Engineering topics

Akimoto, R.

Publications and source records attributed to Akimoto, R..

At least 37 records · Page 2

DOE OSTI2017

Cross section and transverse single-spin asymmetry of muons from open heavy-flavor decays in polarized p + p collisions at s = 200 ? ? GeV

The cross section and transverse single-spin asymmetries of μ - and μ + from open heavy-flavor decays in polarized p+p collisions at √s = 200 GeV were measured in this paper by the PHENIX experiment during 2012 at the Relativistic Heavy Ion Collider. Because heavy-flavor production is dominated by gluon-gluon interactions at √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. Finally, the asymmetry results are consistent with zero within uncertainties, and a model calculation based on twist-3 three-gluon correlations agrees with the data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2017

Measurements of B → J / ψ at forward rapidity in p + p collisions at s = 510 GeV

In this paper, we report the first measurement of the fraction of J / ψ mesons coming from Β-meson decay (F Β→ J / ψ ) in p + p collisions at s = 510 GeV . The measurement is performed using the forward silicon vertex detector and central vertex detector at PHENIX, which provide precise tracking and distance-of-closest-approach determinations, enabling the statistical separation of J / ψ due to Β-meson decays from prompt J / ψ . The measured value of F Β→ J / ψ is 8.1% ± 2.3%(stat) ± 1.9%(syst) for J / ψ with transverse momenta 0 < p T < 5 GeV / c and rapidity 1.2 < |y| < 2.2. The measured fraction F Β→ J / ψ at PHENIX is compared to values measured by other experiments at higher center of mass energies and to fixed-order-next-to-leading-logarithm and color-evaporation-model predictions. The bb cross section per unit rapidity [dσ / dy(pp → bb)] extracted from the obtained F Β→ J / ψ and the PHENIX inclusive J / ψ cross section measured at 200 GeV scaled with color-evaporation-model calculations, at the mean Β hadron rapidity y = ±1.7 in 510 GeV p + p collisions, is 3.63 +1.92 -1.70 μb. Finally, it is consistent with the fixed-order-next-to-leading-logarithm calculations.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2017

Angular decay coefficients of J/ψ mesons at forward rapidity from p+p collisions at √s = 510 GeV

In this paper, we report the first measurement of the full angular distribution for inclusive J/ψ → μ + μ - decays in p+p collisions at √s = 510 GeV. The measurements are made for J/ψ 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 λ θ is strongly negative at low p T and becomes close to zero at high p T , while the azimuthal coefficient λ Φ is close to zero at low p T , and becomes slightly negative at higher p T . The frame-independent coefficient λ ~ is strongly negative at all p T in all frames. Finally, the data are compared to the theoretical predictions provided by nonrelativistic quantum chromodynamics models.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2017

Nonperturbative-transverse-momentum effects and evolution in dihadron and direct photon-hadron angular correlations in p + p collisions at $\sqrt{s}$ = 510 GeV

Dihadron and isolated direct photon-hadron angular correlations are measured in p + p collisions at $\sqrt{s}$=510 GeV. Correlations of charged hadrons of 0.7 < p T < 10 GeV/c with $\pi$ 0 mesons of 4 < p T < 15 GeV/c or isolated direct photons of 7 < p T < 15 GeV/c are used to study nonperturbative effects generated by initial-state partonic transverse momentum and final-state transverse momentum from fragmentation. The nonperturbative behavior is characterized by measuring the out-of-plane transverse momentum component p out perpendicular to the axis of the trigger particle, which is the high-p T direct photon or $\pi$ 0 . Nonperturbative evolution effects are extracted from Gaussian fits to the away-side inclusive-charged-hadron yields for different trigger-particle transverse momenta ($p^{trig}_{T}$). The Gaussian widths and root mean square of p out are reported as a function of the interaction hard scale $p^{trig}_{T}$ to investigate possible transverse-momentum-dependent evolution differences between the $\pi$ 0 -h ± and direct photon-h ± correlations and factorization breaking effects. The widths are found to decrease with $p^{trig}_{T}$, which indicates that the Collins-Soper-Sterman soft factor is not driving the evolution with the hard scale in nearly back-to-back dihadron and direct photon-hadron production in p + p collisions. In conclusion, this behavior is in contrast to Drell-Yan and semi-inclusive deep-inelastic scattering measurements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2016

