Hadron Supercolliders Research Articles

Gaugino physics of split supersymmetry spectra at the LHC and future proton colliders

Discovery of the Higgs boson and lack of discovery of superpartners in the first run at LHC are both predictions of split supersymmetry with thermal dark matter. We discuss what it would take to find gluinos at hadron supercolliders, including the LHC at 14 TeV center of mass energy, and future pp colliders at 100 TeV and 200 TeV. We generalize the discussion by re-expressing the search capacity in terms of gluino to lightest superpartner mass ratio, and apply results to other scenarios, such as gauge mediation and mirage mediation.

Photon- and Z-induced heavy charged lepton pair production at a hadron supercollider.

We investigate the pair production of charged heavy leptons via photon-induced processes at the proposed CERN Large Hadron Collider (LHC). Using effective photon and $Z$ approximations, rates are given for ${L}^{+}{L}^{\ensuremath{-}}$ production due to $\ensuremath{\gamma}\ensuremath{\gamma}$ fusion and $Z\ensuremath{\gamma}$ fusion for the cases of inelastic, elastic, and semielastic $\mathrm{pp}$ collisions. These are compared with the corresponding rates for production via the gluon fusion and Drell-Yan mechanisms. Various $\ensuremath{\gamma}\ensuremath{\gamma}$ and $Z\ensuremath{\gamma}$ differential luminosities for $\mathrm{pp}$ collisions are also presented.

Heavy Higgs boson production in association with three jets at hadron supercolliders.

We consider the real emission QCD correction to heavy Higgs boson production via weak boson fusion in high energy pp collisions. The O(${\mathrm{\ensuremath{\alpha}}}_{\mathit{s}}$) corrections are determined for the complete electroweak qq\ensuremath{\rightarrow}${\mathit{qqW}}^{+}$${\mathit{W}}^{\mathrm{\ensuremath{-}}}$ process. The presence of a third parton in the final state affects the formation of rapidity gaps only slightly. In particular, soft emission into the gap region is severely suppressed. Also, we investigate how the additional hard emission affects forward-jet-tagging and central-jet-vetoing efficiencies in the search for H\ensuremath{\rightarrow}${\mathit{W}}^{+}$${\mathit{W}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\mathit{l}}^{+}$\ensuremath{\nu}${\mathit{l}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\nu}\ifmmode\bar\else\textasciimacron\fi{} decays.

Production of CP-odd Higgs bosons with large transverse momentum at hadron supercolliders

A two Higgs doublet model is employed to study the production of a CP-odd Higgs boson ( A) associated with a large transverse momentum jet ( j) at hadron supercolliders. The cross section of pp → jA + X is evaluated with four subprocesses: gg → gA, gq → qA, g q → qA and q q → gA . We find that pp → jA + A is a significant source of CP-odd Higgs bosons at future hadron supercolliders.

Heavy higgs search with hadron supercolliders up to √s=200 TeV

In addition to a light Higgs (M h≈0.1 TeV) a heavy one is expected (M H≈1 TeV). The knowledge of the two Higgs masses allows to predict the masses of as many as thirty sparticles expected in the simplest Supergravity theory. The production of a heavy Higgs (M H≫2M Z) is studied via Monte Carlo at three hadron supercollider energies: √s=16 TeV (LHC), √s=40 TeV (SSC) and √s=200 TeV (ELN/Eloisatron), for three masses:M H=500, 750, 1000 GeV. The 4-muon decay mode is investigated, in the presence of the «irreducible» background. The collider energy becomes a crucial parameter for the Higgs discovery as the Higgs mass increases. For a Higgs as heavy as 1 TeV the winning parameter is energy, not luminosity.

Proposed new signal for scalar top-squark bound-state production.

We study the production and decay of a scalar \stst\ bound state \sigst\ at hadron supercolliders, where \st\ is the lighter stop eigenstate. If \st\ has no tree--level 2--body decays, the dominant decay modes of \sigst\ are $gg$ or, if $m_h < \mst \ll \mstt$, a pair of light scalar Higgs bosons $h$. Nevertheless the branching ratio into two photons is often large enough to yield a detectable signal.

Detecting the tb decays of a charged Higgs boson at a hadron supercollider

We demonstrate that detection of a charged Higgs boson decaying via H ± → tb will be possible at the LHC in gg → H − bt events, provided the H + → tb coupling, m t ≲ 100 GeV, and reasonably effecient and pure b-tagging can be performed.

