-
A. Adare,
S. Afanasiev,
C. Aidala,
N. N. Ajitanand,
Y. Akiba,
R. Akimoto,
H. Al-Bataineh,
H. Al-Ta'ani,
J. Alexander,
A. Angerami, [......],
G. R. Young,
I. Younus,
I. E. Yushmanov,
W. A. Zajc,
O. Zaudtke,
A. Zelenski,
C. Zhang,
S. Zhou,
J. Zimányi,
L. Zolin
[show abstract]
[hide abstract]
ABSTRACT: The jet fragmentation function is measured with direct photon-hadron
correlations in p+p and Au+Au collisions at sqrt(s_NN)=200 GeV. The p_T of the
photon is an excellent approximation to the initial p_T of the jet and the
ratio z_T=p_T^h/p_T^\gamma 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. I_
AA, the ratio of jet fragment yield 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 z_T. The fragment yield at low z_T
is enhanced at large angles. Such a trend is expected from redistribution of
the lost energy into increased production of low-momentum particles.
12/2012;
-
A. Adare,
S. Afanasiev,
C. Aidala,
N. N. Ajitanand,
Y. Akiba,
R. Akimoto,
H. Al-Bataineh,
H. Al-Ta'ani,
J. Alexander,
K. R. Andrews, [......],
Z. You,
G. R. Young,
I. Younus,
I. E. Yushmanov,
W. A. Zajc,
O. Zaudtke,
A. Zelenski,
C. Zhang,
S. Zhou,
L. Zolin
[show abstract]
[hide abstract]
ABSTRACT: The three Upsilon states, Upsilon(1S+2S+3S), are measured in d+Au and p+p
collisions at sqrt(s_NN)=200 GeV and rapidities 1.2<|y|<2.2 by the PHENIX
experiment at the Relativistic Heavy-Ion Collider. Cross sections for the
inclusive Upsilon(1S+2S+3S) production are obtained. The inclusive yields per
binary collision for d+Au collisions relative to those in p+p collisions
(R_dAu) are found to be 0.62 +/- 0.26 (stat) +/- 0.13 (syst) in the gold-going
direction and 0.91 +/- 0.33 (stat) +/- 0.16 (syst) in the deuteron-going
direction. The measured results are compared to a nuclear-shadowing model,
EPS09 [JHEP 04, 065 (2009)], combined with a final-state breakup cross section,
sigma_br, and compared to lower energy p+A results. We also compare the results
to the PHENIX J/psi results [Phys. Rev. Lett. 107, 142301 (2011)]. The rapidity
dependence of the observed Upsilon suppression is consistent with lower energy
p+A measurements.
11/2012;
-
A. Adare,
S. Afanasiev,
C. Aidala,
N. N. Ajitanand,
Y. Akiba,
H. Al-Bataineh,
J. Alexander,
H. Al-Ta'ani,
A. Angerami,
K. Aoki, [......],
S. Yokkaichi,
G. R. Young,
I. Younus,
Z. You,
I. E. Yushmanov,
W. A. Zajc,
O. Zaudtke,
C. Zhang,
S. Zhou,
L. Zolin
[show abstract]
[hide abstract]
ABSTRACT: 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.
10/2012;
-
S Afanasiev,
C Aidala,
N N Ajitanand,
Y Akiba,
A Al-Jamel,
J Alexander,
K Aoki,
L Aphecetche,
R Armendariz,
S H Aronson, [......],
A Yanovich,
S Yokkaichi,
G R Young,
I Younus,
I E Yushmanov,
W A Zajc,
O Zaudtke,
C Zhang,
J Zimányi,
L Zolin
[show abstract]
[hide abstract]
ABSTRACT: We report the measurement of direct photons at midrapidity in Au+Au collisions at sqrt[s_{NN}]=200 GeV. The direct photon signal was extracted for the transverse momentum range of 4 GeV/c<p_{T}<22 GeV/c, using a statistical method to subtract decay photons from the inclusive photon sample. The direct photon nuclear modification factor R_{AA} was calculated as a function of p_{T} for different Au+Au collision centralities using the measured p+p direct photon spectrum and compared to theoretical predictions. R_{AA} was found to be consistent with unity for all centralities over the entire measured p_{T} range. Theoretical models that account for modifications of initial direct photon production due to modified parton distribution functions in Au and the different isospin composition of the nuclei predict a modest change of R_{AA} from unity. They are consistent with the data. Models with compensating effects of the quark-gluon plasma on high-energy photons, such as suppression of jet-fragmentation photons and induced-photon bremsstrahlung from partons traversing the medium, are also consistent with this measurement.
