17 research outputs found
Recommended from our members
Azimuthal correlations of high transverse momentum jets at next-to-leading order in the parton branching method
AbstractThe azimuthal correlation,
Δ
ϕ
12
, of high transverse momentum jets in pp collisions at
s
=
13
TeV is studied by applying PB-TMD distributions to NLO calculations via MCatNLO together with the PB-TMD parton shower. A very good description of the cross section as a function of
Δ
ϕ
12
is observed. In the back-to-back region of
Δ
ϕ
12
→
π
, a very good agreement is observed with the PB-TMD Set 2 distributions while significant deviations are obtained with the PB-TMD Set 1 distributions. Set 1 uses the evolution scale while Set 2 uses transverse momentum as an argument in
α
s
, and the above observation therefore confirms the importance of an appropriate soft-gluon coupling in angular ordered parton evolution. The total uncertainties of the predictions are dominated by the scale uncertainties of the matrix element, while the uncertainties coming from the PB-TMDs and the corresponding PB-TMD shower are very small. The
Δ
ϕ
12
measurements are also compared with predictions using MCatNLO together Pythia8, illustrating the importance of details of the parton shower evolution.</jats:p
Azimuthal correlations of high transverse momentum jets at next-to-leading order in the parton branching method
AbstractThe azimuthal correlation,
Δ
ϕ
12
, of high transverse momentum jets in pp collisions at
s
=
13
TeV is studied by applying PB-TMD distributions to NLO calculations via MCatNLO together with the PB-TMD parton shower. A very good description of the cross section as a function of
Δ
ϕ
12
is observed. In the back-to-back region of
Δ
ϕ
12
→
π
, a very good agreement is observed with the PB-TMD Set 2 distributions while significant deviations are obtained with the PB-TMD Set 1 distributions. Set 1 uses the evolution scale while Set 2 uses transverse momentum as an argument in
α
s
, and the above observation therefore confirms the importance of an appropriate soft-gluon coupling in angular ordered parton evolution. The total uncertainties of the predictions are dominated by the scale uncertainties of the matrix element, while the uncertainties coming from the PB-TMDs and the corresponding PB-TMD shower are very small. The
Δ
ϕ
12
measurements are also compared with predictions using MCatNLO together Pythia8, illustrating the importance of details of the parton shower evolution.</jats:p
Event-by-event correlations between () hyperon global polarization and handedness with charged hadron azimuthal separation in Au+Au collisions at from STAR
Global polarizations () of () hyperons have been
observed in non-central heavy-ion collisions. The strong magnetic field
primarily created by the spectator protons in such collisions would split the
and global polarizations (). Additionally, quantum chromodynamics (QCD) predicts
topological charge fluctuations in vacuum, resulting in a chirality imbalance
or parity violation in a local domain. This would give rise to an imbalance
() between left- and right-handed
() as well as a charge separation along the magnetic field,
referred to as the chiral magnetic effect (CME). This charge separation can be
characterized by the parity-even azimuthal correlator () and
parity-odd azimuthal harmonic observable (). Measurements of
, , and have not led to definitive
conclusions concerning the CME or the magnetic field, and has not
been measured previously. Correlations among these observables may reveal new
insights. This paper reports measurements of correlation between and
, which is sensitive to chirality fluctuations, and correlation
between and sensitive to magnetic field in Au+Au
collisions at 27 GeV. For both measurements, no correlations have been observed
beyond statistical fluctuations.Comment: 10 pages, 10 figures; paper from the STAR Collaboratio
Observation of the electromagnetic field effect via charge-dependent directed flow in heavy-ion collisions at the Relativistic Heavy Ion Collider
The deconfined quark-gluon plasma (QGP) created in relativistic heavy-ion
collisions enables the exploration of the fundamental properties of matter
under extreme conditions. Non-central collisions can produce strong magnetic
fields on the order of Gauss, which offers a probe into the
electrical conductivity of the QGP. In particular, quarks and anti-quarks carry
opposite charges and receive contrary electromagnetic forces that alter their
momenta. This phenomenon can be manifested in the collective motion of
final-state particles, specifically in the rapidity-odd directed flow, denoted
as . Here we present the charge-dependent measurements of
near midrapidities for , , and
in Au+Au and isobar (Ru+Ru and
Zr+Zr) collisions at 200 GeV, and
in Au+Au collisions at 27 GeV, recorded by the STAR detector at the
Relativistic Heavy Ion Collider. The combined dependence of the signal on
collision system, particle species, and collision centrality can be
qualitatively and semi-quantitatively understood as several effects on
constituent quarks. While the results in central events can be explained by the
and quarks transported from initial-state nuclei, those in peripheral
events reveal the impacts of the electromagnetic field on the QGP. Our data put
valuable constraints on the electrical conductivity of the QGP in theoretical
calculations
Hyperon polarization along the beam direction relative to the second and third harmonic event planes in isobar collisions at = 200 GeV
The polarization of and hyperons along the beam
direction has been measured relative to the second and third harmonic event
planes in isobar Ru+Ru and Zr+Zr collisions at = 200 GeV. This
is the first experimental evidence of the hyperon polarization by the
triangular flow originating from the initial density fluctuations. The
amplitudes of the sine modulation for the second and third harmonic results are
comparable in magnitude, increase from central to peripheral collisions, and
show a mild dependence. The azimuthal angle dependence of the
polarization follows the vorticity pattern expected due to elliptic and
triangular anisotropic flow, and qualitatively disagree with most hydrodynamic
model calculations based on thermal vorticity and shear induced contributions.
