Minutes and Summary

Main purpose of the meeting: Progress with 2026 run; MD on luminosity; vdMeer planning

LPC 23 March 2026

Present (P = in person): Chiara Zampolli (P), Martijn Mulders (P), Sune Jakobsen (P), Eric Torrence (P),  Jörg Stelzer (P), Archie Sharma (P), Julia Negro (P), Krystian Roslon (P), Flavio Pisani (P), Sofia Kostoglou (P), Jorg Wenninger (P), Joanna Wanczyk (P), Michi Hostettler (P), Georges Trad (P), David Stickland (P), Klaus Monig, Matthew Nguyen, Peter Steinberg, Belen Salvachua, Tomasz Bold, Reyes Alemany, Filip Moortgat, Anna Sfyrla, Ivan Amos Cali, Juan Esteban, Roderik Bruce, Mirko Pojer, Richard Hawkings, Dragoslav Lazic, Mario Deile, Stephane Fartoukh, Gerardo Vasquez

LPC intro (Chiara Zampolli)

Chiara Zampolli: [regarding the option of having the vdM coupling MD during the vdM scan, or at a later moment during this year’s run]: the integral time to prepare these beams, I think, is the same if you do it during the vdM block or after.
Jorg Wenninger: that is not clear; keep in mind that in the last period, you will be in conflict also with the ion preparation.

Chiara Zampolli: we are discussing with the injector people, and Richard and David [for the luminosity (LLCM) working group]. What is nice about moving it later is that we can decide based on the integrated luminosity delivered to that point.  One other possibility is clearly that if the VDM ends earlier than expected, one could slot it in. Even though the vdM MD is 8 hours, and I doubt that we will be ahead by 8 hours.

David Stickland [coming back to the proposed vdM coupling MD]: I think the problem is, it's an extremely interesting thing for the future, because it can lead to an understanding of how we can prepare beams better and have less non-factorization which is one of the most complex things to get, because it is different every time, and it's a significant uncertainty.
The problem is that… we have to balance being ready for the future with getting as much data as we can right now. And this year the low-mu run is very important for CMS. And we want to absolutely nail the uncertainty on the vdM as much as possible in the special conditions, where we have cut the time down to 8 or 12 hours. We are doing the best we can to balance this with preparation for the future. And I do wonder how it will actually happen in four years time, if we have people around to do it, and when there will be the opportunity. So clearly, if we could allocate the time later this year, it would be good. 

Martijn Mulders: So do I understand correctly that this would not help understanding better the luminosity calibration for this year? 

David Stickland: I think it is more about getting ready for future vdMs. Do you agree, Joanna? 

Joanna Wanczyk: It is more about the understanding of the [non-factorization] effects that are being observed by the experiments and currently not explained. They cannot say what's the source of the effects. They see evolution, for example, from 2024 to the latest results, but nobody knows where this comes from. So it's a more like a base study to establish if the coupling can be the source of what they observe as an evolution.

Chiara Zampooli: but then if you understand that, indeed, the coupling is the source of this problem, can you use this data to correct the existing calibration, or do you need it only to tune the future vdMs?

David Stickland: I think we've measured what we've measured, and we have to use that.

Joanna Wanczyk: It has not been checked in the past years. We had a discussion within the Luminosity Working Groups in the last year. And now the optics team came up quickly with a correction to the local effects.The assumption is that it works as it's supposed to, so it suppresses the local coupling everywhere as much as possible, but which effect it will have on non-factorization this year is not clear. The experiments will measure it, and then probably the assumption will be, if it's reduced, then this is because they improved the corrections, but there's many components into that, so you cannot draw a direct conclusion. 

Chiara Zampolli: Well, there's also this stocking filler, that in principle could already give you an idea for this year. And I hope we will manage to take it. 

Joanna Wanczyk: Yes, it's just that in 40 minutes, you can run a step scan to check a few things, but you will never get the full distribution. 

Jorg Wenninger: Basically, you have one colliding bunch there, and normally we take just any bunch that comes; we don’t take vdM beam during the loss maps. But this anyway comes from the vdM time. It is in the loss maps, so you extend the loss map fill.

Chiara Zampolli: by 40 minutes, which is less than 8 hours, so should weigh less. Ok, we leave it at that, and if experiments have feedback on the plans it would be great. 

