696 research outputs found
D-meson production by muons in the COMPASS experiment at CERN
One of the physics goals of the COMPASS experiment at CERN was
to measure the contribution of gluons to the nucleon spin. To achieve
this, it was proposed to scatter polarized \Value{160}{GeV/c} muons on a
polarized deuteron target and to detect mesons in the final state.
The underlying process in this meson production
is supposed to be the \Gls{PGF}, where
a virtual photon emitted by the muon interacts
with a gluon from the target nucleon, producing a charm-anticharm quark pair.
Fragmentation of a charm (anticharm) quark leads with high probability to the creation of
a \DZ or meson, which COMPASS detects via
the and decay modes.
From the longitudinal cross section spin asymmetries of the meson production and theoretical
predictions for the \Gls{PGF} cross section, the gluon contribution to the nucleon spin
has been measured by the COMPASS experiment.
The results presented in the thesis are the following.
Based on data from the year 2004 a total visible cross section of \TotalCrossSection,
for the meson production, has been measured, with
the error being dominated by systematic effects.
It is validated that the mesons are indeed produced through
the \Gls{PGF} process, by comparison of measured meson kinematic distributions
to the ones predicted by a theory (AROMA generator).
A good agreement was found for the distribution shapes,
which confirms that \Gls{PGF} plays a major role.
However, a difference was found in the number of
produced \DZ and \aDZ mesons (and for the and mesons as well)
which is significantly larger than predicted by AROMA.
Kinematic distributions of and mesons
were compared with the background
and also with the nearby \KTS resonance,
using all longitudinal data taken in 2002-2006.
The particle-antiparticle
asymmetry has been studied as a function of several kinematic variables. The excess
of mesons decaying into over
mesons decaying into was observed for all three mesons.
The behavior of the \DZ/\aDZ (and ) asymmetries
as a function
of virtual photon energy suggests that associated production of or
may be responsible for the observed effect.
The longitudinal double spin asymmetries have been studied for the , and \KTS mesons
separately for particle, antiparticle and for the sum of particle and antiparticle.
It was found that the asymmetries extracted for and mesons
are compatible with zero. A 3-sigma deviation
from zero asymmetry was observed for the \KTS meson. An investigation of the \KTS double spin asymmetry
reveals a dependence as function of the Bjorken variable
Dynamical properties of the sine-Gordon quantum spin magnet Cu-PM at zero and finite temperature
The material copper pyrimidine dinitrate (Cu-PM) is a quasi-one-dimensional
spin system described by the spin-1/2 XXZ Heisenberg antiferromagnet with
Dzyaloshinskii-Moriya interactions. Based on numerical results obtained by the
density-matrix renormalization group, exact diagonalization, and accompanying
electron spin resonance (ESR) experiments we revisit the spin dynamics of this
compound in an applied magnetic field. Our calculations for momentum and
frequency-resolved dynamical quantities give direct access to the intensity of
the elementary excitations at both zero and finite temperature. This allows us
to study the system beyond the low-energy description by the quantum
sine-Gordon model. We find a deviation from the Lorentz invariant dispersion
for the single-soliton resonance. Furthermore, our calculations only confirm
the presence of the strongest boundary bound state previously derived from a
boundary sine-Gordon field theory, while composite boundary-bulk excitations
have too low intensities to be observable. Upon increasing the temperature, we
find a temperature-induced crossover of the soliton and the emergence of new
features, such as interbreather transitions. The latter observation is
confirmed by our ESR experiments on Cu-PM over a wide range of the applied
field.Comment: 17 pages, 16 figures; published version (including final revisions
Genetic analysis of the grapevine genotypes of the Russian Vitis ampelographic collection using iPBS markers
Cultivated grapevine (Vitis vinifera L. ssp. sativa D.C.) is one of the oldest agricultural crops, each variety comprising an array of clones obtained by vegetative propagation from a selected vine grown from a single seedling. Most clones within a variety are identical, but some show a different form of accession, giving rise to new divergent phenotypes. Understanding the associations among the genotypes within a variety is crucial to efficient management and effective grapevine improvement. Inter-primer binding-site (iPBS) markers may aid in determining the new clones inside closely related genotypes. Following this idea, iPBS markers were used to assess the genetic variation of 33 grapevine genotypes collected from Russia. We used molecular markers to identify the differences among and within five grapevine clonal populations and analysed the variation, using clustering and statistical approaches. Four of a total of 30 PBS primers were selected, based on amplification efficiency. Polymerase chain reaction (PCR) with PBS primers resulted in a total of 1412 bands ranging from 300 to 6000 bp, with a polymorphism ratio of 44%, ranging from 58 to 75 bands per group. In total, were identified seven private bands in 33 genotypes. Results of molecular variance analysis showed that 40% of the total variation was observed within groups and only 60% between groups. Cluster analysis clearly showed that grapevine genotypes are highly divergent and possess abundant genetic diversities. The iPBS PCR-based genome fingerprinting technology used in this study effectively differentiated genotypes into five grapevine groups and indicated that iPBS markers are useful tools for clonal selection. The number of differences between clones was sufficient to identify them as separate clones of studied varieties containing unique mutations. Our previous phenotypic and phenological studies have confirmed that these genotypes differ from those of maternal plants. This work emphasized the need for a better understanding of the genotypic differences among closely related varieties of grapevine and has implications for the management of its selection processes.Peer reviewe
