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Stephen Godfrey

Publications and source records attributed to Stephen Godfrey.

At least 73 records · Page 4Linked to original sources
arXiv2001

Signals for Non-Commutative QED in $e γ$ and $γγ$ Collisions

We study the effects of non-commutative QED (NCQED) in fermion pair production, gamma + gamma -> f + bar{f} and Compton scattering, e + gamma -> e + gamma. Non-commutative geometries appear naturally in the context of string/M-theory and gives rise to 3- and 4-point photon vertices and to momentum dependent phase factors in QED vertices which will have observable effects in high energy collisions. We consider e+ e- colliders with energies appropriate to the TeV Linear Collider proposals and the multi-TeV CLIC project operating in gamma gamma and e gamma modes. Non-commutative scales roughly equal to the center of mass energy of the e+ e- collider can be probed, with the exact value depending on the model parameters and experimental factors. However, we found that the Compton process is sensitive to Lambda_{NC} values roughly twice as large as those accessible to the pair production process.

hep-ph↗
arXiv2001

Production of the D-wave $b \bar b$ states

The first and second families of D-wave $b \bar b$ quarkonium states are expected to have masses near 10.16 and 10.44 GeV/$c^2$. The accuracy of these predictions is discussed, and the prospects of two methods for producing these states in electron-positron collisions are updated. Direct scans in the $e^+ e^-$ center-of-mass can give rise to the $^3D_1$ states. The $1^3D_J$ states have also been searched for in the electromagnetic cascades from $\ups(3S) \to γχ'_b \to γγ^3D_J$. The sample of $\ups(3S)$ decays required to definitively observe the $1^3D_J$ states is found to be only somewhat greater than the present world's total.

hep-ph↗
arXiv2000

Discovery and Identification of W' Bosons in e gamma to nu q +X

We examine the sensitivity of the process e gamma to nu q +X to W' bosons which arise in various extensions of the standard model. We consider photon spectra from both the Weizsacker Williams process and from a backscattered laser. The process is found to be sensitive to W' masses up to several TeV, depending on the model, the center of mass energy, the integrated luminosity, and assumptions regarding systematic errors. If extra gauge bosons were discovered first in other experiments, the process could also be used to measure W' couplings. This measurement would provide information that could be used to unravel the underlying theory, complementary to measurements at the Large Hadron Collider.

hep-ph↗
arXiv2000

Constraints on Extra Gauge Bosons in e gamma Collisions

We investigate the sensitivity of e- gamma ---> nu_e nu_mu(bar) mu- to extra charged gauge bosons. The sensitivity is much below that of e-e+ ---> nu nu(bar) gamma. We conclude that e- gamma ---> d u(bar) nu_e and e- gamma ---> f f(bar) e- are also inferior to e+e- collisions in setting bounds on extra charged and neutral gauge bosons and on four fermion contact interactions.

hep-ph↗
arXiv2000

Discovery and Identifictation of Extra Gauge Bosons in e^+e^- -> nu nubar gamma

We examine the sensitivity of the process e+e- -> nu nubar gamma to extra gauge bosons, Z' and W', which arise in various extensions of the standard model. The process is found to be sensitive to W' masses up to several TeV, depending on the model, the center of mass energy, and the assumed integrated luminosity. If extra gauge bosons were discovered first in other experiments, the process could also be used to measure Z' nu nubar and W' couplings. This measurement would provide information that could be used to unravel the underlying theory, complementary to measurements at the Large Hadron Collider.

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arXiv1999

Constraints on Couplings of Extra Gauge Bosons from e+e- --> nu nubar gamma

If extra gauge bosons are observed at the LHC or at a linear e+e- collider, the reaction e+e- --> nu nubar gamma can give information on the couplings (W' nu l) and (Z' nu nubar). The total cross section and polarization asymmetries are the most sensitive observables for such a measurement. Small systematic errors are crucial to obtain reasonable coupling constraints, especially for a high luminosity collider.

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arXiv1998

Light Meson Spectroscopy

We survey the current status of light meson spectroscopy. We begin with a general introduction to meson spectroscopy and and its importance in understanding the physical states of Quantum Chromo Dynamics (QCD). Phemenological models of hadron spectroscopy are described with particular emphasis on the constituent quark model and the qualitative features it predicts for the meson spectrum. We next discuss expectations for hadrons lying outside the quark model, such as hadron states with excited gluonic degrees of freedom. These states include so-called hybrids glueballs}, as well as multiquark states. The established meson states are compared to the quark model predictions and we find that most meson states are well described by the quark model. However, a number of states in the light-quark sector do not fit in well, suggesting the existence of hadronic states with additional degrees of freedom. We end with a brief description of future directions in meson spectroscopy.

hep-ph↗
arXiv1998

Discovery limits for Techni-Omega production in $eγ$ Collisions

In a strongly-interacting electroweak sector with an isosinglet vector state, such as the techni-omega, $ω_T$, the direct $ ω_T Z γ$ coupling implies that an $ω_T$ can be produced by $Z γ$ fusion in $e γ$ collisions. This is a unique feature for high energy $e^+e^-$ or $e^-e^-$ colliders operating in an $eγ$ mode. We consider the processes $e^- γ\to e^- Zγ$ and $e^- γ\to e^- W^+ W^- Z$, both of which proceed via an intermediate $ω_T$. We find that at a 1.5 TeV $e^+e^-$ linear collider operating in an $eγ$ mode with an integrated luminosity of 200 fb$^{-1}$, we can discover an $ω_T$ for a broad range of masses and widths.

