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 p t, 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 interaction Systematic studies. p t [GeV] Multiplicity Long tracks.

… ALICE … 3

Data set 4 Micro bias 7 TeV data (small pile up, beam gas very small) MC Data

Checks: Charge Asymmetry 5 A Sym = (0.7 ± 0. 2) % (MC ) magnet down A Sym = (0.6 ± 0. 2) % (MC ) magnet up 7 TeV Data Positive Negative

Systematics: Left-right Asymmetry 6 end of Velo first T-Station magnet down A LR = ( 2.8 ± 0.2)% A LR = (1.2 ± 0.1)%

Systematics: Left-right Asymmetry 7 end of Velo first T-Station magnet up A LR = (-0.4 ± 0.2)% A LR = (-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 distribution 10 Less dependent on efficiency / ghost level if one requires minimum p t (assumes approx. constant efficiency / ghost rate for p t > p min ) Idea: M.Schmelling p t > 400 MeVp t > 200 MeV

w/ track efficiency correction 11 2-dim (p t, ) MC efficiency Efficiency vs p t (2< <5) ptpt Data MC MC efficiency corrected >200 MeV >400 MeV Efficiency correction necessary. Ghost rates also not const. over p t

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 K 0 analysis. Need good idea to measure ghost rate is simpler (eff. & ghosts less important) but … Makes a truncated mean sense?

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pt eta Verteilungen Daten, MC, comparison Tuning des LHCb MC Phyiscs Challenges: Track efficiency, ghost rates Data 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