Hadron Supercolliders Research Articles

Searching for CP-even Higgs bosons of the minimal supersymmetric model at hadron supercolliders.

The {ital CP}-odd Higgs boson {ital A}{sup 0} of a nonminimal Higgs model possesses no tree-level couplings to vector-boson pairs. As a result, many of the techniques employed to search for the standard model Higgs boson at the Superconducting Super Collider (SSC) and CERN Large Hadron Collider (LHC) are not likely to be useful in searches for the {ital A}{sup 0}. This paper focuses on the phenomenology of {ital A}{sup 0} production and decay in the minimal supersymmetric model. We evaluate a comprehensive set of branching ratios for {ital A}{sup 0} (which includes all two-body tree-level and one-loop decays into nonsupersymmetric final states), including the effects of leading-log radiative corrections. The one-loop decay {ital A}{sup 0}{r arrow}{ital ZZ} leads to the gold-plated'' signature {ital ZZ}{r arrow}{ital l}{sup +}{ital l{minus}}{ital l+}{ital l{minus}} and provides an observable signature for {ital A}{sup 0} production at the SSC and LHC only over a very narrow region of parameter space. More promising signatures for the {ital A}{sup 0} are also discussed.

Full tree-level calculation of the qq-->qqWZ electroweak process at hadron supercolliders.

We present a full standard model calculation of the $\mathrm{qq}\ensuremath{\rightarrow}\mathrm{qqWZ}$ electroweak process in $\mathrm{pp}$ collisions at the Superconducting Super Collider, including $W$ and $Z$ leptonic decay correlations. We also analyze the backgrounds to this signal from $\mathrm{Zt}\overline{t}\ensuremath{\rightarrow}ZW+\mathrm{jets}$ and $q\overline{q}\ensuremath{\rightarrow}WZ+\mathrm{jets}$. Single forward jet tagging and vetoing of events with \ensuremath{\ge} 2 central jets can suppress the backgrounds with little effect on the signal. With 10 ${\mathrm{fb}}^{\ensuremath{-}1}$ integrated luminosity we expect 50 signal events and 30 background events.

Colored Pseudo Goldstone Bosons and Gauge Boson Pairs

If the electroweak symmetry breaking sector contains colored particles weighing a few hundred GeV, then they will be copiously produced at a hadron supercollider. Colored technipions can rescatter into pairs of gauge bosons. As proposed by Bagger, Dawson, and Valencia, this leads to gauge boson pair rates far larger than in the standard model. In this note we reconsider this mechanism, and illustrate it in a model in which the rates can be reliably calculated. The observation of both an enhanced rate of gauge-boson-pair events and colored particles would be a signal that the colored particles were pseudo-Goldstone bosons of symmetry breaking.

Observability of gamma gamma decays of Higgs bosons from supersymmetry at hadron supercolliders.

Motivated by the recent discovery that radiative corrections can cause the mass of the lightest scalar Higgs boson ${\mathit{H}}_{\mathit{l}}$ of the minimal supersymmetric model (MSSM) to be in the intermediate-mass range, we assess the prospects for discovering the MSSM Higgs bosons via their \ensuremath{\gamma}\ensuremath{\gamma} decay modes at the Superconducting Super Collider (SSC) and at the CERN Large Hadron Collider (LHC). We find that if the charged Higgs boson is not too light, it is possible to discover at least one of the Higgs bosons via this mode within a few years of operation of the SSC, provided the detector has the resolution to identify a standard model Higgs boson in the intermediate-mass range via its \ensuremath{\gamma}\ensuremath{\gamma} decay. Similar conclusions hold at the LHC provided the luminosity is higher by a factor of about 4. In the case where ${\mathit{m}}_{\mathit{H}}^{+}$, and hence ${\mathit{m}}_{\mathit{H}\mathit{p}}$, is somewhat smaller than 200 GeV, we find there are regions of parameter space where all three Higgs bosons are in the intermediate-mass range, and none of them lead to an observable signal. Thus, new strategies may be needed to identify the Higgs bosons of the MSSM.

Probe of CP violation in top quark pair production at hadron supercolliders.

We show that measurement of the difference in the transverse energy distribution of leptons and antileptons from tt\ifmmode\bar\else\textasciimacron\fi{} events at hadron colliders provides an interesting probe of CP violation in the Higgs sector. We predict a CP-violating asymmetry at the ${10}^{\mathrm{\ensuremath{-}}3}$ level.