Measurements of double-helicity asymmetries in inclusive J / ψ production in longitudinally polarized p + p collisions at s = 510 GeV

We report the double-helicity asymmetry, A J/ψ LL , in inclusive J/ψ production at forward rapidity as a function of transverse momentum p T and rapidity |y|. The data analyzed were taken during √s = 510 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/ψ particles are predominantly produced through gluon-gluon scatterings, thus A J/ψ LL is sensitive to the gluon polarization inside the proton. We measured A J/ψ LL by detecting the decay daughter muon pairs μ + μ – within the PHENIX muon spectrometers in the rapidity range 1.2 < |y| < 2.2. In this kinematic range, we measured the A J/ψ LL to be 0.012 ± 0.010 (stat) ±0.003 (syst). The A J/ψ LL 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 ≈ 5 × 10 –2 where recent data of jet and π 0 double helicity spin asymmetries have shown evidence for significant gluon polarization, and the other one covering the poorly known small-x region x ≈ 2 × 10 –3 . Furthermore, our new results could be used to further constrain the gluon polarization for x < 5 × 10 –2 .

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2016

Azimuthally anisotropic emission of low-momentum direct photons in Au + Au collisions at s N N = 200 GeV

In this paper, 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 s N N = 200 GeV for various collision centralities. Combining two different analysis techniques, results were obtained in the transverse momentum range of 0.4 < p T < 4.0 GeV/c. At low p T the second-order coefficients, v 2 , are similar to the ones observed in hadrons. Third-order coefficients, v 3 , are nonzero and almost independent of centrality. These new results on v 2 and v 3 , combined with previously published results on yields, are compared to model calculations that provide yields and asymmetries in the same framework. Finally, those models are challenged to explain simultaneously the observed large yield and large azimuthal anisotropies.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2016

Measurements of directed, elliptic, and triangular flow in Cu + Au collisions at s NN = 200 GeV

In this paper, measurements of anisotropic flow Fourier coefficients (v n ) for inclusive charged particles and identified hadrons π ± ,K ± , p, and $\overline{p}$ produced at midrapidity in Cu + Au collisions at √sNN = 200 GeV are presented. The data were collected in 2012 by the PHENIX experiment at the Relativistic Heavy-Ion Collider (RHIC). The particle azimuthal distributions with respect to different-order symmetry planes Ψ n ,for n = 1, 2, and 3 are studied as a function of transverse momentum p T over a broad range of collision centralities. Mass ordering, as expected from hydrodynamic flow, is observed for all three harmonics. The charged-particle results are compared with hydrodynamical and transport model calculations. In addition, we also compare these Cu + Au results with those in Cu + Cu and Au + Au collisions at the same √sNN and find that the v 2 and v 3 , as a function of transverse momentum, follow a common scaling with 1/(ε n N 1/3 part ).

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2016

Single electron yields from semileptonic charm and bottom hadron decays in Au + Au collisions at s N N = 200 GeV

We measured open heavy flavor production in minimum bias Au + Au collisions at √s( NN ) = 200 GeV via the yields of electrons from semileptonic decays of charm and bottom hadrons, using the PHENIX Collaboration at the Relativistic Heavy Ion Collider. In the past, heavy flavor electron measurements indicated substantial modification in the momentum distribution of the parent heavy quarks owing 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. Here, we compare the fraction of electrons from bottom hadrons to previously published results extracted from electron-hadron correlations in p + p collisions at √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. Finally, we find that electrons from bottom hadron decays are less suppressed than those from charm for the region 3 < p (T) < 4 GeV/c.

43 PARTICLE ACCELERATORS↗

DOE OSTI2016

Forward J / ψ production in U + U collisions at s N N = 193 GeV

We measured the invariant yields, dN/dy, for J/psi production at forward rapidity (1.2 < |y| < 2.2) in U + U collisions at √S NN = 193 GeV 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. In addition, 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 $\bar{c}$ over bar coalescence. Two different parametrizations 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-coll, and these were found to give significantly different N coll values. Our results, using N 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 $\bar{c}$) over bar coalescence becomes more important than the decrease in yield due to increased energy density. Finally, for midcentral collisions, the conclusions about the balance between c $\bar{c}$ over bar coalescence and suppression depend on which deformed Woods-Saxon distribution is used to determine N coll .

