Minutes and Summary

Main purpose of the meeting: Meeting dedicated to short-term activities and outcome of the intensity ramp-up as well as an additional look at the post-TS1 activities. 

Filip (Introduction)

Comments regarding luminosity difference between ATLAS/CMS topic: 

• Slide 7. Witold asked if the geometric factors are folded in the measurements from DOROS. Filip responded indeed there are big uncertainties on these measurements and this should be considered. 

• Slide 8. Witold commented that 0.2% is a big number if it comes from ATLAS entirely.

• Slide 11. David commented that in CMS there is no evidence that the luminosity being published has a non-linearity worse than 0.02% (4 times better than the quoted 0.08% difference). Witold commented that it cannot state an upper limit for non-linearity for ATLAS as data must be analyzed, although if the quoted non-linearity would be entirely due to ATLAS, the number struck him as too high. Valerie added that they need the track counting data to be analyzed however LUCID and the BMA detector (known to be very resilient to non-linearities) follow each other at a level lower than the 0.08%. 

  • Filip commented that it is possible the effect is a combination of CMS, ATLAS and machine non-linearities.

• Witold asked to clarify what “extra subtle” effects that can affect the ATLAS/CMS ratio.

  • George, Michi, Filip responded that it is likely a series of machine effects that sums up, not a single one.

 

Jamie asked a question regarding the value of the crossing angle that is being transmitted over DIP because a change has been observed. To be discussed and checked offline. 

• Witold commented that if the extra knob (of 10 urad) is not transmitted, it would be impossible for the experiments to follow changes. It would be important to either transmit both knobs or the reconstructed crossing angle. 

Jamie asked if the reconstructed luminous region from ATLAS/CMS has been compared. Filip responded that it is best to wait for both offline versions as there is a difference between online and offline. Catrin commented that the offline processing from ATLAS for the latest fills (after the change) have not been completed yet. 

Jamie also commented that the filling scheme names are now very long and they don’t show on page 1. Filip responded that this will be fixed and names will be shortened. 

 

From next LPC onwards, it would be important to start discussing post-TS1 activities, see slide 13 for more information. 

 

Niels (LHCb)

Information in the slides. No questions.

 

Gaelle (CMS)

Information in the slides. No questions.

 

Sarah (ALICE)

Discussion to be followed-up regarding the usage of accelerator/machine mode for magnet ramp-up and TPC power on. 

 

Silvia (ATLAS)

• Currently there is no evidence that the emittances are not round. BSRT calibration fill may shed more light, although no clear situation. 

• The BBA request can be fulfilled if a series of success-oriented actions can happened between the 90m beta* run and the ATLAS/CMS VdM. 

• David accepts to prepare a summary list of luminosity calibration changes in CMS. 

 

Discussion on the BSRT calibration fill (LHC, ATLAS)

• Filling scheme is being prepared by the LHC. LHC requests to add a few non colliding bunches.

• Bunch intensities and emittance should be very similar to last year’s.

• ATLAS requests to have DOROS running and in principle this should be available. 

• Stable Beams are not an issue for the LHC, but then there is a need to slot in dedicated wire scanner activities.

• No follow-up yet regarding the non factorization effects, need to ping the relevant experts. 

 

LHC emittance scan strategy

• The LHC would like to clarify a strategy regarding the emittance scans. Ideally, the LHC would like to have them always at a specific moment in the fill to be able to reproduce similar conditions.

• David for CMS showed a slide regarding how invaluable emittance scans are for CMS. 

• ATLAS requested them at the beginning, a scan of 15 points. 

Conclusion is that the LHC can do their scans at every fill at the same moment,scan of 9 points up to roughly 10 seconds per step at b* = 1.2m. The longer scans for ATLAS can be done from time to time on request, with ATLAS calling the CCC well before Stable Beams. Then the scans would be of 15 points and the LHC can use them nevertheless. CMS can maintain their scans at their requests (the penalty is entirely on CMS integrated luminosity), although it is suggested that once we entered into a more stable data taking conditions (i.e. after TS1) these scans should be minimized.

 

Next LPC is currently foreseen for May 22nd (unless the need for an earlier meeting arises).