JoAnne L. Hewett

The Snowmass points and slopes: Benchmarks for SUSY searches

Abstract. The ”Snowmass Points and Slopes” (SPS) are a set of benchmark points and parameter lines in the MSSM parameter space corresponding to different scenarios in the search for Supersymmetry at present and future experiments. This set of benchmarks was agreed upon at the 2001 ”Snowmass Workshop on the Future of Particle Physics” as a consensus based on different existing proposals.

Bulk gauge fields in the Randall-Sundrum model

Abstract We explore the consequences of placing the Standard Model gauge fields in the bulk of the recently proposed localized gravity model of Randall and Sundrum. We find that the Kaluza–Klein excitations of these fields are necessarily strongly coupled and we demonstrate that current precision electroweak data constrain the lowest states to lie above ≃23 TeV. Taking the weak scale to be ∼1 TeV, the resulting implications on the model parameters force the bulk curvature, R5, to be larger than the higher dimensional Planck scale, M, violating the consistency of the theory. In turn, to preserve |R5|≲M2, the weak scale must be pushed to ≳100 TeV. Hence we conclude that it is disfavored to place the Standard Model gauge fields in the bulk of this model as it is presently formulated.

Indirect Collider Signals for Extra Dimensions

A recent suggestion that quantum gravity may become strong near the weak scale has several testable consequences. In addition to probing for the new large (submillimeter) extra dimensions associated with these theories via gravitational experiments, one could search for the Kaluza Klein towers of massive gravitons which are predicted in these models and which can interact with the fields of the Standard Model. Here we examine the indirect effects of these massive gravitons being exchanged in fermion pair production in e{sup +}e{sup {minus}} annihilation and Drell-Yan production at hadron colliders. In the latter case, we examine a novel feature of this theory, which is the contribution of gluon gluon initiated processes to lepton pair production. We find that these processes provide strong bounds, up to several TeV, on the string scale which are essentially independent of the number of extra dimensions. In addition, we analyze the angular distributions for fermion pair production with spin-2 graviton exchanges and demonstrate that they provide a smoking gun signal for low-scale quantum gravity which cannot be mimicked by other new physics scenarios.

Phenomenology of the randall-sundrum gauge hierarchy model

We explore the phenomenology associated with the recently proposed localized gravity model of Randall and Sundrum where gravity propagates in a 5-dimensional non-factorizable geometry and generates the 4-dimensional weak-Planck scale hierarchy by an exponential function of the compactification radius, called a warp factor. The Kaluza-Klein tower of gravitons which emerge in this scenario have strikingly different properties than in the factorizable case with large extra dimensions. We derive the form of the graviton tower interactions with the Standard Model fields and examine their direct production in Drell-Yan and dijet events at the Tevatron and LHC as well as the KK spectrum line-shape at high-energy linear e + e − colliders. In the case where the first KK excitation is observed, we outline the procedure to uniquely determine the parameters of this scenario. We also investigate the effect of KK tower exchanges in contact interaction searches. We find that present experiments can place meaningful constraints on the parameters of this model.

PARTICLE PHYSICS PROBES OF EXTRA SPACETIME DIMENSIONS

▪ Abstract The possibility that spacetime extends beyond the familiar 3 + 1 dimensions has intrigued physicists for a century. The consequences of a dimensionally richer spacetime would be profound. Recently, new theories with higher-dimensional spacetimes have been developed to resolve the hierarchy problem in particle physics. The distinct predictions of these scenarios allow experiment to probe the existence of extra dimensions in new ways. We review the conceptual framework of these scenarios, their implications in collider and short-range gravity experiments, and their astrophysical and cosmological effects, as well as the constraints placed on them by current data.

