Minutes and Summary

Main purpose of the meeting: The meeting is mostly dedicated to discussing the 2023 LHC commissioning schedule, input towards the decision of the PbPb energy choice and finally a brief update on the 2023/2024 LHC performance estimates for computing resources requests.

Introduction (Filip Moortgat) 

• ATLAS luminosity has been scaled down by 5.4% (Slide 3)

  • Jorg Wenninger commented that the most plausible cause of this was the crossing angle and it would be good to think if we have a way to quickly check this before we declare Stable Beams. If it is not found out before, it may need multiple validations and complications. More precisely, LHC-OP would request an early measurement of the luminous region. 

  • Joerg Stelzer commented that to provide luminous region measurements, Stable Beams declaration is needed for the trackers.

• Ramp-up fills discussion has started and will continue with MPP (Slide 4)

  • Possible option is to increase 36b trains at each required step

  • Joerg Stelzer asked if it is possible to clarify the notation for the “8b4e train” and what it actually means. 

  • Jorg Wenninger comments that the way the filling schemes are thought impose that the “8b4e train” is always at the same position. However, one could flip the 36b trains to after an initial 8b4e. The drawback of this is that the 8b4e cannot be easily dropped if needed. 

  • More discussions are needed after MPP clarifies the steps needed.

• 2023  schedule has been maintained and no changes are noted yet (Slide 5 to 7)

  • A draft of the commissioning schedule has been prepared by Jorg Wenninger. First beam injections can be expected as early as March 25th if machine checkout is successful.

  • The 3/6 km high beta* run is foreseen to happen in week 29, before MD2. A request from ATLAS/ALFA asked to be scheduled on the weekdays Monday to Friday of that week. In order to fulfill this request, MD2 must be advanced to Saturday. Filip will contact Rende Steerenber to understand if this is a possibility.

• Next meeting is tentatively scheduled for March 20th. If anything urgent arises, an earlier meeting can be scheduled.

• A final shoutout to Brian as outgoing LPC after 5 years (+ 2 months) in charge. 

 

Filip also presented dedicated slides for estimates for computing resources requests.

 

Jorg Wenninger presented slides regarding start-up

• DSO test is schedule for March 10th

• Test of signal exchange and communication LHC-experiments is schedule for March 14th (with Thursday 16th as backup)

• Beams to downstream TI2 and TI8 tentatively scheduled for March 24th

• Beam commissioning currently scheduled to start on March 27th but – if machine checkout is successful – beams can be expected as early as March 25th

• Morning meetings @9am will start on Monday 13th.

• Google spreadsheet has been updated and will be updated as we go along. 

• Lastly, a statement from LHCb on the vertical crossing angle for 2023 is welcome. 

 

• Brian Petersen asked about Point 1 polarity choice for 2023.

  • Stephane Fartouk answered that we start with negative polarity and then we see if we have to flip or not

  • Joerg Stelzer clarified that the flip would only make sense if we decide on the flip next year

  • More discussions on this topic are ongoing.

 

Roderick Bruce presented some slides on the considerations for the beam energy choice in the 2023 ion run (6.8 Z TeV vs 6.37 Z TeV)

• There is a risk of reduced availability due to dumps from beam losses, while going at the same time to higher beams intensity, higher energy and lower quench limit at 6.8 Z TeV

  • Possible mitigations involve using crystal collimation, choose lower beam energy, optimized BLM thresholds

• If the beam losses are identical to 2018, then crystal collimation is the baseline.

  • At 6.8 Z TeV we can expect about the same number of dumps as in 2018

  • At 6.37 Z TeV there is significantly better loss tolerance but it is unclear how many dumps could be saved

• At 6.8 Z TeV an expected 3-5% gain in integrated luminosity is foreseen due to smaller beam size

• There are still a few unknowns and caveats

  • After so many years, it is unknown how the 10Hz losses and other beam losses will behave in 2023

  • The actual trigger of more dumps is mostly linked to higher intensity, rather than higher energy. That means a mitigation for lower losses would be to lower intensity, while running at higher energy

• Crystal collimation was only briefly tested in 2022. New horizontal crystals have been installed in YETS 22-23.

  • Very important that crystal collimation is tested as early as possible during the recommissioning. 

• Given the unknowns, we can’t make a firm statement today on which beam energy will give the higher integrated luminosity.

  • Empiric analysis suggests a slightly higher integrated luminosity at 6.8 Z TeV.

 

• Sarah Porteboeuf recapped that the message is that it doesn’t seem that going to higher energy the situation is much worse. 

  • Roderik answered that if conditions are similar to 2018, then going to higher energy is actually better. However, nobody really knows how the machine will behave and only experience will show. A priori there is no reason why it would be better or worse and the best guess is that it will be similar to 2018.

• Andrea Ferrero asked if they know the lifetime of these fills that are dumped. 

  • Jorg Wenninger answered it was random. Some background activity, mostly likely mechanical. Only horizontal.

  • Roderik Bruce commented that it is dependent on what the beam does, it seems the risk is higher with higher intensity. 

  • Stephane Fartouk commented that as the effect is in the horizontal plane, then only B1H should be used. Roderik Bruce responded that this was taken into consideration in slide 21. Stephane also commented that possibly there could be other knobs to use to improve performance and ameliorate on losses, like beta* leveling.

• Sarah Porteboeuf asked when the crystal will be tested in pp. 

