elliptic flow of d mesons francesco prino for the d2h physics analysis group pwg3, april 12 th 2010
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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
4/
4/
2
2
2
2
2
2
2
2
2
2
2 4
4
4v
NNNNA
vN
vN
OUTIN
OUTIN
OUT
IN
OUTIN
OUTIN
NNNNA
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
uQv
2,
8
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
10
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
13
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
14
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
14.0212.0
222.0
)2.0()2.0(
22
222_
2_
TOT
TOTTOT
OUTIN
OUTIN
OUTIN
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
18
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
19
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
21
D* mass histosD* mass histosCentrality: 30-80%AOD set:N. of analyzed events: 4.04M in the considered centrality interval
R. Grajcarek
22
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.);
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