3,713 research outputs found
A new mechanism for electron spin echo envelope modulation
Electron spin echo envelope modulation (ESEEM) has been observed for the
first time from a coupled hetero-spin pair of electron and nucleus in liquid
solution. Previously, modulation effects in spin echo experiments have only
been described in liquid solutions for a coupled pair of homonuclear spins in
NMR or a pair of resonant electron spins in EPR. We observe low-frequency ESEEM
(26 and 52 kHz) due to a new mechanism present for any electron spin with S>1/2
that is hyperfine coupled to a nuclear spin. In our case these are electron
spin (S=3/2) and nuclear spin (I=1) in the endohedral fullerene N@C60. The
modulation is shown to arise from second order effects in the isotropic
hyperfine coupling of an electron and 14N nucleus.Comment: 15 pages, 4 figure
Environmental effects on electron spin relaxation in N@C60
We examine environmental effects of surrounding nuclear spins on the electron
spin relaxation of the N@C60 molecule (which consists of a nitrogen atom at the
centre of a fullerene cage). Using dilute solutions of N@C60 in regular and
deuterated toluene, we observe and model the effect of translational diffusion
of nuclear spins of the solvent molecules on the N@C60 electron spin relaxation
times. We also study spin relaxation in frozen solutions of N@C60 in CS2, to
which small quantities of a glassing agent, S2Cl2 are added. At low
temperatures, spin relaxation is caused by spectral diffusion of surrounding
nuclear 35Cl and 37Cl spins in the S2Cl2, but nevertheless, at 20 K, T2 times
as long as 0.23 ms are observed.Comment: 7 pages, 6 figure
Construction and Expected Performance of the Hadron Blind Detector for the PHENIX Experiment at RHIC
A new Hadron Blind Detector (HBD) for electron identification in high density
hadron environment has been installed in the PHENIX detector at RHIC in the
fall of 2006. The HBD will identify low momentum electron-positron pairs to
reduce the combinatorial background in the mass spectrum, mainly
in the low-mass region below 1 GeV/c. The HBD is a windowless
proximity-focusing Cherenkov detector with a radiator length of 50 cm, a CsI
photocathode and three layers of Gas Electron Multipliers (GEM). The HBD uses
pure CF as a radiator and a detector gas. Construction details and the
expected performance of the detector are described.Comment: QM2006 proceedings, 4 pages 3 figure
Estimation of Collision Impact Parameter
We demonstrate that the nuclear collision geometry (i.e. impact parameter)
can be determined with 1.5 fm accuracy in an event-by-event analysis by
measuring the transverse energy flow in the pseudorapidity region with a minimal dependence on collision dynamics details at the LHC
energy scale. Using the HIJING model we have illustrated our calculation by a
simulation of events of nucleus-nucleus interactions at the c.m.s energy from 1
up to 5.5 TeV per nucleon and various type of nuclei.Comment: 6 pages, 3 figure
A Hadron Blind Detector for the PHENIX Experiment
A novel Hadron Blind Detector (HBD) has been developed for an upgrade of the
PHENIX experiment at RHIC. The HBD will allow a precise measurement of
electron-positron pairs from the decay of the light vector mesons and the
low-mass pair continuum in heavy-ion collisions. The detector consists of a 50
cm long radiator filled with pure CF4 and directly coupled in a windowless
configuration to a triple Gas Electron Multiplier (GEM) detector with a CsI
photocathode evaporated on the top face of the first GEM foil.Comment: 4 pages, 3 figures, Quark Matter 2005 conference proceeding
Modification of the rho meson detected by low-mass electron-positron pairs in central Pb-Au collisions at 158 A GeV/c
We present a measurement of pair production in central Pb-Au
collisions at 158 GeV/. As reported earlier, a significant excess of the
pair yield over the expectation from hadron decays is observed. The
improved mass resolution of the present data set, recorded with the upgraded
CERES experiment at the CERN-SPS, allows for a comparison of the data with
different theoretical approaches. The data clearly favor a substantial
in-medium broadening of the spectral function over a density-dependent
shift of the pole mass. The in-medium broadening model implies that
baryon induced interactions are the key mechanism to in-medium modifications of
the -meson in the hot fireball at SPS energy.Comment: Revised versio
Design, Construction, Operation and Performance of a Hadron Blind Detector for the PHENIX Experiment
A Hadron Blind Detector (HBD) has been developed, constructed and
successfully operated within the PHENIX detector at RHIC. The HBD is a
Cherenkov detector operated with pure CF4. It has a 50 cm long radiator
directly coupled in a window- less configuration to a readout element
consisting of a triple GEM stack, with a CsI photocathode evaporated on the top
surface of the top GEM and pad readout at the bottom of the stack. This paper
gives a comprehensive account of the construction, operation and in-beam
performance of the detector.Comment: 51 pages, 39 Figures, submitted to Nuclear Instruments and Method
Experimental investigation of high-energy photon splitting in atomic fields
The new data analysis of the experiment, where the photon splitting in the
atomic fields has been observed for the first time, is presented. This
experiment was performed at the tagged photon beam of the ROKK-1M facility at
the VEPP-4M collider. In the energy region of 120-450 MeV, the statistics of
photons incident on the BGO target was collected. About 400
candidates to the photon splitting events were reconstructed. Within the
attained experimental accuracy, the experimental results are consistent with
the cross section calculated exactly in an atomic field. The predictions
obtained in the Born approximation significantly differ from the experimental
results.Comment: 11 pages, 6 figures, LaTe
Event-by-event fluctuations at SPS
Results on event-by-event fluctuations of the mean transverse momentum and
net charge in Pb-Au collisions, measured by the CERES Collaboration at
CERN-SPS, are presented. We discuss the centrality and beam energy dependence
and compare our data to cascade calculations.Comment: 4 pages, 4 figures, proceedings to INPC2004 Goteborg, Swede
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