We report the measurements of proton-deuteron ($p$-$d$) and deuteron-deuteron ($d$-$d$) correlation functions in Au+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 3 GeV using fixed-target mode with the STAR experiment at the Relativistic Heavy-Ion Collider (RHIC). For the first time, the source size ($R_{G}$), scattering length ($f_{0}$), and effective range ($d_{0}$) are extracted from the measured correlation functions with a simultaneous fit. The spin-averaged $f_0$ for $p$-$d$ and $d$-$d$ interactions are determined to be -5.28 $\pm$ 0.11(stat.) $\pm$ 0.82(syst.) fm and -2.62 $\pm$ 0.02(stat.) $\pm$ 0.24(syst.) fm, respectively. The measured $p$-$d$ 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.
Proton-Deuteron correlation function in 3 GeV Au+Au collisions.
Deuteron-Deuteron correlation function in 3 GeV Au+Au collisions.
Source size of p-d and d-d correlation function
We present the first forward-rapidity measurements of elliptic anisotropy of open-heavy-flavor muons at the BNL Relativistic Heavy Ion Collider. The measurements are based on data samples of Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV collected by the PHENIX experiment in 2014 and 2016 with integrated luminosity of 14.5~nb$^{-1}$. The measurements are performed in the pseudorapidity range $1.2<|\eta|<2$ and cover transverse momenta $1<p_T<4$~GeV/$c$. The elliptic flow of charged hadrons as a function of transverse momentum is also measured in the same kinematic range. We observe significant elliptic flow for both charged hadrons and heavy-flavor muons. The results show clear mass ordering of elliptic flow of light- and heavy-flavor particles. The magnitude of the measured $v_2$ is comparable to that in the midrapidity region. This indicates that there is no strong longitudinal dependence in the quark-gluon-plasma evolution between midrapidity and the rapidity range of this measurement at $\sqrt{s_{_{NN}}}=200$~GeV.
Lastgap $v_2$
Hadron-Muon Ratio at $1.2 < |\eta| < 2.0$
HF Fraction at $1.2 < |\eta| < 2.0$ Top Tuned Slim
We report the first measurement of the azimuthal anisotropy of J$/\psi$ at forward rapidity ($1.2<|\eta|<2.2$) in Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV at the Relativistic Heavy Ion Collider. The data were collected by the PHENIX experiment in 2014 and 2016 with integrated luminosity of 14.5~nb$^{-1}$. The second Fourier coefficient ($v_2$) of the azimuthal distribution of $J/\psi$ is determined as a function of the transverse momentum ($p_T$) using the event-plane method. The measurements were performed for several selections of collision centrality: 0%--50%, 10%--60%, and 10%-40%. We find that in all cases the values of $v_2(p_T)$, which quantify the elliptic flow of J$/\psi$, are consistent with zero. The results are consistent with measurements at midrapidity, indicating no significant elliptic flow of the J$/\psi$ within the quark-gluon-plasma medium at collision energies of $\sqrt{s_{_{NN}}}=200$ GeV.
JPSI v2 in Au+Au collisions as a function of pT (GeV/c) for 10%--60% centrality with pT binned by [0, 1], [1, 2], [2, 3], and [3, 5] GeV/c.
JPSI v2 in Au+Au collisions as a function of pT (GeV/c) for 10%--60% centrality with pT binned by [0, 0.5], [0.5, 1], [1, 5], and [0, 5] GeV/c.
JPSI v2 in Au+Au collisions as a function of pT (GeV/c) for 10%--40% centrality with pT binned by [0, 2], [2, 5], and [5, 10] GeV/c.
The $J/\psi$ and $\psi(2S)$ charmonium states, composed of $c\bar{c}$ quark pairs and known since the 1970s, are widely believed to serve as ideal probes to test quantum chromodynamics in high-energy hadronic interactions. However, there is not yet a complete understanding of the charmonium-production mechanism. Recent measurements of $J/\psi$ production as a function of event charged-particle multiplicity at the collision energies of both the Large Hadron Collider (LHC) and the Relativistic Heavy Ion Collider (RHIC) show enhanced $J/\psi$ production yields with increasing multiplicity. One potential explanation for this type of dependence is multiparton interactions (MPI). We carry out the first measurements of self-normalized $J/\psi$ yields and the $\psi(2S)$ to $J/\psi$ ratio at both forward and backward rapidities as a function of self-normalized charged-particle multiplicity in $p$$+$$p$ collisions at $\sqrt{s}=200$ GeV. In addition, detailed {\sc pythia} studies tuned to RHIC energies were performed to investigate the MPI impacts. We find that the PHENIX data at RHIC are consistent with recent LHC measurements and can only be described by {\sc pythia} calculations that include MPI effects. The forward and backward $\psi(2S)$ to $J/\psi$ ratio, which serves as a unique and powerful approach to study final-state effects on charmonium production, is found to be less dependent on the charged-particle multiplicity.
