K. Sridhar

New LEP bounds on

We use the precision electroweak data at LEP to place bounds on B-violating Yukawa couplings, two theoretically appealing examples being provided by R-parity violating supersymmetry and diquarks. The couplings involving the third generation quarks are most severely constrained. These bounds are complementary to those obtained from low-energy processes.

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We consider one-loop corrections to partial widths of the Z induced by supersymmetric Yukawa interactions that violate R-parity. The precise experimental values of the leptonic Z partial widths bound these Yukawa couplings, with the most interesting constraints being those on couplings involving τ, since previous constraints on them were very mild.

violating scalar couplings: R-parity violating supersymmetry or diquarks

We compute the contributions due to gluon and heavy-quark fragmentation to quarkonium production at large transverse momentum in ¯ pp and pp collisions. For inclusive J/ production, there is a large contribution from the g ! �c fragmentation. At large pT, this is comparable to the conventional charmonium model prediction via gluon fusion at the ISR and dominates over the latter at the Tevatron energy. This may help to explain, at least partly, the large J/ production cross-section recently observed by

NEW LEP CONSTRAINTS ON SOME SUPERSYMMETRIC YUKAWA INTERACTIONS THAT VIOLATE R-PARITY

Abstract The vertex corrections to the leptonic partial widths of the Z induced by leptoquarks that couple leptons to the top quark are considered. We obtain stringent bounds on the parameter space of the masses and Yukawa couplings of these leptoquarks, using the latest information on the Z → l + l − decay widths measured at LEP. Leptoquarks coupling with electroweak strength to top quarks are constrained to be heavier than several hundred GeV, at 95% C.L. As a consequence, such leptoquarks cannot make a significant contribution to lepton asymmetries, τ polarisation asymmetries or A LR .

Fragmentation contribution to quarkonium production in hadron collision

Abstract In the Standard Model (SM), dilepton production in hadron-hadron collisions proceeds through the conventional Drell-Yan mechanism q q → l + l − with the exchange of a gauge boson. Some extensions of the SM contain a quark-lepton contact interaction via a qlΦ Yukawa coupling, where Φ is a scalar. Theories with scalar leptoquarks and R-parity violating SUSY models are the most important examples of such extensions. These Yukawa couplings induce a different dynamical configuration compared to the SM (t-channel vs. s-channel) in the q q → l + l − process and thus offer the possibility of being identifiable upon imposition of suitable kinematic cuts. We discuss these effects in the context of the dilepton production in the CDF experiment, and explore consequences in the forthcoming Large Hadron Collider (LHC).

Bounds on the masses and couplings of leptoquarks from leptonic partial widths of the Z

Abstract We explore the possible interpretation of the large- Q 2 anomaly reported by the H1 and ZEUS Collaborations in terms of stop squark production off a strange quark in the proton via an R-violating interaction. This “strange stop” interpretation is constrained by LEP measurements of the Z → e+e− decay rate in addition to constraints from the electroweak ϱ parameter and CDF and D0 searches for first-generation leptoquarks. We investigate the interplay between these constraints, taking full account of stop mixing effects. We find that if m t ≤ 200 GeV only relatively small domains of the chargino and neutralino parameters are consistent with these constraints, and explore the extent to which this scenario may be probed further by searches for contact interactions at LEP 2 and experiments with e− and polarized beams at HERA.

R-parity violating SUSY or leptoquarks: Virtual effects in dilepton production

Abstract We investigate the large transverse momentum Drell-Yan process, including the effects of γ - Z interference, at RHIC energies, as a method of studying polarised parton distributions. Both single- and double-spin asymmetries are studied. It is shown that while the double-spin asymmetries are sizeable in the region of small dilepton masses, the single-spin asymmetries become significant at the Z peak. There is a high degree of sensitivity to the input parton distributions. Numerical estimates for the cross-sections at RHIC energies are also presented.

Pursuing the strange stop interpretation of the HERA large-Q2 data

Abstract We consider the contribution of radially excited 23P1,2 states to Ψ′ production at the Tevatron energy. Production of these states via the conventional gluon fusion mechanism and via gluon and charm quark fragmentation processes is considered. With optimistic estimates of the decay branching fractions of these 23P1,2 states into Ψ′, it is possible to account for the large Ψ′ production cross-section observed by the CDF experiment.

Single- and double-spin asymmetries in the Drell-Yan process at RHIC

In a model of supersymmetric SU(5) grand unification with a spatial dimension described by the orbifold S1/(Z2 × Z2), proton decay is naturally suppressed at all orders. This is achieved by a suitable implementation of the discrete symmetries on the brane. But baryon number violating interactions are present in this model. We propose a few possible experimental tests of this model which exploit the effect of the baryon number violating couplings on low-energy observables such as neutron–antineutron oscillations, double nucleon decay into two kaons, hadronic decay widths of the Z boson and t production cross section in Run II of the Tevatron.

A possible resolution of the CDF Ψ′ anomaly

We compute the J/psi+gamma invariant-mass distributions from the QCD subprocess g + g -->J/psi+gamma. At large masses, this subprocess is the dominant mechanism for J/psi+gamma production, and data could provide a good test of QCD. The mass distribution peaks at relatively small masses (3.4 - 4.0 GeV) and the subprocess could, therefore, represent a significant QCD background to J/psi+gamma decay of heavier charmonia. We also analyze the J/psi angular distribution in the J/psi+gamma rest frame.Abstract We compute the J / Ψ + γ invariant-mass distribution from the QCD subprocess g + g → J / Ψ + γ . At large masses, this subprocess is the dominant mechanism for J / Ψ + γ production, and data could provide a good test of QCD. The mass distribution peaks at relatively small masses (3.4–4.0 GeV) and the subprocess could, therefore, represent a significant QCD background to J / Ψ + γ decay of heavier charmonia. We also analyze the J / Ψ + γ rest frame.