Minutes and Summary

Main purpose of the meeting: General updates; Transmutation in pO and OO updates

LPC minutes 30 June 2025

Present (P = in person): Chris Young (P), Chiara Zampolli (P), Robert Münzer (P),  Giulia Negro (P), Andrej Gorisek (P), Eric Torrence (P), David Stickland (P), Ivan Calì (P), Lorenzo Bonechi, Andrea Massironi, Andres Delannoy, Archie (?), Brian Cole, Dragoslav Lazic, Flavio Pisani, Hiroaki Menjo, Jaime Boyd, Matthew Nguyen, Peter Steinberg, Qipeng Hu, Riccardo Longo, Silvia Pisano, Tomasz Bold, Witold Kozanecki, Roderik Bruce (P), Georgios Krintiras, Joanna Wanczyk, Helga Timko, Cedric Hernalsteens, Michi Hostletter (P), Benoit Salvant (P), Juan Esteban (P), Matteo Solfaroli Camillocci (P)

Introduction (Chris Young)

Roderik Bruce: this morning they did not manage to reproduce the 2% satellites, but they had again 5%. So we need to see. 

Robert Muenzer: how much are the satellites suppressed by the crossing angle?

Roderik Bruce/Chris Young: we have 3sigma separation, I would assume it is at least a factor more than 10. It should be checked.

 

ATLAS (Eric Torrence)

Eric Torrence: can SMOG see satellites?

Witold Kozanecki: no, SMOG cannot see satellites. 

Eric Torrence: is the issue that the signal is too low, or is it shifted too out of the acceptance?

Witold Kozanecki: yes, exactly, the VELO is too short, we cannot see vertices that far.

Paula Collins: actually we can: if they collide in SMOG, we should see them.

Eric Torrence: do you have a timing? They will be shifted by ~10ns. Will they fall out of the acceptance of the VELO?

Paula Collins: I think we should see them.

Chris Young: in pO you won’t see them because the O beam is going away from LHCb. The p beam is coming towards your detector, while the O beam is going away.

Paula Collins: it depends on where the collision is happening. If the satellite is 10 ns ahead of the O beam…

Chris Young: but the SMOG interacts only with one beam. 

Paula Collins: it depends on what is colliding with. If you are asking if the satellite is colliding with the proton nominal, then we can see it if the collision happens in SMOG. If you are asking if the satellite is colliding with the SMOG, then it would be only in OO. 

Witold Kozanecki: SMOG does not work with both beams? What does it mean in pp, that we have ghost charge from one beam only [B1, which is the one that collides with SMOG]? We always have ghost charge from LHCb from both beams.

Paula Collins: yes, from both beams. 

 

CMS (Giulia Negro)

Giulia Negro: concerning the single colliding bunch fill: can it be as soon as possible after the VdM run, before the ramp up starts, to avoid a too high HF activation?

David Stickland: is this going to be a conflict with the ATLAS transfer fill?

Eric Torrence: no.

David Stickland: single bunches are not an issue for you?

Eric Torrence: no, since you will not run this for long. 

Andrej Gorisek: we have the 3b fill that is part of the ramp up.

Chris Young: will it be physics of VdM optics?

David Stickland: it is not important.

Chris Young: I don’t think we have a 3b fill but we’ll have a 400b, since we did a 3b one on Fri evening. we should make sure that this counts in the mini-ramp up. 

David Stickland: this is about measuring after the collisions [for afterglow].

Chris Young: we should indeed try to overlay them; if we need both fills, we should make sure that this counts for the 3b.

Witold Kozanecki: what is the proposal?

Chris: normally, after a TS, we have to do a single 3-4 bunch fill, then a 400b fill, then a 1200b fill, before full machine. So the proposal by Andrej was that if we still need a 3-4 bunch fill, this counts as it, since it has similar enough setup to validate the machine, but I said that a 3b fill was already done on Friday night to validate the physics optics.

Andrej Gorisek: what we are advertising is the intensity ramp up from after the TS in 2024: a 3 or 12b fill, then a 75b fill, 2h stable beams, 400b 5 hours, 1200b 5h in stable beams. This is what you shared some time ago.

Chris Young: [see s11 of https://indico.cern.ch/event/1386984/contributions/5830243/attachments/2815728/4915471/2024-03-08_Wiesner_IntensityRampUp_Vers1_0.pdf] yes, it is 75, 400 and then half the maximum number of bunches. 

Witold Kozanecki: where do you put the CT fill with 144 bunches in that sequence?

Chris Young: this needs to be discussed with Jorg and Matteo, how we do the intensity ramp up. The single bunch one we can do early; we should check if we can use the 144b as the 75b one.

 

LHCf (Eugenio Berti)

Chris Young: [concerning the effects of the satellites] since in ATLAS there is quite a large crossing angle, the beams will be very separated when there are these crossings, so it should not be an issue. They should be 10sigma apart.

LHCb (Paula Collins)

Paula Collins: how quickly can the experiments give feedback on the z position?

Andrej Gorisek: 15 minutes.

Robert Muenzer: in ALICE, it is a QC cycle of a few minutes. If there is no SB, we can also use the luminometer. 

Paula Collins: it could be good if we can exchange such information for deciding about closing the VELO.

Paula Collins: could there be a potential risk associated with injection for STABLE BEAMs, when we usually turn on the low voltage of the VELO. If you think that there is any kind of risk, we would delay until ramp.

Matteo Solfaroli Camillocci: it is the usual risk. 

