LPC meeting summary 14-06-2021 - final

Minutes overview      LPC home

Minutes and Summary

Main purpose of the meeting: Pilot beam test, Run 3 lumi levelling and special runs during Run 3.

1) Introduction (Brian)
- Run 3 to 5 running conditions for Computing Reviews are shown, for information. It should be kept in mind that these are optimistic numbers (to guarantee sufficient computing resources).
In 2022, towards the end of the year we could already have significant levelling and thus rather high PU (compared to the average). 
In 2023, the heavy ion periods were clarified: PbPb in 2022 and in 2024 (extended period), pPb in 2023. pp reference run still to be scheduled.
If Run 3 is extended, the HI periods need to be revisited (and we might have PbPb in 2023 then).
- reminder of outcome of LS2 schedule meeting:
  — Pilot beam test moved to week 42-43 this year
  — start of Run 3 delayed to 21 February 2022 (cavern closure)
  — new target energy for training dipoles: 6.8 TeV (+ 100A), awaiting a risk analysis
  — schedule to be reviewed again in October/November.
- new draft LHC schedule was shown (slide 10)
    first beam might be expected on 7 March, 2022
- Motivations for changing LHC beam target energy on slide 11
- Current pilot beam plan on slide 12 
  — expect few shifts (2-3) with collisions at injection energy in stable beam mode
  — planning day to be held in early September
- Reminder of Run 3 beam conditions
  — still outstanding issue on # of beta* steps in IP1/5 beta*-leveling
- we would like to define a baseline plan for special runs during Run 3
  — would like to know lumi/time/energy requirements & requests for special conditions 
- next LPC meetings tentatively on July 5th and August 30th
Topics: collimation/collision energy for PbPb, possible update on collimator settings for AFP/PPS, further input on special runs.
Q (Gianni): is ramp of 2-3 TeV possible/realistic during the pilot beam test?
A (Matteo): it may be technically possible, but not really useful for machine tests.
Q (Brian): is there any request for this from the experiments?
A (Gianni): not yet.
A (Matteo): note that we will most like not have sufficient time to set up collisions at higher energy
Q(Taku): Ti2 to Ti8  transfer line tests … when will they happen?
A (Georg/Matteo): beginning of October … under discussion with injectors. DSO tests (17th of Sept) need to happen first 
Q (Taku): when will the lead ion commissioning at SPS happen (needs to be rescheduled because if pilot beam)?
A: not yet known.
Q (Gaelle): in 2022, when do you expect levelling to start?
A (Stephane): no decisions yet. Depends on intensity ramp up on injector side. Will try to first fill machine with pre-LS2 intensity and then rise bunch population.
A (Matteo): will probably happen rather towards the end of the year.
2) Round table
LHCf (Lorenzo)
Updates on requests for Run 3:
pp run in 2022: with beta* of 0.5 m, expect  beam center spacial fluctuation of 3.4 mm. Expect correction factors of the order of 10-20%. Not big problem.
Combined analysis with ATLAS might be more problematic.
Beam crossing effect: maximum beam crossing angle (downward-going) tp measure precisely the beam center in the lower calorimeter is 290 microrad.
Request not to exceed this number.
Summary on slide 7:
PU not above 0.02.
For beta*: 19m would be ideal (maybe already set up for VdM scans?)
pO run during run 3:
target statistics: 3.5 10^8 collisions. DAQ rate limited.
request not to go below the running time requested in TDR
similar studies for beta* = 0.5 mm: ok for pions, bit worse for neutrons
PU studies: Acceptable PU for LHCf alone is 0.1, acceptable for ALTAS+LHCf is 0.02.
beam crossing: also best 290 microrad
beta*, as large as possible
luminosity per bunch: 24 bunches
limits on bunch spacing: best 2 microsec (acceptable > 200 ns)
request VdM scan for precise measurement of luminosity
Summary on slide 15
Comment on OO run:
interest in participating, but need to move detector up by 25mm. Not strong request, only in case.
Q (Roderick): your request of 0.7 nb-1, is that for one position? or total?
A(Lorenzo): want to positions, so we can get double of this
Q(Roderick): is smaller crossing angle of 290 microrad also fine?
A(Lorenzo): yes, but lose some phase space access
Q(Roderick): did not take into account time for VdM scan. To be followed up
Q(Roderick): for beta*, might be able to do something with injection optics. But might need additional commissioning.
Q (Witold): do you have constraints for radiation on detector? Want your run before or after technical stop?
A(Lorenzo): we are in garage position (protected by TAN), but usually we remove/install the detector to minimize radiation.
But we are flexible on when we can do this.
Q(Brian) for pO run: for standalone run you could run a higher PU? Might profit from part at higher PU and then some period at low PU.
