arXiv subjects

K. Sridhar

Publications and source records attributed to K. Sridhar.

At least 55 records · Page 3Linked to original sources

arXiv2003

Testing orbifold models of Supersymmetric Grand Unification

In a model of supersymmetric SU(5) Grand Unification with a spatial dimension described by the orbifold $S^1/(Z_2 \times Z_2')$, 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 like neutron-antineutron oscillations, double nucleon decay into two kaons, hadronic decay widths of the $Z$ boson, and $t \bar t$ production cross-section in Run II of the Tevatron.

hep-ph↗

arXiv2003

$η_c$ production and dimuon enhancement in heavy ion collisions

Dilepton production in heavy ion collisions, in the Intermediate Mass Region (IMR) has consistently shown an excess over theoretical estimates. An attempt to understand this discrepancy between the observed dilepton pairs and the theoretical estimate is made here through the production of the $η_c$ meson and estimates obtained by NRQCD calculations. We find that $η_c$ production offers a satisfactory quantitative picture for explaining the discrepancy.

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arXiv2002

Combined fits to the supersymmetric explanation of anomalous lepton-photon-missing E_T events

The CDF experiment reported a lepton photon missing transverse energy (E_T) signal 3 sigma in excess of the Standard Model prediction in Tevatron Run I data. The excess can be explained by the resonant production of a smuon, which subsequently decays to a muon, a photon and a gravitino. Here, we perform combined fits of this model to the CDF gamma lepton missing E_T excess, the D0 measurement of the same channel and the CDF photon missing E_T channel. Although the rates of the latter two analyses are in agreement with the Standard Model prediction, our model is in good agreement with these data because their signal to background efficiency is low at the best-fit point. However, they help to constrain the model away from the best fit point.

hep-ph↗

arXiv2002

Explaining Anomalous CDF mu gamma Missing-E_T Events With Supersymmetry

CDF recently reported an excess of events in the mu-gamma-missing E_T channel that disagrees with the Standard Model prediction. No such excess was observed in the e-gamma-mett channel. We explain the excess via resonant smuon production with a single dominant R-parity violating coupling lambda'_{211}, in the context of models where the gravitino is the lightest supersymmetric particle. The slepton decays to the lightest neutralino and a muon followed by neutralino decaying to a gravitino and photon. We determine a viable region of parameter space that fits the kinematical distributions of the Run I excess and illustrate the effect by examining the best fit point in detail. We provide predictions for an excess in the missing E_T and photon channel at Run I and Run II. Run II will decisively rule out or confirm our scenario.

hep-ph↗

arXiv2001

Investigating the Supersymmetric Explanation of Anomalous CDF lepton(s) photon(s) Missing-E_T Events

The recent excess over the Standard Model prediction in the μγmissing-E_T channel reported by CDF can be well-explained by resonant smuon production with a single dominant R-parity violating coupling λ'_{211}, in the context of models where the gravitino is the lightest supersymmetric particle. The slepton decays to the lightest neutralino and a muon followed by neutralino decaying to a gravitino and photon. The kinematical distributions are fitted well by our hypothesis and we use them to constrain the available parameter space. The model also provides an explanation for the eeγγmissing-E_T event observed in Run I of the Tevatron by the CDF experiment. Our model predicts an excess of between 5 and 35 events in a γmissing-E_T channel at Run I. We provide predictions for signatures expected by the model at Run II.

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arXiv2001

Constraining the Randall-Sundrum Model Using Diphoton Production at Hadron Colliders

Virtual effects of gravitons in the production of diphotons at the upgraded Tevatron and at the LHC are analysed with the idea of probing the parameter space of the Randall-Sundrum (RS) model. It is shown that this process yields stringent constraints on the parameter space of the RS model. We show that data on diphoton production from Tevatron Run II will be sensitive to a masses of the first graviton resonance in the range of 700-1150 GeV, while at LHC the mass range probed will be in the region of 3.5 -- 5.5 TeV.

hep-ph↗

arXiv2000

Extra Dimensions: A View from the Top

In models with compact extra dimensions, where the Standard Model fields are confined to a 3+1 dimensional hyperplane, the $t \bar t$ production cross-section at a hadron collider can receive significant contributions from multiple exchange of KK modes of the graviton. These are carefully computed in the well-known ADD and RS scenarios, taking the energy dependence of the sum over graviton propagators into account. Using data from Run-I of the Tevatron, 95% C.L. bounds on the parameter space of both models are derived. For Run-II of the Tevatron and LHC, discovery limits are estimated.

hep-ph↗

arXiv2000

Large Extra Dimensions at Linear Colliders

In this talk, I first present the motivation for theories wherein extra spacetime dimensions can be compactified to have large magnitudes. In particular, I discuss the Arkani-Hamed, Dimopoulos, Dvali (ADD) scenario. I present the constraints that have been derived on these models from current experiments and the expectations from future colliders. I concentrate particularly on the possibilities of probing these extra dimensions at future linear colliders.

hep-ph↗

arXiv2000

The Higgs Working Group: Summary Report

Report of the Higgs working group for the Workshop "Physics at TeV Colliders", Les Houches, France 8-18 June 1999. It contains 6 separate sections: 1. Measuring Higgs boson couplings at the LHC. 2. Higgs boson production at hadron colliders at NLO. 3. Signatures of Heavy Charged Higgs Bosons at the LHC. 4. Light stop effects and Higgs boson searches at the LHC. 5. Double Higgs production at TeV Colliders in the MSSM. 6. Programs and Tools for Higgs Bosons.