Strongly interacting WW system: Gold-plated modes.

In this paper we survey the signals and backgrounds for a strongly-interacting electroweak symmetry breaking sector at hadron supercolliders in the TeV region. We study the process pp->WWX, and compute the rates for the ``gold-plated'' channels, where W^{+/-}->l^{+/-}\nu and Z -> l^+l^- (l = e,\mu), for a wide variety of models. Using a forward jet-tag, a central jet-veto and a back-to-back lepton cut to suppress the Standard Model backgrounds, we demonstrate that the SSC and LHC have substantial sensitivity to strong interactions in the electroweak symmetry breaking sector.

Detecting an invisibly decaying Higgs boson at a hadron supercollider.

We demonstrate that an invisibly decaying Higgs boson with Standard Model coupling strength to top--anti-top can be detected at the LHC for masses up to about 250 GeV.

Finding the leptonic WW decay mode of a heavy Higgs boson at hadron supercolliders.

We reanalyze the extraction of the heavy Higgs boson signal $H\ensuremath{\rightarrow}{W}^{+}{W}^{\ensuremath{-}}\ensuremath{\rightarrow}\overline{\ensuremath{\ell}}\ensuremath{\nu}, \ensuremath{\ell}\overline{\ensuremath{\nu}}$, ($\ensuremath{\ell}=e or \ensuremath{\mu}$) from the standard model background at hadron supercolliders, taking into account revised estimates of the top quark background. With new acceptance criteria the detection of the signal remains viable. Requiring a forward jet tag, a central jet veto, and a large relative transverse momentum of the two charged leptons yields $\frac{S}{\sqrt{B}}&gt;6$ for one year of running at the SSC or CERN LHC.

Estimate of jet activity in tt-bar events.

We present a calculation of jet activity associated with pair production of top quarks at hadron colliders and supercolliders. Our approach is based upon a merger of $2\rightarrow 3$ matrix elements with initial and final state parton showers. We tabulate expected multi-jet rates in $t\bar t$ events, and compare with ${\cal O}(\alpha_s^3 )$ matrix element results and parton showers based upon $2\rightarrow 2$ subprocesses. The merged calculation includes the correct matrix element for the first leg of the parton shower, but also includes the effects of approximate all-orders quark and gluon emission. We also evaluate expected jet activity in top pair events at hadron supercolliders; in particular, a comparison of the jet activity in the far forward region is made. It is found that the merged calculation yields more jet activity in the forward region than pure matrix element estimates, but also more jet activity in the central region. This can be important for background calculations to $H\rightarrow WW$ and strong $WW$ scattering processes.

Guaranteed detection of a minimal supersymmetric model Higgs boson at hadron supercolliders

We demonstrate that expected efficiencies and purities for b-tagging at SSC/LHC detectors should allow detection of at least one of the Higgs bosons of the Minimal Supersymmetric Model in t t Higgs production, with Higgs→b b decay, over a substantial range of supersymmetric parameter space. In particular, with the addition of this mode to those previously considered, there is no region of supersymmetric parameter space for which none of the Higgs bosons of the model can be seen at the SSC/LHC.

Searching for Higgs bosons of minimal supersymmetry

After a brief introduction, we study the constraints on MSSM the Higgs sector parameters from the non-observation of any Higgs boson signals in experiments at LEP. We also review the range of Higgs boson masses that can be searched for at LEP 200. For the most part, we focus on the prospects for the detection of MSSM Higgs bosons in experiments at hadron supercolliders, assuming that these are too heavy to be discovered at LEP 200. We then show that supersymmetric decays of Higgs bosons can significantly reduce the rates for event topologies usually used for Higgs searches. Finally, we discuss some promising new channels for MSSM Higgs boson detection that become possible if these SUSY decays are allowed.

Searching for the pseudoscalar Higgs boson of minimal supersymmetry via its ZHl decay mode at hadron supercolliders

The pseudoscalar Higgs boson ( H p) in the minimal supersymmetric model decays into a Z boson and the lightest scalar Higgs boson ( H l ) with a large branching ratio when M Z + m Hl < m Hp <2 m t . The final state where Z→ l + l − and H l → τ + τ −, with one-prong hadronic τ decays, may provide a promising way to simultaneously detect H l and H p in regions of parameter space where there is no other detectable H p signal the two-body kinematics can allow for an H l and H p mass reconstruction.

