiara Zampolli: it should be.

Chris Young: they changed the wall and replaced it.

Chiara Zampolli: they also added an extra covering for the slow neutrons.

Chris Young: they should discuss it at an LMC.

Eric Torrence: what about the collimator that has a leak in P8?

Chris Young: it should be reported at the LMC but they said that technically there is no problem.

Jorg Wenninger: it will stay out, and probably it will not be replaced during LS3 or the YETS.

 

LHCb polarity flip (Jorg Wenninger)

Robert Muenzer: [referring to the local orbit perturbations on s4] during b* leveling we see sometimes more drift in the lumi. Could this be related?

Jorg: do you see it during the step? Normally this applies only during the step. Once the step is done and we are doing offset leveling in 1 and 5, it should not be different.

Robert Muenzer: this is also why the leveling is disabled for a certain time.

Jorg Wenninger: Yes, when we do the b* leveling we disable it since we have to change all the optics in the machine. We don’t want something to interfere with it.

Chris Young: [concerning the fact that 0.5 um makes 20% jump in LHCb lumi] in ALICE, since the beam is much bigger, then 0.5 um will make a much smaller effect.

Paula Collins: will the corrections be applied at the end of the fill or the b* leveling?

Jorg Wenninger: you could also apply them at the end of the b* leveling, but basically it is for the next fill.

Rosen Matev: what is the difference between the fast b* leveling and the “slow” one?

Jorg Wenninger: once everything is tuned up, we jump in a direct way to 60 cm in b* in ATLAS and CMS. We must be sure that when we go to 60cm from 1.2 m the correction is smooth enough that you don’t have huge excursions. Once we know that it is smooth, we go in one go.

Rosen Matev: how long would the slow step take?

Jorg Wenninger: probably of the order of 30 minutes. We Need to make sure that the leveling is switched on and that it converges etc. which takes 3-4 minutes. Then there are quite a few steps. So 30-40 minutes more. This will not affect you since you are anyway leveled.

Chris Young: when we have an intensity ramp up like this time, this does not apply, right?

Jorg Wenninger: in fact, we have done this (Preparation on s8 bullet 1), we don’t do step 2 because we want to go head on with.2 bunches, and we don’t have the pre-bias of step 3. With the LM, you go head on and you can already find the optimum, so you are in a situation which is between a second and a third fill in this scheme. Anyway now even ATLAS and CMS with the offset pre-bias to go to the combined leveling will have to be re-established carefully. We don’t want to be in an offset leveling for the LMs.

Chris Young: at the moment the fast b* leveling jumps to 60-70 cm round. When we go to 1.75, it will jump to 90. Will this change cause a problem for LHCb?

Jorg Wenninger: no, it will even be better, because we will jump less. 

Rosen Matev: is it an issue if we change the target during the ramp up?

Jorg Wenninger: it is a problem if you change it during the fill, not between the steps of the ramp up. At least until we reach the b* leveling, but after that the fills will last just ~1h longer (for xing angle antileveling). 

Chiara Zampolli: how many times will you (LHCb) switch this year?

Paula Collins: we were wiating to see what is the outcome of this intensity ramp up to make our policy. But not many times. We thought we would have had more freedom this year but with the fast b* which has constrained us, we will discuss internally to come up with a proposal.

Chiara Zampolli: with this, will there be any loss in lumi for LHCb?

Jorg Wenninger: you will lose a very small fraction, like a couple of minutes, and we can tune with experience.

 

ATLAS (Eric Torrence)

Chiara Zampolli: what is the recorded luminosity?

Eric Torrence: there is practically no difference compared to the delivered since we had more than 99% efficiency.

Chris Young: [about the 3b fill] I presume at the beginning we can put you head on and then we can separate you.

Eric Torrence: yes, it is the integrated luminosity that matters. With 1 bunch the level will be negligible.

Witold Kozanecki: we will shorten the first CT fill by 1h, the first mu scan will not be done in the first CT.

Chris Young: I believe we intend on using the 400b fill which has multiple trains, will it be fine? It might have slightly lower trigger rate limit from the IBL.

Eric Torrence: fewer but longer trains?

Chris Young: yes.

Eric Torrence: it should be fine.

 

CMS (Filip Moortgat)

Filip Moortgat: when will the “Michi MD” happen?

Witold Kozanecki /Chris Young: in ~1h, at the end of this fill.

Roderik Bruce: we discussed [opening the TCL4 for PPS] and we will test it in the 75b fill, and if it goes well, we will implement it for the following fills. If we find any problem later, we will revert.

Chris Young: the LMs will be done with the nominal settings, so we can easily revert.

Chiara Zampolli: the improvement for the PPS in case we open the TCL4, is it the result of a simulation?

