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DOE OSTI2024

Estimate of background baseline and upper limit on the chiral magnetic effect in isobar collisions at $\sqrt{S_{NN}}$=200 GeV at the BNL Relativistic Heavy Ion Collider

For the search of the chiral magnetic effect (CME), STAR previously presented the results from isobar collisions ($^{96}_{44}$Ru + $^{96}_{44}$Ru, $^{96}_{40}$Zr + $^{96}_{40}$Zr) obtained through a blind analysis. The ratio of results in Ru+Ru to Zr+Zr collisions for the CME-sensitive charge-dependent azimuthal correlator (Δ⁢𝛾), normalized by elliptic anisotropy (𝑣2), was observed to be close to but systematically larger than the inverse multiplicity ratio. The background baseline for the isobar ratio, 𝑌= (Δ⁢𝛾/𝑣2) Ru /(Δ⁢𝛾/𝑣2) Zr , is naively expected to be (1/𝑁) Ru /(1/𝑁) Zr ; however, genuine two- and three-particle correlations are expected to alter it. We estimate the contributions to 𝑌 from those correlations, utilizing both the isobar data and hijing simulations. After including those contributions, we arrive at a final background baseline for 𝑌, which is consistent with the isobar data. Here, we extract an upper limit for the CME fraction in the Δ⁢𝛾 measurement of approximately 10% at a 95% confidence level on in isobar collisions at $\sqrt{S_{NN}}$=200 GeV, with an expected 15% difference in their squared magnetic fields.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2024

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 (𝑝 𝑇 ) spectra of protons (𝑝) , deuterons (𝑑) , tritons (𝑡) , 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 (𝑑⁢𝑁/𝑑⁢𝑦), average transverse momentum (⟨𝑝 𝑇 ⟩), yield ratios (𝑑/𝑝, 𝑡/𝑝, 3 He/𝑝, 4 He/𝑝), as well as the coalescence parameters (𝐵 2 ,𝐵 3 ). The 4⁢𝜋 yields for various particles are determined by utilizing the measured rapidity distributions, 𝑑⁢𝑁/𝑑⁢𝑦. Furthermore, we present the energy, centrality, and rapidity dependence of the compound yield ratios (𝑁 𝑝 ×𝑁 𝑡 /𝑁$^{2}_{d}$) 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 PHYSICS↗

DOE OSTI2024

Measurement of flow coefficients in high-multiplicity 𝑝 + Au, 𝑑 + Au, and 3 He + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV

Flow coefficients (𝑣 2 and 𝑣 3 ) are measured in high-multiplicity 𝑝 + Au, 𝑑 + Au, and 3 He + Au collisions at a center-of-mass energy of $\sqrt{s_{NN}}$ = 200 GeV using the STAR detector. The measurements utilize two-particle correlations with a pseudorapidity requirement of |𝜂| < 0.9 and a pair gap of |Δ⁢𝜂| > 1.0. The primary focus is on analysis methods, particularly the subtraction of nonflow contributions. Four established nonflow subtraction methods are applied to determine 𝑣 𝑛 , validated using the HIJING event generator. 𝑣 𝑛 values are compared across the three collision systems at similar multiplicities; this comparison cancels the final-state effects and isolates the impact of initial geometry. While 𝑣 2 values show differences among these collision systems, 𝑣 3 values are largely similar, consistent with expectations of subnucleon fluctuations in the initial geometry. The ordering of 𝑣 𝑛 differs quantitatively from previous measurements using two-particle correlations with a larger rapidity gap, which, according to model calculations, can be partially attributed to the effects of longitudinal flow decorrelations. As a result, the prospects for future measurements to improve our understanding of flow decorrelation and subnucleonic fluctuations are also discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2024

Centrality dependence of Lévy-stable two-pion Bose-Einstein correlations in $\sqrt{𝑠{𝑁⁢𝑁}}$ = 200 GeV Au + Au collisions

