46 research outputs found
Dilepton and Four-Lepton Signals at the LHC in the Littlest Higgs Model with T-parity Violation
In the presence of the T-parity violating Wess-Zumino-Witten (WZW) anomaly
term, the otherwise stable heavy photon A_H in the Littlest Higgs model with
T-parity (LHT) decays to either Standard Model (SM) gauge boson pairs, or to SM
fermions via loop diagrams. We make a detailed study of the collider signatures
where the A_H can be reconstructed from invariant mass peaks in the opposite
sign same flavor dilepton or the four-lepton channels. This enables us to
obtain information about the fundamental symmetry breaking scale f in the LHT
and thereby the low-lying mass spectrum of the theory. In addition, indication
of the presence of the WZW term gives us hints of the possible UV completion of
the LHT via strong dynamics. The crucial observation is that the sum of all
production processes of heavy T-odd quark pairs has a sizeable cross-section at
the LHC and these T-odd particles eventually all cascade decay down to the
heavy photon A_H. We show that for certain regions of the parameter space with
either a small f of around 500 GeV or relatively light T-odd quarks with a mass
of around 400 GeV, one can reconstruct the A_H even at the early LHC run with
\sqrt{s}=10 TeV and a modest integrated luminosity of 200 pb^{-1}. At \sqrt{s}
= 14 TeV and with an integrated luminosity of 30 fb^{-1}, it is possible to
cover a large part of the typical parameter space of the LHT, with the scale f
up to 1.5 TeV and with T-odd quark masses almost up to 1 TeV. In this region of
the parameter space, the mass of the reconstructed A_H ranges from 66 GeV to
230 GeV.Comment: 35 pages, 4 figures; v2: additional multiple hard jets included in
background simulation using ALPGEN, main conclusions unchanged, references
added, version as published in JHEP
Same-sign trileptons and four-leptons as signatures of new physics at the Large Hadron Collider
We point out that same-sign multilepton events, not given due attention yet
for new physics search, can be extremely useful at the Large Hadron Collider.
After showing the easy reducibility of the standard model backgrounds, we
demonstrate the viability of same-sign trilepton signals for R-parity breaking
supersymmetry, at both 7 and 14 TeV. We find that same-sign four-leptons, too,
can have appreciable rates. Same-sign trileptons are also expected, for
example, in Little Higgs theories with T-parity broken by anomaly terms.Comment: 5 pages, 1 figure; v2: minor additions to text, references added,
version to appear in Physical Review D (Rapid Communications
Higher dimensional operators and LHC Higgs data : the role of modified kinematics
The inclusion of higher-dimensional gauge invariant operators induces new
Lorentz structures in Higgs couplings with electroweak gauge boson pairs. This
in principle affects the kinematics of Higgs production and decay, thereby
modifying the efficiencies of the experimental cuts compared to what
simulations based on the standard model interactions yield. Taking some sample
cases, we perform a rigorous analysis of how the efficiencies differ for
various strengths of the additional operator vis-a-vis the standard model
interactions, scanning over the values of both of them. While the response to
cuts can be markedly different in some regions, we find that the sensitivity to
new operator structures is relatively limited, so long as we remain confined to
the 2-sigma regions around the best fit signal strengths measured at the Large
Hadron Collider. We also show modifications to certain kinematical
distributions including the new operators in the diphoton final state.Comment: 26 pages, 9 figures; v2: Some numerical factors corrected,
conclusions unchanged. Comments and references added. Version to be published
in Phys.Rev.