Rare Charm Decays in the Standard Model and Beyond

We perform a comprehensive study of a number of rare charm decays, incorporating the first evaluation of the QCD corrections to the short distance contributions, as well as examining the long range effects. For processes mediated by the c → ul + l − transitions, we show that sensitivity to short distance physics exists in kinematic regions away from the vector meson resonances that dominate the total rate. In particular, we find that D → πl + l − and D → ρl + l − are sensitive to non-universal soft-breaking effects in the Minimal Supersymmetric Standard Model with R-parity conservation. We separately study the sensitivity of these modes to R-parity violating effects and derive new bounds on R-parity violating couplings. We also obtain predictions for these decays within extensions of the Standard Model, including extensions of the Higgs, gauge and fermion sectors, as well as models of dynamical electroweak symmetry breaking.

Signatures of long-lived gluinos in split supersymmetry

The authors examine the experimental signatures for the production of gluinos at colliders and in cosmic rays within the split supersymmetry scenario. Unlike in the MSSM, the gluinos in this model are relatively long-lived due to the large value of the squark masses which mediate their decay. Searches at colliders are found to be sensitive to the nature of gluino fragmentation as well as the gluino-hadron interactions with nuclei and energy deposition as it traverses the detector. They find that the worst-case scenario, where a neutral gluino-hadron passes through the detector with little energy deposition, is well described by a monojet signature. For this case, using Run I data they obtain a bound of m{sub {bar g}} > 170 GeV; this will increase to 210(1100) GeV at Run II(LHC) if no excess events are observed. In the opposite case, where a charged gluino-hadron travels through the detector, a significantly greater reach is obtained via stable charged particle search techniques. The authors also examine the production of gluino pairs in the atmosphere by cosmic rays and show they are potentially observable at IceCube; this would provide a cross-check for observations at hadron colliders.

Signals for noncommutative interactions at linear colliders

Recent theoretical results have demonstrated that non-commutative geometries naturally appear within the context of string/M-theory. One consequence of this possibility is that QED takes on a non-abelian nature due to the introduction of 3- and 4-point functions. In addition, each QED vertex acquires a momentum dependent phase factor. We parameterize the effects of non-commutative space-time co-ordinates and show that they lead to observable signatures in several 2 {yields} 2 QED processes in e{sup +}e{sup -} collisions. In particular, we examine pair annihilation, Moller and Bhabha scattering, as well as {gamma}{gamma} {yields} {gamma}{gamma} scattering and show that non-commutative scales of order a TeV can be probed at high energy linear colliders.

Brane-localized kinetic terms in the Randall-Sundrum model

We examine the effects of boundary kinetic terms in the Randall-Sundrum model with gauge fields in the bulk. We derive the resulting gauge Kaluza-Klein (KK) state wavefunctions and their corresponding masses, as well as the KK gauge field couplings to boundary fermions, and find that they are modified in the presence of the boundary terms. In particular, for natural choices of the parameters, these fermionic couplings can be substantially suppressed compared to those in the conventional Randall-Sundrum scenario. This results in a significant relaxation of the bound on the lightest gauge KK mass obtained from precision electroweak data; we demonstrate that this bound can be as low as m{sub 1} {approx}> 5 TeV. Due to the relationship between the lightest gauge KK state and the electroweak scale in this model, this weakened constraint allows for the electroweak scale to be near a TeV in this minimal extension of the Randall-Sundrum model with bulk gauge fields, as opposed to the conventional scenario.

Searching for supersymmetry in rare B decays

We quantify the ability of B-Factories to observe supersymmetric contributions to the rare decays B ! Xs and B ! Xsl + l . A global t to the Wilson coecients which contribute to these decays is performed from Monte Carlo generated data on B(B ! Xs )a nd the kinematic distributions associated with the nal state lepton pair in B! Xsl + l .T hist is then compared to supersymmetric predictions. Evaluation of the Wilson coecients is carried out with several dierent patterns of the superpartner spectrum. We nd thatB-Factories will be able to probe regions of the SUSY parameter space not accessible to LEP II, the Tevatron, and perhaps the LHC. We also employ the recent NLO calculation of the matrix elements for B ! Xs and nd the bound mH > 300 GeV in two-Higgs-doublet models using present data.