119187852
Limiting soft particle emission in e+e−, hadronic and nuclear collisions
In e+e− collisions the particle spectra at low momenta reflect the properties of the underlying “soft” QCD gluon bremsstrahlung: the particle density, in the limit p→0, becomes independent of the incoming energy $\sqrt{s}$ and directly proportional to the colour factors CA, CF for primary gluons or quarks respectively. We find that experimental data from the pp and nuclear reactions reveal the same behaviour: in the limit pT→0 the invariant particle spectra become independent of the collision energy, and their intensities in e+e−, pp and nuclear reactions are compatible with the expected colour factors CF: CA: (Npart/2)CA for Npart nucleons, participating in the interaction. Coherent soft gluon bremsstrahlung is, therefore, suggested to be the dominant QCD mechanism for the soft particle production in all these reactions. These “soft” particles probe the very early stage of hadron formation in the collision. Future measurements at the LHC will provide crucial tests on the contributions from possible incoherent multi-component processes.
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
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.
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.
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.
119771524
Total cross section for anomalous fermion-number violation via dispersion relation
Abstract We investigate the behaviour of the total cross section for electroweak baryon and lepton number violation (in association with multi-W and multi-Higgs production) at low energies (√ s
119236962
Travels on the squark-gluino mass plane
Institut fur Theoretische Physik, Universitat Heidelberg, Germany(Dated: September 12, 2011)Soft supersymmetry breaking appears in the weak-scale e ective action but is usually generated athigher scales. For these models the structure of the renormalization group evolution down to theelectroweak scale leaves only part of the squark-gluino and slepton-gaugino mass planes accessible.Our observations divide these physical mass planes into three wedges: the rst can be reached byall models of high-scale breaking; the second can only be populated by models with a low mediationscale; in the third wedge squarks and gluinos would have to be described by an exotic theory. Allusual benchmark points reside in the rst wedge, even though an LHC discovery in the third wedge
121305872
Instanton vacuum in thermal QCD
The effects of instanton-anti-instanton interactions in high-temperature QCD with colour SU(2) are studied with and without quarks. The instanton potential proves to have no repulsive core, thus creating troubles with the definition of nonperturbative contributions to physical quantities. Also the chiral condensate is calculated, and it is shown to vanish if number of quark flavoursNf≧2, whereas forNf=1 it is nonzero for the arbitrary high temperature.
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.
120263136
Higher twist effects in the Drell‐Yan process
We calculate the angular distribution of the lepton produced in the Drell‐Yan reaction taking into account pion bound state effects. We work in the kinematic region where one of the pion constituents goes far off shell, which allows us to treat the bound state problem pertubatively. We show that the angular distribution is very sensitive to the shape of the pion distribution amplitude. The model we discuss fits the data if we choose a two‐humped pion distribution amplitude suggested by QCD sum rules.