Minutes and Summary

Main purpose of the meeting: Data taking progress p-O/O-O/Ne-Ne news and planning VdM planning

LPC minutes 02 June 2025

Present (P = in person): Chris Young (P), Chiara Zampolli (P), Robert Münzer (P), Andrej Gorisek (P), Paula Collins (P), Eric Torrence (P), Flavio Pisani, Silvia Pisano (P), Rosen Matev (P), Filip Moortgat (P), Andrea Massironi (P), Giulia Negro (P), Roderik Bruce (P), John Jowett (P), Cedric Hernalsteens, Flavio Pisani, Gerardo Vasquez, Juan Esteban, Matthew Nguyen, Peter Steinberg, Riccardo Long, Richard Hawkings, Witold Kozanecki, Jorg Wenninger (P), Michi Hostletter (P), Dragolslav Lazic, Anna Sfyrla, Giulia Ripellino, Qipeng Hu, Benoit Salvant, Georges Trad, Wilke van der Schee

Introduction (Chris Young)

Jorg Wenninger: concerning the planning for the SND emulsion exchange during the week, how flexible is SND? e.g. would at 5 in the afternoon (also useful for QPS) work for them?

Chris Young: SND can do their own transport. They need to be around, meaning that they need the time get to CERN and go down, but it is doable in any access. 

Jorg Wenninger: if they need to get to CERN, then by the time they arrive, the other access may already be over.

Chris Young: yes, but if you have a stop long enough it will be fine.

Jorg Wenninger: there is nervousness in the cryo team since there was another single event upset after LHCb collected another 1 fb-1… A comment also on the VdM shift slide: SPS does not produce an induced beam shift, so this should be clarified.

Chris Young: in the SPS we want to have a zy (ξ, also called Xi) (which is the beam beam parameter) which is related to bunch intensity and emittance.

Jorg Wenninger: yes, we need the bunch intensity and emittance that produce this zy, but the problem is that the way the request is formulated does not tell me if it is doable.

Joanna Wanczyk: I discussed it with Foteini, and she said that it should be no problem, but they will have a dedicated session in the injectors to see if it is possible.

Jorg Wenninger: what does the value on the plot correspond to?

Joanna Wanczyk: the intensity should be close to the brightness of nominal physics beams, for example ~1.3e11 ppb and 1.2-1.25 for emittance, so slightly lower intensity but similar brightness

Jorg Wenninger: one needs to consider that you’ll lose some emittance when you go to LHC.

Joanna Wanczyk: yes. If we have enough time, we can also change it a bit even if not too much.

Chris Young: first, one should prove that we can make high brightness in the injectors.

Joanna Wanczyk: what about the test for the tune shift that is mentioned as requirement? What do you mean?

Chris Young: what you did already.

Joanna Wanczyk: it was the equivalent of 150% of the beam beam parameter but this value comes with a large error bar since the BSRT was not calibrated when the test was done, so we don’t know.

Jorg Wenninger: you may need more than one attempt at injecting to get the right beam. For examply adjusting the ADT.

Joanna Wanczyk: but we hope to not have big losses. Do you expect extra losses?

Jorg Wenninger: in the VdM we don’t have to make special tunes when we collide, while this requires a bit of tuning. The beam gets spoiled when you collide.

Joanna Wanczyk: usually this comes from LR or other effects but these effects should not be the case in VdM beams.

Jorg Wenninger: without test it is difficult to say.

Chris Young: the idea is to show that it is possible to be more on the green than the blue curve (meaning: value of emittance). We can continue offline.

Cedric Hernalsteens: Coming back to the lumi spikes in LHCb. What is the gravity depending on the magnitude of the spikes? I would assume that you go from an inefficiency in the data taking, then a trip, then damage. What is the range for the spike associated to these effects? From acceptable to non acceptable.

Paula Collins: the trip limit is 20% above the nominal. Even like this, it is not comfortable since we have trips, but trips are there to protect the detector. The very high spikes should be completely avoided. We very much appreciated the feedback, as the tuning went on, curing the excursions.

Jorg Wenninger: if you are so worried, then you should not run at nominal lumi in the first fills, but you should stay below significantly till we’re sure there is no problem anymore. Pushing to nominal immediately makes the job very difficult. 

Paula Collins: when things calm down, we should discuss the policy and the procedure. We can cope with 20% spikes which are sudden and momentary, but each time it happened it seemed that every time it was very explainable.

Jorg Wenninger: 20 % spike is just a 1 mum shift in the orbit, which is really tiny.

Paula Collins: after the first fill, we saw very small deviation. The remaining concern is only the first hour. Are you suggesting to have a few fills with lower lumi after a flip?

Jorg Wenninger: yes, the first fill should be fully at lower lumi, Then only the first hour. The first fill fully because we go through all the steps.

Paula Collins: let’s discuss together. For us, for physics efficiency, it is difficult to run not at the target because we’re trying to get to a stability situation in the settings. It is not that if we’re running 30% below target, we collect 70% of the data because we’d need to readjust. We want to continue at nominal as much as possible, but surely within the safety limits. 

Paula Collins: for my education: in the meeting it was said that the B1 losses might imply changes in optics. 

Jorg Wenninger: changes in octupoles, not optics.

Andrej: general question [about the fact that the LHC was down after a power glitch in the night]: what is the prediction to have LHC back? We had quite some issues last time when ramped up the toroid, so we could prefer to not do it in the night, if possible.

Jorg Wenninger: I hope I can close the machine by 2 pm, then we need to wait. I prefer not to give a time, but I think not before 6pm.

Chris Young: but we hope before tomorrow morning, which is what your alternative time for ramping is.

Jorg Wenninger: yes, surely something during the evening.

 

ATLAS (Eric Torrence)

Chris Young: the 0.3 for pileup is for pO and OO?

Andrej Gorisek: for pO it is the LHCf limit.

Andrej Gorisek: [about the 5% difference with CMS at the enf of fill] we believe that our scale is better than 5%.

Chris Young: we should try to understand this but it is tricky.

Cedric Hernalsteens: [comment about the imprecise leveling] this was my first fill, and I tried several things, but it looks like your signal for lumi was less precise. Could it be?

Andre Gorisekj: we did not notice from our side. There was a hiccup during the emittance scan, but not in the others. In the other fills, our publication should be solid.

Cedric Hernalsteens: I will review what I did in detail, also with Michi.

 

CMS (Giulia Negro)

Emittance scan: CMS needs to go first or they don’t pick up correctly the start of the scan.

Giulia Negro: for pileup and contamination we’ll give feedback as soon as possible. The more lumi the better and we’re studying for the contamination.

Chiara Zampolli: what is the issue for the start of the scan if before there is ATLAS?

Giulia Negro: it seems that some of the online detectors don’t pick up the end of ATLAS scan and the start of the CMS. 

Andrej Gorisek: ATLAS is happy to do second.

Giulia Negro: yes. In case we will miss the first minutes of the scan. 

Chris Young: about the lumi leveling going up to 2.2, I also did not know till thur. Please provide feedback privately or public pn MM about pileup and contamination in OO.

 

ALICE (Robert Münzer)

Chris Young: for the test at high rate at end of fill, you can contact the CCC.

Chris Young: update us when you have more precise numbers for the OO pileup and contamination.

 

LHCb (Paula Collins)

Chris Young: update us when you have updates for the pO and OO/NeNe pileup, as well as the contamination from transmutation.