Minutes and Summary

Main purpose of the meeting: Data taking progress; MD2 plans, intensity increase plans, 2026 TS

LPC minutes 28 July 2025

Introduction (Chris Young)

Andrej Gorisek: Why are the left and right orders of magnitude different?
Chris Young: I am not sure but this is expected. Both CMS and ATLAS have one which is more limiting.
Michi Hostettler: What is plotted is a reconstructed value that indicates the amount of the capacity of the cooling available that is being used. We know when it starts rising then it can run-away if you don't react quickly which is why the limit is at 40% rather than near 100%. Additionally values below 10% it is probably not reliable. If you look at some of the valve openings it seems more a factor of 2 difference rather than a factor of 10.

Andrej Gorisek: Is this behaviour the same as at the beginning of the fill when we are limited by cryo.
Chris Young: The logic is the same at the beginning of the fill.
Michi Hostettler: Note that at the beginning of the fill you will approach from below rather than above so it might look smoother. Note that this behaviour is not carved in stone so if you want it changed we can discuss doing a change with cryo.
Eric Torrence: In this case what fixed the cryo. In this case it didn't improve with the lumi dropping.
Chris Young: In this case there was an intervention from Eric from cryo.
Michi Hostettler: This illustrates why the limit is at 40% rather than 80% or 90%.

Robert Munzer: Is it also true we can do the lead run with a broken RF finger at point 1/5?
Chris Young: Yes, this is what we believe, however, if something else breaks, depending what it is then it might affect the PbPb run which is why we want to keep a gap before the ion run.

Eric Torrence: Obviously an intensity increase could have significant negative impact on physics in the case of a problem.
Robert Munzer: The background that ALICE sees since the beginning of the year is highly intensity dependent so an increase would clearly increase the background. It could create some conditioning, but it could be that we get the same physics and worse background.
David Stickland: I haven't understood how the various benefits and drawbacks will be weighed in making a decision?
Chris Young: This decision will not be made by LPC but by the directorate, in particular by Mike on what is safe for the accelerator, balancing the risk of replacing a known component eg. elliptical module which would be 10-14 days, or an unknown component this is more difficult to estimate. He will also have input from Joachim and Fabiola. When it is done is obviously more risky to the ion run if later and risky to the proton run if earlier.
Jorg Wenninger: If there is a broken RF vacuum module probably the best thing for the ion run is not to fix it as this comes with the risk of degraded vacuum and just operate with it broken. There will be no heating due to the low intensity of the beams.
Chris Young: If it breaks just before the ion run then we would probably move to ions early as fixing it would take too long. This would be similar to in 2023. For vacuum modules we know the situation but for other components we don't know. I'm afraid this doesn't really answer your question though David.
Jorg Wenninger: Obviously the best for physics production is just to continue as we are.
Filip Moortgat: Your intermediate solution when a step to 1.7e11 ppb is made this year and then the final step is next year might be favoured as we are already quite close so it is a small step to 1.7e11 ppb.
Jorg Wenninger: When it was discussed with vacuum last week we thought the main worries would be on 6L2 but they were more concerned about the elliptical modules. For 6L2 it might be that if we start to see some effects at higher intensity it may be the case that we can reduce and the effects are reversed. However, with the springs in the elliptical modules if we suddenly break them, then this would not be a reversible change. 
Flavio Pisani: With 1.7e11 would we be able to keep this filling scheme. 
Jorg Wenninger: Yes, and that is another argument not to go beyond this.
Filip Moortgat: Changing filling scheme would not be great.
Robert Munzer: Would shifting it to next year, just be shifting the risk to next year?
Jorg Wenninger: To some degree yes, and we would need to do it pretty early.
Filip Moortgat: At some point the experiments need to acknowledge that we don't want to test this at the start of Run 4.
Eric Torrence: Yes, but we added two weeks at the end of 2026 to specifically test even higher intensities.
Filip Moortgat: You could argue that the 2 weeks in 2026 should test 1.7e11 to 2.3e11 ppb.
Jorg Wenninger: It is clear that if we hit a limit at 1.8e11 then we have a problem and the HL-LHC intensity is out of reach for testing. If this is from the elliptical modules for example then the risk is transferred to Run 4.
Filip Moortgat: Would the modules be redesigned.
Jorg Wenninger: The elliptical ones will be removed as there will be a new cooled D1 without them. This is an annoying part as we might be limited by a part that will not be present at HL-LHC.

