31 research outputs found
Measurement of W+W− production in association with one jet in proton–proton collisions at sqrt(s) = 8TeV with the ATLAS detector
The production of W boson pairs in association with one jet in pp collisions at View the MathML sources=8 TeV is studied using data corresponding to an integrated luminosity of 20.3 fb−1 collected by the ATLAS detector during 2012 at the CERN Large Hadron Collider. The cross section is measured in a fiducial phase-space region defined by the presence of exactly one electron and one muon, missing transverse momentum and exactly one jet with a transverse momentum above 25 GeV and a pseudorapidity of |η|<4.5|η|<4.5. The leptons are required to have opposite electric charge and to pass transverse momentum and pseudorapidity requirements. The fiducial cross section is found to be View the MathML sourceσWWfid,1-jet=136±6(stat)±14(syst)±3(lumi) fb. In combination with a previous measurement restricted to leptonic final states with no associated jets, the fiducial cross section of WW production with zero or one jet is measured to be View the MathML sourceσWWfid,≤1-jet=511±9(stat)±26(syst)±10(lumi) fb. The ratio of fiducial cross sections in final states with one and zero jets is determined to be 0.36±0.050.36±0.05. Finally, a total cross section extrapolated from the fiducial measurement of WW production with zero or one associated jet is reported. The measurements are compared to theoretical predictions and found in good agreement
FORWARD-BACKWARD MULTIPLICITY CORRELATIONS IN PBARP-COLLISIONS AT SQUARE-ROOT S = 540 GEV
THE CPLEAR PARTICLE IDENTIFICATION DETECTOR
The CPLEAR experiment will measure CP violation parameters in the
neutral kaon system, using a low energy antiproton beam from the Low
Energy Antiproton Ring (LEAR) at CERN. One of its subdetectors, the
Particle Identification Detector (PID), makes a fast separation of pions
and kaons, which is essential for the experiment. This article describes
the design of the PID and its performance during beam tests and during
initial runs at LEAR. A pion rejection efficiency of 99.7% for the
first level trigger (after 60 ns) is found in the relevant momentum
region
Pion correlations and resonance effects in (p)over-bar-p annihilation at rest to 2 pi(+)2 pi(-)pi(0)
We study pi pi correlations in the exclusive reaction (p) over bar p –>
2 pi(+)2 pi(-)pi(0) at rest with complete reconstruction of the
kinematics for each event. Inclusive and differential distributions
properly normalized show an enhancement for small invariant masses
M++,M– of like-pion pairs. An even stronger enhancement is seen for the
double differential distributions for low pion-pair masses. The signal
is strongest when the pi(0) energy is large and much weaker when this
energy is small. Dynamical models with resonances in the final state are
confronted with the data. For the kinematic situation where the rho 3 pi
channel is important the simulation predicts a large pion correlation
for the double differential density, qualitatively explaining the
observed bahaviour. The stochastic HBT mechanism is not supported by
these findings for the exclusive annihilation reaction studied