46 research outputs found
Inclusive D* Production in Two-Photon Collisions at LEP
Inclusive D^{*+-} production in two-photon collisions is studied with the L3
detector at LEP, using 683 pb^{-1} of data collected at centre-of-mass energies
from 183 to 208 GeV. Differential cross sections are determined as functions of
the transverse momentum and pseudorapidity of the D^{*+-} mesons in the
kinematic region 1 GeV < P_T < 12 GeV and |eta| < 1.4. The cross sections
sigma(e^+e^- -> e^+e^-D^{*+-}X) in this kinematical region is measured and the
sigma(e^+e^- -> e^+e^- cc{bar}X) cross section is derived. The measurements are
compared with next-to-leading order perturbative QCD calculations
Measurement of Exclusive rho+rho- Production in Mid-Virtuality Two-Photon Interactions and Study of the gamma gamma* -> rho rho Process at LEP
Exclusive rho+rho- production in two-photon collisions between a quasi-real
photon, gamma, and a mid-virtuality photon, gamma*, is studied with data
collected at LEP at centre-of-mass energies root(s)=183-209GeV with a total
integrated luminosity of 684.8pb^-1. The cross section of the gamma gamma* ->
rho+ rho- process is determined as a function of the photon virtuality, Q^2,
and the two-photon centre-of-mass energy, W_gg, in the kinematic region:
0.2GeV^2 < Q^2 <0.85GeV^2 and 1.1GeV < W_gg < 3GeV. These results, together
with previous L3 measurements of rho0 rho0 and rho+ rho- production, allow a
study of the gamma gamma* -> rho rho process over the Q^2-region 0.2GeV^2 < Q^2
< 30 GeV^2
Inclusive Lambda Production in Two-Photon Collisions at LEP
The reactions e^+e^- -> e^+e^- Lambda X and e^+e^- -> e^+e^- Lambda X are
studied using data collected at LEP with the L3 detector at centre-of-mass
energies between 189 and 209 GeV. Inclusive differential cross sections are
measured as a function of the lambda transverse momentum, p_t, and
pseudo-rapidity, eta, in the ranges 0.4 GeV < p_t < 2.5 GeV and |\eta| < 1.2.
The data are compared to Monte Carlo predictions. The differential cross
section as a function of p_t is well described by an exponential of the form A
exp (- p_t / )$
Lambda and Sigma0 Pair Production in Two-Photon Collisions at LEP
Strange baryon pair production in two-photon collisions is studied with the
L3 detector at LEP. The analysis is based on data collected at e+e-
centre-of-mass energies from 91 GeV to 208 GeV, corresponding to an integrated
luminosity of 844 pb-1. The processes gamma gamma -> Lambda Anti-lambda and
gamma gamma -> Sigma0 Anti-sigma0 are identified. Their cross sections as a
function of the gamma gamma centre-of-mass energy are measured and results are
compared to predictions of the quark-diquark model
Proton-Antiproton Pair Production in Two-Photon Collisions at LEP
The reaction e^+e^- -> e^+e^- proton antiproton is studied with the L3
detector at LEP. The analysis is based on data collected at e^+e^-
center-of-mass energies from 183 GeV to 209 GeV, corresponding to an integrated
luminosity of 667 pb^-1. The gamma gamma -> proton antiproton differential
cross section is measured in the range of the two-photon center-of-mass energy
from 2.1 GeV to 4.5 GeV. The results are compared to the predictions of the
three-quark and quark-diquark models
Study of Inclusive Strange-Baryon Production and Search for Pentaquarks in Two-Photon Collisions at LEP
Measurements of inclusive production of the Lambda, Xi- and Xi*(1530) baryons
in two-photon collisions with the L3 detector at LEP are presented. The
inclusive differential cross sections for Lambda and Xi- are measured as a
function of the baryon transverse momentum, pt, and pseudo-rapidity, eta. The
mean number of Lambda, Xi- and Xi*(1530) baryons per hadronic two-photon event
is determined in the kinematic range 0.4 GeV < pt< 2.5 GeV, |eta| < 1.2.
Overall agreement with the theoretical models and Monte Carlo predictions is
observed. A search for inclusive production of the pentaquark theta+(1540) in
two-photon collisions through the decay theta+ -> proton K0s is also presented.
No evidence for production of this state is found
Muon-Pair and Tau-Pair Production in Two-Photon Collisions at LEP
The QED processes e^+ e^- -> e^+ e^- \mu^+ \mu^- and e^+ e^- -> e^+ e^-
\tau^+ \tau^- are studied with the L3 detector at LEP using an untagged data
sample collected at centre-of-mass energies
161 GeV < sqrt{s} < 209 GeV. The tau-pairs are observed through the
associated decay of one tau into e\nu\nu and the other into \pi\pi\nu . The
cross sections are measured as a function of sqrt{s}. For muon pairs, the cross
section of the \gamma\gamma -> \mu^+\mu^- process is also measured as a
function of the two-photon centre-of-mass energy for 3 GeV < W_{\gamma\gamma} <
40 GeV. Good agreement is found between these measurements and the O(\alpha^4)
QED expectations. In addition, limits on the anomalous magnetic and electric
dipole moments of the tau lepton are extracted
Measurement of Exclusive rho^0 rho^0 Production in Mid-Virtuality Two-Photon Interactions at LEP
Exclusive rho^0 rho^0 production in two-photon collisions between a
quasi-real and a mid-virtuality photon is studied with data collected at LEP at
centre-of-mass energies 183GeV < sqrt{s} < 209GeV with a total integrated
luminosity of 684.8/pb. The cross section of the process gamma gamma* -> rho^0
rho^0 is determined as a function of the photon virtuality, q^2, and the
two-photon centre-of-mass energy, Wgg, in the kinematic region: 0.2GeV^2 < q^2
< 0.85GeV^2 and 1.1GeV < Wgg < 3GeV
Measurement of the Photon Structure Function F2gamma with the L3 Detector at LEP
The e+e- -> e+e- hadrons reaction, where one of the two electrons is detected
in a low polar-angle calorimeter, is analysed in order to measure the hadronic
photon structure function F2gamma . The full high-energy and high-luminosity
data set, collected with the L3 detector at centre-of-mass energies 189-209GeV,
corresponding to an integrated luminosity of 608/pb is used. The Q^2 range
11-34GeV^2 and the x range 0.006-0.556 are considered. The data are compared
with recent parton density functions
Measurement of Exclusive \rho^+\rho^- Production in High-Q^2 Two-Photon Collisions at LEP
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 89 GeV < \sqrt{s} < 209 GeV with a total integrated luminosity of
854.7 pb^-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, W_gg, in the kinematic region: 1.2 GeV^2 < Q^2 < 30
GeV^2 and 1.1 GeV < W_gg < 3 GeV. The \rho^+\rho^- production cross section is
found to be of the same magnitude as the cross section of the process gamma
gamma^* -> rho^0 rho^0, measured in the same kinematic region by L3, and to
have similar W_gg and Q^2 dependences