4.2 Measurements Using Jet Substructure
119
Since high x F implies high energies, the fraction of qq initiated events is large for
highly boosted top quarks. Jet substructure methods are therefore the key for precise
measurements of A FB at the LHC. A first measurement of the linearised version of
A
(1)
FB , which approximates the full asymmetry within a few percent, has been carried
out by CMS using 36 fb
−1 of 13 TeV data [671]. Events are classified into t tagged,
W tagged and fully resolved tt events, using the soft drop jet mass and τ 32 . The
measurement of A
(1)
FB is done by a template fit to a triple-differential distribution in
the reconstructed value of x F , the mass of the tt system and the top quark scattering
angle in the centre-of-mass frame. The highest sensitivity to qq initiated tt production is observed in t tagged events, as expected. The result of the measurement
is A
(1)
FB = 0.048
+0.095
−0.087 (stat)
+0.020
−0.029 (syst), which is less precise than the Tevatron combination [665], but is dominated by the statistical uncertainty and can be improved
with future measurements. This measurement also places stringent constraints on
top quark anomalous chromoelectric and chromomagnetic dipole moments, which
would modify the production of the tt system.
119
Since high x F implies high energies, the fraction of qq initiated events is large for
highly boosted top quarks. Jet substructure methods are therefore the key for precise
measurements of A FB at the LHC. A first measurement of the linearised version of
A
(1)
FB , which approximates the full asymmetry within a few percent, has been carried
out by CMS using 36 fb
−1 of 13 TeV data [671]. Events are classified into t tagged,
W tagged and fully resolved tt events, using the soft drop jet mass and τ 32 . The
measurement of A
(1)
FB is done by a template fit to a triple-differential distribution in
the reconstructed value of x F , the mass of the tt system and the top quark scattering
angle in the centre-of-mass frame. The highest sensitivity to qq initiated tt production is observed in t tagged events, as expected. The result of the measurement
is A
(1)
FB = 0.048
+0.095
−0.087 (stat)
+0.020
−0.029 (syst), which is less precise than the Tevatron combination [665], but is dominated by the statistical uncertainty and can be improved
with future measurements. This measurement also places stringent constraints on
top quark anomalous chromoelectric and chromomagnetic dipole moments, which
would modify the production of the tt system.