| 1. |
- Adare, A., et al.
(författare)
-
Cross Section and Parity-Violating Spin Asymmetries of W-+/- Boson Production in Polarized p plus p Collisions at root s=500 Gev
- 2011
-
Ingår i: Physical Review Letters. - Amer Physical Soc. - 0031-9007. ; 106:6
-
Tidskriftsartikel (refereegranskat)abstract
- Large parity-violating longitudinal single-spin asymmetries A(L)(e+) = 0.86(-0.14)(+0.30) and Ae(L)(e-) = 0.88(-0.71)(+0.12) are observed for inclusive high transverse momentum electrons and positrons in polarized p + p collisions at a center-of-mass energy of root s = 500 GeV with the PHENIX detector at RHIC. These e(+/-) come mainly from the decay of W-+/- and Z(0) bosons, and their asymmetries directly demonstrate parity violation in the couplings of the W-+/- to the light quarks. The observed electron and positron yields were used to estimate W-+/- boson production cross sections for the e(+/-) channels of sigma(pp -> W+X) X BR(W+ -> e(+) nu(e)) = 144.1 +/- 21.2(stat)(-10.3)(+3.4)(syst) +/- 21.6(norm) pb, and sigma(pp -> W-X) X BR(W- -> e(-) (nu) over bar (e)) = 3.17 +/- 12.1(stat)(-8.2)(+10.1)(syst) +/- 4.8(norm) pb.
|
|
| 2. |
- Adare, A., et al.
(författare)
-
Double-spin asymmetry of electrons from heavy-flavor decays in p plus p collisions at root s=200 GeV
- 2013
-
Ingår i: Physical Review D. - American Physical Society. - 1550-7998. ; 87:1, s. 012011
-
Tidskriftsartikel (refereegranskat)abstract
- 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 root s = 200 GeV for p(T) = 0.5 to 3.0 GeV/c. The asymmetry was measured at midrapidity (vertical bar eta vertical bar < 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 vertical bar Delta g/g(log(10)(x) = -1.6(-0.4)(+0.5), mu = m(T)(c)vertical bar(2) < 0.030 (1 sigma) based on a leading-order perturbative quantum chromodynamics model, using the measured asymmetry. DOI: 10.1103/PhysRevD.87.012011
|
|
| 3. |
- Adare, A., et al.
(författare)
-
Cold-Nuclear-Matter Effects on Heavy-Quark Production in d+Au Collisions at root S-NN=200 GeV
- 2012
-
Ingår i: Physical Review Letters. - American Physical Society. - 0031-9007. ; 109:24, s. 242301
-
Tidskriftsartikel (refereegranskat)abstract
- The PHENIX experiment has measured electrons and positrons at midrapidity from the decays of hadrons containing charm and bottom quarks produced in d + Au and p + p collisions at root S-NN = 200 GeV in the transverse-momentum range 0.85 <= p(T)(e) <= 8.5 GeV/c. In central d + Au collisions, the nuclear modification factor R-dA at 1.5 < p(T) < 5 GeV/c displays evidence of enhancement of these electrons, relative to those produced in p + p collisions, and shows that the mass-dependent Cronin enhancement observed at the Relativistic Heavy Ion Collider extends to the heavy D meson family. A comparison with the neutral-pion data suggests that the difference in cold-nuclear-matter effects on light- and heavy-flavor mesons could contribute to the observed differences between the pi(0) and heavy-flavor-electron nuclear modification factors R-AA. DOI: 10.1103/PhysRevLett.109.242301
|
|
| 4. |
- Adare, A., et al.
