15 research outputs found
Top Quark Physics at the Tevatron
The discovery of the top quark in 1995, by the CDF and D0 collaborations at
the Fermilab Tevatron, marked the dawn of a new era in particle physics. Since
then, enormous efforts have been made to study the properties of this
remarkable particle, especially its mass and production cross section. In this
article, we review the status of top quark physics as studied by the two
collaborations using the p-pbar collider data at sqrt(s) = 1.8 TeV. The
combined measurement of the top quark mass, m_t = 173.8 +- 5.0 GeV/c^2, makes
it known to a fractional precision better than any other quark mass. The
production cross sections are measured as sigma (t-tbar) = 7.6 -1.5 +1.8 pb by
CDF and sigma (t-tbar) = 5.5 +- 1.8 pb by D0. Further investigations of t-tbar
decays and future prospects are briefly discussed.Comment: 119 pages, 59 figures, 17 tables Submitted to Int. J. Mod. Phys. A
Fixed some minor error
Anomaly in the K^0_S Sigma^+ photoproduction cross section off the proton at the K* threshold
The photoproduction reaction is
investigated in the energy region from threshold to \,MeV. The
differential cross section exhibits increasing forward-peaking with energy, but
only up to the threshold. Beyond, it suddenly returns to a flat
distribution with the forward cross section dropping by a factor of four. In
the total cross section a pronounced structure is observed between the
and thresholds. It is speculated whether this signals
the turnover of the reaction mechanism from t-channel exchange below the
production threshold to an s-channel mechanism associated with the formation of
a dynamically generated -hyperon intermediate state.Comment: 14 pages, 7 figure
Study of B0(s)→K0Sh+h′− decays with first observation of B0s→K0SK±π∓ and B0s→K0Sπ+π−
A search for charmless three-body decays of B 0 and B0s mesons with a K0S meson in the final state is performed using the pp collision data, corresponding to an integrated luminosity of 1.0 fb−1, collected at a centre-of-mass energy of 7 TeV recorded by the LHCb experiment. Branching fractions of the B0(s)→K0Sh+h′− decay modes (h (′) = π, K), relative to the well measured B0→K0Sπ+π− decay, are obtained. First observation of the decay modes B0s→K0SK±π∓ and B0s→K0Sπ+π− and confirmation of the decay B0→K0SK±π∓ are reported. The following relative branching fraction measurements or limits are obtained B(B0→K0SK±π∓)B(B0→K0Sπ+π−)=0.128±0.017(stat.)±0.009(syst.), B(B0→K0SK+K−)B(B0→K0Sπ+π−)=0.385±0.031(stat.)±0.023(syst.), B(B0s→K0Sπ+π−)B(B0→K0Sπ+π−)=0.29±0.06(stat.)±0.03(syst.)±0.02(fs/fd), B(B0s→K0SK±π∓)B(B0→K0Sπ+π−)=1.48±0.12(stat.)±0.08(syst.)±0.12(fs/fd)B(B0s→K0SK+K−)B(B0→K0Sπ+π−)∈[0.004;0.068]at90%CL
Analysis of the resonant components in Bs->J/\psi\pi+\pi-
The decay Bs->J/\psi\pi+\pi- can be exploited to study CP violation. A
detailed understanding of its structure is imperative in order to optimize its
usefulness. An analysis of this three-body final state is performed using a
1.0/fb sample of data produced in 7 TeV pp collisions at the LHC and collected
by the LHCb experiment. A modified Dalitz plot analysis of the final state is
performed using both the invariant mass spectra and the decay angular
distributions. The \pi+\pi- system is shown to be dominantly in an S-wave
state, and the CP-odd fraction in this Bs decay is shown to be greater than
0.977 at 95% confidence level. In addition, we report the first measurement of
the J/\psi\pi+\pi- branching fraction relative to J/\psi\phi\ of (19.79 +/-
0.47 +/- 0.52)%.Comment: 28 pages, 18 figures, updated after journal revie
Search for rare B(s)0→μ+μ-μ+μ- decays
A search for the decays Bs0→μ+μ-μ+μ- and B0→μ+μ-μ+μ- is performed using data, corresponding to an integrated luminosity of 1.0 fb-1, collected with the LHCb detector in 2011. The number of candidates observed is consistent with the expected background and, assuming phase-space models of the decays, limits on the branching fractions are set: B(Bs0→μ+μ-μ+μ-)<1.6(1.2)×10-8 and B(B0→μ+μ-μ+μ-)<6.6(5.3)×10-9 at 95% (90%) confidence level. In addition, limits are set in the context of a supersymmetric model which allows for the B(s)0 meson to decay into a scalar (S) and pseudoscalar particle (P), where S and P have masses of 2.5 GeV/c and 214.3 MeV/c, respectively, both resonances decay into μ+μ-. The branching fraction limits for these decays are B(Bs0→SP)<1.6(1.2)×10-8 and B(B0→SP)<6.3(5.1)×10-9 at 95% (90%) confidence level
Observations of and decays and searches for other and decays to final states
See paper for full list of authors - All figures and tables, along with any supplementary material and additional information, are available at this https URLInternational audienceA search is performed for the charmless three-body decays of the Λ0b and Ξ0b baryons to the final states Λh+h′−, where h(′)=π or K. The analysis is based on a data sample, corresponding to an integrated luminosity of 3fb−1 of pp collisions, collected by the LHCb experiment. The Λ0b→ΛK+π− and Λ0b→ΛK+K− decays are observed for the first time and their branching fractions and CP asymmetry parameters are measured. Evidence is seen for the Λ0b→Λπ+π− decay and limits are set on the branching fractions of Ξ0b baryon decays to the Λh+h′− final states
The two Λ(1405) poles from photoproduction data
We present results extracting the position of the two Λ(1405) poles from experimental photoproduction data measured recently at different energies in the γp → K+π0Σ0 and γp → K+π±Σ∓ reactions at Jefferson Lab. The analysis is done by means of a chiral dynamics motivated potential but with free parameters, which guarantees analyticity and unitarity in the solutions. With the best result we find the two Λ(1405) poles at about 1352 − 48i MeV and 1419 − 29i MeV