17,224,972 research outputs found
Inclusive omega photoproduction off nuclei
We investigate inclusive omega photoproduction off complex nuclei,
concentrating on the feasibility to examine a possible in-medium change of the
omega meson properties by observing the pi^0 gamma invariant mass spectrum. The
simulations are performed by means of a BUU transport model including a full
coupled-channel treatment of the final state interactions. In-medium changes of
the omega spectral density are found to yield a moderate modification of the
observables as compared to the situation in free space. Also the effects of a
momentum dependence of the strong omega potential are discussed.Comment: 19 pages, 12 figures, minor corrections, accepted for publication in
EPJ
Two-pion Bose-Einstein correlations in central Pb-Pb collisions at = 2.76 TeV
The first measurement of two-pion Bose-Einstein correlations in central Pb-Pb
collisions at TeV at the Large Hadron Collider is
presented. We observe a growing trend with energy now not only for the
longitudinal and the outward but also for the sideward pion source radius. The
pion homogeneity volume and the decoupling time are significantly larger than
those measured at RHIC.Comment: 17 pages, 5 captioned figures, 1 table, authors from page 12,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/388
Analysis of the Neutralino System in Three--Body Leptonic Decays of Neutralinos
Neutralinos in supersymmetric theories, the spin--1/2
Majorana--type superpartners of the U(1) and SU(2) neutral electroweak gauge
bosons and SU(2) neutral Higgs bosons, are expected to be among light
supersymmetric particles so that they can be produced copiouslyvia direct pair
production and/or from cascade decays of other sparticles such as sleptons at
the planned Large Hadron Collider and the prospective International Linear
Collider. Considering the prospects of having both highly polarized neutralinos
and possibility of reconstructing their decay rest frames, we provide a
systematic investigation of the three--body leptonic decays of the neutralinos
in the minimal supersymmetric standard model and demonstrate alternative ways
for probing the Majorana nature of the neutralinos and CP violation in the
neutralino system.Comment: Version to appear in Eur.Phys.J.
Determination of MSSM Parameters from LHC and ILC Observables in a Global Fit
We present the results of a realistic global fit of the Lagrangian parameters
of the Minimal Supersymmetric Standard Model assuming universality for the
first and second generation and real parameters. No assumptions on the SUSY
breaking mechanism are made. The fit is performed using the precision of future
mass measurements of superpartners at the LHC and mass and polarized
topological cross-section measurements at the ILC. Higher order radiative
corrections are accounted for whereever possible to date. Results are obtained
for a modified SPS1a MSSM benchmark scenario but they were checked not to
depend critically on this assumption. Exploiting a simulated annealing
algorithm, a stable result is obtained without any a priori assumptions on the
values of the fit parameters. Most of the Lagrangian parameters can be
extracted at the percent level or better if theoretical uncertainties are
neglected. Neither LHC nor ILC measurements alone will be sufficient to obtain
a stable result. The effects of theoretical uncertainties arising from unknown
higher-order corrections and parametric uncertainties are examined
qualitatively. They appear to be relevant and the result motivates further
precision calculations. The obtained parameters at the electroweak scale are
used for a fit of the parameters at high energy scales within the bottom-up
approach. In this way regularities at these scales are explored and the
underlying model can be determined with hardly any theoretical bias. Fits of
high-scale parameters to combined LHC+ILC measurements within the mSUGRA
framework reveal that even tiny distortions in the low-energy mass spectrum
already lead to inacceptable chi^2 values. This does not hold for ``LHC only''
inputs.Comment: 25 pages, 5 figure
Reconclining phi radiative decays with other data for a0(980), fo(980), pi-pi -> KK and pi-pi -> eta-eta
Data for phi -> gamma (eta-pizero) are analysed using the KK loop model and
compared with parameters of a0(980) derived from Crystal Barrel data. The
eta-pi mass spectrum agrees closely and the absolute normalisation lies just
within errors. However, BES parameters for fo(980) predict a normalisation for
phi -> gamma (pizero-pizero) at least a factor 2 lower than is observed. This
discrepancy may be eliminated by including constructive interference between
fo(980) and sigma. The magnitude required for sigma -> KK is consistent with
data on pi-pi -> KK. A dispersion relation analysis by Buttiker, Descotes-Genon
and Moussallam of pi-pi -> KK leads to a similar conclusion. Data on pi-pi ->
eta-eta also require decays of sigma to eta-eta. Four sets of pi-pi -> KK data
all require a small but definite fo(1370) signal.Comment: 21 pages, 11 figures, Small rearrangement of reference
Phenomenological Aspects of Heterotic Orbifold Models at One Loop