The PHENIX experiment measured the centrality dependence of two-pion Bose-Einstein correlation functions in $\sqrt{𝑠{𝑁⁢𝑁}}$ = 200 GeV Au + Au collisions at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. The data are well represented by Lévy-stable source distributions. The extracted source parameters are the correlation-strength parameter 𝜆, the Lévy index of stability 𝛼, and the Lévy-scale parameter 𝑅 as a function of transverse mass 𝑚 𝑇 and centrality. The 𝜆⁡(𝑚 𝑇 ) parameter is constant at larger values of 𝑚 𝑇 , but decreases as 𝑚 𝑇 decreases. The Lévy-scale parameter 𝑅⁡(𝑚 𝑇 ) decreases with 𝑚 𝑇 and exhibits proportionality to the length scale of the nuclear overlap region. The Lévy exponent 𝛼⁡(𝑚 𝑇 ) is independent of 𝑚 𝑇 within uncertainties in each investigated centrality bin, but shows a clear centrality dependence. At all centralities, the Lévy exponent 𝛼 is significantly different from that of Gaussian (𝛼 = 2) or Cauchy (𝛼 = 1) source distributions. Comparisons to the predictions of Monte-Carlo simulations of resonance-decay chains show that, in all but the most peripheral centrality class (50%–60%), the obtained results are inconsistent with the measurements, unless a significant reduction of the in-medium mass of the 𝜂′ meson is included. Finally, in each centrality class, the best value of the in-medium 𝜂′ mass is compared to the mass of the 𝜂 meson, as well as to several theoretical predictions that consider restoration of U 𝐴⁢ (1) symmetry in hot hadronic matter.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2025

Measurement of the nucleon spin structure functions for 0.01 < 𝑄 2 < 1 GeV 2 using CLAS

The spin structure functions of the proton and the deuteron were measured during the EG4 experiment at Jefferson Lab in 2006. Data were collected for longitudinally polarized electron scattering off longitudinally polarized NH 3 and ND 3 targets, for 𝑄 2 values as small as 0.012 and 0.02 GeV 2 , respectively, using the CEBAF Large Acceptance Spectrometer. This is the archival paper of the EG4 experiment that summarizes the previously reported results of the polarized structure functions 𝑔 1 , 𝐴 1 ⁢𝐹 1 , and their moments $\bar{Γ}$ 1 , $\bar{𝛾}$ 0 , and $\bar{𝐼}$ TT , for both the proton and the deuteron. In addition, we report on new results on the neutron 𝑔 1 extracted by combining proton and deuteron data and correcting for Fermi smearing, and on the neutron moments $\bar{Γ}$ 1 , $\bar{𝛾}$ 0 , and $\bar{𝐼}$ TT formed directly from those of the proton and the deuteron. Our data are in good agreement with the Gerasimov-Drell-Hearn sum rule for the proton, deuteron, and neutron. Furthermore, the isovector combination was formed for 𝑔 1 and the Bjorken integral $\bar{Γ}^{𝑝−𝑛}_1$, and it was compared to available theoretical predictions. All of our results, to the best of our knowledge, provide for the first time extensive tests of spin observable predictions from chiral effective field theory (𝜒⁢EFT) in a 𝑄 2 range commensurate with the pion mass. Finally, they motivate further improvement in 𝜒⁢EFT calculations from other approaches such as the lattice gauge method.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2025

Measurement of the mass-changing, charge-changing, and production cross sections of 11 C, 11 B, and 10 B nuclei in 12 C + p interactions at 13.5 GeV/𝑐 per nucleon

