arXiv subjects

Saurabh D. Rindani

Publications and source records attributed to Saurabh D. Rindani.

81 records · Page 5Linked to original sources

arXiv1995

Helicity-Flip Bremsstrahlung and the Measurement of CP-Violating Form Factors in Polarized $e^+e^-$ Collisions

Certain momentum correlations in the production and subsequent decay of heavy fermion pairs in $e^+e^-$ collisions have increased sensitivity to CP-violating electric and ``weak" dipole form factors of the fermion in the presence of longitudinal polarization of the $e^+e^-$ beams. However, unless the polarizations of $e^+$ and $e^-$ are equal and opposite, collinear initial-state radiation accompanied by helicity flip results in a CP-invariant contribution to these and acts as a background, and must be calculated and subtracted in order to isolate the CP-violating contribution due to the dipole form factor.We calculate this background contribution to such correlations, to order $α$, in $e^+e^-\rightarrow τ^+τ^-$ and $e^+e^-\rightarrow t\bar{t}$. For the anticitipated luminosities at $τ$-charm factories and SLC, for the $τ$, and at a future linear collider with centre-of-mass energy of 500 GeV for the top, these backgrounds are smaller than the statistical background and may be safely neglected.

hep-ph↗

arXiv1994

CP violation at colliders

The prospects of experimental detection of $CP$ violation at $e^+e^-$ and $pp/p\overline{p}$ colliders are reviewed. After a general discussion on the quantities which can measure $CP$ violation and on the implications of the $CPT$ theorem, various possibilities of measuring $CP$ violation arising outside the standard model are taken up. $CP$ violation in leptonic processes, especially polarization effects in $e^+e^-\rightarrow l^+l^-$ are discussed next. $CP$ violation in $t\overline{t}$ and $W^+W^-$ production and decay is also described. (Based on talk presented at the WHEPP3, Madras, January 1994).

hep-ph↗

arXiv1994

Measurement of the $τ$ electric dipole moment using longitudinal polarization of $e^+e^-$ beams

Certain CP-odd momentum correlations in the production and subsequent decay of $τ$ pairs in $e^+ e^-$ collisions are enhanced significantly when the $e^+$ and $e^-$ beams are longitudinally polarized. These may be used to probe the real and imaginary parts of $d_τ^γ$, the electric dipole moment of the $τ$. Closed-form expressions for these ``vector correlations'' and the standard deviation of the operators defining them due to standard model interactions are presented for the two-body final states of $τ$ decays. If 42\% average polarization of each beam is achieved, as proposed for the tau-charm factories, with equal integrated luminosities for each sign of polarization and a total yield of $2\cdot 10^7$ $τ^+ τ^-$ pairs, it is possible to attain sensitivities for $\vertδ{\rm Re} d_τ^γ\vert$ of $8\cdot 10^{-19}$, $1\cdot 10^{-19}$, $1\cdot 10^{-19}$ $e$ cm respectively and for $\vertδ{\rm Im} d_τ^γ\vert$ of $4\cdot 10^{-14}$, $6\cdot 10^{-15}$, $5\cdot 10^{-16}$ $e$ cm respectively at the three operating center-of-mass energies of 3.67, 4.25 and 10.58 GeV. These bounds emerge when the effects of a posible weak dipole form factor $d_τ^Z$ are negligible as is the case when it is of the same order of magnitude as $d_τ^γ$. Furthermore, in such a polarization experiment where different polarizations are possible, a model-independent disentangling of their individual effects is possible, and a technique to achieve this is described. A strong longitudinal polarization physics programme at the tau-charm factory appears warranted.

hep-ph↗

arXiv1994

CP-Violatiing Asymmetries in $e^+e^-\ra t\bar{t}$ with Longitudinally Polarized Elecrtons

New CP-violating asymmetries of decay leptons in $e^+\,e^-\;\ra\;t\,\bar{t}$, arising from electric and weak dipole couplings of $t\,\bar{t}$ to $γ$ and $Z$, are examined in the case of unpolarized and longitudinally polarized electrons. The new asymmetries measured together with the old ones can help to determine independently the real and imaginary parts of the electric as well as weak dipole couplings. Longitudinal beam polarization, if present, obviates the need for the simultaneous measurement of more than one asymmetry, and enhances considerably the sensitivity to the CP-violating parameters. Numerical results are presented for the Next Linear Collider with $\sqrt{s}=500$ GeV and $\int{\cal L}\,dt\;=\;10\,{\rm fb}^{-1}$.