43 PARTICLE ACCELERATORS↗

DOE OSTI2016

Scaling properties of fractional momentum loss of high- p T hadrons in nucleus-nucleus collisions at s N N from 62.4 GeV to 2.76 TeV

We present measurements of the fractional momentum loss (S loss = delta pT / pT ) of high-transverse-momentum-identified hadrons in heavy-ion collisions. Using pi 0 in Au + Au and Cu + Cu collisions at √s NN = 62.4 and 200 GeV measured by the PHENIX experiment at the Relativistic Heavy Ion Collider and and charged hadrons in Pb + Pb collisions measured by the ALICE experiment at the Large Hadron Collider, we studied the scaling properties of S loss as a function of a number of variables: the number of participants, N part , the number of quark participants, N qp , the charged-particle density, dN ch /d η , and the Bjorken energy density times the equilibration time, epsilon Bj τ 0 . We also find that the p T , where S loss has its maximum, varies both with centrality and collision energy. Above the maximum, S loss tends to follow a power-law function with all four scaling variables. Finally, the data at √s NN = 200 GeV and 2.76 TeV, for sufficiently high particle densities, have a common scaling of S loss with dN ch /d η and ε Bj τ 0 , lending insight into the physics of parton energy loss.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2016

Φ meson production in the forward/backward rapidity region in Cu + Au collisions at s NN = 200 GeV

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured φ meson production and its nuclear modification in asymmetric Cu + Au heavy-ion collisions at √ s NN = 200 GeV at both forward Cu-going direction (1.2 < y < 2.2) and backward Au-going direction (-2.2 < y < -1.2) rapidities. The measurements are performed via the dimuon decay channel and reported as a function of the number of participating nucleons, rapidity, and transverse momentum. In the most central events, 0%–20% centrality, the φ meson yield integrated over 1 < p T < 5 GeV/c prefers a smaller value, which means a larger nuclear modification, in the Cu-going direction compared to the Au-going direction. Finally and additionally, the nuclear-modification factor in Cu + Au collisions averaged over all centrality is measured to be similar to the previous PHENIX result in d + Au collisions for these rapidities.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2016

Transverse energy production and charged-particle multiplicity at midrapidity in various systems from s N N = 7.7 to 200 GeV

Measurements of midrapidity charged-particle multiplicity distributions, dN ch /dη, and midrapidity transverse-energy distributions, dE T /dη, are presented for a variety of collision systems and energies. Included are distributions for Au+Au collisions at √s NN =200, 130, 62.4, 39, 27, 19.6, 14.5, and 7.7 GeV, Cu+Cu collisions at √s NN =200 and 62.4 GeV, Cu+Au collisions at √s NN =200 GeV, U+U collisions at√s NN =193 GeV, d+Au collisions at √s NN =200 GeV, He3+Au collisions at √s NN =200 GeV, and p+p collisions at √s NN =200 GeV. We present centrality-dependent distributions at midrapidity in terms of the number of nucleon participants, N part , and the number of constituent quark participants, N qp . For all A+A collisions down to √s NN =7.7 GeV, we observed that the midrapidity data are better described by scaling with N qp than scaling with N part . Finally, our estimates of the Bjorken energy density, ε BJ , and the ratio of dE T /dη to dN ch /dη are presented, the latter of which is seen to be constant as a function of centrality for all systems.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2016

Measurement of higher cumulants of net-charge multiplicity distributions in Au + Au collisions at s N N = 7.7 – 200 GeV

