5,326 research outputs found
Effect of hard processes on momentum correlations in and collisions
The HBT radii extracted in p-pbar and pp collisions at SPS and Tevatron show
a clear correlation with the charged particle rapidity density. We propose to
explain the correlation using a simple model where the distance from the
initial hard parton-parton scattering to the hadronization point depends on the
energy of the partons emitted. Since the particle multiplicity is correlated
with the mean energy of the partons produced we can explain the experimental
observations without invoking scenarios that assume a thermal fireball. The
model has been applied with success to the existing experimental data both in
the magnitude and the intensity of the correlation. As well, the model has been
extended to pp collisions at the LHC energy of 14 TeV. The possibilities of a
better insight into the string spatial development using 3D HBT analysis is
discussed.Comment: 12 pages, 6 figure
Vacancy defects in epitaxial thin film CuGaSe2 and CuInSe2
Epitaxial thin film CuGaSe2 and CuInSe2 samples grown on GaAs substrates with varying [Cu]/[Ga,In] ratios were studied using positron annihilation Doppler-broadening spectroscopy and were compared to bulk crystals. We find both Cu monovacancies and Cu-Se divacancies in CuInSe2, whereas, in CuGaSe2, the only observed vacancy defect is the Cu-Se divacancy.Peer reviewe
Forward Neutron Production at the Fermilab Main Injector
We have measured cross sections for forward neutron production from a variety
of targets using proton beams from the Fermilab Main Injector. Measurements
were performed for proton beam momenta of 58 GeV/c, 84 GeV/c, and 120 GeV/c.
The cross section dependence on the atomic weight (A) of the targets was found
to vary as where is for a beam momentum of
58 GeV/c and 0.540.05 for 120 GeV/c. The cross sections show reasonable
agreement with FLUKA and DPMJET Monte Carlos. Comparisons have also been made
with the LAQGSM Monte Carlo.Comment: Accepted for publication in Physical Review D. This version
incorporates small changes suggested by referee and small corrections in the
neutron production cross sections predicted by FLUK
Study of Spin and Decay-Plane Correlations of W Bosons in the e+e- -> W+W- Process at LEP
Data collected at LEP at centre-of-mass energies \sqrt(s) = 189 - 209 GeV are
used to study correlations of the spin of W bosons using e+e- -> W+W- -> lnqq~
events. Spin correlations are favoured by data, and found to agree with the
Standard Model predictions. In addition, correlations between the W-boson decay
planes are studied in e+e- -> W+W- -> lnqq~ and e+e- -> W+W- -> qq~qq~ events.
Decay-plane correlations, consistent with zero and with the Standard Model
predictions, are measured
Search for Branons at LEP
We search, in the context of extra-dimension scenarios, for the possible
existence of brane fluctuations, called branons. Events with a single photon or
a single Z-boson and missing energy and momentum collected with the L3 detector
in e^+ e^- collisions at centre-of-mass energies sqrt{s}=189-209$ GeV are
analysed. No excess over the Standard Model expectations is found and a lower
limit at 95% confidence level of 103 GeV is derived for the mass of branons,
for a scenario with small brane tensions. Alternatively, under the assumption
of a light branon, brane tensions below 180 GeV are excluded
Ultrarelativistic sources in nonlinear electrodynamics
The fields of rapidly moving sources are studied within nonlinear
electrodynamics by boosting the fields of sources at rest. As a consequence of
the ultrarelativistic limit the delta-like electromagnetic shock waves are
found. The character of the field within the shock depends on the theory of
nonlinear electrodynamics considered. In particular, we obtain the field of an
ultrarelativistic charge in the Born-Infeld theory.Comment: 10 pages, 3 figure
Direct Observation of Longitudinally Polarised W Bosons
The three different helicity states of W bosons, produced in the reaction
e+e- -> W+W- -> l nu q q~ are studied using leptonic and hadronic W decays at
sqrt{s}=183GeV and 189GeV. The W polarisation is also measured as a function of
the scattering angle between the W- and the direction of the e- beam. The
analysis demonstrates that W bosons are produced with all three helicities, the
longitudinal and the two transverse states. Combining the results from the two
center-of-mass energies and with leptonic and hadronic W decays, the fraction
of longitudinally polarised W bosons is measured to be 0.261 +/- 0.051(stat.)
+/- 0.016(syst.) in agreement with the expectation from the Standard Model
Search for Charginos with a Small Mass Difference with the Lightest Supersymmetric Particle at \sqrt{s} = 189 GeV
A search for charginos nearly mass-degenerate with the lightest
supersymmetric particle is performed using the 176 pb^-1 of data collected at
189 GeV in 1998 with the L3 detector. Mass differences between the chargino and
the lightest supersymmetric particle below 4 GeV are considered. The presence
of a high transverse momentum photon is required to single out the signal from
the photon-photon interaction background. No evidence for charginos is found
and upper limits on the cross section for chargino pair production are set. For
the first time, in the case of heavy scalar leptons, chargino mass limits are
obtained for any \tilde{\chi}^{+-}_1 - \tilde{\chi}^0_1 mass difference
Measurement of the Cross Section for Open-Beauty Production in Photon-Photon Collisions at LEP
The cross section for open-beauty production in photon-photon collisions is
measured using the whole high-energy and high-luminosity data sample collected
by the L3 detector at LEP. This corresponds to 627/pb of integrated luminosity
for electron-positron centre-of-mass energies from 189GeV to 209GeV. Events
containing b quarks are identified through their semi-leptonic decay into
electrons or muons. The e+e- -> e+e-b b~X cross section is measured within our
fiducial volume and then extrapolated to the full phase space. These results
are found to be in significant excess with respect to Monte Carlo predictions
and next-to-leading order QCD calculations
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