Trilepton Signal Research Articles

Supersymmetry reach of an upgraded Fermilab Tevatron collider.

We examine the capability of a $\sqrt{s}=2$ TeV Tevatron $p\bar p$ collider to discover supersymmetry, given a luminosity upgrade to amass $25\ fb^{-1}$ of data. We compare with the corresponding reach of the Tevatron Main Injector ($1\ fb^{-1}$ of data). Working within the framework of minimal supergravity with gauge coupling unification and radiative electroweak symmetry breaking, we first calculate the regions of parameter space accessible via the clean trilepton signal from $\tw_1\tz_2\to 3\ell +\eslt$ production, with detailed event generation of both signal and major physics backgrounds. The trilepton signal can allow equivalent gluino masses of up to $m_{\tg}\sim 600-700$ GeV to be probed if $m_0$ is small. If $m_0$ is large, then $m_{\tg}\sim 500$ GeV can be probed for $\mu <0$; however, for $\mu >0$ and large values of $m_0$, the rate for $\tz_2\to\tz_1\ell\bar{\ell}$ is suppressed by interference effects, and there is {\it no} reach in this channel. We also examine regions where the signal from $\tw_1\overline{\tw_1}\to \ell\bar{\ell}+\eslt$ is detectable. Although this signal is background limited, it is observable in some regions where the clean trilepton signal is too small. Finally, the signal $\tw_1\tz_2\to jets+\ell\bar{\ell} +\eslt$ can confirm the clean trilepton signal in a substantial subset of the parameter space where the trilepton signal can be seen. We note that although the clean trilepton signal may allow Tevatron experiments to identify signals in regions of parameter space beyond the reach of LEP II, the dilepton channels generally probe much the same region as LEP II.

Supersymmetry dileptons and trileptons at the Fermilab Tevatron.

We consider the production of supersymmetry neutralinos and charginos in $p\bar p$ collisions at the Tevatron, and their subsequent decay via hadronically quiet dileptons and trileptons. We perform our computations in the context of a variety of supergravity models, including generic four-parameter supergravity models, the minimal $SU(5)$ supergravity model, and $SU(5)\times U(1)$ supergravity with string inspired two- and one-parameter moduli and dilaton scenarios. Our results are contrasted with estimated experimental sensitivities for dileptons and trileptons for integrated luminosities of $100\ipb$ and $1\ifb$, which should be available in the short and long terms. We find that the dilepton mode is a needed complement to the trilepton signal when the latter is suppressed by small neutralino leptonic branching ratios. The estimated reaches in chargino masses can be as large as $100\,(150)\GeV$ for $100\ipb\,(1\ifb)$. We also discuss the task left for LEPII once the Tevatron has completed its short-term search for dilepton and trilepton production.

Fermilab Tevatron and CERN LEP II probes of minimal and string-motivated supergravity models.

We explore the ability of the Fermilab Tevatron to probe minimal supersymmetry with high-energy-scale boundary conditions motivated by supersymmetry breaking in the context of minimal and string-motivated supergravity theory. A number of boundary condition possibilities are considered: dilatonlike string boundary conditions applied at the standard GUT unification scale or alternatively at the string scale; and extreme (``no-scale'') minimal supergravity boundary conditions imposed at the GUT scale or string scale. For numerous specific cases within each scenario the sparticle spectra are computed and then fed into isaget 7.07 so that explicit signatures can be examined in detail. We find that, for some of the boundary condition choices, large regions of parameter space can be explored via same-sign dilepton and isolated trilepton signals. For other choices, the mass reach of Tevatron collider experiments is much more limited. We also compare the mass reach of Tevatron experiments with the corresponding reach at CERN LEP 200.

Supersymmetry at a proposed sqrt s =4 TeV upgrade of the Fermilab Tevatron.

