Light Gluinos Research Articles

Low and high energy limits of particle spectra in QCD jets

Charged particle energy spectra in e+e- annihilation are compared with the analytical predictions from the QCD evolution equation in the Modified Leading Log Approximation. With the nonperturbative initial condition shifted down to threshold as suggested by the Local Parton Hadron Duality picture a good description of the data from the lowest up to highest available energies results. The two essential parameters in this approach are determined from a moment analysis. The sensitivity of the fit to the running of alpha_s and to the number of active flavours (including a light gluino) is demonstrated. For very high energies the theory predicts a scaling behaviour in certain rescaled variables (``zeta-scaling''). The data show an approximate behaviour of this type in the present energy range and come close to the predicted asymptotic scaling function for the small particle energies.

Search for Light Gluinos via the Spontaneous Appearance of π+π- Pairs with an 800 GeV/c Proton Beam at Fermilab

We searched for the appearance of π+π− pairs with invariant mass ≥648MeV/c2 in a neutral beam. Such an observation could signify the decay of a long-lived light neutral particle. We find no evidence for this decay. Our null result severely constrains the existence of an R0 hadron, which is the lightest bound state of a gluon and a light gluino (gg̃), and thereby also the existence of a light gluino. Depending on the photino mass, we exclude the R0 in the mass and lifetime ranges of 1.2–4.6GeV/c2 and 2×10−10–7×10−4s, respectively.Received 18 July 1997DOI:https://doi.org/10.1103/PhysRevLett.79.4083©1997 American Physical Society

Constraints on light gluinos from Fermilab Tevatron dijet data

The effects of light, long-lived gluinos on 2\ensuremath{\rightarrow}2 processes at hadron colliders are examined. Such particles can mediate single squark resonant production via $q\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}\ensuremath{\rightarrow}\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{q}\ensuremath{\rightarrow}q\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}$ which would significantly modify the dijet data sample. We find that squark masses in the range 130 ${m}_{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{q}}$694,595,573 GeV are excluded for gluino masses of 0.4,1.3,5.0 GeV from existing UA2 and Fermilab Tevatron data on dijet bump searches and angular distributions. Run II of the Tevatron has the capability of excluding this scenario for squark masses up to \ensuremath{\sim}1 TeV.

Group independent color decomposition of next-to-leading order matrix elements for e+e−→ four partons

We present the next-to-leading order partonic cross sections involving an electroweak vector boson and four massless partons (quarks, gluons or gluinos) in a general gauge theory with a simple Lie Group. The vector boson couples to a massless lepton pair and a quark-antiquark pair. The cross sections are given in terms of group independent kinematical functions multiplying the eigenvalues of the quadratic Casimir operator of the Lie group. This kind of color decomposition is required for the calculation of O( α s 3 ) corrections to the group independent kinematical functions in the four-jet production cross sections in electron-positron annihilation. The knowledge of these corrections facilitates the simultaneous precision measurement of the strong coupling and the color charge factors using the four-jet LEP or SLC data as well as the test whether these data favour or exclude the existence of a light gluino.

Light gluino and Tevatron dijet angular distributions

Abstract We consider the effects of a light gluino on the dijet angular distributions in p p collisions at s =1800 GeV . We show that the slower running of αs and the production q q ,gg → g g do not significantly alter the normalized differential cross-sections. On the other hand, single u , d squard production qg → q g with subsequent q → q g results in dijets whose angular distributions are dramatically different from that in SM. The CDF data on dijet angular distributions with integrated luminosity of 106 pb−1 exclude u and d squarks in the mass ranges 190 ≤ m ≤ 650 and 200 ≤ m ≤ 630 GeV, respectively. We extend our analysis to lower energies and show that in a future experimental analysis for dijet mass below 240 GeV squarks will be observed or ruled out.

Gluino signals in 4jet events and vertex tagging at LEP I

Heavy flavour tagging provides a broad range of possibilities in testing QCD features at LEP. We present here a study of 4jets events at LEP I where the so-called light gluinos could be directly produced. We show that microvertex techniques offer a unique chance to exploit simple kinematical distributions in order to optimise the signal coming from gluino production with respect to the background of ordinary QCD events. Our results indicate that experimental analyses along the lines suggested here can exclude or reveal the presence of a gluino for masses up to 10 GeV and lifetimes below 10 $^{-9}$ sec. We also point out that a large fraction of gluino events could decay in configurations carrying large missing energy, so to escape the usual selection criteria of 4jet samples. In our study, mass effects of quarks and gluinos have been taken into account exactly. Our results are independent from both the jet algorithm and its resolution parameter.

