394 research outputs found
Search for new phenomena in events with high jet multiplicity and low missing transverse momentum in proton–proton collisions at
A dedicated search is presented for new phenomena in inclusive 8- and 10-jet final states with low
missing transverse momentum, with and without identification of jets originating from b quarks. The
analysis is based on data from proton–proton collisions corresponding to an integrated luminosity of
19.7 fb−1 collected with the CMS detector at the LHC at √s = 8 TeV. The dominant multijet background
expectations are obtained from low jet multiplicity control samples. Data agree well with the standard
model background predictions, and limits are set in several benchmark models. Colorons (axigluons) with
masses between 0.6 and 0.75 (up to 1.15) TeV are excluded at 95% confidence level. Similar exclusion
limits for gluinos in R-parity violating supersymmetric scenarios are from 0.6 up to 1.1 TeV. These results
comprise the first experimental probe of the coloron and axigluon models in multijet final states.
© 2017 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY licenseL
Azimuthal Angle Correlations for Rapidity Separated Hadron Pairs in d+Au Collisions at sqrt(s_NN) = 200 GeV
We report on two-particle azimuthal angle correlations between charged
hadrons at forward/backward (deuteron/gold going direction) rapidity and
charged hadrons at mid-rapidity in deuteron-gold (d+Au) and proton-proton (p+p)
collisions at sqrt(s_NN) = 200 GeV. Jet structures are observed in the
correlations which we quantify in terms of the conditional yield and angular
width of away side partners. The kinematic region studied here samples partons
in the gold nucleus carrying nucleon momentum fraction x~0.1 to x~0.01. Within
this range, we find no x dependence of the jet structure in d+Au collisions.Comment: 330 authors, 6 pages text, 4 figures, no tables. Submitted to Phys.
Rev. Lett. 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
Deuteron and antideuteron production in Au+Au collisions at sqrt(s_NN)=200 GeV
The production of deuterons and antideuterons in the transverse momentum
range 1.1 < p_T < 4.3 GeV/c at mid-rapidity in Au + Au collisions at
sqrt(s_NN)=200 GeV has been studied by the PHENIX experiment at RHIC. A
coalescence analysis comparing the deuteron and antideuteron spectra with those
of protons and antiprotons, has been performed. The coalescence probability is
equal for both deuterons and antideuterons and increases as a function of p_T,
which is consistent with an expanding collision zone. Comparing (anti)proton
yields p_bar/p = 0.73 +/- 0.01, with (anti)deuteron yields: d_bar/d = 0.47 +/-
0.03, we estimate that n_bar/n = 0.64 +/- 0.04.Comment: 326 authors, 6 pages text, 5 figures, 1 Table. Submitted to PRL.
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
Jet Structure from Dihadron Correlations in d+Au collisions at sqrt(s_NN) = 200 GeV
Dihadron correlations at high transverse momentum in d+Au collisions at
sqrt(s_NN) = 200 GeV at midrapidity are measured by the PHENIX experiment at
the Relativistic Heavy Ion Collider (RHIC). From these correlations we extract
several structural characteristics of jets; the root-mean-squared (RMS)
transverse momentum of fragmenting hadrons with respect to the jet
sqrt(), the mean sine-squared angle between the scattered partons
, and the number of particles produced within the dijet that are
associated with a high-p_T particle (dN/dx_E distributions). We observe that
the fragmentation characteristics of jets in d+Au collisions are very similar
to those in p+p collisions and that there is also little dependence on the
centrality of the d+Au collision. This is consistent with the nuclear medium
having little influence on the fragmentation process. Furthermore, there is no
statistically significant increase in the value of from p+p to
d+Au collisions. This constrains the amount of multiple scattering that partons
undergo in the cold nuclear medium before and after a hard-collision.Comment: 330 authors, 30 pages text, RevTeX4, 42 figures, 20 tables. Submitted
to Physical Review C. 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
Mid-Rapidity Direct-Photon Production in p+p Collisions at sqrt(s) = 200 GeV
A measurement of direct photons in p+p collisions at sqrt(s)=200 GeV is
presented. A photon excess above background from pi^0 --> gamma+gamma, eta -->
gamma+gamma, and other decays is observed in the transverse momentum range 5.5
< p_T < 7 GeV/c. The result is compared to a next-to-leading-order perturbative
QCD calculation. Within errors, good agreement is found between the QCD
calculation and the measured result.Comment: 330 authors, 7 pages text, RevTeX, 2 figures, 2 tables. Submitted to
Physical Review D. 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
Nuclear Modification Factors for Hadrons At Forward and Backward Rapidities in Deuteron-Gold Collisions at sqrt(s_NN) = 200 GeV
We report on charged hadron production in deuteron-gold reactions at
sqrt(s_NN) = 200 GeV. Our measurements in the deuteron-direction cover 1.4 <
eta < 2.2, referred to as forward rapidity, and in the gold-direction -2.0 <
eta < -1.4, referred to as backward rapidity, and a transverse momentum range
p_T = 0.5-4.0 GeV/c. We compare the relative yields for different deuteron-gold
collision centrality classes. We observe a suppression relative to binary
collision scaling at forward rapidity, sensitive to low momentum fraction (x)
partons in the gold nucleus, and an enhancement at backward rapidity, sensitive
to high momentum fraction partons in the gold nucleus.Comment: 330 authors, 6 pages text, 4 figures, REVTeX4. Published in Physical
Review Letters. Minor changes over previous version in response to referee
and editor comments, plus updating of references. Plain text data tables for
the points plotted in figures for this and previous PHENIX publications are
publicly available at http://www.phenix.bnl.gov/papers.htm
Double Helicity Asymmetry in Inclusive Mid-Rapidity neutral pion Production for Polarized p+p Collisions at sqrt(s)=200 GeV
We present a measurement of the double longitudinal spin asymmetry in
inclusive pi^0 production in polarized proton-proton collisions at sqrt(s)=200
GeV. The data were taken at the Relativistic Heavy Ion Collider with average
beam polarizations of 26%. The measurements are the first of a program to study
the longitudinal spin structure of the proton, using strongly interacting
probes, at collider energies. The asymmetry is presented for transverse momenta
1-5 GeV/c at mid-rapidity, where next-to-leading order perturbative quantum
chromodynamic (NLO pQCD) calculations describe the unpolarized cross section
well. The observed asymmetry is small and is compared with a NLO pQCD
calculation with a range of polarized gluon distributions.Comment: 326 authors, 6 pages text, RevTeX, 3 figures, 1 table. To be
submitted to PRL. 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 transverse momentum eta meson production in p+p, d+Au and Au+Au collisions at sqrt(s_NN) = 200 GeV
Inclusive transverse momentum spectra of eta mesons in the range p_T~2-12
GeV/c have been measured at mid-rapidity (|\eta| < 0,35) by the PHENIX
experiment at RHIC in p+p, d+Au and Au+Au collisions at sqrt(s_NN) = 200 GeV.
