Minutes and Summary

Main purpose of the meeting: Commissioning, MD, RB, VdM

LPC minutes 24th March 2025

Participants (P = present): Andrej Gorisek (P), Robert Muenzer (P), Silvia Pisano (P), Paula Collins (P), Rosen Matev (P), Andrea Massironi (P), Dragoslav Lazic, Lorenzo Bonechi, Matthew Nguyen, Reyes Alemany Fernandez, Roderik Bruce, Stephane Willocq, Valeriia Zhovkovska, Michi Hostletter (P), Jorg Wenninger (P), Flavio Pisano, Vlasidlav Balagura, Andreas Delannoy Sotomayor, Chris Young (P), Chiara Zampolli (P), Matteo Solfaroli Camillocci, Benoit Salvant, Elisabeth Maria Niel

Introduction (Chris Young)

Chris: do we know what the ALICE crossing angle sign will be?

Jorg: should be positive, like last year and before. Since 2017 there is always only one polarity also when the ALICE dipole changes sign.

Chris: let’s wait for Stephane presentation’s tomorrow.

 

CMS (Andrea Massironi)

 

S3: one fill with one bunch colliding only.

Chris: [related to the request of one fill with one bunch colliding only after TS1 - after O]:  only a couple of hours?

Andrea: yes.

Chris: so it can be done during the check list: we can put a single bunch in, ramp it, and you can take a couple of hours of data like this.

Andrea: [about the 50 ns separated bunches] not needed anymore, in case just more isolated bunches will be asked during a normal fill in the ramp up [added here since on the slide it is not clear, in my opinion].

Michi: if you don’t need trains, we can use the BSRT calibration fills where you have 12 out of 12 bunches and isolated bunches for free.

Andrea: not needed.

Andrej: [emittance scan] can we do less often, but with more (15) points for everyone?

Chris: indeed CMS and ATLAS should have the same number of points. we are indeed converging towards 15, with a kind of regular and reliable schedule, to not forget when we should do it. 

Andrej: it was mentioned 2x per week.

Chris: to be defined since CMS would like every 2 days. 

Jorg: [about decreasing the crossing angle to level for ~1h hour longer] the orbit change in the Roman Pot is indeed not insignificant: we move unfortunately closer to the pot, so we are trying to figure out whether maybe PPS should be few hundred um further out during the whole fill or if we have to do change something in the 0-3 mm orbit param that we set on top.

Chris: if the request is to stay at 120 urad for physics, will we do the ramp up to 100 just to validate the machine?

Jorg: it needs to be discussed, we’ll validate the MP with loss maps at 100, but maybe we stop at 120. 

Chris: and then do the intensity ramp up with that?

Jorg: maybe then CMS wants to dump rapidly after. Reaching 100 might not be our interest. 

Chris: we should do the intensity ramp up with 100. 

Michi: you need to do the intensity ramp up to this value only if you go with the full machine to this value. As long as you want to go to a low value with a kind of modest beam, you don’t need the intensity ramp up with this small value. 

Lasla: I think that at ~100 urad we start having parasitic collisions, is this correct?

Chris: I think we have a b* of 50 cm in this plane. This might save us.

Michi: of course you reduce the beam separation and you may see something in the triplets, but we need to see what exactly the separation is. 6-7 sigma should still be guaranteed.

 

ALICE (Robert Muenzer)

 

Robert: from which point should we have the magnet on during the recommissioning?

Jorg: it should be in the middle of the first official week of commissioning, which should be the first week of April, Wednesday +/- 2 days. It depends on the progress, which should go quite quickly. I know you need to have a special beam mode.

Robert: Yes, “no beam” is better for us during the ramp up.

 

ATLAS (Andrej Gorisek)

 

Andrej: [concerning the leak in ATLAS] at the beginning of the YETS opening ATLAS was 3 weeks. One could see if only side A is faster or one can have multiple shifts.

Stephane: yes, 4-5 weeks, with multiple shifts. We’d need more people to make it as short as possible.

 

LHCb (Paula Collins)

 

Chris: the end of the NeNe run, the ZDCs of ATLAS and CMS will be extracted, and this will take ~½ day, so if you want to change something, you’ll have a time window to have access. 

Chris: [concerning the request for higher b* in LHCb during ATLAS and CMS scans (see slide for details). High b* means opening the VELO.] this request means that we need different optics for the ATLAS/CMS and ALICE/LHCb scans, which will add an extra 16 hours.

Michi: yes, 1-2 shifts for commissioning. 

Jorg: we’d need to validate two configurations. 

Michi: it will be like this: we ramp, then we desqueeze to 19-24 m, and then for the ATLAS and CMS fill, we’d add a further desqueeze that would take a few minutes, to whatever you need, 40-50 minutes. From these 2 points, you can go to collision, and we’ll need to validate both branches of the cycle and this takes at least extra fill, an extra setup, that is an extra optics measurement. 

Andrej: could the large beta* in LHCb impact ATLAS/CMS scans?

