-
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;
-
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. 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;
-
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,
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,
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,
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: The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the invariant differential cross section for production of KS0, ω, η′, and ϕ mesons in p+p collisions at √s=200 GeV. Measurements of ω and ϕ production in different decay channels give consistent results. New results for the ω are in agreement with previously published data and extend the measured pT coverage. The spectral shapes of all hadron transverse momentum distributions measured by PHENIX are well described by a Tsallis distribution functional form with only two parameters, n and T, determining the high-pT and characterizing the low-pT regions of the spectra, respectively. The values of these parameters are very similar for all analyzed meson spectra, but with a lower parameter T extracted for protons. The integrated invariant cross sections calculated from the fitted distributions are found to be consistent with existing measurements and with statistical model predictions.
Phys. Rev. D. 03/2011; 83(5).
-
A. Adare,
S. Afanasiev,
C. Aidala,
N. N. Ajitanand,
Y. Akiba,
H. Al-Bataineh,
J. Alexander,
A. Al-Jamel,
A. Angerami,
K. Aoki, [......],
G. R. Young,
I. Younus,
Z. You,
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 has performed systematic measurements of ϕ meson production in the K+K- decay channel at midrapidity in p+p, d+Au, Cu+Cu, and Au+Au collisions at √sNN=200 GeV. Results are presented on the ϕ invariant yield and the nuclear modification factor RAA for Au+Au and Cu+Cu, and RdA for d+Au collisions, studied as a function of transverse momentum (1<pT<7 GeV/c) and centrality. In central and midcentral Au+Au collisions, the RAA of ϕ exhibits a suppression relative to expectations from binary scaled p+p results. The amount of suppression is smaller than that of the π0 and the η in the intermediate pT range (2-5 GeV/c), whereas, at higher pT, the ϕ, π0, and η show similar suppression. The baryon (proton and antiproton) excess observed in central Au+Au collisions at intermediate pT is not observed for the ϕ meson despite the similar masses of the proton and the ϕ. This suggests that the excess is linked to the number of valence quarks in the hadron rather than its mass. The difference gradually disappears with decreasing centrality, and, for peripheral collisions, the RAA values for both particle species are consistent with binary scaling. Cu+Cu collisions show the same yield and suppression as Au+Au collisions for the same number of Npart. The RdA of ϕ shows no evidence for cold nuclear effects within uncertainties.
Phys. Rev. C. 02/2011; 83(2).
-
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: Transverse momentum distributions and yields for $\pi^{\pm}$, $K^{\pm}$, $p$
and $\bar{p}$ in $p+p$ collisions at $\sqrt{s}$=200 and 62.4 GeV at midrapidity
are measured by the PHENIX experiment at the Relativistic Heavy Ion Collider
(RHIC). These data provide important baseline spectra for comparisons with
identified particle spectra in heavy ion collisions at RHIC. We present the
inverse slope parameter $T_{\rm inv}$, mean transverse momentum $ $ and
yield per unit rapidity $dN/dy$ at each energy, and compare them to other
measurements at different $\sqrt{s}$ in $p+p$ and $p+\bar{p}$ collisions. We
also present the scaling properties such as $m_T$ scaling, $x_T$ scaling on the
$p_T$ spectra between different energies. To discuss the mechanism of the
particle production in $p+p$ collisions, the measured spectra are compared to
next-to-leading-order or next-to-leading-logarithmic perturbative quantum
chromodynamics calculations.
02/2011;
-
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: Measurements of double-helicity asymmetries in inclusive hadron production in polarized p+p collisions are sensitive to helicity-dependent parton distribution functions, in particular, to the gluon helicity distribution, Δg. This study focuses on the extraction of the double-helicity asymmetry in η production (p⃗+p⃗→η+X), the η cross section, and the η/π0 cross section ratio. The cross section and ratio measurements provide essential input for the extraction of fragmentation functions that are needed to access the helicity-dependent parton distribution functions.
Phys. Rev. D. 01/2011; 83(3).
