Upgraded Fermilab Tevatron Research Articles

Gg→h→ τ+τ-at the upgraded Fermilab Tevatron

We study the neutral Higgs boson production via the gluon fusion process with the $\tautau$ final state at the upgraded Fermilab Tevatron, including a complete simulation of signal channels and leading background processes. For the SM Higgs boson, this $h\to \tautau$ channel may provide important addition for the Higgs boson discovery in the mass range 120-140 GeV. In minimal supersymmetric models, natural enhancement for the signal rate over the SM expectation makes the $h,H,A\to \tautau$ signal observable for large $\tan\beta$ and low $M_A$, which may lead to full coverage for SUSY Higgs parameters at the Tevatron with a moderate integrated luminosity.

Four body decay of the top squark at the upgraded Fermilab Tevatron

We investigate the prospect of stop squark search at Tevatron RUN-II in mSUGRA motivated as well as unconstrained supersymmetric models, when the lighter stop squark turns out to be the next lightest supersymmetric particle (NLSP). In this case the decay into a 4-body final state consisting of a b quark, the lightest neutralino and two light fermions may compete with the much publicized loop induced two body decay into a charm quark and the lightest neutralino. We systematically study the parameter space in mSUGRA where the lighter stop squark turns out to be the NLSP and calculate the branching ratios of the competing channels in both models. Our results show that the four body decay may indeed be the main discovery channel particularly in the low tan $\beta$ scenarios. We discuss the detectability of stop squark pairs in the 4-body decay channel leading to one lepton with 2 or more jets accompanied by a large amount of missing energy. We also studied the corresponding background processes and the kinematic cuts required to suppress them using parton level Monte Carlo simulations. We have commented upon with illustrative examples, the required revision of the existing mass limits of the stop NLSP assumed to decay solely into the loop induced 2-body channel in the presence of the competing 4-body decay.

Prospects for supersymmetric charged Higgs boson discovery at the Fermilab Tevatron and the CERN Large Hadron Collider

We investigate the prospects for heavy charged Higgs boson production through the mechanisms $p\overline{p}(\mathrm{pp})\ensuremath{\rightarrow}{H}^{\ifmmode\pm\else\textpm\fi{}}tb+X$ at the upgraded Fermilab Tevatron and at the upcoming LHC at CERN, respectively. We focus on the minimal supersymmetric standard model case and include the leading quantum corrections at high $\mathrm{tan}\ensuremath{\beta}.$ A detailed study is performed for all important production modes and basic background processes for the $t\overline{t}b\overline{b}$ signature. At the upgraded Tevatron a charged Higgs signal is potentially viable in the $220--250 \mathrm{GeV}$ range or excluded at 95% C.L. up to $300 \mathrm{GeV}.$ At the LHC, a ${H}^{\ifmmode\pm\else\textpm\fi{}}$ of mass up to $800 \mathrm{GeV}$ can be discovered at $5\ensuremath{\sigma}$ or else be excluded up to a mass of $\ensuremath{\sim}1.5 \mathrm{TeV}.$ The presence of SUSY quantum effects may highly influence the discovery potential in both machines and can typically shift these limits by $200 \mathrm{GeV}$ at the LHC.

Fourth standard model family enhancement to the golden mode at the upgraded Fermilab Tevatron

We study the observability for a Higgs boson at upgraded Tevatron via the modes gg->h->ZZ->4l (l=e,mu). We find that the signal can be observed at an integrated luminosity of 30 fb^(-1) if the fourth SM family exists.

Direct measurement of the top quark charge at hadron colliders

We consider photon radiation in tbar-t events at the upgraded Fermilab Tevatron and the CERN Large Hadron Collider (LHC) as a tool to measure the electric charge of the top quark. We analyze the contributions of tbar-t-gamma production and radiative top quark decays to p-p, pbar-p -> gamma l^+/- nu bbar-b jj, assuming that both b-quarks are tagged. With 20~fb^{-1} at the Tevatron, the possibility that the ``top quark'' discovered in Run I is actually an exotic charge -4/3 quark can be ruled out at the 95% confidence level. At the LHC, it will be possible to determine the charge of the top quark with an accuracy of about 10%.

