Minutes and Summary

Main purpose of the meeting: Schedule update after addition of Magnet Quench tests; initial feedback on beam-beam and coupling MD, and update on PbPb schedule and background tests

LPC 18 May 2026

 

Present (P = in person): Chiara Zampolli (P), Martijn Mulders (P), Eric Torrence (P),  Joerg Stelzer (P), Krystian Roslon(P), Flavio Pisani (P), Julia Negro (P), Archie Sharma (P), Roderik Bruce (P), David Stickland (P), Joanna Wańczyk (P), Sune Jakobsen (P), Michi Hostettler (P), Federica Oliva, Witold Kozanecki, Ivan Amos Cali, Silvia Pisano, Aikaterini Nikou, Juan Estban Muller, Richard Hawkings, Tomasz Bold, Peter Steinberg, Maciej Trzebinski, Gerardo Vasquez, Benoit Salvant, Dragoslav Lazic, Mario Deile, Riccardo Longo, Antonio Sbrizzi, Valeriia Zhvkovska, Kyracos Skoufaris, Andres Delannoy, Wei Li.

 

LPC intro (Chiara Zampolli)

(no comments)

Beam-beam and coupling MD (Joanna Wańczyk)

(Martijn Mulders:) Do you expect these Q factors to stay the same, to be stable for several hours during the fill? 
(Joanna Wańczyk:) No, they were changing, and we were measuring it, so this is something we are looking into right now.

 

2026 PbPb plan and background tests (Roderik Bruce)

(Chiara Zampolli:) For LHCb, we do this scan for the TCT, but actually, we can indeed then put this as a setting only because we go to a lower crossing angle?  
(Roderik Bruce:) That, and the fact that in the aperture measurement that we had last year, we saw that we had a bit of margin also. So combining those two gives us this margin. 
(Chiara Zampolli:) So if we didn't go to a lower crossing angle, would we still open? 
(Roderic Bruce:) We could still open, but for probably less.

(Michi Hostettler:) For the LHCb Velo, we have to see if there is any chance that you can close without stable beams, or it would be possible to put stable beams, if everyone agrees, we just have to make sure that everyone understands, with the manipulations that we do, that this is not really stable beams.
(Flavio Pisani:) As far as I know, we can override the flag. 
(Michi Hostettler:) Without generating an interlock?
(Flavio Pisani:) I have to check with the experts.
(Roderik Bruce:) I think we have to sort out this very carefully beforehand, so we know what to do, and we don't stand there, and maybe in an inconvenient time over a long weekend, then we lose time. 

(Chiara Zampolli:) So I don't know why we would scan the knobs that helped for 2023?
(Roderik Bruce:) The reason is that we saw slightly different optimal values between 23-24 on one hand and 25 on the other hand. I think in 25, we scanned the knob, and we saw that then there was not really any change in the background between the default value and the overcompensation. But in 2024, we saw that the overcompensation was much better.
We also never scanned this knob in a background test with the negative ALICE polarity. There could be some interplay, maybe not. There's some things that have not been tested there. Still, I think it's good to keep the commissioning as short as possible, and not add, let's say, extra luxury tests. So this is why I put it in gray, and if we see in the first part of the test, when we scan the SDISP in IP8, if you see there that we can find the configuration which looks very promising, then we don't have to do this second part and scan the IR1 SDISP.
(Chiara Zampolli:) Yes. So one comment that was made during the LBOC meeting was that it might be worth to spend a bit more time in trying to understand this, as it might be useful for Run 4. But let's proceed with the baseline test and see how it goes. 
(Roderik Bruce:) Yes. One option, of course, could be that we try to elaborate the test, where we actually decrease the SDISP below 0.2 with the full machine, or I say with high intensity, but this has to be discussed beforehand with many people, to work out the strategy for the test, and convince ourselves that the orbit changes that we do there are sort of safe, and we can do them. Maybe I would even do that in the intensity ramp-up first, to see that this is actually safe, and doesn't cause any big losses. I think we can try with higher intensity later. It's something worth thinking about. I didn't want to put this here to add too much entropy, but it's something that we have a bit in the back of our head. I don't know if it's possible or not, also, so something to be checked. But I guess for ALICE, it could be quite interesting if there's a doubt on the extrapolation from low intensity to high intensity, yes.

(Maciej Trzebinski: we still align the Roman ports with respect to TCPC6, right?
(Roderik Bruce:) I saw your mail, I didn't get back to it yet, because I had to think about it. I will try to answer you later today. I wanted to calculate quickly the distance that you would get for the two cases with respect to TCT and to the TCP. We have to keep in mind that the TCP is also a lot more open for ions than for protons, just so you know.
(Maciej Trzebinski:) Okay, so please let me know.

