178 research outputs found
Experimental Signature of Medium Modifications for rho and omega Mesons in the 12 GeV p + A Reactions
The invariant mass spectra of e+e- pairs produced in 12-GeV proton-induced
nuclear reactions are measured at the KEK Proton-Synchrotron. On the low-mass
side of the omega meson peak, a significant enhancement over the known hadronic
sources has been observed. The mass spectra, including the excess, are well
reproduced by a model that takes into account the density dependence of the
vector meson mass modification, as theoretically predicted.Comment: 4 pages, 3 figures, Version accepted for Physical Review Lette
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Nuclear mass number dependence of inclusive production of omega and phi mesons in 12 GeV p + A collisions
The inclusive production of omega and phi mesons is studied in the backward
region of the interaction of 12 GeV protons with polyethylene, carbon, and
copper targets. The mesons are measured in e^+ e^- decay channels. The
production cross sections of the mesons are presented as functions of rapidity
y and transverse momentum p_T. The nuclear mass number dependences (A
dependences) are found to be A^{0.710 +/- 0.021(stat) +/- 0.037(syst)} for
omega mesons and A^{0.937 +/- 0.049(stat) +/- 0.018(syst)} for phi mesons in
the region of 0.9 < y < 1.7 and p_T < 0.75 GeV/c.Comment: 12 pages, 8 figures; typos adde
Nuclear-matter modification of decay widths in the and channels
The invariant mass spectra of are measured in 12 GeV
reactions in order to search for the in-medium modification of
mesons. The observed spectra are well reproduced by the
relativistic Breit-Wigner function with a combinatorial background shape in
three regions between 1.0 and 3.5. The nuclear mass-number
dependence of the yields of the decay channel is compared to the
simultaneously measured decay channel for carbon and copper
targets. We parameterize the production yields as and obtain to be
0.14 0.12. Limits are obtained for the partial decay widths of
mesons in nuclear matter.Comment: 5 pages, 4 figure
Observation of Meson Modification in Nuclear Matter
We have measured invariant mass spectra of electron-positron pairs in the
target rapidity region of 12GeV p+A reactions. We have observed a significant
difference in the mass spectra below the meson between p+C and p+Cu
interactions. The difference is interpreted as a signature of the
modification at normal nuclear-matter density.Comment: 8 pages, 3 figures, submitted to Phys. Rev. Letters. all the figures
changed to Postscript format, text not change
Transverse momentum and centrality dependence of dihadron correlations in Au+Au collisions at sqrt(s_NN)=200 GeV: Jet-quenching and the response of partonic matter
Azimuthal angle \Delta\phi correlations are presented for charged hadrons
from dijets for 0.4 < p_T < 10 GeV/c in Au+Au collisions at sqrt(s_NN) = 200
GeV. With increasing p_T, the away-side distribution evolves from a broad to a
concave shape, then to a convex shape. Comparisons to p+p data suggest that the
away-side can be divided into a partially suppressed "head" region centered at
Delta\phi ~ \pi, and an enhanced "shoulder" region centered at Delta\phi ~ \pi
+/- 1.1. The p_T spectrum for the "head" region softens toward central
collisions, consistent with the onset of jet quenching. The spectral slope for
the "shoulder" region is independent of centrality and trigger p_T, which
offers constraints on energy transport mechanisms and suggests that the
"shoulder" region contains the medium response to energetic jets.Comment: 420 authors from 58 institutions, 6 pages, 4 figures. Submitted to
Physical Review Letters. Plain text data tables for the points plotted in
figures for this and previous PHENIX publications are (or will be) publicly
available at http://www.phenix.bnl.gov/papers.htm
High-pT pi^zero Production with Respect to the Reaction Plane in Au + Au Collisions at sqrt(s_NN) = 200 GeV
Measurements of the azimuthal anisotropy of high-\pT neutral pion neutral
pion production in Au+Au collisions at sqrt(s_NN) = 200 GeV by the PHENIX
experiment are presented. The data included in this paper were collected during
the 2004 RHIC 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 pi^0s 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 (v_2) of the angular distributions
are presented as a function of pi^0 transverse momentum p_T for different bins
in collision centrality. Measured reaction plane dependent pi^0 yields are used
to determine the azimuthal dependence of the pi^0 suppression as a function of
p_T, R_AA (Delta phi,p_T). A jet-quenching motivated geometric analysis is
presented that attempts to simultaneously describe the centrality dependence
and reaction plane angle dependence of the pi^0 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.Comment: 344 authors, 35 pages text, RevTeX-4, 24 figures, 8 tables. Submitted
to Physical Review
Measurement of high-p_T Single Electrons from Heavy-Flavor Decays in p+p Collisions at sqrt(s) = 200 GeV
The momentum distribution of electrons from decays of heavy flavor (charm and
beauty) for midrapidity |y| < 0.35 in p+p collisions at sqrt(s) = 200 GeV has
been measured by the PHENIX experiment at the Relativistic Heavy Ion Collider
(RHIC) over the transverse momentum range 0.3 < p_T < 9 GeV/c. Two independent
methods have been used to determine the heavy flavor yields, and the results
are in good agreement with each other. A fixed-order-plus-next-to-leading-log
pQCD calculation agrees with the data within the theoretical and experimental
uncertainties, with the data/theory ratio of 1.72 +/- 0.02^stat +/- 0.19^sys
for 0.3 < p_T < 9 GeV/c. The total charm production cross section at this
energy has also been deduced to be sigma_(c c^bar) = 567 +/- 57^stat +/-
224^sys micro barns.Comment: 375 authors from 57 institutions, 6 pages, 3 figures. Submitted to
Physical Review Letters. Plain text data tables for the points plotted in
figures for this and previous PHENIX publications are (or will be) publicly
available at http://www.phenix.bnl.gov/papers.htm
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