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

Overview Modified ttg interaction Lagrangian 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 19/09 2006, Durham Paul Dervan, The University of Liverpool

Overview … Solid line is SM. Top pair invariant mass distribution Solid line is SM. Different dot/dash lines are for different values of kappa 19/09 2006, Durham Paul Dervan, The University of Liverpool

Overview … Solid line is SM. Top pt distribution Solid line is SM. Different dot/dash lines are for different values of kappa 19/09 2006, Durham Paul Dervan, The University of Liverpool

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 19/09 2006, Durham Paul Dervan, The University of Liverpool

Break down of the sample 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 19/09 2006, Durham Paul Dervan, The University of Liverpool

Event Selection Event selection 4304 events selected (3%) 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%) 19/09 2006, Durham Paul Dervan, The University of Liverpool

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 1628 events selected as e events 1360 True e events (83.5%) 10 True μ events (0.6%) 258 True τ events (15.8%) 2191 events selected as e events 74 True e events (3.4%) 1794 True μ events (81.9%) 323 True τ events (14.7%) 19/09 2006, Durham Paul Dervan, The University of Liverpool

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. 19/09 2006, Durham Paul Dervan, The University of Liverpool

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) j1 j2 b-jet t Red: Correct Jet Assignment Green: Wrong Jet Assignment 19/09 2006, Durham Paul Dervan, The University of Liverpool

j2 j1 b-jet 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 j1 j2 b-jet t Green: Wrong W Yellow: Wrong b 19/09 2006, Durham Paul Dervan, The University of Liverpool

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. 19/09 2006, Durham Paul Dervan, The University of Liverpool

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) 19/09 2006, Durham Paul Dervan, The University of Liverpool

Top pair invariant mass Red: Reconstructed Black: Truth 19/09 2006, Durham Paul Dervan, The University of Liverpool

One possible thing to look for is anomalous chromo-magnetic coupling 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 19/09 2006, Durham Paul Dervan, The University of Liverpool