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Transcript
Analysis of prompt double jpsi process on CMS Wang Jian1,2 Chen Guo-ming2 Qiao Cong-feng1 Bian Jian-guo2 1. GUCAS 2. IHEP Motivation; Generator; Signals; Selection; Backgrounds; Summary & future plan. Wuhan, 2009-10-25 2 Motivation NRQCD has become a basic theory to parameterize non-perturbative contributions in heavy quarkonium production and decays by color-singlet(CS) and color-octet(CO) matrix elements, and the color-octet mechanism is a central essence of NRQCD. However, color-octet mechanism is still a debatable issue in the theory up to now, and to investigate charmonium production mechanism is now still an urgent and important task in the study of quarkonium physics. Wuhan, 2009-10-25 3 In this research, I try to measure the differential cross-section of 2 jpsi events from 2 gluons directly, and evaluate the contribution of of coloroctet mechanism as accurate as possible. Final particle distributions of color-singlet and color-octet are not same, leading to the reconstruction efficiencies are different. The final particles are 4 muons, which are suitable to be detected on CMS. Wuhan, 2009-10-25 4 Typical Feynman diagrams of collision at leading order J / Wuhan, 2009-10-25 pair production in p p 5 I made a generator including both color-singlet and color-octet models with the results of arXiv:0903.0954 (Qiao Cong-feng, Sun Li-ping, Sun Peng). The generator is on the basis of FDC system(arXiv: hep-ph/0407058), and the generator could generate events in color-singlet and –octet scheme, respectively. The generator would create an LHE document. I embedded the LHE document into CMSSW to do analysis works. Up to now, the generator is only used by me, so I have no competitor on this process. Wuhan, 2009-10-25 6 Muon Pt of color-singlet model would decrease more rapidly than color-octet model, so does Jpsi Pt. So the reconstructed event number of color-singlet model would be great less than that of Wuhan, color-octet. 2009-10-25 7 Signals If set the down limit of Pt of double jpsi at 5GeV, because if Pt of jpsi was lower than 5GeV, the c quark fragmentation is not appropriate. cross-section: 2.25pb(10 TeV, color-singlet and coloroctet together). This result has included branching ratio of jpsi to mumu:5.94% for each jpsi. For the cross-section is so small, Tevatron could not generate enough events to be detected. So LHC is the only collider than could generate enough events to do measurements on this process. Three kinds of background events: B2jpsi, prompt jpsi, QCD background Wuhan, 2009-10-25 8 For final particles are all muons, so muon identification is great important for analysis of this process. Muon identification is the advantage of CMS. TrackerMuon has high reconstruction high efficiency with high mis-identification rate. GlobalMuon’s efficiency is low but is difficult to be mis-identified. Wuhan, 2009-10-25 9 Muon number distribution Here I used TrackerMuon(), only caring events with more than three reconstructed muons. Wuhan, 2009-10-25 10 CMSSW_3_1_1, 10 TeV Signals 100000 events Preselection HLT_Mu5 24575 (3 muons) 14525 HLT_Doubl 14850 eMu0 HLT_Doubl 11425 eMu3 HLT_L1Dou 22800 bleMuOpen 9549 (>=4 muons) 5825 6750 5450 Pre-selection: dimuon with different charge, Pt >0.7, |eta|<2.5, invariant mass (3.0, 3.2) 9024 Wuhan, 2009-10-25 11 Pt distribution of 2 jpsi from MCTruth We could see that pt of 2jpsi are also equal to each other. So I just need to take Pt of one jpsi as base of differential crosssection measurement. Wuhan, 2009-10-25 12 Event selection Select the first good jpsi; Select the second muon pair or muon + track; Cut on doule muon pair or muon pair and muon + track; Fit the mass distribution of the second particle pair in different bins: Four muon cases: (5,7,9,11,15,25); Three muon cases: (5,6,7,8,9,11,25); Bining with Pt of the first good jpsi. Calculate efficiencies: N fittedsecondpair N gen filtered Wuhan, 2009-10-25 13 Pdl distribution of jpsi candidates Promptjpsi B2jpsi signal Wuhan, 2009-10-25 14 Three muon cases: dR of two jpsi candidates Promptjpsi B2jpsi signal Wuhan, 2009-10-25 15 Selection First good jpsi: mass window (3.0,3.2), vertex fitting: normalizedchisquare<4; dR of two muons <1.5; pdl<0.005; nhit of each muon >=11; Second jpsi: vertex fitting: normalizedchisquare<4; dR of two muons <1.5; pdl<0.005; nhit of each muon >=11; Four muon cases: dR of two jpsi candidates (3.03,3.18); the first muons of first jpsi and second jpsi >isGlobalMuon(); Three muon cases: dR of two jpsi candidates (2.7,3.4); the first muon of second jpsi ->isGlobalMuon(). Wuhan, 2009-10-25 16 Backgrounds B2jpsi: 9.6 million – 90/pb; prompt jpsi: 10.9 million – 10/pb; QCD: 10.2 million – 0.009/pb. Four mu case: only 1 prompt jpsi events, 1 B2jpsi events, no QCD event left with the above cuts; Three mu case: only a few events. Wuhan, 2009-10-25 17 Wuhan, 2009-10-25 18 Wuhan, 2009-10-25 19