Angular correlations in multi-jet final states from kt-dependent parton showers

We investigate parton-branching methods based on transverse-momentum dependent (TMD) parton distributions and matrix elements for the Monte Carlo simulation of multi-particle final states at high-energy colliders. We observe that recently measured angular correlations in ep final states with multiple hadronic jets probe QCD coherence effects in the space-like branching, associated with finite-angle gluon radiation from partons carrying small longitudinal momenta, and not included in standard shower generators. We present Monte Carlo calculations for azimuthal two-jet and three-jet distributions, for jet multiplicities and for correlations in the transverse-momentum imbalance between the leading jets. We discuss comparisons with current experimental multi-jet data, and implications of corrections to collinear-ordered showers for LHC final states.Comment: 25 pages. Discussion and references expanded; results unchanged. Additional calculations include

Treating jet correlations in high pile-up at hadron colliders

Experiments in the high-luminosity runs at the Large Hadron Collider face the challenges of very large pile-up. Primary techniques to deal with this are based on precise vertex and track reconstruction. Outside tracker acceptances, however, lie regions of interest for many aspects of the LHC physics program. We explore complementary approaches to pile-up treatment and propose a data-driven jet-mixing method which can be used outside tracker acceptances without depending on Monte Carlo generators. The method can be applied to treat correlation observables and take into account, besides the jet transverse momentum pedestal, effects of hard jets from pile-up.Comment: Latex. 8 pages, 5 figure

Hadroproduction of electroweak gauge boson plus jets and TMD parton density functions

If studies of electroweak gauge boson final states at the Large Hadron Collider, for Standard Model physics and beyond, are sensitive to effects of the initial state's transverse momentum distribution, appropriate generalizations of QCD shower evolution are required. We propose a method to do this based on QCD transverse momentum dependent (TMD) factorization at high energy. The method incorporates experimental information from the high-precision deep inelastic scattering (DIS) measurements, and includes experimental and theoretical uncertainties on TMD parton density functions. We illustrate the approach presenting results for production of W-boson + n jets at the LHC, including azimuthal correlations and subleading jet distributions.Comment: 9 pages, 4 figures. v2: comments and references added, typos corrected; results unchange

A kT-dependent sea-quark density for the CASCADE Monte Carlo event generator

Parton-shower event generators that go beyond the collinear-ordering approximation at small x have so far included only gluon and valence quark channels at transverse momentum dependent level. We describe results of recent work to include effects of the sea-quark distribution with explicit dependence on the transverse quark-momentum.This sea-quark density is then applied to the description of forward Z -production. The qq*->Z matrix element (with one off-shell quark) is calculated in an explicit gauge invariant way, making use of high energy factorization. The kT-factorized result has been implemented into the CCFM Monte-Carlo CASCADE and a numerical comparison with the qg*->Zq matrix element has been carried out.Comment: 4 pages, 4 figures, based on a talk given at the XXI Workshop on Deep-Inelastic Scattering and Related Subjects, 11-15 April, Newport News, Virginia (2011

The CCFM uPDF evolution uPDFevolv

uPDFevolv is an evolution code for TMD parton densities using the CCFM evolution equation. A description of the underlying theoretical model and technical realization is given together with a detailed program description, with emphasis on parameters the user may want to changeComment: Code and description on https://updfevolv.hepforge.org Version to be published in EPJ

Parton shower contributions to jets from high rapidities at the LHC

We discuss current issues associated with the dependence of jet distributions at the LHC on the behavior of QCD parton showers for high rapidities.Comment: Contribution at DIS2012, Univ. of Bonn, March 201

Soft-gluon resolution scale in QCD evolution equations

QCD evolution equations can be recast in terms of parton branching processes. We present a new numerical solution of the equations. We show that this parton-branching solution can be applied to analyze infrared contributions to evolution, order-by-order in the strong coupling $\alpha_s$, as a function of the soft-gluon resolution scale parameter. We examine the cases of transverse-momentum ordering and angular ordering. We illustrate that this approach can be used to treat distributions which depend both on longitudinal and on transverse momenta.Comment: Latex, 8 pages, 4 figure

Oysters and oyster-like bivalves from the Middle Triassic Muschelkalk of the Germanic Basin

Middle Triassic marine deposits of the Germanic Basin (Muschelkalk) record a significant proliferation of cementing bivalves from different families. Based on previously undescribed, excellently preserved material from the Willebadessen Member (late Anisian, Illyrian) of the Upper Muschelkalk Trochitenkalk Formation of Willebadessen (Germany), we propose the new genus Noetlingiconcha, type species N. speculostreum sp. nov., for strongly plicate prospondylids lacking auricles. The new genus differs from Terquemia and Enantiostreon in being plicate rather than costate, and from Newaagia in the absence of auricles. We demonstrate that N. speculostreum was invariably attached by its right valve, in contrast to an externally similar species from the Lower Muschelkalk Freudenstadt Formation (lower Anisian, Bithynian) that was exclusively cemented by its left valve and thus represents the geologically oldest known oyster species. Previous reports of amphi-pleurothetic cemented bivalve species from the Muschelkalk probably result from lumping together these two externally similar species. The constancy of sinistral attachment in the geologically oldest Ostreidae suggests that left-pleurothetic valve orientation was already established in the ancestry of this family. Palaeontological data are therefore in accordance with genetic and larval shell morphology analyses that identified Pterioidea as the sister taxon of Ostreoidea, because Pterioidea contains several Permian-Triassic genera with an anatomically lower left valv

Color coherence in multi-jet final states

We discuss coherent QCD radiation from space-like parton branching and its effects on multi-jet final states at high-energy hadron colliders. Coherence effects for small longitudinal momentum fractions x are not included in the branching algorithms of standard shower Monte Carlo event generators. On the other hand, they are taken into account only partially in perturbative next-to-leading-order calculations for multi-jets. Such effects are present to all orders in alpha_s and can become logarithmically enhanced with \sqrt{s} / E_T, where E_T is the hardest jet transverse energy. We present results of summing coherence effects to all orders by parton-branching Monte Carlo methods based on transverse-momentum dependent matrix elements