Abhisek Datta

The second Fourier component v_2 of the azimuthal anisotropy with respect to the reaction plane was measured for direct photons at midrapidity and transverse momentum (p_T) of 1--13 GeV/c in Au+Au collisions at sqr(s_NN)=200 GeV. Previous measurements of this quantity for hadrons with p_T < 6 GeV/c indicate that the medium behaves like a nearly perfect fluid, while for p_T > 6 GeV/c a reduced anisotropy is interpreted in terms of a path-length dependence for parton energy loss. In this measurement with the PHENIX detector at the Relativistic Heavy Ion Collider we find that for p_T > 4 GeV/c the anisotropy for direct photons is consistent with zero, as expected if the dominant source of direct photons is initial hard scattering. However, in the p_T < 4 GeV/c region dominated by thermal photons, we find a substantial direct photon v_2 comparable to that of hadrons, whereas model calculations for thermal photons in this kinematic region significantly underpredict the observed v_2.

The PHENIX experiment at RHIC has measured the centrality dependence of the direct photon yield from Au+Au collisions at √sNN=200 GeV down to pT=0.4 GeV/c. Photons are detected via photon conversions to e+e− pairs and an improved technique is applied that minimizes the systematic uncertainties that usually limit direct photon measurements, in particular at low pT. We find an excess of direct photons above the Ncoll-scaled yield measured in p+p collisions. This excess yield is well described by an exponential distribution with an inverse slope of about 240MeV/c in the pT range 0.6–2.0 GeV/c. While the shape of the pT distribution is independent of centrality within the experimental uncertainties, the yield increases rapidly with increasing centrality, scaling approximately with Nαpart, where α=1.38±0.03(stat)±0.07(syst).3 MoreReceived 23 May 2014Revised 16 March 2015DOI:https://doi.org/10.1103/PhysRevC.91.064904©2015 American Physical Society

The PHENIX experiment at the BNL Relativistic Heavy Ion Collider has measured second- and third-order Fourier coefficients of the azimuthal distributions of direct photons emitted at midrapidity in Au+Au collisions at √sNN=200 GeV for various collision centralities. Combining two different analysis techniques, results were obtained in the transverse momentum range of 0.4<pT<4.0 GeV/c. At low pT the second-order coefficients, v2, are similar to the ones observed in hadrons. Third-order coefficients, v3, are nonzero and almost independent of centrality. These new results on v2 and v3, combined with previously published results on yields, are compared to model calculations that provide yields and asymmetries in the same framework. Those models are challenged to explain simultaneously the observed large yield and large azimuthal anisotropies.2 MoreReceived 5 October 2015DOI:https://doi.org/10.1103/PhysRevC.94.064901©2016 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasPhoton, lepton & quark productionRelativistic heavy-ion collisionsNuclear Physics

Results are presented from data recorded in 2009 by the PHENIX experiment at the Relativistic Heavy Ion Collider for the double-longitudinal spin asymmetry, $A_{LL}$, for $\pi^0$ and $\eta$ production in $\sqrt{s} = 200$ GeV polarized $p$$+$$p$ collisions. Comparison of the $\pi^0$ results with different theory expectations based on fits of other published data showed a preference for small positive values of gluon polarization, $\Delta G$, in the proton in the probed Bjorken $x$ range. The effect of adding the new 2009 \pz data to a recent global analysis of polarized scattering data is also shown, resulting in a best fit value $\Delta G^{[0.05,0.2]}_{\mbox{DSSV}} = 0.06^{+0.11}_{-0.15}$ in the range $0.05<x<0.2$, with the uncertainty at $\Delta \chi^2 = 9$ when considering only statistical experimental uncertainties. Shifting the PHENIX data points by their systematic uncertainty leads to a variation of the best-fit value of $\Delta G^{[0.05,0.2]}_{\mbox{DSSV}}$ between $0.02$ and $0.12$, demonstrating the need for full treatment of the experimental systematic uncertainties in future global analyses.

About 1% of giant stars have been shown to have large surface Li abundances, which is unexpected according to standard stellar evolution models. Several scenarios for lithium production have been proposed, but it is still unclear why these Li-rich giants exist. A missing piece in this puzzle is the knowledge of the exact stage of evolution of these stars. Using low-and-high-resolution spectroscopic observations, we have undertaken a survey of lithium-rich giants in the Kepler field. In this letter, we report the finding of the first confirmed Li-rich core-helium-burning giant, as revealed by asteroseismic analysis. The evolutionary timescales constrained by its mass suggest that Li-production most likely took place through non-canonical mixing at the RGB-tip, possibly during the helium flash.

The standard model (SM) of particle physics is spectacularly successful, yet the measured value of the muon anomalous magnetic moment ${(g\ensuremath{-}2)}_{\ensuremath{\mu}}$ deviates from SM calculations by $3.6\ensuremath{\sigma}.$ Several theoretical models attribute this to the existence of a ``dark photon,'' an additional U(1) gauge boson, which is weakly coupled to ordinary photons. The PHENIX experiment at the Relativistic Heavy Ion Collider has searched for a dark photon, $U$, in ${\ensuremath{\pi}}^{0},\ensuremath{\eta}\ensuremath{\rightarrow}\ensuremath{\gamma}{e}^{+}{e}^{\ensuremath{-}}$ decays and obtained upper limits of $\mathcal{O}(2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6})$ on $U\ensuremath{-}\ensuremath{\gamma}$ mixing at 90% C.L. for the mass range $30&lt;{m}_{U}&lt;90$ $\mathrm{MeV}/{c}^{2}$. Combined with other experimental limits, the remaining region in the $U\ensuremath{-}\ensuremath{\gamma}$ mixing parameter space that can explain the ${(g\ensuremath{-}2)}_{\ensuremath{\mu}}$ deviation from its SM value is nearly completely excluded at the 90% confidence level, with only a small region of $29&lt;{m}_{U}&lt;32$ $\mathrm{MeV}/{c}^{2}$ remaining.

We present measurements of ${e}^{+}{e}^{\ensuremath{-}}$ production at midrapidity in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{{s}_{{}_{NN}}}=200$ GeV. The invariant yield is studied within the PHENIX detector acceptance over a wide range of mass (${m}_{ee}&lt;5 \mathrm{GeV}/{c}^{2}$) and pair transverse momentum (${p}_{T}&lt;5 \mathrm{GeV}/c$) for minimum bias and for five centrality classes. The ${e}^{+}{e}^{\ensuremath{-}}$ yield is compared to the expectations from known sources. In the low-mass region (${m}_{ee}=0.30--0.76 \mathrm{GeV}/{c}^{2}$) there is an enhancement that increases with centrality and is distributed over the entire pair ${p}_{T}$ range measured. It is significantly smaller than previously reported by the PHENIX experiment and amounts to $2.3\ifmmode\pm\else\textpm\fi{}0.4(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.4(\mathrm{syst})\ifmmode\pm\else\textpm\fi{}0.2(\mathrm{model})$ or to $1.7\ifmmode\pm\else\textpm\fi{}0.3(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.3(\mathrm{syst})\ifmmode\pm\else\textpm\fi{}0.2(\mathrm{model})$ for minimum bias collisions when the open heavy-flavor contribution is calculated with pythia or mc@nlo, respectively. The inclusive mass and ${p}_{T}$ distributions, as well as the centrality dependence, are well reproduced by model calculations where the enhancement mainly originates from the melting of the $\ensuremath{\rho}$ meson resonance as the system approaches chiral symmetry restoration. In the intermediate-mass region (${m}_{ee}=1.2--2.8 \mathrm{GeV}/{c}^{2}$), the data hint at a significant contribution in addition to the yield from the semileptonic decays of heavy-flavor mesons.