hep-ph↗

arXiv1994

Test of $CP$ Violating Neutral Gauge Boson Vertices in $ e^+ e^- \rightarrow γZ $

Forward-backward asymmetry in the process $e^+ e^- \rightarrow γZ$ is proposed as a test for $CP$--violating anomalous $γγZ$ and $ γZ Z$ couplings. Longitudinally polarized electron beams may be used to disentangle the effects of these couplings. We estimate possible limits that can be obtained from $e^+ e^-$ colliders at centre-of-mass energies of 200 GeV and 500 GeV.

hep-ph↗

arXiv1994

Effect of longitudinal electron polarization in the measurement of the $τ$ weak dipole moment in $e^+e^-$ collisions

We show that certain CP-odd momentum correlations in the production and subsequent decay of tau pairs in $e^+e^-$ collisions get enhanced when the electron beam is longitudinally polarized. Analytic expressions for these correlations are obtained when $τ^+τ^-$ have a ``weak" dipole form factor (WDFF) coupling to $Z$ in the case of two-body decay modes of the $τ$. Expressions of the variance of these correlations due to the standard model interactions are also presented. For $e^+e^-$ collisions at the $Z$ peak, a sensitivity of about $10^{-17} e$ cm for the real part of the $τ$ WDFF and $3\times 10^{-17} e$ cm for the imaginary part of the $τ$ WDFF can be reached using $π$ and $ρ$ channels (which are the most sensitive channels) in $τ$ decay, with $10^6\, Z$'s likely to be available at the SLC at Stanford with $e^-$ polarization of 62\%-75\%.

hep-ph↗

arXiv1994

Weak dipole moment of $τ$ in $e^+e^-$ collisions with longitudinally polarized electrons

It is pointed out that certain CP-odd momentum correlations in the production and subsequent decay of tau pairs in $e^+e^-$ collisions get enhanced when the $e^-$ is longitudinally polarized. Analytic expressions for these correlations are obtained for the single-pion decay mode of $τ$ when $τ^+τ^-$ have a ``weak" dipole form factor (WDFF) coupling to $Z$ . For $e^+e^-$ collisions at the $Z$ peak, a sensitivity of about 1-5$\times 10^{-17}$\mbox{$e$ cm} for the $τ$ WDFF can be reached using a {\em single} $τ^+τ^-$ decay channel, with $10^6\, Z$'s likely to be available at the SLC at Stanford with $e^-$ polarization of 62\%-75\%.

hep-ph↗

arXiv1993

Mass Limits of Invisibly Decaying Higgs Particles from the LEP Data

In the Majoron models the $SU(2)$ doublet Higgs can decay invisibly into a Majoron pair via its mixing with a singlet. An analysis of the LEP data shows the invisible decay mode to be more visible than the SM decay. For these models, the dominantly doublet Higgs $H$ is shown to have a mass limit within $\pm 6$ GeV of the SM limit irrespective of the model parameters. But the dominantly singlet one $S$ can be arbitrarily light for sufficiently small mixing angle.

hep-ph↗

arXiv1992

Fast Neutrino Decay in the Minimal Seesaw Model

Neutrino decay in the minimal seesaw model containing three right handed neutrinos and a complex $SU(2)\times U(1)$ singlet Higgs in addition to the standard model fields is considered. A global horizontal symmetry $U(1)_H$ is imposed, which on spontaneous breaking gives rise to a Goldstone boson. This symmetry is chosen in a way that makes a) the contribution of heavy ($\leq$ MeV) majorana neutrinos to the neutrinoless double beta decay amplitude vanish and b) allows the heavy neutrino to decay to a lighter neutrino and the Goldstone boson. It is shown that this decay can occur at a rate much faster than in the original Majoron model even if one does not introduce any additional Higgs fields as is done in the literature. Possibility of describing the 17 keV neutrino in this minimal seesaw model is investigated. While most of the cosmological and astrophysical constraints on the 17 keV neutrino can be satisfied in this model, the laboratory limits coming from the neutrino oscillations cannot be easily met. An extension which removes this inadequacy and offers a consistent description of the 17 keV neutrino is discussed.

hep-ph↗