The polarization of $Λ$ and $\bar{Λ}$ 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 ...$\sqrt{^SNN}$ = 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 pT 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 pT dependence that still disagree with experimental measurements. Thus, our results provide stringent constraints on the thermal vorticity and shear-induced contributions to hyperon polarization. Finally, 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.
Density fluctuations near the QCD critical point can be probed via an intermittency analysis in relativistic heavy-ion collisions. We report the first measurement of intermittency in Au+Au collisions ...at sNN = 7.7-200 GeV measured by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The scaled factorial moments of identified charged hadrons are analyzed at mid-rapidity and within the transverse momentum phase space. We observe a power-law behavior of scaled factorial moments in Au+Au collisions and a decrease in the extracted scaling exponent (ν) from peripheral to central collisions. The ν is consistent with a constant for different collisions energies in the mid-central (10-40%) collisions. Moreover, the ν in the 0-5% most central Au+Au collisions exhibits a non-monotonic energy dependence that reaches a minimum around sNN = 27 GeV. The physics implications on the QCD phase structure are discussed.
We report results on an elastic cross section measurement in proton–proton collisions at a center-of-mass energy s=510 GeV, obtained with the Roman Pot setup of the STAR experiment at the ...Relativistic Heavy Ion Collider (RHIC). The elastic differential cross section is measured in the four-momentum transfer squared range 0.23≤−t≤0.67 GeV2. This is the only measurement of the proton-proton elastic cross section in this t range for collision energies above the Intersecting Storage Rings (ISR) and below the Large Hadron Collider (LHC) colliders. We find that a constant slope B does not fit the data in the aforementioned t range, and we obtain a much better fit using a second-order polynomial for B(t). This is the first measurement below the LHC energies for which the non-constant behavior B(t) is observed. The t dependence of B is also determined using six subintervals of t in the STAR measured t range, and is in good agreement with the phenomenological models. The measured elastic differential cross section dσ/dt agrees well with the results obtained at s=540 GeV for proton–antiproton collisions by the UA4 experiment. We also determine that the integrated elastic cross section within the STAR t-range is σelfid=462.1±0.9(stat.)±1.1(syst.)±11.6(scale)μb.
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 eHFv2 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 eHFv2 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.
Two Multi-Strip Multi-Gap Resistive Plate Counters (MSMGRPCs) designed to cope with the high counting rates and track densities of the most challenging zone of the CBM-TOF wall were successfully ...tested in-beam in the mCBM experimental setup installed at SIS18/GSI Darmstadt facility (FAIR Phase-0). At low counting rate a 96% efficiency plateau and 45 ps time resolution were obtained. The high counting rate test showed ∼50 ps time resolution and an efficiency ≥90% at the maximum delivered counting rate of 30 kHz/cm2. For the mitigation of the gas pollution aging effects, a new detector architecture with a direct gas flow through the gas gaps is proposed. The assembled prototype was tested in-beam in the mCBM setup, obtaining similar performances with the ones obtained for the prototypes with gas exchange via diffusion.
The design of a general-purpose PreAmplifier-DIscriminator ASIC chip, PADI, is presented in this article. PADI is intended to be used as Front-End-Electronics (FEE) for reading out the timing ...Resistive-Plate Chambers (RPCs) in the time-of-flight (ToF) wall of the CBM detector for the future FAIR facility in Darmstadt-Germany, which will comprise about 100,000 channels in a 150 m 2 area. The evolution of this 0.18 μm CMOS technology design will be presented, from the first prototype PADI-1 to the last one, PADI-8, as well as its features and test results.
In contrast to light, matter-wave optics of quantum gases deals with interactions even in free space and for ensembles comprising millions of atoms. We exploit these interactions in a quantum ...degenerate gas as an adjustable lens for coherent atom optics. By combining an interaction-driven quadrupole-mode excitation of a Bose-Einstein condensate (BEC) with a magnetic lens, we form a time-domain matter-wave lens system. The focus is tuned by the strength of the lensing potential and the oscillatory phase of the quadrupole mode. By placing the focus at infinity, we lower the total internal kinetic energy of a BEC comprising 101(37) thousand atoms in three dimensions to 3/2 kB⋅38+6−7 pK. Our method paves the way for free-fall experiments lasting ten or more seconds as envisioned for tests of fundamental physics and high-precision BEC interferometry, as well as opens up a new kinetic energy regime.
The Time-of-Flight (TOF) subsystem, one of the core detectors of the CBM experiment, is dedicated to the identification of all charged hadrons produced in beam-target interaction. The targeted system ...time resolution of 80 ps and an efficiency above 90% should be maintained at a particle flux up to 30 kHz/cm2 in the region of low polar angles. In order to cope with these challenging requirements, CBM-TOF wall will be equipped with Multi-Gap Resistive Plate Counters with Multi-Strip readout (MSMGRPC). Our R&D activity has been focused on the development of a MSMGRPC prototype for the most demanding region of the CBM-TOF wall, the region of low polar angles (from 2.5° to ∼12° around the beam pipe). The results obtained in heavy ion in-beam tests have demonstrated the performances of the developed prototypes in conditions of exposure of the whole active area to high flux and high multiplicity reaction products. The latest developed prototypes have an optimized design which fulfills simultaneously two important requirements for MSMGRPCs, the granularity for the inner zone of the CBM-TOF subdetector and the impedance matching to the front-end electronics. Based on the obtained in-beam test results and the architecture of the developed prototypes, a modular structure of 12 units called modules is proposed. A total number of 470 MSMGRPCs (~30000 readout channels) assures an uniform coverage of the active area.
The free streaming readout concept of the CBM experiment imposes to the Multi-Strip Multi-Gap RPCs (MSMGRPCs) developed for the CBM-TOF wall a very good matching of the characteristic impedance of ...the signal transmission line (corresponding to a single strip) to the input impedance of the front-end electronics in order to reduce fake signals produced by reflections. The design of the MSMGRPC prototype described here exploits in an innovative way the advantage of a strip structure for the readout and the high voltage electrodes, the impedance of the signal transmission line being adjusted independent of the detector granularity. The new design allows to built MSMGRPCs with the impedance corresponding to a single strip matched to the input impedance of the front end electronics. The prototype was tested in-beam at CERN-SPS with reaction products of a 30⋅A GeV Pb beam colliding onto a Pb target, in conditions rather similar in terms of energy and multiplicity with those expected at SIS100/FAIR. The obtained performance of 62 ± 3 ps system time resolution and 97% efficiency shows that the new developed prototype meets the challenging requirements for the inner zone of the CBM-TOF wall.
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