Minutes and Summary

Main purpose of the meeting: Data taking progress Intensity increase discussions. Presentation from Michi on leveling strategy

LPC minutes 25 August 2025

Present (P = in person): Chris Young (P), Chiara Zampolli (P), Robert Münzer (P), Andrea Massironi (P), Giulia Negro (P), Eric Torrence (P), Paula Collins (P), Roderik Brice (P), Witold Kozanecki (P), Ivan Calì, Stephane Willocq, Helga Timko, Andrej Gorisek (P), David Stickland (P), Michi Hostletter (P), Jaime Boyd, Juan, Giulia Ripellino, Matteo Solfaroli Camillocci, Anna Sfyrla, Peter Steinberg, Dragoslav Lazic, Gerardo Vasquez

Introduction (Chris Young)

Paula Collins: in s5 you say that “much of the year’s lumi would be collected prior to the increase”, but is the increase in intensity planned for just after the MD?

Chris Young: one increase was planned towards the beginning of september, but from Jorg’s slides it was not super clear if it would have been the second week in september, but obviously we are half way, so we are not at 90% of the target. But this was the plan in Chamonix, obviously it will have to be adapted.

Robert Muenzer: in the 3rd week of Sept we requested to run the low field so maybe it is not good to do the intensity increase and this at the same time. We can see if we can change the start date, since we have some flexibility.

Michi Hostletter: also for 1.7, we’ll start gently from one fill to another, and plus/minus one day won’t change. We will not so a solid jump to 1.7. Now we are at 1.63, then we could go to 1.65, then 1.67, over the course of several fills. We don’t have a sharp deadline, and we will do it gently.

Silvia Pisano: maybe we could keep the magnets as we have them now so that we can continuously check the background situation, and then when they’re done with the step, change.

Robert Muenzer: yes, we should try to disentangle the effects of the change in B and intensity.

Chris Young: we need to wait for the LMC this week, maybe no increase will happen any time soon.

Michi Hostletter: there was a feedback from the vacuum group: they have enough devices to work in parallel and do everything in one day.

Chris Young: yes, although if it is the same people that do all 12 modules, it is unclear from RP if RP would be happy with that. 

Matteo Solfaroli: yes, for this we need to wait a bit, since the responsible people were just back and gave me an indicative feedback. We need to assess in case we decide to do something, exactly, what is the impact of radiation on people, and see what exactly can be done in what time. The main line is that they may do everything in 1 day, but we need to be seen if it is feasible.

Chris Young: this topic will be brought up at the LMC, we don’t know what the vacuum people are going to say. Obviously from our side we don’t want a long time in access, rather we want to take luminosity.

Paula Collins: To be sure, these xrays will need to be done even before the most gentle step. will be at both sides of both points.

Chris Young: yes we think so, but we need to see what they say on wed.

Roderik Bruce: you said that the ion run is protected, but if we need to replace the vacuum module (6L2) since we break it, we don’t want to do this close to the ion run, as it would increase the background. 

Chiara Zampolli: the vacuum people claim that if we have a new module, the background in PbPb will still be low and not affect ALICE. What matters is the dynamic vacuum which created the background, and in PbPb this is negligible in any case. 

Chris Young: even if you lose the full electrical contact, we can still run in PbPb.

Paula Collins: [about the comment on s6 “all experiments adjust leveling lumi…”] what do you mean, that LHCb would not keep the same?

Chris Young: you would not be at 2100, but you should scale the current lumi with the ratio between the number of bunches in the new scheme and now, to keep the same pileup. Is this a reasonable assumption?

Paula Collins: yes.

Roderik Bruce: why do you need to drop two batches at 1.8?

Chris Young: for the heat load in sector78.

Paula Collins: the other two columns that you did not discuss relate to what?

Chris Young: they are the numbers in case the fill length was the optimal one, which is 11 hours, while we currently keep the fill for 13h.

Eric Torrence: 2.8% on a month assuming 60% stable beams gives about 12h extra data-taking, so if it takes 12h of x-rays before the increase can be made then even without the increased risk it isn't worth it.

Chris Young: the motivations for switching have to be from the machine side rather than from our side.

Michi Hostletter: the main motivation for this is is to probe intensities for HL rather than get more lumi. Any change we make is within the noise and carries some risk. If you calculate 1 day for the xray, this eats up from whatever we may gain. 

Eric Torrence: what is the benefit of 1.7 now, to the two weeks in 2026 where you can run at 2.3?

Michi: if we break anything at 1.7 or 1.8, we get a second chance, you can repair it during the YETS. If you break it in these two weeks at the end of next year, we don’t have a second chance. Then we may be limited in HL to 1.8.