PROSPECTS FOR RUN II BEAUTY PHYSICS AT DØ

In the spring of 2001, the upgraded Fermilab Tevatron will begin its collider physics run with [Formula: see text] collisions at [Formula: see text], where it is expected to deliver an integrated luminosity of 2 fb -1 in the first two years. The DØ detector is undergoing an extensive upgrade in order to take full advantage of the high luminosity running conditions. The upgraded detector's new silicon vertex detector, fiber tracker, and lepton trigger capabilities make a rich B physics program possible at DØ. This paper describes the prospects for several DØ B physics measurements, including CP violation in [Formula: see text] decays, Bs mixing and [Formula: see text] lifetime.

PROBING NEUTRAL GAUGE BOSON SELF-INTERACTIONS IN ZZ PRODUCTION AT THE TEVATRON

We present an analysis of ZZ production at the upgraded Fermilab Tevatron for general ZZZ and ZZγ couplings. Achievable limits on these couplings are shown to be a significant improvement over the limits currently obtained by LEP II.

Implications of new CMB data for neutralino dark matter

Abstract The combination of new cosmic microwave background data with cosmological priors has determined the physical cold dark matter (cdm) density to be Ω cdm h 2 =0.13±0.01 . We find the corresponding regions of parameters in the minimal supergravity model for which the lightest neutralino is the cdm particle. We then compare with the muon anomalous magnetic moment ( a μ ) measurement, the mass of the lighter CP-even Higgs boson ( h 0 ), the trilepton search at the upgraded Fermilab Tevatron collider, and a direct search for relic neutralinos. The intersection of Ω cdm h 2 and a μ constraints selects tan β ≈40–45.

Higgs boson decays toCP-odd scalars at the Fermilab Tevatron and beyond

In extended Higgs models, the Higgs boson may decay into a pair of light $\mathrm{CP}$-odd scalars, with distinctive collider signatures. We study the ensuing Higgs signals at the upgraded Fermilab Tevatron, considering the subsequent decays of the scalars into pairs of gluons or photons. For $\mathrm{CP}$-odd scalars lighter than a few GeV, the Higgs boson manifests itself as a diphoton resonance and can be discovered up to masses of a few hundred GeV. For heavier $\mathrm{CP}$-odd scalars the reach extends at most up to ${M}_{h}\ensuremath{\sim}120\mathrm{GeV}.$ We also discuss the capabilities of the CERN LHC and lepton colliders in these channels.

Erratum: Higgs boson production at hadron colliders with soft gluon effects: Backgrounds [Phys. Rev. D59, 114007 (1999)

The gold-plated discovery mode of a Standard Model like Higgs boson at the CERN Large Hadron Collider (LHC) is the H -> Z^0 Z^0 decay mode. To find and then measure the properties of the Higgs, it is crucial to have the most precise theoretical prediction both for the signal and the QCD background in this mode. In this work we calculate the effects of the initial-state multiple soft-gluon emission on the kinematic distributions of photon and Z^0 pairs produced in hadron collisions. The Collins-Soper-Sterman formalism is extended to resum the large logarithmic terms due to soft-gluons. The resummed total rates, the invariant mass, transverse momentum, and rapidity distributions of the photon and Z^0 pairs, and the transverse momentum distributions of the individual vector bosons are presented and compared to the fixed order predictions in the whole kinematic range, for the LHC energies and for the upgraded Fermilab Tevatron. Our conclusion is that the resummed predictions should be used when extracting the Higgs signal at the LHC.

Higgs boson production: A comparison of parton showers and resummation

The search for the Higgs boson(s) is one of the major priorities at the upgraded Fermilab Tevatron and at the CERN Large Hadron Collider (LHC). Monte Carlo event generators (MCs) are heavily utilized to extract and interpret the Higgs signal, which depends on the details of the multiple soft-gluon emission from the initial state partons in hadronic collisions. Thus, it is crucial to establish the reliability of the MCs used by the experimentalists. In this paper, the MC based parton shower formalism is compared to that of an analytic resummation calculation. Theoretical input, predictions and, where they exist, data for the transverse momentum distribution of Higgs bosons, $Z^0$ bosons, and photon pairs are compared for the Tevatron and the LHC. This comparison is useful in understanding the strengths and the weaknesses of the different theoretical approaches, and in testing their reliability.

