30709826
Precision jet substructure from boosted event shapes.
Jet substructure has emerged as a critical tool for LHC searches, but studies so far have relied heavily on shower Monte Carlo simulations, which formally approximate QCD at the leading-log level. We demonstrate that systematic higher-order QCD computations of jet substructure can be carried out by boosting global event shapes by a large momentum Q and accounting for effects due to finite jet size, initial-state radiation (ISR), and the underlying event (UE) as 1/Q corrections. In particular, we compute the 2-subjettiness substructure distribution for boosted Z→qq[over ¯] events at the LHC at next-to-next-to-next-to-leading-log order. The calculation is greatly simplified by recycling known results for the thrust distribution in e(+)e(-) collisions. The 2-subjettiness distribution quickly saturates, becoming Q independent for Q > or approximately equal to 400 GeV. Crucially, the effects of jet contamination from ISR/UE can be subtracted out analytically at large Q without knowing their detailed form. Amusingly, the Q=∞ and Q=0 distributions are related by a scaling by e up to next-to-leading-log order.
7293408
Semi-annihilation of dark matter
We show that the thermal relic abundance of dark matter can be affected by a new type of reaction: semi-annihilation. Semi-annihilation takes the schematic form ψiψj → ψkφ, where ψi are stable dark matter particles and φ is an unstable state. Such reactions are generically present when dark matter is composed of more than one species with “flavor” and/or “baryon” symmetries. We give a complete set of coupled Boltzmann equations in the presence of semi-annihilations, and study two toy models featuring this process. Semi-annihilation leads to non-trivial dark matter dynamics in the early universe, often dominating over ordinary annihilation in determining the relic abundance. This process also has important implications for indirect detection experiments, by enriching the final state spectrum from dark matter (semi-)annihilation in the Milky Way.
119243170
Hadron Mass Effects in Power Corrections to Event Shapes
We study the effect of hadron masses on the leading power correction of dijet event-shape distributions. We define the transverse velocity operator, that describes the effects of hadron masses. It depends on the "transverse velocity" r, which is different from one only for non-vanishing hadron masses. We find that hadron-mass effects in general break universality. However we provide a simple method to identify universality classes of event shapes with a common power correction. We also compute the anomalous dimension of the power correction and the structure of the corresponding Wilson coefficient, finding a nontrivial result.
14189365
Supergravity computations without gravity complications
The conformal compensator formalism is a convenient and versatile representation of supergravity (SUGRA) obtained by gauge-fixing conformal SUGRA. Unfortunately, practical calculations often require cumbersome manipulations of component field terms involving the full gravity multiplet. In this paper, we derive an alternative gauge fixing for conformal SUGRA which decouples these gravity complications from SUGRA computations. This yields a simplified tree-level action for the matter fields in SUGRA which can be expressed compactly in terms of superfields and a modified conformal compensator. Phenomenologically relevant quantities such as the scalar potential and fermion mass matrix are then straightforwardly obtained by expanding the action in superspace.
118513003
Exotic top partners and Little Higgs
A bstractLittle Higgs models often give rise to top partners beyond the minimal ones necessary for the cancellation of quadratic divergences. We review how this occurs and discuss the phenomenology of these exotic states. We emphasize the possible importance of new pseudo-Nambu-Goldstone bosons in top partner decays. Indeed, cascade decays of exotic top partners may be the best way to discover these new bosons. We illustrate these points with a new Little Higgs construction based on an SO(10)/SO(5)2 coset structure, which fills a gap in the model building literature. These observations motivate new search strategies for top partners at the LHC, including for final states with b-jets and a large multiplicity of electroweak bosons.
118951198
Neutrino constraints on spontaneous Lorentz violation
We study the effect of spontaneous Lorentz violation on neutrinos. We consider two kinds of effects: static effects, where the neutrino acquires a Lorentz-violating dispersion relation, and dynamic effects, which arise from the interactions of the neutrino with the Goldstone boson of spontaneous Lorentz violation. Static effects are well detailed in the literature. Here, special emphasis is given to the novel dynamic effect of Goldstone-Cerenkov radiation, where neutrinos moving with respect to a preferred rest frame can spontaneously emit Goldstone bosons. We calculate the observable consequences of this process and use them to derive experimental bounds from SN1987A and the CMBR. The bounds derived from dynamic effects are complementary to - and in many cases much stronger than - those obtained from static effects.
120104766
Data-acquisition modelling and simulation
Abstract We report on the current status of our program to develop a complete top-down design environment for data-acquisition systems. Our effort now focuses on four distinct projects: (1) a model of the existing CDF muon detector trigger and data acquisition, with one board described down to the gate level; (2) a HyperCard enviroment for the automatic incorporation of manufacturers' parts specifications into the design library; (3) translation of component descriptions between different design tools; (4) coordination of a multi-designer environment.
121630940
Heavy quarks and tau
I present some recent experimental results on τ, charm, and bottom physics. CVC test and Michel parameters of the τ; mixing and fDs; and fB, Nc, η'K, ππ and Kπ, Vcb and Vub, lifetime and mixing, and CP violation searches in B decays.
124645739
Experimental Measurement of K0(L) --> mu+ mu-
10716932
A new approach to track finding and fitting in vector drift chambers
Abstract We describe the algorithm that is used to find and fit charged particle trajectories in the Mark III detector at SPEAR. The computer program uses a novel non-numerical pattern recognition technique analogous to that used by the digital hardware in the experiment's track finding trigger processor. The technique is both fast and efficient. The complete reconstruction of events is performed at a rate of 37 ms per track on an IBM 3081K, compared with 91 ms per track with a more conventional technique. A preliminary fit of all tracks, suitable for online monitoring, is available after 15 ms per track. Similar techniques are also applicable to future experiments operating in high multiplicity environments. The organization of the algorithms is such as to lead to simple implementation on vector processors.
116478167
Study of dalitz-plot distributions of the decays eta ---> pi+ pi- pi0 and eta ---> pi+ pi- gamma