hep-ph↗
arXiv1998

Discovery Limits for Techni-Omega Production in $eγ$ Collisions

In a strongly-interacting electroweak sector with an isosinglet vector state, such as the techni-omega, $ω_T$, the direct $ω_T Z γ$ coupling implies that an $ω_T$ can be produced by $Z γ$ fusion in $eγ$ collisions. This is a unique feature for high energy $e^+e^-$ or $e^-e^-$ colliders operating in an $eγ$ mode. We consider the processes $e^- γ\to e^- Zγ$ and $e^- γ\to e^- W^+ W^-Z$, both of which proceed via an intermediate $ω_T$. We find that at a 1.5 TeV $e^+e^-$ linear collider operating in an $eγ$ mode with an integrated luminosity of 200 fb$^{-1}$, an $ω_T$ can be discovered for a broad range of masses and widths.

hep-ph↗
arXiv1998

Leptoquark Production and Identification at High Energy Lepton Colliders

Leptoquarks can be produced in substantial numbers for masses very close to the collider centre of mass energy in $e^+e^-$, $eγ$, and $μ^+μ^-$ collisions due to the quark content of the photon resulting in equivalently high discovery limits. Using polarization asymmetries in an $eγ$ collider the ten different types of leptoquarks listed by Buchmüller, Rückl and Wyler can be distinquished from one another for leptoquark masses essentially up to the kinematic limit. Thus, if a leptoquark were discovered, an $eγ$ collider could play a crucial role in determining its origins.

hep-ph↗
arXiv1998

New Particles and Interactions at High Energy Muon Colliders

I give an overview of the ability of a high energy $μ^+μ^-$ collider to discover new particles and interactions. I start with heavy fermions which will be the most straightforward to produce and observe. I then discuss single leptoquark production which is produced via the quark content of the photon and the discovery potential for extra gauge bosons which will manifest themselves via deviations of observables from their standard model values. Finally, contact interactions are studied as the generalization of looking for new interactions via deviations from the standard model.

hep-ph↗
arXiv1997

Light $q\bar{q}$ Resonances: Spectrum and Decays

I give a brief introduction to light $q\bar{q}$ resonances. The properties of $q\bar{q}$ states are discussed in the context of the constituent quark model, including predictions for mass and partial decay widths. Problems and puzzles in the meson spectrum are pointed out with an emphasis on how an 8+ GeV photon beam can address these. I also point out some areas where I believe theoretical study would be useful.

hep-ph↗
arXiv1997

Strangeness, Charm, and Beauty: Mesons with One Heavy Quark

I review the properties of mesons with one heavy quark. I start by examining the predicted masses and widths in the context of the quark model and heavy quark effective theory. Some recent experimental results are described and I conclude with comments on potentially interesting future experimental studies.

hep-ph↗
arXiv1997

Single W Boson Production in High Energy e-gamma Collisions

We studied single $W$ boson production in high energy $eγ$ collisions and the sensitivity of various observables to the $WWγ$ gauge boson coupling by evaluating the helicity amplitudes of all Feynman diagrams which contribute to the final state being studied, including the $W$ decay to final state fermions. We examined $W$ production at 500 GeV and 1 TeV $e^+e^-$ colliders, comparing results for photon spectra obtained from a backscattered laser and from beamstrahlung radiation. Here we found that the couplings could best be measured using the backscattered laser photons with $|δκ_γ|\leq 0.07$ and $|λ_γ| \leq 0.05$ at a 500 GeV collider and $|δκ_γ|\leq 0.07$ and $|λ_γ| \leq 0.02$ at a 1 TeV collider, all at 95% C.L.. The measurement of $κ_γ$ is at the threshold of being able to measure loop contributions to the trilinear gauge boson vertex. For completeness we include the limits achievable using single $W$ production at a 200 GeV $e^+e^-$ collider in the Weizacker-Williams approximation. This process can measure $κ_γ$ to $\pm 0.15$ at 95% C.L. which is comparable to the $W$ pair production process.

hep-ph↗
arXiv1997

Comment on $Z'$'s and the H1 and ZEUS High $Q^2$ Anomalies

We investigate the effects of extra neutral gauge bosons on the high $Q^2$ region of the $e^+p \to e^+ X$ cross section at $\sqrt{s}=300$ GeV. We found that the only models with electroweak strength coupling, typical of extended gauge theories, that give a better fit to the H1 and ZEUS high $Q^2$ data than the standard model, are ruled out by existing data from the Tevatron. From general scaling arguments, using the allowed contact interactions, the only allowed models with $Z'$'s would be those with strong couplings although even in this case the statistical evidence is not compelling.

hep-ph↗
arXiv1997

Discovery Potential for New Phenomena

We examine the ability of future facilities to discover and interpret non-supersymmetric new phenomena. We first explore explicit manifestations of new physics, including extended gauge sectors, leptoquarks, exotic fermions, and technicolor models. We then take a more general approach where new physics only reveals itself through the existence of effective interactions at lower energy scales. [Summary Report of the New Phenomena Working Group. To appear in the Proceedings of the 1996 DPF/DPB Summer Study on New Directions for High Energy Physics - Snowmass96, Snowmass, CO, 25 June - 12 July 1996.]

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