Physical Review Letters 10/2012; 109(15):152302. · 7.37 Impact Factor
-
A. Adare,
S. Afanasiev,
C. Aidala,
N. N. Ajitanand,
Y. Akiba,
H. Al-Bataineh,
J. Alexander,
K. Aoki,
L. Aphecetche,
J. Asai, [......],
J. Ying,
S. Yokkaichi,
G. R. Young,
I. Younus,
I. E. Yushmanov,
W. A. Zajc,
O. Zaudtke,
C. Zhang,
S. Zhou,
L. Zolin
[show abstract]
[hide abstract]
ABSTRACT: The energy dependence of the single-transverse-spin asymmetry, A_N, and the
cross section for neutron production at very forward angles were measured in
the PHENIX experiment at RHIC for polarized p+p collisions at sqrt(s)=200 GeV.
The neutrons were observed in forward detectors covering an angular range of up
to 2.2 mrad. We report results for neutrons with momentum fraction of x_F=0.45
to 1.0. The energy dependence of the measured cross sections were consistent
with x_F scaling, compared to measurements by an ISR experiment which measured
neutron production in unpolarized p+p collisions at sqrt(s)=30.6--62.7 GeV. The
cross sections for large x_F neutron production for p+p collisions, as well as
those in e+p collisions measured at HERA, are described by a pion exchange
mechanism. The observed forward neutron asymmetries were large, reaching
A_N=-0.08+/-0.02 for x_F=0.8; the measured backward asymmetries, for negative
x_F, were consistent with zero. The observed asymmetry for forward neutron
production is discussed within the pion exchange framework, with interference
between the spin-flip amplitude due to the pion exchange and nonflip amplitudes
from all Reggeon exchanges. Within the pion exchange description, the measured
neutron asymmetry is sensitive to the contribution of other Reggeon exchanges
even for small amplitudes.
09/2012;
-
S Afanasiev,
C Aidala,
N N Ajitanand,
Y Akiba,
A Al-Jamel,
J Alexander,
K Aoki,
L Aphecetche,
R Armendariz,
S H Aronson, [......],
a Malakhov,
m D Malik,
D Yu,
c Peressounko,
r P Pinkenburg,
m L Pisani,
a K Purschke,
h Purwar,
j Qu,
Rak
[show abstract]
[hide abstract]
ABSTRACT: WereportthemeasurementofdirectphotonsatmidrapidityinAu+Aucollisionsat√sNN=200GeV.Thedirectphotonsignalwasextractedforthetransversemomentumrangeof4GeV/c<pT<22GeV/c,usingastatisticalmethodtosubtractdecayphotonsfromtheinclusivephotonsample.Thedirect-photonnuclear-modificationfactorRAAwascalculatedasafunctionofpTfordifferentAu+Aucollisioncentralitiesusingthemeasuredp+pdirect-photonspectrumandcomparedtotheoreticalpredictions.RAAwasfoundtobeconsistentwithunityforallcentralitiesovertheentiremeasuredpTrange.Theoreticalmodelsthataccountformodificationsofinitial-direct-photonproductionduetomodified-parton-distributionfunctions(PDFs)inAuandthedifferentisospincompositionofthenucleipredictamodestchangeofRAAfromunity.Theyareconsistentwith
Physical Review Letters 08/2012; 233752(110). · 7.37 Impact Factor
-
A. Adare,
S. Afanasiev,
C. Aidala,
N. N. Ajitanand,
Y. Akiba,
H. Al-Bataineh,
J. Alexander,
K. Aoki,
L. Aphecetche,
R. Armendariz, [......],
S. Yokkaichi,
G. R. Young,
I. Younus,
I. E. Yushmanov,
W. A. Zajc,
O. Zaudtke,
C. Zhang,
S. Zhou,
J. Zimanyi,
L. Zolin
[show abstract]
[hide abstract]
ABSTRACT: Heavy-flavor production in p + p collisions is a good test of perturbative-quantumchromodynamics
(pQCD) calculations. Modification of heavy-flavor production in heavy-ion collisions relative
