LPC meeting summary 11-11-2019 - final

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Minutes and Summary

Main purpose of the meeting: Update on Run 3 planning, including the commissioning and potential oxygen run

Introduction (B. Petersen)
* News on O-O run:
Baseline energy is maximal collision energy (7 TeV/NN).
ATLAS (supported by CMS) requested collision energy to match the existing pp dataset energy at 5.02 TeV/nucleon, so no extrapolation is needed.
However, this would require additional commissioning (new optics cycle) which would take 3-5 extra shifts  (~ 2 days).
p-O would then also be at lower energy unless p-p optics is used for p-O run.
Question to experiments: how strong is the request for lower energy given the >2 days of extra setup time?
* Correction for Run 3 lumi region: mistake found in calculation of luminous region transverse size in crossing plane (pointed out by Witold).
Affected ATLAS and CMS luminous regions. Effect seems to be small.
Comment from John Jowett: new optics more likely to take 3 days.
(from ALICE run coordinator): will check if pp optics is fine for pO for ALICE.
(from ALICE run coordinator): if extra 3 days for lower energy commissioning, where will they be taken from: pp or PbPb running?
A: no schedule yet, so to be seen. Would be nice to check the physics effect.
Update on LHC beam modes (J. Wenninger)
Access control of the ATLAS and CMS superconducting magnet power converters:
Following some incidents when commands were accidentally sent by EPC experts to ALL LHC PCs – including the ATLAS and CMS magnets – dedicated rules and roles where introduced in the LHC RBAC system to access those PCs by EPC experts. Extra bits were introduced to define ATLAS and CMS operational mode decoupled from machine mode.
But not defined during shutdown, so unreliable. A better solution based on the LHC software interlock system (SIS) was retained, since SIS is running during shutdown.
Extra SIS tree state: by default the state is false which means no access to the Power converters. On request of the experiment, can request to mask this test.
LHC OP can mast the test, setting the value to true and EPC expert can access the PC.
A mode specification document has been written (includes modes and access to magnet PC) and is ready to pass under EDMS approval.
Please specify 1-2-3 names per experiment for the approval of the EDMS.
First draft of LHC beam commissioning schedule (J. Wenninger)
First draft outlines of beam commissioning schedule after LS2 are available on the LHC machine coordinator WIKI pages, with uncertainty of -1/+2 weeks:
The list of activities should not be considered as complete yet.
Question: does the commissioning time depend on the energy? 
A: not really.
Round table (all experiments):
CMS (Gaelle Boudoul)
* CMS is in favour of having a limited O run at a lower energy of 5.52 TeV/nucleon instead of maximum energy of 7 TeV/nucleon. However, we understand the risk of invest a significant fraction of the time for the setup and for this reason we consider that we would like to express our final opinion only once the schedule for Run 3 as well as the one for the O run is clarified. 
* DSO test end 202 vs 2021: will answer after the Run 3 scheduling meeting.
* Need for early stables beams at 450 GeV?
We can benefit from early stable beams. More quantitative requests will come in the next months.
* Need for early VdM scan?
Indeed it would be valuable to have a fairly early scan. Almost certainly asking for another le later in the (first) year.
Question: full scan?
A: probably yes , but can check with experts
CMS will also have new uses for scans. For example BRIL monitoring experts will want to explore corners of the BeamBeam interaction effects to validate the modelling in as detailed a way as possible. This will probably mean special conditions and setups. Not in the first weeks, but we will come with a more complex scan program in Run3 respect to Run2.
ALICE (Taku Gunji)
* desired collision energy for OO: also prefer 5.52 TeV/nucleon. However, if there are significant risks for extra time, ALICE does not want 
this to be taken from PbPb time.
Question to LPC: 
ALICE is very interested in single bunches (SB) at 450 GeV to commission ALICE upgrade.
How many colliding bunches will there be? Maybe a few bunches?  
What about the bunch intensity? 
What is the maximum time? A few shifts are the maximum?
Answer by Jorg: default is to stay below 5x10^11 total intensity, so 4-5 nominal bunches. Or 6 bunches of 8x10^10.
Time: depends on you. Few fills.
ATLAS (Kerstin Lantzsch)
* O-O run:  if run longer than 1 day, time should be taken out of ion run time.
Energy should be the same as for Run 3 PbPb run. If the energy is different: new reference pp run should be taken (60 pb-1 for each nb-1).
Question to John/Jorg/Roderick: how much time it would take to have a pp reference run?
A: probably also 2-3 days. But maybe the reference run is needed anyway?
Question from John: is there a need for a reference run for p-Pb?
A: Probably yes (CMS/ALICE). Will be part of the pPb run in 2023.
* Effect of round vs flat beams for forward physics
There is a negative impact of the horizontal crossing angle on AFP. Low ξ acceptance and ξ resolution. Radiation damage.
Overall conclusion on round vs flat beams: Since the bulk of the ATLAS physics programme profits from flat beams, and mitigation of radiation damage in AFP seems possible, ATLAS has a slight preference for flat beam optics.
* Mixed filling scheme on trigger: 
Level 1: sustainable well above 30% 8b4e inserts.
HLT: closer look at configuration and operational margins needed for mixed filling scheme
Still outstanding:  effect of bunch-by-bunch pileup dispersion on trigger
* DSO test: agree to do it on Friday and Saturday of week 44 in 2020.
* Need for early stables beams at 450 GeV?
would be good. If more than 1 fill, should be space by 2-3 days.  1-2 hours each fill would allow to collect enough events.
* Need for early VdM scan?
Yes, and also second one towards the end of the year, due to changes in detector and lumi infrastructure.
Question: how big are the effects for acceptance loss for flat/round? Can you quantify this?
LHCb (Federico Alessio)
* Feedback on O-O and p-O:
LHCb strongly interested in p-O: highest priority. p in beam 1.
Energy c.m.s. order of preference is: 
1) 8.8 TeV : to match the Run3 foreseen p-Pb run (?) and preferred higher energy from “cosmic” point of view 
2) 8.16 TeV : to match the 2016 p-Pb data sample and still high enough from “cosmic” point of view
Integrated luminosity request for p-O in LHCb > 2 nb-1 (at least 10000 J/psi)
1 week “special run” is acceptable.
No strong prefernce on OO run. Energy of 5.5 TeV/NN OK, as for Run3 PbPb.
* DSO test in week 44 of 2020: ok
* Highlight requests for early beams/collisions in LHCb:
- request 450 TeV beams (more than once ).  Investiagate if they can close VELO at 450 GeV. 
- 2 x 2 (or few x few) bunches at top energy (more than once)
- request SMOG commissining in quite beam periord (parasitically if possible)
Comment from Jorg: first stable beams will come in 3x3 etc. 
* VdM scans: prefer early one. Second one towards end of year is fine.
Comment from Roderick: different energy for OO and pO is complicated for setup.
Comment from John Jowett: first plan was to have heavy ion optics for OO and then do pO with pp optics to get highest energy.
LHCf (Lorenzo Bonechi) 
Pointing out to remember their interest for p-O.
Highest energy is preferred (allows to reach 2.6 10^ vs 1.6 10^16 energies for cosmic ray physics)
Need vertical beam crossing, otherwise they cannot run. 
(and downward polarity) 
(requires round beams)