Search for supersymmetry at the p collider

Physics Letters B, 1985

If the squark mass mq is 0(40) GeV, as suggested by one interpretation of the CERN pp collider data, then one expects slepton masses m?-0(20-30) GeV in a wide class of models. Sleptons with such masses would be produced copiously in W ~ t~ and Z ° ~ ~Z-decays. We present rates and distributions for these processes, incorporating detector resolutions and experimental cuts. We show how the supersymmetric signals (especially for Z ° ~ ~-t r-) can easily be distinguished from the standard model backgrounds.

Journal of High Energy Physics, 2010

We calculate the relic abundance of thermally produced neutralino cold dark matter in the general 19 parameter supergravity (SUGRA-19) model. A scan over GUT scale parameters reveals that models with a bino-like neutralino typically give rise to a dark matter density Ωχ0 1 h 2 ∼ 1 − 1000, i.e. between 1 and 4 orders of magnitude higher than the measured value. Models with higgsino or wino cold dark matter can yield the correct relic density, but mainly for neutralino masses around 700-1300 GeV. Models with mixed bino-wino or bino-higgsino CDM, or models with dominant co-annihilation or A-resonance annihilation can yield the correct abundance, but such cases are extremely hard to generate using a general scan over GUT scale parameters; this is indicative of high fine-tuning of the relic abundance in these cases. Requiring that mχ0 1 < ∼ 500 GeV (as a rough naturalness requirement) gives rise to a minimal probably dip in parameter space at the measured CDM abundance. For comparison, we also scan over mSUGRA space with four free parameters. Finally, we investigate the Peccei-Quinn augmented MSSM with mixed axion/axino cold dark matter. In this case, the relic abundance agrees more naturally with the measured value. In light of our cumulative results, we conclude that future axion searches should probe much more broadly in axion mass, and deeper into the axion coupling.

Journal of High Energy Physics, 2012

The minimal supergravity (mSUGRA or CMSSM) model is an oft-used framework for exhibiting the properties of neutralino (WIMP) cold dark matter (CDM). However, the recent evidence from Atlas and CMS on a light Higgs scalar with mass m h ≃ 125 GeV highly constrains the superparticle mass spectrum, which in turn constrains the neutralino annihilation mechanisms in the early universe. We find that stau and stop co-annihilation mechanisms -already highly stressed by the latest Atlas/CMS results on SUSY searches -are nearly eliminated if indeed the light Higgs scalar has mass m h ≃ 125 GeV. Furthermore, neutralino annihilation via the A-resonance is nearly ruled out in mSUGRA so that it is exceedingly difficult to generate thermally-produced neutralino-only dark matter at the measured abundance. The remaining possibility lies in the focus-point region which now moves out to m 0 ∼ 10 − 20 TeV range due to the required large trilinear soft SUSY breaking term A 0 . The remaining HB/FP region is more fine-tuned than before owing to the typically large top squark masses. We present updated direct and indirect detection rates for neutralino dark matter, and show that ton scale noble liquid detectors will either discover mixed higgsino CDM or essentially rule out thermally-produced neutralino-only CDM in the mSUGRA model.

Nuclear Physics B, 1986

We study in detail production and decay of neutralinos in e ÷ e annihilation. Formulae for the cross sectiom the single lepton, lepton pair, and missing energy spectra are given. Particular attention is paid to the mixing of gauginos and higgsinos. In order to illustrate its importance numerical results for four different mixing scenarios are presented.

Physics Letters B, 1989

Physical Review D, 2001

We reexamine large CP-violating phases in the general Minimal Supersymmetric Standard Model, as well as more restricted models. We perform a detailed scan over parameter space to find solutions which satisfy the current experimental limits on the electric dipole moments of the electron, neutron and 199 Hg atom, exploring the allowed configurations of phases and masses, and we attempt to quantify the level of tuning of the parameters necessary to populate the regions of cancellations. We then consider the measurement of CP-violating phases at a future linear collider. We find that measurements of chargino and neutralino masses and production crosssections allow for a determination of φ 1 (the phase of M 1 ) to a precision of π/30, while the EDM constraints require that θ µ be too small to be measured. Using the EDM constraints we find that the CP-even model parameters and the phase φ 1 can be determined at a Linear Collider with 400 GeV c.m. energy. As long as some information on the size of |µ| is included in the observables, a measurement of φ 1 is guaranteed for φ 1 > π/10. To unambiguously identify CP violation, we construct CP-odd kinematical variables at a linear collider. However, the CP asymmetries are rather small, typically about 0.1 -1.5%, and it will be challenging to experimentally observe the predicted asymmetries.

