LPC meeting summary 25-03-2019 - final

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Minutes and Summary

Main purpose of the meeting: Discuss plans for Run-3

Recap of Run-3 plans:

 - summarized Run-3 plans as presented in Evian and LMC
 - optimal fill length is 14 hours (round) or 15 hours for flat
 - 2021 start with round optics and same crossing planes as in 2018
 - Q1: issues with mixing filling scheme
 - 40% decrease in luminous region size (and pile-up density) in IP1/5
 - ALICE luminous region size?
 - minimum size in LHCb? vertical crossing in LHCb - feedback?
 - in 2018 saw large spread in luminosity after several hours in SB
   * driven mainly by intensity variations, not transverse emittances
   * could give large variation at end of leveling
   * more study of data for instance BCMS beams in 2017 - could be multiple source
   * mechanism not understood
   * Run-3 might be better since will have more burn-off
 - understand effect on B-B variations on leveling strategy

? how to level IP1/5 separately? beta* is assumed to be same. Would have to use separation leveling on top - need simulation to understand if this has issues

Round table:

  - mixed filling scheme is possible, but prefer to go only if significant. mu should be similar
  - studies needed for beta* leveling and flat optics.
  - energy preference still not decided. But could use 13.5 TeV
  - will come back on pile-up

   - LHCb thanked for Run-3 WG as many of their request were taking into account
   - HL Physics in Run-3
   - ok, not to level at 2x10^33 for full year
   - strong preference for pure BCMS,
   - level to average pile-up and cut high pile-up events at HLT
   - still worried about horizontal crossing angle -> don't need answer soon, willing to sacrifice time to commission this in 2021
   - LHCb will have to redo simulation at end of 2021 in any case
   - no conclusive result yet on lumi region size. not problem with changes in size, but concerned about size<37mm, but can be dealt with
     * main concern is difference between polarities
   - no strong feeling on energy, but willing to sacrifice time in 2021 and don't want to spend time in 2022/23

  - vertex cut can be relaxed from |z|<10cm to 11-12cm due new ITS - will loose some events, but acceptable
  - beta*=10m is ok for 2021. Better ITS resolution again makes less requirement of beam size, but might revise that after/during 2021 * also matters how oxygen-oxygen run is done
  - filling scheme not strong preference
  - for O-O run same beta* for IP1/5
  - machine preference for same beta* in all three years to avoid new optics in 2022


  - no feedback on energy as up to management (prefer to move to 14 TeV soon)
  - vertical crossing in IP5 would make most events miss diamond detector . also pixel loose acceptance
  - CMS strong preference for round optics due to PPS
  - mixed filling scheme with 23% and 45% of 8b4e trains - large increase in trigger rate 8b4e - why?
    * 45% would be disfavoured as it require L1 changes
  - lumi region size: looked at vertex efficiency - see a few % loss for |z|>15cm (not detector acceptance, but tracker software)