Minutes and Summary

Main purpose of the meeting: Data taking progress; RF finger / vacuum module issue; FASER / SND exchanges; Feedback and others

LPC minutes 04 August 2025

Present (P = in person): Chris Young (P), Chiara Zampolli (P), Silvia Pisano (P), Giulia Negro (P), Eric Torrence (P), Paula Collins (P), Witold Kozanecki (P), Joanna Wanczyk, Matteo Solfaroli Cammillocci (P), David Stickland (P), Andrea Massironi, Andres Dellanoy, Dragoslav Lazic, Flavio Pisani, Kyriacos Skoufaris, Rosen Matev, Stephane Willocq, Bjorn Lindstrom, Michi Hostletter

Introduction (Chris Young)

Paula Collins: How long does the intervention for the emulsion exchange take? 

Chris Young: like the normal Wed access, from 8 (with RP, so 9 they start the work) to 12.

Paula Collins: for the magnet being on or off, we should have a stop that is at least 8h long. We cannot stop it otherwise. 

Flavio Pisani: I think it is actually 5 hours, but it needs to be approved by the magnet experts. If the 5h are reached in steps (e.g. there is a stoppage foreseen for 1h only, then prolonged for 1 more hour, then again…), we cannot do it. 

Chris Young: the question that came to us from Management referred to the night when there was beam but there were no collisions.

Flavio Pisani: the LHC wanted it on: we asked the CCC to ramp down the magnet, but we were told it was better not to.

Silvia Pisano: for ALICE it is the same, the stop should be at least 5h.

Stephane Willocq: what is the procedure now with respect to the issue with the RF finger at P2, how will it be decided whether to intervene or not?

Chris Young: they are looking at the X-rays now, and if they find that there is anything that needs further discussion, they will call another meeting like the other that was held last week with the head of the beam department, and deputy of the Accelerator and Technology Director, Rhodri Jones, plus the vacuum and impedance experts. I believe that this is what will happen in terms of procedure since there is no other LMC till the end of August. We’ll keep you informed. 

Stephane Willocq: thanks. We obviously don’t want to have a major problem.

Chris Young: or a major intervention.

 

ATLAS (Andrej Gorisek)

No comments.

 

CMS (Giulia Negro)

Giulia Negro: can cryo do something with the malfunctioning valve in cryo that prevents us to go to 63?

Chris Young: yes, I don’t know if it is something that can be done on the control level, or with access. I don’t know the details, but I know that they are looking at it.

Chris Young: As for the TS time in 2026: it would not be possible to just extend it on the fly as it would run in the HI period. There is the option of making it 2 days long. 

Giulia Negro: 2 days would indeed be better.

Andrej Gorisek: when do you need feedback for 2026 VdM and TS?

Chris Young: Rende was hoping to make a draft for the 2026 timeline in September, even if it is technically not approved before December. So the beginning of September would be good.

Chris Young: for 2024 vs 2025, saying that we swapped the crossing angle so we swapped who is ahead might be an over-simplification. There are many things that changed, the imperfections in the optics may be different in the two years, for example. 

Eric Torrence: and the 3% now only comes from changing the crossing angle.

Chris Young: but indeed the 3% difference was there also in the past.  

Chiara Zampolli: so now you reverted back the calibration of the luminosity, basing your decision on the counting of the Z. 

Giulia Negro: it is not based on the counting of the Z. This is just another measurement that was going in the opposite direction, and since we don’t know what to believe, we decided to go back. 

Chiara Zampolli: so the VdM would keep the results that we had till some days ago?

David Stickland: the results from the VdM were preliminary, not looking at all possible fits. We did not anticipate that it would create such a fuss. 

Chiara Zampolli: so you trust more the other.

Giulia Negro: since it created all these problems, we decided not to change. We have two measurements (VdM and Z-counting) that go in different directions, we don’t know what to trust. We could have kept the new one, but since it was limiting us, we decided to go back to what we had before. When we have more final results, we might updated.

Chiara Zampolli: why are you saying that it was limiting you? Maybe it was discussed when I was not here. 

Silvia Negro: because we changed, but we could then not increase the pileup.

Chris Young: because the definition of 63 changes with a different calibration. 

 

ALICE (Silvia Pisano)

Chiara Zampolli: this background, is it seen just as an uncorrelated background, as noise?

Silvia Pisano: it is just currents seen in the detectors, which are higher. The problem is when the ITS and MFT chips are sent to error and affect the currents in TPC. Now we have to assess the situation in terms of reconstruction. 

Chris Young: probably there is no chance to reconstruct those 15 seconds.

Silvia Pisano: I don’t know this . I expect that we can, but I prefer to assess the situation before giving a final statement. 

Chris Young: one thing that is encouraging is that in this fill (see s.4) where there is this green structure, we don’t see an elevated background, so this is probably acceptable. 

Chiara Zampolli: why the intervention on the power converter for the magnet could be done only in working hours?

Silivia Pisano: because it needed some services from CERN that work only in working hours

Michi Hostletter: I confirm that we did not see anything in coincidence to the spike that you report (from Sunday 03.08.2025, 02:15 am). If there was something, it was surely orders of magnitude lower than the event that we saw before on Wed (the one with the broken RF finger).

 

LHCb (Paula Collins)

Chiara Zampolli: on the plot on s.4: does it mean that after you correct, when you then restart the fill, it goes back to a non optimal value?

Paula Collins: we had plenty of fills that started in the good place. Then it happens by chance, e.g. after a power cut, that it starts high. 

Chiara Zampolli: I thought that the fill after the adjustment should be good. 

Paula Collins: sometimes it is, other times it is not.

Michi Hostletter: I did a bit of feed-forward from one of the last fills. Let’s see how it evolves. 

 

AOB

Chiara Zampolli: let’s keep an eye on the satellites and transmutation in the light ions data.