Minutes and Summary

Main purpose of the meeting: Discussion of beam-beam measurements at 900 GeV and round table of experiment requests.

1) Introduction (B. Petersen)

New LPC webpage has been moved to standard location (lpc.web.cern.ch). 
Old links to sub-pages might be broken, as the name might have been changed.

Commissioning planning on slide 4.
Ramp up plans, see slides 5-8.

Next meeting on May 23.
Upcoming topics: requests for ramp-up, plans for VdM/lumi scans


Q (Witold): slide 4:  does this mean the BB meas. comes right after the 9th?
A (Brian): No, can be come between the 9th and the start of 13 TeV collisions. TBC.
 
Q (Mario): Access to tunnel region limited to before weekend?
A (Matteo): can be requested later too, on request. Monday/Tuesday is possible.



 

2) Proposal for beam-beam measurement at 900 GeV (Joanna Wanczyck)



Introduction on slide 2.
Verification of simulations: overview on slide 3.

Proposal for Test 1 on slide 4: verify impact of relevant BB parameters on luminosity, verify opimization process and prepare for precision test.
Details and operational steps of test 1 on slide 5-6.
Time estimate: 7h.
Proposal for Test 2 on slide 7: verify the multi-IP parametrization by measuring the luminosity bias at witness IP in collision for a beam-beam parameter decided from results of previous Test 1. 
Details and operational steps of test 2 on slide 8-9.
Note about 2.5h needed for optics measurements prior to the test.
Time estimate: 8h.

Summary:
900 GeV: less complicated experimental setup, but low lumi is challenging. So enhance BB effects during separation scan.
High brightness beams needed, or phase advance adjustments.

Expected impact on luminosity is estimated as 1-2.5% for beam-beam parameter (0.008-0.016) at injection optics (zero crossing angles at IP1 and IP5), and > 3.5% for optimized optics.

Exploration of machine protection limitations and validations to be done still needed (ongoing discussions with R. Bruce).
Minimum program shown: ~2 shifts needed. Extensions possible.

Comment from Brian: add 0.5 shift to time estimate for optics measurements.

Comment from JW: bit optimistic in shifts, many injections, adjust tune/orbit. Suggest to add 50% to time estimates.
Machine drifting a lot at injection. Need time to handle this.
Also: no plans for 2x10^11 ppb, needs some setup time if this is needed.

Q from David: How high could you go in ppb? A (JW): not sure.
Q from Brian: also SPS need to prepare: A (JW): well, they have done it, but yes ...
Comment from Witold: most important part is the multi-IP and tune dependence. If not reach highest intensities, not a drama.
Statistical accuracy from Joanna is a solid number, it comes from ATLAS experience. 

Comment (Brian): maybe 2 iterations (drop highest intensity) … still need 2 shifts.

Q (Helmut): space charge effects?
A (Witold): yes, we are aware of it. Have configurations from 2018 that can manage it. Up to 1 x 10^11 ppb. Higher not clear. 

Q (Stephane): phase advance configuration of VdM is not the same as at standard running … is this a problem?
A (Tatiana/Witold): we can simulate that. Purpose is to benchmark simulations.

Q (Brian): discussed with ALICE?
A (Federico): still need some thinking.



3) Round table 


CMS (Andrea)


- request to have indiv. bunches into the filling scheme every now and then (after each TS and if no TS once/month). For calorimetry pulse shape measurement.
- after TS it can be part of the 600b ramp up fills.
- otherwise, e.g. like fill 5183 (2016), 2173 bunches.
- might also possible by shifting the initial 12b bunches and moving 1 bunch into collision
- it is important to have indiv RF tunes to ~0 ps

- thanks for splashes

Comment (Brian): option to move 12b might not be stable, to be discussed.


ALICE (Federico)

- thanks for splashes. Could see beam 2 splashes now.


ATLAS (Joerg)

- thanks for splashes. Beam 2 higher intensity now. NSW participated, but not timed in yet.
- if some free time, another 10 splashes would be very welcome for the NSW.

- very low mu special run: 
- now agreed by CMS as well.
- mu = 0.005, 40 separated bunches, 4 hours
- offset leveling. (JW: cannot go to beta* large enough for this)

For ATLAS, this run can come shortly after the 3b fill.

- horizontal muons: 
- with both beams, one beam at a time, 2 hours of data taking for each beam.
- can be done with nominal bunches by using ADT to blow up the beam.

Q (Brian) : would be good to have requested int. lumi numbers as well.


FASER/SND (Jamie): 

request summer access for emulsion installation now on July 26th.
Need to know in advance, due to preparations. Next exchange in TS1 (Sept 13th) and TS2 (Nov 8th).

Comment from Richard: currently run with 1/5 of emulsion in SND. To understand background etc.
Need minimal amount of data to be useful. If not much data collected in July, would prefer to request the exchange a bit later. 
More flexible, need ~1 w of warning, time needed for SND is ~ 4h.

Comment from Brian: not ideal if there would be 2 accesses. Maybe keep it at “week of July 26th” for now.

Comment from Jamie: for FASER: July 26 is not very flexible, maybe  ~ 1 day (people need to travel from Japan).


SND (Ettore)

- report on splashes seen with SND. Event display on slide 4.