to binary-collision scaling from p + p results, quantified with the nuclear-modification factor (RAA), provides
information on both cold- and hot-nuclear-matter effects. Midrapidity heavy-flavor RAA measurements at the Relativistic Heavy Ion Collider have challenged parton-energy-loss models and resulted in upper limits on the viscosity-entropy ratio that are near the quantum lower bound. Such measurements have not been made in the forward-rapidity region. The charm-production cross section in p + p collisions at √s = 200 GeV, integrated over pT and in the rapidity range 1.4 < y < 1.9, is found to be dσc ¯ c/dy = 0.139 ± 0.029 (stat) +0.051 −0.058 (syst) mb. This result is consistent with a perturbative fixed-order-plus-next-to-leading-log calculation within scale uncertainties and is also consistent with expectations based on the corresponding midrapidity charm-production cross section measured by PHENIX. The RAA for heavy-flavor muons in Cu + Cu collisions is measured in three centrality bins for 1 < pT < 4 GeV/c. Suppression relative to binary-collision scaling (RAA < 1) increases with centrality. Within experimental and theoretical uncertainties, the measured charm yield in p + p collisions is consistent with state-of-the-art pQCD calculations. Suppression in central Cu + Cu collisions suggests the presence of significant cold-nuclear-matter effects and final-state energy loss.
Physical Review C 08/2012; 86:024909. · 3.31 Impact Factor
-
A. Adare,
S. S. Adler,
S. Afanasiev,
C. Aidala,
N. N. Ajitanand,
Y. Akiba,
H. Al-Bataineh,
A. Al-Jamel,
J. Alexander,
A. Angerami, [......],
G. R. Young,
I. Younus,
I. E. Yushmanov,
W. A. Zajc,
O. Zaudtke,
C. Zhang,
S. Zhou,
J. Zimányi,
L. Zolin,
X. Zong
[show abstract]
[hide abstract]
ABSTRACT: Direct photons have been measured in sqrt(s_NN)=200 GeV d+Au collisions at
midrapidity. A wide p_T range is covered by measurements of nearly-real virtual
photons (1<p_T<6 GeV/c) and real photons (5<p_T<16 GeV/c). The invariant yield
of the direct photons in d+Au collisions over the scaled p+p cross section is
consistent with unity. Theoretical calculations assuming standard cold nuclear
matter effects describe the data well for the entire p_T range. This indicates
that the large enhancement of direct photons observed in Au+Au collisions for
1.0<p_T<2.5 GeV/c is due to a source other than the initial-state nuclear
effects.
08/2012;
-
A. Adare,
S. Afanasiev,
C. Aidala,
N.N. Ajitanand,
Y. Akiba,
H. Al-Bataineh,
J. Alexander,
K. Aoki,
L. Aphecetche,
J. Asai, [......],
J. Ying,
S. Yokkaichi,
G.R. Young,
I. Younus,
I.E. Yushmanov,
W.A. Zajc,
O. Zaudtke,
C. Zhang,
S. Zhou,
L. Zolin
[show abstract]
[hide abstract]
ABSTRACT: The differential cross section for the production of direct photons in p+p collisions at √s = 200
GeV at midrapidity was measured in the PHENIX detector at the Relativistic Heavy Ion Collider.
Inclusive-direct photons were measured in the transverse momentum range from 5.5–25 GeV/c,
extending the range beyond previous measurements. Event structure was studied with an isolation
criterion. Next-to-leading-order perturbative-quantum-chromodynamics calculations give a good
description of the spectrum. When the cross section is expressed versus xT , the PHENIX data
are seen to be in agreement with measurements from other experiments at different center-of-mass
energies.