Supersymmetric-Higgs-boson hadroproduction and decays including radiative corrections.

Radiative corrections can produce substantial changes in the masses, production cross sections, and decay branching fractions of Higgs bosons in supersymmetric models, which can greatly modify their experimental detectability. We study variations in the expected event rates at $\mathrm{pp}$ supercolliders caused by radiative effects from the full one-loop effective potential in the minimal model, for the $\mathrm{CP}$-even bosons $h$ and $H$. We note that the masses of $h$, $H$, and the $\mathrm{CP}$-odd boson $A$ can simultaneously fall in the intermediate mass range ${M}_{Z}<m<2{M}_{Z}$ that is difficult to explore at hadron supercolliders. We calculate the one-loop corrections to the triple neutral-Higgs-boson couplings that enter into the $h$ and $H$ branching fractions. We evaluate the $\mathrm{pp}\ensuremath{\rightarrow}h(H)$ production cross sections at the Superconducting Super Collider energy, together with the principal $h$ and $H$ decay fractions, and compare them with standard-model results. We find that the $h$ and $H$ Higgs-boson signals in the $\ensuremath{\gamma}\ensuremath{\gamma}$ and ${\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ decay channels are generally less favorable than for the standard-model Higgs-boson search, except in some special cases.

Colored pseudo Goldstone bosons and gauge boson pairs.

If the electroweak symmetry breaking sector contains colored particles weighing a few hundred GeV, then they will be copiously produced at a hadron supercollider. Colored technipions can rescatter into pairs of gauge bosons. As proposed by Bagger, Dawson, and Valencia, this leads to gauge boson pair rates far larger than in the standard model. In this Letter we reconsider this mechanism, and illustrate it in a model in which the rates can be reliably calculated. The observation of both an enhanced rate of gauge-boson-pair events and colored particles would be a signal that the colored particles were pseudo Goldstone bosons of symmetry breaking.

Multiple-weak-boson signals at hadron supercolliders.

Multiple-weak-boson signals expected at future hadron supercolliders from several sources will provide new ways to probe the underlying interactions. The production of {ital t{bar t}t{bar t}}, {ital t{bar t}} {ital H}{sup 0}, {ital H}{sup 0}{ital H0}, {ital t{bar t}} {ital W}{sup +}{ital W{minus}}, {ital t{bar t}Z}{sup 0}{ital Z0}, Z{sup 0}{ital Z0}, {ital t{bar t}} {ital Z}{sup 0}, and {ital t{bar t}} {ital W}{sup {plus minus}} by standard-model mechanisms will lead to distinctive three-boson and four-boson signals via the decays {ital t}{r arrow}{ital bW} and {ital H}{sup 0}{r arrow}{ital W}{sup +}{ital W{minus}},{ital Z}{sup 0}{ital Z0},{ital t{bar t}},{gamma}{gamma}. In supersymmetric models the production and cascade decay of heavy gluinos can also give multiple {ital W} and {ital Z} configurations. We present calculations of these principal top-quark and Higgs-boson decay channels (plus some less important channels) and compare the resulting multi-weak-boson signals with backgrounds from direct multiboson production at energies of the Superconducting Super Collider and CERN Large Hadron Collider. We also present calculations of typical gluino cascade contributions. Since weak bosons are most readily identified through their leptonic decays, we also evaluate the principal signals and backgrounds at the lepton level. Within the standard model, the signals associated with strong top-quark productionmore » dominate completely over electroweak contributions; the expected event rates are large if we do not insist on all-leptonic {ital W} and {ital Z} decays. In the minimum supersymmetric standard model, gluino cascade decays can lead to still higher event rates; top-quark channels are typically important contributors here too.« less

Multilepton signals from supersymmetry at hadron supercolliders.