  • Roderik Bruce asked in fact if it was really scheduled. 

  • Jorg Wenninger answered that it will be done at night during the beam recommissioning.

 

Gianni Massetti (CMS)

• No major changes in CMS recently

• CMS requests early splashes, O(20) per side

• CMS also requests 1 colliding INDIV for 2023, at least 1 fill / month with INDIV 

  • Filip commented that 1 colliding INDIV for CMS and ATLAS is granted and taken into account

 

Niels Tuning (LHCb)

• Niels updated on the status of the VELO following the vacuum incident

  • LHCb will operate with damaged foil in 2023. At best we can close to 10mm, but an early tomography of the foil with beams will be needed to really decide

  • Physics program is heavily impacted for 2023, however LHCb will plans to take data and perform some analysis with VELO not fully closed.

• A few scenarios of data taking have been devised based on the outcome of the tomography and studies on the VELO motor status.

• There is a number of unknowns that we will tick off in the next weeks

 

• Niels asked when LHCb can inject SMOG

  • Jorg Wenninger responded as soon as possible, it doesn’t disturb the LHC. 

• Filip Moortgat confirmed that mu/luminosity is generally under LHCb control

• Niels also highlighted that a request that the magnet would be cycled at every 5 hours stop was accepted by LHCb, but that is not completely clear in LHCb either. The decision will likely be taken on a fill by fill basis. 

 

Sarah Porteboeuf (ALICE)

• ALICE plans to perform multiple magnet scans and data taking periods (slide 3)

  • Jorg Wenninger commented to be careful about the number of bunches in condition 0,0 in the table in slide 3. 

• ALICE measured its luminous region centroids to (-0.04, +0.02 cm), commenting that the values are very closed to the nominal

• Sarah also mentioned that the machine survey confirmed a shift of +0.02 cm in Y ALICE coordinates and that they were informed the quadrupole position would be adjusted.

  • Jorg commented that this is a discussion that happened a bit uncoordinated and that the quadrupole’s position likely won’t be changed

• Sarah presented studies on the vertex position in ALICE

  • Movements have been observed and patterns emerged

  • Comments are provided in the slides.

  • Niels Tuning also commented that also LHCb saw the same in 2018, which was pointed to triplet movements

 

Joerg Stelzer (ATLAS)

• ATLAS presented early plans for recommissioning with beams

  • Ready for handshake tests

  • Participate in splashes, O(10) per side, in conjunction with CMS

  • Participate in early 450 GeV Stable Beams

  • Horizontal muons data taking requested again

  • Plan to take data during loss maps, in coordination with Roderik Bruce

  • MAgnet non linearity scan at 13.6 TeV

• ATLAS/ALFA repeated that early commissioning of 3/6 high beta* is desired to find out early on on problems. Also ATLAS/ALFA asked about the status of the optics development

  • Jorg Wenninger commented only optics setup was foreseen for the moment

  • Joerg Stelzer still commented that we need to do background measurement with ALFA RPs inserted. 

  • Mario Deile commented it would be nice to have a meeting to clarify these questions. 

  • Filip Moortgat commented that Ilias will be contacted asking for the optics development status.

• ATLAS showed interest in participating in a BSRT fill

  • Jorg Wenninger will forward the request for the BSRT fill

• ATLAS asks for one five-hour fill with ~64 INDIV bunches at very low mu (0.005)

  • ATLAS will also ask for a very low mu fill during one of the 300b, 600b or 900b fill (depending on what MPP decides).

• ATLAS would like to have the ramp-up filling scheme early on

  • Filip Moortgat answered that we need to wait for MPP to define the checklist, but that this will be followed-up soon

• ATLAS also commented that AFP would like to join data taking during the pp reference run. Joerg asked if extra loss maps would be needed.

  • Jorg Wenninger confirmed that new validations for BBA and loss maps are needed. 

  • Roderik Bruce commented that for loss maps, it is needed to count at least one shift.

• ATLAS also asked if a mu of 6 could be provided during the pp reference run

  • Jorg Wenninger commented that mu of 6 depends on intensity, beta* and emittance. In some combination of these cases, questions about aperture will come out. 

  • Witold Kozanecki asked what the largest beta(and lowest bunch intensity could be used for the pp reference run

    • Jorg Wenninger responded 3m, but it can be discussed further

    • Roderik Bruce commented that we can just find out what beat* we can reach at ramp&squeeze to see what could be used. The energy of the reference run is 2.57 TeV and normally the ramp is very compact. 

• ATLAS asked if a decision on TCL6 opening to 2mm was taken or not to reduce radiation at AFP

  • Roderik Bruce commented that the issue will be followed up in a dedicated collimation WG. 

• ATLAS also plans to do a toroid field off fill during the intensity ramp-up

  • Filip Moortgat commented that the schedule will be looked at and a proposal will be done

• ATLAS also commented on the impact of the change of the triplet polarity on their ZDC/RPD detector for the HI program

  • Jorg Wenning responded that the idea behind switching the polarity is also to be able to go back to other polarities for special runs. In that case the issue would not exist. It is only necessary to flip polarity for radiation issues, in that case for ions the polarity can be put back to the right crossing angle if needed as the flip only matters for pp

• Lastly Joerg Stelzer announced the new ATLAS Run Coordination team

  • Joerg will step down from ATLAS Run Coordination on 01/03/2023. Silvia Franchino will take over the main role and Catrin Bernius will be the new deputy.