-
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: Correlations of charged hadrons of 1<pT<10 Gev/c with high pT direct photons and π0 mesons in the range 5<pT<15 Gev/c are used to study jet fragmentation in the γ+jet and dijet channels, respectively. The magnitude of the partonic transverse momentum, kT, is obtained by comparing to a model incorporating a Gaussian kT smearing. The sensitivity of the associated charged hadron spectra to the underlying fragmentation function is tested and the data are compared to calculations using recent global fit results. The shape of the direct photon-associated hadron spectrum as well as its charge asymmetry are found to be consistent with a sample dominated by quark-gluon Compton scattering. No significant evidence of fragmentation photon correlated production is observed within experimental uncertainties.
Phys. Rev. D. 10/2010; 82(7).
-
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: Measurements of double-helicity asymmetries for inclusive hadron production
in polarized p+p collisions are sensitive to helicity--dependent parton
distribution functions, in particular to the gluon helicity distribution,
Delta(g). This study focuses on the extraction of the double-helicity asymmetry
in eta production: polarized p+p --> eta + X, the eta cross section, and the
eta/pi^0 cross section ratio. The cross section and ratio measurements provide
essential input for the extraction of fragmentation functions that are needed
to access the helicity-dependent parton distribution functions.
09/2010;
-
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 event structure and double helicity asymmetry ($A_LL$) of jet
production in longitudinally polarized p+p collisions at $\sqrt{s}$=200 GeV.
Photons and charged particles were measured at midrapidity $|\eta| < 0.35$ with
the requirement of a high-momentum ($>2$ GeV/$c$) photon in each event.
Measured event structure is compared with {\sc pythia} and {\sc geant}
simulations. The shape of jets and the underlying event were well reproduced at
this collision energy. For the measurement of jet $A_{LL}$, photons and charged
particles were clustered with a seed-cone algorithm to obtain the cluster $p_T$
sum ($p_T^{\rm reco}$). The effect of detector response and the underlying
events on $p_T^{\rm reco}$ was evaluated with the simulation. The production
rate of reconstructed jets is satisfactorily reproduced with the NLO pQCD jet
production cross section. For $4 < p_T^{\rm reco} < 12$ GeV/$c$ with an average
beam polarization of $< P > = 49%$ we measured $A_{LL} = -0.0014 \pm
0.0037^{\rm stat}$ at the lowest $p_T^{\rm reco}$ bin (4-5 GeV/$c$) and
$-0.0181 \pm 0.0282^{\rm stat}$ at the highest $p_T^{\rm reco}$ 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 $p_T^{\rm reco}$ range arise primarily from
hard-scattered gluons with momentum fraction $0.02 < x < 0.3$ according to {\sc
pythia}. The measured $A_{LL}$ is compared with predictions that assume various
$\Delta G(x)$ distributions based on the GRSV parameterization. The present
result imposes the limit $-1.1 < \int_{0.02}^{0.3}dx \Delta G(x, \mu^2 = 1 {\rm
GeV}^2) < 0.4$ at 95% confidence level or $\int_{0.02}^{0.3}dx \Delta G(x,
\mu^2 = 1 {\rm GeV}^2) < 0.5$ at 99% confidence level.
09/2010;
-
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: Correlations of charged hadrons of 1 < pT < 10 GeV/c with high pT direct
photons and pi^ 0 mesons in the range 5 <pT < 15 GeV/c are used to study jet
fragmentation in the photon+jet and di-jet channels, respectively. The
magnitude of the partonic transverse momentum, kT, is obtained by comparing to
a model incorporating a Gaussian kT smearing. The sensitivity of the associated
charged hadron spectra to the underlying fragmentation function is tested and
the data are compared to calculations using recent global fit results. The
shape of the direct photon-associated hadron spectrum as well as its charge
asymmetry are found to be consistent with a sample dominated by quark-gluon
Compton scattering. No significant evidence of fragmentation photon correlated
production is observed within experimental uncertainties.
06/2010;
-
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: The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the
invariant differential cross section for production of K^0_S , \omega, \eta
prime, and \phi mesons in p + p collisions at = 200 GeV. Measurements \omega
and \phi production in different decay channels give consistent results. New
results for the \phi are in agreement with previously published data and extend
the measured pT coverage. The spectral shapes of all hadron transverse momentum
distributions measured by PHENIX are well described by a Tsallis distribution
functional form with only two parameters, n and T, determining the high-pT and
characterizing the low-pT regions of the spectra, respectively. The values of
these parameters are very similar for all analyzed meson spectra, but with a
lower parameter T extracted for protons. The integrated invariant cross
sections calculated from the fitted distributions are found to be consistent
with existing measurements and with statistical model predictions.
