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Measurement of directed flow in Au+Au collisions at $\sqrt{s_{NN}}=$ 19.6 and 27 GeV with the STAR Event Plane Detector
Nuclear Experiment · Submitted 22 Jun 2024
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim The model comparison also indicates $v_{1}$ at large $\eta$ might be sensitive to the QGP phase transition.
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The abstract, sentence by sentence
In heavy-ion collision experiments, the global collectivity of final-state particles can be quantified by anisotropic flow coefficients ($v_n$). The first-order flow coefficient, also referred to as the directed flow ($v_{1}$), describes the collective sideward motion of produced particles and nuclear fragments in heavy-ion collisions. It carries information on the very early stage of the collision, especially at large pseudorapidity ($\eta$), where it is believed to be generated during the nuclear passage time. Directed flow therefore probes the onset of bulk collective dynamics during thermalization, providing valuable experimental guidance to models of the pre-equilibrium stage. In 2018, the Event Plane Detector (EPD) was installed in STAR and used for the Beam Energy Scan phase-II (BES-II) data taking. The combination of EPD ($2.1 <|\eta|< 5.1$) and high-statistics BES-II data enables us to extend the $v_{1}$ measurement to the forward and backward $\eta$ regions. In this paper, we present the measurement of $v_{1}$ over a wide $\eta$ range in Au+Au collisions at $\sqrt{s_{NN}}=$ 19.6 and 27 GeV using the STAR EPD. The results of the analysis at $\sqrt{s_{NN}}=$19.6 GeV exhibit excellent consistency with the previous PHOBOS measurement, while elevating the precision of the overall measurement. The increased precision of the measurement also revealed finer structures in heavy-ion collisions, including a potential observation of the first-order event-plane decorrelation. Multiple physics models were compared to the experimental results. Only a transport model and a three-fluid hybrid model can reproduce a sizable $v_{1}$ at large $\eta$ as was observed experimentally. The model comparison also indicates $v_{1}$ at large $\eta$ might be sensitive to the QGP phase transition.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | In heavy-ion collision experiments, the global collectivity of final-state particles can be quantified by anisotropic flow coefficients ($v_n$). | background 1.00 | 0.04 | 0.02 | asserted 0.99 |
| s1 | The first-order flow coefficient, also referred to as the directed flow ($v_{1}$), describes the collective sideward motion of produced particles and nuclear fragments in heavy-ion collisions. | background 1.00 | 0.04 | 0.02 | asserted 1.00 |
| s2 | It carries information on the very early stage of the collision, especially at large pseudorapidity ($\eta$), where it is believed to be generated during the nuclear passage time. | background 0.97 | 0.07 | 0.03 | hedged possibility 0.70 |
| s3 | Directed flow therefore probes the onset of bulk collective dynamics during thermalization, providing valuable experimental guidance to models of the pre-equilibrium stage. | background 0.92 | 0.06 | 0.04 | asserted 0.99 |
| s4 | In 2018, the Event Plane Detector (EPD) was installed in STAR and used for the Beam Energy Scan phase-II (BES-II) data taking. | method 0.85 | 0.36 | 0.02 | asserted 1.00 |
| s5 | The combination of EPD ($2.1 <|\eta|< 5.1$) and high-statistics BES-II data enables us to extend the $v_{1}$ measurement to the forward and backward $\eta$ regions. | method 0.69 | 0.46 | 0.04 | asserted 0.97 |
| s6 | In this paper, we present the measurement of $v_{1}$ over a wide $\eta$ range in Au+Au collisions at $\sqrt{s_{NN}}=$ 19.6 and 27 GeV using the STAR EPD. | contribution 1.00 | 0.95 | 0.10 | asserted 1.00 |
| s7 | The results of the analysis at $\sqrt{s_{NN}}=$19.6 GeV exhibit excellent consistency with the previous PHOBOS measurement, while elevating the precision of the overall measurement. | result 1.00 | 0.88 | 0.17 | asserted 0.94 |
| s8 | The increased precision of the measurement also revealed finer structures in heavy-ion collisions, including a potential observation of the first-order event-plane decorrelation. | result 0.98 | 0.91 | 0.14 | hedged possibility 0.80 |
| s9 | Multiple physics models were compared to the experimental results. | method 0.75 | 0.72 | 0.03 | asserted 0.95 |