PHENIX measurements are presented for the cross section and double-helicity asymmetry ($A_{LL}$) in inclusive $\pi^0$ production at midrapidity from $p$$+$$p$ collisions at $\sqrt{s}=510$~GeV from data taken in 2012 and 2013 at the Relativistic Heavy Ion Collider. The next-to-leading-order perturbative-quantum-chromodynamics theory calculation is in excellent agreement with the presented cross section results. The calculation utilized parton-to-pion fragmentation functions from the recent DSS14 global analysis, which prefer a smaller gluon-to-pion fragmentation function. The $\pi^{0}A_{LL}$ results follow an increasingly positive asymmetry trend with $p_T$ and $\sqrt{s}$ with respect to the predictions and are in excellent agreement with the latest global analysis results. This analysis incorporated earlier results on $\pi^0$ and jet $A_{LL}$, and suggested a positive contribution of gluon polarization to the spin of the proton $\Delta G$ for the gluon momentum fraction range $x>0.05$. The data presented here extend to a currently unexplored region, down to $x\sim0.01$, and thus provide additional constraints on the value of $\Delta G$. The results confirm the evidence for nonzero $\Delta G$ using a different production channel in a complementary kinematic region.

Asymmetric nuclear collisions of $p$$+$Al, $p$$+$Au, $d$$+$Au, and $^{3}$He$+$Au at $\sqrt{s_{_{NN}}}=200$ GeV provide an excellent laboratory for understanding particle production, as well as exploring interactions among these particles after their initial creation in the collision. We present measurements of charged hadron production $dN_{\rm ch}/d\eta$ in all such collision systems over a broad pseudorapidity range and as a function of collision multiplicity. A simple wounded quark model is remarkably successful at describing the full data set. We also measure the elliptic flow $v_{2}$ over a similarly broad pseudorapidity range. These measurements provide key constraints on models of particle emission and their translation into flow.

The jet fragmentation function is measured with direct photon-hadron correlations in p+p and Au+Au collisions at √sNN=200 GeV. The pT of the photon is an excellent approximation to the initial pT of the jet and the ratio zT=phT/pγT is used as a proxy for the jet fragmentation function. A statistical subtraction is used to extract the direct photon-hadron yields in Au+Au collisions while a photon isolation cut is applied in p+p. IAA, the ratio of hadron yield opposite the photon in Au+Au to that in p+p, indicates modification of the jet fragmentation function. Suppression, most likely due to energy loss in the medium, is seen at high zT. The associated hadron yield at low zT is enhanced at large angles. Such a trend is expected from redistribution of the lost energy into increased production of low-momentum particles.Received 17 December 2012DOI:https://doi.org/10.1103/PhysRevLett.111.032301© 2013 American Physical Society

The PHENIX Collaboration at the Relativistic Heavy Ion Collider has measured open heavy-flavor production in minimum bias Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV via the yields of electrons from semileptonic decays of charm and bottom hadrons. Previous heavy-flavor electron measurements indicated substantial modification in the momentum distribution of the parent heavy quarks due to the quark-gluon plasma created in these collisions. For the first time, using the PHENIX silicon vertex detector to measure precision displaced tracking, the relative contributions from charm and bottom hadrons to these electrons as a function of transverse momentum are measured in Au$+$Au collisions. We compare the fraction of electrons from bottom hadrons to previously published results extracted from electron-hadron correlations in $p$$+$$p$ collisions at $\sqrt{s_{_{NN}}}=200$ GeV and find the fractions to be similar within the large uncertainties on both measurements for $p_T>4$ GeV/$c$. We use the bottom electron fractions in Au$+$Au and $p$$+$$p$ along with the previously measured heavy flavor electron $R_{AA}$ to calculate the $R_{AA}$ for electrons from charm and bottom hadron decays separately. We find that electrons from bottom hadron decays are less suppressed than those from charm for the region $3<p_T<4$ GeV/$c$.

We present a measurement of the cross section and transverse single-spin asymmetry ($A_N$) for $\eta$ mesons at large pseudorapidity from $\sqrt{s}=200$~GeV $p^{\uparrow}+p$ collisions. The measured cross section for $0.5<p_T<5.0$~GeV/$c$ and $3.0<|\eta|<3.8$ is well described by a next-to-leading-order perturbative-quantum-chromodynamics calculation. The asymmetries $A_N$ have been measured as a function of Feynman-$x$ ($x_F$) from $0.2<|x_{F}|<0.7$, as well as transverse momentum ($p_T$) from $1.0<p_T<4.5$~GeV/$c$. The asymmetry averaged over positive $x_F$ is $\langle{A_{N}}\rangle=0.061{\pm}0.014$. The results are consistent with prior transverse single-spin measurements of forward $\eta$ and $\pi^{0}$ mesons at various energies in overlapping $x_F$ ranges. Comparison of different particle species can help to determine the origin of the large observed asymmetries in $p^{\uparrow}+p$ collisions.

We present a detailed measurement of charged two-pion correlation functions in 0–30% centrality √sNN=200 GeV Au+Au collisions by the PHENIX experiment at the Relativistic Heavy Ion Collider. The data are well described by Bose-Einstein correlation functions stemming from Lévy-stable source distributions. Using a fine transverse momentum binning, we extract the correlation strength parameter λ, the Lévy index of stability α, and the Lévy length scale parameter R as a function of average transverse mass of the pair mT. We find that the positively and the negatively charged pion pairs yield consistent results, and their correlation functions are represented, within uncertainties, by the same Lévy-stable source functions. The λ(mT) measurements indicate a decrease of the strength of the correlations at low mT. The Lévy length scale parameter R(mT) decreases with increasing mT, following a hydrodynamically predicted type of scaling behavior. The values of the Lévy index of stability α are found to be significantly lower than the Gaussian case of α=2, but also significantly larger than the conjectured value that may characterize the critical point of a second-order quark-hadron phase transition.4 MoreReceived 19 September 2017DOI:https://doi.org/10.1103/PhysRevC.97.064911©2018 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasParticle correlations & fluctuationsQuark-gluon plasmaRelativistic heavy-ion collisionsPhysical SystemsBose-Einstein condensatesPionsNuclear Physics

New measurements by the PHENIX experiment at RHIC for eta production at midrapidity as a function of transverse momentum (p_T) and collision centrality in sqrt(s_NN) = 200 GeV Au+Au and p+p collisions are presented. They indicate nuclear modification factors (R_AA) that are similar both in magnitude and trend to those found in earlier pi^0 measurements. Linear fits to R_AA in the 5--20 GeV/c p_T region show that the slope is consistent with zero within two standard deviations at all centralities although a slow rise cannot be excluded. Having different statistical and systematic uncertainties the pi^0 and eta measurements are complementary at high p_T; thus, along with the extended p_T range of these data they can provide additional constraints for theoretical modeling and the extraction of transport properties.

We report the first measurement of transverse single-spin asymmetries in $J/\psi$ production from transversely polarized $p+p$ collisions at $\sqrt{s} = 200$ GeV with data taken by the PHENIX experiment in 2006 and 2008. The measurement was performed over the rapidity ranges $1.2 < |y| < 2.2$ and $ |y| < 0.35$ for transverse momenta up to 6 GeV/$c$. $J/\psi$ production at RHIC is dominated by processes involving initial-state gluons, and transverse single-spin asymmetries of the $J/\psi$ can provide access to gluon dynamics within the nucleon. Such asymmetries may also shed light on the long-standing question in QCD of the $J/\psi$ production mechanism. Asymmetries were obtained as a function of $J/\psi$ transverse momentum and Feynman-$x$, with a value of $-0.086 \pm 0.026^{\rm stat} \pm 0.003^{\rm syst}$ in the forward region. This result suggests possible nonzero trigluon correlation functions in transversely polarized protons and, if well defined in this reaction, a nonzero gluon Sivers distribution function.