(författare)
-
Dilepton mass spectra in p plus p collisions at root s=200 GeV
- 2009
-
Ingår i: Physics Letters B. - Elsevier B.V. - 0370-2693. ; 670:4-5, s. 313-320
-
Tidskriftsartikel (refereegranskat)abstract
- PHENIX has measured the electron-positron pair mass spectrum from 0 to 8 GeV/c(2) in p + p collisions at root s = 200 GeV. The contributions from light meson decays to e(+)e(-) pairs have been determined based on measurements of hadron production cross sections by PHENIX. Within the systematic uncertainty of similar to 20% they account for all e(+)e(-) pairs in the mass region below similar to 1 GeV/c(2). The e(+)e(-) pair yield remaining after subtracting these contributions is dominated by semileptonic decays of charmed hadrons correlated through flavor conservation. Using the spectral shape predicted by PYTHIA, we estimate the charm production cross section to be 544 +/- 39(stat) +/- 142(syst) +/- 200(model) pb. which is consistent with QCD calculations and measurements of single leptons by PHENIX. (C) 2008 Elsevier BV. All rights reserved.
|
|
| 5. |
- Adare, A., et al.
(författare)
-
Suppression of Back-to-Back Hadron Pairs at Forward Rapidity in d plus Au Collisions at root S-NN=200 GeV
- 2011
-
Ingår i: Physical Review Letters. - American Physical Society. - 0031-9007. ; 107:17, s. 172301
-
Tidskriftsartikel (refereegranskat)abstract
- Back-to-back hadron pair yields in d + Au and p + p collisions at root S-NN = 200 GeV were measured with the PHENIX detector at the Relativistic Heavy Ion Collider. Rapidity separated hadron pairs were detected with the trigger hadron at pseudorapidity vertical bar eta vertical bar < 0: 35 and the associated hadron at forward rapidity (deuteron direction, 3.0< eta < 3.8). Pairs were also detected with both hadrons measured at forward rapidity; in this case, the yield of back-to-back hadron pairs in d + Au collisions with small impact parameters is observed to be suppressed by a factor of 10 relative to p + p collisions. The kinematics of these pairs is expected to probe partons in the Au nucleus with a low fraction x of the nucleon momenta, where the gluon densities rise sharply. The observed suppression as a function of nuclear thickness, p(T), and eta points to cold nuclear matter effects arising at high parton densities.
|
|
| 6. |
- Adare, A., et al.
(författare)
-
Transverse-momentum dependence of the J/psi nuclear modification in d+Au collisions at root s(NN)=200 GeV
- 2013
-
Ingår i: Physical Review C. - American Physical Society. - 0556-2813. ; 87:3, s. 034904
-
Tidskriftsartikel (refereegranskat)abstract
- We present measured J/psi production rates in d + Au collisions at root s(NN) = 200 GeV over broad ranges of transverse momentum (p(T) = 0-14 GeV/c) and rapidity (-2.2 < y < 2.2). We construct the nuclear-modification factor R-dAu for these kinematics and as a function of collision centrality (related to impact parameter for the d + Au collision). We find that the modification is largest for collisions with small impact parameters and observe a suppression (R-dAu < 1) for p(T) < 4 GeV/c at positive rapidities. At negative rapidity we observe a suppression for p(T) < 2 GeV/c then an enhancement (R-dAu > 1) for p(T) > 2 GeV/c. The observed enhancement at negative rapidity has implications for the interpretation of the observed modification in heavy-ion collisions at high p(T). DOI: 10.1103/PhysRevC.87.034904
|
|
| 7. |
- Adare, A., et al.
(författare)
-
Azimuthal Anisotropy of pi(0) Production in Au plus Au Collisions at root s(NN)=200 GeV: Path-Length Dependence of Jet Quenching and the Role of Initial Geometry
- 2010
-
Ingår i: Physical Review Letters. - Amer Physical Soc. - 0031-9007. ; 105:14
-
Tidskriftsartikel (refereegranskat)abstract
- We have measured the azimuthal anisotropy of pi(0) production for 1 < p(T) < 18 GeV/c for Au + Au collisions at root s(NN) = 200 GeV. The observed anisotropy shows a gradual decrease for 3 less than or similar to p(T) less than or similar to 7-10 GeV/c, but remains positive beyond 10 GeV/c. The magnitude of this anisotropy is underpredicted, up to at least similar to 10 GeV/c, by current perturbative QCD (PQCD) energy-loss model calculations. An estimate of the increase in anisotropy expected from initial-geometry modification due to gluon saturation effects and fluctuations is insufficient to account for this discrepancy. Calculations that implement a path-length dependence steeper than what is implied by current PQCD energy-loss models show reasonable agreement with the data.
|
|
| 8. |
- Adare, A., et al.
