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Highlights from Top Quark Physics. Suyong Choi Korea University. Introduction Measurement of Production C ross S ections Properties of the Top Quark Summary and Outlook. Contents. CDF. D Ø. CDF. D Ø. Top Quark. Run 2 results. Top Mass Distributions from 1995 observation paper. - PowerPoint PPT Presentation
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1
Highlights from Top Quark PhysicsSuyong ChoiKorea University
2Contents
• Introduction• Measurement of Production Cross Sections• Properties of the Top Quark• Summary and Outlook
3Top Quark
CDF DØ
Top Mass Distributions from 1995 observation paper
CDF DØ
Run 2 results
4Success of the SM
5The Top Quark
• Top quark is special• Most massive• Interaction only within 3rd generation• top-Higgs coupling ~ 1
• Boundary between metastability and stability
6LHC and Experi-ments
5 fb-1 @ 7 TeV20 fb-1 @ 8 TeV
7
Physics with Top Quarks
• Properties• Mass• Decay width• Spin• Coupling
• Cross section measure-ments• Production and decays
8
Cross Sec-tions at Teva-tron and LHC
• Higher cross sectionand higher luminosity at LHC• Top quark factory• Rare processes with top
quarks• New physics with top quarks
• Tevatron and LHC are complementary
9
PRODUCTION
10 Pair Production
• Strongly produced
• Contribution of and changes as
Pair production diagams
11 channels
Multijet
e+jets
mu+jets
Dilepton:ee, e,
tau+X
• per lepton flavor• Multijet – Highest statistics, but large backgrounds and combinatorics• Lepton+jets – Highest statistics and usually yields best measurement • Dilepton – Smaller statistics but clean, less combinatoric, solving for 2 neutrino
momenta not trivial
Lepton+jets
12
Pair Production Cross Section
• Experimental error comparable to theory error• QCD explains well the inclusive pair production
13
Lepton Forward-Backward Asymmetry
• Lepton asymmetry reflects• Asymmetry in production• Polarization of : vs
• SM predicts small asymmetry in production and no polar-ization
14Lepton AFB in
Channel LuminosityCDF Lepton+jets 9.4 fb-1
D0 Lepton+jets 9.7 fb-1
D0 Dilepton 9.7 fb-1
SM prediction @ NLO:
15
Single Top Produc-tion
• Electroweak production• Cross section of the same
order as pair production
• Sensitive probe of withoutthe assumption of 3 generationof quarks
W associated
s and t channel
16
Single Top Production t-channel
17
Observation of Wt Single Top Production
Signal Region Control Region
𝜎 (𝑝𝑝→𝑊𝑡 )=23.4−5.4+5.5 𝑝𝑏 significance
18Measurement of
• From single top quark production cross section, we can measure directly without assuming 3 generation of quarks
• Current best direct measurement:
19
PROPERTIES
20Mass of Top Quark• Tevatron: GeV – 0.5% accuracy
21
Mass Difference of and
• CPT violated if • and distinguished by electric charged of lepton
Δ𝑚𝑡=−272±196 (𝑠𝑡𝑎𝑡 )±122(𝑠𝑦𝑠𝑡)
22
Decay Width of Top Quark
• In SM, top quark width at NLO is
• 1.29 GeV/c2
• Lifetime of
• Decay width reflected in reconstructed mass distribution
• CDF measures
23
Electric Charge of Top Quark
• B-jet charge calculatedfrom tracks associatedwith b-jet
24
W Polarization from Top
• W from top decays are either left-handed or longitudinal
25Spin Correlation
• and the spins of top quarks are correlated• Due to , spin state of top at pro-
duction reflected in decay prod-ucts
• Lepton is the most sensitive probe of top spin polarization
• Tevatron and LHC has different contributions of and
• ATLAS observed spin correla-tions at 5.1 s.d.
𝑓 𝑆𝑀=1.30±0.14 (𝑠𝑡𝑎𝑡 )−0.22+0.27 (𝑠𝑦𝑠𝑡)
26
Top Coupling with Vec-tor Bosons with and
27 Production
• Major background to
• Number of b-tagged jets distribution
28
Summary and Out-look
• Approaching 20 years of rich physics program at hadron colliders with top quark events
• Top quark production and properties consistent with SM
• Many measurements systematics limited. What can you do with millions of top quark events?
29Introduction
• When was discovered in 1977, it was considered as a bound state of quarks. Hence extra quark was thought to exist.
• It took a long time until top quark was discovered in 1995 by CDF and D-Zero experiments using Fermilab Tevatron accelerators
• Being the most massive quark, it may hold the key.
• With the luminosity and energy reach of the LHC at CERN, top quarks can be studied with unprecedented precision.• 1.96 TeV → 8 TeV
30
Strong Coupling Constant
• is a function of and
31
SEARCHES WITH TOP QUARKS
32
Search for Reso-nances Decaying into
33Search for FCNC
Anomalous Single Top
𝑔𝑞→𝑡Search for
𝐵 (𝑡→𝑍𝑞)<0.0021@95% 𝐶𝐿
34Search for
• Top-Higgs coupling almost 1• Consistent with backgrounds• Cross section limits at