A(Lorenzo): seems so. Need to study it.
ALICE (Taku)
ALICE will start global commissioning in July. Will be ready for PU beam test (6 hours of SB collisions).
Will commission new MB triggers, verify streaming readout and new online data processing framework.
OO goals:
above 0.5 nb-1 integrated lumi. 
PU below mu = 0.2
Request VdM scan (full scan)
Baseline energy of 7 Z TeV 
- requires pp reference interpolation: modest impact on accuracy expected.
- same energy as PbPb in Run 3 or dedicated pp ref run requires extra 3-4 days and is not ALICE priority.
LHCb (Federico)
- not much time for global commissioning, only partial detector ready in time for pilot beam.
- target goals are to validated upgraded detectors in LHCb
- LHCb wishes: 
   — inject gas during collisions and — if possible — also during recommissioning with beam
  — no requirement on amount of data or magnet polarity
  — have collisions spread over multiple time slots during beam test
Note that VELO will not be installed. Interlock will always be “ready”
BCM will not be 
Run 3 running conditions:
ok with beta* = 2,
ok V-xangle from 2023 onwards a with MD in 2022.
LHCb generally indifferent to change of energy, 6.8 TeV ok.
LHC final global commissioning period will be done in parallel with machine recommissioning.
LHCb will likely need to have periods to access the detector (would be great if these periods could be “scheduled" in some way)
LHCb also wishes to inject gas as early as the machine deems acceptable
LHCb wishes to have collisions as early as the machine deems acceptable
Answer from Stephane  on question on slide 4: For the moment everything is prepared for positive crossing angle.
OO and pO run:
Mainly intersted in pO (p in beam 1)
integrated lumi desire for pO in LHCb is > 2 nb-1 (10000 J/psi)
Interested in Op beam (p in beam 2) and OO run (500 mub-1) as well, but less priority.
LHCb not against taking this time out of pp budget, but not more than 1 week.
Q(Roderick): any energy preference for pO or OO run. 
A (Federico): Preference for pO is 9.9 TeV and 7 TeV for OO (highest possible)
Comment (Roderick): will need special filling scheme (individual injection) for pO.
Q (Stephane): request for special crossing angle for OO/pO? Because crossing angle rotation not possible for large beta*.
A(Federico): we can keep horizontal. Will keep same magnet polarity for these runs. Probably best to keep ion configuration.
TOTEM (Mario)
very high beta run in October: happy with (3km, 6km) optics from Helmut. Nothing to add here.
Duration estimated to be 4 days.
90m beta* run: requested if beam energy > 13 TeV.
Run without stable beams and close XRP positions
Run will use the new T2 detector
Duration: ~ 6 hours, ~ 1 nb-1
Scheduling: new T2 cannot withstand high lumi operations.
CMS needs to minimize # of magnet ramps
So install in last TS of any year, run, leave in for ion run, uninstall in YETS.
Beta* = 90m but develop squeeze up to 120m
Need to get PU in range 0.04 - 0.1.
Other machine parameters on slide 3.
Problem with interlocked BPM in IR6: suggest to start at 0.6-0.7 10^11, blow up emittance to 2.5-3 murad and increase beta*
Q (Roderick): could you do separation levelling to lower the PU?
A (Mario): not very popular with analysis team, but I can ask them again.
Comment (Helmut): relatively modest run, shouldn’t pose too many problems to get the PU requested.
This run is on the way to the very high beta.
Q (Roderick) Do you expect background to be an issue? (need to play with collimation settings etc.?)
A (Mario): No, I don’t expect an issue at the 90m run.
ATLAS (Trevor)
Pilot beams:
- desire to start with low rate of collisions (assume 3b_2_2_2, low collision rate accomplished by beam separation) for few hours
- later shift (min. 4 hours) at high rate would be most beneficial
- would be good to have at least some hours in between the periods
- AFP currently discussing 20 mm insertion during pilot beams
- Proposal for studies of magnetic non-linearities in vdM scans (2.5 hours). ATLAS requests including these studies as part of the October pilot beam run.
- HRE-RP have now given ok for beam slashes in ATLAS in open configuration.
Beta* leveling during Run 3:
- x-angle/beta* leveling adds number of complications for ATLAS:
  — variations of luminous region will need to be simulated by ATLAS
  — would be good to confirm that beta* adjustments have little impact on Roman Pots
- ATLAS has preference for small variation in instantaneous luminosity
- Questions: 
   1. are the variations in the luminous regions coming in the same steps as beta*?
   2. what is the duration of the individual luminosity adjustments?
   3. will luminosity optimization be done following a beta* step or will the beam separation remain unchanged?
