815 research outputs found
High-p_T Pion Production in Heavy-Ion Collisions at RHIC energies
Perturbative QCD results on pion production are presented in proton-proton,
proton-nucleus and nucleus-nucleus collisions from CERN SPS up to RHIC energy.
A K_{jet}(s, p_T, Q) factor obtained from jet production is applied to perform
next-to-leading order calculations. Using the intrinsic transverse momentum
(k_T) we determined transverse momentum spectra for pions in wide energy
region. We have investigated nuclear multiscattering and the Cronin effect at
RHIC energies.Comment: Talk given at XXXII. International Symposion on Multiparticle
Dynamics (ISMD'02) Alusha, Crimea, Ukraine, 7-13 September 2002. 4 pages in
Latex, 1 PS figur
Perturbative QCD Results on Pion Production in pp, pA and AA Collisions
We summarize new pQCD results on pion production in proton-proton (pp),
proton-nucleus (pA) and nucleus-nucleus (AA) collisions. Our calculation
introduces intrinsic parton transverse momentum (k_T) and is performed
effectively at next-to-leading order (NLO), applying a K factor extracted for
jet events. Two different factorization scales, Q=p_{T,jet}/2 and p_{T,jet} are
used. Experimental data in pA collisions imply a preference for the latter
choice at NLO level. We display our results at CERN SPS for AA collisions.Comment: Talk given at Budapest Workshop on Quark and Hadron Dynamics in
Relativistic Heavy Ion Collisions (BP 2002) Budapest, Hungary, 3-7 Mar 2002.
11 pages in Latex, 7 PS figure. Submitted to Heavy Ion Physic
Seeing many-body effects in single- and few-layer graphene: Observation of two-dimensional saddle-point excitons
Significant excitonic effects were observed in graphene by measuring its
optical conductivity in a broad spectral range including the two-dimensional
{\pi}-band saddle-point singularities in the electronic structure. The strong
electron-hole interactions manifest themselves in an asymmetric resonance
peaked at 4.62 eV, which is red-shifted by nearly 600 meV from the value
predicted by ab-initio GW calculations for the band-to-band transitions. The
observed excitonic resonance is explained within a phenomenological model as a
Fano interference of a strongly coupled excitonic state and a band continuum.
Our experiment also showed a weak dependence of the excitonic resonance in
few-layer graphene on layer thickness. This result reflects the effective
cancellation of the increasingly screened repulsive electron-electron (e-e) and
attractive electron-hole (e-h) interactions.Comment: 9 pages, 3 figures, In PR
Discovery of Jet Quenching at RHIC and the Opacity of the Produced Gluon Plasma
The predicted quenching of jets in A+A at RHIC energies has been discovered
by STAR and PHENIX in preliminary data reported at this conference. We apply
the GLV theory of QCD radiative energy loss to estimate the opacity,
L/\lambda_g, of the gluon plasma produced in Au+Au collisions at 130 AGeV. We
show that (in contrast to the factor of two Cronin enhancement of \pi^0 found
at the SPS by WA98) the factor of 5-8 suppression of p_T \sim 2-4 GeV \pi^0
reported by PHENIX can be accounted for with an effective static plasma opacity
L/\lambda_g \approx 3-4.Comment: Talk at the conference Quark Matter'2001, 4 pages in Latex, 4 EPS
figures, to appear in Nuclear Physics
High pT pion and kaon production in relativistic nuclear collisions
High-p(T) pion and kaon production is studied in relativistic
proton-proton, proton-nucleus, and nucleus-nucleus collisions in
a wide energy range. Cross sections are calculated based on
perturbative QCD, augmented by a phenomenological transverse-
momentum distribution of partons ("intrinsic k(T)"). An energy
dependent width of the transverse-momentum distribution is
extracted from pion and charged hadron production data in
proton-proton/proton-antiproton collisions. Effects of
multiscattering and shadowing in the strongly interacting medium
are taken into account. Enhancement of the transverse-momentum
width is introduced and parameterized to explain the Cronin
effect. In collisions between heavy nuclei, the model
overpredicts central pion production cross sections (more
significantly at higher energies), hinting at the presence of
jet quenching. Predictions are made for proton-nucleus and
nucleus-nucleus collisions at relativistic heavy ion collider
energies
Jets and produced particles in pp collisions from SPS to RHIC energies for nuclear applications
Higher-order pQCD corrections play an important role in the reproduction of
data at high transverse momenta in the energy range 20 GeV GeV. Recent calculations of photon and pion production in collisions
yield detailed information on the next-to-leading order contributions. However,
the application of these results in proton-nucleus and nucleus-nucleus
collisions is not straightforward. The study of nuclear effects requires a
simplified understanding of the output of these computations. Here we summarize
our analysis of recent calculations, aimed at handling the NLO results by
introducing process and energy-dependent factors.Comment: 4 pages with 5 eps figures include
Some estimates of Wang-Yau quasilocal energy
Given a spacelike 2-surface in a spacetime and a constant future
timelike unit vector in , we derive upper and lower estimates
of Wang-Yau quasilocal energy for a given isometric
embedding of into a flat 3-slice in . The quantity itself depends on the choice of , however the infimum of
over does not. In particular, when lies
in a time symmetric 3-slice in and has nonnegative Brown-York quasilocal
mass \mby(\Sigma), our estimates show that equals \mby (\Sigma). We also study the spatial limit of , where is a large coordinate sphere in a
fixed end of an asymptotically flat initial data set and is
an isometric embeddings of into .
We show that if has future timelike ADM energy-momentum, then
equals the ADM mass
of .Comment: 17 page
Objective measurement for surgical skill evaluation
The purpose of this study was to identify measurable parameters that can be used to quantitatively assess psychomotor skills, specifically for surgical skills assessment. Sixteen participants were recruited from two groups: surgeon (N = 5) and non-surgeon (N = 11). Both groups underwent a psychomotor test using a custom developed âGreen Targetâ module which was designed using a virtual reality system. Six parameters were used to compare the psychomotor skills between the two groups. The results showed that surgeons outperformed the non-surgeons in five out of six parameters investigated and the difference was statistically significant. The average normalised comparison values for surgeons and non-surgeons for motion path accuracy, motion path precision, economy of movement, end-point accuracy and end-point precision were 0.13±0.12 and 0.17±0.12, 0.08±0.11 and 0.10±0.10, 3.76±1.76 and 4.08±2.24, 0.12±0.10 and 0.17±0.11, 0.04±0.10 and 0.07±s0.10 respectively, p < 0.05). These parameters can potentially be used to objectively assess the performance of surgical skill
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