arXiv subjects

Howard Baer

Publications and source records attributed to Howard Baer.

247 records · Page 14Linked to original sources

arXiv1996

Signals for the Minimal Gauge-mediated Supersymmetry Breaking Model at the Fermilab Tevatron Collider

We investigate the experimental implications of the minimal gauge-mediated low energy supersymmetry breaking (GMLESB) model for Fermilab Tevatron collider experiments. We map out the regions of parameter space of this model that have already been excluded by collider searches and by limits on $b\to sγ$. We use ISAJET to compute the cross sections for a variety of topological signatures which include photons in assocation with multiple leptons, jets and missing transverse energy. The reach in the parameter $Λ$, which fixes the scale of sparticle masses, is estimated to be $\sim 60$, 100 and 135 TeV for Tevatron integrated luminosities of 0.1, 2 and 25 fb$^{-1}$, respectively. The largest signals occur in photon(s) plus lepton(s) plus multi-jet channels; jet-free channels containing just photons plus leptons occur at much smaller rates, at least within this minimal framework.

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arXiv1996

Impact of Hadronic Decays of the Lightest Neutralino on the Reach of the CERN LHC

If $R$-parity is not conserved, the lightest supersymmetric particle (LSP) could decay via lepton number violating or baryon number violating interactions. The latter case is particularly insidious since it leads to a reduction of the $\eslt$ as well as leptonic signals for supersymmetry. We evaluate cross sections for jets plus $\eslt$, 1$\ell$, $2\ell$ (same-sign and opposite sign) and $3\ell$ event topologies that result from the simultaneous production of all sparticles at the CERN Large Hadron Collider (LHC), assuming that the lightest supersymmetric particle $\tz_1$ decays hadronically inside the detector via $R$-parity violating interactions. We assume that these interactions do not affect the production rates or decays of other sparticles. We examine the SUSY reach of the LHC for this ``pessimistic'' scenario, and show that experiments at the LHC will still be able to search for gluinos and squarks as heavy as 1 TeV, given just 10 fb$^{-1}$ of integrated luminosity, even with cuts designed to explore the canonical SUSY framework with a {\it conserved} $R$-parity.

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arXiv1996

Constraints on the Minimal Supergravity Model from Non-standard Vacua

We evaluate regions of parameter space in the minimal supergravity model where ``unbounded from below'' (UFB) or charge or color breaking minima (CCB) occur. Our analysis includes the most important terms from the 1-loop effective potential. We note a peculiar discontinuity of results depending on how renormalization group improvement is performed: One case leads to a UFB potential throughout the model parameter space, while the other typically agrees quite well with similar calculations performed using only the tree level potential. We compare our results with constraints from cosmology and naturalness and find a preferred region of parameter space which implies $m_{\tg}\alt 725$ GeV, $m_{\tq}\alt 650$ GeV, $m_{\tw_1}\alt 225$ GeV and $m_{\tell_R}\alt 220$ GeV. We discuss the consequences of our results for supersymmetry searches at various colliding beam facilities.

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arXiv1996

Supersymmetry Studies at Future Linear $e^+e^-$ Colliders

We examine various aspects of supersymmetric particle production at linear $e^+e^-$ colliders operating at a centre of mass energy of $\sqrt{s}=500$ GeV, and integrated luminosity of $\int {\cal L}dt=20-50$ fb$^{-1}$. Working within the framework of the minimal supergravity model with gauge coupling unification and radiative electroweak symmetry breaking (SUGRA), we study various signatures for detection of sparticles, taking into account their cascade decays, and map out the regions of parameter space where these are observable. We also examine strategies to isolate different SUSY processes from another. In addition, we perform four detailed SUGRA case studies and examine the detectability of sparticles when several SUSY processes are simultaneously occuring. We show that precision mass measurements of neutralinos, sneutrinos and top-squarks are possible, in addition to previously studied precision mass measurements of sleptons and charginos.

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arXiv1996

Supersymmetry Reach of Tevatron Upgrades: A Comparative Study

We use ISAJET to perform a detailed comparison of the supersymmetry reach of the current Tevatron (100~pb$^{-1}$) with that of the Main Injector (2~fb$^{-1}$) and the proposed TeV33 upgrade designed to yield an integrated luminosity of 25~fb$^{-1}$. Our analysis is performed within the framework of the minimal supergravity model with gauge coupling unification and radiative electroweak symmetry breaking. For each of these three luminosity options, we delineate the regions of parameter space where jets plus missing energy plus 0, 1, 2 (opposite sign and same-sign dileptons), and 3 isolated lepton signals from the cascade decays of sparticles should be visible above standard model backgrounds. We compare these with the parameter regions where signals in the clean isolated dilepton and trilepton channels (from chargino/neutralino and slepton production) should be observable.

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arXiv1996

Simultaneous Search for Two Higgs Bosons of Minimal Supersymmetry at the LHC

The prospects of detecting the CP-odd Higgs pseudoscalar ($A$) in the minimal supersymmetric model via its decay into a $Z$ boson and the lighter CP-even Higgs scalar ($h$) at the CERN Large Hadron Collider are investigated. The final state of $Z \to l^+l^-$ and $h \to b\bar{b}$, may provide a promising way to simultaneously detect the $A$ and the $h$. The compact muon solenoid detector performance is adopted for a realistic study of observability. In this discovery channel, the masses of the $h$ and the $A$ can be reconstructed. The impact of supersymmetric decay modes is considered.