05/2010;
-
A. Adare,
S Afanasiev,
C Aidala,
N N Ajitanand,
Y Akiba,
H. Al-Bataineh,
J Alexander,
A Al-Jamel,
K Aoki,
L Aphecetche, [......],
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: Transverse momentum (p^e_T) spectra of electrons from semileptonic weak decays of heavy flavor mesons in the range of 0.3 < p^e_T < 9.0 GeV/c have been measured at mid-rapidity (|eta| < 0.35) by the PHENIX experiment at the Relativistic Heavy Ion Collider in p+p and Au+Au collisions at sqrt(s_NN)=200 GeV. The nuclear modification factor R_AA with respect to p+p collisions indicates substantial energy loss of heavy quarks in the produced medium. In addition, the azimuthal anisotropy parameter v_2 has been measured for 0.3 < p^e_T < 5.0 GeV/c in Au+Au collisions. Comparisons of R_AA and v_2 are made to various model calculations. Comment: 422 authors from 59 institutions, 48 pages, 46 figures, 18 tables. v2 removes line numbers and matches submission to PRC. Plain text data tables for points plotted in figures, but not in tables are at http://www.phenix.bnl.gov/papers.html
05/2010;
-
A Adare,
S Afanasiev,
C Aidala,
N N Ajitanand,
Y Akiba,
H Al-Bataineh,
J Alexander,
A Al-Jamel,
K Aoki,
L Aphecetche, [......],
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: The production of e+ e- pairs for m(e+ e-)<0.3 GeV/c2 and 1<p(T)<5 GeV/c is measured in p+p and Au+Au collisions at square root(S(NN))=200 GeV. An enhanced yield above hadronic sources is observed. Treating the excess as photon internal conversions, the invariant yield of direct photons is deduced. In central Au+Au collisions, the excess of the direct photon yield over p+p is exponential in transverse momentum, with an inverse slope T=221+/-19(stat)+/-19(syst) MeV. Hydrodynamical models with initial temperatures ranging from T(init) approximately 300-600 MeV at times of approximately 0.6-0.15 fm/c after the collision are in qualitative agreement with the data. Lattice QCD predicts a phase transition to quark gluon plasma at approximately 170 MeV.
Physical Review Letters 04/2010; 104(13):132301. · 7.37 Impact Factor
-
S. Afanasiev,
C. Aidala,
N. N. Ajitanand,
Y. Akiba,
J. Alexander,
A. Al-Jamel,
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: Measurements of the azimuthal anisotropy of high-pT neutral pion (π0) production in Au+Au collisions at √sNN=200 GeV by the PHENIX experiment are presented. The data included in this article were collected during the 2004 Relativistic Heavy Ion Collider running period and represent approximately an order of magnitude increase in the number of analyzed events relative to previously published results. Azimuthal angle distributions of π0 mesons detected in the PHENIX electromagnetic calorimeters are measured relative to the reaction plane determined event-by-event using the forward and backward beam-beam counters. Amplitudes of the second Fourier component (v2) of the angular distributions are presented as a function of π0 transverse momentum (pT) for different bins in collision centrality. Measured reaction plane dependent π0 yields are used to determine the azimuthal dependence of the π0 suppression as a function of pT, RAA(Δϕ,pT). A jet-quenching motivated geometric analysis is presented that attempts to simultaneously describe the centrality dependence and reaction plane angle dependence of the π0 suppression in terms of the path lengths of hypothetical parent partons in the medium. This set of results allows for a detailed examination of the influence of geometry in the collision region and of the interplay between collective flow and jet-quenching effects along the azimuthal axis.
Phys. Rev. C. 11/2009; 80(5).
-
A. Adare,
S. Afanasiev,
C. Aidala,
N. N. Ajitanand,
Y. Akiba,
H. Al-Bataineh,
J. Alexander,
A. Al-Jamel,
A. Angerami,
K. Aoki, [......],
G. R. Young,
I. Younus,
Z. You,
I. E. Yushmanov,
W. A. Zajc,
O. Zaudtke,
C. Zhang,
S. Zhou, J. Zimányi,
L. Zolin
Nuclear Physics A 10/2009; 830:963-966. · 1.54 Impact Factor
