Download prompt_double_jpsi

Analysis of prompt double jpsi
process on CMS
Wang Jian1,2 Chen Guo-ming2 Qiao Cong-feng1 Bian Jian-guo2
1. GUCAS
2. IHEP
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Motivation;
Generator;
Signals;
Selection;
Backgrounds;
Summary & future plan.
Wuhan, 2009-10-25
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Motivation
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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
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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.
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Typical Feynman diagrams of
collision at leading order
J /
Wuhan, 2009-10-25
pair production in p p
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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
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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
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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
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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
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Muon number distribution
Here I used
TrackerMuon(), only
caring events with
more than three
reconstructed muons.
Wuhan, 2009-10-25
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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
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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
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Event selection
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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 fittedsecondpair
N gen filtered
Wuhan, 2009-10-25
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Pdl distribution of jpsi candidates
Promptjpsi B2jpsi
signal
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Three muon cases: dR of two jpsi candidates
Promptjpsi B2jpsi
signal
Wuhan, 2009-10-25
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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
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Backgrounds
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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
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