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Register a new userEstimating non-flow effects in measurements of directed flow of protons with the HADES experiment at GSI
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Centrality dependence of the directed flow of protons in Au+Au collisions at the beam energy of 1.23A GeV collected by the HADES experiment at GSI is presented. Measurements are performed with respect to the spectators plane estimated using the Forward Wall hodoscope. Biases due to non-flow correlations and correlated detector effects are evaluated. The corresponding systematic uncertainties are quantified using estimates of the spectators plane from various forward rapidity regions constructed from groups of Forward Wall channels and protons reconstructed with the HADES tracking system.
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Rapidity-odd directed flow($v_1$) measurements for charged pions, protons and antiprotons near mid-rapidity ($y=0$) are reported in $sqrt{s_{NN}} =$ 7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV Au + Au collisions as recorded by the STAR detector at the Relativistic Heavy Ion Collider (RHIC). At intermediate impact parameters, the proton and net-proton slope parameter $dv_1/dy|_{y=0}$ shows a minimum between 11.5 and 19.6 GeV. In addition, the net-proton $dv_1/dy|_{y=0}$ changes sign twice between 7.7 and 39 GeV. The proton and net-proton results qualitatively resemble predictions of a hydrodynamic model with a first-order phase transition from hadronic matter to deconfined matter, and differ from hadronic transport calculations.
The anisotropic collective flow is one of the key observables to study the properties of dense matter created in heavy-ion collisions. The performance of Multi-Purpose Detector (MPD) at NICA collider for directed and elliptic flow measurements is studied with Monte-Carlo simulations of heavy-ion collisions at energies $sqrt{s_{NN}}$ = 4 - 11 GeV.
The TRB hardware module is a multi-purpose Trigger and Readout Board with on-board DAQ functionality developed for the upgrade of the HADES experiment. It contains a single computer chip (Etrax) running Linux as a well as a 100 Mbit/s Ethernet interface. It has been orginally designed to work as a 128-channel Time to Digital Converter based on the HPTDC chip from CERN. The new version contains a 2 Gbit/s optical link and an interface connector (15 Gbit/s) in order to realize an add-on card concept which makes the hardware very flexible. Moreover, an FPGA chip (Xilinx, Virtex 4 LX 40) and a TigerSharc DSP provide new computing resources which can be used to run on-line analysis algorithms. The TRB is proposed as a prototype for new modules for the planned detector systems PANDA and CBM at the future FAIR facility at GSI-Darmstadt.
The directed flow of particles produced in ultrarelativistic heavy ion collisions at SPS and RHIC is so small that currently available methods of analysis are at the border of applicability. Standard two-particle and flow-vector methods are biased by large nonflow correlations. On the other hand, cumulants of four-particle correlations, which are free from this bias, are plagued by large statistical errors. Here, we present a new method based on three-particle correlations, which uses the property that elliptic flow is large at these energies. This method may also be useful at intermediate energies, near the balance energy where directed flow vanishes.
Flow harmonics ($v_n$) in the Fourier expansion of the azimuthal distribution of particles are widely used to quantify the anisotropy in particle emission in high-energy heavy-ion collisions. The symmetric cumulants, $SC(m,n)$, are used to measure the correlations between different orders of flow harmonics. These correlations are used to constrain the initial conditions and the transport properties of the medium in theoretical models. In this Letter, we present the first measurements of the four-particle symmetric cumulants in Au+Au collisions at $sqrt{s_{NN}}$ = 39 and 200 GeV from data collected by the STAR experiment at RHIC. We observe that $v_{2}$ and $v_{3}$ are anti-correlated in all centrality intervals with similar correlation strengths from 39 GeV Au+Au to 2.76 TeV Pb+Pb (measured by the ALICE experiment). The $v_{2}$-$v_{4}$ correlation seems to be stronger at 39 GeV than at higher collision energies. The initial-stage anti-correlations between second and third order eccentricities are sufficient to describe the measured correlations between $v_{2}$ and $v_{3}$. The best description of $v_{2}$-$v_{4}$ correlations at $sqrt{s_{NN}}$ = 200 GeV is obtained with inclusion of the systems nonlinear response to initial eccentricities accompanied by the viscous effect with $eta/s$ $>$ 0.08. Theoretical calculations using different initial conditions, equations of state and viscous coefficients need to be further explored to extract $eta/s$ of the medium created at RHIC.
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