Exclusive rho rho production in two-photon collisions involving a single highly virtual photon is studied with data collected at LEP at centre-of-mass energies 89GeV < \sqrt{s} < 209GeV with a total ...integrated luminosity of 854.7pb^-1 The cross section of the process gamma gamma^* -> rho rho is determined as a function of the photon virtuality, Q^2 and the two-photon centre-of-mass energy, Wgg, in the kinematic region: 1.2GeV^2 < Q^2 < 30GeV^2 and 1.1GeV < Wgg < 3GeV.
Design and construction of the prototype synchrotron radiation detector Anderhub, H; Bates, J.R; Bätzner, D ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2002, Letnik:
491, Številka:
1-2
Journal Article
Recenzirano
Odprti dostop
The Prototype Synchrotron Radiation Detector (PSRD) is a small-scale experiment designed to measure the rate of low-energy charged particles and photons in near the Earth's orbit. It is a precursor ...to the Synchrotron Radiation Detector (SRD), a proposed addition to the upgraded version of the Alpha Magnetic Spectrometer (AMS-02).
The SRD will use the Earth's magnetic field to identify the charge sign of electrons and positrons with energies above 1TeV by detecting the synchrotron radiation they emit in this field. The differential energy spectrum of these particles is astrophysically interesting and not well covered by the remaining components of AMS-02. Precise measurements of this spectrum offer the possibility to gain information on the acceleration mechanism and characteristics of all cosmic rays in our galactic neighbourhood. The SRD will discriminate against protons as they radiate only weakly.
Both the number and energy of the synchrotron photons that the SRD needs to detect are small. The identification is complicated by the presence of a large particle and photon background. Existing measurements of these backgrounds are insufficient for the construction of the large-scale SRD, so a measurement in space was indispensable.
The PSRD was designed to fly as a Space Shuttle secondary payload, within the Shuttle Small Payloads Project. The flight on board the Space Shuttle Endeavour took place from 5 to 17 December 2001.
The scientific goal, hardware and the flight of the PSRD are described in this report.
Using data collected with the L3 detector at LEP from 1992 to 1995 on the Z peak, we determine the branching fractions of the τ lepton into one, three and five charged particles to be: ...B(τ→(1-prong))=85.274±0.105±0.073%,B(τ→(3-prong))=14.556±0.105±0.076%,B(τ→(5-prong))=0.170±0.022±0.026%. The first uncertainties are statistical and the second systematic. The accuracy of these measurements alone is similar to that of the current world average.
The measurements of hadron and lepton-pair production cross sections and lepton-pair forward–backward asymmetries performed with the L3 detector at centre-of-mass energies between 130 GeV and 172 GeV ...are used to search for new physics phenomena. New physics effects involving four fermion vertices – contact interactions – are looked for in all channels. For hadron production the exchange of virtual leptoquarks and scalar quarks is studied. No evidence for deviations from the Standard Model expectations is found. Lower limits on the scale
Λ of contact interactions in the range 1.2–7.1 TeV are obtained at the 95% confidence level for various models. Upper limits on the coupling strengths of leptoquarks and scalar quarks are derived.
The coupling of the Z boson to quarks is studied in a sample of about 3.5 million hadronic Z decays collected by the L3 experiment at LEP from 1991 to 1995. The forward–backward quark charge ...asymmetry is measured by means of a jet charge technique. From the measured asymmetries, the effective weak mixing angle is determined to be
sin
2
θ
W
=0.2327±0.0012(stat.)±0.0013(syst.)
.
The total and differential cross sections of the process e
+e
−→
nγ with
n≥2 are measured using data collected by the L3 experiment at centre-of-mass energies of
s
=183
and
189
GeV
. The results are ...in agreement with the Standard Model expectations. Limits are set on deviations from QED, contact interaction cut-off parameters and masses of excited electrons.
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