Physical Review D, 2008

The mSUGRA parameter space corresponding to light sleptons well within the reach of LHC and relatively light squarks and gluinos (mass ≤ 1 TeV) has three regions consistent with the WMAP data on dark matter relic density and direct mass bounds from LEP 2. Each region can lead to distinct leptonic signatures from squark-gluino events during the early LHC experiments (integrated luminosity ∼ 10 fb −1 or even smaller). In the much studied stau-LSP coannihilation region with a vanishing common trilinear coupling (A 0) at the GUT scale a large fraction of the final states contain electrons and / or muons and eµτ universality holds to a good approximation. In the not so well studied scenarios with non-vanishing A 0 both LSP pair annihilation and stau-LSP coannihilation could contribute significantly to the dark matter relic density for even smaller squark-gluino masses. Our simulations indicate that the corresponding signatures are final states rich in τ-leptons while final states with electrons and muons are suppressed leading to a violation of lepton universality. These features may be observed to a lesser extent even in the modified parameter space (with non-zero A 0) where the coannihilation process dominates. We also show that the generic m-leptons + n-jets+ E / T signatures without flavour tagging can also discriminate among the three scenarios. However, the signals become more informative if the τ and b-jet tagging facilities at the LHC experiments are utilized.

Physics Letters B, 1990

Nuclear Physics B, 1986

We present a comprehensive analysis of missing transverse-energy events at the CERN p~ collider which would arise from a supersymmetric theory. This analysis takes into account, the new 1984 UA1 cuts, triggers and resolutions. Our conclusions from the newly reported 1984 data are that any excess number of monojet events is highly unlikely to come from gluino or scalar quark production. The new data lead to the very restrictive limits: M(g) and M(~) > 60-70 GeV. The two intriguing dijet events with E x (missing) > 55 GeV are not inconsistent with an 80 GeV ghiino or scalar quark source. The above conclusions have been obtained assuming that photinos are lighter than gluinos and live long enough to escape collider detectors. An alternative picture where the higgsino is the lightest supersymmetric particle is briefly discussed.

Physical Review D, 1984

We describe a simple, softly broken supersymmetric model of electroweak interactions. In its simplest form, supersymmetry breaking is imposed via explicit mass terms for scalar quarks and leptons. We apply this model to the discussion of the decay properties of the scalar neutrino, vg. The one-loop process V,-+ u+? (7 = photino) is computed as well as multi-body (tree-level) decays of the vs. The relative branching ratios are crucial for determining the phenomcnological signatures of the scalar neutrino. Complications to the model due to Majorana mass terms for the gauge fermions are discussed. Explicit Feynman rules for the model are listed.

Physics Letters B, 1984

For certain ranges of masses of the supersymmetric partners of the gluons, quarks and W-bosons, it is expected that a few events of production and decay of the partners could be observed at the CERN pp collider. The characteristic signatures are events with Q*jpff, Q*jj&, jjjh, jj&_and j& w ere Q* is an isolated charged lepton, j is a hadron jet and h h stands for missing PT. Some recently reported events are of this type.

Nuclear Physics B

We examine non-minimal supergravity models by omitting some of the usual simplifying assumptions. In particular, the SU(2)x U(1) breaking is uncoupled from the higgsino mass parameter, and the photino to gluino mass ratio is not rigidly fixed. We construct and examine in detail an interesting, and perhaps phenomenologically relevant model, with heavy squarks and light gluinos; the lightest supersymmetric particle is a higgsino ia, so the photino decays $ ~ "tia. We discuss ways to determine all of the parameters of the model, and its experimental implications. One interesting consequence is a new way to produce Higgs bosons, e ÷ e-~ Z°~ ~.-, lalaH °, with a rate that depends on the ~. mass but could be as large as almost one percent of all Z ° decays even for mrt up to about ] of Mz; the signature is H ° + missing energy, which is quite good for detection.

