1,896 research outputs found
A Radiation Imaging Detector Made by Postprocessing a Standard CMOS Chip
An unpackaged microchip is used as the sensing element in a miniaturized gaseous proportional chamber. Thisletter reports on the fabrication and performance of a complete radiation imaging detector based on this principle. Our fabrication schemes are based on wafer-scale and chip-scale postprocessing.\ud
Compared to hybrid-assembled gaseous detectors, our microsystem shows superior alignment precision and energy resolution, and offers the capability to unambiguously reconstruct 3-D radiation tracks on the spot.\u
Charge asymmetry ratio as a probe of quark flavour couplings of resonant particles at the LHC
We show how a precise knowledge of parton distribution functions, in
particular those of the u and d quarks, can be used to constrain a certain
class of New Physics models in which new heavy charged resonances couple to
quarks and leptons. We illustrate the method by considering a left-right
symmetric model with a W' from a SU(2)_R gauge sector produced in
quark-antiquark annihilation and decaying into a charged lepton and a heavy
Majorana neutrino. We discuss a number of quark and lepton mixing scenarios,
and simulate both signals and backgrounds in order to determine the size of the
expected charge asymmetry. We show that various quark-W' mixing scenarios can
indeed be constrained by charge asymmetry measurements at the LHC, particularly
at 14 TeV centre of mass energy.Comment: 14 pages, 3 figure
PDF and scale uncertainties of various DY distributions in ADD and RS models at hadron colliders
In the extra dimension models of ADD and RS we study the dependence of the
various parton distribution functions on observable of Drell-Yan process to NLO
in QCD at LHC and Tevatron energies. Uncertainties at LHC due to factorisation
scales in going from leading to next-to-leading order in QCD for the various
distributions get reduced by about 2.75 times for a range . Further uncertainties arising from the error on experimental
data are estimated using the MRST parton distribution functions.Comment: 27 pages, 11 figures, the version to appear in European Physical
Journal
Microscopic origin of universality in Casimir forces
The microscopic mechanisms for universality of Casimir forces between
macroscopic conductors are displayed in a model of classical charged fluids.
The model consists of two slabs in empty space at distance containing
classical charged particles in thermal equilibrium (plasma, electrolyte). A
direct computation of the average force per unit surface yields, at large
distance, the usual form of the Casimir force in the classical limit (up to a
factor 2 due to the fact that the model does not incorporate the magnetic part
of the force). Universality originates from perfect screening sum rules obeyed
by the microscopic charge correlations in conductors. If one of the slabs is
replaced by a macroscopic dielectric medium, the result of Lifshitz theory for
the force is retrieved. The techniques used are Mayer expansions and integral
equations for charged fluids.Comment: 31 pages, 0 figures, submitted to Journal of Statistical Physic
QCD factorization for the pion diffractive dissociation to two jets
We calculate the cross section of a pion diffraction dissociation in two jets
with large transverse momenta originating from a hard gluon exchange between
the pion constituents. To the leading logarithmic accuracy (in energy), the
contribution coming from small transverse separations between the quark and the
antiquark in the pion acquires the expected factorized form, the longitudinal
momentum distribution of the jets being proportional to the pion distribution
amplitude. The hard gluon exchange can in this case be considered as a part of
the unintegrated gluon distribution. Beyond the leading logarithms (in energy)
this proportionality does not hold. Moreover, the collinear factorization
appears to be broken by the end-point singularities. Remarkably enough, the
longitudinal momentum distribution of the jets for the non-factorizable
contribution is calculable, and turns out to be the same as for the
factorizable contribution with the asymptotic pion distribution amplitude.Comment: Original version from 9 April restore
Impurity induced resonant state in a pseudogap state of a high temperature superconductor
We predict a resonance impurity state generated by the substitution of one Cu
atom with a nonmagnetic atom, such as Zn, in the pseudogap state of a high-T_c
superconductor. The precise microscopic origin of the pseudogap is not
important for this state to be formed, in particular this resonance will be
present even in the absence of superconducting fluctuations in the normal
state. In the presence of superconducting fluctuations, we predict the
existence of a counterpart impurity peak on a symmetric bias.
