1,747 research outputs found
Inelastic Photoproduction off Nuclei: Gluon Enhancement or Double Color Exchange?
The nuclear enhancement observed in inelastic photoproduction of
should not be interpreted as evidence for an increased gluon density in nuclei.
The nuclear suppression of the production rate due to initial and final state
interactions is calculated and a novel two-step color exchange process is
proposed, which is able to explain the data.Comment: Latex file, 23 pages including 5 Postscript figure
Are B to PI K CP-asymmetries quantized ?
Search for patterns in the numerous B-decay modes now available is necessary
in order to test the Cabibbo-Kobayashi-Maskawa theory of CP-violation. In
particular, the well-structured pattern of B to PI K branching ratios may lead
to a quantized spectrum for direct CP-asymmetries, providing in this way a
rather unique opportunity to discriminate between strong final state
interaction models.Comment: Latex, 12 pages, 3 ps figures. Few comments added, final version to
appear in Eur.Phys.J.
Leptoproduction of J/psi
We study leptoproduction of at large within the
nonrelativistic QCD (NRQCD) factorization formalism. The cross section is
dominated by color-octet terms that are of order . The color-singlet
term, which is of order , is shown to be a small contribution to
the total cross section. We also calculate the tree diagrams for color-octet
production at order in a region of phase space where there is no
leading color-octet contribution. We find that in this regime the color-singlet
contribution dominates. We argue that non-perturbative corrections arising from
diffractive leptoproduction, higher twist effects, and higher order terms in
the NRQCD velocity expansion should be suppressed as is increased.
Therefore, the color-octet matrix elements can be reliably extracted from this process.
Finally, we point out that an experimental measurement of the polarization of
leptoproduced will provide an excellent test of the NRQCD
factorization formalism.Comment: 33 pages latex. 10 figures. Uses revtex, epsf, and rotate macros.
This paper is also available via the UW phenomenology archives at
http://phenom.physics.wisc.edu/pub/preprints
Form Factors from QCD Light-Cone Sum Rules
We derive new QCD sum rules for and form factors. The
underlying correlation functions are expanded near the light-cone in terms of
-meson distribution amplitudes defined in HQET, whereas the -quark mass
is kept finite. The leading-order contributions of two- and three-particle
distribution amplitudes are taken into account. From the resulting light-cone
sum rules we calculate all B\to \Dst form factors in the region of small
momentum transfer (maximal recoil). In the infinite heavy-quark mass limit the
sum rules reduce to a single expression for the Isgur-Wise function. We compare
our predictions with the form factors extracted from experimental B\to \Dst l
\nu_l decay rates fitted to dispersive parameterizations.Comment: 20 pages, 6 figures; one reference, one figure and several comments
added; version to appear in European Physical Journal
Examining leptogenesis with lepton flavor violation and the dark matter abundance
Within a supersymmetric (SUSY) type-I seesaw framework with flavor-blind
universal boundary conditions, we study the consequences of requiring that the
observed baryon asymmetry of the Universe be explained by either thermal or
non-thermal leptogenesis. In the former case, we find that the parameter space
is very constrained. In the bulk and stop-coannihilation regions of mSUGRA
parameter space (that are consistent with the measured dark matter abundance),
lepton flavor-violating (LFV) processes are accessible at MEG and future
experiments. However, the very high reheat temperature of the Universe needed
after inflation (of about 10^{12} GeV) leads to a severe gravitino problem,
which disfavors either thermal leptogenesis or neutralino dark matter.
Non-thermal leptogenesis in the preheating phase from SUSY flat directions
relaxes the gravitino problem by lowering the required reheat temperature. The
baryon asymmetry can then be explained while preserving neutralino dark matter,
and for the bulk or stop-coannihilation regions LFV processes should be
observed in current or future experiments.Comment: 20 pages, 5 figures, 1 tabl
A Study of Time-Dependent CP-Violating Asymmetries and Flavor Oscillations in Neutral B Decays at the Upsilon(4S)
We present a measurement of time-dependent CP-violating asymmetries in
neutral B meson decays collected with the BABAR detector at the PEP-II
asymmetric-energy B Factory at the Stanford Linear Accelerator Center. The data
sample consists of 29.7 recorded at the
resonance and 3.9 off-resonance. One of the neutral B mesons,
which are produced in pairs at the , is fully reconstructed in
the CP decay modes , , , () and , or in flavor-eigenstate
modes involving and (). The flavor of the other neutral B meson is tagged at the time of
its decay, mainly with the charge of identified leptons and kaons. The proper
time elapsed between the decays is determined by measuring the distance between
the decay vertices. A maximum-likelihood fit to this flavor eigenstate sample
finds . The value of the asymmetry amplitude is determined from
a simultaneous maximum-likelihood fit to the time-difference distribution of
the flavor-eigenstate sample and about 642 tagged decays in the
CP-eigenstate modes. We find , demonstrating that CP violation exists in the neutral B meson
system. (abridged)Comment: 58 pages, 35 figures, submitted to Physical Review
Atmospheric Muon Flux at Sea Level, Underground, and Underwater
The vertical sea-level muon spectrum at energies above 1 GeV and the
underground/underwater muon intensities at depths up to 18 km w.e. are
calculated. The results are particularly collated with a great body of the
ground-level, underground, and underwater muon data. In the hadron-cascade
calculations, the growth with energy of inelastic cross sections and pion,
kaon, and nucleon generation in pion-nucleus collisions are taken into account.
