Документ взят из кэша поисковой машины. Адрес оригинального документа : http://nuclphys.sinp.msu.ru/conf/epp10/Benucci.pdf Дата изменения: Sat Sep 7 17:31:21 2013 Дата индексирования: Fri Feb 28 02:27:55 2014 Кодировка:

Lomonosov Conference on Elementary Particle Physics

Top at the

quark CMS

physics experiment

Leonardo Benucci - University of Ghent On behalf of the CMS Collaboration Moscow, August 27th, 2013


The top quark is special
Most massive elementary particle known to date Special role in many theories beyond the Standard Model Short-lived, so it decays before hadronizing. Possible to study the properties of a bare quark.



Precision tests of perturbative QCD Possible window to new physics Main background in many BSM searches.
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Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics


How to produce a top quark

~ 7 pb @Tevatron, ~ 107 pb @LHC 7 TeV, ~ 240 pb @LHC 8 TeV

2 pb @Tevatron 65 pb @LHC 7 TeV 87 pb @LHC 8 TeV

1 pb @Tevatron 5 pb @LHC 7 TeV 6 pb @LHC 8 TeV

0.3 pb @Tevatron 16 pb @LHC 7 TeV 22 pb @LHC 8 TeV

Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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How to produce a top quark

~ 7 pb @Tevatron, ~ 107 pb @LHC 7 TeV, ~ 240 pb @LHC 8 TeV

After 2011 and 2012 runs we have : ~ ~ 5,300,000 2,800,000 t-t pairs single-t

2 pb @Tevatron 65 pb @LHC 7 TeV 87 pb @LHC 8 TeV

1 pb @Tevatron 5 pb @LHC 7 TeV 6 pb @LHC 8 TeV

0.3 pb @Tevatron 16 pb @LHC 7 TeV 22 pb @LHC 8 TeV

Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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How a top quark decays

The top quark decays almost exclusively to a W boson and a b quark The W boson in turn decays hadronically (BR ~ 70%) or leptonically (BR ~ 30%)

All-jets: largest BR but largest background Semi-leptonic: large BR and manageable background Di-leptonic: small BR and small background

Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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What can be measured with the top
Measurements in Top production: Pair production cross section (tt) Single top production cross section: t-channel, s- and Wt-channel Associated production with Z/W and jets Differential cross section production asymmetries Measurements Top mass Top mass in Top properties: from final state from constraints on (tt) and S

Top mass from decay length of B mesons Wtb coupling Spin correlations

Searches for New Physics: Limits on FCNC and baryon number violation decays ...many, mony others!
Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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What can be measured with the top
Measurements in Top production: Pair production cross section (tt) Single top production cross section: t-channel, s- and Wt-channel Associated production with Z/W and jets Differential cross section Public results on: production asymmetries Measurements Top mass Top mass in Top properties: from final state from constraints on (tt) and S

https://twiki.cern.ch/twiki/bin/view/CMSPublic /PhysicsResultsTOP https://twiki.cern.ch/twiki/bin/view/CMSPublic /PhysicsResultsB2G

Top mass from decay length of B mesons Wtb coupling Spin correlations

Searches for New Physics: Limits on FCNC and baryon number violation decays ...many, mony others!
Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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What can be measured with the top
Measurements in Top production: Pair production cross section (tt) Single top production cross section: t-channel, s- and Wt-channel Associated production with Z/W and jets Differential cross section production asymmetries Measurements Top mass Top mass in Top properties: from final state from constraints on (tt) and S

Top mass from decay length of B mesons Wtb coupling Spin correlations

Searches for New Physics: Limits on FCNC and baryon number violation decays ...many, mony others!
Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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Pair-production cross-section

Phys. Lett. B 720 (2013) 83 JHEP 1305 (2013) 065

Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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Pair-production cross-section
Cross sections consistent both with theory and across channels Systematic uncertainties now comparable with statistic. Generator modeling uncertainties dominating. New Physics can be effectively constrained

(tt) now available at full NNLO (Czakon, Fiedler, Mitov arXiv:1303.6254)
Phys. Lett. B 720 (2013) 83 JHEP 1305 (2013) 065

Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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(tt) related to S and mt
Cross section dependence on s and mt
pol e

is used to constrain s and/or mt

p ol e

Pole mass determination complementary to direct top mass measurements (different systematics and theoretically well defined).

arXiv:1307.1907
Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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Differential cross-section
Enough data to make a large set of differential cross-section measurements vs.: kinematics of tЇt system top quark decay products Good agreement with tested generators Most bins are systematics limited

Eur. Phys. J. C73 (2013) 2339
Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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Top pair production with Z,W
Dilepton analysis: tt + W/Z Trilepton analysis: tt + Z

Phys. Rev. Lett. 110 (2013) 172002

Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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Single-top studies
Can directly probe the Wtb coupling and Vtb in CKM matrix Challenging, mainly due to the background from W+jets Need MVA techniques s + t-channel production observed at CDF and D0 in 2009 t-channel observed both at Tevatron and LHC Evidence for s-channel production at D0 Observation of Wt-channel production at CMS Evidence by both ATLAS and CMS 2012/2013

JHEP 12 (2012) 035
Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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Single-top studies
Ratio is sensitive to u/d content of proton

