409 research outputs found
Higher Twist Contributions To R-Hadron Phenomenology In The Light Gluino Scenario
The open light gluino window allows non-trivial higher twist gluino
contributions to the proton wave function. Using a two-component model
originally developed for charm hadroproduction, higher twist intrinsic gluino
contributions to final state R-hadron formation are shown to enhance leading
twist production in the forward region. We calculate R-hadron
production at GeV in pp, pBe, and pCu interactions with
light gluino masses of 1.2, 1.5, 3.5, and 5.0 GeV.Comment: 22 pages, 10 figures, revte
Motion Sickness Lessons from the Southern Ocean
BACKGROUND:
The objectives were to assess the prevalence, severity, and medication taken, and to look for predictive factors, in order to better identify characteristics of passengers at risk of motion sickness during transport from Hobart in Tasmania to the French polar stations in Antarctica.
METHODS:
There were 239 passengers who were surveyed over 4 yr with 4 round trips per year using the Motion Sickness Susceptibility Questionnaire (MSSQ), Simulator Sickness Questionnaire (SSQ), state-trait anxiety test (STAI -Trait and STAI -State), and general parameters (age, gender, number of trips, jet-lag, direction of the trip), medication, calculation of the distance of each passenger’s cabin to the Centre of Gravity (CoG.).
RESULTS:
While the passengers had a low intrinsic sensitivity to motion sickness (MSSQ), 94% reported at least one SSQ symptom of motion sickness, and 38% vomited. Five associated factors were discovered: greater initial sensitivity (MSSQ), anticipation of being ill, younger age, higher level of anxiety at midtrip, and greater distance from the CoG. Of the passengers, there were 54% who took anti-motion sickness medication at different times of the trip, however, these
passengers experienced more nausea. This could be due to self-selection since they were more sensitive to motion
sickness.
CONCLUSION:
We identified three predictive factors of motion sickness (greater intrinsic susceptibility, younger age, and greater cabin distance from the CoG). For preventive purposes, two associated factors of MS (anticipation of being ill, MSSQ score) were determined to classify three groups of risk of MS to improve passenger care during the trip
Electronic structure and ferroelectricity in SrBi2Ta2O9
The electronic structure of SrBi2Ta2O9 is investigated from first-principles,
within the local density approximation, using the full-potential linearized
augmented plane wave (LAPW) method. The results show that, besides the large
Ta(5d)-O(2p) hybridization which is a common feature of the ferroelectric
perovskites, there is an important hybridization between bismuth and oxygen
states. The underlying static potential for the ferroelectric distortion and
the primary source for ferroelectricity is investigated by a lattice-dynamics
study using the Frozen Phonon approach.Comment: 17 pages, 7 figures. Phys. Rev. B, in pres
ON THE INTRINSIC CHARM COMPONENT OF THE NUCLEON
Using a meson cloud model we calculate the squared charm radius
of the nucleon . The ratio between this squared radius and the ordinary baryon
squared radius is identified with the probability of ``seeing'' the intrinsic
charm component of the nucleon. Our estimate is compatible with those used to
successfully describe the charm production phenomenology.Comment: 9 pages, 2 figures not included, avaiable from the author
Quark exchange model for charmonium dissociation in hot hadronic matter
A diagrammatic approach to quark exchange processes in meson-meson scattering
is applied to the case of inelastic reactions of the type
(Q\barQ)+(q\barq)\rightarrow (Q\barq) + (q\barQ), where and refer to
heavy and light quarks, respectively. This string-flip process is discussed as
a microscopic mechanism for charmonium dissociation (absorption) in hadronic
matter. The cross section for the reaction is
calculated using a potential model, which is fitted to the meson mass spectrum.
The temperature dependence of the relaxation time for the \J/Psi distribution
in a homogeneous thermal pion gas is obtained. The use of charmonium for the
diagnostics of the state of hot hadronic matter produced in ultrarelativistic
nucleus-nucleus collisions is discussed.Comment: 24 pages, 3 tables, 7 figure
A systematic study of J/psi suppression in cold nuclear matter
Based on a Glauber model, a statistical analysis of all mid-rapidity J/psi
hadroproduction and leptoproduction data on nuclear targets is carried out.