The cross section and transverse single-spin asymmetries of $\mu^{-}$ and $\mu^{+}$ from open heavy-flavor decays in polarized $p$+$p$ collisions at $\sqrt{s}=200$ GeV were measured by the PHENIX experiment during 2012 at the Relativistic Heavy Ion Collider. Because heavy-flavor production is dominated by gluon-gluon interactions at $\sqrt{s}=200$ GeV, these measurements offer a unique opportunity to obtain information on the trigluon correlation functions. The measurements are performed at forward and backward rapidity ($1.4<|y|<2.0$) over the transverse momentum range of $1.25<p_T<7$ GeV/$c$ for the cross section and $1.25<p_T<5$ GeV/$c$ for the asymmetry measurements. The obtained cross section is compared to a fixed-order-plus-next-to-leading-log perturbative-quantum-chromodynamics calculation. The asymmetry results are consistent with zero within uncertainties, and a model calculation based on twist-3 three-gluon correlations agrees with the data.

The PHENIX experiment reports systematic measurements at the Relativistic Heavy Ion Collider of ϕ-meson production in asymmetric Cu+Au collisions at sNN=200GeV and in U+U collisions at sNN=193GeV. Measurements were performed via the ϕ→K+K− decay channel at midrapidity |η|<0.35. Features of ϕ-meson production measured in Cu+Cu, Cu+Au, Au+Au, and U+U collisions were found to not depend on the collision geometry, which was expected because the yields are averaged over the azimuthal angle and follow the expected scaling with nuclear-overlap size. The elliptic flow of the ϕ meson in Cu+Au, Au+Au, and U+U collisions scales with second-order-participant eccentricity and the length scale of the nuclear-overlap region (estimated with the number of participating nucleons). At moderate pT, ϕ-meson production measured in Cu+Au and U+U collisions is consistent with coalescence-model predictions, whereas at high pT the production is in agreement with expectations for in-medium energy loss of parent partons prior to their fragmentation. The elliptic flow for ϕ mesons measured in Cu+Au and U+U collisions is well described by a (2+1)-dimensional viscous-hydrodynamic model with specific-shear viscosity η/s=1/4π.5 MoreReceived 25 July 2022Accepted 28 September 2022DOI:https://doi.org/10.1103/PhysRevC.107.014907©2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasLeptonic, semileptonic & radiative decaysParticle productionRelativistic heavy-ion collisionsPhysical SystemsStrange quarkVector mesonsTechniquesHadron collidersNuclear Physics

We present measurements of the J/psi invariant yields in sqrt(s_NN)=39 and 62.4 GeV Au+Au collisions at forward rapidity (1.2

Advanced detector R&D requires performing computationally intensive and detailed simulations as part of the detector-design optimization process. We propose a general approach to this process based on Bayesian optimization and machine learning that encodes detector requirements. As a case study, we focus on the design of the dual-radiator Ring Imaging Cherenkov (dRICH) detector under development as part of the particle-identification system at the future Electron-Ion Collider (EIC). The EIC is a US-led frontier accelerator project for nuclear physics, which has been proposed to further explore the structure and interactions of nuclear matter at the scale of sea quarks and gluons. We show that the detector design obtained with our automated and highly parallelized framework outperforms the baseline dRICH design within the assumptions of the current model. Our approach can be applied to any detector R&D, provided that realistic simulations are available.

The PHENIX collaboration presents a systematic study of $\pi^0$ production from $p$$+$$p$, $p$$+$Al, $p$$+$Au, $d$$+$Au, and $^{3}$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV. Measurements were performed with different centrality selections as well as the total inelastic, 0%--100%, selection for all collision systems. For 0%--100% collisions, the nuclear modification factors, $R_{xA}$, are consistent with unity for $p_T$ above 8 GeV/$c$, but exhibit an enhancement in peripheral collisions and a suppression in central collisions. The enhancement and suppression characteristics are similar for all systems for the same centrality class. It is shown that for high-$p_T$-$\pi^0$ production, the nucleons in the $d$ and $^3$He interact mostly independently with the Au nucleus and that the counter intuitive centrality dependence is likely due to a physical correlation between multiplicity and the presence of a hard scattering process. These observations disfavor models where parton energy loss has a significant contribution to nuclear modifications in small systems. Nuclear modifications at lower $p_T$ resemble the Cronin effect -- an increase followed by a peak in central or inelastic collisions and a plateau in peripheral collisions. The peak height has a characteristic ordering by system size as $p$$+$Au $>$ $d$$+$Au $>$ $^{3}$He$+$Au $>$ $p$$+$Al. For collisions with Au ions, current calculations based on initial state cold nuclear matter effects result in the opposite order, suggesting the presence of other contributions to nuclear modifications, in particular at lower $p_T$.

The measurement of direct photons from Au+Au collisions at √sNN=39 and 62.4 GeV in the transverse-momentum range 0.4<pT<3Gev/c is presented by the PHENIX collaboration at the BNLRelativistic Heavy Ion Collider. A significant direct-photon yield is observed in both collision systems. A universal scaling is observed when the direct-photon pT spectra for different center-of-mass energies and for different centrality selections at √sNN=62.4 GeV is scaled with (dNch/dη)α for α=1.21±0.04. This scaling also holds true for direct-photon spectra from Au+Au collisions at √sNN=200 GeV measured earlier by PHENIX, as well as the spectra from Pb+Pb at √sNN=2760 GeV published by ALICE. The scaling power α seems to be independent of pT, center of mass energy, and collision centrality. The spectra from different collision energies have a similar shape up to pT of 2 Gev/c. The spectra have a local inverse slope Teff increasing with pT of 0.174±0.018Gev/c in the range 0.4<pT<1.3Gev/c and increasing to 0.289±0.024Gev/c for 0.9<pT<2.1Gev/c. The observed similarity of low-pT direct-photon production from √sNN=39 to 2760 GeV suggests a common source of direct photons for the different collision energies and event centrality selections, and suggests a comparable space-time evolution of direct-photon emission.9 MoreReceived 24 March 2022Accepted 21 October 2022DOI:https://doi.org/10.1103/PhysRevC.107.024914©2023 American Physical SocietyPhysics Subject Headings (PhySH)Photon, lepton & quark productionResearch AreasRelativistic heavy-ion collisionsPhoton, lepton & quark productionResearch AreasPhoton, lepton & quark productionRelativistic heavy-ion collisionsTechniquesHadron collidersNuclear Physics

The invariant yield of electrons from open-heavy-flavor decays for 1<pT<8 GeV/c at midrapidity |y|<0.35 in Au+Au collisions at √sNN = 200 GeV has been measured by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider. A displaced-vertex analysis with the PHENIX silicon-vertex detector enables extraction of the fraction of charm and bottom hadron decays and unfolding of the invariant yield of parent charm and bottom hadrons. The nuclear-modification factors RAA for electrons from charm and bottom hadron decays and heavy-flavor hadrons show both a centrality and a quark-mass dependence, indicating suppression in the quark-gluon plasma produced in these collisions that is medium sized and quark-mass dependent.11 MoreReceived 5 April 2022Revised 31 January 2024Accepted 23 February 2024DOI:https://doi.org/10.1103/PhysRevC.109.044907©2024 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasHadronic decaysJets & heavy flavor physicsParticle & resonance productionPhysical SystemsBottom quarkCharm quarkTechniquesHadron collidersNuclear Physics

