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LPC meeting summary 25-11-2024 - final

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Minutes and Summary

Main purpose of the meeting: End of PbPb feedback, points for Montreux, first mention of Ne-Ne

LPC minutes 25th November

Introduction (Federico Alessio)

(Roderik Bruce) The beta star would be reduced to possibly 40cm. 30cm would probably not be possible at IP2. However the main request came from LHCb to get them to similar values to the other experiments. However, without the data from the MD it is difficult to promise anything.

(Roderik Bruce) To clarify it isn't a double slip-stacking but slip-stacking of a 75ns beam rather than a 100ns beam.

(Chiara Zampolli) You didn't mention 10723. This is because it is less interesting for the experiments.

(Jorg Wenninger, Roderik Bruce) There is not much of the work that can be done during the commissioning as we don't have ions. For the beta* at IP8 the pure optics part can be done with protons but the impact on backgrounds, beam losses, etc. need ions.

(Catrin Bernius) Do all these ion MDs need to be done as the gains might be offset by the additional time taken to do them? This needs to be evaluated based on the overall schedule.

(Chris Young) Note that we have put MD2 a little later to try to make sure that the

(Catrin Bernius, Georges Trad) Would it be a possibility to move the vdM to after MD2? This would require that MD2 is mainly low intensity. This would not be very good for MD planning as it puts a large constraint on what MDs can be done. The reasoning is that if the Oxygen run goes poorly and needs to be extended then the vdM block gets shifted later and later making planning later.

(Jorg Wenninger) In Chamonix I will point out that there is a very strong interest to push the intensity to as high as possible (eg.2e11 ppb). This makes people nervous. The desire is to test the parts of the machine that won't be changed for the HL-LHC. We believe that we will be close to the PbPb target after 2025 so 2026 might be a pPb run and if it is lost then we have to live with it. Another possibility is to run without collisions such that there is no issue with cool-down and it can be done after the ion run in 2026. In 2025 we hope to get to 1.8e11 for physics and these tests will be proposed for 2026. Also, we can't fill the machine with 2e11 ppb in any case. There could also be scenarios where we test as high as possible (eg. 1.9e11 ppb in collision earlier in 2026 (eg. in April).

(Andrea Ferrero, Roderik Bruce) For ALICE the integrated luminosity for pPb probably doesn't depend on the energy as we will be leveled. It could be that the same beta* cannot be achieved at the lower energy. Some of this will need to be studied to make concrete statements.

(Catrin Bernius) Is the optics choice only fixed for 2025 and not for 2026? We will need to look at the state of the radiation dose and more discussions will happen towards the end of next year.

(Roderik Bruce, Jorg Wenninger, Andrea Ferrero, Catrin Bernius, Filip Moortgat) The Neon suggestion comes from the injectors as they believe they can switch the gases very quickly so if the . Would this come out the pp budget? It cannot come out the Oxygen budget. It could be classified as a special run such that it would take a fraction from both pp and PbPb. However we are constrained by the techinical stop placement. One day seems very short, although as it is the same charge:mass ratio very little changes are needed. For Montreux we will not make a statement at all. For Chamonix it would be good to have a statement if people are interested in either p-Ne or Ne-Ne. One thing that needs to be clarified is how quickly the Neon can be setup in the injectors and how long we would have to wait for the Neon to be setup. Reyes indicated that this should be significantly less than 1 day. The experiments will ask their communities about the degree of interest.

(Roderik Bruce, Chris Young) For the other ion improvements as we haven't done the MDs then we need to balance the risk that the changes introduce problems against the potential gains. Any change in beta* would require tightening all the TCTs and does introduce risks. For the cycle if we commissioned it differently it could be almost free but the gains are very low. For the emittance we don't know the source of the blow-up so it is difficult to improve this.

(Catrin Bernius, Roderik Bruce) Is there margin to gain on the injection time in PbPb? It is difficult with the current filling scheme. There are some things that could be developed but it is not easy as we need so many injections from LEIR and therefore a fixed number of SPS cycles and 23 LHC injections.

(Chris Young) The experiments are free to leave it up to the machine to pick the optimal parameters for eg. emittance vs intensity in PbPb, rather than trying to guess at exact machine parameters.

CMS (Andrea Massironi)

(Filip Moortgat, Federico Alessio) We will discuss the Neon internally and get back to you. We won't make a statement at Montreux so you have some time to discuss it.

ATLAS (Catrin Bernius)

(Filip Moortgat, Michi Hostettler) At the moment CMS are not claiming an accuracy of better than 5% on the luminosity. The beams are not completely round which tends to favour CMS, but this would favour ATLAS next year.

ALICE (Andrea Ferrero)

No questions/comments

LHCb (Elena Dall'Occo)

(Michi Hostettler, Roderik Bruce) For the effect on DOROS we can have a closer look and a similar thing was seen at point 5. It is unlikely to be a radiation effect but more likely an intensity dependence as at the end of these fills we are at the limit of the operation range of the component. It wasn't seen in earlier fills where there were similarly weak beams. We should check how the auto-gain behaved in this fill to see if it was frozen and didn't resume for some reason.