A measurement of the QCD colour factors and a limit on the light gluino

Using data collected from 1992 to 1995 with the ALEPH detector at LEP, a measurement of the colour factor ratios C-A/C-F and T-F/C-F and the strong coupling constant = C-F alpha(s), (M-Z)/(2 pi) has been performed by fitting theoretical predictions simultaneously to the measured differential two-jet rate and angular distributions in four-jet events. The result is found to be in excellent agreement with QCD.C-A/C-F = 2.20 +/- 0.09 (stat) +/- 0.13 (syst),T-F/C-F = 0.29 +/- 0.05 (stat) +/- 0.06 (syst).Fixing C-A/C-F and T-F/C-F to the QCD values permits a determination of alpha(s) (M-Z) and n(f), the number of active flavours. With this measurement the existence of a gluino with mass below 6.3 GeV/c(2) is excluded at 95% confidence level.

New Messenger Sector for Gauge Mediated Supersymmetry Breaking

We propose a new class of gauge mediated supersymmetry breaking models where the standard model gauge group is embedded into the gauge group $SU(2)_L\times U(1)_{I_{3R}}\times U(1)_{B-L}$ [or $SU(2)_L\times SU(2)_R\times U(1)_{B-L}$] at the supersymmetry breaking scale $\Lambda_S$. The messenger sector in these models can consist of color singlet but $U(1)_{I_{3R}}$ and $U(1)_{B-L}$ nonsinglet fields. The distinguishing feature of these models are (i)exact R-parity conservation, (ii) nonvanishing neutrino masses and (iii) a unified hidden and messenger sector potential. The simplest version of these models predicts the existence of light gluinos which can however be made heavier by a simple modification of the supersymmetry breaking sector.

Determining theβFunction of the Strong Interaction Coupling and Closing the Light Gluino Window

We discuss the perturbative running of alpha_s in a model independent way. Our analysis contains data on the hadronic tau decay and hadronic cross sections in e+e- annihilation between 5 GeV and M_Z. We determine the color coefficients and the perturbative beta-function of the strong interaction. The results are in agreement with QCD and rule out the QCD+light gluino scenarios on the 70.8 - 93.0% CL. We combine our method with that of the multi-jet analysis at LEP. The combined result rules out light gluinos at least on the 99.76% CL, provided that nonperturbative effects are not large.

Excluding light gluinos from Z decays

We reanalyze the constraints on light gluinos ( m g ≤ 5 GeV/c 2 ) from the hadronic Z decays into four jets. We find that the published OPAL data from the 1991 and 1992 runs exclude a light quasi-stable gluino with mass ≲ 1.5 GeV/ c 2 at more than 90% confidence level. This limit depends little on assumptions about the gluino fragmentation and the definition of the gluino mass. The exclusion confidence level is shown as a function of the mass. A future projection is briefly discussed. We also discuss quantitatively how the distributions in the Bengtsson-Zerwas and the modified Nachtmann-Reiter angles change due to the finite bottom quark or gluino mass. The analysis is limited to the leading-order calculations. We, however, give an empirical reason to why the next-to-leading-order corrections are unlikely to change our conclusions.

Gluino contribution to the three-loopβfunction in the minimal supersymmetric standard model

We deduce the gluino contribution to the three-loop QCD \beta function within the minimal supersymmetric Standard Model (MSSM) from its standard QCD expression. The result is a first step in the computation of the full MSSM three-loop \beta function. In addition, in the case of a light gluino it provides the strong three-loop SUSY correction to the extrapolation of the strong coupling constant from the low energy regime to the Z region and up to the squark threshold.

Light Gluino Contribution in Hadronic Decays of theZBoson andτLepton toO(αs3)

The results of calculation of light gluino contributions to Gamma(Z--->hadrons) and Gamma(tau--->hadrons) to O(alpha_s^3) are presented. The net effect in the case of Z decay is noticeable. For the tau width the effect is very large and, if a light gluino exists, suggests that alpha_s increases by more than 15% relative to the Standard Model analysis.