Physical Review C 06/2012; · 3.31 Impact Factor
-
S. Afanasiev,
C. Aidala,
N. N. Ajitanand,
Y. Akiba,
A. Al-Jamel,
J. Alexander,
K. Aoki,
L. Aphecetche,
R. Armendariz,
S. H. Aronson, [......],
A. Yanovich,
S. Yokkaichi,
G. R. Young,
I. Younus,
I. E. Yushmanov,
W. A. Zajc,
O. Zaudtke,
C. Zhang,
J. Zimányi,
L. Zolin
[show abstract]
[hide abstract]
ABSTRACT: We report the measurement of direct photons at midrapidity in Au+Au
collisions at sqrt{s_NN} = 200 GeV. The direct photon signal was extracted for
the transverse-momentum range of 4 GeV/c < p_T < 22 GeV/c, using a statistical
method to subtract decay photons from the inclusive-photon sample. The
direct-photon nuclear-modification factor R_AA was calculated as a function of
p_T for different Au+Au collision centralities using the measured p+p
direct-photon spectrum and compared to theoretical predictions. R_AA was found
to be consistent with unity for all centralities over the entire measured p_T
range. Theoretical models that account for modifications of
initial-direct-photon production due to modified-parton-distribution functions
in Au and the different isospin composition of the nuclei, predict a modest
change of R_AA from unity and are consistent with the data. Models with
compensating effects of the quark-gluon plasma on high-energy photons, such as
suppression of jet-fragmentation photons and induced-photon bremsstrahlung from
partons traversing the medium, are also consistent with this measurement.
05/2012;
-
A. Adare,
S. Afanasiev,
C. Aidala,
N. N. Ajitanand,
Y. Akiba,
H. Al-Bataineh,
J. Alexander,
K. Aoki,
L. Aphecetche,
J. Asai, [......],
J. Ying,
S. Yokkaichi,
G. R. Young,
I. Younus,
I. E. Yushmanov,
W. A. Zajc,
O. Zaudtke,
C. Zhang,
S. Zhou,
L. Zolin
[show abstract]
[hide abstract]
ABSTRACT: The differential cross section for the production of direct photons in p+p
collisions at sqrt(s)=200 GeV at midrapidity was measured in the PHENIX
detector at the Relativistic Heavy Ion Collider. Inclusive-direct photons were
measured in the transverse-momentum range from 5.5--25 GeV/c, extending the
range beyond previous measurements. Event structure was studied with an
isolation criterion. Next-to-leading-order perturbative-quantum-chromodynamics
calculations give a good description of the spectrum. When the cross section is
expressed versus x_T, the PHENIX data are seen to be in agreement with
measurements from other experiments at different center-of-mass energies.
05/2012;
-
A. Adare,
S. Afanasiev,
C. Aidala,
N. N. Ajitanand,
Y. Akiba,
H. Al-Bataineh,
J. Alexander,
A. Angerami,
K. Aoki,
N. Apadula, [......],
S. Yokkaichi,
Z. You,
G. R. Young,
I. Younus,
I. E. Yushmanov,
W. A. Zajc,
O. Zaudtke,
C. Zhang,
S. Zhou,
L. Zolin
[show abstract]
[hide abstract]
ABSTRACT: We report on charmonium measurements [J/ψ (1S), ψ′ (2S), and χc (1P)] in p+p collisions at √s=200 GeV. We find that the fraction of J/ψ coming from the feed-down decay of ψ′ and χc in the midrapidity region (|y|<0.35) is 9.6±2.4% and 32±9%, respectively. We also present the pT and rapidity dependencies of the J/ψ yield measured via dielectron decay at midrapidity (|y|<0.35) and via dimuon decay at forward rapidity (1.2<|y|<2.2). The statistical precision greatly exceeds that reported in our previous publication [ Phys. Rev. Lett. 98 232002 (2007)]. The new results are compared with other experiments and discussed in the context of current charmonium production models.
Phys. Rev. D. 05/2012; 85(9).
