Single production of leptoquarks at the Fermilab Tevatron

Abstract

We study single production of first generation leptoquarks in association with e Ϯ at the Fermilab Tevatron. We focus our attention on final states exhibiting an e ϩ e Ϫ pair and jets, and perform a detailed analysis of the signal and background. The single leptoquark production cross section depends on the leptoquark Yukawa coupling to lepton-quark pairs and we show that the study of this mode can extend considerably the leptoquark search for a large range of these couplings. In fact, for Yukawa couplings of electromagnetic strength, the combined results of the Tevatron experiments can exclude the existence of leptoquarks with masses up to 260-285 ͑370-425͒ GeV at the run I ͑run II͒, depending on their type.

Spin analysis ofs-channel diphoton resonances at the LHC

“…2 is of higher order in α s and, as discussed in the next section, for the values of the γγ invariant mass M in the TeV range of interest here, its contribution turns out to be negligible, as earlier noticed also in Ref. [29]. Using Feynman rules for graviton exchange [20,30], the z-even angular dependencies needed in (5) can be written as [31][32][33]:…”

Cornering scalar leptoquarks at LHC

“…Note, however, that the sizeable Yukawa couplings of the leptoquarks with the SM fermions could influence pair production as we demonstrate later on. This regime would also make single leptoquark production very relevant at hadron colliders [4][5][6][7][8][9]. Again, existing experimental studies do not address this part of parameter space.…”

“…It can be substantially influenced by the presence of relatively large Yukawa couplings of leptoquarks to the SM fermions. Moreover, if these couplings are taken to be large one also needs to take into consideration a single leptoquark production [4][5][6][7][8][9] and a t-channel leptoquark pair production.…”

A new two Higgs doublet model

“…However, because of the dominance of the invisible decay mode, it will be very difficult to observe a signal at the LHC in the usual production and decay channels such as qqh → qqW W , qqh → qqτ τ , h → γγ, h → ZZ → 4l, tth (with h → bb) and h → W W → lνlνl [13]. However, a signal with such an invisible decay mode of the Higgs (as in our model) can be easily observed at the LHC through the weak boson fusion processes, qq → qqW + W − → qqH and qq → qqZZ → qqH [14] if appropriate trigger could be designed for the ATLAS and CMS detector. For example, with only 10f b −1 of data at the LHC, such a signal can be observed at the 95 percent CL with an invisible branching ratio of 31 percent or less for a Higgs mass of upto 400 GeV [14].…”

“…However, a signal with such an invisible decay mode of the Higgs (as in our model) can be easily observed at the LHC through the weak boson fusion processes, qq → qqW + W − → qqH and qq → qqZZ → qqH [14] if appropriate trigger could be designed for the ATLAS and CMS detector. For example, with only 10f b −1 of data at the LHC, such a signal can be observed at the 95 percent CL with an invisible branching ratio of 31 percent or less for a Higgs mass of upto 400 GeV [14]. Thus our model can be easily tested at the LHC for a large region of the Higgs mass.…”