Off resonance background effects in

Abstract

The top quark Yukawa coupling to the intermediate mass Higgs boson can be determined in the reaction e + e − → ttH that, after taking into account decays, will be detected at the International Linear Collider through reactions with 8 particles in the final state. Such 2 → 8 reactions receive contributions from tens thousands of Feynman diagrams, already in the lowest order of Standard Model, most of which comprise background to resonant associated production and decay of the top quark pair and Higgs boson. We illustrate the background effects by comparing cross sections of three reactions, which represent different detection channels of e + e − → ttH, calculated with the complete sets of the lowest order Feynman diagrams with the corresponding signal cross sections calculated with the diagrams of associated production and decay of off mass shell top quark pair and Higgs boson only. The comparison that is performed with different selections of cuts shows that the background effects are sizeable, but they can be reduced by appropriate choice of cuts.

Secondary lepton distributions as a probe of the top-Higgs coupling at the LHC

“…Cuts (3.3)-(3.6) should allow to identify the secondary W bosons, the top quarks and the higgs boson. They were used before in the context of the associated production of the top quark pair and higgs boson in e + e − collisions at the LC [31,32]. For the sake of illustration, the tth couplings of (2.1) are assigned the following values: f = 1, 0 and f ′ = 0, ±1 and the differential distributions of the final state muon, generally referred to as lepton, of reaction (3.1) are computed, first with the 56 signal Feynman diagrams of the associated production of the top quark pair and higgs boson and then with the complete set of 67 300 Feynman diagrams, as discussed in section 1.…”

Probing the top-Higgs coupling through the secondary lepton distributions in the associated production of the top-quark pair and Higgs boson at the LHC

“…[16][17][18], the dominant contribution to the cross section comes from the phase space region, where both the t-quark and thet-quark are close to their mass shells and hence the off-shell spinors u and v should satisfy the following approximate equations:…”

“…This is why in the past few years the associated production of the top-quark a e-mail: karol.kolodziej@us.edu.pl b e-mail: aleksandra.slapik@gmail.com pair and Higgs boson has invoked quite some interest also from the theoretical side; see, e.g., [16][17][18][19][20][21][22][23][24][25]. It was shown in Ref.…”

Measuring the Higgs boson self-coupling at high energye+e−colliders

“…The HELAC-PHEGAS code compiled successfully, but failed to run with an error in an underlying basic linux library. Another program which may be able to handle a process such as e + e − → ννbb4j is carlomat [63], which, however, is not publically available yet.…”