Tracking the baryon number with nuclear collisions
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73 NUCLEAR PHYSICS AND RADIATION PHYSICSβ
Engineering topics
Bellwied, R.
Publications and source records attributed to Bellwied, R..
First Observation of Deuteron-Ξ Correlations at RHIC
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73 NUCLEAR PHYSICS AND RADIATION PHYSICSβ
Large-scale real-time signal processing in physics experiments: the ALICE TPC FPGA pipeline
For LHC Run 3, the ALICE Time Projection Chamber was upgraded to operate in continuous readout mode. Interaction rates of up to 50 kHz in Pb-Pb collisions require real-time processing of more than 3 TB s -1 of raw detector data. This requirement is met by a custom FPGA-based processing pipeline that performs the complete front-end data treatment fully in-stream, including common-mode correction, pedestal subtraction, ion-tail filtering, zero suppression, and dense data packing. A central element of the design is a highly parallel common-mode correction algorithm operating directly on the streaming data. It robustly identifies signal-free readout channels on a time-bin basis and applies pad-dependent scaling to compensate for local variations in capacitive coupling in the GEM readout. In combination with pedestal subtraction and ion-tail filtering, this enables accurate baseline restoration under extreme high-occupancy conditions, preventing signal loss while efficiently suppressing noise prior to zero suppression. The pipeline operates continuously at the full detector bandwidth and reduces the raw input rate of approximately 3 TB s -1 to about 900 GBps for Pb-Pb collisions at the target interaction rate. Overall, it represents a large-scale FPGA-based real-time signal-processing implementation for high-energy physics detector readout.
Digital signal processing (DSP)β
Measurement of inclusive $J/Ο$ production in Au+Au collisions at $\sqrt{s_{\textrm{NN}}}$ = 54.4 GeV at STAR
This article presents measurements of inclusive J/Ο production at midrapidity (|y| < 1.0) in Au+Au collisions at $\sqrt{s_{\textrm{NN}}}$ = 54.4 GeV with the STAR detector at the Relativistic Heavy Ion Collider. A suppression of the J/Ο yield, quantified using the nuclear modification factors (R AA , R CP ), is observed with respect to the scaled production p + p in collisions. The dependence of R AA on collision centrality and J/Ο transverse momentum is measured with improved precision compared to previous measurements at 39 and 62.4 GeV, while the centrality dependence of R CP is measured and compared to the same results at 39, 62.4, and 200 GeV. In central collisions, no significant collision energy dependence of R AA is found within uncertainties for collision energies between 17.3 and 200 GeV. Two transport model calculations that include dissociation and regeneration contributions are consistent with the experimental results within uncertainties. Although no significant collision energy dependence of the J/Ο suppression in high energy heavy-ion collisions up to $\sqrt{s_{\textrm{NN}}}$ = 200 GeV is observed within uncertainties, the newly measured results at 54.4 GeV Au+Au collisions provide additional constraints on theoretical calculations of the hot medium evolution and cold nuclear matter effects.
73 NUCLEAR PHYSICS AND RADIATION PHYSICSβ
Measuring spin correlation between quarks during QCD confinement
The vacuum is now understood to have a rich and complex structure, characterized by fluctuating energy fields and a condensate of virtual quarkβantiquark pairs. The spontaneous breaking of the approximate chiral symmetry, signalled by the nonvanishing quark condensate $\langle$$q\bar{q}$$\rangle$, is dynamically generated through topologically nontrivial gauge configurations such as instantons. The precise mechanism linking the chiral symmetry breaking to the mass generation associated with quark confinement remains a profound open question in quantum chromodynamics (QCD)βthe fundamental theory of strong interaction. High-energy protonβproton collisions could liberate virtual quarkβantiquark pairs from the vacuum that subsequently undergo confinement to form hadrons, whose properties could serve as probes into QCD confinement and the quark condensate. Here we report evidence of spin correlations in $Ξ\bar{Ξ}$ hyperon pairs inherited from spin-correlated strange quarkβantiquark virtual pairs. Measurements by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory reveal a relative polarization signal of (18 Β± 4)% that links the virtual spin-correlated quark pairs from the QCD vacuum to their final-state hadron counterparts. Crucially, this correlation vanishes when the hyperon pairs are widely separated in angle, consistent with the decoherence of the quantum system. Our findings provide a new experimental model for exploring the dynamics and interplay of quark confinement and entanglement.
