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Pennington, Michael

Publications and source records attributed to Pennington, Michael.

11 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Detection of the BICT State in a Borafluorene with High Stokes Shift Fluorescence

Four-coordinate aryl borafluorenes with boron–oxygen and boron–nitrogen dative bonds can exhibit very large fluorescence Stokes shifts. The large Stokes shifts are hypothesized to arise from cleavage of the boron-donor dative bond in the excited state, via a mechanism called bond-cleavage-induced intramolecular charge transfer (BICT). The primary goal of this current investigation is to directly observe the BICT state by performing transient absorption spectroscopy (TAS) on four-coordinate borafluorenes, which have improved optical stability. A novel four-coordinate aryl borafluorene was synthesized which features a dative B–O bond and two tert-butyl moieties on the aryl ring. TAS of the new borafluorene is consistent with the existence of a single, three-coordinate species in the excited state, as predicted by the BICT hypothesis. In conclusion, the TAS data is supported by fluorescence lifetime measurements and DFT calculations.

Absorption↗
DOE OSTI2016

Resonances in QCD

We report on the EMMI Rapid Reaction Task Force meeting 'Resonances in QCD', which took place at GSI October 12-14, 2015 (Fig.~1). A group of 26 people met to discuss the physics of resonances in QCD. The aim of the meeting was defined by the following three key questions; what is needed to understand the physics of resonances in QCD?; where does QCD lead us to expect resonances with exotic quantum numbers?; and what experimental efforts are required to arrive at a coherent picture? For light mesons and baryons only those with up, down and strange quark content were considered. For heavy-light and heavy-heavy meson systems, those with charm quarks were the focus.This document summarizes the discussions by the participants, which in turn led to the coherent conclusions we present here.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

A New Amplitude Analysis of two Photon Meson Production Implementing S-Matrix Constraints

Two photon production of nn, KK are wonderful reactions for exposing hadron dynamics showing the transition from chiral behaviour, to resonances, to quark counting within a few GeV. The data from e+e- colliders, even with the statistics from the Belle experiment, inevitably cover a limited angular range that makes partial wave analysis impossible. However, by exploiting the constraints of analyticity, crossing and unitarity, Amplitude Analysis is possible. The results of the first Amplitude Analysis of the Belle results on both n+n-, ?0?0 channels will be presented. The emphasis will be on the union of S-matrix technology with experimental data.

Pennington, Michael↗
DOE OSTI2013

Prospects for Global Analyses of Mesons and Baryons

21st century data on the many observables of meson and baryon production have such precision that in principle they enable not only the confirmation of excited states of which we only previously had hints, but also the discovery of very small signals: signals that might reveal the full range of hadronic states that QCD predicts. The unambiguous extraction of the confirmatory partial wave signals requires the simultaneous analysis of all existing data on as many channels as possible with a complete suite of S-matrix constraints. This is the challenge for the next decade. Steps to be made to achieve this programme will be discussed.

Pennington, Michael↗
DOE OSTI2012

Glimpsing Colour in a World of Black and White

The past 40 years have taught us that nucleons are built of constituents that carry colour charges with interactions governed by Quantum Chromodynamics (QCD). How experiments (past, present and future) at Jefferson Lab probe colourless nuclei to map out these internal colour degrees of freedom is presented. When combined with theoretical calculations, these will paint a picture of how the confinement of quarks and gluons, and the structure of the QCD vacuum, determine the properties of all (light) strongly interacting states.

Pennington, M. R.↗
DOE OSTI2012

Physics Opportunities with the 12 GeV Upgrade at Jefferson Lab

We are at the dawn of a new era in the study of hadronic nuclear physics. The non-Abelian nature of Quantum Chromodynamics (QCD) and the resulting strong coupling at low energies represent a significant challenge to nuclear and particle physicists. The last decade has seen the development of new theoretical and experimental tools to quantitatively study the nature of confinement and the structure of hadrons comprised of light quarks and gluons. Together these will allow both the spectrum and the structure of hadrons to be elucidated in unprecedented detail. Exotic mesons that result from excitation of the gluon field will be explored. Multidimensional images of hadrons with great promise to reveal the dynamics of the key underlying degrees of freedom will be produced. In particular, these multidimensional distributions open a new window on the elusive spin content of the nucleon through observables that are directly related to the orbital angular momenta of quarks and gluons. Moreover, computational techniques in Lattice QCD now promise to provide insightful and quantitative predictions that can be meaningfully confronted with, and elucidated by, forthcoming experimental data. In addition, the development of extremely high intensity, highly polarized and extraordinarily stable beams of electrons provides innovative opportunities for probing (and extending) the Standard Model, both through parity violation studies and searches for new particles. Thus the 12 GeV upgrade of the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab will enable a new experimental program with substantial discovery potential to address these and other important topics in nuclear, hadronic and electroweak physics.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Exciting Baryons: now and in the future

This is the final talk of NSTAR2011 conference. It is not a summary talk, but rather a looking forward to what still needs to be done in excited baryon physics. In particular, we need to hone our tools connecting experimental inputs with QCD. At present we rely on models that often have doubtful connections with the underlying theory, and this needs to be dramatically improved, if we are to reach definitive conclusions about the relevant degrees of freedom of excited baryons. Conclusions that we want to have by NSTAR2021.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Hadron Analyses Data Repository Online Project

The study of excited states of the nucleon is a major effort of present day nuclear physics. The spectrum reflects the internal dynamics of QCD. The past decade has seen a dramatic increase in the precision and range of experimental measurements from MAMI@Mainz and CEBAF@JLab. The analyses of these data, both in Europe and the US, have reached a level of robustness and sophistication that the results on the production of N*'s demand to be shared openly in the nuclear reaction community and beyond. Indeed, there is a demand for such information in fields beyond hadron spectroscopy, such as Heavy Ion collisions. Reaction calculations demand amplitudes and not just simple representations in terms of resonances. The aim of this project is to set up a publicly accessible database to archive (a) the full range of data on cross-sections and polarization asymmetries measured in hadro and photo-production of baryon resonances, (b) for each excited baryon its mass, width, couplings and transition formfactors, (c) for each analysis, the partial wave amplitudes with a detailed exposition of the methods used, (e) where appropriate these will be compared with the detailed predictions of QCD.

Pennington, Michael↗