We provide a detailed study of the phenomenology of orbifold
compactifications of the heterotic string within the context of supergravity
effective theories. Our investigation focuses on those models where the soft
Lagrangian is dominated by loop contributions to the various soft supersymmetry
breaking parameters. Such models typically predict non-universal soft masses
and are thus significantly different from minimal supergravity and other
universal models. We consider the pattern of masses that are governed by these
soft terms and investigate the implications of certain indirect constraints on
supersymmetric models, such as flavor-changing neutral currents, the anomalous
magnetic moment of the muon and the density of thermal relic neutralinos. These
string-motivated models show novel behavior that interpolates between the
phenomenology of unified supergravity models and models dominated by the
superconformal anomaly.Comment: 47 pages, 14 figure
Suppression of charged particle production at large transverse momentum in central Pb-Pb collisions at TeV
Inclusive transverse momentum spectra of primary charged particles in Pb-Pb
collisions at = 2.76 TeV have been measured by the ALICE
Collaboration at the LHC. The data are presented for central and peripheral
collisions, corresponding to 0-5% and 70-80% of the hadronic Pb-Pb cross
section. The measured charged particle spectra in and GeV/ are compared to the expectation in pp collisions at the same
, scaled by the number of underlying nucleon-nucleon
collisions. The comparison is expressed in terms of the nuclear modification
factor . The result indicates only weak medium effects ( 0.7) in peripheral collisions. In central collisions,
reaches a minimum of about 0.14 at -7GeV/ and increases
significantly at larger . The measured suppression of high- particles is stronger than that observed at lower collision energies,
indicating that a very dense medium is formed in central Pb-Pb collisions at
the LHC.Comment: 15 pages, 5 captioned figures, 3 tables, authors from page 10,
published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/98
Sneutrino Production at e+e- Linear Colliders: Addendum to Slepton Production
Complementing the preceding study of charged scalar leptons, the sector of
the neutral scalar leptons, sneutrinos, is investigated in a high-precision
analysis for future e+e- linear colliders. The theoretical predictions for the
cross-sections are calculated at the thresholds for non-zero widths and in the
continuum including higher-order corrections at the one-loop level. Methods for
measuring the sneutrino masses and the electron-sneutrino-gaugino Yukawa
couplings are presented, addressing theoretical problems specific for the
sneutrino channels.Comment: 21 pp, Addendum to Eur.Phys.J. C34 (2004) 487-512 [hep-ph/0310182],
Version to appear in Eur.Phys.J.
Updated Post-WMAP Benchmarks for Supersymmetry
We update a previously-proposed set of supersymmetric benchmark scenarios,
taking into account the precise constraints on the cold dark matter density
obtained by combining WMAP and other cosmological data, as well as the LEP and
b -> s gamma constraints. We assume that R parity is conserved and work within
the constrained MSSM (CMSSM) with universal soft supersymmetry-breaking scalar
and gaugino masses m_0 and m_1/2. In most cases, the relic density calculated
for the previous benchmarks may be brought within the WMAP range by reducing
slightly m_0, but in two cases more substantial changes in m_0 and m_1/2 are
made. Since the WMAP constraint reduces the effective dimensionality of the
CMSSM parameter space, one may study phenomenology along `WMAP lines' in the
(m_1/2, m_0) plane that have acceptable amounts of dark matter. We discuss the
production, decays and detectability of sparticles along these lines, at the
LHC and at linear e+ e- colliders in the sub- and multi-TeV ranges, stressing
the complementarity of hadron and lepton colliders, and with particular
emphasis on the neutralino sector. Finally, we preview the accuracy with which
one might be able to predict the density of supersymmetric cold dark matter
using collider measurements.Comment: 43 pages LaTeX, 13 eps figure
A new analysis of scattering from Roy and Steiner type equations
With the aim of generating new constraints on the OZI suppressed couplings of
chiral perturbation theory a set of six equations of the Roy and Steiner type
for the - and -waves of the scattering amplitudes is derived. The
range of validity and the multiplicity of the solutions are discussed. Precise
numerical solutions are obtained in the range E\lapprox 1 GeV which make use
as input, for the first time, of the most accurate experimental data available
at GeV for both and amplitudes.
Our main result is the determination of a narrow allowed region for the two
S-wave scattering lengths. Present experimental data below 1 GeV are found to
be in generally poor agreement with our results. A set of threshold expansion
parameters, as well as sub-threshold parameters are computed. For the latter,
matching with the SU(3) chiral expansion at NLO is performed.Comment: 45 pages, 17 figures. v2: New title, minor correction
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