We have developed a new event generator SUSYSM to simulate the production of squarks and gluinos at hadron supercolliders including all the cascade decays as given by the minimal supersymmetric model. The simulation incorporates final-state hadronization and fragmentation effects for the decays of heavy flavors. We have used this to compute the rates for {ital E}{sub {ital T}} events, same-sign dilepton events, {ital n}{sub {ital l}}=3, 4, and 5 isolated-lepton events, and single or double {ital Z}{sup 0}+{ital E}{sub {ital T}} events from squark and gluino production at the CERN Large Hadron Collider (LHC) and the Superconducting Super Collider (SSC) for cuts inspired by the Solenoidal Detector Collaboration. We have identified and estimated several backgrounds to the various event topologies and shown that it should be possible to extract signals in several channels both at the LHC and SSC. We have shown that after accumulating one year's worth of design luminosity, it should be possible to identify a gluino with mass up to 2 TeV at the SSC, while the corresponding reach of the LHC is 1.2--1.7 TeV, depending on the luminosity.

Single-forward-jet tagging and central-jet vetoing to identify the leptonic WW decay mode of a heavy Higgs boson.

We study 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. By tagging a single forward jet with energy ${E}_{j}>3$ TeV and pseudorapidity $3<|{\ensuremath{\eta}}_{j}|<5$ and by vetoing central jets of transverse momenta ${p}_{\mathrm{Tj}}>60$ GeV in the pseudorapidity range $0<|{\ensuremath{\eta}}_{j}|<3$, the QCD $\mathrm{WWj}$ and $t\overline{t}j\ensuremath{\rightarrow}\mathrm{WWb}\overline{b}j$ backgrounds are suppressed. For ${m}_{H}=1$ TeV there are about 46 signal events from electroweak-vector-boson scattering (of which 36 events are of Higgs-boson origin) at the Superconducting Super Collider (SSC) for an integrated luminosity of 10 ${\mathrm{fb}}^{\ensuremath{-}1}$ and 10 other events from the $\mathrm{WWj}$ and $t\overline{t}j$ backgrounds for ${m}_{t}=140$ GeV. The experimental separation of the vector-boson-scattering subprocess is thereby possible. At the CERN Large Hadron Collider, with an ${E}_{j}>2$ TeV jet energy cut, all cross sections are about a factor of 10 below the SSC values.

Observability of a heavy Higgs boson at hadron supercolliders.

We present a coherent analysis of Higgs-boson production in the channels $\mathrm{pp}\ensuremath{\rightarrow}\mathrm{ZZX}\ensuremath{\rightarrow}{l}^{+}{l}^{\ensuremath{-}}{l}^{\ensuremath{'}+}{l}^{\ensuremath{'}\ensuremath{-}}X(l, {l}^{\ensuremath{'}}=e, \ensuremath{\mu})$ and $\mathrm{pp}\ensuremath{\rightarrow}\mathrm{ZZX}\ensuremath{\rightarrow}{l}^{+}{l}^{\ensuremath{-}}\ensuremath{\nu}\overline{\ensuremath{\nu}}X(\ensuremath{\nu}={\ensuremath{\nu}}_{e}, {\ensuremath{\nu}}_{\ensuremath{\mu}}, {\ensuremath{\nu}}_{\ensuremath{\tau}})$ for ${m}_{H}\ensuremath{\ge}600$ GeV at hadron supercolliders, using the exact matrix elements for $\mathrm{gg}\ensuremath{\rightarrow}\mathrm{ZZ}$ and $\mathrm{qq}\ensuremath{\rightarrow}\mathrm{qqZZ}$. The importance of a complete understanding of the shape of the perturbative $\mathrm{pp}\ensuremath{\rightarrow}\mathrm{ZZX}$ background from nonresonant diagrams is emphasized. We find that for the CERN Large Hadron Collider (LHC) to have a Higgs-boson discovery potential comparable to that of the Superconducting Super Collider (SSC) requires at least a factor of 10 times more integrated luminosity. In particular, assuming an integrated luminosity of ${10}^{4}$ ${\mathrm{pb}}^{\ensuremath{-}1}$ and perfect lepton identification efficiency, the LHC (SSC) can identify Higgs bosons as resonances with mass up to 600 (800) GeV in $\mathrm{pp}\ensuremath{\rightarrow}\mathrm{ZZX}\ensuremath{\rightarrow}{l}^{+}{l}^{\ensuremath{-}}{l}^{\ensuremath{'}+}{l}^{\ensuremath{'}\ensuremath{-}}X$. To extend the discovery range of the LHC to ${m}_{H}=800$ GeV in this channel requires an integrated luminosity of at least ${10}^{5}$ ${\mathrm{pb}}^{\ensuremath{-}1}$. For ${m}_{H}>800$ GeV, a clear resonance structure is missing; however, one can still discriminate between a heavy Higgs boson with ${m}_{H}\ensuremath{\sim}1$ TeV and a light Higgs boson (${m}_{H}\ensuremath{\lesssim}2{M}_{z}$) at the SSC.

