Minutes and Summary

Main purpose of the meeting: Data taking, pp ref + PbPb prep. and first 2026 schedule discussions.

LPC minutes 30th September

Introduction (Federico Alessio)

(Filip Moortgat) Will there be a 2nd VIP visit? This is discussed later in the slides.

(Andrea Ferrero) How much pp reference setup is still to be done? This is discussed later in the slides.

(Matteo Solfaroli Camillocci) The only things left for pp reference is about 4 hours of tests, the rest has to be done after TS2. The first will need BCM masked to test the tune in ramp. The second would have collisions like the last fill in the previous setup period. After TS2 there will be the BBA for AFP and then final loss maps. This should be less than 1 day in total.

(Witold Kozanecki, Matteo Solfaroli Camillocci, Michi Hostettler) We would like to have the same beam tailoring as for the previous vdM scans. Does this require any preparation? This needs to be checked offline. It might be good to pre-warn them as this won't have been used since May and the cycle will need to be updated. It was checked that Witold has the correct contact people.

(Roderik Bruce, Chris Young) There is the potential to anticipate 1-2 shifts of Pb commissioning. In principle we would like to add this as we have done so well with pp already (until this week), but after the emulsion installation has been planned such that physics data is taken up to the TS to get the correct maximal lumi. If there are problems then we don't want to add things, if it goes extremely well then we might end up needing extra activities. It was clarified that this would be an optics test with protons rather than Pb ions.

(Roderik Bruce) There is a new bump that might be better, but simulations were running last time it was checked, but they will hopefully be done in time for the LBS group meeting and it can be discussed there.

(Catrin Bernius, Matteo Solfaroli Camillocci) Do you know if the VIP on the 8th will go to Point 1? This is not known but usually they go to Point 1.

(Michi Hostettler) So far only LHCb has uploaded their files for the vdM scans.

(Witold Kozanecki) Does the request to be first for the vdM apply to pp reference or PbPb. In principle it will apply to both. ATLAS will show some constraints from their side. It isn't required that the two vdM fills are consecutive.

(Catrin Bernius, Witold Kozanecki) We can send you feedback on the filling scheme. Last year we used the 204 ALICE/LHCb scheme, but in general more colliding bunches is better.

(Michi Hostettler) The files sent by LHCb has 4.5 sigma separation while last year the maximum for the prepared run was 4 sigma so it will need to be checked this is safe. It should be ok though.

(Andrea Ferrero) In the LMC presentation the end-of-2025 date was later than 1st December. This is what we assumed - it needs to be determined what the optimal location of the YETS is as we can shift it back/forwards a week. We will shift it to the optimal point for the works over the break. Some of the dates in the LMC presentation refer to the injectors and it wasn't an agreed plan at this stage.

(Filip Moortgat, Rende Steerenberg) Will 7 days of MD be enough cool down for LS3? At the LMC they said that MD would be fine for cool down and 7 days was suggested. The LS3 committee will be looking at re-optimizing the schedule and seeing what is on the critical path and what cool down these activities require.

(Maciej Trzebinski, Catrin Bernius) After the oxygen run there is one green block for the LHCf/ZDC deinstallation. Is it optimistic to do this in one day? There might be conflict with the transport team but this is a detail that can be discussed nearer the time. At this stage we are looking at blocks rather than the small details and exact positions.

(Andrea Ferrero) Should there not be 4 days of HI setup. Yes, this is a typo. Previously there were 18 days of HI and now there are 26, so only 8 days more PbPb physics. Is this the correct ratio? Rende will the the precise maths including all the MDs, commissioning etc. It should be around 10 days but he will do it precisely. It should also be noted that the TS cannot be over the weekend.

(Andrea Ferrero) How reliable is the duration of 2026? It is what is Research Board decided so it is not expected to change without major new developments.

(Chris Young, Filip Moortgat, Andrea Ferrero) In particular if everyone could check with their spokespeople and physics conveners if p-Pb is desired (in exchange for PbPb days) in the extra days as this negates the argument of putting all the PbPb data taking together. We ideally want an answer before this years data-taking such that we have an idea how much pp reference data we need to target.

(Maciej Trzebinski, Reyes Alemany Fernandez) For the oxygen run will there be commissioning earlier in the year or just in the period right before the run. Oxygen will only be in the machine just before the run, but the optics could be setup earlier using protons but this isn't important for the experiments.

(Filip Moortgat) For the pO,OO,PbPb is the crossing plane already decided? No this isn't decided, and it could be different from pp. However the polarity of the magnets will be the same as pp such that re-wiring is not required.

