1,261 research outputs found
VALIDATION OF THE HADRONIC CALIBRATION OF THE ATLAS CALORIMETER WITH TESTBEAM DATA CORRESPONDING TO THE PSEUDORAPIDITY RANGE 2.5<|eta|<4.0}
The pseudorapidity region 2.5<|eta|<4.0 in ATLAS is a particularly complex transition zone between the endcap and forward calorimeters. A set-up consisting of 1/4 resp. 1/8 of the full azimuthal acceptance of the ATLAS liquid argon endcap and forward calorimeters has been exposed to beams of electrons, pions and muons in the energy range E < 200 GeV at the CERN SPS. Data have been taken in the endcap and forward calorimeter regions as well as in the transition region. This beam test set-up corresponds very closely to the geometry and support structures in ATLAS. Pion data have been analyzed using the standard local hadronic calibration scheme as forseen for the ATLAS calorimeter. In particular the weighting scheme to compensate for the different electron to pion response as well as corrections for dead material in the transition region have been extensively tested and compared to simulation based on GEANT 4 models
Constraints on muon-specific dark forces
The recent measurement of the Lamb shift in muonic hydrogen allows for the
most precise extraction of the charge radius of the proton which is currently
in conflict with other determinations based on scattering and hydrogen
spectroscopy. This discrepancy could be the result of some new muon-specific
force with O(1-100) MeV force carrier---in this paper we concentrate on vector
mediators. Such an explanation faces challenges from the constraints imposed by
the of the muon and electron as well as precision spectroscopy of muonic
atoms. In this work we complement the family of constraints by calculating the
contribution of hypothetical forces to the muonium hyperfine structure. We also
compute the two-loop contribution to the electron parity violating amplitude
due to a muon loop, which is sensitive to the muon axial-vector coupling.
Overall, we find that the combination of low-energy constraints favors the mass
of the mediator to be below 10 MeV, and that a certain degree of tuning is
required between vector and axial-vector couplings of new vector particles to
muons in order to satisfy constraints from muon . However, we also observe
that in the absence of a consistent standard model embedding, high energy
weak-charged processes accompanied by the emission of new vector particles are
strongly enhanced by , with a characteristic energy scale and
the mass of the mediator. In particular, leptonic decays impose the
strongest constraints on such models completely disfavoring the remainder of
the parameter space.Comment: 10 pages, 7 figure
Electric dipole and magnetic quadrupole moments of the boson via a CP-violating vertex in effective Lagrangians
The possibility of nonnegligible electric dipole ()
and magnetic quadrupole () moments induced by the most general
vertex is examined via the effective Lagrangian technique. It is assumed
that new heavy fermions induce an anomalous CP-odd component of the
vertex, which can be parametrized by an -invariant
dimension-six operator. This anomalous contribution, when combined with the
standard model CP-even contribution, lead to CP-odd electromagnetic properties
of the boson, which are characterized by the form factors and . It is found that is divergent, whereas is finite,
which reflects the fact that the latter cannot be generated at the one-loop
level in any renormalizable theory. Assuming reasonable values for the unknown
parameters, we found that e-cm,
which is eight orders of magnitude larger than the SM prediction and close to
the upper bound derived from the neutron electric dipole moment. The estimated
size of the somewhat less-studied moment is of the order of
e-cm^2, which is fifteen orders of magnitude above the SM
contribution.Comment: 7 pages, 6 figures, REVTEX styl
Lorentz Violating Supersymmetric Quantum Electrodynamics
Theory of Supersymmetric Quantum Electrodynamics is extended by interactions
with external vector and tensor backgrounds, that are assumed to be generated
by some Lorentz-violating (LV) dynamics at an ultraviolet scale perhaps related
to the Planck scale. Exact supersymmetry requires that such interactions
correspond to LV operators of dimension five or higher, providing a solution to
the naturalness problem in the LV sector. We classify all dimension five and
six LV operators, analyze their properties at the quantum level and describe