Intermediate-mass Higgs boson at hadron supercolliders.

We study the inclusive production at future hadron supercolliders of the standard-model Higgs boson in the intermediate-mass region (${M}_{W}\ensuremath{\lesssim}{M}_{H}\ensuremath{\lesssim}2{M}_{Z}$) and its subsequent decay into two virtual $W$ bosons that decay leptonically. Backgrounds from continuum $W$ pair production and from topquark pair production with semileptonic decays are investigated. We conclude that the Higgsboson signal may be observed via the decay $H\ensuremath{\rightarrow}{W}^{*}{W}^{*}\ensuremath{\rightarrow}(l{\overline{\ensuremath{\nu}}}_{l})({\overline{l}}^{\ensuremath{'}}{\ensuremath{\nu}}_{{l}^{\ensuremath{'}}})$ at the Superconducting Super Collider for $145 \mathrm{GeV}<{M}_{H}\ensuremath{\lesssim}2{M}_{Z}$ if ${m}_{t}>150$ GeV. Here ${W}^{*}$ denotes an on- or off-shell $W$ boson.

Z-boson pair production via vector boson scattering and the search for the Higgs boson at hadron supercolliders

We present the results of a complete perturbative calculation of Z-boson pair production via the O( α W 4) electroweak process qq → qqZZ, and the O( α s 2 α W 2) mixed QCD-electroweak processes, gg → q q ZZ , qg → qgZZ, q q → ggZZ and qq → qqZZ at supercollider energies. Compact analytic expressions for the helicity amplitudes for all contributing diagrams, including the subsequent decay of the Z boson into massless fermions and all interference effects, are given. Detailed results for the event characteristics and the jet activity in electroweak qq → qqZZ events are presented for the full range of invariant masses of the Z pair, m ZZ, as well as in the Higgs boson resonance region, m ZZ = m H ± Γ H, where we compare the results of the exact calculation with the effective W approximation, and the approximation where only s-channel Higgs resonance diagrams are taken into account. We also compute the background resulting from the mixed QCD-electroweak ZZ + 2 jet processes at large jet transverse momenta in the resonance region and suggest techniques to suppress this background. Cross sections for Higgs boson production in the ZZ channel and the continuum ZZ background, in association with up to 2 jets, are given. We find that jet identification in the forward rapidity region,  η j  > 2.5 may considerably facilitate the detection of a heavy Higgs boson with m H ∼ O(1 TeV) at the LHC and SSC.

Gluino and squark production in association with gauginos at hadron supercolliders.

We calculate production cross sections for gluinos and squarks produced in association with charginos and neutralinos at $\mathrm{pp}$ supercollider energies. We show that, with rather stiff cuts, a signal for $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{Z}}_{1}$ and $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{Z}}_{1}$ may be isolated from the standard-model background as well as from other super-symmetric processes; this channel may offer the best hope of a gluino mass measurement. We also estimate potential signal rates from hemispherically separated multilepton-plus-jet events that result if the chargino or neutralino decays via the purely leptonic mode.

Heavy leptons at hadron supercolliders.

The production, decay, and detection of a fourth-generation charged heavy lepton L at multi-TeV hadron supercolliders is discussed for masses m/sub L/>M/sub W/ and m/sub ..nu..//sub >//sub L/approx. =0. The leptonic and hadronic decay signals for single L production and LL-bar pair production are evaluated. In all channels examined the heavy-lepton signal is smaller than backgrounds from single and pair production of W/sup +- / and Z bosons. However, it may still be possible to detect a heavy lepton from its contribution to pX/sub T/+2 or 4 jets events where the Z(..--> nu..nu-bar)+jets background may be determined from measurements of (Z..-->..ll-bar)+jets events.

Higgs-boson signals in superstring-inspired models at hadron supercolliders.