The |(j)| distribution is exploited to extract the signal simultaneously in the events with positively and negatively charged leptons
CMS-PAS-TOP-12-038
Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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Observation of Wt production
First observation of Wt production by CMS The measurement is performed selecting events with two leptons and a jet originated from a b quark A multivariate analysis based on kinematic properties is used to separate the signal from the tЇt background. very interesting production mechanism because of its interference with top quark pair production, sensitivity to new physics and role as a background to several SUSY and Higgs searches

CMS-PAS-TOP-12-040
Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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What can be measured with the top
Measurements in Top production: Pair production cross section (tt) Single top production cross section: t-channel, s- and Wt-channel Associated production with Z/W and jets Differential cross section production asymmetries Measurements Top mass Top mass in Top properties: from final state from constraints on (tt) and S

Top mass from decay length of B mesons Wtb coupling Spin correlations

Searches for New Physics: Limits on FCNC and baryon number violation decays
Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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Top quark mass
Tevatron (CDF-D0 combination) still provides the best mass measurement: 173.20 ± 0.51 ± 0.71 GeV (arXiv:1305.3929) Best single LHC measurement from CMS: ±1.06 GeV, i.e. 0.6% Best experiment-wide measurement from CMS: ±1.00 GeV Updated LHC mass combination in progress (harmonise systematic treatment)

arXiv:1307.4617

Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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Top mass from transverse decay length
Lifetime-based technique, using

First used at CDF (Phys. Rev. D75, 071102 (2007)) Linear mass dependence, Lxy/GeV = 25 - 30 m/GeV Complementary systematics to traditional measurements, e.g. minimal dependence on jet energy scale

In each event, select secondary vertex with largest Lxy the median of Lxy is used to extract m t

CMS-PAS-TOP-12-030

Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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Further Mass Measurements
Differential mass measurements, to probe e.g. color reconnections and initial/final state radiation

CMS-TOP-12-029

Top-antitop mass difference, to test CPT theorem Mass reconstructed with the Ideogram Likelihood method part of (theoretical) systematics cancel out
CMS-TOP-12-031
Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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Spin Correlations
Spins of top and anti-top are correlated in SM Short top quark lifetime ( 5 в 10-25 s) means spin information is carried on to decay products.

Measure fraction of SM-like events using template fit to () distribution fSM = 0 no correlations. fSM = 1 correlations (SM)

CMS-TOP-12-004

Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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Anomalous Couplings and CP Violation

CMS-PAS-TOP-12-025
Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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Fwd-Bkwd and Charge Asymmetries

Phys. Lett. B 717, 129 (2012)

Tevatron AFB(tt) measurements in tension with SM at 2.5 CMS AC(tt) measurements consistent with SM
Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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What can be measured with the top
Measurements in Top production: Pair production cross section (tt) Single top production cross section: t-channel, s- and Wt-channel Associated production with Z/W and jets Differential cross section production asymmetries Measurements Top mass Top mass in Top properties: from final state from constraints on (tt) and S

Top mass from decay length of B mesons Wtb coupling Spin correlations

Searches for New Physics: Limits on FCNC and baryon number violation decays
Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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Flavour Changing Neutral Currents
The tZq decay is highly suppressed in the Standard Model (BR ~10 -14) However,there are several models (R-parity-violating supersymmetric models, top-color-assisted technicolor models etc.) that predict enhancements as large as BR ~10-4 An upper limit to this process can be beneficial to constrain various models beyond SM

CMS-PAS-TOP-12-037

Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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Search for Z' resonances
A search for resonances decaying to top quark-antiquark pairs is performed using a dilepton+jets data sample Upper limits for the production of Z' tt resonances in the 750-3000 GeV range existence of a leptophobic topcolor particle Z' excluded at the 95% confidence level for MZ' < 1.3 TeV for Z' = 0.012 MZ' , and MZ' < 1.9 TeV for Z' = 0.10 MZ'

arXiv:1211.3338 [hep-ex]

Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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Baryon Number Violating Decays

CMS-B2G-12-023
Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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Summary
Very rich top physics program at CMS experiments Most analyses are only systematics limited Top Top production: Pair production cross section with O(4-6%) uncertainty. Single top t-channel cross section with O(20%) uncertainty. s- and Wt-channel production observed at 3.7 and 6 level. Associated production (tЇtV, tЇtj), differential cross section measured properties: Top mass uncertainty is currently 0.5% (0.87 GeV). Polarization, asymmetry and coupling measurements all consistent with SM Spin correlations observed Limits on FCNC and baryon number violation decays

Searches: Wide range of searches for new phenomena
Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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Summary
What is still hidden in the interplay of QCD, Electroweak and Higgs sector ? Top quark is the THE key to enter this realm

Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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Summary
What is still hidden in the interplay of QCD, Electroweak and Higgs sector ? Top quark is the THE key to enter this realm

t
Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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Backup

Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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Top mass by kinematic endpoints
A simultaneous measurement of the top-quark, W-boson, and neutrino masses based on endpoint determinations in kinematic distributions When the neutrino and W-boson masses are constrained to their worldaverage:

Eur. Phys. J. C73 (2013) 2494

When constraints are not used, the three particle masses are obtained in a simultaneous fit the method may be used to search for unknown masses in BSM physics
Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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(tt) related to S and mt
Cross section dependence on s and mt
pol e

is used to constrain s and/or mt

p ol e

Pole mass determination complementary to direct top mass measurements (different systematics and theoretically well defined).

arXiv:1307.1907
Leonardo Benucci, Top quark physics at the CMS, Lomonosov Conference on Elementary Particle Physics

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