T.Ruf, N.Brook, R.Kumar, M.Meissner,
S.Miglioranzi , U.Uwer D.Voong
Charge Particle Multiplicity
Disclaimer: Work has started only recently! I am not an expert of “soft” minimum bias physics.
Motivation
2
pt , charged particle distribution in data and MC
Comparison for prompt particles:Improve MC generator tuning
challenge
Learn about tracking: ghosts rates, track efficiency, secondaries from material interactionSystematic studies.
pt [GeV]
Multiplicity
Long tracks.
Long tracks.
… ALICE …
3
Data set
4
Micro bias 7 TeV data (small pile up, beam gas very small)
MCData
Checks: Charge Asymmetry
5
ASym = (0.7 ± 0. 2) % (MC 0.90.1)
magnet down
ASym = (0.6 ± 0. 2) % (MC 1.00.2)
magnet up
7 TeV DataPositive Negative
Systematics: Left-right Asymmetry
6
end of Velofirst T-Station
magnet down
+
-
+-
ALR = ( 2.8 ± 0.2)%
ALR = (1.2 ± 0.1)%
Systematics: Left-right Asymmetry
7
end of Velofirst T-Station
magnet up
ALR = (-0.4 ± 0.2)%
ALR = (-0.8 ± 0.1) %
Long track multiplicity (1)
8
higher ghosts rate
Mean:11.9 (data)10.1 (MC)
Mean:11.1 (data) 9.7 (MC)
Track Chi2 Multiplicity
B
+ 18%
+ 14%
Different ghost contributions!
Long track multiplicity (2)
9
require 1 PV and track_IPSig < 10
Mean:11.6 (data)10.9 (MC)
IP significance cut clearly rejects ghosts but requires a min. number of tracks!
More work/thinking needed to define what we want to measure and how to measure the ghost level.
No efficiency corrections applied
better agreement
effect of min. #tracks to form PV
+ 6%
Truncated <pt> distribution
10
Less dependent on efficiency / ghost level if one requires minimum pt (assumes approx. constant efficiency / ghost rate for pt > pmin)
Idea: M.Schmelling
pt > 400 MeV pt > 200 MeV
<pt> w/ track efficiency correction
11
2-dim (pt ,) MC efficiency
Efficiency vs pt (2<<5)
pt
Data
MC
MC efficiency corrected <pt>
>200 MeV
>400 MeV
Efficiency correction necessary.Ghost rates also not const. over pt
Conclusion
12
Baron Münchhausen, trying to pull himself out of the swamp.
• Track multiplicity analysis has started. Interpretation of distributions tricky:
Effects from tracking & charged particle production.
• Track efficiency from K0 analysis.
• Need good idea to measure ghost rate
• <pt> is simpler (eff. & ghosts less important) but … Makes a truncated mean sense?
13
pt eta Verteilungen Daten, MC, comparison
Tuning des LHCb MC Phyiscs
Challenges: Track efficiency, ghost ratesData set: April / May micro bias events
Low lumi (pile up small), beam gas also small (Rajev plot)
Unterschied in multiplicitaets verteiltung daten/MC – unterschiedliche Unterschiede je nachdem was man macht!
Systematische Studien (manche Veretkungen stimme erstaunlich gut).
Welche tuning Paramter , Mean pt in Daten groesser als in MC – kann man durch fixen des kt Paramerters die Verteilungen fixien ???
Koennen wir damit schon einen grossteil der 30% Occupancy erklaeren die wir in TT und IT, OT sehen ?
Conlcusion:
Pt Verteilung sicher moeglich (efficency correctur = acceptanz)
Multiplizitaet: Fragen,, … Ghostrate?, Efficency mit pt Cut – K0