Research of Z generation
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Transcript of Research of Z generation
30/Jul/2010 1
Research of Z generation
Ken-ichiro KOIKE
30/Jul/2010 2
Contents
Ken-ichiro KOIKE
What is Z boson
Event Selection ~ Z candidates
Isolation Cut study
Z→μμ Cross Section study
To Do
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Z boson
QZ = 0, spin 1, MZ = 91.1876±0.023 GeV
mediate weak force
Discovery Gargamelle bubble chamber observed Weak Neutral Current in 1973 In May 1983, Z bozon was discovered with UA1 and UA2 experiment at
Super Proton Synchrotron(SPS)
Decay modeneutrino(νe, νμ, ντ)up-type quark(u, c)down-type quark(d, s, b)lepton(e, μ, τ)
BR = ( 20.00 ± 0.06 ) %BR = ( 15.6 ± 0.6 ) %BR = ( 11.6 ± 0.4 ) %BR = ( 3.3658 ± 0.0023 ) %
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Z Event SelectionFit Collision Event High Pt Event Z->μμ EventBest Match |Zvtx| < 150 mm Combined Opposite Charge
Match χ square < 100 Pt > 15 GeV Pt > 15, 20 GeV
Fit χ square < 100 |η| < 2.5 |η| < 2.5, 2.4
ΣPt/Pt < 0.2
80 < Mμμ < 100 GeV
Jet Background Electroweak Background Cosmic Background Z → ττ → muons
W → μν w/ second high Pt muon in a jet t-tbar decay → di muon → μ + jet di boson production
small fraction !
negligible!heavy-flavor quark → b/c hadrons → muons
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di-muon Invariant MassMass Window : 80 < M < 100 → 71 candidates of Z boson
∫Ldt = 290 nb-1Constant 20.58±3.38Mean 90.79±0.36Sigma 3.12±0.38
status (Monte Carlo)
Monte Carlo histogram is scaled to Real Data by Integrated Luminosity
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Kinematics(Pt,η,φ) of Z candidatesLeading Pt
Second Pt
Phi
Eta
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Isolation cutFit Collision Event High Pt Event Z->μμ EventBest Match |Zvtx| < 150 mm Combined Opposite Charge
Match χ square < 100 Pt > 15 GeV Pt > 15, 20 GeV
Fit χ square < 100 |η| < 2.5 |η| < 2.5, 2.4
ΣPt/Pt < 0.2
80 < Mμμ < 100 GeV
μ
Mass Window : 80 < M < 100→ 74 candidates
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~ Tag and Probe method ~
Real Data and MC show agreement within the statistical uncertainty.
∫Ldt = 290 nb-1
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Z→μμ Cross Section
LdtA
NZZ
formula for calculation of cross section
# of Z candidate
acceptance
efficiency (reconstruction, trigger)
integrated luminosity
the cross section is predicted to be 989 pb (√s=7 TeV) by Pythia Monte Carlo uncertainty is about 3%
ZN
A
trigreco
Ldt
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Z→μμ Cross Section
ZN
A
trigreco
Ldt 71 candidates 290 nb-1
reconstruction efficiency ・・・ relative efficiency technique (ID and MS)Scale Factor : 0.989±0.010(stat.)±0.038(sys.)
trigger efficiency ・・・ L1_MU0 triggerScale Factor : 0.970±0.012(stat.)±0.037(sys.)
acceptance : 45.32±0.02(stat.)%
LdtA
NZZ
572.33±0.0156(stat.)±0.053(sys.) pb-1
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less than prediction of MC 989nb-1 …
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Summary & To Do
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Summary I researched the Z boson generation.
71 candidates of Z→μμ were discovered with my event selection.
Study of Isolation Cut showed agreement between real data and MC.
Z cross section from real data was less than prediction from MC.
To Do More research with much amount of statistics
Study other physics quantities
Check the cause of disagreement of Z→μμ cross section
More and more study for myself Thank you so much.
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Back Up
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Muon Detector
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MDTRPCTGC
・・・ Barrel : |η|<1.0 End Cap : 1.0<|η|<2.4・・・ Barrel : |η|<1.05・・・ End Cap : 1.0<|η|<2.7
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Inner Detector
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PixelSCTTRT
・・・ B layer : |η|<2.5 Barrel : |η|<1.7 End Cap : 1.7<|η|<2.5・・・ Barrel : |η|<1.4 End Cap : 1.4<|η| <2.5・・・ Barrel : |η|<0.7 End Cap : 0.7<|η|<2.5
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Isolation cut
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Invariant Mass ~ Isolation cut comparison ~
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∫Ldt = 290 nb-1
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Invariant Mass ~ Isolation cut comparison ~
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