In superstring-inspired ${\mathrm{E}}_{6}$ supergravity models, the mass of the lightest Higgs scalar (${H}_{L}$) is expected to be below \ensuremath{\sim}170 GeV if ${\mathrm{E}}_{6}$ is broken directly to a rank-5 subgroup and below \ensuremath{\sim}210 GeV if intermediate scales of \ensuremath{\sim}${10}^{10}$ GeV are allowed. We show that if the mass of the additional neutral gauge boson ${Z}^{0\mathcal{'}}$ is less than about 600 GeV, then \ensuremath{\sim}${10}^{4}$--${10}^{5}$ ${Z}^{0\mathcal{'}}$\ensuremath{\rightarrow}${Z}^{0}$${H}_{L}$ pairs may be expected per ${10}^{4}$ ${\mathrm{pb}}^{\mathrm{\ensuremath{-}}1}$, the annual integrated luminosity anticipated at the proposed 40-TeV pp supercollider. This large rate allows us to use the clean ${Z}^{0}$\ensuremath{\rightarrow}ll\ifmmode\bar\else\textasciimacron\fi{} decays as a trigger for the Higgs-boson search. We find that even if ${H}_{L}$\ensuremath{\rightarrow}tt\ifmmode\bar\else\textasciimacron\fi{} decays dominate, a signal-to-background ratio substantially exceeding unity is expected for reasonable experimental resolutions on the measurement of ${Z}^{0}$tt\ifmmode\bar\else\textasciimacron\fi{} and tt\ifmmode\bar\else\textasciimacron\fi{} invariant masses. We further show that for a wide range of parameters, ${H}_{L}$ can decay into chargino and neutralino pairs. These decays lead to hadron-free ${Z}^{0}$+missing ${p}_{T}$ (p${?}_{T}$) events which may stand out over the ${Z}^{0}$${Z}^{0}$ background and also to spectacular ${Z}^{0}$+n lepton+p${?}_{T}$ events (n\ensuremath{\le}4) which are almost free of standard-model backgrounds.

Detecting gluinos at hadron supercolliders.

If the gluino mass exceeds 150--200 GeV, searches for gluinos will likely have to be made at multi-TeV hadron colliders. Unlike the case of light gluinos (${m}_{g\ifmmode \tilde{}\else \~{}\fi{}}$\ensuremath{\lesssim}60 GeV), which dominantly decay via g\ifmmode \tilde{}\else \~{}\fi{}\ensuremath{\rightarrow}qq\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\gamma}\ifmmode \tilde{}\else \~{}\fi{}, heavy-gluino decays proceed via g\ifmmode \tilde{}\else \~{}\fi{}\ensuremath{\rightarrow}qq\ifmmode\bar\else\textasciimacron\fi{}W${\ifmmode \tilde{}\else \~{}\fi{}}_{i}$ and g\ifmmode \tilde{}\else \~{}\fi{}\ensuremath{\rightarrow}qq\ifmmode\bar\else\textasciimacron\fi{}Z${\ifmmode \tilde{}\else \~{}\fi{}}_{j}$ where W${\ifmmode \tilde{}\else \~{}\fi{}}_{i}$ and Z${\ifmmode \tilde{}\else \~{}\fi{}}_{j}$ are charged and neutral mass eigenstates in the gauge-Higgs-fermion sector. The usual missing-${p}_{T}$ signatures are altered and new strategies may be required for gluino detection. We analyze heavy-gluino and scalar-quark decays and estimate the production rates for W${\ifmmode \tilde{}\else \~{}\fi{}}_{i}$W${\ifmmode \tilde{}\else \~{}\fi{}}_{j}$, W${\ifmmode \tilde{}\else \~{}\fi{}}_{i}$Z${\ifmmode \tilde{}\else \~{}\fi{}}_{j}$, and Z${\ifmmode \tilde{}\else \~{}\fi{}}_{i}$Z${\ifmmode \tilde{}\else \~{}\fi{}}_{j}$ pairs at a 40-TeV pp collider. Since a heavy gluino decays dominantly into jets and the heavy chargino, which in turn decays into a ${Z}^{0}$ or W boson plus a lighter chargino or neutralino, a typical gluino-pair event contains several leptons and/or jets in the final state.

Technipionium bound state formation and decays

Color octet technipion pairs bound together by the strong interaction could be produced at hadron colliders via gluon-gluon fusion. They would decay to W +W −, γγ, and Zγ with branching fractions of order (0.1–0.3)%. These signals are easily detectable at multi-TeV hadron supercolliders.