Rapidity Gaps Between Jets

An excess of events with a rapidity gap between jets, over what would be expected from non-diffractive processes, has been observed at HERA. A process based on a perturbative QCD calculation of colour singlet exchange has been added to HERWIG. With this addition, HERWIG is able to describe the number of events with a gap between jets over the number without a gap. This gap fraction is predicted to rise at large rapidity intervals between jets which would only be visible if the detector coverage were increased.Comment: 5 pages including 3 figures. To appear in the conference proceedings of the Workshop "Future Physics at HERA

HepForge: A lightweight development environment for HEP software

Setting up the infrastructure to manage a software project can become a task as significant writing the software itself. A variety of useful open source tools are available, such as Web-based viewers for version control systems, "wikis" for collaborative discussions and bug-tracking systems, but their use in high-energy physics, outside large collaborations, is insubstantial. Understandably, physicists would rather do physics than configure project management tools. We introduce the CEDAR HepForge system, which provides a lightweight development environment for HEP software. Services available as part of HepForge include the above-mentioned tools as well as mailing lists, shell accounts, archiving of releases and low-maintenance Web space. HepForge also exists to promote best-practice software development methods and to provide a central repository for re-usable HEP software and phenomenology codes.Comment: 3 pages, 0 figures. To be published in proceedings of CHEP06. Refers to the HepForge facility at http://hepforge.cedar.ac.u

HepData and JetWeb: HEP data archiving and model validation

The CEDAR collaboration is extending and combining the JetWeb and HepData systems to provide a single service for tuning and validating models of high-energy physics processes. The centrepiece of this activity is the fitting by JetWeb of observables computed from Monte Carlo event generator events against their experimentally determined distributions, as stored in HepData. Caching the results of the JetWeb simulation and comparison stages provides a single cumulative database of event generator tunings, fitted against a wide range of experimental quantities. An important feature of this integration is a family of XML data formats, called HepML.Comment: 4 pages, 0 figures. To be published in proceedings of CHEP0

TLEP: A High-Performance Circular e+e- Collider to Study the Higgs Boson

The recent discovery of a light Higgs boson has opened up considerable interest in circular e+e- Higgs factories around the world. We report on the progress of the TLEP concept since last year. TLEP is an e+e- circular collider capable of very high luminosities in a wide centre-of-mass (ECM) spectrum from 90 to 350 GeV. TLEP could be housed in a new 80 to 100 km tunnel in the Geneva region. The design can be adapted to different ring circumference (e.g. LEP3 in the 27 km LHC tunnel). TLEP is an ideal complementary machine to the LHC thanks to high luminosity, exquisite determination of ECM and the possibility of four interaction points, both for precision measurements of the Higgs boson properties and for precision tests of the closure of the Standard Model from the Z pole to the top threshold.Comment: Contribution to IPAC13, 12-17 May 2013, Shanghai, Chin

Photon Structure and Quantum Fluctuation

Photon structure derives from quantum fluctuation in quantum field theory to fermion and anti-fermion, and has been an experimentally established feature of electrodynamics since the discovery of the positron. In hadronic physics, the observation of factorisable photon structure is similarly a fundamental test of the quantum field theory Quantum Chromodynamics (QCD). An overview of measurements of hadronic photon structure in e+e- and ep interactions is presented, and comparison made with theoretical expectation, drawing on the essential features of photon fluctuation into quark and anti-quark in QCD.Comment: 29 pages, 15 figures, to appear in Philosophical Transactions of the Royal Society of London (Series A: Mathematical, Physical and Engineering Sciences

KtJet: A C++ implementation of the Kt clustering algorithm

A C++ implementation of the Kt jet algorithm for high energy particle collisions is presented. The time performance of this implementation is comparable to the widely used Fortran implementation. Identical algorithmic functionality is provided, with a clean and intuitive user interface and additional recombination schemes. A short description of the algorithm and examples of its use are given

Quadrupole moments of rotating neutron stars

Numerical models of rotating neutron stars are constructed for four equations of state using the computer code RNS written by Stergioulas. For five selected values of the star's gravitational mass (in the interval between 1.0 and 1.8 solar masses) and for each equation of state, the star's angular momentum is varied from J=0 to the Keplerian limit J=J_{max}. For each neutron-star configuration we compute Q, the quadrupole moment of the mass distribution. We show that for given values of M and J, |Q| increases with the stiffness of the equation of state. For fixed mass and equation of state, the dependence on J is well reproduced with a simple quadratic fit, Q \simeq - aJ^2/M c^2, where c is the speed of light, and a is a parameter of order unity depending on the mass and the equation of state.Comment: ReVTeX, 7 pages, 5 figures, additional material, and references adde

Quasars: a supermassive rotating toroidal black hole interpretation

A supermassive rotating toroidal black hole (TBH) is proposed as the fundamental structure of quasars and other jet-producing active galactic nuclei. Rotating protogalaxies gather matter from the central gaseous region leading to the birth of massive toroidal stars whose internal nuclear reactions proceed very rapidly. Once the nuclear fuel is spent, gravitational collapse produces a slender ring-shaped TBH remnant. These events are typically the first supernovae of the host galaxies. Given time the TBH mass increases through continued accretion by several orders of magnitude, the event horizon swells whilst the central aperture shrinks. The difference in angular velocities between the accreting matter and the TBH induces a magnetic field that is strongest in the region of the central aperture and innermost ergoregion. Due to the presence of negative energy states when such a gravitational vortex is immersed in an electromagnetic field, circumstances are near ideal for energy extraction via non-thermal radiation including the Penrose process and superradiant scattering. This establishes a self-sustaining mechanism whereby the transport of angular momentum away from the quasar by relativistic bi-directional jets reinforces both the modulating magnetic field and the TBH/accretion disk angular velocity differential. Quasar behaviour is extinguished once the BH topology becomes spheroidal. Similar mechanisms may be operating in microquasars, SNe and GRBs when neutron density or BH tori arise. In certain circumstances, long-term TBH stability can be maintained by a negative cosmological constant, otherwise the classical topology theorems must somehow be circumvented. Preliminary evidence is presented that Planck-scale quantum effects may be responsible.Comment: 26 pages, 14 figs, various corrections and enhancements, final versio

Snowmass 2001: Jet Energy Flow Project

Conventional cone jet algorithms arose from heuristic considerations of LO hard scattering coupled to independent showering. These algorithms implicitly assume that the final states of individual events can be mapped onto a unique set of jets that are in turn associated with a unique set of underlying hard scattering partons. Thus each final state hadron is assigned to a unique underlying parton. The Jet Energy Flow (JEF) analysis described here does not make such assumptions. The final states of individual events are instead described in terms of flow distributions of hadronic energy. Quantities of physical interest are constructed from the energy flow distribution summed over all events. The resulting analysis is less sensitive to higher order perturbative corrections and the impact of showering and hadronization than the standard cone algorithms.Comment: REVTeX4, 13 pages, 6 figures; Contribution to the P5 Working Group on QCD and Strong Interactions at Snowmass 200