The nature of impurity resonance is similar to the previously studied
resonance in the d-wave superconducting state.Comment: 4 pages, 2 figure
Flavour SU(3) Symmetry in Charmless B Decays
QCD sum rules are used to estimate the flavour SU(3)-symmetry violation in
two-body B decays to pions and kaons. In the factorizable amplitudes the
SU(3)-violation manifests itself in the ratio of the decay constants f_K/f_pi
and in the differences between the B->K, B_s->K and B->pi form factors. These
effects are calculated from the QCD two-point and light-cone sum rules,
respectively, in terms of the strange quark mass and the ratio of the strange
and nonstrange quark-condensate densities. Importantly, QCD sum rules predict
that SU(3) breaking in the heavy-to-light form factors can be substantial and
does not vanish in the heavy-quark mass limit. Furthermore, we investigate the
strange-quark mass dependence of nonfactorizable effects in the B->K pi decay
amplitudes. Taking into account these effects we estimate the accuracy of
several SU(3)-symmetry relations between charmless B-decay amplitudes.Comment: Two references added, version to be published in Phys.Rev.D, 21
pages, 12 postscript figure
Spin-Orbit-Induced Kondo Size Effect in Thin Films with 5/2-spin Impurities
Recently, for spin impurities quite different size dependence of the
Kondo contribution to the resistivity was found experimentally than for S=2.
Therefore previous calculation about the effect of the spin-orbit-induced
magnetic anisotropy on the Kondo amplitude of the resistivity is extended to
the case of impurity spin which differs from the integer spin case as
the ground state is degenerated. In this case the Kondo contribution remains
finite when the sample size goes to zero and the thickness dependence in the
Kondo resistivity is much weaker for Cu(Mn). The behavior of the Kondo
coefficient as a function of the thickness depends on the Kondo temperature,
that is somewhat stronger for larger . Comparing our results with a recent
experiment in thin Cu(Mn) films, we find a good agreement.Comment: 8 pages, ReVTeX + 4 figures (Postscript
Combinatorial Alexander Duality -- a Short and Elementary Proof
Let X be a simplicial complex with the ground set V. Define its Alexander
dual as a simplicial complex X* = {A \subset V: V \setminus A \notin X}. The
combinatorial Alexander duality states that the i-th reduced homology group of
X is isomorphic to the (|V|-i-3)-th reduced cohomology group of X* (over a
given commutative ring R). We give a self-contained proof.Comment: 7 pages, 2 figure; v3: the sign function was simplifie
Heavy-quark mass dependence in global PDF analyses and 3- and 4-flavour parton distributions
We study the sensitivity of our recent MSTW 2008 NLO and NNLO PDF analyses to
the values of the charm- and bottom-quark masses, and we provide additional
public PDF sets for a wide range of these heavy-quark masses. We quantify the
impact of varying m_c and m_b on the cross sections for W, Z and Higgs
production at the Tevatron and the LHC. We generate 3- and 4-flavour versions
of the (5-flavour) MSTW 2008 PDFs by evolving the input PDFs and alpha_S
determined from fits in the 5-flavour scheme, including the eigenvector PDF
sets necessary for calculation of PDF uncertainties. As an example of their
use, we study the difference in the Z total cross sections at the Tevatron and
LHC in the 4- and 5-flavour schemes. Significant differences are found,
illustrating the need to resum large logarithms in Q^2/m_b^2 by using the
5-flavour scheme. The 4-flavour scheme is still necessary, however, if cuts are
imposed on associated (massive) b-quarks, as is the case for the experimental
measurement of Z b bbar production and similar processes.Comment: 40 pages, 11 figures. Grids can be found at
http://projects.hepforge.org/mstwpdf/ and in LHAPDF V5.8.4. v2: version
published in EPJ
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