ATLAS (Catrin Bernius)

(Michi Hostettler) We can test the luminosity during the TS but you will need to fake a luminosity signal to not just show 0 for both quantities.

(Michi Hostettler) From the machine side we would just need to load the injection + ramp RF settings sequence and check that you moved across successfully. We can test this during the TS. Any other experiment who wants should test at the same time as the clock signal will be sent to all experiments.

(Roderik Bruce, Federico Alessio) The signal will be very weak with 4 bunches, do you not want to do this with 20 bunches? We do not want to add another step to the sequence so if we can replace the 4b step with 20b this would work, otherwise you can do it with 4b or with the INDIVs later.

(David Stickland, Michi Hostettler, Chris Young, Andrea Ferrero) Does everyone agree on the same total cross-section pp and PbPb? In principle everyone can use different values for the tools but there is one physics parameter and it will avoid confusing situations. Do we all agree on 68.3mb? Everyone will check with colleagues and offline that this is agreed upon, but barring objections we go with this. For PbPb it would also be good to agree on a number. It is thought to be 7.67barns. However in PbPb the leveling is usually done on luminosity.

(Roderik Bruce, Michi Hostettler) If the injectors are able to provide it and there aren't R2E issues, then IP1/2/5 will level at 6.4e27 cm-2 s-1. It is therefore more important that the luminosity is correct and the cross-section will not enter the equation. If there are machine limitations so leveling lower is required then this can be done with the OP leveling tools.

ATLAS vdM Planning (Witold Kozanecki)

(David Stickland) For pp reference we are happy to go second.

(Filip Moortgat) CMS would like to level at 7 in the pp reference run. It would not be a problem to go higher for half an hour. It was clarified that this would ideally be in the 1200b fill or the first with the full machine.

(All) There wasn't an objection doing both vdM fills at the start between 75b and 400b. It was thought that it was still better to do 2 fills splitting LHCb/ALICE and ATLAS/CMS. This avoids emmitance blow-up.

(Chris Young, David Stickland) Will CMS also do a 2.5h LSC in the 400b fill? Ideally yes, but the total length of this fill is only 5h so it will be tight. One could be in 1200b, but hopefully they can both "just" fit in the 400b fill. We don't want to waste time during this ramp-up so that we can take several very long physics fills with the full machine. We will assume that both will try to fit in the 400b fill, and CMS expect to be shorter than 2.5 hours. We will decide in advance who goes first but not at this meeting.

CMS (Andrea Massironi)

(Chris Young, Federico Alessio) Rotation of the crossing plane is quite likely and we can try to get an intermediate version for PPS to decide how much to rotate. This we will follow-up on.

(Michi Hostettler, Chris Young) Going to pile-up 7 should not be a problem from a machine limitation point of view. However the leveling will not be active at the end of the fill so you will need to call the CCC to restart the active leveling and the operator can help it to try to reach the target faster than the default steps. This will also be circulated to the other EiCs. The operator will also tell the cryo shifter so they won't be surprised but their system should be able to cope with changes in this direction. The first time it will be done during the day.

ALICE (Andrea Ferrero)

(Chris Young) For the pp reference run which polarity will you start with? This needs to be discussed with the experts which they prefer for the vdM fill. +/+ is the more critical one in terms of effective crossing angle but the arguments there have been reduced by settling on 340 urad crossing angle.

(Federico Alessio, Elena Dall'Occo) For the PbPb vdM do you anticipate the same as pp reference. For ALICE it will be similar, for LHCb it will be a bit different but will still have a SMOG off/on configuration and the swapping can still happen in the same way.

LHCb (Elena Dall'Occo)

(Witold Kozanecki) Are the scanning ranges on the slides in sigma, are they for single beam? Yes.

(Federico Alessio, Michi Hostettler) Each time the magnet flips we see a different feed-forward is needed so it is likely that a detector OFF period is required after the next magnet flip. To be safe it would be better to have the detector SAFE just until we are back in collision. There is a risk of over-shooting but it is unlikely to go completely head-on. It is a suggestion from the LHC so it is a decision for the experiment to evaluate the impact of over-shooting. It should only take a few minutes to check, but then the detector takes a little longer to recover. It will be discussed within LHCb how risky it is and how safe it needs to be, and separately for different sub-systems. Currently the detector is in a safer state than for injection. Does the requirement of the luminometer being on lead to this long recovery? No this isn't an issue.

(Chris Young) For the questions on slide 3 they are all fine from our point of view.