Round table of experiments (all)
Input for MD days:
Lumi-related special MD requests:
- vdM scan related
---- check the change in beta* (vdM optics configuration)
---- beam current normalization: recheck reliability, reproducibility, precision; making use of the multiple instruments (target: 0.1%)
- emittance measurement related
---- cross check to the calibration with the specific device at LHC (BSRT)
---- beta* study
---- crossing angle study: up to now known to precision of ~12%
---- longitudinal beam profiles study: need for profiles not just sigmas
- beam-beam effects studies
---- cross-IP configurations: different beta* at IP2/8 maximize the effects at IP1/5 (during regular vdM scans the effect is only visible at <0.5% level)
---- calibrate predictions/models for BB effects
- luminometer checks
---- performance study of CMS hadronic forward (HF) luminometer with high-pileup MD (PU ~ 200)
- length scale measurement
---- length scale measurement scan in physics optics
Special MD for collimator studies for PPS
Maximum mass within PPS XRP acceptance given by opening of collimators TCL4 and TCL5.
Maximum mass is very relevant for potential new physics.
Assumptions on Run 3 TCL scheme:
- TCL4 at constant distance: 15sigma (beta* = 30 cm)
- assuming TCL5 constant @ 40sigma (beta* = 30 cm) (not imposing any limitation)
—> upper mass cut well below 2TeV. For comparison: Run 2 optimum: 2.2 TeV (2017)
Proposal (discussion with Collimation WG just starting, earlier initiative, including preliminary MD plan, was already taken during Run 2 but not carried out):
MD at lower intensity (either end of fill or dedicated fill): Scan TCL4 (> 15 sigma) with open TCL5 and study losses.
How far can it be safely opened? MD possibly to be complemented with FLUKA simulations
This MD should happen early enough, in order to be useful for 2022.
Comment (Roderick et al.): can probably play with TCL’s during luminosity ramp-up.
Q to machine: possibility to have low PU run during Run 3?
A: can be done in each expt. separately on request. If both ATLAS/CMS want it, we can put it together.
Q: Is it technically possible to have a number of low intensity bunches colliding at the same time as the standard collisions?
A (Jorg, David): difficult but probably possible. But may have beam instabilities and difficulties to have precise determination of lumi.
1) beam-beam effects:
To perform measurements on this, we would need:
- vdM optics as done in the past (i.e. 19m beta*, nominal energy 13/14 TeV, collisions, filling pattern with indivs, …),
- zero crossing angle (as is normally the case for vdM),
- high brightness beam (i.e bunches with high charge, 1.1-1.2 E11 and small emittance (< 2 microns), to maximize the effect of beam-beam. No bunch tailoring as normally done in vdM).
The bare running would likely need few hours (2-3 hours) of stable collisions (not necessarily stable beams declared), but we should be prepared in having more than one fill including machine cycles (i.e. allocate a full shift) as it would be important to have all conditions stable and established also since the injection chain in Run-3 and the machine are or might be different.
Early in Run3: 2021 MD
Was discussed also already in the LLCMWG (of interest not only to ATLAS).
2) For now, no explicit interest in dedicated very high pileup MD.
(Might be of interest parasitically in the later part of Run 3.)
Q: Will there be opportunity to run (with stable beams?) with different beam configuration (e.g. flat beams) ahead of time?
A: yes, there will be some MD’s and some test runs in the year before we move to flat beams. But not before 2022.
Optics for Run 3:
AFP interested in collision optics for stable beams.
Three steps of beta*-luminosity levelling were considered: 84 cm, 43 cm and 20 cm.
Betatron functions for these conditions differ by a factor of ∼ 4 in places where TCL4, TCL5 and AFP pots are placed.
Q: will collimators and pots move during stable beams to be at constant sigma? If not, what which distances should be taken?
A(Roderick): can be set at 25 cm (or whatever endpoint) and calculate 15 sigma and keep it there. To be discussed further.
If collimators are closed accordingly to sigma from a given optics then AFP will lose a lot in the high-xi (high-mass) region in case of larger beta*. For 20 cm settings acceptance is OK.
To be followed up with collimator experts. (Action item)
Q: running efficiencies in 2021?
A (Jorg): numbers seem reasonable for computing budget requests.
Q: what about pp reference run in 2021?
A (Brian): will be included in HI period. Still to be decided how much pp reference run to be included in 2021 HI run.
For upcoming LPC we will will ask for experimental input. (Action Item)
No particular requests from LHCb.
Questions already answered above.