Michi: it should not, but this is why we need an extra optics measurement to make sure that we don’t introduce an extra beta-beating. In principle the effect is small. 

Chris: this is one example when we should check the cost/benefit: the time to set it up and the availability of the experts, the time for the optics, the time for the extra measurement… to be compared to the benefit. We’d need a time estimate.

Jorg: 2 shifts is reasonable, we have to make an extra optics measurement, setup with a bit more loss maps… 2 shifts is probably a reasonable upper bound. All little steps may take a bit longer. 

Chris: when would we do it? In June?

Jorg: it’d be better to commission the VdM all together, and not split it. Or do you want to see how things go?

Michi: there could be some synergy, e.g. to redo a certain fill to redo a loss map that went wrong. If everything goes fine, the gain might be little, but if you have to repeat something for whatever reason, we could profit if we continue from there. If we know in advance, there is the chance to have synergy.

Chris: also other experiments should think if such a program can be beneficial for them, with the cost of  ½ - ¾ of a day, and tell us if they support this request.

Jorg: [concerning the request to have variability in bunches during VdM] what is not clear is if these intensity have all the same non factorization. This could explode the time the injectors need to setup the beam. 

Michi: if I understood correctly in the LumiDays, in LHCb you don’t care as much about the non-factorization issue as ATLAS and CMS do, because the way LHCb does the analysis is intrinsically taking this into account. But this is of course up to LHCb.

Paula: this is something that we can discuss and finalize later. 

Michi: if we have a different filling scheme for ALICE and LHCb compared to ATLAS/CMS, the only thing to agree with ALICE is how you distribute the bunches and which bunches will be different, while ATLAS and CMS have their own filling schemes.

Chris: in the current scheme, there are only two bunches colliding both in ALICE and LHCb. In almost all there is ATLAS and CMS and one of the other two.

Michi: if you take your own bunches, there is no problem for ALICE. ATLAS and CMS have their own fills. Probably they come in batches and depending how we produce them, either 2, or 4, or 8, all those injected together will have to have the same intensity, otherwise it is a mess to setup. But it is relative straightforward, especially if you stay in within 20% or so. If you want to go super high, it is different. If it is just increasing the intensity, within 20% intensity, it is not complicated. 

Chris: for the continuous scan, only LHCb is interested, right?

Jorg: this should be done only at the end of the fill, since it is tricky. During the continuos scan, you stop the b* leveling. It can only be done at the very end.

Michi: anyway it can only be done as soon as LHCb can go head on.

Jorg: this is why we can do it only in the intensity ramp up, when you can go head on in the first steps.

Rosen: could we limit the intensity for these tests?

Michi: the manipulation on our side are similar to putting in the separation in steps, since we touch the same things as in separation (correctors and knobs); maybe good to test at the end of fill and maybe even before the intensity ramp up. If you have a fill at flat top at the end of collisions, even if it only in adjust and not stable beams, just to make sure that technically it works, then we can say when to do it. In the beginning, until it is clear that it is something that we want to have regularly, and is analyzable from LHCb side, it is something that is a bit for experts to run, not operational since this would be more work on our side. It only makes sense when we are sure that it is something we want to keep in the long term.

Chris: you would do this only in VdM, right?

Michi: I understood in low beta to test and maybe in VdM, but it is not confirmed. 

Jorg: don’t forget that the scans are quite long.

Vladic: maybe 1D continuous for this year? It should be faster.

Chris: is this in VdM or in std data taking?

Vladic: we need to see how it goes. 

Chris: let’s see how complicated it becomes.

Chris: not clear whether the DOROS scan could be requested as collimation MD. Let’s see what they present. 

Michi: it depends on how far we want to go: if it is only a gain scan, then it is rather quick, and can be done at the end of VdM. If you want to optimize gain vs constants, it should become MD, because it takes more time to see how the measurement evolves during the changes.

 

AOB

 

Chris: From Lumi days: Michi is waiting for people to analyse the data with the orbit feedback on. It would be nice that CMS takes the lead since they were more present in the LumiDays.

 

Andrea: If OO is extended by 1 day, will this be taken from 2026 HI?

Chris: in principle yes, or we scale back the O request. The hope is that the machine can fit the schedule. So we need to wait for further discussions. 

 

Michi: something that came up discussing with Witold for VdM publication: I sent an email to the experiment contacts with a proposal to add two fields in the publication, with the crossing and separation planes. For ATLAS and CMS the planes are flipped by 90 deg, but not in VdM, and also probably not in PbPb. We propose to add two fields there that may be useful or not, the experiments should check that this does not disturb them even if they don’t use them. It will say whether the crossing planes are tilted. Even if the crossing plane is tilted, we can forse the scan to be in x and y. We’d like to transmit what is the crossing plane and what is the separation plane. 

Chris: what would be sent? 

Michi: two fields: config_crossing_plane and config_separation_plane which would be a string, “X”, or “Y”.