Physical Review D, 2002

Within the low-energy effective Minimal Supersymmetric extension of Standard Model (effMSSM) we calculated the neutralino relic density taking into account slepton-neutralino and neutralino-chargino/neutralino coannihilation channels. We performed comparative study of these channels and obtained that both of them give sizable contributions to the reduction of the relic density. Due to these coannihilation processes some models (mostly with large neutralino masses) enter into the cosmologically interesting region for relic density, but other models leave this region. Nevertheless, in general, the predictions for direct and indirect dark matter detection rates are not strongly affected by these coannihilation channels in the effMSSM.

Nuclear Physics B, 1984

We study extrema of the general conformally invariant action: Sc= | ~C Cabcd+TR abccl*~*-~-i~l)abcd*D lXabcd ,vax lXabcd. ja We find the first examples in four dimensions of asymptotically euclidean gravitational instantons. These have arbitrary Euler number and Hirzebruch signature. Some of these instantons represent tunneling between zero-curvature vacua that are not related by small gauge transformations. Others represent tunneling between flat space and topologically non-trivial zero-energy initial data. A general formula for the one-loop determinant is derived in terms of the renormalization group invariant masses, the volume of space-time, the Euler number and the Hirzebruch signature. * The relevance of infrared behavior to the unitarity problem has recently been emphasised by Pisarski [7].

Journal of Cosmology and Astroparticle Physics, 2004

The lightest neutralino of R-parity conserving supersymmetric models serves as a compelling candidate to account for the presence of cold dark matter in the universe. In the minimal supergravity (mSUGRA) model, a relic density can be found in accord with recent WMAP data for large values of the parameter tan β, where neutralino annihilation in the early universe occurs via the broad s-channel resonance of the pseudoscalar Higgs boson A. We map out rates for indirect detection of neutralinos via 1. detection of neutrinos arising from neutralino annihilation in the core of the earth or sun and 2. detection of gamma rays, antiprotons and positrons arising from neutralino annihilation in the galactic halo. If indeed A-resonance annihilation is the main sink for neutralinos in the early universe, then signals may occur in the gamma ray, antiproton and positron channels, while a signal in the neutrino channel would likely be absent. This is in contrast to the hyperbolic branch/focus point (HB/FP) region where all indirect detection signals are likely to occur, and also in contrast to the stau co-annihilation region, where none of the indirect signals are likely to occur.

Physical Review D - PHYS REV D, 2008

Traditional searches for supersymmetry (SUSY) at hadron colliders rely heavily on the presence of large missing transverse energy (MET) to reject background compared to signal. On the other hand, initial searches for new physics at the CERN LHC may not be able to rely on MET due to a variety of detector calibration issues. We show that much of SUSY parameter space is accessible to discovery even without using MET, and with rather low integrated luminosities, 0.1 1fb-1. A key role is played by isolated lepton multiplicity which arises from gluino and squark cascade decays. Requiring &gt;=3 isolated leptons plus jets yields a high rate of background rejection compared to signal. We find an LHC reach in m gtilde of about 700 750 GeV for just 0.1fb-1 of integrated luminosity by requiring events with &gt;=4 jets plus &gt;=3 isolated leptons but without using MET. If a large enough event sample is assembled, then kinematic reconstruction of sparticle mass properties should be possible jus...

Physical Review D, 1998

We calculate expected event rates for direct detection of relic neutralinos as a function of parameter space of the minimal supergravity model. Numerical results are presented for the specific case of a 73 Ge detector. We find significant detection rates (R > 0.01 events/kg/day) in regions of parameter space most favored by constraints from B → X s γ and the cosmological relic density of neutralinos. The detection rates are especially large in regions of large tan β, where many conventional signals for supersymmetry at collider experiments are difficult to detect. If the parameter tan β is large, then there is a significant probability that the first direct evidence for supersymmetry could come from direct detection experiments, rather than from collider searches for sparticles.