-
A. Adare,
S. Afanasiev,
C. Aidala,
N. N. Ajitanand,
Y. Akiba,
H. Al-Bataineh,
J. Alexander,
A. Angerami,
K. Aoki,
N. Apadula, [......],
S. Yokkaichi,
Z. You,
G. R. Young,
I. Younus,
I. E. Yushmanov,
W. A. Zajc,
O. Zaudtke,
C. Zhang,
S. Zhou,
L. Zolin
[show abstract]
[hide abstract]
ABSTRACT: We report on charmonium measurements [J/ψ (1S), ψ′ (2S), and χc (1P)] in p+p collisions at √s=200 GeV. We find that the fraction of J/ψ coming from the feed-down decay of ψ′ and χc in the midrapidity region (|y|<0.35) is 9.6±2.4% and 32±9%, respectively. We also present the pT and rapidity dependencies of the J/ψ yield measured via dielectron decay at midrapidity (|y|<0.35) and via dimuon decay at forward rapidity (1.2<|y|<2.2). The statistical precision greatly exceeds that reported in our previous publication [ Phys. Rev. Lett. 98 232002 (2007)]. The new results are compared with other experiments and discussed in the context of current charmonium production models.
Physical Review D 05/2012; 85:092004. · 4.56 Impact Factor
-
A. Adare,
S. Afanasiev,
C. Aidala,
N. N. Ajitanand,
Y. Akiba,
H. Al-Bataineh,
J. Alexander,
K. Aoki,
L. Aphecetche,
R. Armendariz, [......],
S. Yokkaichi,
G. R. Young,
I. Younus,
I. E. Yushmanov,
W. A. Zajc,
O. Zaudtke,
C. Zhang,
S. Zhou,
J. Zimányi,
L. Zolin
[show abstract]
[hide abstract]
ABSTRACT: Background: Heavy-flavor production in p+p collisions tests
perturbative-quantum-chromodynamics (pQCD) calculations. Modification of
heavy-flavor production in heavy-ion collisions relative to binary-collision
scaling from p+p results, quantified with the nuclear-modification factor
(R_AA), provides information on both cold- and hot-nuclear-matter effects.
Purpose: Determine transverse-momentum, pt, spectra and the corresponding
R_AA for muons from heavy-flavor mesons decay in p+p and Cu+Cu collisions at
sqrt(s_NN)=200 GeV and y=1.65.
Method: Results are obtained using the semi-leptonic decay of heavy-flavor
mesons into negative muons. The PHENIX muon-arm spectrometers measure the p_T
spectra of inclusive muon candidates. Backgrounds, primarily due to light
hadrons, are determined with a Monte-Carlo calculation using a set of input
hadron distributions tuned to match measured-hadron distributions in the same
detector and statistically subtracted.
Results: The charm-production cross section in p+p collisions at sqrt{s}=200
GeV, integrated over pt and in the rapidity range 1.4<y<1.9 is found to be
dsigma_ccbar/dy = 0.139 +/- 0.029 (stat) ^{+0.051}_{-0.058} (syst) mb. This
result is consistent with calculations and with expectations based on the
corresponding midrapidity charm-production cross section measured earlier by
PHENIX. The R_AA for heavy-flavor muons in Cu+Cu collisions is measured in
three centrality intervals for 1<pt<4 GeV/c. Suppression relative to
binary-collision scaling (R_AA<1) increases with centrality.
Conclusions: Within experimental and theoretical uncertainties, the measured
heavy-flavor yield in p+p collisions is consistent with state-of-the-art pQCD
calculations. Suppression in central Cu+Cu collisions suggests the presence of
significant cold-nuclear-matter effects and final-state energy loss.
