1,663 research outputs found
An Updated Historical Profile of the Higgs Boson
The Higgs boson was postulated in 1964, and phenomenological studies of its
possible production and decays started in the early 1970s, followed by studies
of its possible production in electron-positron, antiproton-proton and
proton-proton collisions, in particular. Until recently, the most sensitive
searches for the Higgs boson were at LEP between 1989 and 2000, which were
complemented by searches at the Fermilab Tevatron. Then the LHC experiments
ATLAS and CMS entered the hunt, announcing on July 4, 2012 the discovery of a
"Higgs-like" particle with a mass of about 125~GeV. This identification has
been supported by subsequent measurements of its spin, parity and coupling
properties. It was widely anticipated that the Higgs boson would be accompanied
by supersymmetry, although other options, like compositeness, were not
completely excluded. So far there are no signs any new physics, and the
measured properties of the Higgs boson are consistent with the predictions of
the minimal Standard Model. This article reviews some of the key historical
developments in Higgs physics over the past half-century.Comment: 22 pages, 5 figures, update of arXiv:1201.6045, to be published in
the volume "The Standard Theory of Particle Physics", edited by Luciano
Maiani and Gigi Roland
Event Structure at RHIC from p-p to Au-Au
Several correlation analysis techniques are applied to p-p and Au-Au
collisions at RHIC. Strong large-momentum-scale correlations are observed which
can be related to local charge and momentum conservation during hadronization
and to minijet (minimum-bias parton fragment) correlations.Comment: 6 pages, 6 figures, 20th Winter Workshop on Nuclear Dynamics,
Trelawny Beach, Jamaica, March 15-20, 200
Proton - Lambda correlations in Au-Au Collisions at GeV from the STAR experiment
The space-time evolution of the source of particles formed in the collision
of nuclei can be studied through particle correlations. The STAR experiment is
dedicated to study ultra-relativistic heavy ions collisions and allows to
measure non-identical strange particle correlations. The source size can be
extracted by studying , ,
and correlation functions. Strong interaction potential has
been studied for these systems using an analytical model. Final State
Interaction (FSI) parameters have been determined and has shown a significant
annihilation process present in and systems
not present in and .Comment: contribution to the 20th Winter Workshop on Nuclear Dynamic
Recent Results on Searches for Pentaquark States from STAR at RHIC
We present results on pentaquark searches from nuclear collisions at RHIC
with the STAR detector system. An intriguing peak has been observed in the
invariant mass distribution of from 18.6 Million
d+Au collision events at ~GeV. The peak centers at a
mass ~MeV/c and the FWHM MeV/c limited
by detector responses. The statistical significance of the peak is .
Such a state if confirmed is manifestly exotic and implies a family of isospin
one states. A weak signal of less statistical significance () has
been observed in 5.6M Au+Au collision events at 62.4 GeV. Searches in 10.7M
Au+Au collision events at 200 GeV yield no significant signal. The Au+Au
results neither confirm nor rule out the d+Au observation as a possible state.Comment: To appear in proceedings of International Conference on QCD and
Hadron Physics at Beijing, June 200
First Results from Photon Multiplicity Detector at RHIC
We present the first measurement of multiplicity and pseudorapidity
distributions of photons in the pseudorapidity region 2.3 < eta < 3.7 for
different centralities in Au + Au collisions at sqrt{s_NN} = 62.4 GeV. The
pseudorapidity distribution of photons, dominated by neutral pion decays, has
been compared to those of identified charged pions, photons, and inclusive
charged particles from heavy ion and nucleon-nucleon collisions at various
energies. Scaling of photon yield with number of participating nucleons and
limiting fragmentation scenario for inclusive photon production has been
studied.Comment: Talk given at 5th International Conference on Physics and
Astrophysics of Quark Gluon Plasma (February 8 - 12, 2005); 4 pages and 6
figure
Event by Event fluctuation in K/pi ratio at RHIC
We present the preliminary results from our analysis of event by event
fluctuation in K/pi ratio in Au+Au collision at \sqrt s_{NN} = 200 GeV and at
62.4 GeV using STAR detector at RHIC. Two different methods have been used to
extract the strength of dynamical fluctuation and the centrality dependence of
that. The results from the study of energy and centrality dependence of the
dynamical fluctuation are presented. From the excitation function it is seen
that at two RHIC energies the measure of dynamical fluctuation is constant with
values very close to that at 12.3 GeV at SPS. The dynamical fluctuation is
found to be positive and decreasing with increasing centrality at RHIC. The
results are compared with HIJING model calculation with jets. Results from
HIJING are found to be very close to data from central collisions whereas it
over predicts the data for peripheral events.Comment: 4 pages, 3 figures, for ICPAQGP - 2005 (Recalculated the errors shown
in Fig 2 and Table 1
Anisotropic flow at RHIC
We present the first measurement of directed flow () at the Relativistic
Heavy Ion Collider (RHIC). is found to be consistent with zero at
pseudorapidities from -1.2 to 1.2, then rises to the level of a couple
of percent over the range . The latter observation is similar
to that from NA49 if the SPS rapidities are shifted by the difference in beam
rapidity between RHIC and SPS. We studied the evolution of elliptic flow from
p+p collisions through d+Au collision, and onto Au+Au collisions. Measurements
of higher harmonics are presented and discussed.Comment: 6 pages, 3 figures. Proceeding for the 20th Winter Workshop on
Nuclear Dynamics, Jamaic
Baryonic Resonance Studies with STAR
Yields and spectra of are measured in , d+Au and Au+Au
collisions at GeV . The nuclear modification factors in
d+Au collisions are presented. The dependent medium effects are
investigated via the nuclear modification factors. The implications of these
results on various models are discussed.Comment: Strange Quark Matter 2006 Conference Talk Proceeding
Centrality Dependence of Azimuthal Anisotropy of Strange Hadrons in 200 GeV Au+Au Collisions
Measurements of azimuthal anisotropy for strange and multi-strange hadrons
are presented for the first time in their centrality dependence. The high
statistics results of v2(pT) allow for a more detailed comparison to
hydrodynamical model calculations. Number-of-constituent-quark scaling was
tested for different centrality classes separately. Higher order anisotropies
like v4(pT) are measured for multi-strange hadrons. While we observe agreement
between measured data and models a deeper understanding and refinement of the
models seem to be necessary in order to fully understand the details of the
data.Comment: 4 pages, 2 figures; Strange Quark Matter 2006 conference proceedings,
to appear in J. Phys.
Measurement of and Production in +Au collisions at = 200 GeV
The measurements of the transverse momentum spectra and the invariant mass
distributions of , resonances
in +Au collisions at = 200 GeV using the STAR Time
Projection Chamber (TPC) at RHIC are presented. The in-medium modification of
the and mass and width has been studied as a function of
transverse momentum (). The particle ratios , and the
average transverse momentum () as a function of different collision
centrality has been reported. The nuclear modification factors ( and
) of and are discussed.Comment: 5 pages, 9 figures, proceeding (poster) of the 18th International
Conference on Nucleus-Nucleus Collisions (QM2005), Aug.4-9, Budapest, Hungar
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