Spontaneous R-parity breaking at hadron supercolliders

If supersymmetry (SUSY) is realized with spontaneous breaking of R -parity, there can be large rates for single sparticle production. We make a detailed study of the rates for Drell-Yan-like single chargino and single neutralino production at a hadron supercollider. The attainable rates are promising in view of the luminosities expected at these facilities. All observational restrictions from cosmology, astrophysics and laboratory are taken into account in our analysis, including the recent LEP results as well as neutrino physics constraints.

Search for Higgs bosons of minimal supersymmetry: Impact of supersymmetric decay modes.

We investigate the prospects for the detectability of the Higgs bosons of the minimal supersymmetric model (MSSM) at future colliders. First we delineate regions of MSSM parameter space where the various Higgs bosons may be observable at the CERN [ital e][sup +][ital e[minus]] collider LEP 200 or hadron supercolliders, assuming (as usual) that Higgs-boson decay modes to supersymmetric particles are not allowed. We find that, even with optimistic assumptions of detector capabilities, there exist regions of parameter space where none of the Higgs bosons are visible. Next, we show that there are substantial regions of parameter space where rates for Higgs-boson decays to supersymmetric particles are large, and even dominant. These decays reduce the rates for conventional Higgs-boson signatures, thus making conventional detection of Higgs bosons even more difficult. However, a number of new, promising modes for Higgs-boson detection have opened up. These include a gold-plated'' Higgs scalar or pseudoscalar decay to four leptons plus missing energy which may make possible a precise mass measurement of the lightest and second lightest neutralino. Furthermore, rare decays of the top quark into a [ital b] quark plus three leptons may be visible, and signal charged-Higgs-boson decays to a chargino plus neutralino.

Production of Z' associated with photons or jets as a probe of new gauge-boson couplings.

We examine the production of a new ${Z}^{\ensuremath{'}}$ gauge boson in association with photons or jets at future hadron supercolliders as a probe of its couplings to fermions. Associated jet production is found to be rather insensitive to these couplings and suffers from large uncertainties as well as substantial backgrounds. On the other hand, the ratio of rates for associated photon ${Z}^{\ensuremath{'}}$ production to that of conventional ${Z}^{\ensuremath{'}}$ production has a rather clean signature (once appropriate cuts are made), and is found to be quite sensitive to the choice of extended electroweak model, while being simultaneously insensitive to structurefunction uncertainties and QCD corrections. Rates at both the Superconducting Super Collider (SSC) and the CERN Large Hadron Collider (LHC) are significant for ${Z}^{\ensuremath{'}}$ masses in the 1-TeV range.

Production of a pseudoscalar Higgs boson with a Z boson from gluon fusion.

The minimal supersymmetric model is adopted to study the production of a pseudoscalar Higgs boson ($A$) in association with a $Z$ gauge boson from gluon fusion ($\mathrm{gg}\ensuremath{\rightarrow}\mathrm{ZA}$) at future hadron supercolliders. Its production rate is determined and compared to that of the associated production of the standard model Higgs boson (${H}_{\mathrm{SM}}$) with a $Z$ boson from quark-antiquark annihilation ($q\overline{q}\ensuremath{\rightarrow}Z{H}_{\mathrm{SM}}$) and gluon fusion ($\mathrm{gg}\ensuremath{\rightarrow}Z{H}_{\mathrm{SM}}$). Some promising decay modes are suggested for detection.

Transverse momentum distribution of Z-boson pairs at hadron supercolliders

We present the transverse-momentum distribution of the Z-pairs for pp → ZZX at supercollider energies. The full p T(ZZ) spectrum is obtained by matching the low- p T result (from soft gluon resummation to all orders in α s) to the high- p T result (from the O( α s) perturbative calculation). We examine where the fixed O( α s) perturbative calculation is unreliable. We also present a comparison of our result with the Monte Carlo program PYTHIA. The results are significant for background calculations to heavy Higgs boson searches at hadron supercolliders, as well as for testing perturbative QCD.

T→W +b→ τ+ντb decays as a probe of CP violation in the charged Higgs sector

We assess the extent to which CP violation in the charged Higgs sector of a three-doublet model could lead to an observable difference between the rate for t→W +b→ τ + ν τ b versus t→ W − b →τ − gn τ b decays in tt̄ production at a hadron supercollider.