PHYS08200604017 Manimala Mitra - Homi Bhabha National Institute

heavy fermions Σ ± → l ± h 0 and Σ 0 → l ± H ∓ , (ii) from the decays of W → l¯ν. The charged
leptons released from the Σ ±/0 decays are different from those from W ± in two respects.
Firstly, the former carry the information on the flavor structure of the model as discussed
in the previous sections, while the latter do not. Secondly, since they come from decays
of the heavier Σ ±/0 , they are expected to be harder than the ones from W ± decays. We
refer to the charged leptons from the Σ ±/0 decays as l and the ones from W ± decays as
l ′ . The notation OSD stands for opposite sign dileptons from Σ ±/0 decays, while OSD ′
stands for opposite sign dileptons from W ± decays. When we have one charged lepton
from Σ ±/0 decay and an opposite sign charged lepton from W ± decay, then it is denoted
as OSD(l+l ′ ) and so on.
While we provide an exhaustive list of channels for the Σ + Σ − decay mode in Table
3.8, not all of them can be effectively used at the LHC. We will highlight below a few of
these channels which appear to be particularly interesting.
• One of the main decay channels of Σ ± is Σ ± → l ± h 0 . The h 0 with mass of 40/70
GeV, then decays subsequently to b¯b pairs giving rise to a final state signal of a pair
of opposite sign dileptons (OSD) + 4 b-jets.
Σ + Σ − → l + l − h 0 h 0 → l + l − b¯bb¯b → 4b+OSD.
We have seen from Table 3.2 that the branching ratio for Σ ± → l ± A 0 is also
comparable. This will also produce the same collider signature of 4b + OSD for
140 GeV A 0 mass . The only observable difference will be that the b-jets produced
from the A 0 decay will be harder as A 0 is much more massive than h 0 . Here and
everywhere else in this section, we will ignore the information on the hardness of the
b-jets and present the sum of the cross-sections with h 0 and A 0 in the intermediate
state. Weshouldalsostressthatwhilewewriteonlyh 0 explicitlyintheintermediate
channels in the Tables, the cross-sections given in the final column always also
include A 0 as well as h 0 . One finds that the effective cross-section for this channel is
35.84 fb for 40 GeV M h 0, which is rather high. For M h 0=70 GeV, the cross section
differs very small, as can be seen from Table 3.12. The OSD released are expected
to be hard, as they come from the decay of the massive fermions.
Instead of decaying into b¯b pair, the h 0 s could decay into τ¯τ. If one of the h 0 decays
into b¯b and the other into τ¯τ, we will get
Σ + Σ − → l + l − h 0 h 0 → l + l − b¯bτ¯τ → 2b+OSD+2τ.
This has an effective cross-section of 3.67 fb. A third possibility exists where both
the h 0 decay into τ¯τ pairs. The effective cross-section for this channel is small as
can be seen from the Table 3.8, and will get smaller once the τ detection efficiencies
are folded.
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