3,470 research outputs found
The Time of Flight System of the AMS-02 Space Experiment
The Time-of-Flight (TOF) system of the AMS detector gives the fast trigger to
the read out electronics and measures velocity, direction and charge of the
crossing particles. The new version of the detector (called AMS-02) will be
installed on the International Space Station on March 2004. The fringing field
of the AMS-02 superconducting magnet is kG where the
photomultiplers (PM) are installed. In order to be able to operate with this
residual field, a new type of PM was chosen and the mechanical design was
constrained by requiring to minimize the angle between the magnetic field
vector and the PM axis. Due to strong field and to the curved light guides, the
time resolution will be ps, while the new electronics will allow
for a better charge measurement.Comment: 5 pages, 4 figures. Proc. of 7th Int. Conf. on Adv. Tech. and Part.
Phys., 15-19 October 2001,Como (Italy
Semi-classical stability of AdS NUT instantons
The semi-classical stability of several AdS NUT instantons is studied.
Throughout, the notion of stability is that of stability at the one-loop level
of Euclidean Quantum Gravity. Instabilities manifest themselves as negative
eigenmodes of a modified Lichnerowicz Laplacian acting on the transverse
traceless perturbations. An instability is found for one branch of the
AdS-Taub-Bolt family of metrics and it is argued that the other branch is
stable. It is also argued that the AdS-Taub-NUT family of metrics are stable. A
component of the continuous spectrum of the modified Lichnerowicz operator on
all three families of metrics is found.Comment: 18 pages, 3 figures; references adde
The AMS-02 Time of Flight System. Final Design
The AMS-02 detector is a superconducting magnetic spectrometer that will
operate on the International Space Station. The time of flight (TOF) system of
AMS-02 is composed by four scintillator planes with 8, 8, 10, 8 counters each,
read at both ends by a total of 144 phototubes. This paper describes the new
design, the expected performances, and shows preliminary results of the ion
beam test carried on at CERN on October 2002.Comment: 4 pages, 6 EPS figures. Proc. of the 28th ICRC (2003
The Escape Problem in a Classical Field Theory With Two Coupled Fields
We introduce and analyze a system of two coupled partial differential
equations with external noise. The equations are constructed to model
transitions of monovalent metallic nanowires with non-axisymmetric intermediate
or end states, but also have more general applicability. They provide a rare
example of a system for which an exact solution of nonuniform stationary states
can be found. We find a transition in activation behavior as the interval
length on which the fields are defined is varied. We discuss several
applications to physical problems.Comment: 24 page
Supersymmetric photonic signals at LEP
We explore and contrast the single-photon and diphoton signals expected at
LEP 2, that arise from neutralino-gravitino (e^+ e^- -> chi + gravitino ->
gamma + E_miss) and neutralino-neutralino (e^+ e^- -> chi + chi -> gamma +
gamma + E_miss) production in supersymmetric models with a light gravitino. LEP
1 limits imply that one may observe either one, but not both, of these signals
at LEP 2, depending on the values of the neutralino and gravitino masses:
single-photons for m_chi > Mz and m_gravitino < 3 x 10^-5 eV; diphotons for
m_chi < Mz and all allowed values of m_gravitino.Comment: 11 pages, LaTeX, 4 figures (included). Shortened version to appear in
Physical Review Letter
New Precision Electroweak Tests of SU(5) x U(1) Supergravity
We explore the one-loop electroweak radiative corrections in supergravity via explicit calculation of vacuum-polarization and
vertex-correction contributions to the and
parameters. Experimentally, these parameters are obtained from a global fit to
the set of observables , and . We
include -dependent effects, which induce a large systematic negative shift
on for light chargino masses (m_{\chi^\pm_1}\lsim70\GeV). The
(non-oblique) supersymmetric vertex corrections to \Zbb, which define the
parameter, show a significant positive shift for light chargino
masses, which for can be nearly compensated by a negative
shift from the charged Higgs contribution. We conclude that at the 90\%CL, for
m_t\lsim160\GeV the present experimental values of and
do not constrain in any way supergravity in
both no-scale and dilaton scenarios. On the other hand, for m_t\gsim160\GeV
the constraints on the parameter space become increasingly stricter. We
demonstrate this trend with a study of the m_t=170\GeV case, where only a
small region of parameter space, with \tan\beta\gsim4, remains allowed and
corresponds to light chargino masses (m_{\chi^\pm_1}\lsim70\GeV). Thus
supergravity combined with high-precision LEP data would
suggest the presence of light charginos if the top quark is not detected at the
Tevatron.Comment: LaTeX, 11 Pages+4 Figures(not included), the figures available upon
request as an uuencoded file(0.4MB) or 4 PS files from [email protected],
CERN-TH.7078/93, CTP-TAMU-68/93, ACT-24/9
The EEE Project
The new experiment ``Extreme Energy Events'' (EEE) to detect extensive air
showers through muon detection is starting in Italy. The use of particle
detectors based on Multigap Resistive Plate Chambers (MRPC) will allow to
determine with a very high accuracy the direction of the axis of cosmic ray
showers initiated by primaries of ultra-high energy, together with a high
temporal resolution. The installation of many of such 'telescopes' in numerous
High Schools scattered all over the Italian territory will also allow to
investigate coincidences between multiple primaries producing distant showers.
Here we present the experimental apparatus and its tasks.Comment: 4 pages, 29th ICRC 2005, Pune, Indi
SUSY signals at HERA in the no-scale flipped SU(5) supergravity model
Sparticle production and detection at HERA are studied within the recently
proposed no-scale flipped supergravity model. Among the various
reaction channels that could lead to sparticle production at HERA, only the
following are within its limit of sensitivity in this model: , where are the
two lightest neutralinos and is the lightest chargino. We study the
elastic and deep-inelastic contributions to the cross sections using the
Weizs\"acker-Williams approximation. We find that the most promising
supersymmetric production channel is right-handed selectron ()
plus first neutralino (), with one hard electron and missing energy
signature. The channel leads to comparable rates but also
allows jet final states. A right-handedly polarized electron beam at HERA would
shut off the latter channel and allow preferentially the former one. With an
integrated luminosity of {\cal L}=100\ipb, HERA can extend the present LEPI
lower bounds on by
\approx25\GeV, while {\cal L}=1000\ipb will make HERA competitive with
LEPII. We also show that the Leading Proton Spectrometer (LPS) at HERA is an
excellent supersymmetry detector which can provide indirect information about
the sparticle masses by measuring the leading proton longitudinal momentum
distribution.Comment: 11 pages, 8 figures (available upon request as uuencoded file or
separate ps files), tex (harvmac) CTP-TAMU-15/93, CERN/LAA/93-1
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