2,263 research outputs found
Flow with PMD: Past and Future
Measurements of azimuthal distribution of inclusive photons using the fine
granularity preshower photon multiplicity detector (PMD) at CERN SPS are used
to obtain anisotropy in the azimuthal distributions. These results are used to
estimate the anisotropy in the neutral pion distributions. The results are
compared with results of charged particle data, both for first order and second
order anisotropy. Assuming the same anisotropy for charged and neutral pions,
the anisotropy in photons is estimated and compared with the measured
anisotropy. The effect of neutral pion decay on the correlation between the
first order and the second order event plane is also discussed. Data from PMD
can also be used to estimate the reaction plane for studying any anisotropy in
particle emission characteristics in the ALICE experiment at the Large Hadron
Collider. In particular, we show that using the event plane from the PMD, it
will be possible to measure the anisotropy in Jpsi absorption (if any) in the
ALICE experiment.Comment: Invited talk in the Fourth International Conference on the Physics
and Astrophysics of Quark Gluon Plasma, 26-30 Nov.2001, Jaipur, Indi
Effect of Finite Granularity of Detectors on Anisotropy Coefficients
The coefficients that describe the anisotropy in the azimuthal distribution
of particles are lower when the particles are recorded in a detector with
finite granularity and measures only hits. This arises due to loss of
information because of multiple hits in any channel. The magnitude of this loss
of signal depends both on the occupancy and on the value of the coefficient.
These correction factors are obtained for analysis methods differing in detail,
and are found to be different.Comment: 11 pages including 2 figure
Photon Multiplicity Measurements : From SPS to RHIC and LHC
Results from the photon multiplicity measurements using a fine granularity
preshower photon multiplicity detector (PMD) at CERN SPS are discussed. These
include study of pseudo-rapidity distributions of photons, scaling of photon
multiplicity with number of participating nucleons, centrality dependence of
mean transverse momentum of photons, event-by-event fluctuations in photon
multiplicity and localised charged-neutral fluctuations. Basic features of the
PMD to be used in STAR experiment at RHIC and in ALICE experiment at LHC are
also discussed.Comment: 12 pages, Invited talk at the 4th International Conference on the
Physcis and Astrophysics of the Quark-Gluon-Plasma, November 2001, Jaipur,
India, to appear in Praman
Interferometry of Direct Photons in Central 280Pb+208Pb Collisions at 158A GeV
Two-particle correlations of direct photons were measured in central
208Pb+208Pb collisions at 158 AGeV. The invariant interferometric radii were
extracted for 100<K_T<300 MeV/c and compared to radii extracted from charged
pion correlations. The yield of soft direct photons, K_T<300 MeV/c, was
extracted from the correlation strength and compared to theoretical
calculations.Comment: 5 pages, 4 figure
Pion Freeze-Out Time in Pb+Pb Collisions at 158 A GeV/c Studied via pi-/pi+ and K-/K+ Ratios
The effect of the final state Coulomb interaction on particles produced in
Pb+Pb collisions at 158 A GeV/c has been investigated in the WA98 experiment
through the study of the pi-/pi+ and K-/K+ ratios measured as a function of
transverse mass. While the ratio for kaons shows no significant transverse mass
dependence, the pi-/pi+ ratio is enhanced at small transverse mass values with
an enhancement that increases with centrality. A silicon pad detector located
near the target is used to estimate the contribution of hyperon decays to the
pi-/pi+ ratio. The comparison of results with predictions of the RQMD model in
which the Coulomb interaction has been incorporated allows to place constraints
on the time of the pion freeze-out.Comment: 9 pages, 12 figure
Improving throughput and fairness by improved channel assignment using topology control based on power control for multi-radio multi-channel wireless mesh networks
Flow analysis from multiparticle azimuthal correlations
We present a new method for analyzing directed and elliptic flow in heavy ion
collisions. Unlike standard methods, it separates the contribution of flow to
azimuthal correlations from contributions due to other effects. The separation
relies on a cumulant expansion of multiparticle azimuthal correlations, and
includes corrections for detector inefficiencies. This new method allows the
measurement of the flow of identified particles in narrow phase-space regions,
and can be used in every regime, from intermediate to ultrarelativistic
energies.Comment: 31 pages, revtex. Published version (references added
Particle density fluctuations
Event-by-event fluctuations in the multiplicities of charged particles and
photons at SPS energies are discussed. Fluctuations are studied by controlling
the centrality of the reaction and rapidity acceptance of the detectors.
Results are also presented on the event-by-event study of correlations between
the multiplicity of charged particles and photons to search for DCC-like
signals.Comment: Talk presented at Quark Matter 2002, Nantes, Franc
Suppression of High-p_T Neutral Pion Production in Central Pb+Pb Collisions at sqrt{s_NN} = 17.3 GeV Relative to p+C and p+Pb Collisions
Neutral pion transverse momentum spectra were measured in p+C and p+Pb
collisions at sqrt{s_NN} = 17.4 GeV at mid-rapidity 2.3 < eta_lab < 3.0 over
the range 0.7< p_T < 3.5 GeV/c. The spectra are compared to pi0 spectra
measured in Pb+Pb collisions at sqrt{s_NN} = 17.3 GeV in the same experiment.
For a wide range of Pb+Pb centralities (N_part < 300) the yield of pi0's with
p_T > 2 GeV/c is larger than or consistent with the p+C or p+Pb yields scaled
with the number of nucleon-nucleon collisions (N_coll), while for central Pb+Pb
collisions with N_part > 350 the pi0 yield is suppressed.Comment: 5 pages, 4 figure
Azimuthal Anisotropy of Photon and Charged Particle Emission in Pb+Pb Collisions at 158 A GeV/c
The azimuthal distributions of photons and charged particles with respect to
the event plane are investigated as a function of centrality in Pb + Pb
collisions at 158 A GeV/c in the WA98 experiment at the CERN SPS. The
anisotropy of the azimuthal distributions is characterized using a Fourier
analysis. For both the photon and charged particle distributions the first two
Fourier coefficients are observed to decrease with increasing centrality. The
observed anisotropies of the photon distributions compare well with the
expectations from the charged particle measurements for all centralities.Comment: 8 pages and 6 figures. The manuscript has undergone a major revision.
The unwanted correlations were enhanced in the random subdivision method used
in the earlier version. The present version uses the more established method
of division into subevents separated in rapidity to minimise short range
correlations. The observed results for charged particles are in agreement
with results from the other experiments. The observed anisotropy in photons
is explained using flow results of pions and the correlations arising due to
the decay of the neutral pion
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