A good knowledge of nuclear fragmentation cross sections is important to interpret the fluxes of secondary cosmic rays from the Galaxy. Here we report new measurements of nuclear fragmentation with the NA61/SHINE experiment at the CERN SPS. The specific focus is on cross sections important for the production of boron in the Galaxy from the interactions of 12 C nuclei with hydrogen in the interstellar medium, including the contribution from the decay of the short-lived 11 C fragments. The data were taken with the secondary 12 C beam at beam momentum of 13.5 GeV/𝑐per nucleon and two fixed targets, polyethylene (CH 2 ) and graphite (C), from which we derive the cross sections of carbon on hydrogen. We present the measurement of the fragmentation cross sections of 11 C, 11 B, and 10 B as well as the mass- and charge-changing cross sections.

nuclear fragmentation↗

DOE OSTI2011

Dynamically generated N* and {Lambda}* resonances in the hidden charm sector around 4.3 GeV

The interactions of D-bar{Sigma}{sub c}-D-bar{Lambda}{sub c}, D-bar*{Sigma}{sub c}-D-bar*{Lambda}{sub c}, and related strangeness channels, are studied within the framework of the coupled-channel unitary approach with the local hidden gauge formalism. A series of meson-baryon dynamically generated relatively narrow N* and {Lambda}* resonances are predicted around 4.3 GeV in the hidden charm sector. We make estimates of production cross sections of these predicted resonances in p-barp collisions for the experiment of antiproton annihilation at Darmstadt (PANDA) at the forthcoming GSI Facility for Antiproton and Ion Research (FAIR) facility.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2011

Production of omega mesons in p plus p, d plus Au, Cu plus Cu, and Au plus Au collisions at root s(NN)=200 Gev

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured {omega} meson production via leptonic and hadronic decay channels in p + p, d + Au, Cu + Cu, and Au + Au collisions at {radical}s{sub NN} = 200 GeV. The invariant transverse momentum spectra measured in different decay modes give consistent results. Measurements in the hadronic decay channel in Cu + Cu and Au + Au collisions show that {omega} production has a suppression pattern at high transverse momentum, similar to that of {pi}{sup 0} and {eta} in central collisions, but no suppression is observed in peripheral collisions. The nuclear modification factors, R{sub AA}, are consistent in Cu + Cu and Au + Au collisions at similar numbers of participant nucleons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2011

Heavy-quark production in p + p and energy loss and flow of heavy quarks in Au + Au collisions at sqrt(s_NN)=200 GeV.

Transverse momentum spectra of electrons (p{sub T}{sup e}) from semileptonic weak decays of heavy-flavor mesons in the range of 0.3 < p{sub T}{sup e} < 9.0 GeV/c have been measured at midrapidity (|y| < 0.35) by the PHENIX experiment at the Relativistic Heavy Ion Collider in p+p and Au+Au collisions at {radical}s{sub NN} = 200 GeV. In addition, the azimuthal anisotropy parameter v{sub 2} has been measured for 0.3 < p{sub T}{sup e} < 5.0 GeV/c in Au+Au collisions. The substantial modification in the p{sub T}{sup e} spectra in Au+Au compared with p+p collisions as well as the nonzero v{sub 2} indicate substantial interactions and flow of heavy quarks in traversing the produced medium. Comparisons of these observables with detailed theoretical calculations can be used to identify the nature of these interactions and to quantify their extent.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2011

J/psi suppression at forward rapidity in Au + Au collisions at sqrt(s_NN)=200 GeV

Heavy quarkonia are observed to be suppressed in relativistic heavy-ion collisions relative to their production in p+p collisions scaled by the number of binary collisions. In order to determine if this suppression is related to color screening of these states in the produced medium, one needs to account for other nuclear modifications including those in cold nuclear matter. In this paper, we present new measurements from the PHENIX 2007 data set of J/{psi} yields at forward rapidity (1.2 < |y| < 2.2) in Au+Au collisions at {radical}s{sub NN} = 200 GeV. The data confirm the earlier finding that the suppression of J/{psi} at forward rapidity is stronger than at midrapidity, while also extending the measurement to finer bins in collision centrality and higher transverse momentum (p{sub T}). We compare the experimental data to the most recent theoretical calculations that incorporate a variety of physics mechanisms including gluon saturation, gluon shadowing, initial-state parton energy loss, cold nuclear matter breakup, color screening, and charm recombination. We find J/{psi} suppression beyond cold-nuclear-matter effects. However, the current level of disagreement between models and d+Au data precludes using these models to quantify the hot-nuclear-matter suppression.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2012