| s10 | Only a transport model and a three-fluid hybrid model can reproduce a sizable $v_{1}$ at large $\eta$ as was observed experimentally. | result 0.53 | 0.70 | 0.28 | asserted 1.00 |
| s11 | The model comparison also indicates $v_{1}$ at large $\eta$ might be sensitive to the QGP phase transition. | interpretation 0.99 | 0.72 | 0.30 | hedged possibility 0.88 |
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The paper
Original abstract
In heavy-ion collision experiments, the global collectivity of final-state particles can be quantified by anisotropic flow coefficients ($v_n$). The first-order flow coefficient, also referred to as the directed flow ($v_{1}$), describes the collective sideward motion of produced particles and nuclear fragments in heavy-ion collisions. It carries information on the very early stage of the collision, especially at large pseudorapidity ($\eta$), where it is believed to be generated during the nuclear passage time. Directed flow therefore probes the onset of bulk collective dynamics during thermalization, providing valuable experimental guidance to models of the pre-equilibrium stage. In 2018, the Event Plane Detector (EPD) was installed in STAR and used for the Beam Energy Scan phase-II (BES-II) data taking. The combination of EPD ($2.1 <|\eta|< 5.1$) and high-statistics BES-II data enables us to extend the $v_{1}$ measurement to the forward and backward $\eta$ regions. In this paper, we present the measurement of $v_{1}$ over a wide $\eta$ range in Au+Au collisions at $\sqrt{s_{NN}}=$ 19.6 and 27 GeV using the STAR EPD. The results of the analysis at $\sqrt{s_{NN}}=$19.6 GeV exhibit excellent consistency with the previous PHOBOS measurement, while elevating the precision of the overall measurement. The increased precision of the measurement also revealed finer structures in heavy-ion collisions, including a potential observation of the first-order event-plane decorrelation. Multiple physics models were compared to the experimental results. Only a transport model and a three-fluid hybrid model can reproduce a sizable $v_{1}$ at large $\eta$ as was observed experimentally. The model comparison also indicates $v_{1}$ at large $\eta$ might be sensitive to the QGP phase transition.
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References
How the literature uses it
1 arXiv paper cite this in 1 sentence
What it cites · 56 sentences without a confident label
Uses the method or tool of 8 papers
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In this paper, we use the STAR Event Plane Detector [ref] (EPD) to measure directed flow at $√(s_NN)=19.6$ and 27 GeV, from $2.1<|η|<5.1$.
The STAR Event Plane Detector · Introduction · 1.00
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MUFFIN [ref] is an event-by-event three-fluid dynamic model based on the vHLLE code [ref] .
Next-generation multi-fluid hydrodynamic model for RHIC BES · Results · 0.91
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MUFFIN [ref] is an event-by-event three-fluid dynamic model based on the vHLLE code [ref] .
A 3+1 dimensional viscous hydrodynamic code for relativistic heavy ion collisions · Results · 0.91
Uses data or values from 1 paper
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At $μ_B=0$, first-principle lattice QCD calculations have established the transition between the QGP and hadron gas to be a crossover transition at the critical temperature $T_c=154±9$ MeV [ref] .
The equation of state in (2+1)-flavor QCD · Introduction · 0.90
Cites as background 7 papers
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In 2010, RHIC embarked upon the Beam Energy Scan (BES) program [ref] , with a goal to further explore the QCD phase diagram at finite $μ_B$.
An Experimental Exploration of the QCD Phase Diagram: The Search for the Critical Point and the Onset of De-confinement · Introduction · 0.92
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Nuclear collisions at ultra-relativistic energies create a deconfined system of partons in the midrapidity region [ref] .
Formation of dense partonic matter in relativistic nucleus-nucleus collisions at RHIC: Experimental evaluation by the PHENIX collaboration · Introduction · 0.80
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Nuclear collisions at ultra-relativistic energies create a deconfined system of partons in the midrapidity region [ref] .
Quark Gluon Plasma an Color Glass Condensate at RHIC? The perspective from the BRAHMS experiment · Introduction · 0.80
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