Filip Moortgat: yes, by Mario.

Chiara Zampolli: I thought maybe it was coming from the FLUKA people.

Roderik Bruce: The FLUKA teams simulate the energy deposition in the magnets, not the physics reach.

Chiara Zampolli: maybe there were doing something similar to what they did for FASER and SND when they gave input to the experiments.

Roderik Bruce: that was different, it was for the background. Here it is a MADX study by Mario, with the tracks from the IP going to PPS.

Chris Young: it would be good that the next time something like this comes, they include both LPC and CMS RC in copy.

Filip Moortgat: yes, completely agreed.

Witold Kozanecki: going back to the CT fill with 140b INDIVS (tomorrow night): I propose that we go in collisions at 120 cm as usual, ATLAS does its usual things, we go as quickly as possible to 60 cm, at which stage we should still be below mu=60 (or close to it), then we judge from the CMS view (since ATLAS will be separated at that time) what the target b* would be. Is this ok for Jorg?

Jorg Wenninger: yes, but we’ll go as quickly as possible, but in steps.

Witold Kozanecki: then for the target b* which is determined by the largest mu desired, which therefore determines the minimum beta-star at IP1 and IP5 for the fill, do I understand that both ATLAS and CMS are happy with target mu 75 for the INDIV fill? I till ask the same for the CT trains.

Eric Torrence: yes.

 

ALICE (Robert Münzer)

Jorg Wenninger: [talking about the high rate tests with the increased OFB gain] if you do it in a b* leveling period, you will be sort of interrupted in every step.

Robert Muenzer: last time we did it after the b* leveling.

Jorg Wenninger: 2 hours, like you are asking, is more than 1 b* leveling step.

Chris Young: yes, last time we kept the run longer. And we have 1h of xing angle leveling and then we have another hour, this can get 2h.

Roderik Bruce: on the background: there was an e-cloud meeting last week and there is no clear and obvious way to fix it. The scrubbing at injection is not clear if it would help, and would be very long; some people think that this will not be a rapid conditioning. The other option is to do some baking, but then you could cause a real leak. It is not obvious on the machine side what to do and it is not clear to what value it will condition itself by the end. The machine is hoping that the impact for ALICE will not be that severe and you can cut away the background. 

Chris Young: there were studies on the spike in the pressure seen in the cycle but there is no consisten behaviour in the different fills.

Roderik Bruce: what is the timescale to have a feedback?

Robert Muenzer: we are checking if we see it in the offline trigger efficiency, which should come quite soon. Other observables seemed quite ok, without differences in different moments of the fill. It should come very soon.

Chris Young: in Ne we used normal collimators, did you see any difference in the background compared to OO where we used crystals?

Robert Muenzer: no.

 

LHCb (Paula Collins)

Chiara Zampolli: the DOROS gain scan was supposed to last 2 minutes, anyone checked that this was the case?

Chris Young: yes, it was.

Chris Young: I think that the difference compared to the LPC page is that we did not include the spiral scan. 

Chris Young: during the BB MD, at the very end of the progam, the LHCb will be brought back to collision, I suspect the VELO won’t automatically come back?

Paula Collins: it will not.

Chiara Zampolli: [concerning the issue with the mismatch between the resolver and the potentiometer measurement] does it mean that you don’t know exactly the position of the VELO?

Paula Collins: no the position is known, for aperture it is fine. The movements do not correspond to the expected movements when going completely back at the end or when moving completely in. It is not adding up everything we would expect. But from the point of view of aperture, it is perfectly safe.

Jorg Wenninger: what numbers are we talking about?

Rosen Matev: tens of um.

Chris Young: so you want to look at the belt and look at the rivets. Now it is a very sensible time to do it. The MD will end at 16, then we have 1.5h of test for Michi. 

Paula Collins: we will check with the experts.

Dragoslav Lazic: what if CMS uses the LHCb access?

Chris Young: ok if it is strictly 1 hour. 

 

AOB

John Jowett: comparing luminosities within species, we always look at the center of mass energy per colliding nucleon pair. It is also sometimes done to compare the nucleon-nucleon luminosity, when you compare different species, for example RHIC did that. If anybody is making comparisons for different species, maybe that is a good idea.

Chris Young: I looked at that a little bit with nucleon-nucleaon ones, and if you compare to PbPb, we smashed the 2010 PbPb stats with OO. If you are comparing with 2011, so the full Run 1 PbPb stats, I think that ALICE beat it because they were leveled in Run 1, while ATLAS and CMS are at about ½ Run 1 PbPb stats. For this few days, we are looking at similar order of magnitudes as the full Run 1 statistics, which is fantastic!

John Jowett: yes, it is amazing.