Production of K⁺K⁻ pairs in proton-proton collisions at 2.83 GeV

Differential and total cross sections for the pp→ppK⁺K⁻ reaction have been measured at a proton beam energy of 2.83 GeV using the COSY-ANKE magnetic spectrometer. Detailed model descriptions fitted to a variety of one-dimensional distributions permit the separation of the pp→ppφ cross section from that of non-φ production. The differential spectra show that higher partial waves represent the majority of the pp→ppφ total cross section at an excess energy of 76 MeV, whose energy dependence would then seem to require some s-wave φp enhancement near threshold. The non-φ data can be described in terms of the combined effects of two-body final state interactions using the same effective scattering parameters determined from lower energy data.

Ye, Q. J.↗

DOE OSTI2012

Final analysis of proton form factor ratio data at Q 2 = 4.0, 4.8, and 5.6 GeV 2

Recently published measurements of the proton electromagnetic form factor ratio R = μ p G E p /G M p at momentum transfers Q 2 up to 8.5 GeV 2 in Jefferson Lab Hall C deviate from the linear trend of previous measurements in Jefferson Lab Hall A, favoring a slower rate of decrease of R with Q 2 . While statistically compatible in the region of overlap with Hall A, the Hall C data hint at a systematic difference between the two experiments. This possibility was investigated in a reanalysis of the Hall A data. We find that the original analysis underestimated the background in the selection of elastic events. The application of an additional cut to further suppress the background increases the results for R, improving the consistency between Halls A and C.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2012

Amplitude analysis of gamma n --> pi- p data above 1 GeV

We report a new extraction of nucleon resonance couplings using pi- photoproduction cross sections on the neutron. The world database for the process gamma n --> pi- p above 1 GeV has quadrupled with the addition of new differential cross sections from the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab in Hall B. Differential cross sections from CLAS have been improved with a new final-state interaction determination using a diagramatic technique taking into account the NN and piN final-state interaction amplitudes. Resonance couplings have been extracted and compared to previous determinations. With the addition of these new cross sections, significant changes are seen in the high-energy behavior of the SAID cross sections and amplitudes.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2012

Inclusive neutrino scattering off deuteron from threshold to GeV energies

Cross sections for inclusive neutrino scattering off deuteron induced by neutral and charge-changing weak currents are calculated from threshold up to GeV energies, using the Argonne v{sub 18} potential and consistent nuclear electroweak currents with one- and two-body terms. Two-body contributions are found to be small, and increase the cross sections obtained with one-body currents by less than 10% over the whole range of energies. Total cross sections obtained by describing the final two-nucleon states with plane waves differ negligibly, for neutrino energies {approx}> 500 MeV, from those in which interaction effects in these states are fully accounted for. The sensitivity of the calculated cross sections to different models for the two-nucleon potential and/or two-body terms in the weak current is found to be weak. In order to illustrate nuclear structure effects, the cross sections are compared to those obtained in a naive model in which the deuteron is taken to consist of a free proton and neutron at rest.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2013

Υ(1S+2S+3S) production in d+Au and p+p collisions at √sNN=200 GeV and cold-nuclear-matter effects

