star focus: Precise Measurements of the Open Charm Meson Prodution at STAR

The STAR Collaboration has recently published “Centrality and transverse momentum dependence of D0-meson production at mid-rapidity in Au + Au collisions at √sNN = 200 GeV,” in Physical Review C 99, 034908 (2019).

This paper presents a new measurement of D0 meson production enabled by the Heavy Flavor Tracker (HFT) high-resolution silicon detector system in Au + Au collisions at √sNN = 200 GeV. Compared to the previous measurement with the TPC only, the new data contain greatly improved precision which allows us to systematically investigate the D0 meson production in wide centrality and transverse momentum regions. The new improved data are expected to further constrain our understanding of the charm medium interaction as well as to better determine the medium transport parameters together with the previous publication on D0 elliptic flow measurement.

Left: D0 RCP for different centrality classes with the 40–60% spectrum as the reference compared to that of other light and strange mesons (π, Κs, and φ) as well as the model calculations. Right: Integrated D0 cross section per nucleon-nucleon collision at mid-rapidity for pT > 0 (a) and pT > 4 GeV/c (b) as a function of centrality Npart. The green boxes on the data points depict the overall normalization uncertainties in p + p and Au + Au data respectively.

The nuclear modification factors RCP of D0 meson are shown in the left figure, and show significantly suppression at high pT and the suppression level is comparable to that of light hadrons at pT > 5 GeV/c, indicates that charm quarks lose significant energy when traversing through the hot QCD medium. Right figure shows the pT-integrated D0 production cross section per nucleon-nucleon collisions in Au + Au collisions together with the measurement in p + p. The full-pT integrated cross section in Au + Au collisions seem to be smaller than that in p + p collisions by 1.5σ, indicating that cold nuclear matter effects (CNM) and/or hadronization through quark coalescence may play an important role in Au + Au collisions. While for pT > 4GeV/c, it shows a clear decreasing trend from peripheral to mid-central and central collisions.

Slope parameter Teff from the exponential function fits to the mT spectra for different particles in central Au + Au collisions. The dashed lines depict linear function fits to π, K, p and φ, Ξ, Ω, D0 respectively.

The low pT D0 spectra are fit to various thermal model inspired functions to study the D0 meson radial collectivity. The observations suggest that D0 hadrons show a radial collective behavior with the medium, but freeze-out from the system earlier and gain less radial collectivity compared to π, K, and p particles, while D0 mesons have similar kinetic freeze-out properties as multi-strange-quark hadrons such as φ and Ξ.

The paper also presents a detail description of the HFT detector performance and efficiency corrections for charmed hadron reconstruction, particularly the usage of data-driven simulation method that may inspire the efficiency correction procedure for other detectors.

Posted March 27, 2018

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