The measurement of the direct-photon spectrum from Au+Au collisions at √sNN=200 GeV is presented by the PHENIX Collaboration using the external-photon-conversion technique for 0%–93% central collisions in a transverse-momentum (pT) range of 0.8–10 GeV/c. An excess of direct photons, above prompt-photon production from hard-scattering processes, is observed for pT<6GeV/c. Nonprompt direct photons are measured by subtracting the prompt component, which is estimated as Ncoll-scaled direct photons from p+p collisions at 200 GeV, from the direct-photon spectrum. Results are obtained for 0.8<pT<6.0GeV/c and suggest that the spectrum has an increasing inverse slope from ≈0.2 to 0.4 GeV/c with increasing pT, which indicates a possible sensitivity of the measurement to photons from earlier stages of the evolution of the collision. In addition, like the direct-photon production, the pT-integrated nonprompt direct-photon yields also follow a power-law scaling behavior as a function of collision-system size. The exponent, α, for the nonprompt component is found to be consistent with 1.1 with no apparent pT dependence.23 MoreReceived 5 April 2022Revised 18 December 2023Accepted 26 January 2024DOI:https://doi.org/10.1103/PhysRevC.109.044912©2024 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasPhoton, lepton & quark productionRelativistic heavy-ion collisionsTechniquesHadron collidersNuclear Physics

The Kepler satellite has provided photometric timeseries data of unprecedented length, duty cycle and precision. To fully analyse these data for the tens of thousands of stars observed by Kepler, automated methods are a prerequisite. Here we present an automated procedure to determine the period spacing of gravity modes in red-giant stars ascending the red-giant branch. The gravity modes reside in a cavity in the deep interior of the stars and provide information on the conditions in the stellar core. However, for red giants the gravity modes are not directly observable on the surface, hence this method is based on the pressure-gravity mixed modes that present observable features in the Fourier power spectrum. The method presented here is based on the vertical alignment and symmetry of these mixed modes in a period echelle diagram. We find that we can obtain reliable results for both model frequencies and observed frequencies. Additionally, we carried out Monte Carlo tests to obtain realistic uncertainties on the period spacings with different set of oscillation modes (for the models) and uncertainties on the frequencies. Furthermore, this method has been used to improve mode detection and identification of the observed frequencies in an iterative manner.

Production of $\pi^0$ and $\eta$ mesons has been measured at midrapidity in Cu$+$Au collisions at $\sqrt{s_{_{NN}}}$=200 GeV. Measurements were performed in $\pi^0(\eta)\rightarrow\gamma\gamma$ decay channel in the 1(2)-20 GeV/$c$ transverse momentum range. A strong suppression is observed for $\pi^0$ and $\eta$ meson production at high transverse momentum in central Cu$+$Au collisions relative to the $p$$+$$p$ results scaled by the number of nucleon-nucleon collisions. In central collisions the suppression is similar to Au$+$Au with comparable nuclear overlap. The $\eta/\pi^0$ ratio measured as a function of transverse momentum is consistent with $m_T$-scaling parameterization down to $p_T=$2 GeV/$c$, its asymptotic value is constant and consistent with Au$+$Au and $p$$+$$p$ and does not show any significant dependence on collision centrality. Similar results were obtained in hadron-hadron, hadron-nucleus, and nucleus-nucleus collisions as well as in $e^+e^-$ collisions in a range of collision energies $\sqrt{s_{_{NN}}}=$3--1800 GeV. This suggests that the quark-gluon-plasma medium produced in Cu$+$Cu collisions either does not affect the jet fragmentation into light mesons or it affects the $\pi^0$ and $\eta$ the same way.

We report on $J/\psi$ production from asymmetric Cu+Au heavy-ion collisions at $\sqrt{s_{_{NN}}}$=200 GeV at the Relativistic Heavy Ion Collider at both forward (Cu-going direction) and backward (Au-going direction) rapidities. The nuclear modification of $J/\psi$ 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, $J/\psi$ 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. 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.

A powerful new electron–ioncollider (EIC) has been recommended in the 2015 Long Range Plan for Nuclear Science for probing the partonic structure inside nucleons and nuclei with unprecedented precision and versatility [1]. EIC detectors are currently under development [2], all of which require hadron identification over a broad kinematic range. A prototype ring imaging Cherenkov detector has been developed for hadron identification in the momentum range from 3 GeV/c to 10 GeV/c. The key feature of this new detector is a compact and modular design, achieved by using aerogel as radiator and a Fresnel lens for ring focusing. In this paper, the results from a beam test of a prototype device at Fermilab are reported.

We have measured the cross section and single-spin asymmetries from forward ${W}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\nu}$ production in longitudinally polarized $p+p$ collisions at $\sqrt{s}=510\text{ }\text{ }\mathrm{GeV}$ using the PHENIX detector at the Relativistic Heavy Ion Collider. The cross sections are consistent with previous measurements at this collision energy, while the most forward and backward longitudinal single spin asymmetries provide new insights into the sea quark helicities in the proton. The charge of the $W$ bosons provides a natural flavor separation of the participating partons.

An Electron-Ion Collider (EIC) has been proposed to further explore the strong force and QCD, focusing on the structure and the interaction of gluon-dominated matter. A generic detector R&D program (EIC PID consortium) for the particle identification in EIC experiments was formed to explore technologically advanced solutions in this scope. In this context two Ring Imaging Cherenkov (RICH) counters have been proposed: a modular RICH detector which consists of an aerogel radiator, a Fresnel lens, a mirrored box, and pixelated photon sensor; a dual-radiator RICH, consisting of an aerogel radiator and C2F6 gas in a mirror-focused configuration. We present the simulations of the two detectors and their estimated performance.

We present measurements of azimuthal correlations of charged hadron pairs in $\sqrt{{s}_{\mathit{NN}}}=200$ GeV $\mathrm{Au}+\mathrm{Au}$ collisions for the trigger and associated particle transverse-momentum ranges of $1&lt;{p}_{T}^{t}&lt;10\phantom{\rule{4pt}{0ex}}\mathrm{GeV}/c$ and $0.5&lt;{p}_{T}^{a}&lt;10\phantom{\rule{4pt}{0ex}}\mathrm{GeV}/c$. After subtraction of an underlying event using a model that includes higher-order azimuthal anisotropy ${v}_{2}, {v}_{3}$, and ${v}_{4}$, the away-side yield of the highest trigger-${p}_{T}$(${p}_{T}^{t}&gt;4\phantom{\rule{4pt}{0ex}}\mathrm{GeV}/c$) correlations is suppressed compared with that of correlations measured in $p+p$ collisions. At the lowest associated particle ${p}_{T}$($0.5&lt;{p}_{T}^{a}&lt;1\phantom{\rule{4pt}{0ex}}\mathrm{GeV}/c$), the away-side shape and yield are modified relative to those in $p+p$ collisions. These observations are consistent with the scenario of radiative-jet energy loss. For the low-${p}_{T}$ trigger correlations ($2&lt;{p}_{T}^{t}&lt;4\phantom{\rule{4pt}{0ex}}\mathrm{GeV}/c$), a finite away-side yield exists and we explore the dependence of the shape of the away-side within the context of an underlying-event model. Correlations are also studied differentially versus event-plane angle ${\mathrm{\ensuremath{\Psi}}}_{2}$ and ${\mathrm{\ensuremath{\Psi}}}_{3}$. The angular correlations show an asymmetry when selecting the sign of the difference between the trigger-particle azimuthal angle and the ${\mathrm{\ensuremath{\Psi}}}_{2}$ event plane. This asymmetry and the measured suppression of the pair yield out-of-plane is consistent with a path-length-dependent energy loss. No ${\mathrm{\ensuremath{\Psi}}}_{3}$ dependence can be resolved within experimental uncertainties.

