Minutes and Summary

Main purpose of the meeting: This meeting is dedicated to the LHC start-up of 2023 data taking and the ramp-up schedule.

 

Filip (Introduction)

• ATLAS low mu run will happen in the post-TS1 ramp-up

• (Slide 6) SPS still no ready for 200ns train spacing

  • Jorg commented that we need to change filling schemes at least until middle of next week

  • Filling schemes will change from the second 400b fill onwards

    • Likely from the 900b step the filling schemes will be prepared with 4x36b trains rather than 5x36b

  • 3 INDIVs (2 colliding at each IPs) are available until 1800b

• Open issues:

  • 2 UFOs in 75b fills: one dumped by ATLAS and one dumped during TCL6 movement

  • RF voltage drop during 12b fill, full detuning was switched off during the week-end. Currently it is being recommissioned. 

    • Witold commented that a movement of beam 2 was observed.

    • LHC will follow up, could be related

  • Still a few mm adjustment is possible on the beamspot in Z

  • Rather large luminosity difference between CMS/ATLAS of ~13%. Surprisingly there is also a ~13% difference in the luminous region Z-width difference. 

    • Discussion on whether this is real or due to calibration

• Next Monday is 1st May (holiday). We’ll decide over the week whether we call for a meeting on Tuesday the 2nd if necessary. 

  • To be discussed. 

 

Luminosity imbalance discussion

 

CMS

• 34-36mm measured online at the end of the fill (consistent over several fills) for the beamspot Z-width

• CMS luminosity calibration can be trusted within 2% (at most 3%).

 

ATLAS

• 33mm measured offline (10% between offline and online)

• ATLAS’s 3 luminometers agree within 2% (a fourth one is off by 4% running 2022 calibration). 

 

LHC (Michi)

• Some indication from BSRT that B2H is very large, but this is not seen in the LHC emittance scans (dots in slide 5) 

• Crossing angle is corrected at injection, but as soon as ramp is conclude, the 10urad different (in favor of CMS) reappears. This is seen in the crossing angle from DOROS BPM.

• BLMs do not show differences. Calibration is done against FLUKA simulation. The ATLAS measured is the only measurement that differs

  • This needs to be confirmed.

• Michi would like feedback on the autopilot for IP1&5. 

  • David commented that in the fine structure this is observed, but on the global scale the effect is not so big. 

  • Small trimming steps are needed to “train” the autopilot in knowing in which direction to move. 

• George asked about the measured changes between ATLAS/CMS ratio at the beginning of the fill

  • Michi explained this is probably due to optimization

• Stephane commented that already an imbalance at large beta* should be adjusted as soon as possible. 

  • Jorg and Michi commented this is still possible

  • Could be done at next 75b fill

• Valerie Lang asked why the BSRT and the emittance scans are so different. 

  • Emittance scans are from CMS (IP5) just because the online analysis we get from CMS is a bit easier to process as it doesn’t present the 1min recalibration jump. Michi also looked at the ATLAS one and there seems not to be big difference: both are around 2um emittance. 

• Witold asked that if you take the ratio of the CapSigma product would it show a difference?

  • Michi will do this afterwards. Witold suggests using the ATLAS bunch-by-bunch data over DIP. 

 

CMS (Andrea Massironi)

• (Slide 2) Beamspot Z position seems to have been compensated: at 450 GeV it was +1cm (towards ALICE) and at 6.8 TeV it seems to be centered around 0. Possibly request a few mm tuning

• Slide 6 and slide 7 outlines some requests for emittance scans and luminometers calibration

  • Next 75b fill level CMS at PU=65

  • Coordination ensured between CCC and CMS

  • Program would need to be done in the 1st fill at 400b (that has trains of 36b). 

• At the meeting, Matteo Solfaroli (current LHC coordinator) commented that it is not clear yet that scrubbing can start as soon as tomorrow and the 400b first step may already happened tomorrow Tuesday 25 April

 

ALICE (Sarah Porteboeuf)

• Vertex position looks good in IP2, a few mm shift only. No request for adjustment. 

• Corrected the mu measurement when head-on. Overestimation is corrected. 

• 0-B field fill was completed. Data are expected to be of good quality, but offline analysis will tell. 

• Automatic target lumi level computed as filling scheme steps are increased.

  • Michi asked that before doing scans to call CCC to make sure everything is ready.

• Request to keep the luminosity low before going into collisions.

• A few requests for access, it may happen during the week.

 

ATLAS (Silvia Franchino)

• Slide 3 VdM program is outlined in detail

  • Mu scan can be fitted in the post-TS1 intensity ramp-up .Preferred to stop the beta* leveling and go to 30cm and then let the lumi decay. 

  • More clarifications as it is schedule for July

• Beamspot Z position is at around -3mm

 

LHCb (Niels Tuning)

• Heating is happening in the VELOand for that investigation in the main chiller is needed. For that, the VELO is being warmed up and cannot be operated for the next two days. 

  • Tomography can happen anytime after that. 

• VELO experts do not believe the local aperture limitations are due to VELO. 

  • More investigations needed. 

• Request a mini-VDM scan in the 75b fill, towards the end.

 

Next meeting to be decided, but otherwise if no news it will be on May 8th.