Squark and gluino production with jets

Abstract

We present cross section predictions for squark and gluino production at the LHC, in association with up to two additional hard jets. These cross sections can be very large in comparison to the inclusive Born rates. Because hadron collider experiments utilize hard jets in the reconstruction of cascade decays or as a way to separate squark and gluino production, the understanding of these processes is crucial. We show to what degree hard jet radiation can be described by shower algorithms and point out how tuning these showers, for example to top quark pair production, could help reduce theoretical uncertainties for new physics searches at the LHC.In the Standard Model (SM), the mechanism of the observed electroweak symmetry breaking is widely believed to involve a Higgs boson. This fundamental scalar poses a theoretical problem: the stability of its mass after the inclusion of radiative corrections. A possible solution is TeV-scale supersymmetry. The minimal supersymmetric extension of the Standard Model (MSSM) simultaneously solves several problems in high energy physics and cosmology: gauge coupling unification; radiative electroweak symmetry breaking [1]; and a stable weakly-interacting dark matter candidate [2].With the Tevatron in operation and the LHC only a few years distant, the TeV scale is rapidly coming within reach. Squark and gluino production cross sections approach O(pb) at the Tevatron and O(nb) at the LHC, for masses around the present Tevatron exclusion limits of up to 400 GeV.MSSM searches and jets: The main difference between R-parity-conserving MSSM signals and SM QCD backgrounds at a hadron collider comes from the stable lightest supersymmetric particle, an end product of all superpartner decays, which escapes the detector unobserved. Requiring a large amount of missing transverse energy is thus the first ingredient to enhance the signal. The QCDstrength production channels for squarks and gluinos are pp →gg,qq * ,qq,qg [3,4]. To a good approximation, the light-flavor MSSM squarks are mass degenerate, while the lighter of the two top squarks is often the lightest strongly-interacting MSSM particle. Searching for squarks and gluinos in an inclusive analysis the signature is jets plus / E T , possibly plus leptons. The shortest cascade of two-particle decays isg →qq andq → qχ 0 1 , where the lightest neutralinoχ 0 1 is stable. Such an inclusive search is well-suited to find MSSM-type deviations from the Standard Model. Because the gluino decay gives one more hard jet in the final state, an event's jet multiplicity provides discrimination between the relative rates of squarks and gluinos.We can also make use of longer decay chains, e.g. of the classic typeg →qq →χ 0 2 qq →llqq →χ 0 1 ℓlqq with five unknown masses. These masses can be extracted from kinematic distributions, i.e. thresholds and edges of different momentum combinations [5]. Alternative methods have been developed to improve the mass reconstruction [6] and the associated statistical and systematic errors. These measurements can in...

Where the sidewalk ends: jets and missing energy search strategies for the 7 TeV LHC

“…The effects of including additional radiation in signal processes have been documented in several studies [30,31,[77][78][79].…”

“…The matrix elements better describe hard radiation, while the parton shower generates softer radiation that fills out jets [81][82][83][84][85][86]. The MLM parton shower/matrix element matching scheme is used with a shower-k ⊥ scheme introduced in [87][88][89][90]. The matching scales used in this article are listed in the table below.…”

Establishing jet scaling patterns with a photon

“…In a similar spirit, searches for example for supersymmetry benefit from the measurement of the number of jets which includes information on the color structure of the new heavy states [14]; the only caveat is that we need to carefully separate decay jets from QCD jet radiation associated with hard processes [14][15][16][17]. What is missing for all such analyses is an experimentally established and theoretically sound link between choosing n-jet samples for an analysis and a systematic study of the corresponding n jets distribution for signal and background processes [12].…”

Squark pair production in the MSSM with explicitCPviolation

“…These processes have been analyzed in the past [5,6] (with increasing precision in Refs. [7][8][9]) by considering only the (dominant) 6. supersymmetric QCD (SUSY-QCD) contributions.…”