73 NUCLEAR PHYSICS AND RADIATION PHYSICSβ
Temperature measurement of Quark-Gluon plasma at different stages
In a Quark-Gluon Plasma (QGP), the fundamental building blocks of matter, quarks and gluons, are under extreme conditions of temperature and density. A QGP could exist in the early stages of the Universe, and in various objects and events in the cosmos. The thermodynamic and hydrodynamic properties of the QGP are described by Quantum Chromodynamics (QCD) and can be studied in heavy-ion collisions. Despite being a key thermodynamic parameter, the QGP temperature is still poorly known. Thermal lepton pairs (e + e β and ΞΌ + ΞΌ β ) are ideal penetrating probes of the true temperature of the emitting source, since their invariant-mass spectra suffer neither from strong final-state interactions nor from blue-shift effects due to rapid expansion. Here we measure the QGP temperature using thermal e+eβ production at the Relativistic Heavy Ion Collider (RHIC). The average temperature from the low-mass region (in-medium Ο 0 vector-meson dominant) is (2.01 Β± 0.23) Γ 10 12 K, consistent with the chemical freeze-out temperature from statistical models and the phase transition temperature from Lattice QCD. The average temperature from the intermediate mass region (above the Ο0 mass, QGP dominant) is significantly higher at (3.25 Β± 0.60) Γ 10 12 K. This work provides essential experimental thermodynamic measurements to map out the QCD phase diagram and understand the properties of matter under extreme conditions.
73 NUCLEAR PHYSICS AND RADIATION PHYSICSβ
Semi-inclusive direct photon + jet and π 0 + jet correlations measured in π + π and central Au + Au collisions at $\sqrt{s_{NN}}$ = 200GeV
The STAR experiment at RHIC reports new measurements of jet quenching based on the semi- inclusive distribution of charged-particle jets recoiling from direct photon (Ξ³ dir ) and neutral pion (Ο 0 ) triggers in pp and central Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV, for triggers in the range 9 < $E$$^{trig}_{T}$ < 20 GeV. The datasets have integrated luminosities of 3.9nb β1 for Au + Au and 23pb β1 for ππ collisions. Jets are reconstructed using the anti-π π algorithm with resolution parameters π = 0.2 and 0.5. The large uncorrelated jet background in central Au + Au collisions is corrected using a mixed-event approach, which enables precise charged-particle jet measurements at low transverse momentum π$^{ch}_{π,jet}$ and large π . Recoil-jet distributions are reported in the range π$^{ch}_{π,jet}$ < 25 GeV/π. Comparison of the distributions measured in ππ and Au + Au collisions reveals strong medium-induced jet yield suppression for π = 0.2 with markedly less suppression for π = 0.5. Comparison is also made to theoretical models incorporating jet quenching. Furthermore, these data provide new insight into the mechanisms underlying jet quenching and the angular dependence of medium-induced jet-energy transport and provide new constraints on modeling such effects.
73 NUCLEAR PHYSICS AND RADIATION PHYSICSβ
Light nuclei femtoscopy and baryon interactions in 3 GeV Au+Au collisions at RHIC
We report the measurements of proton-deuteron (π-π) and deuteron-deuteron (π-π) correlation functions in Au + Au collisions at $\sqrt{s_{NN}}$ = 3 GeV using fixed-target mode with the STAR experiment at the Relativistic Heavy-Ion Collider (RHIC). For the first time, the source size (π πΊ ), scattering length (π 0 ), and effective range (π 0 ) are extracted from the measured correlation functions with a simultaneous fit. The spin-averaged π 0 for π-π and π-π interactions are determined to be -5.28 Β± 0.11(stat.) Β± 0.82(syst.) fm and -2.62 Β± 0.02(stat.) Β±0.24(syst.) fm, respectively. The measured π-π interaction is consistent with theoretical calculations and low energy scattering experiment results, demonstrating the feasibility of extracting interaction parameters using the femtoscopy technique. The reasonable agreement between the experimental data and the calculations from the transport model indicates that deuteron production in these collisions is primarily governed by nucleon coalescence.