Probing neutral gauge boson self-interactions in ZZ production at hadron colliders

A detailed analysis of ZZ production at the upgraded Fermilab Tevatron and the CERN Large Hadron Collider is presented for general ZZZ and ZZ\gamma couplings. Deviations from the Standard Model gauge theory structure for each of these can be parameterized in terms of two form factors which are severely restricted by unitarity at high energy. Achievable limits on these couplings are shown to be a dramatic improvement over the limits currently obtained by e^+e^- experiments.

Natural fermion mass hierarchy and new signals for the Higgs boson

We suggest a novel approach towards resolving the fermion mass hierarchy problem within the framework of the standard model. It is shown that the observed masses and mixings can be explained with order one couplings using successive higher dimensional operators involving the SM Higgs doublet field. This scenario predicts a flavor-dependent enhancement in the Higgs boson coupling to the fermions. It also predicts a flavor changing $\overline{t}{\mathrm{ch}}^{0}$ interaction with a strength comparable to that of $\overline{b}{\mathrm{bh}}^{0},$ opening up new discovery channels for the Higgs boson at the upgraded Fermilab Tevatron and the CERN LHC. Additional tests of the framework include observable ${D}^{0}\ensuremath{-}{D}^{0}$ mixing and a host of new phenomena associated with flavor physics at the TeV scale.

R-parity violation and top quark polarization at the Fermilab Tevatron collider

The lepton or baryon number violating top quark interactions in the supersymmetric standard model with R parity violation contribute to the process d dbar to t tbar at the tree level via the t- or u-channel sfermion exchange. Since these interactions are chiral, they induce polarization to the top quark in the t tbar events at hadron colliders. We show in this article that the polarization can be a useful observable for probing these interactions at the upgraded Fermilab Tevatron collider, because the polarization is expected to be very small in the standard model.

Trilepton signature of minimal supergravity at the upgraded Fermilab Tevatron

The prospects for detecting trilepton events ($\ell = e$ or $\mu$) from chargino-neutralino ($\chi^\pm_1 \chi^0_2$) associated production are investigated for the upgraded Fermilab Tevatron Collider in the context of the minimal supergravity model (mSUGRA). In some regions of parameter space, $\chi^\pm_1$ and $\chi^0_2$ decay dominantly into final states with $\tau$ leptons and the contributions from $\tau-$leptonic decays enhance the trilepton signal substantially when soft cuts on lepton transverse momenta are used. Additional sources of the mSUGRA trilepton signal and dominant irreducible backgrounds are discussed. The dilepton ($\ell^+\ell^-$) invariant mass distribution near the endpoint is considered as a test of mSUGRA mass relations. Discovery contours for $p\bar{p} \to 3\ell +X$ at 2 TeV with an integrated luminosity of 2 fb$^{-1}$ to 30 fb$^{-1}$ are presented in the mSUGRA parameter space of $(m_0,m_{1/2})$ for several choices of $\tan\beta$.

Higgs boson production at hadron colliders with soft gluon effects: Backgrounds

The gold-plated discovery mode of a standard model like Higgs boson at the CERN Large Hadron Collider (LHC) is the $\stackrel{\ensuremath{\rightarrow}}{H}{Z}^{0}{Z}^{0}$ decay mode. To find and then measure the properties of the Higgs boson, it is crucial to have the most precise theoretical prediction both for the signal and the QCD background in this mode. In this work we calculate the effects of the initial-state multiple soft-gluon emission on the kinematic distributions of ${Z}^{0}$ boson and photon pairs produced in hadron collisions. The Collins-Soper-Sterman formalism is extended to resum the large logarithmic terms due to soft gluons. The resummed total rates, the invariant mass, transverse momentum, and rapidity distributions of the ${Z}^{0}$ and photon pairs, and the transverse momentum distributions of the individual vector bosons are presented and compared to the fixed order predictions in the whole kinematic range, for the LHC energies and for the upgraded Fermilab Tevatron. Our conclusion is that the resummed predictions should be used when extracting the Higgs signal at the LHC.