Self-normalized $J/\psi$ yields as a function of self-normalized $N_{ch}$ for the same arm before subtraction
Self-normalized $J/\psi$ yields as a function of self-normalized $N_{ch}$ for the same arm after subtraction
Self-normalized $J/\psi$ yields as a function of self-normalized $N_{ch}$ for opposite arms
This paper reports the first measurement of the transverse momentum ($p_{\mathrm{T}}$) spectra of primary charged pions, kaons, (anti)protons, and unidentified particles as a function of the charged-particle flattenicity in pp collisions at $\sqrt{s}=13$ TeV. Flattenicity is a novel event shape observable that is measured in the pseudorapidity intervals covered by the V0 detector, $2.8<\eta<5.1$ and $-3.7<\eta<-1.7$. According to QCD-inspired phenomenological models, it shows sensitivity to multiparton interactions and is less affected by biases toward larger $p_{\mathrm{T}}$ due to local multiplicity fluctuations in the V0 acceptance than multiplicity. The analysis is performed in minimum-bias (MB) as well as in high-multiplicity events up to $p_{\mathrm{T}}=20$ GeV/$c$. The event selection requires at least one charged particle produced in the pseudorapidity interval $|\eta|<1$. The measured $p_{\mathrm{T}}$ distributions, average $p_{\mathrm{T}}$, kaon-to-pion and proton-to-pion particle ratios, presented in this paper, are compared to model calculations using PYTHIA 8 based on color strings and EPOS LHC. The modification of the $p_{\mathrm{T}}$-spectral shapes in low-flattenicity events that have large event activity with respect to those measured in MB events develops a pronounced peak at intermediate $p_{\mathrm{T}}$ ($2<p_{\mathrm{T}}<8$ GeV/$c$), and approaches the vicinity of unity at higher $p_{\mathrm{T}}$. The results are qualitatively described by PYTHIA, and they show different behavior than those measured as a function of charged-particle multiplicity based on the V0M estimator.
Transverse momentum spectrum of $\pi^{+} + \pi^{-}$ measured at midrapidity ($|y|<0.5$) in INEL>0 pp collisions at $\sqrt{s}$ = 13 TeV for different flattenicity event classes selected with the V0M estimator at forward rapidity (top figure, upper panel)
Transverse momentum spectrum of $K^{+} + K^{-}$ measured at midrapidity ($|y|<0.5$) in INEL>0 pp collisions at $\sqrt{s}$ = 13 TeV for different flattenicity event classes selected with the V0M estimator at forward rapidity (top figure, upper panel)
Transverse momentum spectrum of $p + \overline{p}$ measured at midrapidity ($|y|<0.5$) in INEL>0 pp collisions at $\sqrt{s}$ = 13 TeV for different flattenicity event classes selected with the V0M estimator at forward rapidity (top figure, upper panel)
We report the differential yields at mid-rapidity of the Breit-Wheeler process ($\gamma\gamma\rightarrow e^{+}e^{-}$) in peripheral Au+Au collisions at $\sqrt{s_{_{\rm{NN}}}} = $ 54.4 GeV and 200 GeV with the STAR experiment at RHIC, as a function of energy $\sqrt{s_{_{\rm{NN}}}}$, $e^{+}e^{-}$ transverse momentum $p_{\rm T}$, $p_{\rm T}^{2}$, invariant mass $M_{ee}$ and azimuthal angle. In the invariant mass range of 0.4 $<$$M_{ee}$$<$ 2.6 GeV/$c^{2}$ at low transverse momentum ($p_{\rm T}$$ < $0.15 GeV/$c$), the yields increase while the pair $\sqrt{\langle p_{\rm T}^{2} \rangle}$ decreases with increasing $\sqrt{s_{_{\rm{NN}}}}$, a feature is correctly predicted by the QED calculation. The energy dependencies of the measured quantities are sensitive to the nuclear form factor, infrared divergence and photon polarization. The data are compiled and used to extract the charge radius of the Au nucleus.
'54.4 GeV, Centrality: 40-60%'
'54.4 GeV, Centrality: 60-80%'
'54.4 GeV, Centrality: 80-100%'
A search for long-lived heavy neutral leptons (HNLs) using proton-proton collision data corresponding to an integrated luminosity of 138 fb$^{-1}$ collected at $\sqrt{s}$ = 13 TeV with the CMS detector at the CERN LHC is presented. Events are selected with a charged lepton originating from the primary vertex associated with the proton-proton interaction, as well as a second charged lepton and a hadronic jet associated with a secondary vertex that corresponds to the semileptonic decay of a long-lived HNL. No excess of events above the standard model expectation is observed. Exclusion limits at 95% confidence level are evaluated for HNLs that mix with electron and/or muon neutrinos. Limits are presented in the mass range of 1-16.5 GeV, with excluded square mixing parameter values reaching as low as 2 $\times$ 10$^{-7}$. For masses above 11 GeV, the presented limits exceed all previous results in the semileptonic decay channel, and for some of the considered scenarios are the strongest to date.