Filip Moortgat: Why did FASER not put a new one in?
Eric Torrence: It is 100kCHF per box so they only have 4 for the year.
Filip Moortgat: Why not take the data now?
Chris Young: This was due to the logistics of producing and preparing the boxes it was easier to do it in the 2nd half of the year.

Flavio Pisani: The DAQ probably wouldn't be stable at high pile-up so we will probably level at lower luminosity. Do we know how long the fill will be?
Chris Young: I think the request is 8h so this would imply around 4h of stable beams.
Witold Kozanecki: In the case of 600b, what is limiting the luminosity such that we level at 132?
Chris Young: This is to replicate the conditions at the start of HL-LHC where the first years are at 132.
Witold Kozanecki: The reason I ask is that these are very bright and is there a concern about having both IP1 & 5 both offset?
(some shrugging)
Chris Young: This works with similar bunches in operation at the moment, and it will be what we want to do at the start of Run 4 so it will be good to test/check it.
Michi Hostettler: Yes, this is how we want to do the leveling at least at the start of HL-LHC. Crabbing could possibly be used later.

Michi Hostettler: A reminder that if you update your MASSI files then you need to increment the version number otherwise they don't propagate into the LHC systems.

Flavio Pisani: Probably advancing this would be possible but I need to check with the experts. For the energy the main concerns at the start of the year were aperture.
Michi Hostettler: Preliminary studies showed 1 TeV would be Ok, but more advanced checks should be done.
Flavio Pisani: For us 1 TeV should be Ok.
Chris Young: From our side at some stage we would want a table on our website of the beam parameters, crossing angles etc.
Jorg Wenninger: Once you have validated it for stable beams, then it might be that you can put in 20 bunches without problems, at least in a similar way to the Oxygen run.
Eric Torrence: Would this be early or late in the year.
Chris Young: Probably early, but this depends a bit on how long it turns out being estimated to take.
Filip Moortgat: Why will the special run discussions be done in the spokesperson meeting?
Chris Young: This is to ensure that they can follow all the arguments from the different experiments.

LHCb (Flavio Pisani)

Chris Young: For the emittance scan this doesn't affect the other experiments so feel free to coordinate with the CCC.
Jorg Wenninger: Probably after 13h your head-on luminosity should be low enough for you to do a scan.
Michi Hostettler: There is a pre-set in x,y rather than crossing/separation so this should be stated when making the request.

ALICE (Robert Munzer)

Jorg Wenninger: They will continue to test at the construction site, but informally we have already given the go-ahead as we can't even see anything.
Robert Munzer: Offline we will look to see if we can see anything in when looking in detail.
Jorg Wenninger: In the frequency spectrum we can see 6.5Hz and all the harmonics. We will look in the ADT to see if we can see anything.
Chris Young: In general this is good news. We can continue running while they build the school. 

Chris Young: Thanks for the time evolution plot - this is very useful.

Chris Young: I think there have been other spikes that have not been in stable beams.
Jorg Wenninger: They are quite often at injection, or in the ramp.
Robert Munzer: These affect us a lot less.

Chris Young: As soon as one experiment asks for the vdM optics then we have to do it so it will be there for them all, and I think this is likely. But thanks for the suggestion to try to save time.

CMS (Filip Moortgat)

Chris Young: When you used the other lumi detector does it have the same scale?
Filip Moortgat: HF is what is usually used, when we skip to PLT there can be a small shift in the scale.
Giulia Negro: They should have adjusted their scale so it should be very close to the HF scale.

Chris Young: Note that we didn't discuss shortening the 2025 TS before the ion run.
Chris Young: For the 2026 TS we are looking at scheduling 2 days and hoping that we can be done earlier than usual on the 2nd day. The injectors would be down for the 1st day.

Chris Young: Thanks for the transmutation plot, this would be great to show.

ATLAS (Eric Torrence)

Chris Young: Would ATLAS/CMS be interested in going to 64.5 or do we not want to push cryo.
Eric Torrence: We could improve this a bit but we don't have a strong motivation to push them.
Filip Moortgat: We would be ok with 64.5 but we are not asking for it.
Chris Young: As no one is asking for it I will tell cryo the experiments are now happy, and thank them for their efforts.

Chris Young: Thanks for the transmutation plot, this would be great to show.
Eric Torrence: We might need some approval for showing to the LHCC.
Chris Young: For the closed session the rules might be more relaxed so maybe check that as well.

Chris Young: Only at rMPP this Friday (which is yet to be announced) will be know the filling scheme, but it should be by the end of this week.

Chris Young: The 1% shift in the luminosity for 2024, would this also be applied to 2025.
Eric Torrence: No, but it might hint which way the scale will shift at the end of the year.