39 research outputs found
Measurement of the cross-section for Z â e<sup>+</sup>e<sup>-</sup> production in pp collisions at √<span style="text-decoration:overline">s</span>=7 TeV
A measurement of the cross-section for ppâââZâââe+eâ is presented using data at sâ=7 TeV corresponding to an integrated luminosity of 0.94 fbâ1. The process is measured within the kinematic acceptance p Tâ>â20 GeV/c and 2â<âηâ<â4.5 for the daughter electrons and dielectron invariant mass in the range 60â120 GeV/c 2. The cross-section is determined to be Ï(ppâZâe+eâ)=76.0±0.8±2.0±2.6pb where the first uncertainty is statistical, the second is systematic and the third is the uncertainty in the luminosity. The measurement is performed as a function of Z rapidity and as a function of an angular variable which is closely related to the Z transverse momentum. The results are compared with previous LHCb measurements and with theoretical predictions from QCD
Study of eta-eta ' mixing from measurement of B-(s)(0) -> J/psi eta((')) decay rates
A study of B and Bs meson decays into J/Ï Î· and J/Ï Î·âČ final states is performed using a data set of proton-proton collisions at centre-of-mass energies of 7 and 8 TeV, collected by the LCHb experiment and corresponding to 3.0 fbâ1 of integrated luminosity. The decay B0 â J/Ï Î·âČ is observed for the first time. The following ratios of branching fractions are measured:
B(B0âJ/ÏηâČ)B(B0sâ J/ÏηâČ)=(2.28±0.65 (stat)±0.10 (syst)±0.13 (fs/fd))Ă10â2,B(B0â J/Ïη)B(B0sâ J/Ïη)=(1.85±0.61 (stat)±0.09 (syst)±0.11 (fs/fd))Ă10â2, where the third uncertainty is related to the present knowledge of fs/fd, the ratio between the probabilities for a b quark to form a Bs or a B0 meson. The branching fraction ratios are used to determine the parameters of η â ηâČ meson mixing. In addition, the first evidence for the decay Bs â Ï(2S)ηâČ is reported, and the relative branching fraction is measured,
B(B0sâ Ï(2S)ηâČ)B(B0sâ J/ÏηâČ)=(38.7±9.0 (stat)±1.3 (syst)±0.9(B))Ă10â2, where the third uncertainty is due to the limited knowledge of the branching fractions of J/Ï and Ï(2S) mesons
Measurement of the Z plus b-jet cross-section in pp collisions at root s=7 TeV in the forward region
The associated production of a Z boson or an off-shell photon with
a bottom quark in the forward region is studied using proton-proton collisions
at a centre-of-mass energy of . The Z bosons
are reconstructed in the
final state from muons with a transverse momentum larger than
, while two transverse momentum thresholds are
considered for jets ( and
). Both muons and jets are reconstructed in
the pseudorapidity range . The results are based on data
corresponding to 1.0{\,\mbox{fb}^{-1}} recorded in 2011 with the LHCb
detector. The measurement of the Z+b-jet cross-section is normalized to the
Z+jet cross-section. The measured cross-sections are \begin{equation*}
\sigma(\text{+b-jet}) = 295 \pm
60~(\text{stat}) \pm 51~(\text{syst}) \pm 10~(\text{lumi}) {\,\mbox{fb}}
\end{equation*} for (jet), and
\begin{equation*} \sigma(\text{+b-jet}) =
128 \pm 36~(\text{stat}) \pm 22~(\text{syst}) \pm 5~(\text{lumi}) {\,\mbox{fb}}
\end{equation*} for (jet)
Precise measurements of the properties of the B-1(5721)(0,+) and B-2*(5747)(0,+) states and observation of B-+,B-0 pi(-,+) mass structures
Invariant mass distributions of B+pi- and B0pi+ combinations are investigated
in order to study excited B mesons. The analysis is based on a data sample
corresponding to 3.0 fb-1 of pp collision data, recorded by the LHCb detector
at centre-of-mass energies of 7 and 8 TeV. Precise measurements of the masses
and widths of the B_1(5721)^(0,+) and B_2*(5747)^(0,+) states are reported.
Clear enhancements, particularly prominent at high pion transverse momentum,
are seen over background in the mass range 5850--6000 MeV in both B+pi- and
B0pi+ combinations. The structures are consistent with the presence of four
excited B mesons, labelled B_J(5840)^(0,+) and B_J(5960)^(0,+), whose masses
and widths are obtained under different hypotheses for their quantum numbers.Comment: 29 pages, 5 Figures, 8 Table