Charmonium is a valuable probe in heavy-ion collisions to study the properties of the quark gluon plasma, and is also an interesting probe in small collision systems to study cold nuclear matter effects, which are also present in large collision systems. With the recent observations of collective behavior of produced particles in small system collisions, measurements of the modification of charmonium in small systems have become increasingly relevant. We present the results of $J/\psi$ measurements at forward and backward rapidity in various small collision systems, $p$$+$$p$, $p$$+$Al, $p$$+$Au and $^3$He$+$Au, at $\sqrt{s_{_{NN}}}$=200 GeV. The results are presented in the form of the observable $R_{AB}$, the nuclear modification factor, a measure of the ratio of the $J/\psi$ invariant yield compared to the scaled yield in $p$$+$$p$ collisions. We examine the rapidity, transverse momentum, and collision centrality dependence of nuclear effects on $J/\psi$ production with different projectile sizes $p$ and $^3$He, and different target sizes Al and Au. The modification is found to be strongly dependent on the target size, but to be very similar for $p$$+$Au and $^{3}$He$+$Au. However, for 0%--20% central collisions at backward rapidity, the modification for $^{3}$He$+$Au is found to be smaller than that for $p$$+$Au, with a mean fit to the ratio of $0.89\pm0.03$(stat)${\pm}0.08$(syst), possibly indicating final state effects due to the larger projectile size.

We present midrapidity charged-pion invariant cross sections, the ratio of the ${\ensuremath{\pi}}^{\ensuremath{-}}$ to ${\ensuremath{\pi}}^{+}$ cross sections and the charge-separated double-spin asymmetries in polarized $p+p$ collisions at $\sqrt{s}=200\text{ }\mathrm{GeV}$. While the cross section measurements are consistent within the errors of next-to-leading-order (NLO) perturbative quantum chromodynamics predictions (pQCD), the same calculations overestimate the ratio of the charged-pion cross sections. This discrepancy arises from the cancellation of the substantial systematic errors associated with the NLO-pQCD predictions in the ratio and highlights the constraints these data will place on flavor-dependent pion fragmentation functions. The charge-separated pion asymmetries presented here sample an $x$ range of $\ensuremath{\sim}0.03--0.16$ and provide unique information on the sign of the gluon-helicity distribution.

Received 25 October 2012DOI:https://doi.org/10.1103/PhysRevD.86.099904© 2012 American Physical Society

We report on the first measurement of the double-spin asymmetry, ${A}_{LL}$, of electrons from the decays of hadrons containing heavy flavor in longitudinally polarized $p+p$ collisions at $\sqrt{s}=200\text{ }\text{ }\mathrm{GeV}$ for ${p}_{T}=0.5$ to $3.0\text{ }\text{ }\mathrm{GeV}/c$. The asymmetry was measured at midrapidity ($|\ensuremath{\eta}|&lt;0.35$) with the PHENIX detector at the Relativistic Heavy Ion Collider. The measured asymmetries are consistent with zero within the statistical errors. We obtained a constraint for the polarized gluon distribution in the proton of $|\ensuremath{\Delta}g/g({log}_{10}x=\ensuremath{-}{1.6}_{\ensuremath{-}0.4}^{+0.5},\ensuremath{\mu}={m}_{T}^{c}){|}^{2}&lt;0.030$ ($1\ensuremath{\sigma}$) based on a leading-order perturbative quantum chromodynamics model, using the measured asymmetry.

We report the double-helicity asymmetry, ${A}_{LL}^{J/\ensuremath{\psi}}$, in inclusive $J/\ensuremath{\psi}$ production at forward rapidity as a function of transverse momentum ${p}_{T}$ and rapidity $|y|$. The data analyzed were taken during $\sqrt{s}=510\text{ }\text{ }\mathrm{GeV}$ longitudinally polarized $p+p$ collisions at the Relativistic Heavy Ion Collider in the 2013 run using the PHENIX detector. At this collision energy, $J/\ensuremath{\psi}$ particles are predominantly produced through gluon-gluon scatterings, thus ${A}_{LL}^{J/\ensuremath{\psi}}$ is sensitive to the gluon polarization inside the proton. We measured ${A}_{LL}^{J/\ensuremath{\psi}}$ by detecting the decay daughter muon pairs ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ within the PHENIX muon spectrometers in the rapidity range $1.2&lt;|y|&lt;2.2$. In this kinematic range, we measured the ${A}_{LL}^{J/\ensuremath{\psi}}$ to be $0.012\ifmmode\pm\else\textpm\fi{}0.010$ (stat) $\ifmmode\pm\else\textpm\fi{}0.003$ (syst). The ${A}_{LL}^{J/\ensuremath{\psi}}$ can be expressed to be proportional to the product of the gluon polarization distributions at two distinct ranges of Bjorken $x$: one at moderate range $x\ensuremath{\approx}5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ where recent data of jet and ${\ensuremath{\pi}}^{0}$ double helicity spin asymmetries have shown evidence for significant gluon polarization, and the other one covering the poorly known small-$x$ region $x\ensuremath{\approx}2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$. Thus our new results could be used to further constrain the gluon polarization for $x&lt;5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$.

Small nuclear collisions are mainly sensitive to cold-nuclear-matter effects; however, the collective behavior observed in these collisions shows a hint of hot-nuclear-matter effects. The identified-particle spectra, especially the $\phi$ mesons which contain strange and antistrange quarks and have a relatively small hadronic-interaction cross section, are a good tool to study these effects. The PHENIX experiment has measured $\phi$ mesons in a specific set of small collision systems $p$$+$Al, $p$$+$Au, and $^3$He$+$Au, as well as $d$$+$Au [Phys. Rev. C {\bf 83}, 024909 (2011)], at $\sqrt{s_{_{NN}}}=200$ GeV. The transverse-momentum spectra and nuclear-modification factors are presented and compared to theoretical-model predictions. The comparisons with different calculations suggest that quark-gluon plasma may be formed in these small collision systems at $\sqrt{s_{_{NN}}}=200$ GeV. However, the volume and the lifetime of the produced medium may be insufficient for observing strangeness-enhancement and jet-quenching effects. Comparison with calculations suggests that the main production mechanisms of $\phi$ mesons at midrapidity may be different in $p$$+$Al versus $p/d/$$^3$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV. While thermal quark recombination seems to dominate in $p/d/$$^3$He$+$Au collisions, fragmentation seems to be the main production mechanism in $p$$+$Al collisions.

The Large Hadron Collider (LHC) in the High Luminosity (HL-LHC) era will be upgraded to deliver instantaneous luminosities up to 5 × 10 34 cm -2 s -1 , five times more than the original design value.In order to maintain performance of the Compact Muon Solenoid (CMS) Experiment under these conditions, ME0 is one of the new muon detectors being added, along with GE1/1, GE2/1, RE3/1 and RE4/1.ME0 will use the triple Gas Electron Multiplier (GEM) technology and is designed to cover the far-forward region of 2.0 < |η| < 2.8.The readout electronics for ME0 must be designed to deal with high data rates and be sufficiently radiation hard to operate very close to the beamline.The design and development status of the readout electronics for ME0 will be presented, along with recent results from integration tests performed using the latest electronics prototypes with GEM chambers.

