arXiv subjects

L. M. Sehgal

Publications and source records attributed to L. M. Sehgal.

41 records · Page 3Linked to original sources

arXiv1994

Rare $K$ Decays

The rare decays of the $K$ meson have had a long tradition as a laboratory for testing the symmetry properties of the weak interactions, and the manner in which these symmetries are broken by higher order effects. Present--day interest is focussed on decays that are suppressed by $CP$--symmetry or GIM symmetry. Such decays, in the standard theory, are sensitive to effects of the virtual top quark, and could also reveal new interactions transcending the standard model. In addition, the radiative decays of the $K$ meson have become a useful testing--ground for effective Lagrangians describing the low energy interactions of pions, kaons and photons.

hep-ph↗

arXiv1994

Energy Spectra and Energy Correlations in the Decay $H\to ZZ\to μ^+μ^-μ^+μ^-$

It is shown that in the sequential decay $H\to ZZ\to (f_1\bar{f_1})+ (f_2\bar{f_2})$, the energy distribution of the final state particles provides a simple and powerful test of the $HZZ$ vertex. For a standard Higgs boson, the energy spectrum of any final fermion, in the rest frame of $H$, is predicted to be $dΓ/dx\sim 1+β^4-2(x-1)^2$, with $β= \sqrt{1-4m^2_Z/m^2_H}$ and $1-β\le x=4E/m_H\le 1+β$. By contrast, the spectrum for a pseudoscalar Higgs is $dΓ/dx \sim β^2+(x-1)^2$. There are characteristic energy correlations between $f_1$ and $f_2$ and between $f_1$ and $\bar{f_2}$. These considerations are applied to the ``gold--plated'' reaction $H\to ZZ\to μ^+μ^-μ^+μ^-$, including possible effects of CP--violation in the $HZZ$ coupling. Our formalism also yields the energy spectra and correlations of leptons in the decay $H\to W^+W^-\to l^+ν_ll^- \bar{ν_l}$.

hep-ph↗

arXiv1994

Energy correlation and asymmetry of secondary leptons in $H\to t\bar t$ and $H\to W^+W^-$

We study the energy correlation of charged leptons produced in the decay of a heavy Higgs particle $H\to t\bar t\to bl^+ν_l\bar bl^-\barν_l$ and $H\to W^+W^-\to l^+ν_ll^-\barν_l.$ The possible influence of $CP$--violation in the $Ht\bar t$ and $HW^+W^-$ vertices on the energy spectrum of the secondary leptons is analyzed. The energy distribution of the charged leptons in the decay $H\to W^+W^-\to l^+ν_ll^-\barν_l$ is sensitive to the $CP$--parity of the Higgs particle and yields a simple criterion for distinguishing scalar Higgs from pseudoscalar Higgs.

hep-ph↗

arXiv1994

$W^+-H^+$ Interference and Partial Width Asymmetry in Top and Antitop Decays

We re-examine the question of a possible difference in the partial decay widths of $t$ and $\overline t$, induced by an intermediate scalar boson $H^+$ with $CP$-violating couplings. The interference of $W^+$ and $H^+$ exchanges is analysed by constructing the $2\times 2$ propagator matrix of the $W^+-H^+$ system, and determining its absorptive part in terms of fermion loops. Results are obtained for the partial rate difference in the channels $t\to bl^+ν_l $ and $t\to bc\overline s$, which fulfil explicitly the constraints of $CPT$ invariance. These results are contrasted with those in previous work.

hep-ph↗

arXiv1994

$K^0 $ Decays into Three Photons

The decays $K_{L,S} \to 3 γ$ are not forbidden by any selection rules or symmetry principles. However, gauge invariance and Bose statistics dictate that every photon pair in these transitions has at least two units of angular momentum. This gives rise to an extraordinary suppression. Using a simple model, we obtain the branching ratios $B(K_L \to 3 γ) \sim 3 \cdot 10^{-19}$, $B(K_S \to 3 γ) \sim 5 \cdot 10^{-22} $.

hep-ph↗