Minutes and Summary

Main purpose of the meeting: Discuss 2026 planning; look back at the low-E run; presentation about the Lumi mini-MD and discussion about a possible MD.

LPC 4 May 2026

 

Present (P = in person): Chiara Zampolli (P), Martijn Mulders (P), Eric Torrence (P), Dragoslav Lazic (P), Flavio Pisani (P), Silvia Pisano (P), Krystian Roslon(P), Julia Negro (P), Filip Moortgat (P), David Stickland (P), Tatiana Pieloni (P), Roderik Bruce (P), Georges Trad (P), Joanna Wańczyk (P), Matthew Nguyen, Witold Kozanecki, Ivan Amos Cali, Stephane Willocq, Aikaterini Nikou, Brian Petersen, Joerg Stelzer, Federica Oliva, Kyriacos Skoufaris, Matteo Solfaroli, Richard Hawkings, Anna Sfyrla, Maciej Trzebinski, Giulia Ripellino, Peter Steinberg, Antonio Sbrizzi, Mirko Pojer, Juan Estban Muller, Kartik Deepak Bhide, Tomasz Bold

 

LPC intro (Chiara Zampolli)

Witold Kozanecki [about the instabilities encountered during the 1.2 TeV runs]: I am perplexed by these instabilities with colliding at 4 IPs … we do this all the time … I also remind you that in November 2018, we ran 4 hours at injection energy and collision, 900 GV per beam, stable beams, with only one IP Atlas colliding. So is there some understanding of what happened here?
 
Chiara Zampolli: The post-mortem will be done in the coming days. I can tell you that I asked the same question; not many answers are known yet, but people are looking at this. 

Georges Trad: the intensity plays a role here as well.

 

Lumi MD: physics objectives (Tatiana Pieloni)

Chiara Zampolli [Summary slide]: So here you say that you have an effect of 0.4, 0.8 on sigma visible, with one single IP. Yeah. So if you have more IPs, you expect it to be larger, smaller, or  what would be the effect? 

Tatiana Pieloni: This is a very nonlinear thing, so I can say multiply by 2, but I think it's a bit simplistic. The fact is that the other IP will introduce a tune shift, okay? So when you move the tunes, you might be getting closer to the coupling resonance, further away, so it changes the total and also the dynamics, so one has to be careful. We don’t know exactly. [...] In the MD we would like only one IP in collisions, and we might have another fill adding the one in collision. We will discuss the options at the calibration working group, to make the best use of these 8 hours, if they come. 

David Stickland: This is on the agenda for the LLCMWG meeting  next week. So it is very nice to have this presentation of the overall picture today. And by that time, we will have a clearer picture of how we are on target for the luminosity. This will be a very active discussion next week, I think, amongst all the experts. 
Eric Torrence:  Am I supposed to be looking at the difference between the two yellow points, for instance? 

Tatiana Pieloni: So yellow is if you have an initial beam distribution with a Q factor of 1.4, so you'll feed more the tails with respect to your Gaussian correction. This is if you do on-axis counts. The deviation on the sigma visible is just coming from the coupling, when you add coupling to the beam-beam. 

Eric Torrence: But that's still only about 0.4%, which was kind of at the limit of what you could measure. 

Tatiana Pieloni: Yes, but this is for a very small coupling term. So this is a very small one that we took in simulations, which is smaller than what they measured, actually, in reality. So, we are not one-to-one, up-to-date with the actual machine, because then we asked, in fact, for coupling measurements during the calibration working group, we said we need coupling measurements and a correction that really brings these values as small as possible for you.

Eric Torrence: So this would still be pretty… at the limit of what you try to measure, right?

Tatiana Pieloni: Yes, but the idea is, since we have a much bigger coupling, this yellow point should go at least by a factor of 2 or 3 up. 

Chiara Zampolli: But in the scan, which of the 3 are we using? 

Tatiana Pieloni:  We do 2D scans. Peter (from CMS) has come up with a 2D scan that will allow to extract an on-axis, and also 45 degrees, etc. It's optimized to be very fast in the scanning and get all the information of the luminous region in also these non-access cases, because the picture becomes quite complex.

Witold Kozanecki: IF it is approved, when would it take place? 

Chiara Zampolli: we have agreed with the MD coordinators to have the beams prepared during the preparation of the beams for the MD2, which will be on Friday next week. Proton physics ends on Monday, included. So then, it would be either Saturday or Sunday. By then we will know where we are in terms of luminosity, whether these 8 hours will really make an impact on the experiments, or if the experiments accept to have it. 

Flavio Pisani: How many bunches are you planning to use? 

Tatiana Pieloni: 12 INDIVs. Because like this, we can always scan with a wire scanner and have the profile and the Q-factor. 

 

ATLAS (Eric Torrence)

[... some discussion about the problems with the inner layer of the pixel detector during the very-high PU runs…]

[... discussion about including the AFP Roman Pots in the heavy-ion running…]

Roderik Bruce: We discussed with Maciej, and if it is really only aligning and finding a center, and if it's only the four pots, the beam-based alignment could potentially be quite fast, because we could actually take over another fill where we align the TCTs, for example. With 30 minutes per station we would need 2 hours, plus a bit of overhead just to set stuff up at the beginning, so probably 3 hours in total. 

George: Back to the high-mu running: we see a z shift in ATLAS and CMS … is this an issue? It only happens when out of leveling – during the leveling we use the longitudinal feedback to keep the longitudinal position stable. We don’t activate it after leveling, to optimize luminosity; if we need to correct for it, it is an exercise we need to do when all of you should be head-on.  

Eric Torrence: We will check and let you know. 

 

ALICE (Silvia Pisano)

Silvia Pisano: a question for Roderik – can we say to our ZDC friends that we stay with 150 microrad external crossing angle for heavy ions? 

Roderik Bruce: I think this is likely. I'm still double-checking the final numbers. I mean, it will for sure not be larger. There is no reason to make it larger. I'm looking to see if it's possible to make it slightly smaller. I am trying to tune in the sense that, for Alice, the difference is not very big, because you have this very long leveling time anyway. Changing the crossing will slightly change this leveling time, but not very much. While for Atlas and CMAS, the difference is much larger if they go down in crossing. But still I don't want that ALICE loses any luminosity, so I'm trying to fine-tune these numbers. When do you have to know?

Silvia Pisano: let's put it in this way, Roderick, I mean, as soon as possible, but we still have some margin, because the agreement is that as soon as we have the range, our ZDC colleague can provide the tolerable opening of the collimators.

 

LHCb (Flavio Pisani)

 

CMS (Giulia Negro)

[... some discussion about the recurring extractions of the CMS roman pots due to overheating in the high-mu runs. CMS is wondering whether this is due to the reduced lower limit for beam blow-up in beam 2, and whether this can be increased back from 1.15 nanoseconds back to the original value at the beginning of the year... ]

Georges Trad believes that beam 2 is still behaving worse than beam 1 so any increase would have to be done gradually. And it would not help in the beginning of the fill in the first hour, only later in the fill, after 4.5 hours or so.

It is agreed to check and follow up on this.