Finite-temperature dynamical magnetic susceptibility of quasi-one-dimensional frustrated spin-1/2 Heisenberg antiferromagnets
We study the dynamical response of frustrated, quasi-one-dimensional spin-1/2
Heisenberg antiferromagnets at finite temperatures. We allow for the presence
of a Dzyaloshinskii-Moriya interaction. We concentrate on a model of weakly
coupled planes of anisotropic triangular lattices. Combining exact results for
the dynamical response of one dimensional Heisenberg chains with a Random Phase
Approximation (RPA) in the frustrated interchain couplings, we calculate the
dynamical susceptibility in the disordered phase. We investigate the
instability of the disordered phase to the formation of collective modes. We
find a very weak instability to the formation of incommensurate magnetic order
and determine the ordering temperature and wave vector. We also determine the
effects of uniform magnetic fields on the ordering transition.Comment: 17 pages, 17 Postscript figure
Effective one-dimensionality of AC hopping conduction in the extreme disorder limit
It is argued that in the limit of extreme disorder AC hopping is dominated by
"percolation paths". Modelling a percolation path as a one-dimensional path
with a sharp jump rate cut-off leads to an expression for the universal AC
conductivity, that fits computer simulations in two and three dimensions better
than the effective medium approximation.Comment: 6 postscript figure
Differential branching fraction and angular analysis of the decay B0âKâ0ÎŒ+ÎŒâ
The angular distribution and differential branching fraction of the decay B 0â K â0 ÎŒ + ÎŒ â are studied using a data sample, collected by the LHCb experiment in pp collisions at sâ=7 TeV, corresponding to an integrated luminosity of 1.0 fbâ1. Several angular observables are measured in bins of the dimuon invariant mass squared, q 2. A first measurement of the zero-crossing point of the forward-backward asymmetry of the dimuon system is also presented. The zero-crossing point is measured to be q20=4.9±0.9GeV2/c4 , where the uncertainty is the sum of statistical and systematic uncertainties. The results are consistent with the Standard Model predictions
Opposite-side flavour tagging of B mesons at the LHCb experiment
The calibration and performance of the oppositeside
flavour tagging algorithms used for the measurements
of time-dependent asymmetries at the LHCb experiment
are described. The algorithms have been developed using
simulated events and optimized and calibrated with
B
+ âJ/ÏK
+, B0 âJ/ÏK
â0 and B0 âD
ââ
Ό
+
ΜΌ decay
modes with 0.37 fbâ1 of data collected in pp collisions
at
â
s = 7 TeV during the 2011 physics run. The oppositeside
tagging power is determined in the B
+ â J/ÏK
+
channel to be (2.10 ± 0.08 ± 0.24) %, where the first uncertainty
is statistical and the second is systematic
Search for CP violation in D+âÏÏ+ and D+sâK0SÏ+ decays
A search for CP violation in D + â ÏÏ + decays is performed using data collected in 2011 by the LHCb experiment corresponding to an integrated luminosity of 1.0 fbâ1 at a centre of mass energy of 7 TeV. The CP -violating asymmetry is measured to be (â0.04 ± 0.14 ± 0.14)% for candidates with K â K + mass within 20 MeV/c 2 of the Ï meson mass. A search for a CP -violating asymmetry that varies across the Ï mass region of the D + â K â K + Ï + Dalitz plot is also performed, and no evidence for CP violation is found. In addition, the CP asymmetry in the D+sâK0SÏ+ decay is measured to be (0.61 ± 0.83 ± 0.14)%
Measurement of the branching fraction
The branching fraction is measured in a data sample
corresponding to 0.41 of integrated luminosity collected with the LHCb
detector at the LHC. This channel is sensitive to the penguin contributions
affecting the sin2 measurement from The
time-integrated branching fraction is measured to be . This is the most precise measurement to
date
Model-independent search for CP violation in D0âKâK+ÏâÏ+ and D0âÏâÏ+Ï+Ïâ decays
A search for CP violation in the phase-space structures of D0 and View the MathML source decays to the final states KâK+ÏâÏ+ and ÏâÏ+Ï+Ïâ is presented. The search is carried out with a data set corresponding to an integrated luminosity of 1.0 fbâ1 collected in 2011 by the LHCb experiment in pp collisions at a centre-of-mass energy of 7 TeV. For the KâK+ÏâÏ+ final state, the four-body phase space is divided into 32 bins, each bin with approximately 1800 decays. The p-value under the hypothesis of no CP violation is 9.1%, and in no bin is a CP asymmetry greater than 6.5% observed. The phase space of the ÏâÏ+Ï+Ïâ final state is partitioned into 128 bins, each bin with approximately 2500 decays. The p-value under the hypothesis of no CP violation is 41%, and in no bin is a CP asymmetry greater than 5.5% observed. All results are consistent with the hypothesis of no CP violation at the current sensitivity
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