Elliptic flow of D mesonsElliptic flow of D mesons

Francesco Prinofor the D2H physics analysis group

PWG3, April 12th 2010

2

Goal of the analysisGoal of the analysis

....2cos2)cos(212 210 RPRP vvN

ddN

RPv 2cos2

Measure the elliptic flow (v2) of D mesons from their fully reconstructed hadronic decay channels

Elliptic flow coefficient 2cos21 2v

3

Methods : Event planeMethods : Event planeEvent plane method(s): Estimate the reaction plane from

track azimuthal anisotropy

Need to subtract from Q vector the contribution of D-meson daughters Alternatively: use azimuthal distribution of VZERO signals

Build the invariant mass of D0->K, D+->Kand D*->D0 ->K candidates in bins of = D-2.

Extract signal vs. and then fit to get v2. Three approaches implemented (see next)

Correct for event plane resolution

N

iii

N

iii

n

nw

nwQ

1

1

sin

cos

N

iii

N

iii

xn

ynn

nw

nw

nQQ

n1

11

,

,1

cos

sintan1tan1

x

y

2

D+

φφ

4

EP method 1: N bins of EP method 1: N bins of φφExtract D meson yield in N bins of φ How many bins in φ can we afford, depends a lot on statistical

significance we will be able to achieve N=8 would be ideal, but requires big statistics

Fit the number of D mesons vs. φ with K[1 + 2v2cos(2φ) ] Possibly sum D0 and D+ yields

Toy MC simulation:• 1000 D-mesons generated• Input v2 = 0.1

5

EP method 2: 2 bins of EP method 2: 2 bins of φφNon-zero v2 difference between numbers of D ± in-plane and out-of-planeExtract number of D-mesons in 90º “cones”: in-plane (-45<φ<45 U 135<φ<225) out-of-plane (45<φ<135 U 225<φ<315)

Quantify anisotropy as:

In case of only v2 and perfect 2 resolution:

dNdNN

dNdNN

DDOUT

DDIN

)()(

)()(

4/7

4/5

4/3

4/

4/5

4/3

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2 4

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6

EP method 3: cos(2EP method 3: cos(2φφ) vs. mass) vs. massBuild cos(2φ) vs. mass distribution in the signal mass region and in the side-bands and then subtract contribution of side bands from peak region

Toy MC simulation

7

Methods: Scalar ProductMethods: Scalar ProductScalar Product method: 2-particle correlation method

Basically a refinement of the Event Plane method Event divided in 2 sub-events Qn

a and Qnb.

Sub-events defined in ranges: a=[-0.9,-0.5] , b=[0.5,0.9] Elliptic flow calculated as:

where un,i=e-ini is the unit momentum vector of the analyzed track/candidate auto-correlation removed by subtracting contribution of particle i to Qn.

Elliptic flow of signal extracted from the v2 of candidates measured in three invariant mass region (signal +2 side bands)

bn

an

innn

QQ

uQv

2,

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Status of the codeStatus of the codeAll this methods implemented in dedicated analysis tasks Task to fill histos of for D-meson candidates passing the cuts

has been developed and tested already with p-p events using random event plane

Code to compute the event plane from VZERO developed and implemented in our task

Event plane from tracks: Q-vector from full and sub-events by calling PWG2 flow libraries in our taskContribution of D-meson daughters subtracted from Q-vector inside our taskBeing compared with the output of the recently developed event plane task (by

Johanna Gramling) Code for Scalar Product method from PWG2-flow libraries

Allow for track selection, daughter removal from Q-vectorMulti-band approach tested and validated for and K0s -> can be easily extended

to 3-prong decays

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ResultsResults

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Event plane from VZEROEvent plane from VZEROCentrality: 30-80%AOD set: 040 Run-by-run correction for event plane flattening from the

sector occupancyTried also re-centering after efficiency equalization, bit does not improve Expected Better performance in pass2

Run Number

2 event plane (rad)

without correctionwith correction

G. Ortona

11

Event plane from TracksEvent plane from TracksCentrality: 30-80%AOD set 040 pt, phi weights not used

Should cure the small deviation from flatness that is observed

R. Grajcarek

12

DD00 mass histos in 2 bins of mass histos in 2 bins of φφCentrality: 30-80%AOD set: 040N. of analyzed events: 6.97M, 3.02M in

the selected centrality class

C. Bianchin

5<pt<8 GeV/c pt>8 GeV/c

In plane

Out of plane

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DD++ mass histos in 2 bins of mass histos in 2 bins of φφAOD set: 040Centrality: 30-80%N. of analyzed events: 10.56M 5.24M in the considered centrality class

G. Ortona

In plane

Out of plane

3<pt<8 GeV/c pt>8 GeV/c

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D* mass histos in 2 bins of D* mass histos in 2 bins of φφCentrality: 30-80%AOD set:N. of analyzed events: 4.04M in the considered centrality interval

R. Grajcarek

15

From counts to anisotropyFrom counts to anisotropyThe statistics is marginal to allow a physically significant measurement of anisotropy/v2

Back-of-the-envelope: Statistical significance (in pt>8 GeV, 2 φ bins) ≈ 3 with 10M

events Assuming to gain x3 statistics

In each bin -> significance ≈ 5 relative stat. error ≈ 20%Propagating to anisotropy:

to be compared with expected v2 signals of the order of 0.1-0.15

Also: Expect better significance from pass2 due to improved

reconstruction + resolutions + PID Maybe still room to improve the cuts

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TOT

TOTTOT

OUTIN

OUTIN

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OUTNINNA N

NN

NNNN

NN

16

Mass vs. cos(2Mass vs. cos(2))Centrality: 30-80%AOD set: 040N. of analyzed events: 6.97M, 3.02M in the selected centrality class

C. Bianchin

17

SP method (1)SP method (1)Centrality: 30-80%AOD set: 040 Global tracks used as reference particles

C. PerezC. Ivan

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SP method (2)SP method (2)Centrality: 30-80%AOD set: 040Number of analyzed events: 2.67M 1.2M in the selected centrality class

C. PerezC. Ivan

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Conclusions and perspectivesConclusions and perspectivesThe tools for the analysis have been developed and tested and are ready to be usedDifferent methods implemented From their comparison, insight into systematics

Next: The analysis will continue on pass2, where more statistics, better

resolution and PID performance should be available. Maybe, also room for improvement from cut optimization.

Available statistics is very low e.g. for the EP method no more than 2 bins possible. Does not allow to do any claim on charm thermalization or

anisotropy introduced by path-length dependence of energy loss

Our (D2H) feeling: not enough for a talk at QM Performance plots describing the analysis steps can go in the D-

meson posters

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Backup slidesBackup slides

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D* mass histosD* mass histosCentrality: 30-80%AOD set:N. of analyzed events: 4.04M in the considered centrality interval

R. Grajcarek

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Track selection for SP and QCTrack selection for SP and QCSelection cuts for RP tracks: cuts->SetParamType(kGlobal); cuts->SetPtRange(0.2,5.); cuts->SetEtaRange(-0.8,0.8); cuts->SetMinNClustersTPC(70); cuts->SetMinChi2PerClusterTPC(0.1); cuts->SetMaxChi2PerClusterTPC(4.0); cuts->SetMinNClustersITS(2); cuts->SetRequireITSRefit(kTRUE); cuts->SetRequireTPCRefit(kTRUE); cuts->SetMaxDCAToVertexXY(0.3); cuts->SetMaxDCAToVertexZ(0.3); cuts->SetAcceptKinkDaughters(kFALSE); cuts->SetMinimalTPCdedx(10.);