Minutes and Summary

Main purpose of the meeting: Commissioning, MDs, VdM, pO (LHCf), anti-leveling,

LPC minutes 31st March 2025

Present (P = in person): Chiara Zampolli (P), Robert Muenzer (P), Andrea Massironi (P), Andrej Gorisek (P), Filip Moortgat (P), Paula Collins (P), Eric Torrence (P), Rosen Matv (P), Chris Young, Andrés Delannoy, Dragoslav Lazic, Flavio Pisani, Gabriella Pasztor, Gerardo Vasquez, Giula Negro, Ivan Calí, Klaus Monig, Lorenzo Bonechi, Peter Steinberg, Rende Steerenber, Riccardo Longo, Roderik Bruce (P), Silvia Pisano (P), Jorge (P), Michi Hostletter (P), Joanna Wanczyk (P), Reyes Alemany, Benoit Salvant, Maciej Trzebinski, George Trad (P) , Anna Sfyrla, Cedric Hernalsteens

Introduction (Chris Young)

Michi: [concerning the minimum crossing angle for leveling] the aspect of how low we go is minor, because going down to 100 urad is 1 hour, then we would just change by 20% if we stop at 120 instead. But yes, if we cannot go below 120 urad, we can stop immediately.

Andrej: for ATLAS, we need the BBA to know if AFP can go to 100 urad.

Michi: which happens at the beginning.

Roderik: why does the BBA matter?

Andrej: they cannot know just from simulation.

Filip: Depending on how good the alignment is, they can tolerate different sigmas for the distance of the beam. To go below 120, it might depend on the quality of the alignment.

Maciej: from simulation, when you take MADX and the design optics, the xing angle is compensated by the position of the detector. Then it depends on what the reality is compared to the simulation. So it depends on how much the beam moves compared to design.

Chris: Let’s do loss maps with the minimum. But we should consider for the intensity ramp up that BB effects can get larger if we go lower in xing angle, and if in production we don’t do that, we’d be exposed to issues which we then won’t really see. 

Eric: [concerning the VdM program to be discussed during the LPC meeting on 28th] only about pp or also OO?

Chris: in OO each experiment does not depend on the others, so we don’t need many details, while in pp each VdM is time when other people do other things. So this is a higher priority in the discussion.

CMS (Andrea Massironi)

Andrea: Length of BBA?

Roderik: presently I put 4 hours for the planning for both ATLAS and CMS. This estimate has a large uncertainty. First we need some fixed time at the beginning to setup which is independent from the number of stations. Then I counted ½ hour per station. This is for pO, in the O side. We then need to know how many stations you have.

Filip: 4 should be a good estimate.

Roderik: if you tell me that there is 1 station less, I will not remove ½ hour from the planning, since we have not such precision.

Chris: the important point is that it is only on the p-side, and therefore it is not 7 stations or 8 or whatever they are, and that it is not in OO either. It is much quicker to do it on side only. In OO, you’d have it on both sides, and it’d take quite some time, so it’d need quite a physics case to justify it. We’d double the time for each experiment. 

Roderik: it depends also if we can reuse the beam from previous fill, otherwise we lose two hours for the refill. My hope is to reuse existing fills.

ALICE (Robert Muenzer)

Chris: the issue with the luminometer can be fixed in time to close on Wed?

Robert: yes the intervention went faster than initially thought.

ATLAS (Andrej Gorisek)

Andrej: is it possible to insert AFP without BBA? This was done in the past.

Chris: [concerning the points on s.3] high mu in October MD: for now we did not have plans to indivs, but I think it might be useful to compare to trains for luminosity, and there should be room in the machine. We’ll give feedback to the MD people about this that having indivs might be useful. The total number of bunches would go up by 1 or 2, and it should be well within the limits.

Chris: [angle leveling] Changes will be in very small steps, but many small steps. This is a  pseudo-continuous change in steps of ~3 urad. 

Eric: what we mean is that if the minimum angle turns out to be 140, this is better for us than if it is 90. 

Chris: is this is a problem for online luminosity only, or also offline?

Eric: if we use all tubes and do the normal algorithm it cancels out at first order, but single tubes have significant acceptance changes so if we’re in a situation like in 2018, it is a problem, but we hope not.

Chris: if we reduce the number of tubes, we might need to see if we still want this. 

Michi: end of 2018, what were we doing? We were doing x-ing leveling.

Eric: we had a correction for this.

Chris: for the OO question, it is for collimation.

Roderik: we need to check with the collimator team. I don’t have a definitive answer to the OO question. But in principle I don’t see an issue to insert to a predefined distance which is safe from the beam, we need to decide the margin that we want to use. We need to discuss a bit offline. We’ll come back to you.

Michi: for the transfer line test does not need the experiment injection permit. If we have the downstream TEDs in closed, then the injection permits are ignored, and the only ones checked are those from ALICE and LHCb to be able to shoot on that beam dump block because it could give some light showers in the IPs. You could even block the injection from ATLAS and we could still do the test. If you put TEDs closed, then you don’t need the injection permit from the experiments.

George: We need to be sure that we can pulse the kicker. 

Michi: yes, for that we need the injection permit. But if you only shoot the TEDs, you don’t.

Andrej: it would be good to have a more definite plan, to narrow down the period when you need the injection permit.

George: on the morning meeting on Wed we might give you the precise schedule to organize, with a slot in the afternoon.

Paula: are we talking in a week from now?

George: it should be around Friday, more than next Monday. So that we don’t delay the restart on Tuesday in case there is a problem. 

Andrej: this run with inner detector HV on should be this weekend, so we can organize to avoid to have this done when there is the test. 

Chris: for when the beam will go first in the LHC, it is the Tue when ATLAS is planning to close the shaft. The test of Michi of kicker ramping needs the injection permits, but no beam will enter the LHC.

Paula: this test is on April 11th on the spreadsheet?

Michi: it is the TI2 and TI8 test. 

George: I think it will be shifted back by 1 week, from 11 to 4th April. 

Michi: also the magnet powering planned for 17th should come back by one week?

George: the planning was rigidly shifted forward by one week, not it needs to be shifted back. 

Michi: it will shift not by a week, but a few days. The t0 is not clear at the moment.

Chris: Everything that depended on ATLAS should be moved back by 3-4 days, but some things that can be moved back entirely.

Eric: is it true that you can inject with the shaft not completely closed? Or you have to wait that all the shielding is in place? The question refers to circulating beam.

George: it is not from our side.

Michi: this is not nominal. We’d need HSE and RP. 

Chris: but this is the top of the shaft, that they are closing. So it is a kind of technicality since we don’t have high intensity collisions, but surely it has to be signed off by someone. It might be discussed on Wed, to see if we can have beam on Tue or we have to wait for Wed (the week after).

George: All is in the hands of RP, which signs the document that allows to give green light to inject the beam, which will be finalized after the ATLAS repair. There are other two documents for the TI2 and TI8 tests, which were signed by RP, and now it is in the hands of ALICE and LHCb. Please, ALICE, LHCb, remind people to take care. 

Chris: it might be the TC that sign it. But to be checked.

LHCb (Paula Collins)

Paula: a reminder that the previous requests still stand: the magnet off fill during the 400b step. Possibility to commissiong the LHCb b* during the ATLAS and CMS VdM. 

Chris: the magnet off should be as short as possible, so we need to get rid of the full leveling procedure, not trivial but we’ll do our best. We can discuss next week, when we’ll be closer to the time when we do it.