Gluino Distribution Research Articles

Light gluinos and the parton structure of the nucleon

We study the effects of light gluinos with mass below about 1 GeV on the nucleon parton densities and the running of alpha_(S). It is shown that from the available high-statistics DIS data no lower bound on the gluino mass can be derived. Also in the new kinematical region accessible at HERA the influence of such light gluinos on structure f unctions is found to be very small and difficult to detect. For use in more direct searches involving final state signatures we present a radiative estimate of the gluino distribution in the nucleon.

Light gluinos and the longitudinal structure function

The leading effect of light gluinos on the deep inelastic longitudinal structure function is calculated. We present the explicit analytic expression for the Wilson coefficient. After convolution with quark, gluon and gluino distributions we found that the size of the contribution is of order a few percent of the total F L . Some phenomenological implications for HERA and LEP/LHC are given.

Light gluinos in high- Q2 deep inelastic scattering

A slight incompatibility in recent low-energy and high-energy α s measurements can be interpreted as evidence for new light colour degrees of freedom. Assuming that these are the gluinos of a supersymmetric extension of the Standard Model, we investigate to what extent they change the standard QCD predictions for deep inelastic structure functions, and in particular whether they can be detected in such measurements at HERA. We present a modified set of parton distributions which includes a light gluino distribution and which can be used for further phenomenological investigation.

Light-gluino scenario.

We investigate in detail the consequences of the supersymmetry scenario with a light (approx.5 GeV) gluino and heavy (approx.100 GeV) scalar quarks, including gluino distribution and fragmentation effects, proposed to explain large-missing-p/sub T/ events observed at the CERN pp-bar collider. The effective gluino distribution in the nucleon is evaluated using the Altarelli-Parisi equations. Ambiguities in evaluating scalar-quark production with the effective gluino distribution are discussed. A plausible gluino fragmentation function is deduced from heavy-quark fragmentation functions; scaling violations in the gluino fragmentation function are taken into account. Fragmentation effects drastically reduce the missing p/sub T/ in light-gluino jets. The present collider data do not rule out a light gluino with mass in the range of 3-5 GeV even if the g lifetime, from decay into a photino and a quark pair, is short.

Gluino contributions to high-transverse-momentum hadron production at very high energies.

We calculate the contributions to high-transverse-momentum pion production, in the present CERN p\ifmmode\bar\else\textasciimacron\fi{}p collider energy range and beyond, of all subprocesses involving at the partonic level lowest-order gluino interactions, in the framework of supersymmetric quantum chromodynamics (SQCD). We employ ${Q}^{2}$-dependent models for the gluino distribution and fragmentation functions, which are constructed in the SQCD Altarelli-Parisi framework. These are found to be very strongly peaked for small momentum fractions, where they can become comparable to the corresponding gluon functions, decreasing very rapidly as the momentum fraction approaches unity. The gluino mass is treated as a parameter: we present results at the indicative values m=2, 10, and 30 GeV. It is found that although gluino subinteractions give unimportant contributions to the inclusive production of ordinary hadrons at present collider energies, they increase considerably in the TeV energy range and may be unraveled by future experiments.

Implications of a systematic study of the CERN monojets for supersymmetry.

We report on a comprehensive study of supersymmetric processes which could give events similar to those observed at the CERN $\mathrm{S}\overline{p}p\mathrm{S}$ collider. The present limited data seem to suggest a gluino mass \ensuremath{\lesssim} 20 GeV and a scalar-quark mass of 100- 120 GeV, although certain other supersymmetric masses are not yet excluded. With this choice of masses we also predict that other events with different characteristics should be observed. An essential ingredient of our analysis is the inclusion of events originating from a perturbatively generated gluino distribution function inside the proton.

Leptoproduction of supersymmetric particles

We study the production of scalar leptons ( l ) , scalar quarks ( q ) and gluinos ( g ) in ep → ν X , and ep → e X and the associated production of q and g in ep → eX and ep → νX. We find that v q and e q production is probably measurable at HERA for masses of order 40 GeV with exchanged ticle masses of order 80 GeV. We derive and solve the asymptotic supersymmetric evolution equations for quark, gluon, scalar quark and gluino distributions. We find sum rules for the asymptotic momentum fractions and for the partition of the net quark number between quarks and scalar quarks. We use a fusion model to study associated leptoproduction in the threshold region. The only appreciable contribution is from small Q 2 electroproduction but the rates are low even for scalar quarks and gluinos with masses close to the present limits.

Short-distance structure of hadrons in supersymmetric QCD

Assuming supersymmetry to be a real symmetry in particle physics, we study the short-distance internal structure of nucleons (structure functions at large Q 2). We determine all calculable quantities in the leading logarithm approximation and discuss the N = 1 supersymmetry relations between them. Further relations are obtained by observing that the N = 1 supersymmetric lagrangian becomes N = 2 supersymmetric if the quarks and squarks are (formally) put into the adjoint representation of SU(3) colour. From the calculated elements of the 4 × 4 matrix of the Q 2 evolution kernels and knowing the quark and gluon distributions at low Q 2 we are able to determine the quark, squark, gluon, and gluino distributions for Q 2 above the threshold for the production of supersymmetric particles. We find that in the asymptotic limit ( Q 2 → ∞) the quarks carry only 2 3 of the nucleon's baryon number and the remaining 1 3 is carried by the squarks. We also find that in this limit 0.32 of the longitudinal nucleon momentum is carried by gluons, 0.08 by gluinos, 0.36 by the quarks and 0.24 by the squarks.

Light gluinos in deep inelastic scattering

We extend the standard QCD predictions, up to second order, to the scaling violation of the deep inelastic structure functions in the presence of light gluinos (supersymmetric partners of gluons). We show that these new particles give rise to scaling violations which are very close to the standard ones. Therefore present experimental data are also consistent with the existence of light gluinos of mass m λ < 10 GeV. Only more precise data would be able to conclude on their existence. All scaling violation effects observed in non-singlet and singlet structure functions are obtained with a single mass scale parameter Λ eff. We also find the gluon and gluino distributions inside the nucleon, as a function of the gluino mass m λ .