(författare)
-
Deviation from quark number scaling of the anisotropy parameter v(2) of pions, kaons, and protons in Au+Au collisions at root s(NN)=200 GeV
- 2012
-
Ingår i: Physical Review C. - American Physical Society. - 0556-2813. ; 85:6
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of the anisotropy parameter v(2) of identified hadrons (pions, kaons, and protons) as a function of centrality, transverse momentum p(T), and transverse kinetic energy KET at midrapidity (vertical bar eta vertical bar < 0.35) in Au + Au collisions at root s(N N) = 200 GeV are presented. Pions and protons are identified up to p(T) = 6 GeV/c, and kaons up to p(T) = 4 GeV/c, by combining information from time-of-flight and aerogel Cerenkov detectors in the PHENIX Experiment. The scaling of v(2) with the number of valence quarks (n(q)) has been studied in different centrality bins as a function of transverse momentum and transverse kinetic energy. A deviation from previously observed quark-number scaling is observed at large values of KET/n(q) in noncentral Au + Au collisions (20-60%), but this scaling remains valid in central collisions (0-10%).
|
|
| 9. |
- Adare, A., et al.
(författare)
-
Elliptic and Hexadecapole Flow of Charged Hadrons in Au plus Au Collisions at root s(NN)=200 GeV
- 2010
-
Ingår i: Physical Review Letters. - American Physical Society. - 0031-9007. ; 105:6, s. 062301
-
Tidskriftsartikel (refereegranskat)abstract
- Differential measurements of the elliptic (upsilon(2)) and hexadecapole (upsilon(4)) Fourier flow coefficients are reported for charged hadrons as a function of transverse momentum (p(T)) and collision centrality or number of participant nucleons (N-part) for Au + Au collisions at root s(NN) = 200 GeV/ The upsilon(2,4) measurements at pseudorapidity vertical bar eta vertical bar <= 0.35, obtained with four separate reaction-plane detectors positioned in the range 1.0 < vertical bar eta vertical bar < 3.9, show good agreement, indicating the absence of significant Delta eta-dependent nonflow correlations. Sizable values for upsilon(4)(p(T)) are observed with a ratio upsilon(4)(p(T), N-part)/upsilon(2)(2)(p(T), N-part) approximate to 0.8 for 50 less than or similar to N-part less than or similar to 200, which is compatible with the combined effects of a finite viscosity and initial eccentricity fluctuations. For N-part greater than or similar to 200 this ratio increases up to 1.7 in the most central collisions.
|
|
| 10. |
- Adare, A., et al.
(författare)
-
J/psi suppression at forward rapidity in Au plus Au collisions at root s(NN)=200 GeV
- 2011
-
Ingår i: Physical Review C. - American Physical Society. - 0556-2813. ; 84:5, s. 054912
-
Tidskriftsartikel (refereegranskat)abstract
- Heavy quarkonia are observed to be suppressed in relativistic heavy-ion collisions relative to their production in p + p collisions scaled by the number of binary collisions. In order to determine if this suppression is related to color screening of these states in the produced medium, one needs to account for other nuclear modifications including those in cold nuclear matter. In this paper, we present new measurements from the PHENIX 2007 data set of J/psi yields at forward rapidity (1.2 < vertical bar y vertical bar < 2.2) in Au + Au collisions at root s(NN) = 200 GeV. The data confirm the earlier finding that the suppression of J/. at forward rapidity is stronger than at midrapidity, while also extending the measurement to finer bins in collision centrality and higher transverse momentum (p(T)). We compare the experimental data to the most recent theoretical calculations that incorporate a variety of physics mechanisms including gluon saturation, gluon shadowing, initial-state parton energy loss, cold nuclear matter breakup, color screening, and charm recombination. We find J/psi suppression beyond cold-nuclear-matter effects. However, the current level of disagreement between models and d + Au data precludes using these models to quantify the hot-nuclear-matter suppression.
|
|