Physical Review D, 1996

Working within the framework of the minimal supergravity model with gauge coupling unication and radiative electroweak symmetry breaking, we evaluate the cosmological relic density from lightest neutralinos produced in the early universe. Our numerical calculation is distinct in that it involves direct evaluation of neutralino annihilation cross sections using helicity amplitude techniques, and thus avoids the usual expansion as a power series in terms of neutralino velocity. Thus, our calculation includes relativistic Boltzmann averaging, neutralino annihilation threshold eects, and proper treatment o f i n tegration over Breit-Wigner poles. We map out regions of parameter space that give rise to interesting cosmological dark matter relic densities. We compare these regions with recent calculations of the reach for supersymmetry by LEP2 and Tevatron Main Injector era experiments. The cosmologically f a v ored regions overlap considerably with the regions where large trilepton signals are expected to occur at the Tevatron. The CERN LHC pp collider can make a thorough exploration of the cosmologically favored region via gluino and squark searches. In addition, over most of the favored region, sleptons ought to be light enough to be detectable at both LHC and at a p s = 500 GeV e + e collider.

Journal of High Energy Physics, 2002

We evaluate the relic density of neutralinos in the minimal supergravity (mSUGRA) model. All 2 → 2 neutralino annihilation diagrams, as well as all processes involving sleptons, charginos, neutralinos and third generation squarks are included. Relativistic thermal averaging of the velocity times cross sections is performed. We find that co-annihilation effects are only important on the edges of the model parameter space, where some amount of fine-tuning is necessary to obtain a reasonable relic density. Alternatively, at high tan β, annihilation through very broad Higgs resonances gives rise to an acceptable neutralino relic density over broad regions of parameter space where little or no fine-tuning is needed. Finally, we compare our results against the reach of various e + e − and hadron colliders for supersymmetric matter.

Journal of High Energy Physics, 2005

In supersymmetric models with gravity-mediated SUSY breaking and gaugino mass unification, the predicted relic abundance of neutralinos usually exceeds the strict limits imposed by the WMAP collaboration. One way to obtain the correct relic abundance is to abandon gaugino mass universality and allow a mixed wino-bino lightest SUSY particle (LSP). The enhanced annihilation and scattering cross sections of mixed wino dark matter (MWDM) compared to bino dark matter lead to enhanced rates for direct dark matter detection, as well as for indirect detection at neutrino telescopes and for detection of dark matter annihilation products in the galactic halo. For collider experiments, MWDM leads to a reduced but significant mass gap between the lightest neutralinos so that Z 2 two-body decay modes are usually closed. This means that dilepton mass edges-the starting point for cascade decay reconstruction at the CERN LHC-should be accessible over almost all of parameter space. Measurement of the m Z 2 -m Z 1 mass gap at LHC plus various sparticle masses and cross sections as a function of beam polarization at the International Linear Collider (ILC) would pinpoint MWDM as the dominant component of dark matter in the universe.

Physical Review D, 2001

A SU(3) X SU(2),x U(1) supersymmetri<: theory is constructed with a TeV sized extra dimension compactified on the orbifold 8 1 /(Zz x Z~). The compactification breaks supersymmetry leaving a set of zero modes which correspond precisely to the states of the 1 Higgs doublet standard model. Supersymmetric Yukawa interactions are localized at orbifold fixed points. The top quark hypermultiplet radiatively triggers electroweak symmetry breaking, yielding a Higgs potential which is finite and exponentially insensitive to physics above the compactification scale. This potential depends ~n only a single free parameter, the compactification scale, yielding a Higgs mass prediction of 127 ± 8 GeV. The masses of the all superpartners, and the Kaluza-Klein excitations are also predicted. The lightest supersymmetric particle is a top squark of mass 197 ± 20 GeV. The top Kaluza-Klein tower leads to the p parameter having quadratic sensitivity to unknown physics in the ultraviolet.

Nuclear Physics B, 1984

We consider the cosmological constraints on supersymmetric theories with a new, stable particle. Circumstantial evidence points to a neutral gauge/Higgs fermion as the best candidate for this particle, and we derive bounds on the parameters in the Lagrangian which govern its mass and couplings. One favored possibility is that the lightest neutral supersymmetric particle is predominantly a photino 7 with mass above % GeV, while another is that the lightest neutral supersymmetric particle is a Higgs fermion with mass above 5 GeV or less than O(lOG)eV. We also point out that a gravitino mass of 10 to 100 GeV implies that the temperature after completion of an inflationary phase cannot be above 1o14 GeV, and probably not above 3 X 10 12 GeV. This imposes constraints on mechanisms for generating the baryon number of the universe.

