4,729 research outputs found
Electromagnetic radiation from nuclear collisions at RHIC energies
The hot and dense strongly interacting matter created in collisions of heavy
nuclei at RHIC energies is modeled with relativistic hydrodynamics, and the
spectra of real and virtual photons produced at mid-rapidity in these events
are calculated. Several different sources are considered, and their relative
importance is compared. Specifically, we include jet fragmentation, jet-plasma
interactions, the emission of radiation from the thermal medium and from
primordial hard collisions. Our calculations consistently take into account jet
energy loss, as evaluated in the AMY formalism. We obtain results for the
spectra, the nuclear modification factor (R_AA), and the azimuthal anisotropy
(v_2) that agree with the photon measurements performed by the PHENIX
collaboration at RHIC
Low Mass Dimuons Produced in Relativistic Nuclear Collisions
The NA60 experiment has measured low-mass muon pair production in In-In
collisions at 158 A GeV with unprecedented precision. We show that this data is
reproduced very well by a dynamical model with parameters scaled from fits to
measurements of hadronic transverse mass spectra and Hanbury-Brown and Twiss
correlations in Pb-Pb and Pb-Au collisions at the same energy. The data is
consistent with in-medium properties of and -mesons at finite
temperature and density as deduced from empirical forward-scattering
amplitudes. Inclusion of the vacuum decay of the -meson after freeze-out
is necessary for an understanding of the mass and transverse momentum spectrum
of dimuons with M \apprle 0.9 {\rm GeV}/c^2.Comment: 4 pages, 3 figures, updated hadronic analysi
High momentum lepton pairs from jet-plasma interactions
We discuss the emission of high momentum lepton pairs (p_T>4 GeV) with low
invariant masses (M << p_T) in central Au+Au collisions at RHIC
(\sqrt{s_{NN}}=200 GeV). The spectra of dileptons produced through interactions
of quark and antiquark jets with the quark-gluon plasma (QGP) have been
calculated. Annihilation and Compton scattering processes, as well as processes
benefitting from collinear enhancement, including Landau-Pomeranchuk-Migdal
(LPM) effects, are calculated and convolved with a one dimensional hydrodynamic
expansion. The jet-induced contributions are compared to thermal dilepton
emission and Drell-Yan processes, and are found to dominate around p_T=4 GeV.Comment: Parallel talk given at QM2006, Shanghai November 2006. 4 pages, 3
figure
Cytotoxic antibody in acute myeloblastic leukaemia during immunotherapy: lack of tumour specificity.
Cytotoxic antibodies to antigens specific for leukaemic myeloblasts have been sought in the serum of patients with acute myeloblastic leukaemia treated by immunotherapy with irradiated allogeneic myeloblasts and BCG. Assays of complement- and K-cell-mediated activity were used. Cytotoxicity to allogeneic myeloblasts was detected in both assays. When sera from 15 patients, taken at various times during immunotherapy, were systematically tested against a panel of 5 myeloblasts, the following patterns emerged: 1. No antibody was cytotoxic against all myeloblasts of the panel in either the K-cell or complement-dependent assay. However, all myeloblasts of the panel were lysed by a number of sera. 2. Cytotoxic antibody was detected as often against a panel of lymphocytes from healthy donors as against the panel of allogeneic myeloblasts. 3. Fresh and cryopreserved myeloblasts were equally susceptible to lysis in both assays. 4. Experiments failed to demonstrate any deterioration of cytotoxic antibody on storage. 5. The number of K-cell-revealed cytotoxic antisera increased with length of immunotherapy. This pattern was not apparent for antibodies revealed by complement. 6. No instance of cytotoxicity in either assay was seen when serum was tested against 12 autologous myeloblasts. It is considered that cytotoxic antibody detected with allogeneic myeloblasts is probably directed against HLA antigens common to immunizing and test target myeloblasts and target lymphocytes
Properties of the phi meson at high temperatures and densities
We calculate the spectral density of the phi meson in a hot bath of nucleons
and pions using a general formalism relating self-energy to the forward
scattering amplitude (FSA). In order to describe the low energy FSA, we use
experimental data along with a background term. For the high energy FSA, a
Regge parameterization is employed. We verify the resulting FSA using
dispersion techniques. We find that the position of the peak of the spectral
density is slightly shifted from its vacuum position and that its width is
considerably increased. The width of the spectral density at a temperature of
150 MeV and at normal nuclear density is more than 90 MeV.Comment: 4 pages, 5 figures, Poster presented at Quark Matter 200
Dilepton Production in Nucleon-Nucleon Reactions With and Without Hadronic Inelasticities
We calculate elementary proton-proton and neutron-proton bremsstrahlung and
their contribution to the invariant mass distribution. At 4.9 GeV, the
proton-proton contribution is larger than neutron-proton, but it is small
compared to recent data. We then make a first calculation of bremsstrahlung in
nucleon-nucleon reactions with multi-hadron final states. Again at 4.9 GeV, the
many-body bremsstrahlung is larger than simple nucleon-nucleon bremsstrahlung
by more than an order of magnitude in the low-mass region. When the
bremsstrahlung contributions are summed with Dalitz decay of the ,
radiative decay of the and from two-pion annihilation, the result
matches recent high statistics proton-proton data from the Dilepton
Spectrometer collaboration.Comment: 1+17 pages plus 11 PostScript figures uuencoded and appended,
McGill/93-9, TPI-MINN-93/18-
Radiative and Collisional Jet Energy Loss in the Quark-Gluon Plasma at RHIC
We calculate and compare bremsstrahlung and collisional energy loss of hard
partons traversing a quark-gluon plasma. Our treatment of both processes is
complete at leading order in the coupling and accounts for the probabilistic
nature of the jet energy loss. We find that the nuclear modification factor
for neutral production in heavy ion collisions is sensitive to
the inclusion of collisional and radiative energy loss contributions while the
averaged energy loss only slightly increases if collisional energy loss is
included for parent parton energies . These results are important for
the understanding of jet quenching in Au+Au collisions at at
RHIC. Comparison with data is performed applying the energy loss calculation to
a relativistic ideal (3+1)-dimensional hydrodynamic description of the
thermalized medium formed at RHIC.Comment: 4 pages, 3 figure
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