2,520,626 research outputs found
Reweighting of the form factors in exclusive B --> X ell nu decays
A form factor reweighting technique has been elaborated to permit relatively
easy comparisons between different form factor models applied to exclusive B
--> X l nu decays. The software tool developped for this purpose is described.
It can be used with any event generator, three of which were used in this work:
ISGW2, PHSP and FLATQ2, a new powerful generator. The software tool allows an
easy and reliable implementation of any form factor model. The tool has been
fully validated with the ISGW2 form factor hypothesis. The results of our
present studies indicate that the combined use of the FLATQ2 generator and the
form factor reweighting tool should play a very important role in future
exclusive |Vub| measurements, with largely reduced errors.Comment: accepted for publication by EPJ
p/pi Ratio in Di-Hadron Correlations
Particle ratios are important observables used to constrain models of
particle production in heavy-ion collisions. In this work we report on a
measurement of the p/pi ratio in the transverse momentum range 2.0 <
p_{T,assoc} < 4.0 GeV/c, associated with a charged trigger particle of 5.0 <
p_{T,trig} < 10.0 GeV/c, in 0-10% central Pb--Pb collisions at
sqrt{s_{NN}}=2.76 TeV. The ratio is measured in the jet peak and in a region at
large Delta eta separation from the peak (bulk region). The presented results
are based on 14M minimum-bias Pb--Pb collisions, recorded by the ALICE
detector. It is observed that the p/pi ratio in the bulk region is compatible
with the p/pi ratio of an inclusive measurement, and is much larger than the
p/pi ratio in the jet peak. The p/pi ratio in the jet peak is compatible with a
PYTHIA reference, in which fragmentation in the vacuum is the dominant
mechanism of particle production
Towards e+e- --> 3 jets at NNLO by sector decomposition
A method based on sector decomposition has been developed to calculate the
double real radiation part of the process e+e- to 3 jets at
next-to-next-to-leading order. It is shown in an example that the numerical
cancellation of soft and collinear poles works well. The method is flexible to
include an arbitrary measurement function in the final Monte Carlo program,
such that it allows to obtain differential distributions for different kinds of
observables. This is demonstrated by showing 3-, 4- and 5-jet rates at order
alpha_s^3 for a subpart of the process.Comment: 14 pages, 4 figure
Microscopic Models of Heavy Ion Interactions
An introduction to dynamical microscopic models of hadronic and nuclear
interactions is presented. Special emphasis is put in the relation between
multiparticle production and total cross-section contributions. In heavy ion
collisions, some observables, considered as signals of the production of a
Quark Gluon Plasma (QGP), are studied. It is shown that they can only be
described if final state interactions are introduced. It is argued that the
cross-sections required are too small to drive the system to thermal
equilibrium within the duration time of the final state interaction.Comment: 39 pages, 18 figures. Lectures at VIII Hispalensis International
Summer School, Seville (Spain), to be published by Springer Verla
The Heavy Hadron Spectrum
I discuss the spectrum of hadrons containing heavy quarks ( or ), and
how well the experimental results are matched by theoretical ideas. Useful
insights come from potential models and applications of Heavy Quark Symmetry
and these can be compared with new numerical results from the ab initio methods
of Lattice QCD.Comment: 64 pages, Latex, lectures at Schladming Winter School 199
QCD explanation of oscillating hadron and jet multiplicity moments
Ratios of multiplicity moments, H_q (cumulant over factorial moments
K_q/F_q), have been observed to show an oscillatory behaviour with respect to
order, q. Recent studies of e^+e^- annihilations at LEP have shown, moreover,
that the amplitude and oscillation length vary strongly with the jet resolution
parameter y_{cut}. We study the predictions of the perturbative QCD parton
cascade assuming low non-perturbative cut-off (Q_0\sim \Lambda_{QCD}\sim few
100 MeV) and derive the expectations as a function of the cms energy and jet
resolution from threshold to very high energies. We consider numerical
solutions of the evolution equations of gluodynamics in Double Logarithmic and
Modified Leading Logarithmic Approximations (DLA,MLLA), as well as results from
a parton MC with readjusted parameters. The main characteristics are obtained
in MLLA, while a more numerically accurate description is obtained by the MC
model. A unified description of correlations between hadrons and correlations
between jets emerges, in particular for the transition region of small y_{cut}.Comment: 31 pages, 14 figure
ATLAS silicon module assembly and qualification tests at IFIC Valencia
ATLAS experiment, designed to probe the interactions of particles emerging
out of proton proton collisions at energies of up to 14 TeV, will assume
operation at the Large Hadron Collider (LHC) at CERN in 2007. This paper
discusses the assembly and the quality control tests of forward detector
modules for the ATLAS silicon microstrip detector assembled at the Instituto de
Fisica Corpuscular (IFIC) in Valencia. The construction and testing procedures
are outlined and the laboratory equipment is briefly described. Emphasis is
given on the module quality achieved in terms of mechanical and electrical
stability.Comment: 23 pages, 38 EPS figures, uses JINST LaTeX clas
Updates to the Dualized Standard Model on Fermion Masses and Mixings
The Dualized Standard Model has scored a number of successes in explaining
the fermion mass hierarchy and mixing pattern. This note contains updates to
those results including (a) an improved treatment of neutrino oscillation free
from previous assumptions on neutrino masses, and hence admitting now the
preferred LMA solution to solar neutrinos, (b) an understanding of the
limitation of the 1-loop calculation so far performed, thus explaining the two
previous discrepancies with data, and (c) an analytic derivation and
confirmation of the numerical results previously obtained.Comment: 15 pages, Latex, 1 figure using ep
Probing the QCD equation of state with thermal photons in nucleus-nucleus collisions at RHIC
Thermal photon production at mid-rapidity in Au+Au reactions at
= 200 GeV is studied in the framework of a 2D+1 hydrodynamical
model that describes efficiently the bulk identified hadron spectra at RHIC.
The combined thermal plus NLO pQCD photon spectrum is in good agreement with
the yields measured by the PHENIX experiment for all Au+Au centralities. Within
our model, we demonstrate that the correlation of the thermal photon slopes
with the charged hadron multiplicity in each centrality bin provides direct
empirical information on the underlying degrees of freedom and on the equation
of state, , of the strongly interacting matter.Comment: Version to appear in EPJ-C (extended discussion and refs. and a few
corrections
Mixing of Pentaquark and Molecular States
There are experimental evidences for the existence of narrow states
and with the same quantum numbers of and
pentaquarks and also and molecular states.
Their masses deviate from many theoretical estimates of the pure pentaquark and
molecular states. In this work we study the possibility that the observed
and are mixtures of pure pentaquark and molecular states.
The mixing parameters are in general related to non-perturbative QCD which are
not calculable at present. We determine them by fitting data from known states
and then generalize the mechanism to to predict its mass and width.
The mixing mechanism can also naturally explain the narrow width for
and through destructive interferences, even if the pure pentaquark
and molecular states have much larger decay widths. We also briefly discuss the
properties of the partner eigenstates of and and the
possibility of experimentally observe them. Moreover, probable consequences of
multi-state mixing are also addressed.Comment: 23 pages, 4 figures. Published version in EPJ
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