 

ALICE (Krystian Roslon)

Chiara Zampolli: we should schedule the magnet polarity switch. For ALICE this is transparent, no? 

Krystian Roslon: it takes about one and a half hour to ramp down, wait a bit, and ramp up again.
Jorg Wenninger: we have to change some settings. It is good to announce the day before. The interfill can become modestly longer, as we have to wait for the field to ramp up.  

Chiara Zampolli: is it profitable to do it when there is an access scheduled, or it does not matter? Martijn Mulders: for example together with the FASER access?

Krystian Roslon: I will have to double-check what the flexibility is on the timing for the magnet flip.

CMS (Archie Sharma)

No comments

ATLAS (Eric Torrence)

[discussion about emittance scans during the low-mu runs] : to conclude, we will do an emittance scan in ATLAS and CMS at the start of every fill, before separating the beams. 

Filip Moortgat [about the planned starting date of April 1st for the low-mu run]: since you plan a FASER access on Tuesday morning, maybe the most convenient would be to do the switch to low-mu during the access, to give everyone time to adjust the settings. 

Chiara Zampolli: if the timing with the FASER access works we will do it, but otherwise we will just make sure the switch to low-mu happens during normal working hours. We will decide this Friday, depending on the list of access requests that we accumulate. 

Eric Torrence and Flavio Pisano: both ATLAS and LHCb would like to do an extended emittance scan during the 75b step of the 1.2 TeV ramp-up. Each would need about 1h, and it has to fit within the fill for which currently 3h is planned, so may need some careful planning. 

Eric Torrence asks if AFP can do a beam based alignment during the heavy ion commissioning. Roderik Bruce: well, it is not there in the planning. It is clear that if we add more time to the commissioning there will be less time for physics. We may also need one more loss map fill if we have roman pots in. It is up to LPC and experiments to decide if this is worth it. 

Eric Torrence: Ok we can show some physics motivations to justify this. 

Roderik Bruce: did you consider to insert the AFP to ‘safe’ positions like for the 1.2 TeV run? Because that would be transparent for the commissioning. 

Eric Torrence: I think that is not what they are interested in but I can take that back as an option if we can’t make the case for a shift of beam based alignment. 

Chiara Zampolli: so ATLAS is ready to sacrifice that fill of physics to do the alignment? 
Eric Torrence: that is not the official ATLAS position, but I was hoping that this was already in the schedule. I will discuss and come back. 

Roderic Bruce: and as I said it might be more than one fill if we also have to add a loss map for that. And of course the other experiments have to accept that. 

Chiara Zampolli: and it might be that PPS wants to do the same, and then it would add more time. 

Stephane Fartoukh: I'm not sure whether PPS can take data in ions, because… so we are back with horizontal crossing, and the Roman ports are not tilted.

Filip Moortgat: indeed – Stephane is right.

Giulia Negro: Yes, we don't insert PPS in the heavy ion. By the way, I wanted to mention also that during the 1.2TeV fill we initially wanted also to be included, but at the end, with the position that we got, the acceptance will basically be zero, so also there we will not use the PPS. 

Filip Moortgat: To be clear, the PPS will not be inserted for the 1.2 TV, but we will still take the collision data.

Chiara: yes. 

Jorg Wenninger: if AFP participates in the ion run, maybe it would be good if they are also part of the famous background test. Not that they intercept a funny part of the beam and have a surprise. 

Georges Trad: This movement of 1 centimeter in the vertex z position for ATLAS at the beginning of each fill, does it correspond to the moment when our bunch length is just decaying until we start leveling?

Eric Torrence: Probably, yeah, I'd have to look it up, but that seems likely. I mean, the point at the start is really the start of stable beams. 

Jorg Wenniger: There's also a strong correlation with beta star, of course. I don’t see why the bunch length should change the z position.

Chiara Zampolli: Would it not then be seen also by the others, if it is the bunch length? 

Eric Torrence: this is not a problem for ATLAS. I mean, you can actually see this in all the fills, except for the one where we didn't take the first 30 minutes of data. So I think it really just comes, as the beta star gets adjusted from 1.2 down to whatever the value is. Like I said, it's not really a problem for us, but it's just… it's interesting that we have this, but nobody else does.

LHCb (Flavio Pisani)

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