The invariant yields for $J/\psi$ production at forward rapidity $(1.2<|y|<2.2)$ in U$+$U collisions at $\sqrt{s_{_{NN}}}$=193 GeV have been measured as a function of collision centrality. The invariant yields and nuclear-modification factor $R_{AA}$ are presented and compared with those from Au$+$Au collisions in the same rapidity range. Additionally, the direct ratio of the invariant yields from U$+$U and Au$+$Au collisions within the same centrality class is presented, and used to investigate the role of $c\bar{c}$ coalescence. Two different parameterizations of the deformed Woods-Saxon distribution were used in Glauber calculations to determine the values of the number of nucleon-nucleon collisions in each centrality class, $N_{\rm coll}$, and these were found to give significantly different $N_{\rm coll}$ values. Results using $N_{\rm coll}$ values from both deformed Woods-Saxon distributions are presented. The measured ratios show that the $J/\psi$ suppression, relative to binary collision scaling, is similar in U$+$U and Au$+$Au for peripheral and midcentral collisions, but that $J/\psi$ show less suppression for the most central U$+$U collisions. The results are consistent with a picture in which, for central collisions, increase in the $J/\psi$ yield due to $c\bar{c}$ coalescence becomes more important than the decrease in yield due to increased energy density. For midcentral collisions, the conclusions about the balance between $c\bar{c}$ coalescence and suppression depend on which deformed Woods-Saxon distribution is used to determine $N_{\rm coll}$.

Two-pion interferometry measurements are used to extract the Gaussian radii $R_{\rm out}$, $R_{\rm side}$, and $R_{\rm long}$, of the pion emission sources produced in Cu$+$Cu and Au$+$Au collisions at several beam collision energies $\sqrt{s_{_{NN}}}$ at PHENIX. The extracted radii, which are compared to recent STAR and ALICE data, show characteristic scaling patterns as a function of the initial transverse size $\bar{R}$ of the collision systems and the transverse mass $m_T$ of the emitted pion pairs, consistent with hydrodynamiclike expansion. Specific combinations of the three-dimensional radii that are sensitive to the medium expansion velocity and lifetime, and the pion emission time duration show nonmonotonic $\sqrt{s_{_{NN}}}$ dependencies. The nonmonotonic behaviors exhibited by these quantities point to a softening of the equation of state that may coincide with the critical end point in the phase diagram for nuclear matter.

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the longitudinal double spin asymmetries, ${A}_{LL}$, for charged pions at midrapidity ($|\ensuremath{\eta}|&lt;0.35$) in longitudinally polarized $p+p$ collisions at $\sqrt{s}=510\text{ }\text{ }\mathrm{GeV}$. These measurements are sensitive to the gluon spin contribution to the total spin of the proton in the parton momentum fraction $x$ range between 0.04 and 0.09. One can infer the sign of the gluon polarization from the ordering of pion asymmetries with charge alone. The asymmetries are found to be consistent with global quantum-chromodynamics fits of deep-inelastic scattering and data at $\sqrt{s}=200\text{ }\text{ }\mathrm{GeV}$, which show a nonzero positive contribution of gluon spin to the proton spin.

The fraction of $J/\ensuremath{\psi}$ mesons which come from $B$-meson decay, ${\mathrm{F}}_{B\ensuremath{\rightarrow}J/\ensuremath{\psi}}$, is measured for $\mathrm{J}/\ensuremath{\psi}$ rapidity $1.2&lt;|y|&lt;2.2$ and ${p}_{T}&gt;0$ in $p+p$ and Cu+Au collisions at $\sqrt{{s}_{{}_{NN}}}$ = 200 GeV with the PHENIX detector. The extracted fraction is ${\mathrm{F}}_{B\ensuremath{\rightarrow}J/\ensuremath{\psi}}=0.025\ifmmode\pm\else\textpm\fi{}0.006$ (stat) $\ifmmode\pm\else\textpm\fi{}$ 0.010(syst) for $p+p$ collisions. For Cu+Au collisions, ${\mathrm{F}}_{B\ensuremath{\rightarrow}J/\ensuremath{\psi}}$ is 0.094 $\ifmmode\pm\else\textpm\fi{}$ 0.028(stat) $\ifmmode\pm\else\textpm\fi{}$ 0.037(syst) in the Au-going direction ($\ensuremath{-}2.2&lt;y&lt;\ensuremath{-}1.2$) and 0.089 $\ifmmode\pm\else\textpm\fi{}$ 0.026(stat) $\ifmmode\pm\else\textpm\fi{}$ 0.040(syst) in the Cu-going direction ($1.2&lt;y&lt;2.2$). The nuclear modification factor, ${R}_{\mathrm{CuAu}}$, of $B$ mesons in Cu+Au collisions is consistent with binary scaling of measured yields in $p+p$ at both forward and backward rapidity.

The PHENIX experiment at the Relativistic Heavy Ion Collider measured $\pi^0$ and $\eta$ mesons at midrapidity in U$+$U collisions at $\sqrt{s_{_{NN}}}=192$ GeV in a wide transverse momentum range. Measurements were performed in the $\pi^0(\eta)\rightarrow\gamma\gamma$ decay modes. A strong suppression of $\pi^0$ and $\eta$ meson production at high transverse momentum was observed in central U$+$U collisions relative to binary scaled $p$$+$$p$ results. Yields of $\pi^0$ and $\eta$ mesons measured in U$+$U collisions show similar suppression pattern to the ones measured in Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV for similar numbers of participant nucleons. The $\eta$/$\pi^0$ ratios do not show dependence on centrality or transverse momentum, and are consistent with previously measured values in hadron-hadron, hadron-nucleus, nucleus-nucleus, and $e^+e^-$ collisions.

The PHENIX collaboration presents here a concept for a detector at a future Electron Ion Collider (EIC). The EIC detector proposed here, referred to as ePHENIX, will have excellent performance for a broad range of exciting EIC physics measurements, providing powerful investigations not currently available that will dramatically advance our understanding of how quantum chromodynamics binds the proton and forms nuclear matter.

The standard model (SM) of particle physics is spectacularly successful, yet the measured value of the muon anomalous magnetic moment $(g-2)_\mu$ deviates from SM calculations by 3.6$\sigma$. Several theoretical models attribute this to the existence of a "dark photon," an additional U(1) gauge boson, which is weakly coupled to ordinary photons. The PHENIX experiment at the Relativistic Heavy Ion Collider has searched for a dark photon, $U$, in $\pi^0,\eta \rightarrow \gamma e^+e^-$ decays and obtained upper limits of $\mathcal{O}(2\times10^{-6})$ on $U$-$\gamma$ mixing at 90% CL for the mass range $30<m_U<90$ MeV/$c^2$. Combined with other experimental limits, the remaining region in the $U$-$\gamma$ mixing parameter space that can explain the $(g-2)_\mu$ deviation from its SM value is nearly completely excluded at the 90% confidence level, with only a small region of $29<m_U<32$ MeV/$c^2$ remaining.