Our report presents the measurement of cumulants (C n ,n=1,...,4) of the net-charge distributions measured within pseudorapidity (|η|<0.35) in Au+Au collisions at √s NN =7.7–200GeV with the PHENIX experiment at the Relativistic Heavy Ion Collider. The ratios of cumulants (e.g., C 1 /C 2 , C 3 /C 1 ) of the net-charge distributions, which can be related to volume independent susceptibility ratios, are studied as a function of centrality and energy. These quantities are important to understand the quantum-chromodynamics phase diagram and possible existence of a critical end point. The measured values are very well described by expectation from negative binomial distributions. We do not observe any nonmonotonic behavior in the ratios of the cumulants as a function of collision energy. These measured values of C 1 /C 2 and C 3 /C 1 can be directly compared to lattice quantum-chromodynamics calculations and thus allow extraction of both the chemical freeze-out temperature and the baryon chemical potential at each center-of-mass energy. Moreover, the extracted baryon chemical potentials are in excellent agreement with a thermal-statistical analysis model.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2016

Dielectron production in Au + Au collisions at s N N = 200 GeV

Here, we present measurements of e(+)e-production at midrapidity in Au + Au collisions at √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. We compare the e + e - yield 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 p T range measured. It is significantly smaller than previously reported by the PHENIX experiment and amounts to 2.3 ± 0.4(stat) ± 0.4(syst) ± 0.2(model) or to 1.7 ± 0.3(stat) ± 0.3(syst) ± 0.2(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 ρ meson resonance as the system approaches chiral symmetry restoration. Finally, 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.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2015

Centrality dependence of low-momentum direct-photon production in Au + Au collisions at s N N = 200 GeV

The PHENIX experiment at RHIC has measured the centrality dependence of the direct photon yield from Au+Au collisions at √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 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. In this study, 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 α part , where α = 1.38±0.03(stat)±0.07(syst).

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2015

Measurement of long-range angular correlation and quadrupole anisotropy of pions and (anti)protons in central d + Au collisions at s N N = 200 GeV

In this study, we present azimuthal angular correlations between charged hadrons and energy deposited in calorimeter towers in central d+Au and aluminum bias p+p collisions at √s NN = 200 GeV. The charged hadron is measured at midrapidity lηl < 0.35, and the energy us measured at large rapidity (–3.7 < η < –3.1, Au-going direction). An enhanced near-side angular correlation across lΔηl > 2.75 is observed in d+Au collisions. Using the event plane method applied to the Au-going energy distribution, we extract the anisotropy strength v₂ for inclusive charged hadrons at midrapidity up to p T = 4.5 GeV/c. We also present the measurement of v₂ for identified π ± and (anti)protons in central d+Au collisions, and observe a mass-ordering pattern similar to that seen in heavy ion collisions. These results are compared with viscous hydrodynamic calculations and measurements from p+Pb at √s NN = 5.02 TeV. The magnitude of the mass-ordering in d+Au is found to be smaller than that in p+Pb collisions, which may indicate smaller radial flow in lower energy d+Au collisions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2015

Search for dark photons from neutral meson decays in p+p and d+Au collisions at √s NN = 200 GeV

In this study, the standard model (SM) of particle physics is spectacularly successful, yet the measured value of the muon anomalous magnetic moment (g-2) μ deviates from SM calculations by 3.6σ. 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 π⁰, η → γe⁺e⁻ decays and obtained upper limits of O(2×10⁻⁶) on U-γ mixing at 90% CL for the mass range 30 < m U < 90 MeV/c². Combined with other experimental limits, the remaining region in the U-γ mixing parameter space that can explain the (g-2) μ 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/c² remaining.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2015

Measurement of Υ(1S + 2S +3S) production in p + p and Au + Au collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV

Measurements of bottomonium production in heavy-ion and p+p collisions at the Relativistic Heavy Ion Collider (RHIC) are presented. The inclusive yield of the three Υ states, Υ(1S + 2S + 3S), was measured in the PHENIX experiment via electron-positron decay pairs at midrapidity for Au+Au and p+p collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV. The Υ(1S + 2S + 3S) → e⁺e⁻ differential cross section at midrapidity was found to be B ee dσ/dy = 108 ± 38 (stat) ± 15 (syst) ± 11 (luminosity) pb in p+p collisions. The nuclear modification factor in the 30% most central Au+Au collisions indicates a suppression of the total Υ state yield relative to the extrapolation from p+p collision data. Thus, the suppression is consistent with measurements at higher energies by the CMS experiment at the Large Hadron Collider.

200 GeV↗