REVIEW
$\gamma p$ and $\gamma \gamma$ scattering from $\bar{p}p$, $pp$ forward amplitudes in a QCD eikonal model with a dynamical gluon mass
High Energy Physics - Phenomenology · Submitted 20 Feb 2006 · 34 references
Pith's reading: A QCD eikonal model with a dynamical gluon mass, calibrated on pp data, describes gamma-p and gamma-gamma total cross sections once a photon-hadron probability is fitted, and this favors PHOJET over PYTHIA unfolding at high energy.
The paper
The paper claims
A QCD eikonal model with a dynamical gluon mass, calibrated on pp data, describes gamma-p and gamma-gamma total cross sections once a photon-hadron probability is fitted, and this favors PHOJET over PYTHIA unfolding at high energy.
The reading
The main adjustable quantity is P_had, the probability that a photon acts as a hadron. In the simplest picture P_had is about 1/249, but the authors fit it to the data, obtaining values near 1/220. They also allow a normalization factor N for the photon-photon data, because extracting these cross sections from e+e- collisions depends on Monte Carlo generators. Using PHOJET-unfolded data, the model fits well with constant P_had; using PYTHIA-unfolded data, the photon-photon cross section above about 100 GeV rises faster than the model and, by extension, faster than the factorization relation sigma_pp/sigma_gp = sigma_gp/sigma_gg permits. The authors read this as evidence that the PYTHIA unfolding may be problematic. When they allow P_had to grow logarithmically with energy, the fit improves, but in the PHOJET data set the growth parameter is consistent with zero.
Extended reading notes
Core claim
The central assertion (Sec. III, Sec. V) is that "the total photoproduction sigma_gamma_p and the total hadronic sigma_gamma_gamma cross sections can be derived from the pp and pbarp forward amplitudes using vector meson dominance and the additive quark model," and that with these assumptions an eikonal QCD-inspired model based on a nonperturbative infrared dynamical gluon mass scale "can successfully describe" the gamma-p and gamma-gamma data. If correct, the pp/pbarp eikonal parameters transferred unchanged to photon channels reproduce the measured total cross sections once P_had is fitted.
Load-bearing premise
The load-bearing premise is that the eikonal for a photon is obtained from the nucleon eikonal by the VMD/AQM substitutions in Eqs. (11) and (15): sigma_ij -> (2/3)sigma_ij, mu_ij -> sqrt(3/2)mu_ij for gamma-p, and sigma_ij -> (4/9)sigma_ij, mu_ij -> (3/2)mu_ij for gamma-gamma, with P^gamma_gamma_had = (P^gamma_p_had)^2 (Eq. 17). No derivation of these scaling rules is given; they are heuristic assumptions carried over from hadron phenomenology. If the photon's hadronic fluctuations do not scale this way, for instance if the overlap-function widths scale differently or P_had is process-dependent, the predicted cross sections and the factorization test fail.
Original abstract
We examine the $\gamma p$ photoproduction and the hadronic $\gamma \gamma$ total cross sections by means of a QCD eikonal model with a dynamical infrared mass scale. In this model, where the dynamical gluon mass is the natural regulator for the tree level gluon-gluon scattering, the $\gamma p$ and $\gamma \gamma$ total cross sections are derived from the $pp$ and $\bar{p}p$ forward scattering amplitudes assuming vector meson dominance and the additive quark model. We show that the validity of the cross section factorization relation $\sigma_{pp}/\sigma_{\gamma p}=\sigma_{\gamma p}/\sigma_{\gamma \gamma}$ is fulfilled depending on the Monte Carlo model used to unfold the hadronic $\gamma \gamma$ cross section data, and we discuss in detail the case of $\sigma (\gamma \gamma \to hadrons)$ data with $W_{\gamma \gamma} > 10$ GeV unfolded by the Monte Carlo generators PYTHIA and PHOJET. The data seems to favor a mild dependence with the energy of the probability ($P_{had}$) that the photon interacts as a hadron.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
We examine the $\gamma p$ photoproduction and the hadronic $\gamma \gamma$ total cross sections by means of a QCD eikonal model with a dynamical infrared mass scale. In this model, where the dynamical gluon mass is the natural regulator for the tree level gluon-gluon scattering, the $\gamma p$ and $\gamma \gamma$ total cross sections are derived from the $pp$ and $\bar{p}p$ forward scattering amplitudes assuming vector meson dominance and the additive quark model. We show that the validity of the cross section factorization relation $\sigma_{pp}/\sigma_{\gamma p}=\sigma_{\gamma p}/\sigma_{\gamma \gamma}$ is fulfilled depending on the Monte Carlo model used to unfold the hadronic $\gamma \gamma$ cross section data, and we discuss in detail the case of $\sigma (\gamma \gamma \to hadrons)$ data with $W_{\gamma \gamma} > 10$ GeV unfolded by the Monte Carlo generators PYTHIA and PHOJET. The data seems to favor a mild dependence with the energy of the probability ($P_{had}$) that the photon interacts as a hadron.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We examine the $\gamma p$ photoproduction and the hadronic $\gamma \gamma$ total cross sections by means of a QCD eikonal model with a dynamical infrared mass scale. | contribution 0.89 | 0.90 | 0.06 | asserted 0.92 |
| s1 | In this model, where the dynamical gluon mass is the natural regulator for the tree level gluon-gluon scattering, the $\gamma p$ and $\gamma \gamma$ total cross sections are derived from the $pp$ and $\bar{p}p$ forward scattering amplitudes assuming vector meson dominance and the additive quark model. | method 0.99 | 0.77 | 0.09 | asserted 1.00 |
| s2 | We show that the validity of the cross section factorization relation $\sigma_{pp}/\sigma_{\gamma p}=\sigma_{\gamma p}/\sigma_{\gamma \gamma}$ is fulfilled depending on the Monte Carlo model used to unfold the hadronic $\gamma \gamma$ cross section data, and we discuss in detail the case of $\sigma (\gamma \gamma \to hadrons)$ data with $W_{\gamma \gamma} > 10$ GeV unfolded by the Monte Carlo generators PYTHIA and PHOJET. | result 0.85 | 0.87 | 0.49 | asserted 0.93 |
| s3 | The data seems to favor a mild dependence with the energy of the probability ($P_{had}$) that the photon interacts as a hadron. | result 0.67 | 0.68 | 0.29 | hedged possibility 1.00 |
What was examined, and what was not
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Figures
Showing 1 of the paper's 3 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:hep-ph/0602181 by the authors.
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Discussion
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