Twiki contents:

Centrality Studies for LHC13 d,e,f (EMCal triggered periods)

Motivation

Motivation is to start the study of the different biases, period by period, that we need cope with in the analysis of QpPb HFE. The periods studied correspond to the ones where the EMCal triggers were activated. 4 types of triggers were studied (EG1,EG2,EMC7 and INT7).

According to https://twiki.cern.ch/twiki/bin/viewauth/ALICE/PACentStudies, the estimators available are:

• V0M = V0A+C multiplicity
• V0A = V0A multiplicity
• V0C = V0C multiplicity
• V0MEq = V0A+C multiplicity, signal equalized azimuthally
• V0AEq = V0A multiplicity, signal equalized azimuthally
• V0CEq = V0C multiplicity, signal equalized azimuthally
• TRK = N. of tracks
• CND = N. of tracks according to the candle condition (pT>0.5 GeV and |y|<0.8)
• CL1 = N. of clusters in layer 1
• ZNA = Energy in Zero-Degree Neutron Calorimeter (A side, for pPb)
• ZNC = Energy in Zero-Degree Neutron Calorimeter (C side,for Pbp)

Period LHC13f has an opposite direction of the beam (Pb-p) so, ZNC was also computed. So V0M, V0A, V0C, ZNA and ZNC were studied

Data and Total Number of events

LHC13d

Estimator	EG1	EG2	EMC7	INT7
V0M	220.3 kevts	82.5 kevts	83.3 kevts	576.4 kevts
V0A	220.6 kevts	82.7 kevts	83.4 kevts	577.2 kevts
ZNA	218.8 kevts	82.0 kevts	82.8 kevts	556.6 kevts

LHC13e

Estimator	EG1	EG2	EMC7	INT7
V0M	441.1 kevts	210.1 kevts	190.5 kevts	1315.2 kevts
V0A	450.7 kevts	212.8 kevts	193.0 kevts	1337.1 kevts
ZNA	439.0 kevts	208.9 kevts	189.6 kevts	1265.6 kevts

LHC13f

Estimator	EG1	EG2	EMC7	INT7
V0M	460.1 kevts	155.1 kevts	150.1 kevts	869.2 kevts
V0C	461.8 kevts	156.7 kevts	151.8 kevts	877.6 kevts
ZNC	464.8 kevts	156.9 kevts	152.2 kevts	853.7 kevts

Results

Note that all the results were normalised by the number of events.

V0M

Figure 1 - Centrality distributions for V0M (LHC13def)

V0A,C

Figure 2 - Centrality distributions for V0M (LHC13def)

ZNA,C

Figure 3 - Centrality distributions for ZNA,C (LHC13def)

Some Conclusions

The difference of shape among the three different periods is up to around 5% for ZNA and ZNC. Not only ZNC(LHC13f) x ZNA (LHC13d), but also ZNA(LHC13d) x ZNA(LHC13e), which may reflect that ZNC is not causing too much systematic bias (maybe one can check track and EMCal cluster distributions). For the V0 estimators, which are used for a cross check analysis, V0M provided very small difference among the three periods.

-- MarcelFigueredo - 2016-07-26