- Additional concerns:
 — if the lumi changes by more than 5%, would want to optimize trigger bandwidth
 — HLT and offline clusering use per-BCID
- Concerns for ATLAS lumi measurements:
— ALTAS LUCID response is very non-linear at high mu
— if luminosity varies a lot, an get biased result for lumi block integrated luminosity.
- Handshake with the LHC during beta* leveling could serve as cue or trigger changes, synching LBs to beta* transitions, etc.
A DIP folder is alreay set up for the standard (separation) leveling, so perhaps could be adapted.
Special runs during Run 3:
- currently in the process of collecting input for special runs in 2022
- ATLAS in communications with LHCf regarding combined LHCf + ZDC running during earliest pp collisions with low mu (June 2022)
- regarding emittance scans in Run 3:
  — would like to have regular emittance scans (but not as frequent as in Run 2)
  — emittance scans during special runs also useful to get early lumi calibration
Input for OO and pO runs:
- ATLAS supports this run, but duration should be limited to strict minimum
- preference for same energy as pp run at 14 TeV (13.6 TeV):
    OO energy 7 TeV (6.8TeV)
    pO energy 9.9 TeV (9.6 TeV)
- ATLAS target integrated luminosity is 0.5 nb-1
- OO energy discussion is driven by pp reference
  — needed by many HI physics measurements, no useable pp reference at the moment. 
  — any change in beam energy would need a few hours of additional commissioning
  — considering two options:
       1) use pp energy for OO
       2) use Run-3 PbPb energy for OO (reference in hand). ATLAS prefers this option
Q (Stephane): comment on beta* steps: change of luminous region due to crossing angle, length of bunches and beta*. So several causes.
Stephane's answers the questions on slide 3:
              1. yes, same steps, linear effect
              2. duration of steps: less than 1 minute
              3. will need to see. Difficult to predict.
Q (Ilias): when does LUCID become non-linear?
A (Richard): already at PU of 50-60, a change of 10% give a 0.5% effect
Comment (Witold): suspect that from the OP group there will be a preference to use the DIP folder mechanism during beta* optimization 
Q (Roderick): energy preference in OO and pO: why this preference?
A (Trevor): TBA
Q (Brian) slide 4: signal or handshake?
A (Trevor) : signal
CMS (Gianni)
Beam test: no changes in request
- injection energy is fine, SB requested
- considering using data to measure total charm cross section at 900 GeV
- CMS magnet during beam test should be ON. No HF installed (online lumi will not be very accurate)
- Also interested in beam splashes.
OO and pO special run:
 - requests of today are the same as in 2019:
   —  OO samples of ~ 2 nb-1 to match 2010 PbPb sample, or 30 nb-1 to match the PbPb 2011 sample
   — pO: a few million events.
- OO energy: slight preference for equivalent energy of the 2022 PbPb run, but shorter commissioning time is the priority
- pp reference run: need the same PbPb data
Beta* leveling stops:
 - have been looking at 5% (3-4% change of lumi) and 15% steps (10% change of lumi)
 - fine from CT-PPS point of view.
 -  from trigger point of view, preferred option is to keep the lumi step as small as possible. 10% lumi step is probably ok.
VdM scan: 
- two completely new luminometers will be installed in CMS
- expect to use emittance scans in the ramp up period to obtain first approx. calibrations for these, as well as for the HF luminometers
- expect rapid pressure to be more precise, so a full VdM program will be requested e.g. after first TS. A program similar to that in 2018 is envisaged.
- need enough pixel commissioning time before VdM program, to ensure a well characterized pixel detector for the VdM program.
CMS considering a special low PU run (to be further defined) for SM physics measurements. Considering 0.5-1.0 fb-1. This run should be close to a VdM scan.
Goal is to extend the reach of SM precision physics. Will come with official request after internal decision is made.
Q (Brian): what is low PU?
A (Gianni) PU of 2-3. Couple of weeks.
Q(Roderick): pp reference run: do you prefer a separate run or interpolation?
A (Matthew): not a dedicated ref run for OO, prefer to do an interpolation
Q(Roderick): And if we do run at max energy, you don’t require dedicated ref run, you will interpolate?
A (Matthew): Yes.
Q (Roderick): would CMS be very unhappy if they get less than 2 nb-1 in OO (similar for the others)?
A (Matthew): not very
Q (Brian) would you like signal when beta* step is happening?
A (Gianni): yes, would like to be warned
Stephane mentioned a IBS effect that makes a difference between ATLAS and CMS (lumi bit lower in ATLAS), so slight beam separation in CMS to compensate.
This may cause lumi to briefly exceed 2 10^34 during emittance scan in CMS then. To be studied further.
Brian and Filip will assess the possibility for the VdM proposal during the pilot beam.