252 research outputs found
Flavour physics of the RS model with KK masses reachable at LHC
The version of the higher-dimensional Randall-Sundrum (RS) model with matter
in the bulk, which addresses the gauge hierarchy problem, has additional
attractive features. In particular, it provides an intrinsic geometrical
mechanism that can explain the origin of the large mass hierarchies among the
Standard Model fermions. Within this context, a good solution for the gauge
hierarchy problem corresponds to low masses for the Kaluza-Klein (KK)
excitations of the gauge bosons. Some scenarios have been proposed in order to
render these low masses (down to a few TeV) consistent with precision
electroweak measurements. Here, we give specific and complete realizations of
this RS version with small KK masses, down to 1 TeV, which are consistent with
the entire structure of the fermions in flavour space: (1) all the last
experimental data on quark/lepton masses and mixing angles (including massive
neutrinos of Dirac type) are reproduced, (2) flavour changing neutral current
constraints are satisfied and (3) the effective suppression scales of
non-renormalizable interactions (in the physical basis) are within the bounds
set by low energy flavour phenomenology. Our result, on the possibility of
having KK gauge boson modes as light as a few TeV, constitutes one of the first
theoretical motivations for experimental searches of direct signatures at the
LHC collider, of this interesting version of the RS model which accommodates
fermion masses.Comment: 27 pages, Latex file. References and comments adde
First Model-Independent Measurement of the Spin Triplet Scattering Length from Final State Interaction in the Reaction
The reaction has been measured with the
COSY-TOF detector at a beam momentum of . The polarized
proton beam enables the measurement of the beam analyzing power by the
asymmetry of the produced kaon (). This observable allows the
spin triplet scattering length to be extracted for the first time
model independently from the final-state interaction in the reaction. The
obtained value is . This value is
compatible with theoretical predictions and results from model-dependent
analyses.Comment: Revised version as accepted for publication in PR
High precision measurement of the associated strangeness production in proton proton interactions
A new high precision measurement of the reaction pp -> pK+Lambda at a beam
momentum of 2.95 GeV/c with more than 200,000 analyzed events allows a detailed
analysis of differential observables and their inter-dependencies. Correlations
of the angular distributions with momenta are examined. The invariant mass
distributions are compared for different regions in the Dalitz plots. The cusp
structure at the N Sigma threshold is described with the Flatt\'e formalism and
its variation in the Dalitz plot is analyzed.Comment: accepted for publication in Eur. Phys. J.
The Straw Tube Trackers of the PANDA Experiment
The PANDA experiment will be built at the FAIR facility at Darmstadt
(Germany) to perform accurate tests of the strong interaction through bar pp
and bar pA annihilation's studies. To track charged particles, two systems
consisting of a set of planar, closed-packed, self-supporting straw tube layers
are under construction. The PANDA straw tubes will have also unique
characteristics in term of material budget and performance. They consist of
very thin mylar-aluminized cathodes which are made self-supporting by means of
the operation gas-mixture over-pressure. This solution allows to reduce at
maximum the weight of the mechanical support frame and hence the detector
material budget. The PANDA straw tube central tracker will not only reconstruct
charged particle trajectories, but also will help in low momentum (< 1 GeV)
particle identification via dE/dx measurements. This is a quite new approach
that PANDA tracking group has first tested with detailed Monte Carlo
simulations, and then with experimental tests of detector prototypes. This
paper addresses the design issues of the PANDA straw tube trackers and the
performance obtained in prototype tests.Comment: 7 pages,16 figure
History-dependent domain and skyrmion formation in 2D van der Waals magnet Fe3GeTe2
The discovery of two-dimensional magnets has initiated a new field of research, exploring both fundamental low-dimensional magnetism, and prospective spintronic applications. Recently, observations of magnetic skyrmions in the 2D ferromagnet Fe3GeTe2 (FGT) have been reported, introducing further application possibilities. However, controlling the exhibited magnetic state requires systematic knowledge of the history-dependence of the spin textures, which remains largely unexplored in 2D magnets. In this work, we utilise real-space imaging, and complementary simulations, to determine and explain the thickness-dependent magnetic phase diagrams of an exfoliated FGT flake, revealing a complex, history-dependent emergence of the uniformly magnetised, stripe domain and skyrmion states. The results show that the interplay of the dominant dipolar interaction and strongly temperature dependent out-of-plane anisotropy energy terms enables the selective stabilisation of all three states at zero field, and at a single temperature, while the Dzyaloshinksii-Moriya interaction must be present to realise the observed Néel-type domain walls. The findings open perspectives for 2D devices incorporating topological spin textures
Single \pi^- production in np collisions for excess energies up to 90 MeV
The quasifree reaction np\to pp\pim was studied in a kinematically complete
experiment by bombarding a liquid hydrogen target with a deuteron beam of
momentum 1.85 GeV/c and analyzing the data along the lines of the spectator
model. In addition to the three charged ejectiles the spectator proton was also
detected in the large-acceptance time-of-flight spectrometer COSY-TOF. It was
identified by its momentum and flight direction thus yielding access to the
Fermi motion of the bound neutron and to the effective neutron 4-momentum
vector which differed from event to event. A range of almost 90
MeV excess energy above threshold was covered. Energy dependent angular
distributions, invariant mass spectra as well as fully covered Dalitz plots
were deduced. Sizeable FSI effects were found as were contributions of
and partial waves. The behavior of the elementary cross section
close to threshold is discussed in view of new cross section
data. In comparison with existing literature data the results provide a
sensitive test of the spectator model.Comment: 21 pages, 9 figures, 4 tables, submitted to EPJ
Measurement of the Eta Production in Proton Proton Collisions with the COSY Time of Flight Spectrometer
The reaction pp -> pp eta was measured at excess energies of 15 and 41 MeV at
an external target of the Juelich Cooler Synchrotron COSY with the Time of
Flight Spectrometer. About 25000 events were measured for the excess energy of
15 MeV and about 8000 for 41 MeV. Both protons of the process pp eta were
detected with an acceptance of nearly 100% and the eta was reconstructed by the
missing mass technique. For both excess energies the angular distributions are
found to be nearly isotropic. In the invariant mass distributions strong
deviations from the pure phase space distributions are seen.Comment: 15 pages, 14 figures, 4 table
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