Gluons in quarkonium decay

Koller, K.; Walsh, Thomas

doi:10.1016/0550-3213(78)90006-8

Cited by 115 publications

(51 citation statements)

References 13 publications

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“…The only application is therefore likely to be for Υ, which unfortunately also is on the low side in mass. The matrix element for qq → ggg is (in lowest order) [Kol78] …”

Section: Decays Of Onia Resonancesmentioning

confidence: 99%

“…If the mass of the recoiling gg system is lower than some cut-off (by default 2 GeV), the event is rejected. In the present implementation the angular orientation of the ggg and γgg events is given for the e + e − → γ * → onium case [Kol78] (optionally with beam polarization effects included), i.e. weak effects have not been included, since they are negligible at around 10 GeV.…”

Section: Decays Of Onia Resonancesmentioning

confidence: 99%

See 1 more Smart Citation

PYTHIA 6.4 physics and manual

Sjöstrand

Mrenna

Skands

2006

J. High Energy Phys.

9,610

10,151

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The Pythia program can be used to generate high-energy-physics 'events', i.e. sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide as accurate as possible a representation of event properties in a wide range of reactions, with emphasis on those where strong interactions play a rôle, directly or indirectly, and therefore multihadronic final states are produced. The physics is then not understood well enough to give an exact description; instead the program has to be based on a combination of analytical results and various QCDbased models. This physics input is summarized here, for areas such as hard subprocesses, initial-and final-state parton showers, beam remnants and underlying events, fragmentation and decays, and much more. Furthermore, extensive information is provided on all program elements: subroutines and functions, switches and parameters, and particle and process data. This should allow the user to tailor the generation task to the topics of interest.

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“…The only application is therefore likely to be for Υ, which unfortunately also is on the low side in mass. The matrix element for qq → ggg is (in lowest order) [Kol78] …”

Section: Decays Of Onia Resonancesmentioning

confidence: 99%

Section: Decays Of Onia Resonancesmentioning

confidence: 99%

PYTHIA 6.4 physics and manual

Sjöstrand

Mrenna

Skands

2006

J. High Energy Phys.

9,610

10,151

View full text Add to dashboard Cite

show abstract

“…Thus, for direct radiative decays J/ψ → ggγ, theory prescribes the correlation of z γ with photon polar angle cos θ γ , defined relative to the beam axis. Köller and Walsh considered the angular spectrum in detail [4], demonstrating that, if the parent is polarized along the beam axis, then, as the energy of the most energetic primary (photon or gluon) in J/ψ → γgg or J/ψ → ggg approaches the beam energy, the event axis tends to increasingly align with the beam axis: z γ → 1 corresponds to α(z γ ) → 1 for an angular distribution specified as dN/d cos θ γ ∼ 1 + α(z γ ) cos 2 θ γ . We note that, according to the Köller-Walsh prescription, the value of α(z γ ) for intermediate values, where most of the events occur, is relatively small (0.2).…”

Section: B Energy and Angular Spectrum Shapesmentioning

confidence: 99%

“…We perform two-dimensional fits comprised of the following components: a) the background, which is modeled either using the pseudo-photon, Monte Carlo-based, or χ c0 -based backgrounds described above, b) three two-body components of the direct photon signal: γη and γη ′ and a wide resonance which corresponds to γη(1440), with shapes determined from Monte Carlo simulation, and c) a smooth signal component which has a shape in photon energy taken from our previous Upsilon decay measurement [7], and an angular distribution based on the Köller-Walsh prescription [4]. Ideally, we could avoid having to include a signal component.…”

Section: E Fits and Signal Extractionmentioning

confidence: 99%

Inclusive radiativeJ/ψdecays

Besson¹,

Pedlar²,

Cronin-Hennessy³

et al. 2008

Phys. Rev. D

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Using data taken with the CLEO-c detector at the Cornell Electron Storage Ring, we have investigated the direct photon momentum spectrum in the decay J/ψ(1S) → γgg, via the "tagged" process: e + e − → ψ(2S); ψ(2S)→ J/ψ π + π − ; J/ψ → γ+X. Including contributions from two-body radiative decay processes, we find the ratio of the inclusive direct photon branching fraction to that of the dominant three-gluon branching fraction (R γ = B(ggγ)/B(ggg)) to be R γ = 0.137 ± 0.001 ± 0.016 ± 0.004, where the errors shown are statistical, systematic, and the model-dependent uncertainty related to the extrapolation to zero photon energy. The shape of the scaled photon energy spectrum in J/ψ → ggγ is observed to be very similar to that of Υ → ggγ. The R γ value obtained is roughly consistent with that expected by a simple quark-charge scaling (R γ ∼ (q c /q b ) 2 ) of the value determined at the Υ(1S), but somewhat higher than the value expected from the running of the strong coupling constant.

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“…Among the interesting features, it looked like the strong coupling constant α s could be neatly extracted from the ratio Γ(H → γgg)/Γ(H → ggg), for which both the wave function at the origin and the relativistic corrections cancel out [1,2] 1 . The first measurements of J/ψ inclusive radiative decays by the Mark II collaboration [4] delivered a photon spectrum not compatible with the early QCD predictions.…”

Section: Introductionmentioning

confidence: 99%