Heavy Flavor Lepton

Heavy flavor leptons provide an extra handle on the open heavy flavor mesons, since they come from semi-leptonic decays of D and B mesons with significant branching ratios. Once produced, leptons do not participate in the strong interaction in the later stages of the collision, and remain a clean probe into the whole evolution of the system. Apart from TPC and TOF, BEMC is used to improve electron identification, and MTD is used for muon detection.

Heavy flavor muons

Non-photonic electrons

Hidden Heavy Flavor

J/psi suppression was one of the proposed QGP signatures in the early days. Later, various cold nuclear matter effects were brought up to complicate the interpretation of J/psi measurements. Still, the study of J/psi collective motion deepens our understanding of the coalescence mechanism and the charm quark collectivity. We also reconstructed Upsilon and observed the suppression of Upsilon(1S+2S+3S).



Open Heavy Flavor

More than 99% of charm quarks hadronize into open charm, D mesons. So the measurement of D mesons is a must for the determination of charm cross section. Due to the short life time, the low production rate and the high combinatorial background, the direct reconstruction of D mesons is difficult with the TPC pointing resolution. HFT will be employed to reconstruct the displaced vertex and greatly suppress the combinatorial background. This will also enable the D0 flow analysis, to ascertain the charm quark collectivity. Other open heavy flavor hadrons like Ds and Lambdac will also be studied with HFT.

D mesons

D0 v1 analysis documents

This page is designed to assemble the D0 v1 analysis details.

==> Section 1 <===

This analysis is based on the Au+Au collisions at \snn=200 GeV collected by the STAR experiments during the 2014 and 2016 runs. The 2014 run is processed with P16id library. The 2016 run is processed with P16ij. The analysis uses picoDst which is produced from MuDst. The details of the datasets can be found at:

Event cuts:

A minimum-bias trigger is used. For run14, it denoted as “vpdmb-5-p-nobsmd” (450005,450015,450025) and “vpdmb-5-p-nobsmd-hlt” (450050,450060). For run16, it is denoted as “VPDMB-5-p-sst” (520001, 520011, 520021, 520031, 520041, 520051). The event selection cuts are:
1) |primary vertex in z direction| < 6 cm
2) |primary vertex in transverse direction| < 2 cm
3) |primary vertex z – vpdVz| < 3 cm 
4)     ! ( PV_x < e-5 & PV_y < e-5 & PV_z < e-5)
vpdVz is the vertex z position calculated from time difference measured by two sides of VPD. 
After passing cuts there are 831 M events in run14 and 990 M events in run16.

 Good run list:


==> Section 2 <===
D0 reconstruction
Single track cuts:

1Daughter selection
1) Global tracks
2) pT > 0.6 GeV/c
3) |eta| < 1
4) nHitsFit ≥ 20, in TPC
5) nHits/nHitsMax ≥ 0.52
6) HFT track: hasPxl1Hit() && hasPxl2Hit() && (hasIstHit() || hasSstHit())
7) fabs(geometricSignedDistance(pVtx)) > 0.005


pion PID:
isTPCPion = |nSigmaPion| < 3.0, based on TPC dE/dx
If TOF is available: |1/β − 1/βexp| < 0.03 and isTPCPion
If TOF is not available: isTPCPion 
kaon PID:
isTPCKaon = |nSigmaKaon| < 2.0, based on TPC dE/dx 
If TOF is available: |1/β − 1/βexp| < 0.03 and isTPCKaon
If TOF is not available: isTPCKaon 

D0 topological cuts:

The geometrical cuts are same as in the D0 v2 analysis, which is from TMVA estimation. (https://drupal.star.bnl.gov/STAR/system/files/note_6.pdf). The values are:

==> Section 3 <===
Efficiency calculation and spectra

==> Section 4 <===
D0 v1 results

==> Section 5 <===
Charged hadron v1 (Run14 vs. Run16)

v2 in different rapidity bins Run14 vs. Run16

Luminosity dependence

Link to Overleaf page for analysis note preparation: