Minutes and Summary

Main purpose of the meeting: Summary of JAPW and 2025/2026 planning

LPC minutes 16th December

Summary of JAPW (Chris Young)

(Catrin Bernius) Are the fault plots including the MDs and ion run? No these are just the proton physics ones. The ion ones were also in the workshop slides in the backup but are limited in statistics.

(Catrin Bernius, Witold Kozanecki, Filip Moortgat) For the high pile-up tests with notice this can be very useful for the experiments. In particular if they could be done both with single bunches and short trains in the same fill. This would only be for a single test fill. It is not extremely useful so it isn't clear that we want to request it from the experiments side but they would certainly like to benefit if this is done in an MD. A request for a single short fill might come later from either ATLAS or CMS.

(Jorg Wenninger) I will present the 2025/2026 plan in Chamonix and intend on suggesting that the 1.8e11 is tried this year, slowly approaching it in normal physics production. For the 2.3e11 ppb we need some MDs prior to any tests such as the RF MDs. One option is to do all the full machine 2.3e11 ppb things at the end of 2026 by shifting the ion Run 1 week earlier and doing these tests without collisions at the very end. If there is a triplet problem before the end of Run 3 then these tests can probably still be done with ballistic optics. Would there be a prior test at an intermediate step? This is not what I would suggest, other than running in physics production at 1.8e11 ppb. After the ion run the experiments are happy for any risky activities to take place provided there is not activation at IP1/5. This would require re-arranging the 2026 timetable, and this would imply moving MDs and possibly losing some physics days. It is possible that some people will raise doing some (eg. an intermediate intensity) or all of this program at the end of 2025 so a statement from the experiments would be good. It is also a short YETS so depending on what breaks there is the possibility that we wouldn't be back again for the start of 2026 in this scenario.

(Witold Kozanecki, Jorg Wenninger) What is meant by beam-beam corrections in this case? It is the long-range higher order corrections with the sextupole.

(Filip Moortgat, Jorg Wenninger) Why can't the final 4 RF modules be replaced? We suspect it is where they are but they are also lower priority ones. They are in point 4 where there is a single beam rather than two and the beam is centered in the beam pipe both of which are mitigating factors such that they shouldn't be limiting.

(Filip Moortgat, Jorg Wenninger) Do we have the step size during leveling in beta*? Will this be eg. 3cm? We don't have this yet but with separation leveling this should have little effect on the experiments. We will move both together until 60 cm then one direction will continue to lower values. Will the amount of time be roughly equal between round and eliptical beams? This is tricky to tell at the moment as it depends on the bunch intensity. If we go up to 1.8 then we will spend more time with round beams.

(Reyes Alemany Fernandez) This issue is not so much technical but it is because the NA61 oxygen run is happening during this time such that unless it can be moved the injectors will not be able to provide Neon to the LHC. LPC believes that if there is a request from the LHC experiments for this run to happen productive discussions can be had with the SPS program coordinator to enable this to happen. The hope is that you can inject Oxygen and during this last run the injectors can switch over to Neon such that they will be ready in time for the next fill. This does mean that if we only have 2 fills of OO we risk the 2nd one in the situation it dumps near the beginning. We could put in a fill after the targets have been made but this is still harder than using the ZDC access which we know has to be done. In January the experiments will all voice their

(Brian Cole) It is a little complicated from the ZDC side. If there is a strong physics case and this is the only way the program is accepted by the experiments then clearly ATLAS ZDC won't stand in the way. However, it would be very nice to have exactly the same configuration as in the OO run, in particular the ZDC is used heavily in the trigger and it would be good to use the same triggers for the two species so there is a good motivation to have the ZDC present. Obviously this question doesn't apply to the ALICE ZDC.

(Reyes Alemany Fernandez) 10h in stable beams is expected to give 0.1 nb-1 from the projections from Natalia if the experiments need an estimate of the luminosity reach.

(Elena Dall'Occo, Federico Alessio) For LHCb the number of bunches does affect our physics performance as it means that we can run at a lower pile-up. Yes, but the number of bunches in this table are not optimized, LPC can pass you the optimized values. For IP1/5 the numbers are optimized. It needs to be seen how much margin we have but from the experiments side it is probably better to go to 5x36b and skip the 1.8e11. During Chamonix and possibly during the year this will need to be discussed again. It would be possible to run at 5x36b over the summer and then step back to test 1.8e11, or the other way round.

(Chiara Zampolli) For the luminosity projections for Ne-Ne I don't think these have been shown. A short presentation will be given in January and the plots will be circulated by the LPC coordinators before the break.

ATLAS (Catrin Bernius)

(Chris Young) The top energy for OO is 6.8 TeV, so to run at 5.36 TeV we would setup a lower energy beam. I would assume this would also then be used in pO such that this would be at a lower energy. LHCb will look into this as one of the main requesters of pO. Having multiple energies would clearly add complications.

(Filip Moortgat, Chris Young, Jorg Wenninger, Lorenzo Bonechi) Running at a lower energy will take additional setup time and in principle this was discussed before and it was decided against doing this. It would involve commissioning an additional cycle separate from the PbPb cycle. Doing it at beta* of 1m would simplify the setup. Is there an idea of how much longer this would take? An exact statement will take some time to work out, but quite a bit of the commissioning would be done at the beginning of the year. Some corners could possibly be cut if you accept some luminosity imbalances etc. from a lack of optics corrections. There is also a slight reduction in the luminosity due to lower gamma factor in the luminosity formula. For LHCf we would like the highest possible energy for pO as we need to extrapolate up to higher energies. This is likely the last and most important physics run for LHCf and has been requested for more than 10 years. The beta* has an effect on our experiment due to the angular spread at the experiment. It certainly can't be bigger than the beta* ~10m at injection and this would also mean different optics to the ion optics. The beta* at IP1 needs to be agreed between LHCf and ATLAS.

(Chris Young) In the pO and OO runs we don't have any vdM programs scheduled so it is up to all the experiments to check that only doing eg. an extended emmitance scan, will not have disastrous results on the experimental program.

CMS (Filip Moortgat)

(Chris Young, Federico Alessio, Chiara Zampolli) If there is a very good reason to move days between 2025 and 2026 eg. to put significant number of MD days at the end of 2026, then certainly this can be done. Without good reasons we wouldn't want to re-open the box. What about adding a couple of days to 2025 to open the possibility of pPb -- ie. get to the targets. We are not sure that we know the performance well enough to evaluate what would make the target. Which direction would you be looking at? It would be 2026 to 2025 to make the PbPb target. The main deadline is the location of the TS and injector schedule, while in the RB there was not a clear statement that things shouldn't change. There is also the issue that if you move days to 2025 then there are very few days for pPb in 2026. It is even possible to move a TS after Chamonix but it does become more difficult.