Monitoring of background events in 2010 run Giuseppe Zito

1. Monitoring of background events in 2010 run Giuseppe Zito PFG/MIG Topical meeting on beam background

2. Method used Classify all events in all PD writing around 20 quantities for event that are relevant for  monitoring. Classification done by a FWLite macro on promptreco data and saved in simple text files available (zipped) from the following address: http://cmstac05.cern.ch/event_display/run1nxxxx/run/eventlist.log.gz or from /castor/cern.ch/user/g/gzito/run.log.gz Quantities found to be interesting for background studies: Number of hit modules Number of clusters Number of tracks Number of vertices Mean cluster charge in Tib Mean cluster charge in TobL6

3. Method used Beginning of classification of run 149442 • Three possible parameters to separate the background sample from good collisions: • 1) cluster density in pixel (histogram 2) • 2) mean cluster charge in TIB (histogram 3) • 3)Number of tracks vs number of hit sistrip modules (histogram4) See: http://indico.cern.ch/getFile.py/access?contribId=8&sessionId=0&resId=0&materialId=slides&confId=82592 https://hypernews.cern.ch/HyperNews/CMS/get/trackerperformance/1015.html

4. Results : typical pp run Run149442 PKAMs selected using red cut PKAM rate in this run 0.007 % This rate is typical of pp runs It varies only slightly around this value during fill lifetime. Run 149442 lasted all fill so this is a kind of average but if we consider fill 1444 with many runs: run %PKAMs 149003 0.00843 149011 0.00448 149058 0.00272 149063 0.00249 21/09/2014

5. Results: typical ion collision run Run 151240 Background events (PKAMs?) selected using red cut PKAM rate 0.034 PKAM rates of other ion collisions runs (not all runs yet processed) run %PKAM 151350 0.018 151351 0.018 151975 0.027 152349 0.032 152706 0.036 21/09/2014

6. Results: selecting a pure PKAMs sample Run 149442 Run 151240 • % background events 0.007 • Mean TIB cluster charge 310 • Typical collision track distribution • % background events 0.034 • Mean TIB cluster charge 401 • No tracks!

7. Results : interesting features • The low energy background events peak on the right of histogram 2 in pp collision has completely disappeared from ion collisions • The high energy background peak in ion collisions has moved from 310 to 401. • Most of the ion collisions PKAMs have no tracks at all; instead most of the pp PKAMs have tracks and also one or more vertices • More than 90% of PKAMs in ion collisions have TT42 XOR TT43 true (in this case 95%). In pp collisions this never happens. • Low energy background events have very small number of pixel clusters (<150)

8. Solution of puzzle of increase of Tib mean charge Run 133877 • Looking at Tib mean charge distribution in one of the last pp runs before the new era of many PD, the average tib cluster charge for PKAMs is 400 exactly like it is now with ion collisions. • Could this be connected to the fact that in first pp runs PKAMs were mostly with very few tracks and no vertex at all, like it is now for ion collisions?. • Yes, in fact the number of PKAMs with vertices ha increased steadily with increasing beam intensity and number of bunches. (For example:133877 8%, 140240 41%, 142442 93%) • So the solution of the puzzle is that in last pp collisions most of the PKAMs overlap normal collision events and this decreases the mean cluster charge.

9. Is PKAM rate dependent on trigger? Run 149442 has 93% PKAMs overlapping collision events 7% pure PKAMs (83% of these have no tracks at all) Is this rate the same for each one of the 13 PD : i.e. does this rate depend on trigger? The answer is no (but see the complete details in the hypernews post below). PKAMs are present in all PD with similar rate. Only 3 PD seem to have a rate doubled in comparison to the other PD (Commissioning, JetMETTauMonitor and METFwd). https://hypernews.cern.ch/HyperNews/CMS/get/tracker-performance/1166/2/1/1.html

10. Low energy background events Run 140158 Run 136100 Run 142135 Run 143727 The histogram 3 on Tib mean charge contains sometime “structures” like peaks, clouds, vertical lines on the right of the central peak produced by collision events. The origin of these structures can be some problem during a few LS (I process all LS good and bad). The most common structure is a peak at around 100 produced by low energy beam background. This peak is present in many (but not all) runs. I show here just 4 examples.

11. Conclusion The presence of background events has been monitored systematically in all events and all runs. Although the limited number of variables used doesn’t allow me to do sophisticated analysis (for example on cluster quality) and compute the exact rate of these events, nevertheless it is enough to see if there is a new problem or if the things are gradually changing in time. The main result of these studies is that high energy background event are present in all pp runs at a rate of around 0.007 % and in all ion collision runs at a rate of around 0.025 %. These events in last high intensity pp runs are almost always overlapped on normal collisions. In addition low energy background events are present sporadically.

12. Extra slides 21/09/2014

13. Extra slides Average cluster charge of high energy background events in ion collisions 21/09/2014

14. Extra slides Average cluster charge in ion collisions 21/09/2014

15. Extra slides Run 139458 The unique run with a sizeable amount of electronic noise events 21/09/2014