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