PHYS08200604017 Manimala Mitra - Homi Bhabha National Institute

Figure 3.4: Variation of production cross section of Σ ± m , Σ0 m with the mass of exotic
leptons. The blue, red and pink lines correspond to Σ − m Σ0 m , Σ+ m Σ0 m and Σ− m Σ+ m production
respectively.
given in Eqs. (B16) and (B17) with the Σ + mΣ − mh 0 coupling given in Table 3.13. It is
easy to see that the Σ + m Σ− m Z/γ coupling has terms proportional to T† 22T 22 and S † 22S 22 ,
while the Σ + m Σ− m h0 coupling depends on terms which have an off-diagonal mixing matrix
block. Since the off-diagonal mixing matrix blocks are much smaller than the diagonal
ones (as discussed before), it is not surprising that the couplings of two exotic fermions to
the Higgs particles are much smaller than to the gauge bosons. Hence the heavy exotic
fermions will be produced predominantly via the gauge boson mediated processes. We
calculate the cross-sections using the Calchep package [30].
InFig. 3.4weshowtheproductioncross-sectionforΣ − m Σ0 m (bolddottedline), Σ+ m Σ0 m
(solid line), andΣ + mΣ − m (fine dotted line), at LHC as a function of the corresponding heavy
fermion mass. It is straightforward to see that the Σ 0 m Σ0 m Z (and Σ0 m Σ0 m W± ) couplings
are absent. A very small Σ 0 m Σ0 m Z is generated through mixing from the ν0 ν 0 Z coupling.
However, this is extremely small. Hence, Σ 0 mΣ 0 m production through gauge interactions
is heavily suppressed and is not shown in Fig. 3.4. The production cross-sections of
the heavy fermions fall sharply with their mass. More precisely, σ(Σ ± mΣ ∓ m) = 112 fb,
σ(Σ + m Σ0 m ) = 206 fb and σ(Σ− m Σ0 m ) = 95 fb, for M Σ i
≃ 300 GeV. However, for M Σi ≃
600 GeV this quickly falls to σ(Σ ± m Σ∓ m ) = 6 fb, σ(Σ+ m Σ0 m ) = 13 fb, and σ(Σ− m Σ0 m ) = 4
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