04/2012;
-
A. Adare,
S. Afanasiev,
C. Aidala,
N. N. Ajitanand,
Y. Akiba,
H. Al-Bataineh,
J. Alexander,
K. Aoki,
L. Aphecetche,
J. Asai, [......],
J. Ying,
S. Yokkaichi,
G. R. Young,
I. Younus,
I. E. Yushmanov,
W. A. Zajc,
O. Zaudtke,
C. Zhang,
S. Zhou,
L. Zolin
[show abstract]
[hide abstract]
ABSTRACT: Unpolarized cross sections and double-helicity asymmetries of
single-inclusive positive and negative charged hadrons at midrapidity from p+p
collisions at sqrt(s)=62.4 GeV are presented. The PHENIX measurements for 1.0 <
p_T < 4.5 GeV/c are consistent with perturbative QCD calculations at
next-to-leading order in the strong coupling constant, alpha_s. Resummed pQCD
calculations including terms with next-to-leading-log accuracy, yielding
reduced theoretical uncertainties, also agree with the data. The
double-helicity asymmetry, sensitive at leading order to the gluon polarization
in a momentum-fraction range of 0.05 ~< x_gluon ~< 0.2, is consistent with
recent global parameterizations disfavoring large gluon polarization.
02/2012;
-
A Adare,
S Afanasiev,
C Aidala,
N N Ajitanand,
Y Akiba,
H Al-Bataineh,
J Alexander,
A Angerami,
K Aoki,
N Apadula, [......],
S Yokkaichi,
Z You,
G R Young,
I Younus,
I E Yushmanov,
W A Zajc,
O Zaudtke,
C Zhang,
S Zhou,
L Zolin
[show abstract]
[hide abstract]
ABSTRACT: We present measurements of J/ψ yields in d+Au collisions at sqrt[s(NN)]=200 GeV recorded by the PHENIX experiment and compare them with yields in p+p collisions at the same energy per nucleon-nucleon collision. The measurements cover a large kinematic range in J/ψ rapidity (-2.2<y<2.4) with high statistical precision and are compared with two theoretical models: one with nuclear shadowing combined with final state breakup and one with coherent gluon saturation effects. In order to remove model dependent systematic uncertainties we also compare the data to a simple geometric model. The forward rapidity data are inconsistent with nuclear modifications that are linear or exponential in the density weighted longitudinal thickness, such as those from the final state breakup of the bound state.
Physical Review Letters 09/2011; 107(14):142301. · 7.37 Impact Factor
-
A. Adare,
S. Afanasiev,
C. Aidala,
N. N. Ajitanand,
Y. Akiba,
H. Al-Bataineh,
J. Alexander,
K. Aoki,
L. Aphecetche,
R. Armendariz, [......],
S. Yokkaichi,
G. R. Young,
I. Younus,
I. E. Yushmanov,
W. A. Zajc,
O. Zaudtke,
C. Zhang,
S. Zhou,
J. Zimányi,
L. Zolin
[show abstract]
[hide abstract]
ABSTRACT: We report on the event structure and double helicity asymmetry (ALL) of jet production in longitudinally polarized p+p collisions at √s=200 GeV. Photons and charged particles were measured by the PHENIX experiment at midrapidity |η|<0.35 with the requirement of a high-momentum (>2 GeV/c) photon in the event. Event structure, such as multiplicity, pT density and thrust in the PHENIX acceptance, were measured and compared with the results from the pythia event generator and the geant detector simulation. The shape of jets and the underlying event were well reproduced at this collision energy. For the measurement of jet ALL, photons and charged particles were clustered with a seed-cone algorithm to obtain the cluster pT sum (pTreco). The effect of detector response and the underlying events on pTreco was evaluated with the simulation. The production rate of reconstructed jets is satisfactorily reproduced with the next-to-leading-order and perturbative quantum chromodynamics jet production cross section. For 4<pTreco<12 GeV/c with an average beam polarization of ⟨P⟩=49% we measured ALL=-0.0014±0.0037stat at the lowest pTreco bin (4–5 GeV/c) and -0.0181±0.0282stat at the highest pTreco bin (10–12 GeV/c) with a beam polarization scale error of 9.4% and a pT scale error of 10%. Jets in the measured pTreco range arise primarily from hard-scattered gluons with momentum fraction 0.02<x<0.3 according to pythia. The measured ALL is compared with predictions that assume various ΔG(x) distributions based on the Gluck-Reya-Stratmann-Vogelsang parameterization. The present result imposes the limit -1.1<∫0.020.3dxΔG(x,μ2=1 GeV2)<0.4 at 95% confidence level or ∫0.020.3dxΔG(x,μ2=1 GeV2)<0.5 at 99% confidence level.
