Abstract
The t t-bar charge asymmetry is measured in proton-proton collisions at a centre-of-mass energy of 8 TeV. The data, collected with the CMS experiment at the LHC, correspond to an integrated luminosity of 19.7 inverse femtobarns. Selected events contain an electron or a muon and four or more jets, where at least one jet is identified as originating from b-quark hadronization. The inclusive charge asymmetry is found to be 0.0010 +/- 0.0068 (stat) +/- 0.0037 (syst). In addition, differential charge asymmetries as a function of rapidity, transverse momentum, and invariant mass of the t t-bar system are studied. For the first time at the LHC, the measurements are also performed in a reduced fiducial phase space of top quark pair production, with an integrated result of -0.0035 +/- 0.0072 (stat) +/- 0.0031 (syst). All measurements are consistent within two standard deviations with zero asymmetry as well as with the predictions of the standard model.
Highlights
The top quark offers an excellent opportunity to search for deviations from the standard model (SM), as its large mass makes it unique among all quarks
This discrepancy has become smaller as the measurements and SM calculations [6,7] have been refined, it has generated a number of theoretical explanations invoking contributions from physics beyond the SM (BSM)
This makes the difference in the absolute values of the rapidities1 of the top quark and antiquark, | y| = | yt| − | yt|, a suitable observable to measure the ttcharge asymmetry at the LHC experiments
Summary
The top quark offers an excellent opportunity to search for deviations from the standard model (SM), as its large mass makes it unique among all quarks. At the LHC, the larger average momentum fraction of the valence quarks leads to an excess of top quarks produced in the forward and backward directions, while the top antiquarks are produced more centrally This makes the difference in the absolute values of the rapidities of the top quark and antiquark, | y| = | yt| − | yt|, a suitable observable to measure the ttcharge asymmetry at the LHC experiments. Where N+ and N− represent the number of events with positive and negative values of | y|, respectively Theoretical predictions for this observable are of order 1% in the SM [10,11], but its sensitivity to new physics makes measurements of the effect interesting even when the precision is not high enough to establish the existence of the SM charge asymmetry. An additional extrapolation to the full phase space of top quark pair production is provided as well, which allows for an easier comparison to the results of other measurements and theoretical calculations
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
