856 research outputs found
Search for Single Leptoquark Production in Electron-Photon Scattering at = 161 and 172 GeV
A search for a first generation scalar leptoquark (LQ) has been performed using the data collected by the OPAL detector in 1996 at e+e- centre-of-mass energies sqrt{s} of 161 and 172 GeV. It is assumed that a single leptoquark can be produced in the process eq->LQ, where the initial state quark originates from a hadronic fluctuation of a quasi-real photon which has been radiated by one of the LEP beams. Lower limits at the 95 % confidence level on the mass of a first generation scalar leptoquark of 131 GeV for beta=0.5 and beta=1, coupling values lambda larger than sqrt{4*pi*alpha_em) and leptoquark charges -1/3 or -5/3 are obtained
and scattering from , forward amplitudes in a QCD eikonal model with a dynamical gluon mass
We examine the photoproduction and the hadronic
total cross sections by means of a QCD eikonal model with a dynamical infrared
mass scale. In this model, where the dynamical gluon mass is the natural
regulator for the tree level gluon-gluon scattering, the and total cross sections are derived from the and forward
scattering amplitudes assuming vector meson dominance and the additive quark
model. We show that the validity of the cross section factorization relation
is
fulfilled depending on the Monte Carlo model used to unfold the hadronic
cross section data, and we discuss in detail the case of
data with GeV
unfolded by the Monte Carlo generators PYTHIA and PHOJET. The data seems to
favor a mild dependence with the energy of the probability () that the
photon interacts as a hadron.Comment: 16 pages, 3 figures; misprints corrected; to appear in Phys. Rev.
Light Higgs production at the Compton Collider
We have studied the production of a light Higgs boson with a mass of 120 GeV
in photon-photon collisions at a Compton collider. The event generator for the
backgrounds to a Higgs signal due to bbbar and ccbar heavy quark pair
production in polarized gamma-gamma collisions is based on a complete
next-to-leading order (NLO) perturbative QCD calculation. For J_z=0 the large
double-logarithmic corrections up to four loops are also included. It is shown
that the two-photon width of the Higgs boson can be measured with high
statistical accuracy of about 2 % for integrated gamma-gamma luminosity in the
hard part of the spectrum of 40 fb**-1. As a result the total Higgs boson width
can be calculated in a model independent way to an accuracy of about 14 %Comment: submitted to the proceedings of the International Workshop on Linear
Colliders (LCWS99) at Sitges, Spain, 28 April - 5 May 199
A Novel Electrical Method to Measure Wire Tensions for Time Projection Chambers
We present a novel electrical technique to measure the tension of wires in
multi-wire drift chambers. We create alternating electric fields by biasing
adjacent wires on both sides of a test wire with a superposition of positive
and negative DC voltages on an AC signal (). The
resulting oscillations of the wire will display a resonance at its natural
frequency, and the corresponding change of the capacitance will lead to a
measurable current. This scheme is scalable to multiple wires and therefore
enables us to precisely measure the tension of a large number of wires in a
short time. This technique can also be applied at cryogenic temperatures making
it an attractive solution for future large time-projection chambers such as the
DUNE detector. We present the concept, an example implementation and its
performance in a real-world scenario and discuss the limitations of the
sensitivity of the system in terms of voltage and wire length.Comment: 7 pages, 8 figures. Accepted by NIM
Gamma(*)Gamma(*) reaction at high energies
The energy available for gamma(*)gamma(*) physics at LEP2 is opening a new
window on the study of diffractive phenomena, both non-perturbative and
perturbative. We discuss some of the uncertainties and problems connected with
the experimental measurements and their interpretation.Comment: 6 pages, 6 figures, submitted to proceedings of the Durham Collider
