LPC meeting summary 18-03-2016 - final

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Minutes and Summary

Main purpose of the meeting: Discussion on finding a Z-counting based method to compare the luminosities of ATLAS and CMS on a intermediate timescale and precision.


ATLAS Paul Laycock
Eric Torrence
Witold Kozanecki
CMS Jakob Salfeld-Nebgen
Chris Palmer
LPC Jamie Boyd
Christoph Schwick


Introduction (Jamie Boyd)

Jamie introduced the topic with a few slides. The aim of the exercise is to find a way to compare the luminosiies of ATLAS and CMS with a precision better than the online luminometers (an approximate value of 5% was suggested) and on a time scale of two weeks after the data has been taken. The motivation for this initiative is to have an additional improved comparison at hand in case the online luminosities of both experiments differ by a significant amount (as has happened in the past). This additional method could help to distinguish between real luminosity differences and differences due to imperfections of the online measurements. Z-counting results should have very different systematics to the other online lumi measurements so even if they have a similar level of precision they can still provide useful information.

Experts from both experiments have ideas to implement such a method. Eric suggested an automated offline workflow whereas CMS thinks that an offline based analysis would be too manpower intensive in the long run. Therefore CMS wants to investigate if either a workflow in the offline DQM or in the HLT with a dedicated HLT trigger could be implemented to deliver the desired results on the requested timescale and precision.

Some technical aspects have been discussed:


Witold pointed out that it has to be guaranteed that enough manpower can be provided from both collaborations to support this analysis over the year. Both collaborations will look into the issue. CMS needs to evaluate the required manpower once the preferred method has been worked out.

The present experts of both experiments will check with their respective managements if they would approve such a workflow and if they can find ways to deliver the results of the discussed analysis to the LPC in the time frame suggested above (O(2 weeks)) for the purpose of comparison and for information for LHC experts.

The experiment experts will inform the LPC within approximately one week of the progress on the disucssion with the experiment management, in order to proceed.