This allows us to determine the J/psi-nucleon inelastic cross section, whose
knowledge is crucial to interpret the J/psi suppression observed in heavy-ion
collisions, at SPS and at RHIC. The values of sigma are extracted from each
experiment. A clear tension between the different data sets is reported. The
global fit of all data gives sigma=3.4+/-0.2 mb, which is significantly smaller
than previous estimates. A similar value, sigma=3.5+/-0.2 mb, is obtained when
the nDS nuclear parton densities are included in the analysis, although we
emphasize that the present uncertainties on gluon (anti)shadowing do not allow
for a precise determination of sigma. Finally, no significant energy dependence
of the J/psi-N interaction is observed, unless strong nuclear modifications of
the parton densities are assumed.Comment: 25 pages, 5 figure
Soft-gluon effects in WW production at hadron colliders
We consider QCD radiative corrections to WW pair production in hadron
collisions. We perform a calculation that consistently combines next-to-leading
order predictions with soft-gluon resummation valid at small transverse momenta
ptWW of the WW pair. We present results for the ptWW distribution at the LHC up
to (almost) next-to-next-to-leading logarithmic accuracy, and study the effect
of resummation on the charged-lepton distributions. Soft-gluon effects are
typically mild, but they can be strongly enhanced when hard cuts are applied.
The relevant distributions are generally well described by the MC@NLO event
generator.Comment: 15 pages, 12 postscript figures. Error corrected in NLO plot for WW
transverse-mass distribution. Results unchange
Inclusive Heavy-Flavor Production from Nuclei
We describe a light-cone wave function formulation for hadroproduction of
heavy-flavors at high energies. At moderate values of heavy-flavor
production can be viewed as a diffractive excitation of heavy quark-antiquark
Fock states, present in the interacting gluon from the projectile. The approach
developed here is well suited to address coherence effects in heavy-quark
production from nuclei at small values of x_{t} \lsim 0.1\cdot A^{-1/3}.Comment: 14 pages with 3 figures. To appear in Z. Phys.
The leading particle effect from light quark fragmentation in charm hadroproduction
The asymmetry of and meson production in scattering
observed by the E791 experiment is a typical phenomenon known as the leading
particle effect in charm hadroproducton. We show that the phenomenon can be
explained by the effect of light quark fragmentation into charmed hadrons
(LQF). Meanwhile, the size of the LQF effect is estimated from data of the E791
experiment.
A comparison is made with the estimate of the LQF effect from prompt
like-sign dimuon rate in neutrino experiments. The influence of the LQF effect
on the measurement of nucleon strange distribution asymmetry from charged
current charm production processes is briefly discussed.Comment: 6 latex pages, 1 figure, to appear in EPJ
Cold Nuclear Matter Effects on Dijet Productions in Relativistic Heavy-ion Reactions at LHC
We investigate the cold nuclear matter(CNM) effects on dijet productions in
high-energy nuclear collisions at LHC with the next-to-leading order
perturbative QCD. The nuclear modifications for dijet angular distributions,
dijet invariant mass spectra, dijet transverse momentum spectra and dijet
momentum imbalance due to CNM effects are calculated by incorporating EPS, EKS,
HKN and DS param-etrization sets of parton distributions in nucleus . It is
found that dijet angular distributions and dijet momentum imbalance are
insensitive to the initial-state CNM effects and thus provide optimal tools to
study the final-state hot QGP effects such as jet quenching. On the other hand,
the invariant mass spectra and the transverse momentum spectra of dijet are
generally enhanced in a wide region of the invariant mass or transverse
momentum due to CNM effects with a feature opposite to the expected suppression
because of the final-state parton energy loss effect in the QGP. The difference
of EPS, EKS, HKN and DS parametrization sets of nuclear parton distribution
functions is appreciable for dijet invariant mass spectra and transverse
momentum spectra at p+Pb collisions, and becomes more pronounced for those at
Pb+Pb reactions.Comment: 10 pages, 11 figure
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