Workshop, 22-26 September 199
CP--violating Chargino Contributions to the Higgs Coupling to Photon Pairs in the Decoupling Regime of Higgs Sector
In most supersymmetric theories, charginos belong to
the class of the lightest supersymmetric particles and the couplings of Higgs
bosons to charginos are in general complex so that the CP--violating chargino
contributions to the loop--induced coupling of the lightest Higgs boson to
photon pairs can be sizable even in the decoupling limit of large pseudoscalar
mass with only the lightest Higgs boson kinematically accessible at
future high energy colliders. We introduce a specific benchmark scenario of CP
violation consistent with the electric dipole moment constraints and with a
commonly accepted baryogenesis mechanism in the minimal supersymmetric Standard
Model. Based on the benchmark scenario of CP violation, we demonstrate that the
fusion of the lightest Higgs boson in linearly polarized photon--photon
collisions can allow us to confirm the existence of the CP--violating chargino
contributions {\it even in the decoupling regime of the Higgs sector} for
nearly degenerate SU(2) gaugino and higgsino mass parameters of about the
electroweak scale.Comment: 1+13 pages, 3 eps figure
Large enhancement of D -> e nu and Ds -> e nu in R Parity violating SUSY models
The purely leptonic decays D -> e nu and Ds -> e nu, for which no
experimental limits exist, are highly suppressed in the Standard Model. Mere
observation of these decays at the B factories BELLE/BaBar or forthcoming
CLEO-c would be a clear signal of physics beyond the SM. We show that R parity
violating slepton contributions can give rise to spectacular enhancements of
the decay rates, resulting in branching ratios as large as 5 x 10^-3, which
strongly motivates a search in these channels.Comment: 10 pages, 4 figure
Measurement of double beta decay of ¹⁰⁰Mo to excited states in the NEMO 3 experiment
The double beta decay of ¹⁰⁰Mo to the 0_{1}^{+} and 2_{1}^{+} excited states of ¹⁰⁰Ru is studied using the NEMO 3 data. After the analysis of 8024 h of data the half-life for the two-neutrino double beta decay of ¹⁰⁰Mo to the excited 0_{1}^{+} state is measured to be T_{1/2}^{2v} = [5.7_{-0.9}^{+1.3} (stat.) ± 0.8 (syst.)] x 10²⁰ y. The signal-to-background ratio is equal to 3. Information about energy and angular distributions of emitted electrons is also obtained. No evidence for neutrinoless double beta decay to the excited 0_{1}^{+} state has been found. The corresponding half-life limit is T_{1/2}^{0v} (0⁺→0_{1}^{+}) > 8.9 x 10²² y (at 90% C.L.). The search for the double beta decay to the 2_{1}^{+} excited state has allowed the determination of limits on the half-life for the two neutrino mode T_{1/2}^{0v} (0⁺→2_{1}^{+}) > 1.1 x 10²¹ y (at 90% C.L.) and for the neutrinoless mode T_{1/2}^{0v} (0⁺→2_{1}^{+}) > 1.6 x 10²³ y (at 90% C.L.)
Measurement of double beta decay of 100Mo to excited states in the NEMO 3 experiment
The double beta decay of 100Mo to the 0^+_1 and 2^+_1 excited states of 100Ru
is studied using the NEMO 3 data. After the analysis of 8024 h of data the
half-life for the two-neutrino double beta decay of 100Mo to the excited 0^+_1
state is measured to be T^(2nu)_1/2 = [5.7^{+1.3}_{-0.9}(stat)+/-0.8(syst)]x
10^20 y. The signal-to-background ratio is equal to 3. Information about energy
and angular distributions of emitted electrons is also obtained. No evidence
for neutrinoless double beta decay to the excited 0^+_1 state has been found.
The corresponding half-life limit is T^(0nu)_1/2(0^+ --> 0^+_1) > 8.9 x 10^22 y
(at 90% C.L.).
The search for the double beta decay to the 2^+_1 excited state has allowed
the determination of limits on the half-life for the two neutrino mode
T^(2nu)_1/2(0^+ --> 2^+_1) > 1.1 x 10^21 y (at 90% C.L.) and for the
neutrinoless mode T^(0nu)_1/2(0^+ --> 2^+_1) > 1.6 x 10^23 y (at 90% C.L.).Comment: 23 pages, 7 figures, 4 tables, submitted to Nucl. Phy
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