We report the first measurement of the full angular distribution for inclusive $J/\psi\rightarrow\mu^{+}\mu^{-}$ decays in $p$$+$$p$ collisions at $\sqrt{s}=510$ GeV. The measurements are made for $J/\psi$ transverse momentum $2<p_{T}<10$ GeV/$c$ and rapidity $1.2<y<2.2$ in the Helicity, Collins-Soper, and Gottfried-Jackson reference frames. In all frames the polar coefficient $\lambda_{\theta}$ is strongly negative at low $p_{T}$ and becomes close to zero at high $p_{T}$, while the azimuthal coefficient $\lambda_{\phi}$ is close to zero at low $p_{T}$, and becomes slightly negative at higher $p_{T}$. The frame-independent coefficient $\tilde{\lambda}$ is strongly negative at all $p_{T}$ in all frames. The data are compared to the theoretical predictions provided by nonrelativistic quantum chromodynamics models.

We present direct photon-hadron correlations in 200 GeV/A Au$+$Au, $d$$+$Au and $p$$+$$p$ collisions, for direct photon $p_T$ from 5--12 GeV/$c$, collected by the PHENIX Collaboration in the years from 2006 to 2011. We observe no significant modification of jet fragmentation in $d$$+$Au collisions, indicating that cold nuclear matter effects are small or absent. Hadrons carrying a large fraction of the quark's momentum are suppressed in Au$+$Au compared to $p$$+$$p$ and $d$$+$Au. As the momentum fraction decreases, the yield of hadrons in Au$+$Au increases to an excess over the yield in $p$$+$$p$ collisions. The excess is at large angles and at low hadron $p_T$ and is most pronounced for hadrons associated with lower momentum direct photons. Comparison to theoretical calculations suggests that the hadron excess arises from medium response to energy deposited by jets.

The quadrupole magnets for FAIR Super FRS energy buncher have large usable aperture, high magnetic pole-tip field and high gradient field quality. The iron-dominated magnets with superconducting coils have to be used in this application. The NbTi coil, laminated iron, and support structure of about 22 tons is immersed in liquid helium. The 4.5 K helium chamber is completely covered with a thermal shield cooled by helium at 50–80 K on its outer and inner surface. The helium chamber and thermal shield is enclosed in a vacuum shell. The paper presents design details of the long quadrupole. Coupled thermal, magnetic and structural analysis was carried out to design the magnet iron, magnet coil, helium vessel and support links and ensure the required gradient field quality is achieved. The paper also presents the design of support links and outer vacuum chamber.

The Superconducting Fragment Separator of the Facility for Antiproton and Ion Research at GSI in Darmstadt is a large-acceptance superconducting fragment separator to efficiently separate rare isotopes. Design of the outer vacuum chamber of the long superconducting quadrupole magnet is presented in this paper.

The upgrade of the CMS detector for the high luminosity LHC (HL-LHC) will include gas electron multiplier (GEM) detectors in the end-cap muon spectrometer. Due to the limited supply of large area GEM detectors, the Korean CMS (KCMS) collaboration had formed a consortium with Mecaro Co., Ltd. to serve as a supplier of GEM foils with area of approximately 0.6 m2. The consortium has developed a double-mask etching technique for production of these large-sized GEM foils. This article describes the production, quality control, and quality assessment (QA/QC) procedures and the mass production status for the GEM foils. Validation procedures indicate that the structure of the Korean foils are in the designed range. Detectors employing the Korean foils satisfy the requirements of the HL-LHC in terms of the effective gain, response uniformity, rate capability, discharge probability, and hardness against discharges. No aging phenomena were observed with a charge collection of 82 mC cm−2. Mass production of KCMS GEM foils is currently in progress.

Abstract The Gas Electron Multiplier (GEM) detectors of the GE1/1 station of the CMS experiment have been operated in the CMS magnetic field for the first time on the 7 th of October 2021. During the magnetic field ramps, several discharge phenomena were observed, leading to instability in the GEM High Voltage (HV) power system. In order to reproduce the behavior, it was decided to conduct a dedicated test at the CERN North Area with the Goliath magnet, using four GE1/1 spare chambers. The test consisted in studying the characteristics of discharge events that occurred in different detector configurations and external conditions. Multiple magnetic field ramps were performed in sequence: patterns in the evolution of the discharge rates were observed with these data. The goal of this test is the understanding of the experimental conditions inducing discharges and short circuits in a GEM foil. The results of this test lead to the development of procedure for the optimal operation and performance of GEM detectors in the CMS experiment during the magnet ramps. Another important result is the estimation of the probability of short circuit generation, at 68 % confidence level, p short HV OFF = 0.42 -0.35 +0.94 % with detector HV OFF and p short HV OFF &lt; 0.49% with the HV ON. These numbers are specific for the detectors used during this test, but they provide a first quantitative indication on the phenomenon, and a point of comparison for future studies adopting the same procedure.

Multiferroics are materials in which ferroelectric and magnetic e.g., ferromagnetic or antiferromagnetic orders co-exist. Some of these show the magnetoelectric effect which is the coupling between electric and magnetic degrees of freedom leading to induction of electric polarization by an applied magnetic field and also induction of magnetic polarization by an applied electric field. Multiferroic substances have attracted attention in recent times as they are expected to show relatively larger magnetoelectric effect than others. TbMnO3 and DyMnO3 are prototypical magnetoelectric multiferroics where ferroelectricity develops due to a magnetic phase transition to a spiral magnetic ordered phase. Cu2OSeO3 is another magneto-electric material and is the only one in which magnetoelectric (ME) susceptibility dM/dE (i.e. the change in magnetization by the application of an AC electric field) measurements have been performed to successfully map the magneto-electric phase diagram. During this work, dM/dE measurements were used to map the phase di- agram of Cu2OSeO3 for directions of applied magnetic and electric fields different from that reported so far. This success in Cu2OSeO3 thus became the motivation to make similar attempts on TbMnO3 and DyMnO3. The samples were first oriented to identify the crystallographic axes, then DC magnetic susceptibility and AC mag- netoelectric susceptibility measurements were carried out. The DC magnetization measurements for TbMnO3 showed clear signatures of phase transitions and thus subsequently dM/dE measurements were performed with an AC applied electric field in order to perform a sensitive probe of the phase diagram. But for TbMnO3, dM/dE response could not be observed in any portion of the phase diagram i.e. at ifferent magnetic field and temperature. This entire procedure from Cu2OSeO3 to he manganates have been presented here in this report.

We present measurements of $e^+e^-$ production at midrapidity in Au$+$Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV. The invariant yield is studied within the PHENIX detector acceptance over a wide range of mass ($m_{ee} <$ 5 GeV/$c^2$) and pair transverse momentum ($p_T$ $<$ 5 GeV/$c$), for minimum bias and for five centrality classes. The \ee yield is compared to the expectations from known sources. In the low-mass region ($m_{ee}=0.30$--0.76 GeV/$c^2$) there is an enhancement that increases with centrality and is distributed over the entire pair \pt range measured. It is significantly smaller than previously reported by the PHENIX experiment and amounts to $2.3\pm0.4({\rm stat})\pm0.4({\rm syst})\pm0.2^{\rm model}$ or to $1.7\pm0.3({\rm stat})\pm0.3({\rm syst})\pm0.2^{\rm model}$ for minimum bias collisions when the open-heavy-flavor contribution is calculated with {\sc pythia} or {\sc mc@nlo}, respectively. The inclusive mass and $p_T$ distributions as well as the centrality dependence are well reproduced by model calculations where the enhancement mainly originates from the melting of the $\rho$ meson resonance as the system approaches chiral symmetry restoration. In the intermediate-mass region ($m_{ee}$ = 1.2--2.8 GeV/$c^2$), the data hint at a significant contribution in addition to the yield from the semileptonic decays of heavy-flavor mesons.