Michi Hostletter: we are injecting much less than in pp. The first injections were a bit rocky because it was the first time we used this configuration in the injectors. How we steer the beam to enter the LHC depends also at which angle and position they extract of the SPS, and this after the stop slightly changed, but now everything is set up. SPS fixed something at the extraction this morning and now in the LHC we adjusted to match that. Everything should also be reproducible from fill to fill, so there is no particular risk. 

 

ALICE (Robert Münzer)

 

Roderik Bruce: [about the background measurement] note that the fill yesterday was done with the anominal settings where there are no satellites. So maybe you can not compare. And we have these two options, either the nominal settings, or the anominal the intensity is 30% lower.

Chris Young: we should go for the standard since the experiments now use the xing angle.

Paula Collins: is it still the case that the satellites are still in the same position as before, as 10 and 15 ns?

Roderik Bruce: this is what the injectors and Giulia say. It comes from the bunch spacing in the PS before they do the splitting.

Witold Kozanecki: maybe the BSRL experts can come in when there is first beam and they can check, since they can do a time distribution. 

Eric Torrence/Andrej Gorisek: how were exactly the cycles yesterday?

Roderik Bruce: yesterday probably all the cycles were with anominal, I am not 100% sure about the first ones. But then I think they were since this is what we had in the injectors at that time. The intensity yesterday for the cycle with one bunch had a lifetime that was very bad, so when you take 4 bunches, it is even worse. So probably the bunch intensity we had was probably slightly higher than when we go with nominal. With anominal it will be much lower.

Chris Young: so your 0.4 peak mu value is not unreasonable.

Eric Torrence: right now it is more 0.8.

Roderik Bruce: the mu depends also on the p beam, and the p beam is going up and down.

Andrej Gorisek: but we don’t have the calibration in, yet.

Giulia Negro: since the beam intensity is lower, can we have more bunches?

Ivan Calì: at this point, with lower intensity we could increase the number of bunches.

Chris Young: we’re going to get a reasonably high intensity beam and we’re going to smash all the targets, and this is what everyone is prepared for, so it is simpler to stick to the 48 bunches scheme rather than to change 12 hours before we take data.

Chiara Zampolli: we are anyway not going to use the lower intensity beams, we’ll run with nominal and crossing angles in ALICE and LHCb. This should reduce the satellites. ATLAS was concerned by the maximum mu to not damage the ZDC and mostly LHCf.

Ivan Calì: yes, but what is the intensity of the nominal beam? It is ~2.5e10, while ~10 days ago we were discussing to have higher, up to 5e10. 

Chris Young: 5 was the maximum we could possibly imagine. 3 was what we were working with, and now we’re looking at 2.something.

Chiara Zampolli: the request is coming a bit late, and we even thought that for ATLAS, CMS, LHCb it was better to not change last minute since you’d need to adjust the trigger.

Ivan Calì: we would do it without problems if there is more luminosity.

Roderik Bruce: we can in principle change, we should just make sure that we stay below the machine protection limit. It is a bit late, but technically it is possible. 

Andrej Gorisek: for us, it would be a bit of a nuisance. 

Chris Young: this is a better discussion for OO. 

Andrej Gorisek: would this introduce any commissioning time?

Roderik Bruce: no.

Chris Young: it would increase slightly the time for the injection but not significantly. This is more for OO rather than now. 

Paula Collins: LHCb wants whatever gives us the maximum luminosity. We would modify whatever needed to match the filling scheme.

Ivan Calì: same for CMS.

Chiara Zampolli: it would not a great change.

Andrej Gorisek: how much are we talking about?

Chris Young: from 48 to 60 colliding bunches, which means 25% increase in colliding bunches, and so 25% increase in trigger rate for everyone. Then you’d need to have only 2 non-colliding bunches instead of 4.

Decision: aim for OO to have more bunches.

Robert Muenzer: would this mitigate further the satellites?

Chiara Zampolli: no. It compensates for the anominal settings.

Robert Muenzer: how would it impact the OO schedule if we go for lower intensity?

Roderik Bruce: for you not much, since you’re leveled anyway regardless which filling scheme we use.

Robert Muenzer: for us it would be better to go with lower intensity, but for sure not for the others.

Chris Young: in OO you have the same satellite configuration you have in pO, but the crossing angle mitigates this massively. You will also have satellite-satellite collisions, but these will have a luminosity of the intensity squared, so 5% squared, which means that 1 in 400 of the nominal-nominal collisions. So it should be quite a low effect, but please investigate. If you’re looking at mu 0.5, and we take 1/400 of that, it should be very rare that you have a satellite-satellite collision masking the nominal collisions. But please think about it for OO, which is decoupled from pO.

Chiara Zampolli: for OO, if satellites are a concern, we could use the anominal with more bunches.

Ivan Calì: for us it would not be optimal. Adding bunches would be fine, while if you reduce the intensity you change completely the scale between 0-bias and hadronic.

Roderik Bruce: if we increase the number of bunches, I think it is good for you, because you [ALICE] can level at a higher luminosity: at the same mu, you can get higher luminosity.

Paula Collins: can we check that the luminosity does not go down with more bunches?

Roderik Bruce: why should it go down with the same intensity? Only with anominal it would go down. 

Ivan Calì: for the CMS the best would be to go to 5e10 and increase the number of bunches. 

Roderik Bruce: there is quite some uncertainty on what we can get from the SPS. The reason why we mentioned 5e10 is because we had a bit more than that at PS extraction and we were not sure how much we could get to the SPS. The space charge at SPS injection is extremely strong and it drops a lot, which is why we have 2.7-2.8e10. The only way to do better would be to strip between PS and LEIR because then we get a better gamma out of PS and you get a better space charge at SPS injection due to the higher gamma. But this is for the far future.