Exploiting h→W*W* decays at the upgraded Fermilab Tevatron

We study the observability of a standard-model-like Higgs boson at an upgraded Fermilab Tevatron via the mode $\stackrel{\ensuremath{\rightarrow}}{h}{W}^{*}{W}^{*}.$ We concentrate on the main channel $g\stackrel{\ensuremath{\rightarrow}}{g}\stackrel{\ensuremath{\rightarrow}}{h}{W}^{*}{W}^{*}\ensuremath{\rightarrow}l\overline{\ensuremath{\nu}}\overline{l}\ensuremath{\nu}.$ We also find the mode $q{q}^{\ensuremath{'}}\ensuremath{\rightarrow}{W}^{\ifmmode\pm\else\textpm\fi{}}\stackrel{\ensuremath{\rightarrow}}{h}{W}^{\ifmmode\pm\else\textpm\fi{}}{W}^{*}{W}^{*}\ensuremath{\rightarrow}{l}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\nu}{l}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\nu}\mathrm{jj}$ useful. We perform detector level simulations by making use of a Monte Carlo program SHW. Optimized searching strategy and kinematical cuts are developed. We find that with a c.m. energy of 2 TeV and an integrated luminosity of $30 {\mathrm{fb}}^{\ensuremath{-}1}$ the signal should be observable at a $3\ensuremath{\sigma}$ level or better for the mass range of $145 \mathrm{GeV}\ensuremath{\lesssim}{m}_{h}\ensuremath{\lesssim}180 \mathrm{GeV}.$ For 95% confidence-level exclusion, the mass reach is $135 \mathrm{GeV}\ensuremath{\lesssim}{m}_{h}\ensuremath{\lesssim}190 \mathrm{GeV}.$ We also present results of studying these channels with a model-independent parametrization. Further improvement is possible by including other channels. We conclude that the upgraded Fermilab Tevatron will have the potential to significantly advance our knowledge of Higgs boson physics.

Extending the Higgs Boson Reach at the Upgraded Fermilab Tevatron

We study the observability of a standard-model-like Higgs boson at the upgraded Fermilab Tevatron via the modes $p\overline{p}\ensuremath{\rightarrow}\mathrm{gg}\ensuremath{\rightarrow}h\ensuremath{\rightarrow}{W}^{*}{W}^{*}\ensuremath{\rightarrow}\ensuremath{\ell}\ensuremath{\nu}\mathrm{jj}$ and $\ensuremath{\ell}\overline{\ensuremath{\nu}}\overline{\ensuremath{\ell}}\ensuremath{\nu}$. We find that, with c.m. energy of 2 TeV and an integrated luminosity of $30{\mathrm{fb}}^{\ensuremath{-}1}$, the signal may be observable for the mass range of $135\ensuremath{\lesssim}{m}_{h}\ensuremath{\lesssim}180\mathrm{GeV}$ at a $(3\ensuremath{-}5)\ensuremath{\sigma}$ statistical level. We conclude that the upgraded Fermilab Tevatron may have the potential to detect a standard-model-like Higgs boson in the mass range from the CERN ${e}^{+}{e}^{\ensuremath{-}}$ collider LEP II reach to 180 GeV.

Glue constraining asymmetries inW,γ, orZproduction at CERN LHC

We propose a class of forward-backward asymmetries with respect to the subprocess c.m. scattering angle in $V+\mathrm{jet}$ production at hadron colliders, with $V$ being any of $(W,Z,\ensuremath{\gamma},H),$ which are directly proportional to the gluon distribution $g(x).$ The information that these asymmetries can provide is complementary to that reachable from measurements of the transverse momentum and/or the rapidity distributions of a $V$ in kinematical regimes where gluon scattering subprocesses dominate. The accuracy which can be reached in the $W,$ $Z$ and \ensuremath{\gamma} cases, at the upgraded Fermilab Tevatron and at CERN LHC, should allow a considerable improvement of our knowledge of the gluon distribution function, especially at large $x.$

Probing anomalous top quark interactions at the Fermilab Tevatron collider

We study the effects of dimension-six operators contributing to the $\mathrm{gt}\overline{t}$ vertex in top quark pair production at the Fermilab Tevatron collider. We derive both the limits from run 1 data and the potential bounds from future runs (runs 2 and 3). Although the current constraints are not very strong, the future runs are quite effective in probing these operators. We investigate the possibility of disentangling different operators with the $t\overline{t}$ invariant mass distribution and the top quark polarization asymmetry. We also study the effects of a different set of operators contributing to single top quark production via the $\mathrm{Wt}\overline{b}$ coupling. We derive the current and potential future bounds on these anomalous operators and find that the upgraded Fermilab Tevatron collider can improve the existing constraints from ${R}_{b}$ for one of the operators.