(Maciej Trzebinski:) I assume that because we have more bunches than during the BBA for protons, we must increase the BLM thresholds, right?
(Roderik Bruce:) Well, you have more bunches, but the intensity per bunch is much lower, so the total intensity in the ring is similar, so I'm not sure you need that.
(Maciej Trzebinski:) But the losses are, when we touch, are probably just proportional to the bare number of bunches, right?
(Roderik Bruce:) The losses are proportional to intensity.
(Maciej Trzebinski:) So, but at the end, shall we adjust it, or not really?
(Roderik Bruce:) for the proton BBA, did you need to adjust it or not? I don't remember this year, how did you do it?
(Maciej Trzebinski:) We always adjust, historically, let's say.
(Roderik  Bruce:) Okay, if you always adjust, maybe it's wise to adjust at this time as well. That's a good point. I didn't think about it.
(Chiara Zampolli:) But will take care of communicating it to Belen, or… 
(Roderik  Bruce:) Yeah, I will, I will contact them afterwards, yes. Okay.

CMS (Giulia Negro)

(Chiara Zampolli:) So the test that you did at PU=7 was to see whether in PbPb you can have a different approach for the pixel detector? 
(Giulia Negro:) Yes, at the moment, we have to exclude the inner rings for Pixel for, okay, luckily, only for a few days of pp, and then anyway, the LHC did not give us much new data, so… only for a few fills. Because otherwise, the only way we can program certain components is to power cycle them. But of course, power cycling the detector is not great, and we were doing this basically in every fill in the last week. So we decided to stop, to increase the chance to have it fully working in PbPb.

And we were trying to test this in a lower PU condition, because sometimes in the middle of the fill, we managed to configure them. So maybe at the beginning of the fill, the high intensity is giving issues, so we wanted to try with PU=7, to see if there is a difference.
Investigations are ongoing, where we're really trying to understand the issue. 

(Martijn Mulders:) And why PU 7? Is that similar in occupancy to heavy ions?
(Giulia Negro:) In the beginning of PbPb we'll have a PU 7. That's why we took those 12 hours at Pileup 7. 
(Martijn Mulders:) I was just wondering, Proton-proton is still quite different from Heavy Ion. 
(Giulia Negro:) Of course, but this was to try to see if we managed to make them work during pp. It is not really clear why sometimes later in a fill it works, so we planned to try also at the beginning of the fill to have a lower intensity. Of course, we couldn't ask to change the intensity in the machine, so we changed our PU.

(Chiara Zampolli:) And, so in PbPb you said that you hope that it will work better?
(Giulia Negro:) Well, we don't have high hopes. What we will do is that we will power cycle them every time as long as this is possible, because at some point they might die. So that's why we decided, okay, let's stop for now. We reached the target and we give a possibility to PbPb at least to have some period of time with the full pixels included. Then it may work until the end, we need to see. It is a radiation effect, because it's the inner rings on the forward pixel on both sides, so, okay, the accumulated radiation, as we can see that the layer 1 of the barrel and also the inner rings are suffering. We don't really understand exactly the full issue, because as I said, sometimes it works, sometimes not.

(Chiara Zampolli:) And it got worse and worse with time? Like, exponential, or… 
(Giulia Negro:) Well, yew it has been quite exponential. In the last week it was really bad. It started in the last weeks, with different symptoms. But more recently, we had, basically, at the beginning of last week, to power cycle the full detector corresponding to those partitions at every fill, and apart from this being time-consuming for people, it's really bad for the detector.
So, we decided to stop here. We still tried a few different things. That one on Saturday was the last one, and now, okay, let's see when we resume with heavy ions. If it is better, great. If not, we will try to mitigate as much as possible, until it dies. Okay. We knew it was going to be tough at the end, so…

ATLAS (Eric Torrence)

[slide 5: some discussion about collisions during the MD2 schedule] 

[some discussion about whether CMS also would like to do an IP angle scan, like in ATLAS, to understand better the asymmetry seen in the ZDC last year, and when to do it in the schedule]

(Ivan Amos Cali:) Yes, we should do it for sure. The background that we have, that we had last year was a background that we said is less important, but we are actually losing 10% of our triggers, so if doing this scan could allow us to recover, or at least to understand the source, that would be extremely good.
(Chiara Zampolli:) And for example ALICE doesn’t need it? 
(Roderic Bruce:) We can do it, but I never heard that there was a need for it.
(Chiara Zampolli:) I may double-check it. However, I also haven't heard about this kind of need. For us, it's very important to have the collimators open. But let us double-check.

ALICE (Krystian Roslon)

[some discussion about the timing of the polarity flip in ALICE, and intensity ramp-up] (Chiara Zampolli:) And is there going to be an MPP for the intensity ramp up? To validate the steps, like we had last year?
(Roderik Bruce:) No, I think there was no MPP to validate the steps. Last year, there was a presentation where we agreed beforehand on the steps that we should do. That's what you did, because then, during the actual steps, there was no MPP. The actual step is just a checklist for people to sign. There might be an MPP meeting coming this Friday, yes?
(Chiara Zampolli:) Okay, because then this could also be brought up, like, asking in case we have to change the configuration, what is required.

LHCb (Flavio Pisani)

[some discussion about opening and closing the VELO depending on background conditions. How far to close it during PbPb running, and what are the plans during LS3 to fix (or not) the damaged parts.]

AOB

none.