Helga Timko: in addition, Run 3 baseline is 1.8e11, and it is what all equipment should be able to deliver. So it is important also to prove the availability of the equipment to run at 1.8 over an increased amount of time (a month or so).

Andrej Gorisek: if we manage to run at 1.8, also next year we will keep 1.8?

Chris Young: yes.

 

Z-centroid feedback from xing plane drift control (Michi Hostletter)

David Stickland: what are the benefits of the procedure?

Michi Hostletter: For point 1 and 5, you avoid drifting off in the crossing plane during the separation leveling. Sometimes we found that we have up to half sigma separation in the xing plane at the end of leveling. Normally it is less, but we cannot work out the correction at the end, because we don’t have points between start and end. We could assume it is linear, or we could optimize during the leveling regularly, but this would disturb the lumi so it is not on all the time, but once per month. This procedure would allow for a continuous correction. For 2 and 8 it is to avoid to drift out of the 10 mm acceptance. With this, we’d stay close to zero continuously.

Chris Young: is the target to zero? If I take e.g. [see s3] the CMS curve after the autopilot is on, it seems to be at something like -1.

Michi Hostletter: at the beginning it is very close to zero, then with probably a xing angle change it goes close to -1. At this level, one should define a deadband, e.g. 1 or 2 mm. Below a certain value it is hard to tell. This might correspond to 0.5 um separation in the crossing plane, which is very small, which is a fraction of a sigma.

David Stickland: could the separation leveling last longer? Because you would gain back the fact that you would have not lost because you moved. Maybe just a few minutes.

Michi Hostletter: it might be. What we see sometimes is that when we put the autopilot over the first 5-10 minutes, it manages to keep the lumi constant since it removes the drift that it had taken during the course of several hours. It will most likely last a little bit longer, but it will not be a large effect. Unless there is a strong drift. 

David Stickland: is the anticorrelation CMS vs ATLAS real?

Michi Hostletter: it should not be. 

Chris Young: if you are forcing everything to zero, you might artificially force and increase the separation. 

Michi Hostletter: yes. If this happens, one can think of introducing a reference different from zero. In the first order, +/- 2 mm it looks to be ok. This would also be only during separation leveling, when you are out of it, and head on, you will use the usual autopilot. It is to gain some handle during the separation leveling. In this phase, instead of just touching the separation plane, it will also apply a regular correction in the xing plane. 

Chris Young: if you run the optimization, for LHCb for example you never have the head on value to take as a reference value. Then you can take the one from the optimization as your reference.

Michi Hostletter: for ALICE and LHCb, as long as they don’t run out of leveling, what is more important is that you get the z position to zero, than to have zero separation in the xing plane because that is what in the end affects the acceptance. If you achieve this with a little separation in the xing plane, it might be better. Especially with ALICE which has a huge margin for leveling.

David Stickland: do we (in CMS) have any dependence on the z position?

Giulia Negro: we are affected only when it is a few cm. 

Michi Hostletter: the behaviour depends also from fill to fill.

Paula Collins: what is the effect on the RMS of the beam?

Michi Hostletter: it should have no effect, only the central position in the longitudinal plane is affected. 

Paula Collins: from LHCb, the data come from DIP?

Michi Hostletter: yes, the luminous region centroid.

Michi Hostletter: note that the ATLAS sign on s3 is inverted (since there is a different convention in the DIP publication), so there is no anticorrelation.

Chris Young: can it be turned on per experiment?

Michi Hostletter: yes, we could switch it with a limited gain and watch how it behaves, what it closely and see if it is beneficial or not. It is also limited in trim. So the very worst thing that can happen if the data is really bad but looks good and is stuck at a certain value is that it will reach its limit which is now set to 1.5 sigma separation in the xing plane and stop with a warning, and then we correct for it. 

Chris Young: if the experiments are interested, we can test it in a fill. If others are not interested, they don’t have to turn it on. 

Andrej Goriske: this should be transparent.

Chris Young: yes.

Andrej Gorisek: there will be a glitch in luminosity.

Michi Hostletter: we will move very gently, and normally what this corresponds to something that is less than a sigma or even half a sigma in the crossing plane so with very little impact on luminosity.

Andrej Gorisek: could it dump the beam?

Michi Hostletter: it should not, it is a simple trim on the orbit with the same knob that we use for optimization and it is limited to 1.5 sigma, while in an emittance scan we use 4. In the worst case you have an effect of 1.5 sigma in luminosity in the wrong plane, and then we react and fix it. It is deliberately limited in the power of what it can do it.