Light gluino mass and condensate from properties of η and η′

We investigate whether known properties of the η′ meson are consistent with its being the Goldstone boson of the spontaneously broken anomaly-free R symmetry required in the light gluino scenario. We fit the masses and 2γ decays of the η and η′ mesons, and also their production in radiative J ψ decays. We find that the η - η′ system is well-described in the light gluino scenario, if m λ ⋍ (84–144) MeV and 〈 λ λ〉 ⋍ −(0.15–0.36) GeV 3. These values are in the range expected when the gluino gets its mass entirely from radiative corrections.

Corrections of order αs3 to Rhad in pQCD with light gluinos

By a completely independent analytic calculation made in general covariant gauge we confirm the known result for the massless O (α s 3) correction to R had and check explicitly its gauge independence. We extend the calculations to include contributions due to a hypothetical existence of a colour octet of (light) neutral fermions known also under the name of gluinos. In numerical form and for five active flavours we found (in MS scheme) that R(s) = 11 3 [1 + α s π + (1.409 − 0.346n g ) ( α s π ) 2 + (−12.805 − 3.006n g − 0.0466n g 2) ( α s π ) 3] where n g is the number of such colour octets. The gluino O (α s 3) contribution to the Z-boson hadronic decay rate proves to be relatively small while it is significant for τ-lepton semihadronic width.

Light gluinos and jet production in [formula omitted] collisions

The impact of a light, long lived gluino on jet production cross sections in pp collisions is estimated. The effect is found to be relatively modest, particularly when gluinos are incorporated into the parton densities of the proton. Although a light gluino does enhance the production of jets at high E T , the effect is insufficient, by itself, to explain the high E T excess observed by CDF.

Inclusive Jet ET Distributions and Light Gluinos.

In the light gluino variant of the minimal supersymmetric model gluino pairs can be readily produced in collider experiments even if the squarks are arbitrarily heavy. This enhances the jet transverse energy distributions. In addition the slower running of the strong coupling constant in the presence of light gluinos leads to a further enhancement at higher transverse energies relative to the standard $QCD$ expectations. Finally, the enhanced squark gluino production would lead to a Jacobian peak in the $E_T$ distribution at about $M_{\tilde Q}/2$. These effects are of about the right magnitude to explain anomalies observed by the $CDF$ and $D0$ collaborations.

Light gluino and squark production in Tevatron dijet experiments

We consider single squark production in p p collisions at s =1800 GeV in the light gluino scenario, where production is dominated by the parton subprocess qg → q g → g g . Computed are the total production cross sections as well as the contribution of such production to the dijet mass distribution. We compare our cross sections to the experimental data from the CDF collaboration with integrated luminosity of 19 pb −1.

Bdecay into light gluinos

Flavor changing interactions of the gluino allow the $b$ quark to decay into the strange quark plus a gluino pair if the gluino is in the ultra low mass window below 1 GeV. In this case the enhancement of the nonleptonic $b$ decay could explain the anomalous semileptonic branching ratio.

Electroproduction and hadroproduction of light gluinos.

In a class of supergravity models, the gluino and photino are massless at tree level and receive small masses through radiative corrections. In such models, one expects a gluino-gluon bound state, the $R_0$, to have a mass of between 1.0 and 2.2 GeV and a lifetime between $10^{-10}$ and $10^{-6}$ seconds. Applying peturbative QCD methods (whose validity we discuss), we calculate the production cross sections of $R_0$'s in $e-p$, $\pi-p$, $K-p$, $\overline{p}-p$ and $p-p$ collisions. Signatures are also discussed.

Reconciling supersymmetric grand unification with alpha s(mZ)

We argue that supersymmetric grand unification of gauge couplings is not incompatible with small $\alpha_s$, even without large GUT-scale corrections, if one relaxes a usual universal gaugino mass assumption. A commonly assumed relation $M_2\simeq m_{\rm gluino}/3$ is in gross contradiction with $\alpha_s\approx 0.11$. Instead, small $\alpha_s$ favors $M_2\gg m_{\rm gluino}$. If this is indeed the case our observation casts doubt on another commonly used relation $M_1\simeq 0.5 M_2$ which originates from the same constraint of a common gaugino mass at the GUT scale. One firm prediction emerging within the small $\alpha_s$ scenario with the unconstrained gaugino masses is the existence of a relatively light gluino below $\sim$ 200\gev.