7,107 research outputs found
Nonperturbative deformation of D-brane states by the world sheet noncommutativity
By introducing the noncommutativity in the world sheet, we discuss a
modification of the D-brane states in the closed string theory. In particular
we show how the world sheet noncommutativity induces a nonperturbative effect
to the D-brane states.Comment: 10 pages, no figure
Mixing of Active and Sterile Neutrinos
We investigate mixing of neutrinos in the MSM (neutrino Minimal Standard
Model), which is the MSM extended by three right-handed neutrinos. Especially,
we study elements of the mixing matrix between three
left-handed neutrinos () and two sterile
neutrinos () which are responsible to the seesaw mechanism
generating the suppressed masses of active neutrinos as well as the generation
of the baryon asymmetry of the universe (BAU). It is shown that
can be suppressed by many orders of magnitude compared with
and , when the Chooz angle is large in the
normal hierarchy of active neutrino masses. We then discuss the neutrinoless
double beta decay in this framework by taking into account the contributions
not only from active neutrinos but also from all the three sterile neutrinos.
It is shown that and give substantial, destructive contributions
when their masses are smaller than a few 100 MeV, and as a results receive no stringent constraint from the current bounds on such decay.
Finally, we discuss the impacts of the obtained results on the direct searches
of in meson decays for the case when are lighter than pion
mass. We show that there exists the allowed region for with such
small masses in the normal hierarchy case even if the current bound on the
lifetimes of from the big bang nucleosynthesis is imposed. It is also
pointed out that the direct search by using and might miss such since the branching ratios can be
extremely small due to the cancellation in , but the search by
can cover the whole allowed region by improving the
measurement of the branching ratio by a factor of 5.Comment: 30 pages, 32 figure
Leading order analysis of neutrino induced dimuon events in the CHORUS experiment
We present a leading order QCD analysis of a sample of neutrino induced
charged-current events with two muons in the final state originating in the
lead-scintillating fibre calorimeter of the CHORUS detector. The results are
based on a sample of 8910 neutrino and 430 antineutrino induced opposite-sign
dimuon events collected during the exposure of the detector to the CERN Wide
Band Neutrino Beam between 1995 and 1998. % with GeV
and GeV collected %between 1995 and 1998. The analysis yields a
value of the charm quark mass of \mc = (1.26\pm 0.16 \pm 0.09) \GeVcc and a
value of the ratio of the strange to non-strange sea in the nucleon of , improving the results obtained in similar analyses
by previous experiments.Comment: Submitted to Nuclear Physics
Neutrino Mass and from a Mini-Seesaw
The recently proposed "mini-seesaw mechanism" combines naturally suppressed
Dirac and Majorana masses to achieve light Standard Model neutrinos via a
low-scale seesaw. A key feature of this approach is the presence of multiple
light (order GeV) sterile-neutrinos that mix with the Standard Model. In this
work we study the bounds on these light sterile-neutrinos from processes like
\mu ---> e + \gamma, invisible Z-decays, and neutrinoless double beta-decay. We
show that viable parameter space exists and that, interestingly, key
observables can lie just below current experimental sensitivities. In
particular, a motivated region of parameter space predicts a value of BR(\mu
---> e + \gamma) within the range to be probed by MEG.Comment: 1+26 pages, 7 figures. v2 JHEP version (typo's fixed, minor change to
presentation, results unchanged
Comparison of large-angle production of charged pions with incident protons on cylindrical long and short targets
The HARP collaboration has presented measurements of the double-differential
pi+/pi- production cross-section in the range of momentum 100 MeV/c <= p 800
MeV/c and angle 0.35 rad <= theta <= 2.15 rad with proton beams hitting thin
nuclear targets. In many applications the extrapolation to long targets is
necessary. In this paper the analysis of data taken with long (one interaction
length) solid cylindrical targets made of carbon, tantalum and lead is
presented. The data were taken with the large acceptance HARP detector in the
T9 beam line of the CERN PS. The secondary pions were produced by beams of
protons with momenta 5 GeV/c, 8 GeV/c and 12 GeV/c. The tracking and
identification of the produced particles were performed using a small-radius
cylindrical time projection chamber (TPC) placed inside a solenoidal magnet.