The PHENIX experiment at RHIC has measured the centrality dependence of the direct photon yield from Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV down to $p_T=0.4$ GeV/$c$. Photons are detected via photon conversions to $e^+e^-$ pairs and an improved technique is applied that minimizes the systematic uncertainties that usually limit direct photon measurements, in particular at low $p_T$. We find an excess of direct photons above the $N_{\rm coll}$-scaled yield measured in $p$$+$$p$ collisions. This excess yield is well described by an exponential distribution with an inverse slope of about 240 MeV/$c$ in the $p_T$ range from 0.6--2.0 GeV/$c$. While the shape of the $p_T$ distribution is independent of centrality within the experimental uncertainties, the yield increases rapidly with increasing centrality, scaling approximately with $N_{\rm part}^\alpha$, where $\alpha=1.48{\pm}0.08({\rm stat}){\pm}0.04({\rm syst})$.

The Super-Conducting Fragment Separator (Super FRS) of the Facility for Antiproton and Ion Research (FAIR) at GSI Darmstadt is a large-acceptance superonducting fragment separator. The separator consists of large dipole, quadrupole and hexapole superconducting magnets. The long quadrupole magnet cryostat houses the helium chamber, which has the magnet iron and NbTi superconducting coil. The magnet weighs about 30 tons. The helium chamber is enclosed in vacuum inside the magnet cryostat. Multilayer Insulation (MLI) will be wrapped around the thermal shield to reduce radiation loss. Polyster of MLI comprises the major component responsible for outgassing. In order to reduce outgassing, pumping at elevated temperatures has to be carried out. In view of the large size and weight of the magnet, a seal off approach might not be operationally feasible. Continuous pumping of the cryostat has also been examined. Pump has been kept at a distance from the magnet considering the effect of stray magnetic fields. Oil free turbo molecular pump and scroll pump combination will be used to pump down the cryostat. The ultimate heat load of the cryostat will be highly dependent on the pressure attained. Radiation and conduction plays an important role in the heat transfer at low temperatures. This paper presents the vacuum design of the long quadrupole magnet cryostat and estimates the heat load of the cryostat.

We previously reported [Phys. Rev. D 82, 112008 (2010)] measurements of transverse single-spin asymmetries, A_N, in J/psi production from transversely polarized p+p collisions at sqrt(s)=200 GeV with data taken by the PHENIX experiment at the Relativistic Heavy Ion Collider in 2006 and 2008. Subsequently, we have found errors in the analysis procedures for the 2008 data, which resulted in an erroneous value for the extracted A_N. The errors affected the sorting of events into the correct left/right and forward/backward bins. This produced an incorrect value for the 2008 result, but the 2006 result is unaffected. We have conducted two independent reanalyses with these errors corrected, and we present here the corrected values for the 2008 data and the combined results for 2006 and 2008. The new combined spin asymmetry in the forward region is A_N = -0.026+/-0.026(stat)+/-0.003(sys). Since this asymmetry is consistent with zero, we no longer claim that our results suggest a possible non-zero trigluon correlation function in transversely polarized protons.

The second Fourier component v_2 of the azimuthal anisotropy with respect to the reaction plane has been measured for direct photons at midrapidity and transverse momentum (p_T) of 1.15 GeV/c in Au+Au collisions at sqr(s_NN)=200 GeV. Previous measurements of this quantity for hadrons with p_T 6 GeV/c a reduced anisotropy is interpreted in terms of a path-length dependence for parton energy loss. In this measurement we find that for p_T > 4 GeV/c, the anisotropy for direct photons is consistent with zero and current uncertainties prevent a conclusive test of predicted small v_2 values from jet conversion and fragmentation photons. However, in the p_T < 4 GeV/c region, dominated by thermal photons, we find a substantial direct photon v_2 comparable to that of hadrons, whereas model calculations for thermal photons in this kinematic region significantly underpredict the observed v_2.

The PHENIX collaboration presents a systematic study of $\pi^0$ production from $p$$+$$p$, $p$$+$Al, $p$$+$Au, $d$$+$Au, and $^{3}$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV. Measurements were performed with different centrality selections as well as the total inelastic, 0%--100%, selection for all collision systems. For 0%--100% collisions, the nuclear modification factors, $R_{xA}$, are consistent with unity for $p_T$ above 8 GeV/$c$, but exhibit an enhancement in peripheral collisions and a suppression in central collisions. The enhancement and suppression characteristics are similar for all systems for the same centrality class. It is shown that for high-$p_T$-$\pi^0$ production, the nucleons in the $d$ and $^3$He interact mostly independently with the Au nucleus and that the counter intuitive centrality dependence is likely due to a physical correlation between multiplicity and the presence of a hard scattering process. These observations disfavor models where parton energy loss has a significant contribution to nuclear modifications in small systems. Nuclear modifications at lower $p_T$ resemble the Cronin effect -- an increase followed by a peak in central or inelastic collisions and a plateau in peripheral collisions. The peak height has a characteristic ordering by system size as $p$$+$Au $>$ $d$$+$Au $>$ $^{3}$He$+$Au $>$ $p$$+$Al. For collisions with Au ions, current calculations based on initial state cold nuclear matter effects result in the opposite order, suggesting the presence of other contributions to nuclear modifications, in particular at lower $p_T$.

The PHENIX experiment at the Relativistic Heavy Ion Collider measured $\pi^0$, $\eta$, and $K_S$ mesons at midrapidity in U$+$U collisions at $\sqrt{s_{_{NN}}}$=192 GeV in a wide transverse momentum range. Measurements were performed in the $\pi^0$($\eta$)$\rightarrow\gamma\gamma$ and $K_S\rightarrow\pi^0\pi^0$ decay modes. A strong suppression of $\pi^0$, $\eta$, and $K_S$ meson production at high transverse momentum was observed in central U$+$U collisions relative to binary scaled $p$$+$$p$ results. Yields of $\pi^0$, $\eta$ and $K_S$ mesons measured in U$+$U collisions show similar suppression pattern to the ones measured in Au$+$Au collisions at $\sqrt{s_{NN}}=200$ GeV for similar numbers of participant nucleons. The $\eta$/$\pi^0$ and $K_S$/$\pi^0$ ratios do not show dependence on centrality or transverse momentum, and are consistent with previously measured values in hadron-hadron, hadron-nucleus, nucleus-nucleus, and $e^+e^-$ collisions.

New physics associated with the heavy top quark can affect top quark production and the partial decay width of $Z \rightarrow b \bar b$. In this paper, we examine the correlated effects of possible new physics on ${R_b}$ measured at LEP I and the single top quark production rate at Tevatron by using an effective lagrangian technique. We point out that certain operators in the effective lagrangian, constrained by the measured value of $R_b$, can lead to significant and potentially observable effects in single top production.

Relatively light sneutrinos, which are experimentally allowed, may significantly affect the currently popular search strategies for supersymmetric particles by decaying dominantly into an invisible channel. In certain cases the second lightest neutralino may also decay invisibly leading to two extra carriers of missing energy -- in addition to the lightest supersymmetric particle (LSP) \zi\ -- the virtual LSPs (VLSPs). It is shown that these VLSPs are allowed in supergravity models with common scalar and gaugino masses at the unification scale for a sizable region of parameter space and are consistent with all constraints derived so far from SUSY searches. The pair production of right handed sleptons, which can very well be the lightest charged SUSY particles in this scenario, at LEP 200 and their decay signatures are discussed. The signal survives kinematical cuts required to remove the standard model background. Charginos are also pair produced copiously if kinematically accessible; they also decay dominantly into hadronically quiet di--lepton + \etmiss\ modes leading to interesting unlike sign dilepton events which are again easily separable from the Standard Model backgrounds at LEP 200 energies.