15306416
Hadronic returns to the Z in electron positron annihilation at high-energy
The production of four hadronic jets in e+e− collisions above the Z pole is dominated by the QCD e+e−→qq,qgg processes and, for sufficiently high energy, the electroweak e+e−→W+W−→qq process. However, there is another mechanism for producing four jets, e+e−→Zgg→qgg, which can be regarded as a ``hadronic return'' to the Z pole. We investigate this process in detail.
119436494
QCD Interconnection Effects
Heavy objects like the W, Z and t are short-lived compared with typical hadronization times. When pairs of such particles are produced, the subsequent hadronic decay systems may therefore become interconnected. We study such potential effects at Linear Collider energies.
125850380
Multiple Hadron Production in Parton {QCD} Jets
124029542
On the sensitivity of the inclusive distributions in parton jets to the coherence effects in QCD gluon cascades
The KNO multiplicity distributions and properties of two-particle correlations in QCD jets are considered in the framework of the perturbative approach accounting for effects of the coherence in the soft gluon bremsstrahlung.
117871006
Pomeron universality from identical pion correlations at the LHC
Abstract Bose–Einstein correlations of identical pions produced in high-energy pp collisions at the LHC allow a probe of the Pomeron exchange mechanism. The size of the domain which emits the pions depends on the multiplicity of events, but not on the collider energy. This confirms the universal structure of Pomeron exchange. The data at relatively low multiplicities indicate that the size of the source created by one-Pomeron exchange is much less than the size of the proton.
119379184
Radiative corrections to the hadronic cross-section measurement at DA$\Phi$NE
Abstract. The hadronic invariant mass distribution for the process of electron–positron annihilation into a pair of charged pions accompanied by a photon radiated from the initial state has been studied for the region of DA$\Phi$NE energies. The Born cross–section and the electromagnetic radiative corrections to it are calculated for realistic conditions of the KLOE detector. The dependence on the physical parameters which define the event selection is obtained.
8011091
Non-MHV tree amplitudes in gauge theory.
We show how all non-MHV tree-level amplitudes in 0 ? ? 4 gauge theories can be obtained directly from the known MHV amplitudes using the scalar graph approach of Cachazo, Svrcek and Witten. Generic amplitudes are given by sums of inequivalent scalar diagrams with MHV vertices. The novel feature of our method is that after the `Feynman rules' for scalar diagrams are used, together with a particular choice of the reference spinor, no further helicity-spinor algebra is required to convert the results into a numerically usable form. Expressions for all relevant individual diagrams are free of singularities at generic phase space points, and amplitudes are manifestly Lorentz- (and gauge-) invariant. To illustrate the method, we derive expressions for n-point amplitudes with three negative helicities carried by fermions and/or gluons. We also write down a supersymmetric expression based on Nair's supervertex which gives rise to all such amplitudes in 0 ? ? 4 gauge theories.
62799412
Constraining Dark Sectors at Colliders: Beyond the Effective Theory Approach
We outline and investigate a set of benchmark simplified models with the aim of providing a minimal simple framework for an interpretation of the existing and forthcoming searches of dark matter particles at the LHC. The simplified models we consider provide microscopic QFT descriptions of interactions between the Standard Model partons and the dark sector particles mediated by the four basic types of messenger fields: scalar, pseudoscalar, vector and axial-vector. Our benchmark models are characterized by four to five parameters, including the mediator mass and width, the dark matter mass and the effective coupling(s). In the gluon fusion production channel we resolve the top quark in the loop and compute full top-mass effects for scalar and pseudoscalar messengers. We show the LHC limits and reach at 8 and 14 TeV for models with all four messenger types. We also outline the complementarity of direct detection, indirect detection and LHC bounds for dark matter searches. Finally, we investigate the effects which arise from extending the simplified model to include potential new physics contributions in production. Using the scalar mediator as an example, we study the impact of heavy new physics loops which interfere with the top-mediated loops. Our computations are performed within the mcfm framework, and we provide fully flexible public Monte Carlo implementation.
120078928
Non-perturbative contribution to total cross sections in non-abelian gauge theories
Abstract We consider the instanton-induced contribution to the total cross section of vector boson scattering in the SU (2) gauge theory with and without Higgs mechanism. The exponential suppression of instanton-induced processes disappears asymptotically at energies for above the infrared cutoff for the instanton scale size, which is provided, in the Higgs (confinement) phase, by the vacuum expectation value (virtuality of the gluons). Instanton-induced processes may therefore be important in close-to-mass-shell gluon collisions. Our finding also suggests that electroweak baryon-and lepton-number violation with the associated production of many W-bosons may become important at very high energies.
120532941
Screening of multi-instanton corrections to anomalous processes in the standard model
Abstract We calculate the multi-instanton contribution to the logarithm of the cross-section for (B+L)-violating (anomalous) high-energy collisions in the next-to-leading order (in terms of ( E M sp ) 2 3 ) approximation. It is demonstrated that in this approximation there is no sign of “premature unitarization” of anomalous processes, i.e. there is no indication that multi-instanton contributions become of the same magnitude as the single-instanton contribution at energies where the single-instanton result is still exponentially suppressed.
56217615
New constraints on gauge mediation and beyond from LHC SUSY searches at 7 TeV
The first results from the LHC on jets plus missing energy provide powerful new data to test SUSY models. Initial theoretical interpretations of these data have concentrated on gravity mediation, usually the CMSSM and its variations. In this paper we confront a large class of gauge mediation models with these new data. More precisely we consider models of pure general gauge mediation (pure GGM) and confront them with the recent experimental results of the ATLAS collaboration. We use Herwig++ and RIVET, incorporating the full set of experimental cuts, to calculate the signal rates and compare them to the data. Although based on only 35pb−1 of integrated luminosity, we show that these new data probe and exclude a portion of previously allowed parameter space of GGM. In addition we investigate the viability of standard SUSY benchmark points, including the Snowmass, CMS and ATLAS sets which encompass other mediation scenarios such as gravity, anomaly and gaugino mediation.