-
A Adare,
S Afanasiev,
C Aidala,
N N Ajitanand,
Y Akiba,
R Akimoto, H Al-Ta'ani,
J Alexander,
K R Andrews,
A Angerami, [......],
J S Yoo,
Z You,
G R Young,
I Younus,
I E Yushmanov,
W A Zajc,
A Zelenski,
S Zhou,
L Zolin,
PHENIX Collaboration
[show abstract]
[hide abstract]
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
Physical Review D 01/2013; 87(1). · 4.56 Impact Factor
-
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;
-
A Adare,
S Afanasiev,
C Aidala,
N N Ajitanand,
Y Akiba,
R Akimoto, H Al-Ta'ani,
J Alexander,
A Angerami,
K Aoki, [......],
R Yang,
A Yanovich,
J Ying,
S Yokkaichi,
Z You,
I Younus,
I E Yushmanov,
W A Zajc,
A Zelenski,
L Zolin
[show abstract]
[hide abstract]
ABSTRACT: Neutral-pion π^{0} spectra were measured at midrapidity (|y|<0.35) in Au+Au collisions at sqrt[s_{NN}]=39 and 62.4 GeV and compared with earlier measurements at 200 GeV in a transverse-momentum range of 1<p_{T}<10 GeV/c. The high-p_{T} tail is well described by a power law in all cases, and the powers decrease significantly with decreasing center-of-mass energy. The change of powers is very similar to that observed in the corresponding spectra for p+p collisions. The nuclear modification factors (R_{AA}) show significant suppression, with a distinct energy, centrality, and p_{T} dependence. Above p_{T}=7 GeV/c, R_{AA} is similar for sqrt[s_{NN}]=62.4 and 200 GeV at all centralities. Perturbative-quantum-chromodynamics calculations that describe R_{AA} well at 200 GeV fail to describe the 39 GeV data, raising the possibility that, for the same p_{T} region, the relative importance of initial-state effects and soft processes increases at lower energies. The p_{T} range where π^{0} spectra in central Au+Au collisions have the same power as in p+p collisions is ≈5 and 7 GeV/c for sqrt[s_{NN}]=200 and 62.4 GeV, respectively. For the sqrt[s_{NN}]=39 GeV data, it is not clear whether such a region is reached, and the x_{T} dependence of the x_{T}-scaling power-law exponent is very different from that observed in the sqrt[s_{NN}]=62 and 200 GeV data, providing further evidence that initial-state effects and soft processes mask the in-medium suppression of hard-scattered partons to higher p_{T} as the collision energy decreases.
Physical Review Letters 10/2012; 109(15):152301. · 7.37 Impact Factor
-
A. Adare,
S. Afanasiev,
C. Aidala,
N. N. Ajitanand,
Y. Akiba,
R. Akimoto, H. Al-Ta'ani,
J. Alexander,
K. R. Andrews,
A. Angerami, [......],
S. Yokkaichi,
J. S. Yoo,
Z. You,
G. R. Young,
I. Younus,
I. E. Yushmanov,
W. A. Zajc,
A. Zelenski,
S. Zhou,
L. Zolin
[show abstract]
[hide abstract]
ABSTRACT: We report on the first measurement of 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 GeV for p_T= 0.5 to 3.0 GeV/c. The
asymmetry was measured at mid-rapidity (|eta|<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 |Delta g/g(log{_10}x=
-1.6^+0.5_-0.4, {mu}=m_T^c)|^2 < 0.033 (1 sigma), based on a leading-order
perturbative-quantum-chromodynamics model, using the measured asymmetry.
09/2012;
-
A. Adare,
C. Aidala,
N. N. Ajitanand,
Y. Akiba,
R. Akimoto, H. Al-Ta'ani,
J. Alexander,
A. Angerami,
K. Aoki,
N. Apadula, [......],
Y. L. Yamaguchi,
R. Yang,
A. Yanovich,
J. Ying,
S. Yokkaichi,
Z. You,
I. Younus,
I. E. Yushmanov,
W. A. Zajc,
A. Zelenski
[show abstract]
[hide abstract]
ABSTRACT: 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<|y|<2.2). Invariant yields
are presented as a function of both collision centrality and transverse
momentum. Nuclear modifications are obtained for central relative to peripheral
Au+Au collisions (R_CP) and for various centrality selections in Au+Au relative
to scaled p+p cross sections obtained from other measurements (R_AA). The
observed suppression patterns at 39 and 62.4 GeV are quite similar to those
previously measured at 200 GeV. This similar suppression presents a challenge
to theoretical models that contain various competing mechanisms with different
energy dependencies, some of which cause suppression and others enhancement.
08/2012;
-
A Adare,
S Afanasiev,
C Aidala,
N N Ajitanand,
Y Akiba,
R Akimoto,
J Alexander, H Al-Ta'ani,
K R Andrews,
A Angerami, [......],
S Yokkaichi,
J S Yoo,
G R Young,
I Younus,
Z You,
I E Yushmanov,
W A Zajc,
A Zelenski,
S Zhou,
L Zolin
[show abstract]
[hide abstract]
ABSTRACT: Large parity-violating longitudinal single-spin asymmetries A(L)(e+) = -0.86(-0.14) (+0.30) and A(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 sqrt[s] = 500 GeV with the PHENIX detector at RHIC. These e± come mainly from the decay of W± and Z0 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 σ(pp → W+ X) × BR(W+ → e+ ν(e)) = 144.1 ± 21.2(stat)(-10.3) (+3.4) (syst) ± 21.6(norm) pb, and σ(pp → W- X) × BR(W- → e- ν[over ¯](e)) = 31.7 ± 12.1(stat)(-8.2) (+10.1) (syst) ± 4.8(norm) pb.
Physical Review Letters 02/2011; 106(6):062001. · 7.37 Impact Factor
-
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 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.
09/2010;