The model results based on one of existing implementations of the shear
contribution lead to a correct azimuthal angle dependence, but predict
centrality and dependence that still disagree with experimental
measurements. Thus, our results provide stringent constraints on the thermal
vorticity and shear-induced contributions to hyperon polarization. Comparison
to previous measurements at RHIC and the LHC for the second-order harmonic
results shows little dependence on the collision system size and collision
energy.Comment: 6 pages, 5 figures, Published in Physical Review Letter
Elliptic Flow of Heavy-Flavor Decay Electrons in Au+Au Collisions at = 27 and 54.4 GeV at RHIC
We report on new measurements of elliptic flow () of electrons from
heavy-flavor hadron decays at mid-rapidity () in Au+Au collisions at
= 27 and 54.4 GeV from the STAR experiment. Heavy-flavor
decay electrons () in Au+Au collisions at =
54.4 GeV exhibit a non-zero in the transverse momentum ()
region of 2 GeV/ with the magnitude comparable to that at
GeV. The measured at 54.4 GeV is
also consistent with the expectation of their parent charm hadron
following number-of-constituent-quark scaling as other light and strange flavor
hadrons at this energy. These suggest that charm quarks gain significant
collectivity through the evolution of the QCD medium and may reach local
thermal equilibrium in Au+Au collisions at GeV. The
measured in Au+Au collisions at 27
GeV is consistent with zero within large uncertainties. The energy dependence
of for different flavor particles () shows an
indication of quark mass hierarchy in reaching thermalization in high-energy
nuclear collisions.Comment: 12 pages, 7 figures, 1 tabl
Measurement of electrons from open heavy-flavor hadron decays in Au+Au collisions at GeV with the STAR detector
We report a new measurement of the production of electrons from open
heavy-flavor hadron decays (HFEs) at mid-rapidity ( 0.7) in Au+Au
collisions at GeV. Invariant yields of HFEs are
measured for the transverse momentum range of GeV/ in
various configurations of the collision geometry. The HFE yields in head-on
Au+Au collisions are suppressed by approximately a factor of 2 compared to that
in + collisions scaled by the average number of binary collisions,
indicating strong interactions between heavy quarks and the hot and dense
medium created in heavy-ion collisions. Comparison of these results with models
provides additional tests of theoretical calculations of heavy quark energy
loss in the quark-gluon plasma
Recommended from our members
Elliptic flow of heavy-flavor decay electrons in Au+Au collisions at s NN = 27 and 54.4 GeV at RHIC
We report on new measurements of elliptic flow (v2) of electrons from heavy-flavor hadron decays at mid-rapidity (|y|<0.8) in Au+Au collisions at sNN = 27 and 54.4 GeV from the STAR experiment. Heavy-flavor decay electrons (eHF) in Au+Au collisions at sNN = 54.4 GeV exhibit a non-zero v2 in the transverse momentum (pT) region of pT< 2 GeV/c with the magnitude comparable to that at sNN=200 GeV. The measured eHF v2 at 54.4 GeV is also consistent with the expectation of their parent charm hadron v2 following number-of-constituent-quark scaling as other light and strange flavor hadrons at this energy. These suggest that charm quarks gain significant collectivity through the evolution of the QCD medium and may reach local thermal equilibrium in Au+Au collisions at sNN=54.4 GeV. The measured eHF v2 in Au+Au collisions at sNN= 27 GeV is consistent with zero within large uncertainties. The energy dependence of v2 for different flavor particles (π,ϕ,D0/eHF) shows an indication of quark mass hierarchy in reaching thermalization in high-energy nuclear collisions