73 NUCLEAR PHYSICS AND RADIATION PHYSICSβ
Design of the ECCE detector for the Electron Ion Collider
The EIC Comprehensive Chromodynamics Experiment (ECCE) detector has been designed to address the full scope of the proposed Electron Ion Collider (EIC) physics program as presented by the National Academy of Science and provide a deeper understanding of the quark-gluon structure of matter. To accomplish this, the ECCE detector offers nearly acceptance and energy coverage along with excellent tracking and particle identification. The ECCE detector was designed to be built within the budget envelope set out by the EIC project while simultaneously managing cost and schedule risks. Finally, this detector concept has been selected to be the basis for the EIC project detector.
47 OTHER INSTRUMENTATIONβ
Measurement of beauty production via non-prompt charm hadrons in pβPb collisions at $\sqrt{s_{\textrm{NN}}}$ = 5.02 TeV
The production cross sections of D 0 , D + , and Ξ$^{+}_{c}$ hadrons originating from beauty-hadron decays (i.e. non-prompt) were measured for the first time at midrapidity in protonβlead (pβPb) collisions at the center-of-mass energy per nucleon pair of $\sqrt{s_{\textrm{NN}}}$ = 5.02 TeV. Nuclear modification factors (R pPb ) of non-prompt D 0 , D + , and Ξ$^{+}_{c}$ are calculated as a function of the transverse momentum (p T ) to investigate the modification of the momentum spectra measured in pβPb collisions with respect to those measured in protonβproton (pp) collisions at the same energy. The R pPb measurements are compatible with unity and with the measurements in the prompt charm sector, and do not show a significant p T dependence. The p T -integrated cross sections and p T -integrated R pPb of non-prompt D 0 and D + mesons are also computed by extrapolating the visible cross sections down to p T = 0. The non-prompt D-meson R pPb integrated over p T is compatible with unity and with model calculations implementing modification of the parton distribution functions of nucleons bound in nuclei with respect to free nucleons. The non-prompt Ξ$^{+}_{c}$/D 0 and D + /D 0 production ratios are computed to investigate hadronisation mechanisms of beauty quarks into mesons and baryons. The measured ratios as a function of p T display a similar trend to that measured for charm hadrons in the same collision system.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDSβ
Production of protons and light nuclei in Au +Au collisions at $\sqrt{s_{NN}}$ = 3 GeV with the STAR detector
We report the systematic measurement of protons and light nuclei production in Au +Au collisions at $\sqrt{s_{NN}}$ = 3 GeV by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The transverse momentum (π π ) spectra of protons (π) , deuterons (π) , tritons (π‘) , 3 He , and 4 He have been measured from midrapidity to target rapidity for different collision centralities. We present the rapidity and centrality dependence of particle yields (πβ’π/πβ’π¦), average transverse momentum (β¨π π β©), yield ratios (π/π, π‘/π, 3 He/π, 4 He/π), as well as the coalescence parameters (π΅ 2 ,π΅ 3 ). The 4β’π yields for various particles are determined by utilizing the measured rapidity distributions, πβ’π/πβ’π¦. Furthermore, we present the energy, centrality, and rapidity dependence of the compound yield ratios (π π Γπ π‘ /π$^{2}_{d}$) and compare them with various model calculations. Furthermore, the physics implications of these results on the production mechanism of light nuclei and the QCD phase structure are discussed.
73 NUCLEAR PHYSICS AND RADIATION PHYSICSβ