observational consequences of LV in this theory. We show that LV operators do
not induce destabilizing D-terms, gauge anomaly and the Chern-Simons term for
photons. We calculate the renormalization group evolution of dimension five LV
operators and their mixing with dimension three LV operators, controlled by the
scale of the soft-breaking masses. Dimension five LV operators are constrained
by the low-energy precision measurements at 10^{-10}-10^{-5} level in units of
the inverse Planck scale, while the Planck-scale suppressed dimension six LV
operators are allowed by observational data.Comment: 37 pages LaTeX, minor revisions, and typos correcte
CP-odd static electromagnetic properties of the W gauge boson and the t quark via the anomalous tbW coupling
In the framework of the electroweak chiral Lagrangian, the one-loop induced
effects of the anomalous coupling, which includes both left- and
right-handed complex components, on the static electromagnetic properties of
the boson and the quark are studied. The attention is focused mainly on
the CP-violating electromagnetic properties. It is found that the
anomalous coupling can induce both CP-violating moments of the boson,
namely, its electric dipole () and magnetic quadrupole
() moments. As far as the quark is concerned, a potentially
large electric dipole moment can arise due to the anomalous
coupling. The most recent bounds on the left- and right-handed parameters from
meson physics lead to the following estimates e-cm and e-cm, which
are 7 and 14 orders of magnitude larger than the standard model (SM)
predictions, whereas may be as large as e-cm, which is about 8
orders of magnitude larger than its SM counterpart.Comment: This paper has been merged with hep-ph/0612171 for publication in
Physical Review
Metastable GeV-scale particles as a solution to the cosmological lithium problem
The persistent discrepancy between observations of 7Li with putative
primordial origin and its abundance prediction in Big Bang Nucleosynthesis
(BBN) has become a challenge for the standard cosmological and astrophysical
picture. We point out that the decay of GeV-scale metastable particles X may
significantly reduce the BBN value down to a level at which it is reconciled
with observations. The most efficient reduction occurs when the decay happens
to charged pions and kaons, followed by their charge exchange reactions with
protons. Similarly, if X decays to muons, secondary electron antineutrinos
produce a similar effect. We consider the viability of these mechanisms in
different classes of new GeV-scale sectors, and find that several minimal
extensions of the Standard Model with metastable vector and/or scalar particles
are capable of solving the cosmological lithium problem. Such light states can
be a key to the explanation of recent cosmic ray anomalies and can be searched
for in a variety of high-intensity medium-energy experiments.Comment: 50 pages, 13 figures; references added, typo correcte
Decay in the Left-Right Supersymmetric Model
We calculate the rate of the decay and the electric dipole
moment of the electron in the left-right supersymmetric model when the breaking
of parity occurs at a considerably large scale. The low-energy flavor violation
in the model originates either from the nonvanishing remnants of the left-right
symmetry in the slepton mass matrix or from the direct flavor changing
lepton-slepton-neutralino interaction. The result is found to be large for the
masses of the supersymmetric particles not far from the electroweak scale and
already accessible at the current experimental accuracy. It also provides
nontrivial constraints of the lepton mixing in the model.Comment: 10 pages, LaTeX, 1 figur
Test of the ATLAS pion calibration scheme in the ATLAS combined test beam
Pion energy reconstruction is studied using the data collected during the
2004 ATLAS combined test beam. The strategy to extract corrections for the
non-compensating nature of the ATLAS calorimeters for dead material losses and
for leakage effects is discussed and assessed. The default ATLAS strategy based
on a weighting technique of the energy deposits in calorimeter cells is
presented and compared to a novel technique exploiting correlations among
energy deposited in calorimeter layers.Comment: 8 pages, 6 figures, to appear in the Proceedings of the XIII
International Conference on Calorimetry in High Energy Physics (CALOR08), May
2008, Pavia, Italy - Journal of Physics: Conference Serie
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