The 95% CL limits on $|V_{Ne}|^2$ as a function of the HNL mass for a Majorana HNL. Values of $-1$ indicate that no limit is available for the mass point.
The 95% CL limits on $|V_{N\mu}|^2$ as a function of the HNL mass for a Majorana HNL. Values of $-1$ indicate that no limit is available for the mass point.
The 95% CL limits on mixed coupling as a function of the HNL mass for a Majorana HNL. Values of $-1$ indicate that no limit is available for the mass point.
We report multi-differential measurements of strange hadron production ranging from mid- to target-rapidity in Au+Au collisions at a center-of-momentum energy per nucleon pair of $\sqrt{s_{\rm NN}}=3$ GeV with the STAR experiment at RHIC. $K^0_S$ meson and $\Lambda$ hyperon yields are measured via their weak decay channels. Collision centrality and rapidity dependences of the transverse momentum spectra and particle ratios are presented. Particle mass and centrality dependence of the average transverse momenta of $\Lambda$ and $K^0_S$ are compared with other strange particles, providing evidence of the development of hadronic rescattering in such collisions. The 4$\pi$ yields of each of these strange hadrons show a consistent centrality dependence. Discussions on radial flow, the strange hadron production mechanism, and properties of the medium created in such collisions are presented together with results from hadronic transport and thermal model calculations.
dN/dy of lambda for different centrality bins.
dN/dy of Ks0 for different centrality bins.
Rapidity dependence of Lambda/p for different centrality bins.
The PHENIX experiment measured the centrality dependence of two-pion Bose-Einstein correlation functions in $\sqrt{s_{_{NN}}}=200$~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 $\lambda$, the Lévy index of stability $\alpha$, and the Lévy-scale parameter $R$ as a function of transverse mass $m_T$ and centrality. The $\lambda(m_T)$ 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 $\alpha(m_T)$ is independent of $m_T$ within uncertainties in each investigated centrality bin, but shows a clear centrality dependence. At all centralities, the Lévy exponent $\alpha$ is significantly different from that of Gaussian ($\alpha=2$) or Cauchy ($\alpha=1$) 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 $\eta'$ meson is included. In each centrality class, the best value of the in-medium $\eta'$ mass is compared to the mass of the $\eta$ meson, as well as to several theoretical predictions that consider restoration of $U_A(1)$ symmetry in hot hadronic matter.
The transverse-mass dependence of the correlation-strength parameter $\lambda$ in 0-10% centrality bin obtained from Lévy fits with Eq. (9).
The transverse-mass dependence of the correlation-strength parameter $\lambda$ in 10-20% centrality bin obtained from Lévy fits with Eq. (9).
The transverse-mass dependence of the correlation-strength parameter $\lambda$ in 20-30% centrality bin obtained from Lévy fits with Eq. (9).
The spin-exotic hybrid meson $\pi_{1}(1600)$ is predicted to have a large decay rate to the $\omega\pi\pi$ final state. Using 76.6~pb$^{-1}$ of data collected with the GlueX detector, we measure the cross sections for the reactions $\gamma p \to \omega \pi^+ \pi^- p$, $\gamma p \to \omega \pi^0 \pi^0 p$, and $\gamma p\to\omega\pi^-\pi^0\Delta^{++}$ in the range $E_\gamma =$ 8-10 GeV. Using isospin conservation, we set the first upper limits on the photoproduction cross sections of the $\pi^{0}_{1}(1600)$ and $\pi^{-}_{1}(1600)$. We combine these limits with lattice calculations of decay widths and find that photoproduction of $\eta'\pi$ is the most sensitive two-body system to search for the $\pi_1(1600)$.
Measured $\sigma(\gamma p\to\omega\pi^+\pi^-p)$ values for $8<E_\gamma<10$ GeV and $0.1<-t<0.5$ (GeV$^2$). There are normalization uncertainties that are 100% correlated between the three cross section measurements. These include 5% for the luminosity, 13.5% for the tracking efficiency, and 8.1% for the photon efficiency.
Measured $\sigma(\gamma p\to\omega\pi^0\pi^0p)$ values for $8<E_\gamma<10$ GeV and $0.1<-t<0.5$ (GeV$^2$). There are normalization uncertainties that are 100% correlated between the three cross section measurements. These include 5% for the luminosity, 9.1% for the tracking efficiency, and 24.3% for the photon efficiency.
Measured $\sigma(\gamma p\to\omega\pi^-\pi^0\Delta^{++})$ values for $8<E_\gamma<10$ GeV and $0.1<-t<0.5$ (GeV$^2$). There are normalization uncertainties that are 100% correlated between the three cross section measurements. These include 5% for the luminosity, 16% for the tracking efficiency, and 16.3% for the photon efficiency.
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