Monitoring of background events in 2010 run

Giuseppe Zito

21/04/23 PFG/MIG Topical meeting on beam background

21/04/23

Method usedMethod 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

Method usedMethod used

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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)

Beginning of classification of run 149442

See:http://indico.cern.ch/getFile.py/access?contribId=8&sessionId=0&resId=0&materialId=slides&confId=82592https://hypernews.cern.ch/HyperNews/CMS/get/trackerperformance/1015.html

Results : typical pp runResults : typical pp run

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Run 149442

PKAMs selected using red cutPKAM 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 thisis a kind of average but if we consider fill 1444 with many runs:

run %PKAMs149003 0.00843149011 0.00448149058 0.00272149063 0.00249

Results: typical ion collision runResults: typical ion collision run

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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 %PKAM151350 0.018151351 0.018151975 0.027152349 0.032152706 0.036

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Results: selecting a pure PKAMs sampleResults: 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!

Results : interesting featuresResults : interesting features

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1) The low energy background events peak on the right of histogram 2 in pp collision has completely disappeared from ion collisions

2) The high energy background peak in ion collisions has moved from 310 to 401.

3) 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

4) More than 90% of PKAMs in ion collisions have TT42 XOR TT43 true (in this case 95%). In pp collisions this never happens.

5) Low energy background events have very small number of pixel clusters (<150)

Solution of puzzle of increase of Tib mean Solution of puzzle of increase of Tib mean chargecharge

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• 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.

Run 133877

21/04/23

Is PKAM rate dependent on trigger?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 hypernewspost below).PKAMs are present in all PD with similar rate. Only 3 PD seem tohave 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

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Low energy background eventsLow energy background events

Run 136100 Run 140158

Run 142135 Run 143727

The histogram 3 on Tib mean charge contains sometime “structures” likepeaks, clouds, vertical lines on the right of the central peak produced bycollision events. The origin of these structures can be some problem duringa few LS (I process all LS good and bad). The most common structure isa 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.

ConclusionConclusion

21/04/23

The presence of background events has been monitored systematicallyin all events and all runs.

Although the limited number of variables used doesn’t allow me to dosophisticated analysis (for example on cluster quality) and compute theexact rate of these events, neverthelessit 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 eventare 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 intensitypp runs are almost always overlapped on normal collisions.

In addition low energy background events are present sporadically.

Extra slidesExtra slides

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Extra slidesExtra slides

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Average cluster charge of high energy background events in ion collisions

Extra slidesExtra slides

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Average cluster charge in ion collisions

Extra slidesExtra slides

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Run 139458

The unique run with a sizeable amountof electronic noise events