Triangular flow $v_3$ of identified and inclusive particles in Pb+Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV is studied as a function of centrality and transverse momentum within the ...\textsc{hydjet++} model. The model enables one to investigate the influence of both hard processes and final-state interactions on the harmonics of particle anisotropic flow. Decays of resonances are found to increase the magnitude of the $v_3(p_{\rm T})$ distributions at $p_{\rm T} \geq 2$ GeV/$c$ and shift their maxima to higher transverse momenta. The $p_{\rm T}$-integrated triangular flow, however, becomes slightly weakened for all centralities studied. The resonance decays also modify the spectra towards the number-of-constituent-quark scaling fulfillment for the triangular flow, whereas jets are the main source of the scaling violation at the energies available at the CERN Large Hadron Collider (LHC). Comparison with the corresponding spectra of elliptic flow reveals that resonance decays and jets act in a similar manner on both $v_3(p_{\rm T})$ and $v_2(p_{\rm T})$ behavior. Obtained results are also confronted with the experimental data on differential triangular flow of identified hadrons, ratio $v_3^{1/3}(p_{\rm T}) / v_2^{1/2}(p_{\rm T})$ and $p_{\rm T}$-integrated triangular flow of charged hadrons.
The strong suppression of high pT hadrons observed at RHIC has led to the interpretation that energetic partons lose their energy via induced gluon radiation in the hot and dense matter before ...fragmenting into hadrons. The study of heavy quark production can extend our understanding of this scenario. Due to the dead cone effect, the suppression of heavy quark mesons at high pT is expected to be smaller than that observed for charged hadrons at the same energy. The measurement of non-photonic single electrons up to high pT provides information on charm and beauty production. The semi-leptonic decays of D and B mesons are the dominant contribution to the non-photonic electron spectra. The preliminary spectra from p+p, d+Au and Au+Au collisions at =200 GeV have been extracted for mid-rapidity non-photonic electrons in the range 1.5<pT (GeV/c)<10. The corresponding nuclear modification factors (RAA) are presented and show a large suppression in central Au+Au collisions, indicating an unexpectedly large energy loss for heavy quarks in the hot and dense matter created at RHIC. This observed suppression is compared to recent theoretical models.
In heavy-ion collisions at large particle colliders, such asLHC or RHIC, heavy-flavour (charm and beauty) quarks are producedmainly through initial hard scatterings. Therefore, they can serveas the ...probes of properties of the hot medium created in suchcollisions. Additionally, in small collision systems, such asd/p+Au collisions, cold nuclear matter effects can also affect thecharm quark production with respect to p+p collisions.Hadrons, that contain heavy-flavour quarks, could not be directlydetected, thus they are measured via reconstruction of their decayproducts. However, due to a large number of particles produced insuch collisions, separation of the decay products from combinatorialbackground is challenging and advanced statistical analysis isneeded.In this article, we exploitD0 (D0)→K-π+ (K+ π-) decay in order to investigateperformance of several machine learning algorithms with differentimplementation approaches to find the most effective way how toseparate signal from random combinatorial background. For thisstudy, we use HIJING and STAR detector simulation of d+Au collisionsat √(sNN)=200 GeV embedded to the collisions recorded with theSTAR. In this paper we compare deep neural network implementedusing Keras with TensorFlow backend, random forest model implementedusing scikit-learn and boosted decision trees implemented by meansof the Toolkit for Multivariate Data Analysis with ROOT. Describedmethods might be applied on reconstruction of any two-body decay inhigh-energy physics experiments.
We present preliminary measurements of electron production in p+p, d+Au, and Au+Au collisions at
S
N
N
=
200
GeV
for transverse momenta
1.5
GeV
/
c
<
p
T
<
8
GeV
/
c
as a function of centrality. ...These measurements were carried out using the STAR Time Projection Chamber and Barrel Electromagnetic Calorimeter. In this manuscript we describe the measurement techniques used to discriminate electrons from hadrons and the method used to evaluate the non-photonic contributions from semi-leptonic decays of heavy flavor mesons. The observed nuclear modification factors,
R
AA
, of non-photonic electrons indicate at substantial energy loss of heavy quarks at moderate to high
p
T
.
We present STAR measurements of strange hadron ( K S0, Λ , Λ ¯, Ξ -, Ξ ¯+, Ω -, Ω ¯+ , and Φ ) production at midrapidity ( |y|<0.5 ) in Au+Au collisions at sNN = 7.7–39 GeV from the Beam Energy Scan ...Program at the Relativistic Heavy Ion Collider (RHIC). Transverse-momentum spectra, averaged transverse mass, and the overall integrated yields of these strange hadrons are presented versus the centrality and collision energy. Antibaryon-to-baryon ratios ( Λ ¯/ Λ , Ξ ¯+/ Ξ -, Ω ¯+/ Ω - ) are presented as well and used to test a thermal statistical model and to extract the temperature normalized strangeness and baryon chemical potentials at hadronic freeze-out ( μB/Tch and μS/Tch ) in central collisions. Strange baryon-to-pion ratios are compared to various model predictions in central collisions for all energies. The nuclear modification factors ( RCP ) and antibaryon-to-meson ratios as a function of transverse momentum are presented for all collision energies. The K S0 RCP shows no suppression for pT up to 3.5 GeV/c at energies of 7.7 and 11.5 GeV. The Λ ¯/ K S0 ratio also shows baryon-to-meson enhancement at intermediate pT ( ≈2.5 GeV/c ) in central collisions at energies above 19.6 GeV. Lastly, both observations suggest that there is likely a change of the underlying strange quark dynamics at collision energies below 19.6 GeV.
Heavy flavor in STAR Bielcik, J
Journal of physics. Conference series,
05/2008, Letnik:
110, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The strong suppression of high pT hadrons in central Au+Au collisions observed at RHIC is generally interpreted as being a consequence of the energy loss of energetic partons in the hot and dense ...matter before fragmenting. The study of heavy quark production is testing our understanding of this scenario. The recent results on heavy flavor measurements from the STAR experiment at RHIC are presented. The total charm production cross section, extracted from d+Au, Au+Au and Cu+Cu collisions at s√S N N 200 GeV, scales with the number of binary collisions. The high pT non-photonic electron spectra show a strong suppression in central Au+Au collisions. Current theoretical models do not explain this observation satisfactorily. The relative contribution of electrons from bottom decays in the non-photonic electron spectrum predicted in FONLL calculations is consistent with the value determined from azimuthal electron-hadron correlations. The measurement of the T cross section in p+p collision is also presented and is found to be consistent with NLO calculations.
The HADES tracking system Müntz, C.; Markert, J.; Agakichiev, G. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2004, Letnik:
535, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The HADES dielectron spectrometer has recently launched its physics program at the heavy ion synchrotron SIS at GSI Darmstadt. The spectroscopy of vector mesons in heavy ion collisions via their ...dielectron decay channel makes great demands on the HADES tracking system regarding acceptance and spatial resolution. The tracking system is formed out of 24 low-mass, trapezoidal multi-layer drift chambers providing about
30
m
2
of active area. Low multiple scattering in the in total four planes of drift chambers before and after the magnetic field is ensured by using helium-based gas mixtures and aluminum cathode and field wires. First in-beam performance results are contrasted with expectations from simulations. Emphasis is placed on the energy loss information, exploring its relevance regarding track recognition.
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