The Cross-section Measurement Of Bc Meson With J/ψπ Decays On CMS/LHC

In this thesis we used the dataset which was collected by the CMS experiment atthe LHC in2011and corresponds to an integrated luminosity of4.8fb-1to measure theBc cross sections times branching fraction of Bcâ†'J/ψπ and also the differentialproduction cross sections times branching fraction dσ/dp_T^Bc×B （Bcâ†'Jψ π）and dσ/d\y^Bc×B （Bcâ†'Jψ π）.To get the signal of Bc, we selected two oppositely charged muon to combin a J/ψcandidate, also two muons must pass the kinematic vertex fit and in the width with300MeV/c2of J/ψ mass window. Bc Candidates are formed by combining the candidateof J/ψ meson with a track, constrainted kinematic vertex fit also needed. To minimizethe uncertainties of cross-section, we optimize the selection critieria to increase thesignal to noise ratio. After all the cut selection we got383±38Bcâ†'J/ψπ signal eventsby maximum likely hood fit. Then we calculate the acceptance, trigger efficiency andselection efficiency by the data or MC. Use the total efficiency divide by fited signalevents we got the Bc cross sections times branching fraction of Bcâ†'J/ψπ which is61.00±6.17±3.71pb where the first error is statistical, the second is systematic. Weseparate the signal events into three bin of Bc PTand|y|, use the efficiency divide byfited signal events in each P/Tor|y|bin we got the Bc differential cross sections timesbranching fraction of Bcâ†'J/ψπ.From the result we can see the difference of Bc cross-section we measured with thetheoretical prediction that’s because the uncertainty of Bc production and the decaybrach ratio in the theory.