For evaluating the prompt muon contribution to the muon flux, we apply two
phenomenological approaches to the charm production problem: the recombination
quark-parton model and the quark-gluon string model. To solve the muon
transport equation at large depths of homogeneous medium, a semi-analytical
method is used. The simple fitting formulas describing our numerical results
are given. Our analysis shows that, at depths up to 6-7 km w. e., essentially
all underground data on the muon intensity correlate with each other and with
predicted depth-intensity relation for conventional muons to within 10%.
However, the high-energy sea-level data as well as the data at large depths are
contradictory and cannot be quantitatively decribed by a single nuclear-cascade
model.Comment: 47 pages, REVTeX, 15 EPS figures included; recent experimental data
and references added, typos correcte
Memristive and neuromorphic behavior in a Li x CoO 2 nanobattery
International audienceThe phenomenon of resistive switching (RS), which was initially linked to non-volatile resistive memory applications, has recently also been associated with the concept of memristors, whose adjustable multilevel resistance characteristics open up unforeseen perspectives in cognitive computing. Herein, we demonstrate that the resistance states of Li(x)CoO2 thin film-based metal-insulator-metal (MIM) solid-state cells can be tuned by sequential programming voltage pulses, and that these resistance states are dramatically dependent on the pulses input rate, hence emulating biological synapse plasticity. In addition, we identify the underlying electrochemical processes of RS in our MIM cells, which also reveal a nanobattery-like behavior, leading to the generation of electrical signals that bring an unprecedented new dimension to the connection between memristors and neuromorphic systems. Therefore, these LixCoO2-based MIM devices allow for a combination of possibilities, offering new perspectives of usage in nanoelectronics and bio-inspired neuromorphic circuits
A Non-Targeted Approach Unravels the Volatile Network in Peach Fruit
Volatile compounds represent an important part of the plant metabolome and are of particular agronomic and biological interest due to their contribution to fruit aroma and flavor and therefore to fruit quality. By using a non-targeted approach based on HS-SPME-GC-MS, the volatile-compound complement of peach fruit was described. A total of 110 volatile compounds (including alcohols, ketones, aldehydes, esters, lactones, carboxylic acids, phenolics and terpenoids) were identified and quantified in peach fruit samples from different genetic backgrounds, locations, maturity stages and physiological responses. By using a combination of hierarchical cluster analysis and metabolomic correlation network analysis we found that previously known peach fruit volatiles are clustered according to their chemical nature or known biosynthetic pathways. Moreover, novel volatiles that had not yet been described in peach were identified and assigned to co-regulated groups. In addition, our analyses showed that most of the co-regulated groups showed good intergroup correlations that are therefore consistent with the existence of a higher level of regulation orchestrating volatile production under different conditions and/or developmental stages. In addition, this volatile network of interactions provides the ground information for future biochemical studies as well as a useful route map for breeding or biotechnological purposes
Measurement of the Branching Fraction for B- --> D0 K*-
We present a measurement of the branching fraction for the decay B- --> D0
K*- using a sample of approximately 86 million BBbar pairs collected by the
BaBar detector from e+e- collisions near the Y(4S) resonance. The D0 is
detected through its decays to K- pi+, K- pi+ pi0 and K- pi+ pi- pi+, and the
K*- through its decay to K0S pi-. We measure the branching fraction to be
B.F.(B- --> D0 K*-)= (6.3 +/- 0.7(stat.) +/- 0.5(syst.)) x 10^{-4}.Comment: 7 pages, 1 postscript figure, submitted to Phys. Rev. D (Rapid
Communications
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