Minutes and Summary

Main purpose of the meeting: Schedule: Run3 data taking completed MD3 & LHCb background test G7 High-intensity test Next meetings

LPC 15 June 2026

Present (P = in person): Chiara Zampolli (P), Eric Torrence (P),  Silvia Pisano (P), Martijn Mulders (P), Paula Collins (P), Federica Oliva (P), Filip Moortgat, Roderik Bruce, Archie Sharma, Brian Petersen, Giulia Negro, Ivan Calì, Krystian Roslon, Maciej Trzebinski, Roderik Bruce, Sune Jakobsen, Witold Kozanecki, Peter Steinnerg, Stephane Willocq, Dragoslav Lazic, Tomasz Bold, Jorg Wenninger, Anna Sfyrla, Joanna Wańczyk, Antonello, Jorg Wenninger

LPC intro (Martijn Mulders)

No comments.

 

 

CMS (Archie Sharma)

 

Martijn Mulders: do you understand what is the problem with the PXI that could not allow for the alignment of PPS?

Archie Sharma: no, but the automatic insertion works, so they are going to use that next week.

Filip Moortgat: the special insertion mode that is needed to align did not work, while the regular one does. In any case for the 3 TeV the test is not so meaningful, since the pots would be very far and heating wise it is not the most challenging scenario, while the 6.8 TeV will be more useful, and there it works.

 

ATLAS (Eric Torrence)

 

Filip Moortgat: 8b4e has no heating at all as it has no ecloud because it gets killed by the gaps between bunches, but sometimes you can accept some heating, so you can mix the 8b4e with BCMS, with 36 or 48 trains, which is what we did in the hybrid scheme. If the coating strategy to mitigate ecloud is not good enough to limit the heating issues in Run 4, they might need to use some 8b4e in the first years. Pure 8b4e would decrease the number of bunches in total in the machine (max ~1900), while with hybrid we have approximately the same number of bunches as now. 

Jorg Wenninger: for the time in collisions next week, it will be more than 30 minutes in total, to also accommodate scraping tests which will take between 30 minutes and 1 hour. The possible stability tests [which are mentioned in the spreadsheet], are not yet approved [so for now one should not count them]. We will know more in the coming days

 

ALICE (Silvia Pisano)

 

No comments.

LHCb (Federica Oliva)

Federica Oliva: I confirm that removing the IP shift, the hotspot was moving with the beam. What we saw was a ~2 mm shift but this corresponded to the fact that the beam moved.

Roderik Bruce: do you have the frequency of the background? Does it change when you change the vertical crossing?

Federica Oliva: the rates on s6 are in arbitrary units: they are the rates selecting a particular region where we expect background, selecting large clusters in VELO and with an eta cut (in acceptance). The point at the bottom slipped in the plot from a moment when we had other activities, like opening the VELO or checking the voltage - since during the test we ran all the time. 

Chiara Zampolli: how can we compare the size of the background? Here it seems that it was increasing. Would it mean that vertical crossing would be worse?

Paula Collins: if you change the rotation angle of the remora, you can see that by the shape of the VELO which is a diamond, with a different angle but the same amount of background we could end up accepting more. I would not then say that it is worse, but it gives a deeper understanding of the origin of the remora. We are convinced that these events are linked to damage in the VELO, and they can come either from remora, so traveling with the beam, or from beam-gas interactions. So what we proved is that the remora and the cowlick are the same thing. It would be incredibly cool if the simulations could be transported to pp. And my feeling is that the more we understand this background, the more we can do something about it. 

Chiara Zampolli: I was hoping that we could find a configuration that was improving the situation, even if we cannot still fully understand it, but like this it seems that we get worse. 

Paula Collins: yes, because of the acceptance. 

Silvia Pisano: isn’t the background too much localized to come from beam-gas interactions?

Paula Collins: there are two types of background. One is localized, which is the remora, which travels with the beam. Then we have another background, that is from beam-gas interactions, which is also damaging. Maybe we can reduce the beam-gas background by adding a vacuum pump. We know for sure that this is proportional to the vacuum level of the beam pump. The remora background is proportional to the beam current. So they are completely different background that caused the same damage. For the beam-gas background, if we could add a pump at the sector valve, maybe that could help. For the remora background, we hope that by seeing that it is there both in pp and in PbPb and linked to the crossing angles, we hope there can be some understanding. 

Chiara Zampolli: can you remind me if the damage this year in pp was in the same region as last year in PbPb?

Paula Collins: we have one heavy damage which is bang on the remora. Then we have one which is a bit on the side of the remora. For the rest of the damage, it follows the smog mechanics, which is where we're picking up more of the beam gas. So we think it is from both sources, and it seems mitigated by the voltage settings.

Federica Oliva: just to remind that the settings were done with voltage at 300 V as we have in PbPb and VELO opened 0.5 mm per side.

Roderik Bruce: as far as the simulations for the background are concerned, before extending them to protons, I think we should take a step back, because the simulations that we did so far assumed the losses coming from the TCTs: ions scattered out of the TCTs and giving this remora spot. However we did not see any dependence on TCT losses nor from IR7. So the simulation presently assumes a wrong source. We should think about what the real source could be and then extend the simulations to pp.