693 research outputs found
LHCb RICH Online-Monitor and Data-Quality
The LHCb experiment at the LHC (CERN) has been optimised for high precision measurements of the beauty quark sector. Its main objective is to precisely determine and over-constrain the parameters of the CKM mixing matrix, and to search for further sources of CP violation and new physics beyond the Standard Model in rare B-decays. Efficient particle identification at high purities over a wide momentum range from around 1 to ~100GeV/c is vital to many LHCb analyses. Central to the LHCb particle identification strategy are two Ring Imaging CHerenkov (RICH) detectors which use Silica Aerogel and C4F10 and CF4 gas radiators. A rigorous quality control scheme is being developed to insure that the data recorded by the RICH detector meets the stringent requirements of the physics analyses. The talk summarises the LHCb RICH online monitoring and data-quality strategy. Multiple dedicated algorithms are deployed to detect any potential issue already during data-taking ranging from integrity checks, mis-alignments to changes in the refractive determined from changes in the radii of Cherenkov rings found using a Markov Chain approach. A further key ingredient is the online monitoring of the particle ID performance using multiple exclusively reconstructed decay channels where the particle identity can be determined from kinematic constraints. In addition, any re-calibration of the detector can be performed using a dedicated express stream covering a dedicated data-taking period. The same tests are performed during the reconstruction phase of the full statistics of the recorded data to verify the quality of the data before made available for physics analyses
The LHCb RICH detectors
The LHCb experiment at the Large Hadron Collider has been optimised for high precision measurements of the charm and beauty quark sector. The different particle species produced in the high-energy collision are identified using two Ring-Imaging Cherenkov detectors
Early data from the LHCb experiment
The LHCb experiment at the Large Hadron Collider (LHC) has
been optimised for high-precision measurements of the charm and beauty sector. This talk summarised the first results obtained from the pilot run of the LHC at the end of 2009
Measurement of the B_s^0→K^+K^- lifetime relative to the B_d^0→K^+π^- lifetime
The study of B decays to charmless charged hadrons offers an opportunity to improve our understanding CP violation and to search for New Physics beyond the Standard Model. We present an analysis to make a measurement of the B_s^0→K^+K^- lifetime relative to B_d^0 lifetime which removes systematic bias introduced to the lifetime by distance of flight based selections
Measurement and Interpretation of Fermion-Pair Production at LEP energies above the Z Resonance
This paper presents DELPHI measurements and interpretations of
cross-sections, forward-backward asymmetries, and angular distributions, for
the e+e- -> ffbar process for centre-of-mass energies above the Z resonance,
from sqrt(s) ~ 130 - 207 GeV at the LEP collider. The measurements are
consistent with the predictions of the Standard Model and are used to study a
variety of models including the S-Matrix ansatz for e+e- -> ffbar scattering
and several models which include physics beyond the Standard Model: the
exchange of Z' bosons, contact interactions between fermions, the exchange of
gravitons in large extra dimensions and the exchange of sneutrino in R-parity
violating supersymmetry.Comment: 79 pages, 16 figures, Accepted by Eur. Phys. J.
Study of Leading Hadrons in Gluon and Quark Fragmentation
The study of quark jets in e+e- reactions at LEP has demonstrated that the
hadronisation process is reproduced well by the Lund string model. However, our
understanding of gluon fragmentation is less complete. In this study enriched
quark and gluon jet samples of different purities are selected in three-jet
events from hadronic decays of the Z collected by the DELPHI experiment in the
LEP runs during 1994 and 1995. The leading systems of the two kinds of jets are
defined by requiring a rapidity gap and their sum of charges is studied. An
excess of leading systems with total charge zero is found for gluon jets in all
cases, when compared to Monte Carlo Simulations with JETSET (with and without
Bose-Einstein correlations included) and ARIADNE. The corresponding leading
systems of quark jets do not exhibit such an excess. The influence of the gap
size and of the gluon purity on the effect is studied and a concentration of
the excess of neutral leading systems at low invariant masses (<~ 2 GeV/c^2) is
observed, indicating that gluon jets might have an additional hitherto
undetected fragmentation mode via a two-gluon system. This could be an
indication of a possible production of gluonic states as predicted by QCD.Comment: 19 pages, 6 figures, Accepted by Phys. Lett.
A Determination of the Centre-of-Mass Energy at LEP2 using Radiative 2-fermion Events
Using e+e- -> mu+mu-(gamma) and e+e- -> qqbar(gamma) events radiative to the
Z pole, DELPHI has determined the centre-of-mass energy, sqrt{s}, using energy
and momentum constraint methods. The results are expressed as deviations from
the nominal LEP centre-of-mass energy, measured using other techniques. The
results are found to be compatible with the LEP Energy Working Group estimates
for a combination of the 1997 to 2000 data sets.Comment: 20 pages, 6 figures, Accepted by Eur. Phys. J.
Study of Tau-pair Production in Photon-Photon Collisions at LEP and Limits on the Anomalous Electromagnetic Moments of the Tau Lepton
Tau-pair production in the process e+e- -> e+e-tau+tau- was studied using
data collected by the DELPHI experiment at LEP2 during the years 1997 - 2000.
The corresponding integrated luminosity is 650 pb^{-1}. The values of the
cross-section obtained are found to be in agreement with QED predictions.
Limits on the anomalous magnetic and electric dipole moments of the tau lepton
are deduced.Comment: 20 pages, 9 figures, Accepted by Eur. Phys. J.
Evidence for an Excess of Soft Photons in Hadronic Decays of Z^0
Soft photons inside hadronic jets converted in front of the DELPHI main
tracker (TPC) in events of qqbar disintegrations of the Z^0 were studied in the
kinematic range 0.2 < E_gamma < 1 GeV and transverse momentum with respect to
the closest jet direction p_T < 80 MeV/c. A clear excess of photons in the
experimental data as compared to the Monte Carlo predictions is observed. This
excess (uncorrected for the photon detection efficiency) is (1.17 +/- 0.06 +/-
0.27) x 10^{-3} gamma/jet in the specified kinematic region, while the expected
level of the inner hadronic bremsstrahlung (which is not included in the Monte
Carlo) is (0.340 +/- 0.001 +/- 0.038) x 10^{-3} gamma/jet. The ratio of the
excess to the predicted bremsstrahlung rate is then (3.4 +/- 0.2 +/- 0.8),
which is similar in strength to the anomalous soft photon signal observed in
fixed target experiments with hadronic beams.Comment: 37 pages, 9 figures, Accepted by Eur. Phys. J.
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