The three Υ states, Υ(1S+2S+3S), are measured in d+Au and p+p collisions at √sNN=200 GeV and rapidities 1.2<|y|<2.2 by the PHENIX experiment at the Relativistic Heavy Ion Collider. Cross sections for the inclusive Υ(1S+2S+3S) production are obtained. The inclusive yields per binary collision for d+Au collisions relative to those in p+p collisions (RdAu) are found to be 0.62±0.26(stat)±0.13(syst) in the gold-going direction and 0.91±0.33(stat)±0.16(syst) in the deuteron-going direction. The measured results are compared to a nuclear-shadowing model, EPS09 [Eskola et al., J. High Energy Phys. 04 (2009) 065], combined with a final-state breakup cross section, σbr, and compared to lower energy p+A results. We also compare the results to the PHENIX J/ψ results [Adare et al., Phys. Rev. Lett. 107, 142301 (2011)]. The rapidity dependence of the observed Υ suppression is consistent with lower energy p+A measurements.

PPG or IRC↗

DOE OSTI2014

Measurement of K 0 S and K *0 in p+p, d+Au, and Cu+Cu collisions at sqrt S NN = 200 GeV

The PHENIX experiment at the Relativistic Heavy Ion Collider has performed a systematic study of K 0 S and K *0 meson production at midrapidity in p+p, d+Au, and Cu+Cu collisions at sqrt S NN = 200 GeV. The K 0 S and K *0 mesons are reconstructed via their K 0 S and π 0 (→γγ)π 0 (→γγ) and K *0 → K ± π ± decay modes, respectively. The measured transverse-momentum spectra are used to determine the nuclear modification factor of K 0 S and K *0 mesons in d+Au and Cu+Cu collisions at different centralities. In the d+Au collisions, the nuclear modification factor of K 0 S and K *0 mesons is almost constant as a function of transverse momentum and is consistent with unity showing that cold-nuclear-matter effects do not play a significant role in the measured kinematic range. In Cu+Cu collisions, within the uncertainties no nuclear modification is registered in peripheral collisions. In central collisions, both mesons show suppression relative to the expectations from the p+p yield scaled by the number of binary nucleon-nucleon collisions in the Cu+Cu system. In the p T range 2–5 GeV/c, the strange mesons ( K 0 S , K *0 ) similarly to the Φ meson with hidden strangeness, show an intermediate suppression between the more suppressed light quark mesons (π 0 ) and the nonsuppressed baryons (p, p-bar). At higher transverse momentum, p T > 5 GeV/c, production of all particles is similarly suppressed by a factor of ≈2. (auth)

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2014

Nuclear matter effects on J/ψ production in asymmetric Cu + Au collisions at $\sqrt{s_{\mathrm{NN}}} = 200$ GeV

We report on J/ψ production from asymmetric Cu+Au heavy-ion collisions at $\sqrt{s_{\mathrm{NN}}} = 200$ GeV at the Relativistic Heavy Ion Collider at both forward (Cu-going direction) and backward (Au-going direction) rapidities. The nuclear modification of J/ψ yields in Cu+Au collisions in the Au-going direction is found to be comparable to that in Au+Au collisions when plotted as a function of the number of participating nucleons. In the Cu-going direction, J/ψ production shows a stronger suppression. This difference is comparable in magnitude and has the same sign as the difference expected from shadowing effects due to stronger low-x gluon suppression in the larger Au nucleus. Thus, the relative suppression is opposite to that expected from hot nuclear matter dissociation, since a higher energy density is expected in the Au-going direction.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2015

Cross section for b b ¯ production via dielectrons in d + Au collisions at s N N = 200 GeV

We report a measurement of e⁺e⁻ pairs from semileptonic heavy-flavor decays in d+Au collisions at √s NN = 200 GeV. Thus, exploring the mass and transverse-momentum dependence of the yield, the bottom decay contribution can be isolated from charm, and quantified by comparison to PYTHIA and MC@NLO simulations. The resulting bb-production cross section is σ d Au bb =1.37±0.28(stat)±0.46(syst) mb, which is equivalent to a nucleon-nucleon cross section of σ NN bb =3.4 ± 0.8(stat)±1.1(syst) µb.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