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arXiv1996

Multiple Parton Emission Effects in Next-to-Leading Order Direct Photon Production

A recent global analysis of direct photon production at hadron collider and fixed target experiments has noted a disturbing trend of disagreement between next-to-leading-order (NLO) calculations and data. The conjecture has been made that the discrepancy is due to explicit multiple parton emission effects which are not accounted for in the theoretical calculations. We investigate this problem by merging a NLO calculation of direct photon production with extra multiple parton emissions via the parton shower (PS) algorithm. Our calculation maintains the integrity of the underlying NLO calculation while avoiding ambiguities due to double counting of multiple parton emissions. We find that the NLO+PS calculation can account for much of the theory/CDF data discrepancy at $\sqrt{s}=1.8$ TeV. It can also account for much of the theory/UA2 discrepancy if a very large virtuality is assumed to initiate the initial state parton shower. For lower energy data sets ({\it e.g.} $\sqrt{s}< 63$ GeV), NLO+PS calculations alone cannot account for the data/theory discrepancy, so that some additional non-perturbative $k_T$ smearing is needed.

hep-ph↗

arXiv1995

Signals for Minimal Supergravity at the CERN Large Hadron Collider II: Multilepton Channels

We use ISAJET to perform a detailed study of the multilepton signals expected from cascade decays of supersymmetric particle produced at the CERN LHC. Our analysis is performed within the framework of the minimal supergravity model with gauge coupling unification and radiative electroweak symmetry breaking. We delineate the regions of parameter space where jets plus missing energy plus 1, 2 (opposite sign and same-sign dileptons), and 3 isolated lepton events should be visible above standard model backgrounds. We find that if any $\eslt$ signal at the LHC is to be attributed to gluino and/or squark production, and if $m_{\tg} \alt 1$~TeV, then several of these signals must be simultaneously observable. Furthermore, assuming $10\,\fb^{-1}$ of integrated luminosity, we find that the reach for supersymmetry in the 1$\ell + \jets +\eslt$ channel extends to $m_{\tg}\sim 2300\ (1600)$ GeV for $m_{\tq}\sim m_{\tg}$ ($m_{\tq} \sim 1.5m_{\tg}$), and exceeds the corresponding reach in the $0\ell+\eslt$ channel. We show that measurements of the various topological cross sections, jet and $B$-hadron multiplicities in these events, together with the charge asymmetry for single lepton and same-sign dilepton events, and flavor asymmetry for opposite sign dilepton events, serve to narrow the allowed range of underlying SUGRA parameter values. We also delineate parameter regions where signals with clean isolated dilepton (from slepton production) and trilepton events (from chargino/neutralino production) are visible at the LHC, and examine the extent to which these signals can be separated from other SUSY sources.

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arXiv1995

Anomaly-Free Gauged R-Symmetry

We review the gauging of an R-symmetry in local and global susy. We then construct the first anomaly-free models. We break the R-symmetry and susy at the Planck scale and discuss the low-energy effects. We include a solution to the mu-problem, and the prediction of observable effects at HERA. The models also nicely allow for GUT-scale baryogenesis and R-parity violation without the sphaleron interactions erasing the baryon-asymmetry.

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arXiv1995

Prospects for Supersymmetry at LEP2

Working within the framework of the minimal supergravity model with gauge coupling unification and radiative electroweak symmetry breaking (SUGRA), we map out regions of parameter space explorable by experiments at LEP2, for center of mass energy options of $\sqrt{s}=150,\ 175$, $190$ and 205 GeV. We compute signals from all accessible $2 \rightarrow 2$ SUSY pair production processes using the ISAJET simulation program, and devise cuts that enhance the signal relative to Standard Model backgrounds, and which also serve to differentiate various supersymmetric processes from one another. We delineate regions of SUGRA parameter space where production of neutralino pairs, chargino pairs, slepton pairs and the production of the light Higgs scalar of SUSY is detectable above Standard Model backgrounds and distinguishable from other SUSY processes. In addition, we find small regions of SUGRA parameter space where $\te\te$, $\tz_2\tz_2$ and $\tnu_L\tnu_L$ production yields spectacular events with up to four isolated leptons. The combined regions of parameter space explorable by LEP2 are compared with the reach of Tevatron Main Injector era experiments. Finally, we comment on how the reach via the neutralino pair channel is altered when the radiative electroweak symmetry breaking constraint is relaxed.

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arXiv1995

SUPERSYMMETRY REACH OF AN UPGRADED 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 $μ<0$; however, for $μ>0$ 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.

hep-ph↗

arXiv1995

THE SEARCH FOR SUPERSYMMETRY

The minimal supergravity model (SUGRA), with gauge coupling unification and radiative electroweak symmetry breaking, is a well-motivated paradigm for physics Beyond the Standard Model. In this talk, I review the capabilities of various present and future collider experiments to make definitive tests of the SUGRA model, including LEP and LEP II, the Tevatron and its upgrades, and finally the CERN LHC project.

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arXiv1993

Aspects of Chargino-Neutralino Production at the Tevatron Collider

We have used ISAJET 7.0/ISASUSY 1.0 to evaluate the rates and study distributions for trilepton events from the leptonic decays of charginos and neutralinos produced at the Fermilab Tevatron via the reaction, $p\bar p\rightarrow \tilde{W_1} \tilde{Z_2}$ + X for cuts inspired by the CDF and D0 experiments. We find that about 60\% of these events do not contain any jets, and so should be easily identifiable over Standard Model backgrounds from $t\bar{t}$ and WZ production, provided that the decay $\tilde{Z_2}\rightarrow\tilde{Z_1}Z$ is kinematically inaccessible. We further show that, with suitable cuts, these backgrounds can be reduced to less than 1-2 $fb$ even if $n_{jet} = 1$, effectively increasing the SUSY sample by 50\%. We confirm that the signal is only rate-limited, and that the Fermilab Tevatron after an accumulation of 100 $pb^{-1}$ of integrated luminosity will be able to explore parameters well beyond the range of LEP and, if sleptons are substantially lighter than squarks, close to the reach of LEP 200.

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