We study the signals for supersymmetry at the Tevatron and DiTevatron ($\sqrt{s}=4\TeV$) in various well-motivated supersymmetric models. We consider the trilepton signature in the decay of pair-produced charginos and neutralinos, the missing energy signature in gluino and squark production, and the $b\bar b$ signal in the decay of the lightest supersymmetric Higgs boson produced in association with a $W$ or $Z$ boson. In each case we perform signal and background studies, using Monte Carlo and/or real data to estimate the sensitivity to these signals at the Tevatron and DiTevatron with the Main Injector, for short- and long-term integrated luminosities of ${\cal L}=10$ and $25\ifb$, and $5\sigma$ statistical significance. We conclude that one could probe chargino masses as high as $m_{\chi^\pm_1}\sim180\,(200)\GeV$, gluino masses as high as $m_{\tilde g}\sim450\,(750)\GeV$, and lightest Higgs boson masses as high as $m_h\sim110\,(120)\GeV$ at the Tevatron (DiTevatron). A high-luminosity option at the Tevatron ($10^{33}\cm^{-2}\s^{-1}$) may compensate somewhat for the higher reach of the DiTevatron, but only in the trilepton and Higgs signals. However, these gains may be severely compromised once the multiple-interaction environment of the high-luminosity Tevatron is accounted for.

Trileptons from chargino-neutralino production at the CERN Large Hadron Collider.

We study direct production of charginos and neutralinos at the CERN Large Hadron Collider. We simulate all channels of chargino and neutralino production using ISAJET 7.07. The best mode for observing such processes appears to be $pp\to\tw_1\tz_2\to 3\ell +\eslt$. We evaluate signal expectations and background levels, and suggest cuts to optimize the signal. The trilepton mode should be viable provided $m_{\tg}\alt 500-600$~GeV; above this mass, the decay modes $\tz_2\to\tz_1 Z$ and $\tz_2\to H_{\ell}\tz_1$ become dominant, spoiling the signal. In the first case, the leptonic branching fraction for $Z$ decay is small and additional background from $WZ$ is present, while in the second case, the trilepton signal is essentially absent. For smaller values of $m_{\tg}$, the trilepton signal should be visible above background, especially if $|\mu|\simeq m_{\tg}$ and $m_{\tell}\ll m_{\tq}$, in which case the leptonic decays of $\tz_2$ are enhanced. Distributions in dilepton mass $m(\ell\bar{\ell})$ can yield direct information on neutralino masses due to the distribution cutoff at $m_{\tz_2}-m_{\tz_1}$. Other distributions that may lead to an additional constraint amongst the chargino and neutralino masses are also examined.

Improved LEP lower bound on the lightest SUSY Higgs mass from radiative electroweak breaking and its experimental consequences

We show that the present LEPI lower bound on the Standard Model Higgs boson mass (M H⪆60 GeV) applies as well to the lightest Higgs boson ( h) of the minimal SU (5) and no-scale flipped SU (5) supergravity models. This result would persist even for the ultimate LEPI lower bound (M H⪆70 GeV) . We show that this is a consequence of a coupling phenomenon in the Higgs sector driven by radiative electroweak breaking for increasingly larger sparticle masses, and thus it should be common to a large class of superconductivity models. A consequence of m h⪆60 GeV in the minimal SU(5) supergravity model is the exclusion from the allowed space of “spoiler modes” ( χ 2 0→ χ 1 0 h) which would make the otherwise very promising trilepton signal in p p→χ 1 ±χ 2 0X unobservable at Fermilab. Within this model we also obtain stronger upper bounds on the lighter neutral ino and chargino masses, i.e., m χ 1 0⪅50 GeV, m χ 2 0, χ 1 ±⪅100GeV. This should encourage experimental searches with existing facilities.

SUPERSYMMETRIC SIGNALS AT THE TEVATRON

The possibility of detecting SUSY signals arising from Wino and Zino production at the Tevatron is examined. If the Tevatron is operated at peak luminosity of 1031cm−2 sec −1 with full lepton detection capabilities, we estimate for a UA1 type apparatus that the trilepton signal is sensitive to Winos with mass up to ≈70–80 GeV , the dilepton signal up to ≈50–60 GeV and the monojet signal up to ≈45–50 GeV .

Multilepton signals from W ± and Z 0 decays to gauginos at [formula omitted]p colliders

One of the interpretations of the CERN monojet events requires the squark mass to be about 40–50 GeV implying a slepton mass around 20–30 GeV in a wide variety of models. If, in this scenario, the wino (W̃) and zino (Z̃) masses are light enough so that the decays W → W̃Z̃ and Z → W̃W̃ are allowed, a variety of spectacular dilepton and trilepton signals are expected to occur at a substantial rate and with negligible backgrounds. We present rates and distributions for these multilepton events which may be used to pin down the gaugino masses.