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Register a new userEnd-point resummation in squark decays
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We study soft and collinear gluon emission in squark decays to quark--neutralino pair, at next-to-next-to-leading logarithmic (NNLL) accuracy in the end-point region, using Soft Collinear Effective Theory (SCET), and at next-to-leading (NLO) fixed order in the rest of the phase space. As a phenomenological case study we discuss the impact of radiative corrections on the simultaneous measurements of squark and neutralino masses at a linear $e^{+}e^{-}$ collider based on $sqrt{s} = 3$ TeV Compact Linear Collider (CLIC). Since the majority of mass measurement techniques are based on edges in kinematic distributions, and these change appreciably when there is additional QCD radiation in the final state, the knowledge of higher-order QCD effects is required for precise mass determinations.
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Within the Minimal Supersymmetric Standard Model we study the three body decay of the lighter top squark into a b-quark, a W-boson and the lightest neutralino and compare this decay with the flavour changing two body decay of the lighter top squark into a c-quark and the lightest neutralino. We do this for scenarios where two body decays at tree level are forbidden for the light top squark. We give the complete analysis for the three body and compare it with the mentioned two body decay. We discuss our numerical results in view of the upgraded Tevatron, the LHC and a 500~GeV $e^+ e^-$ Linear Collider.
We consider the resummation of soft and Coulomb gluons for pair-production processes of heavy coloured particles at hadron colliders, and discuss recent results on the construction of a basis in colour space that diagonalizes the soft function to all orders in perturbation theory and the determination of the two-loop soft anomalous dimension needed for NNLL resummations. We present results for the combined NLL resummation of soft gluon and Coulomb-gluon effects for squark-antisquark production at the LHC.
We perform the resummation of soft-gluon emissions for squark and gluino production at next- to-next-to-leading-logarithmic (NNLL) accuracy. We include also the one-loop hard matching coefficients as well as Coulomb corrections to second order, using Mellin-moment methods. We study the characteristics of this resummation in detail for a centre-of-mass (CM) energy of 8 TeV at the LHC, and for squark and gluino masses up to 2.5 TeV. We find significant enhancing effects for all four processes of squark- and gluino-pair production. Scale dependence is generally reduced compared to NLL resummation, except for gluino-pair production where we find a moderate enhancement.
We study the effect of squark generation mixing on squark production and decays at the LHC in the Minimal Supersymmetric Standard Model (MSSM). We show that the effect can be very large despite the very strong constraints on quark flavour violation (QFV) from experimental data on B mesons. We find that the two lightest up-type squarks ${tilde u}_{1,2}$ can have large branching ratios for the decays into $c {tildechi_1^0}$ and $t {tildechi_1^0}$ at the same time, leading to QFV signals $p p to c bar t, (t bar c)$ + missing-$E_T$ + $X$ with a significant rate. The observation of this remarkable signature would provide a powerful test of supersymmetric QFV at LHC. This could have a significant impact on the search for squarks and the determination of the underlying MSSM parameters.
Quark flavour conserving (QFC) fermionic squark decays, such as ~t_{1,2} -> t neutralino_i, are usually assumed in squark search analyses. Here we study quark flavour violating (QFV) bosonic squark decays, such as ~u_2 -> ~u_1 h^0/Z^0, where the mass eigenstates ~u_{1,2} are mixtures of scharm and stop quarks. We show that the branching ratios of such QFV decays can be very large due to sizable ~c_R - ~t_{R/L} and ~t_R - ~t_L mixing effects despite the very strong constraints on the QFV parameters from B meson data. This can result in remarkable QFV signatures with significant rates at LHC (14 TeV), such as pp -> gluino gluino X -> t c bar{c} bar{c} h^0/Z^0 missing-E_T X and pp -> gluino gluino X -> t t bar{c} bar{c} h^0/Z^0 missing-E_T X. The QFV bosonic squark decays can play an important role in the squark and gluino searches at LHC (14 TeV).
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