hep-ph↗

arXiv1999

Large extra dimensions and dijet production in $γγ$ collisions

We have studied dijet production in $γγ$ collisions with a view to probing the physics of large extra dimensions. The exchange of virtual spin-2 Kaluza-Klein excitations is found to modify the dijet cross-section substantially from its Standard Model value and allows the effective string scale to be probed to values between 2.5 and 6.4 TeV in the unpolarised case. In the case where the photons are polarised, the limits are seen to improve by roughly 20%. Dijet production in $γγ$ collisions is thus shown to be a very effective probe of large extra dimensions.

hep-ph↗

arXiv1999

Seeking TeV-Scale Quantum Gravity at an $e γ$ collider

Theories with large extra compact dimensions predict exciting phenomenological consequences at the TeV scale. Such theories can, consequently, be tested/verified in experiments at future colliders like the Next Linear Collider (NLC). In this paper, we study the production of the spin-2 Kaluza-Klein excitations in NLC operating in the $e γ$ mode. Results for unpolarised and polarised cases are presented and it is shown that it is possible to use this process to test these theories to values of the effective string scale between about 1 - 7 TeV.

hep-ph↗

arXiv1999

A new proposal for glueball exploration in hard gluon fragmentation

An unambiguous identification of glueballs in experiments will be of great significance, because their existence is an important test of QCD. The proposal, advanced here, is to experimentally search for glueballs as peaks in the invariant mass of a leading K_S-pair fragmenting from an energetic gluon jet out of high-statistics three-jet events in hadronic decays of the weak neutral Z boson. Using a physically motivated model of the gluon-glueball fragmentation function, we find a substantial fragmentation rate into a leading glueball. It is very likely that a search, along the lines suggested here by any of the four groups at the Large Electron Positron collider at CERN, will prove fruitful.

hep-ph↗

arXiv1999

Probing Large Extra Dimensions Using Top Production in Photon-Photon Collisions

Theories with large extra dimensions predict an infinite tower of Kaluza-Klein states in the 1 TeV range, which can consequently have significant implications for experimental observables. One such observable, which gets affected by the exchange of spin-2 Kaluza-Klein particles, is the t t(bar) production cross-section in photon-photon collisions at NLC energies. We study this process and obtain bounds on the effective quantum gravity scale M_S between 700 and 2400 GeV (depending on the centre-of-mass energy). We show that the use of polarisation will further strengthen these bounds.

hep-ph↗

arXiv1999

J/psi+gamma production at the LHC

The associated production of J/psi + gamma at the LHC is studied within the NRQCD framework. The signal we focus on is the production of a J/psi and an isolated photon produced back-to-back, with their transverse momenta balanced. It is shown that even for very large values of transverse momentum (pT of the order of 50 GeV) the dominant contribution to this process is not fragmentation. This is because of the fact that fragmentation-type contributions to the cross-section come from only a q q(bar) initial state, which is suppressed at the LHC. We identify gg-initiated diagrams higher-order in alpha(s) which do have fragmentation-type vertices. We find, however, that the contribution of these diagrams is negligibly small.

hep-ph↗

arXiv1999

Testing TeV Scale Quantum Gravity using Dijet Production at the Tevatron

Dijet production at the Tevatron including effects of virtual exchanges of spin-2 Kaluza-Klein modes in theories with large extra dimensions is considered. The experimental dijet mass and angular distribution are exploited to obtain stringent limits ($\sim 1.2$ TeV) on the effective string scale $M_S$.

hep-ph↗

arXiv1999

SUSY Higgs at the LHC: Large stop mixing effects and associated production

We revisit the effect of the large stop mixing on the decay and production of the lightest SUSY Higgs at the LHC. We stress that whenever the inclusive 2-photon signature is substantially reduced, associated production, $Wh$ and $t\bar t h$, with the subsequent decay of the Higgs into photons is enhanced and becomes an even more important discovery channel. We also point out that these reductions in the inclusive channel do not occur for the smallest Higgs mass where the significance is known to be lowest. We show that in such scenarios the Higgs can be produced in the decay of the heaviest stop. For not too heavy masses of the pseudo-scalar Higgs where the inclusive channel is even further reduced, we show that large stop mixing also allows the production of the pseudo-scalar Higgs through stop decays. These large mixing scenarios therefore offer much better prospects than previously thought. As a by-product we have recalculated stop1-stop1-h production at the LHC and give a first evaluation of stop1-stop1-Z.

hep-ph↗

arXiv1999

Getting to the top with extra dimensions

The prospect of large extra dimensions and an effective theory of gravity at around a TeV has interesting experimental consequences. In these models, the Kaluza-Klein modes interact with Standard Model particles and these interactions lead to testable predictions at present and planned colliders. We investigate the effect of virtual exchanges of the spin-2 Kaluza-Klein modes in the production cross-section of $t \bar t$ pairs at the Tevatron and the LHC and find that the $t \bar t$ cross-section can be an effective probe of the large extra dimensions. This enables us to put bounds on the effective low-energy scale.

hep-ph↗

arXiv1999

Large extra dimensions and deep-inelastic scattering at HERA

In scenarios motivated by string theories, it is possible to have extra Kaluza-Klein dimensions compactified to rather large magnitudes, leading to large effects of gravity at scales down to a TeV. The effect of the spin-2 Kaluza-Klein modes on the deep-inelastic cross-section at HERA is investigated. We find that the data can be used to obtain bounds on the effective low energy scale, $M_S$.

hep-ph↗