Paula Collins: for LHCb it would be nice to have it on, we would just like to be warned so that we can prepare. 

Michi Hostletter: if there is no objection, we’d test it on all experiments in the same fill so that we can watch carefully. Then we can see if we want to turn it off again. 

Chiara Zampolli: why if it works for one experiment it might not work for the others?

Michi Hostletter: the different experiments could behave differently because the data that they publish is not produced in exactly the same way, and the relation between the crossing plane separation and the z position depend on the experiment since it depends on the xing angle and the sign that is provided of the z coordinate. 

Chris Young: since there is no objection, we can do for all experiments, with a warning. 

Michi Hostletter: yes, we’ll announce it and it should happen during a day time fill this week.

Robert Muenzer: is there a protection if we provide a bad value?

Michi Hosteletter: the integral of all trims applied in a fill is limited to a value (1.5 sigma separation) and it will never trim more, and there is a cut-off in the z value which at the moment is set to 25 mm. If you have a value outside that range, it will do nothing, since it is very unlikely that it drifted to such a value.

 

ATLAS (Andrej Gorisek)

Chris Young: for VdM and ZDC ok. For the UPS, you should wait till Wed to see if we do xrays. The Fri morning after the MD is though a probable slot for access. How long this access will be, we’ll have to see.

Eric Torrence: it is probable that also this year lumi scale is 1% low, since the online is the same as last year.

Roderik Bruce: will you need to remove the ZDC before the high lumi test?

AndrejGorisek / Chris Young: we are checking with ATLAS and CMS 1.1. The high lumi test will have fb-1 of data max, which could include 1h max at 2.3e34 or long runs at e33. The TAN will also not look the same so they won’t install the same detector as in Run 3. If cryo is reconfigured for ion, then the ZDCs could be taken out then which would not cost any time, otherwise we’d need to take one day from the ion run.

 

CMS (Giulia Negro)

Roderik Brice: I am not sure we can mix the TS and the machine setup. For setup we need a lot of experts around, and they might not be there during the night. The commissioning might not be as efficient.

Chris Young: we might also not have ions in the TS. 

Michi Hosteletter: if it is just access in the expt cavern it should be ok, but if we interleave machine activities, after every access, there is a negliglible risk that something can happen: it can happen that something can not restart properly. If you have a lot of people going in the machine during the day, and you want to start in the night, quite often you need to intervene to turn back on the machine and it is not efficient.

Roderik Bruce: in addition some of the machine people might not be available in the night.

Chris Young: so the answer is no.

Chris Young: for the installation of the ZDC, we are counting 2 days in the timetable, and the injectors TS should be on the first day, so if things are quicker, we can start in advance. For the cryo reconfiguration in 2026, it will depend on what we are doing. If we are doing pPb and we want a high intensity p beam, like 6e11, we cannot reconfigure. In general, it would save 3 GWh. I think that last year for the 3 weeks of PbPb it was 250K CHF. Last year we did not use it in case there was a quench, which then would recover faster if you are not in ECO mode.

 

ALICE (Robert Muenzer)

No comments.

 

LHCb (Paula Collins)

Michi Hostletter: [about the shift discussed on s4] in y it is ~100 um, so to correct it, it should not be an issue, since it is the order of what we have in lumi scans. To be confirmed. 

Michi Hostletter: PROTON PHYSICS for the HL-LHC MD is now a step in the procedure, so if it is followed, it should be ok.

Chris Young: for the magnet flip, you just need some time with no beam, right?

Paula Collins: yes

Chiara Zampolli: how much time is it needed?

Paula Collins: just ramp down and up.

Chiara Zampolli: so it can be also between fills.

Paula Collins: yes.

 

AOB

Eric Torrence: how final is the MD schedule? Will there be last minute changes?

Chris Young: in principle, based on previous experience, reshuffling could happen if they have downtime. There was a reshuffling for the HL test from Wed to Tue in order to not have collisions close to the xrays. From the MD coordination, there should be no other change. The plan will be presented at the LMC today.

Eric Torrence: for us that would be good since we would like to do a Tile Cs scan. 

Michi Hosteltter: I asked for a little change, but it should not affect you, apart from the BCM masking in ATLAS which is light-weight. It is for the combined ramp squeeze and rotate, which I asked to be swapped to the previous MD since it is my MD, but I will be on night shift that night, and I would prefer not to start it after 6h of night shift for 4h.

Giulia Negro: for the stable beam slot with high pileup, is the filling scheme confirmed?

Chris Young: yes, 600b only, more is vetoed by MPP.