Reports on Progress in Physics, 1996

The physics of supersymmetry is reviewed from the perspective of physics at ever increasing energies. Starting from the minimal supersymmetric extension of the Standard Model at the electroweak scale, we proceed to higher energies seeking to understand the origin of the many model parameters. Supersymmetric grand unification, supergravity, and superstrings are introduced sequentially, and their contribution to the sought explanations is discussed. Typical low-energy supersymmetric models are also presented, along with their possible experimental consequences via direct and indirect processes at high-energy physics experimental facilities.

Surveys in High Energy Physics, 1995

In these lectures I review the progress made over the last few years in the subject of string and string-inspired phenomenology. I take a practical approach, thereby concentrating more on explicit examples rather than on formal developments. Topics covered include: introduction to string theory, the free-fermionic formulation and its general features, generic conformal field theory properties, SU (5)×U (1) GUT and string model-building, supersymmetry breaking, the bottom-up approach to string-inspired models, radiative electroweak symmetry breaking, the determination of the allowed parameter space of supergravity models and the experimental constraints on this class of models, and prospects for direct and indirect tests of string-inspired models.

Nuclear Physics B, 1989

In a general supergravity theory, with minimal particle content, we describe the area of the parameter space that gives rise to a massive, stable neutralino X, with a cosmologically significant relic density. In this region of parameters we show the effect of the lightest Higgs exchange on the elastic neutralino-nucleus cross section, relevant to the direct detection methods. Finally, we visualize how the same parameter space can be probed expcrimcntally by studying chargino and neutralino pair production at e*e collidcrs.

Physical Review D, 2002

We calculate the neutralino relic density within the low-energy effective Minimal Supersymmetric extension of the Standard Model (effMSSM) taking into account slepton-neutralino, squark-neutralino and neutralino/chargino-neutralino coannihilation channels. By including squark (stop and sbottom) coannihilation channels we extend our comparative study to all allowed coannihilations and obtain the general result that all of them give sizable contributions to the reduction of the neutralino relic density. Due to these coannihilation processes some models (mostly with large neutralino masses) fall within into the cosmologically interesting region for relic density, but other models drop out at this region. Nevertheless, the predictions for direct and indirect dark matter detection rates are not strongly affected by these coannihilation channels in the effMSSM.

International Journal of Modern Physics A, 2004

The existence of dark matter was suggested, using simple gravitational arguments, seventy years ago. Although we are now convinced that most of the mass in the Universe is indeed some nonluminous matter, we still do not know its composition. The problem of the dark matter in the Universe is reviewed here. Particle candidates for dark matter are discussed with particular emphasis on Weakly Interacting Massive Particles (WIMP&#39;s). Experiments searching for these relic particles, carried out by many groups around the world, are also reviewed, paying special attention to their direct detection by observing the elastic scattering on target nuclei through nuclear recoils. Finally, we concentrate on the theoretical models predicting WIMP&#39;s, and in particular on supersymmetric extensions of the standard model, where the leading candidate for WIMP, the neutralino, is present. There, we compute the cross-section for the direct detection of neutralinos, and compare it with the sensitivi...

Physics Letters B, 1985

A search was performed for the associated production of two different Higgs bosons via a virtual Z ° in e+e -annihilation (e-e-~ h°hoe) using the JADE detector at PETRA. This was motivated by the interpretation of the monojet events observed at the CERN p~ collider as anomalous Z ° decays into two neutral Higgs bosons (h ° and h°2), where h ° is stable and escapes detection while hOe decays into hadrons. Single-or di-jet events with large momentum imbalance are then expected at PETRA energies. No evidence for such events was found in our data; this excludes hOe masses in the range of 1 to 21 GeV with 95% CL, if the branching fraction for Z ° --* h°h ° is larger than one half that for Z ° ~ ~. The possibility that the monojets could originate from supersymmetric higgsino production from Z ° decay is also examined.