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The Top Chromo-magnetic Moment

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The Top Chromo-magnetic Moment

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  1. The Top Chromo-magnetic Moment Paul Dervan The University of Liverpool Overview of the theory Event Selection Summary ATLAS UK Physics Meeting, Durham 18th-13th September 2006

  2. Overview • Top is the most massive particle – a likely place to find new physics • Modified ttg interaction Lagrangian • Kappa, Chromo-magnetic moment (CP conserving) • Kappa tilda, Chromo-electric moment (CP violating), set to 0 References: • SLAC-PUB-7153 • Phys.Rev.D52:6264-6270, 1995 Paul Dervan, The University of Liverpool

  3. Overview … • Top pair invariant mass distribution • Solid line is SM. • Different dot/dash lines are for different values of kappa Paul Dervan, The University of Liverpool

  4. Overview … • Top pt distribution • Solid line is SM. • Different dot/dash lines are for different values of kappa Paul Dervan, The University of Liverpool

  5. Event Type In order to get the top pt distribution and the top pair invariant mass distribution • Need to fully reconstruct the top pair event • Should use the lepton + Jets Channel • tt  WbWb  jjblvb Paul Dervan, The University of Liverpool

  6. Data Sample • Data Sample • CSC 11.0.41 Nikhef Ntuple (Thanks to the Nikhef people) • 147000 non hadronic events • Break down of the sample • 113136 Lepton + Jets (77%) • 32273 Leptonic (22%) • 0 Hadronic (0%) • 1591 Other (1%) • 33% Electrons • 33% Muons • 33% Tau Paul Dervan, The University of Liverpool

  7. Event Selection • Event selection • 1 high pt lepton (pt > 20 GeV ||<2.5) • Missing Energy (Et miss > 20 GeV) • At least 4 Jets (pt > 40 GeV ||<2.5) (0.4 Cone) • At least 2 Jets must be tagged as b-jets (weight > 4.5) 4304 events selected (3%) Paul Dervan, The University of Liverpool

  8. Event Selection… • 4304 events selected • 3819 True Lepton + Jets (88.7%) • 456 True Leptonic (10.6%) • 29 Other (0.7%) Of the true Lepton +Jet events 2191 events selected as e events • 74 True e events (3.4%) • 1794 True μ events (81.9%) • 323 True τ events (14.7%) 1628 events selected as e events • 1360 True e events (83.5%) • 10 True μ events (0.6%) • 258 True τ events (15.8%) Paul Dervan, The University of Liverpool

  9. Event Reconstruction: Hadronic Side Hadronic Side: t  Wb  jjb • Combine all light jets to try and reconstruct the W • Pick the combination with an inv. mass closest to the W • Select the event if the reconstructed inv. mass is within 20 GeV of Mw • Do a chi2 minimisation on the jets constrained to the W mass (JES) • The combine the b jets to the W to form the top • Pick the combination with an inv. mass closest to the top. Paul Dervan, The University of Liverpool

  10. j2 j1 b-jet t jj invariant mass reconstruction • Hadronic side • W from light jet pair with closest invariant mass to MW • Require |MW-Mjj|<20 GeV • (no jet energy scale correction) Red: Correct Jet Assignment Green: Wrong Jet Assignment Paul Dervan, The University of Liverpool

  11. j2 j1 b-jet t jjb invarient mass • Hadronic side • Assign a b-jet to the W to reconstruct Mjjb • Take the b-jet that gives Mjjb closest to Mtop Green: Wrong W Yellow: Wrong b Paul Dervan, The University of Liverpool

  12. Event Reconstruction: Leptonic Side Leptonic Side: t  Wb  lvb • Assign missing px and py to the neutrino • Constrain Mlv to MW and solve for pz of the neutrino • Combine the reconstructed W with the remaining b jets • Pick the combination with an inv. mass closest to the top. Paul Dervan, The University of Liverpool

  13. lvb invarient mass • Leptonic side • Need to reconstruct the neutrino pz • Et miss = Et neutrino • mW = mlv Get two solutions Combine with b-jet (best invariant mt) Paul Dervan, The University of Liverpool

  14. Top pair invariant mass Red: Reconstructed Black: Truth Paul Dervan, The University of Liverpool

  15. Summary • Top is the most massive particle – likely place to look for new physics • One possible thing to look for is anomalous chromo-magnetic coupling • Need the pt distribution of the top and the top pair invariant mass dist. • So need to fully reconstruct the top events • Started to reconstruct Lepton + Jets events • Need to look into backgrounds etc…. • Need a lot of work on the theory side to get the distributions to fit the distributions too Paul Dervan, The University of Liverpool