Asymmetry in top-antitop production in proton-antiproton collisions

Regina Demina, University of Rochester02/08/2012

Forward-backward asymmetry in top-antitop production in proton-antiproton collisions

Asymmetry in top-antitop production

Reconstruction levelGenerator levelIn early 80s asymmetry observed in e+e-m+m- at sqrt(s)=34.6 GeV0 and Dy200GeVEW precision (Zbb, GZ, shad) MG>500GeVDirect dijet resonancesLHC ppG2 jetsAtlas MG>2TeV (G/M1.7TeV

Predicted asymmetries: axigluons01/18/2012Regina Demina, University of Rochester20

t-channel: Z, W01/18/2012Regina Demina, University of Rochester21

Direct constraint : from like-sign tops at LHC

Introduce SU(2)X that places (u t)R in the same doubletW carries top number thus suppressing like-sign top production at LHCPredicted asymmetry due to W ~30%More forward than SM or s-channel productionAs a result observed asymmetry reduced to 20%Least constrained by other experimental data, asymmetries in agreement with observedTest this hypothesis by using top polarizationTop quark asymmetry at LHC01/18/2012Regina Demina, University of Rochester222 problems compared to Tevatron:Large fraction of top pairs (~90%) are produced in gluon fusionDirection of quark (vs antiquark) is determined from the boost with ~70% accuracy

ConclusionsUsing 5.4 fb-1 of data D0 measured asymmetry in top-antitop production

Asymmetry in leptons from top decay is

Presently D0 has recorded 10.56 fb-1Combination with CDFGetting more clever in increasing the statSoon LHC will have enough qqbarttbar events to probe the asymmetries as well

01/18/201223Regina Demina, University of Rochester

Its a lovely mystery!Systematics on A01/18/2012Regina Demina, University of Rochester24

Systematics on Al01/18/2012Regina Demina, University of Rochester25