Minutes and Summary

Main purpose of the meeting: Feedback on data taking and HI planning

LPC minutes 15th July

Introduction (Federico Alessio)

(David Stickland) I will followup on the missing MASSI file from CMS. This was then fixed during the meeting.

(Mirko Pojer, Federico Alessio, Jorg Wenninger) Since last Monday we are running with the low tails BCMS beams again. There is an interest in the injectors to try to develop this further which is why we have continued with this even without observed improvements. It would be nice to get a summary in an LBOC meeting. We can see if someone is available for this.

(David Stickland, Georges Trad) Is this change in crossing angle thought to be real or from DOROS? It is not known at that level of precision but there are intensity related effects which could lead to a variation. There is feedback corrections from the BPMs but there could be residual intensity effects or something un-understod.

(David Stickland, Witold Kozanecki) There was also another change of 1% that came last week due to further aging which has moved the two experiments closer. Does ATLAS account for similar aging effects? ATLAS does not make luminosity calibration changes thoughout the year. After every fill there is an adjustment of each phototube to account for aging based on a calibration run using Bismuth sources although this does obviously have an associated error meaning the online luminosity will not be as accurate as the final calibration. There is therefore an update each run but not something dynamic. All 8 newer design phototubes are used, 4 on each side of the IP at all times. The calibration itself is not updated regularly, but the linearity is corrected using the reference source.

(Roderik Bruce, Brian Cole) There is no fundamental showstopper to have the positive sign in both ATLAS and CMS and this is the baseline. The experiments will provide feedback but we think it will be positive for ATLAS. The crossing angle range should also be followed up by the experiements and CMS will present this in their report. ATLAS confirmed that they prefer positive crossing angle sign as well for the pp reference run.

(Jorg Wenninger, David Stickland) The background numbers are not used by the machine at all. For issues like the RF finger then you see the effect in the background numbers but you also see it vacuum gauges, for example, and other systems. How the luminous region is defined is not trivial as the distributions will not be perfectly Gaussian and will depend on detector efficiencies. However, the aim is to at least document how the experiments are defining these.

(Catrin Bernius) As the fills shown are very recent one might be using the online tracking and one might have been updated to the offline tracking.

(David Stickland) In the past in CMS the background numbers have been useful for data quality checks, but at the moment they are not used very much.

(Federico Alessio) For LHCb when SMOG is injected there will be a large change in the background number so it is a way that others can tell when SMOG is in use.

(Federico Alessio) Previously backgrounds 1-4 were unified between the experiments and numbers beyond this were defined independently.

(Andres Delannoy, Federico Alessio) It would be nice to collect the definitions of what is in Timber, and what is useful, in some central page such that people know what they are looking at in Timber. There are some links of definitions on the LPC page but we can try to make this more useful.

CMS (Giulia Negro)

(Andres Delannoy, David Stickland) Every 10-15 fb-1 there will be similar updates in the future such that we will see steps every ~15 fb-1 and before it is made we should see a difference of this order from the fill at the beginning of the period to the end of the period.

(Federico Alessio, Roderik Bruce) The ion sharer has been updated but there are a couple of final things that Roderik will send to Federico. It is likely that for HI running the machine will conclude on 140 urad crossing angle due to beam-beam limitations.

(Catrin Bernius) Will you change the mu target across the 15 fb-1 to account for the 1% difference. No currently we don't intend to change this but this might be re-evaluated.

(Michi Hostettler, Jorg Wenninger) The update of the fill number is in the preparation sequence for the subsequent run which is why it sometimes doesn't change during the long gaps between fills. The beam dump mode needs to be kept in the previous fill so it can't be changed immediately. It can be done manually but maybe something smarter can be devised. We don't know if there will be a Y2k issue with the run number hitting 5 digits.

ATLAS (Catrin Bernius)

(Federico Alessio) It is understood that this is the CERN Phone application rather than the mobile phones which is seen as non-essential. The call forwarding will not work when this is down. Mobile phones should be advertised and ATLAS will ensure that their shift leader has a SIM card as well as their landline.

(Roderik Bruce) Currently the plan is to stick with one fixed crossing angle though the fill, but there could be advantages to varying it. This will be discussed between Brian Cole and Roderik in the coming weeks.

ALICE (Robert Helmut Munzer)

(Chris Young) Was the 750kHz test successful? Yes, this was very useful in anticipation of the pp reference run for testing the system stability, and was also successful.

LHCb (Elena Dall'Occo)

(Mirko Pojer) What material is the belt? We can find this out.

(Federico Alessio, Jorg Wenninger) Can we do the magnet change during the day with the full machine? This will need to be followed up to see if doing it with the full machine is ok.

(Federico Alessio) The request of the change in HI filling scheme comes from the LHCb spokesperson. From the machine side Roderik has confirmed that this change in filling scheme would not cause issues/problems. From the research director side there is a request for LHCb to summarize the physics case in an LPC meeting which we will summarize for them. The research director can then make an informed decision. For other changes that don't penalize the other experiments eg. crossing angle, this is obviously not controversial and can be worked on. The 40% would be on top of the 20% improvement from last year due to the change in beam parameters.

(Chris Young) Is the cause of the problem with the velo belt known? The cause is not known but it is under investigation. It might have initially been caused during the vacuum incident last year and then degraded over time.