The eta mesons are reconstructed through their eta--> \gamma\gamma channel for
the three colliding systems as well as through the eta-->pi^0 pi+ pi- decay
mode in p+p and d+Au collisions. The nuclear modification factor in d+Au
collisions, R_dAu(p_T~1.0-1.1, suggests at most only modest p_T broadening
("Cronin enhancement"). In central Au+Au reactions, the eta yields are
significantly suppressed, with R_AuAu(pT)~0.2. The ratio of eta to pi^0 yields
is approximately constant as a function of p_T for the three colliding systems
in agreement with the high-p_T world average of R_eta/pi^0 \approx 0.5 in
hadron-hadron, hadron-nucleus, and nucleus-nucleus collisions for a wide range
of center-of-mass energies [sqrt(s_NN)~3-1800 GeV] as well as, for high scaled
momentum x_p, in e+e- annihilations at sqrt(s)=91.2 GeV. These results are
consistent with a scenario where high-p_T eta production in nuclear collisions
at RHIC is largely unaffected by initial-state effects, but where light-quark
mesons (pi^0;eta) are equally suppressed due to final-state interactions of the
parent partons in the dense medium produced in Au+Au reactions.Comment: 391 authors, NN pages text, RevTeX4, figures, tables. Submitted to
Physical Review C. 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
A Detailed Study of High-pT Neutral Pion Suppression and Azimuthal Anisotropy in Au+Au Collisions at \sqrt{s_{NN}} = 200 GeV
Measurements of neutral pion production at midrapidity in sqrt(s_NN) = 200
GeV Au+Au collisions as a function of transverse momentum, p_T, collision
centrality, and angle with respect to reaction plane are presented. The data
represent the final pi^0 results from the PHENIX experiment for the first RHIC
Au+Au run at design center-of-mass-energy. They include additional data
obtained using the PHENIX Level-2 trigger with more than a factor of three
increase in statistics over previously published results for p_T > 6 GeV/c. We
evaluate the suppression in the yield of high-p_T pi^0's relative to point-like
scaling expectations using the nuclear modification factor R_AA. We present the
p_T dependence of R_AA for nine bins in collision centrality. We separately
integrate R_AA over larger p_T bins to show more precisely the centrality
dependence of the high-p_T suppression. We then evaluate the dependence of the
high-p_T suppression on the emission angle \Delta\phi of the pions with respect
to event reaction plane for 7 bins in collision centrality. We show that the
yields of high-p_T pi^0's vary strongly with \Delta\phi, consistent with prior
measurements. We show that this variation persists in the most peripheral bin
accessible in this analysis. For the peripheral bins we observe no suppression
for neutral pions produced aligned with the reaction plane while the yield of
pi^0's produced perpendicular to the reaction plane is suppressed by more than
a factor of 2. We analyze the combined centrality and \Delta\phi dependence of
the pi^0 suppression in different p_T bins using different possible
descriptions of parton energy loss dependence on jet path-length averages to
determine whether a single geometric picture can explain the observed
suppression pattern.Comment: 330 authors, pages text, RevTeX4, figures, tables. Submitted to
Physical Review C. 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
Transverse-energy distributions at midrapidity in , Au, and AuAu collisions at --200~GeV and implications for particle-production models
Measurements of the midrapidity transverse energy distribution, d\Et/d\eta,
are presented for , Au, and AuAu collisions at
GeV and additionally for AuAu collisions at
and 130 GeV. The d\Et/d\eta distributions are first
compared with the number of nucleon participants , number of
binary collisions , and number of constituent-quark participants
calculated from a Glauber model based on the nuclear geometry. For
AuAu, \mean{d\Et/d\eta}/N_{\rm part} increases with , while
\mean{d\Et/d\eta}/N_{qp} is approximately constant for all three energies.
This indicates that the two component ansatz, , which has been used to represent
distributions, is simply a proxy for , and that the term
does not represent a hard-scattering component in distributions. The
distributions of AuAu and Au are then calculated from
the measured distribution using two models that both reproduce
the AuAu data. However, while the number-of-constituent-quark-participant
model agrees well with the Au data, the additive-quark model does not.Comment: 391 authors, 24 pages, 19 figures, and 15 Tables. Submitted to Phys.
Rev. C. Plain text data tables for the points plotted in figures for this and
previous PHENIX publications are publicly available at
http://www.phenix.bnl.gov/papers.htm
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