Incident protons were identified by an elaborate system of beam detectors.
Results are obtained for the double-differential yields per target nucleon d2
sigma / dp dtheta. The measurements are compared with predictions of the MARS
and GEANT4 Monte Carlo simulations.Comment: 43 pages, 20 figure
Forward production of charged pions with incident on nuclear targets measured at the CERN PS
Measurements of the double-differential production cross-section
in the range of momentum 0.5 \GeVc \leq p \le 8.0 \GeVc and angle 0.025 \rad
\leq \theta \le 0.25 \rad in interactions of charged pions on beryllium,
carbon, aluminium, copper, tin, tantalum and lead are presented. These data
represent the first experimental campaign to systematically measure forward
pion hadroproduction. The data were taken with the large acceptance HARP
detector in the T9 beam line of the CERN PS. Incident particles, impinging on a
5% nuclear interaction length target, were identified by an elaborate system of
beam detectors. The tracking and identification of the produced particles was
performed using the forward spectrometer of the HARP detector. Results are
obtained for the double-differential cross-sections mainly at four incident pion beam
momenta (3 \GeVc, 5 \GeVc, 8 \GeVc and 12 \GeVc). The measurements are compared
with the GEANT4 and MARS Monte Carlo simulationComment: to be published on Nuclear Physics
Measurement of the production of charged pions by protons on a tantalum target
A measurement of the double-differential cross-section for the production of
charged pions in proton--tantalum collisions emitted at large angles from the
incoming beam direction is presented. The data were taken in 2002 with the HARP
detector in the T9 beam line of the CERN PS. The pions were produced by proton
beams in a momentum range from 3 \GeVc to 12 \GeVc hitting a tantalum target
with a thickness of 5% of a nuclear interaction length. The angular and
momentum range covered by the experiment (100 \MeVc \le p < 800 \MeVc and
0.35 \rad \le \theta <2.15 \rad) is of particular importance for the design
of a neutrino factory. The produced particles were detected using a
small-radius cylindrical time projection chamber (TPC) placed in a solenoidal
magnet. Track recognition, momentum determination and particle identification
were all performed based on the measurements made with the TPC. An elaborate
system of detectors in the beam line ensured the identification of the incident
particles. Results are shown for the double-differential cross-sections
at four incident
proton beam momenta (3 \GeVc, 5 \GeVc, 8 \GeVc and 12 \GeVc). In addition, the
pion yields within the acceptance of typical neutrino factory designs are shown
as a function of beam momentum. The measurement of these yields within a single
experiment eliminates most systematic errors in the comparison between rates at
different beam momenta and between positive and negative pion production.Comment: 49 pages, 31 figures. Version accepted for publication on Eur. Phys.
J.
Charged-Particle Multiplicities in Charged-Current Neutrino-- and Anti-Neutrino--Nucleus Interactions
The CHORUS experiment, designed to search for
oscillations, consists of a nuclear emulsion target and electronic detectors.
In this paper, results on the production of charged particles in a small sample
of charged-current neutrino-- and anti-neutrino--nucleus interactions at high
energy are presented. For each event, the emission angle and the ionization
features of the charged particles produced in the interaction are recorded,
while the standard kinematic variables are reconstructed using the electronic
detectors. The average multiplicities for charged tracks, the pseudo-rapidity
distributions, the dispersion in the multiplicity of charged particles and the
KNO scaling are studied in different kinematical regions. A study of
quasi-elastic topologies performed for the first time in nuclear emulsions is
also reported. The results are presented in a form suitable for use in the
validation of Monte Carlo generators of neutrino--nucleus interactions.Comment: 17 pages, 5 figure
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