Phys. Rev. D. 07/2011; 84(1).
-
A. Adare,
S Afanasiev,
C Aidala,
N N Ajitanand,
Y Akiba,
H. Al-Bataineh,
A Al-Jamel,
J Alexander,
A. Angerami,
K Aoki, [......],
Z You,
G R Young,
I. Younus,
I E Yushmanov,
W A Zajc,
O. Zaudtke,
C Zhang,
S Zhou,
J Zimányi,
L Zolin
[show abstract]
[hide abstract]
ABSTRACT: The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) has
measured omega meson production via leptonic and hadronic decay channels in
p+p, d+Au, Cu+Cu, and Au+Au collisions at sqrt(s_NN) = 200 GeV. The invariant
transverse momentum spectra measured in different decay modes give consistent
results. Measurements in the hadronic decay channel in Cu+Cu and Au+Au
collisions show that omega production has a suppression pattern at high
transverse momentum, similar to that of pi^0 and eta in central collisions, but
no suppression is observed in peripheral collisions. The nuclear modification
factors, R_AA, are consistent in Cu+Cu and Au+Au collisions at similar numbers
of participant nucleons.
05/2011;
-
A. Adare,
S. Afanasiev,
C. Aidala,
N. N. Ajitanand,
Y. Akiba,
H. Al-Bataineh,
J. Alexander,
A. Angerami,
K. Aoki,
N. Apadula, [......],
S. Yokkaichi,
Z. You,
G. R. Young,
I. Younus,
I. E. Yushmanov,
W. A. Zajc,
O. Zaudtke,
C. Zhang,
S. Zhou,
L. Zolin
[show abstract]
[hide abstract]
ABSTRACT: We report on charmonium measurements [J/psi(1S), psi'(2S), and chi_c(1P)] in
p+p collisions at sqrt(s)=200 GeV. We find that the fraction of J/psi coming
from the feed-down decay of psi' and chi_c in the midrapidity region
($|\eta|<0.35$) is 9.6+/-2.4% and 32+/-9%, respectively. We also report new,
higher statistics p_T and rapidity dependencies of the J/psi yield via
dielectron decay in the same midrapidity range and at forward rapidity
(1.2<|eta|<2.4) via dimuon decay. These results are compared with measurements
from other experiments and discussed in the context of current charmonium
production models.
05/2011;
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A. Adare,
S. Afanasiev,
C. Aidala,
N. N. Ajitanand,
Y. Akiba,
H. Al-Bataineh,
J. Alexander,
K. Aoki,
L. Aphecetche,
Y. Aramaki, [......],
S. Yokkaichi,
G. R. Young,
I. Younus,
Z. You,
I. E. Yushmanov,
W. A. Zajc,
O. Zaudtke,
C. Zhang,
S. Zhou,
L. Zolin
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ABSTRACT: Measurements of electrons from the decay of open-heavy-flavor mesons have shown that the yields are suppressed in Au+Au collisions compared to expectations from binary-scaled p+p collisions. These measurements indicate that charm and bottom quarks interact with the hot dense matter produced in heavy-ion collisions much more than expected. Here we extend these studies to two-particle correlations where one particle is an electron from the decay of a heavy-flavor meson and the other is a charged hadron from either the decay of the heavy meson or from jet fragmentation. These measurements provide more detailed information about the interactions between heavy quarks and the matter, such as whether the modification of the away-side-jet shape seen in hadron-hadron correlations is present when the trigger particle is from heavy-meson decay and whether the overall level of away-side-jet suppression is consistent. We statistically subtract correlations of electrons arising from background sources from the inclusive electron-hadron correlations and obtain two-particle azimuthal correlations at √sNN=200 GeV between electrons from heavy-flavor decay with charged hadrons in p+p and also first results in Au+Au collisions. We find the away-side-jet shape and yield to be modified in Au+Au collisions compared to p+p collisions.
Phys. Rev. C. 04/2011; 83(4).
