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The STAR Collaboration reports on the photoproduction of $\pi^+\pi^-$ pairs in gold-gold collisions at a center-of-mass energy of 200 GeV/nucleon-pair. These pion pairs are produced when a nearly-real photon emitted by one ion scatters from the other ion. We fit the $\pi^+\pi^-$ invariant mass spectrum with a combination of $\rho$ and $\omega$ resonances and a direct $\pi^+\pi^-$ continuum. This is the first observation of the $\omega$ in ultra-peripheral collisions, and the first measurement of $\rho-\omega$ interference at energies where photoproduction is dominated by Pomeron exchange. The $\omega$ amplitude is consistent with the measured $\gamma p\rightarrow \omega p$ cross section, a classical Glauber calculation and the $\omega\rightarrow\pi^+\pi^-$ branching ratio. The $\omega$ phase angle is similar to that observed at much lower energies, showing that the $\rho-\omega$ phase difference does not depend significantly on photon energy. The $\rho^0$ differential cross section $d\sigma/dt$ exhibits a clear diffraction pattern, compatible with scattering from a gold nucleus, with 2 minima visible. The positions of the diffractive minima agree better with the predictions of a quantum Glauber calculation that does not include nuclear shadowing than with a calculation that does include shadowing.

13 data tables match query

Figure 4

The $\pi^+\pi^-$ invariant-mass distribution for all selected $\pi\pi$ candidates with $p_T~<~100~\textrm{MeV}/c$.

Figure 5 a

The ratio $|B/A|$ of amplitudes of nonresonant $\pi^+\pi^-$ and $\rho^0$ mesons in the present STAR analysis.

Figure 5 b

The ratio $|B/A|$ of amplitudes of nonresonant $\pi^+\pi^-$ and $\rho^0$ mesons in the previous STAR analysis, Phys. Rev. C 77 034910 (2008).

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K+ P AND K- P ELASTIC SCATTERING AT 32.1-GEV/C. FRANCE-SOVIET UNION AND CERN-SOVIET UNION COLLABORATIONS

Lewin, C. ; Denegri, D. ; Givernaud, A. ; et al.

Z.Phys.C 3 (1979) 275-284, 1979.

Inspire Record 148166 DOI 10.17182/hepdata.15899

None

2 data tables match query

Table 1

CROSS-OVER IS AT -T = 0.17 +- 0.02 GEV**2. DIVIDE BY 20 TO GET D(SIG)/DT IN MB/GEV**2. CORRECTED FOR LOST EVENTS FOR -T < 0.12 GEV**2.

Table 2

FROM QUADRATIC EXPONENTIAL FIT TO D(SIG)/DT. BOTH STATISTICAL AND SYSTEMATIC ERRORS INCLUDED IN VALUES.

Observation of color-transparency in diffractive dissociation of pions.

The E791 collaboration Aitala, E.M. ; Amato, S. ; Anjos, J.C. ; et al.

Phys.Rev.Lett. 86 (2001) 4773-4777, 2001.

Inspire Record 535233 DOI 10.17182/hepdata.42972

We have studied the diffractive dissociation into di-jets of 500 GeV/c pions scattering coherently from carbon and platinum targets. Extrapolating to asymptotically high energies (where t_{min} approaches 0) we find that when the per-nucleus cross-section for this process is parameterized as $ \sigma = \sigma_0 A^{\alpha} $, $ \alpha $ has values near 1.6, the exact result depending on jet transverse momentum. These values are in agreement with those predicted by theoretical calculations of color-transparency.

1 data table match query

Table 1

Cross sections is fitted to A**POWER.

Date

Collaboration

Subject_areas

Phrases

Reactions

Observables

CM Energies (GeV)

Authors Reset

STUDY OF DIFFRACTIVE PROCESSES IN EXCLUSIVE CHANNEL anti-p p ---> anti-p p (2 pi+) (2 pi-) AT 32-GeV/c

ON STUDY OF PION MULTIPLE PRODUCTION IN NONDIFFRACTIVE EXCLUSIVE REACTIONS IN K- p INTERACTIONS AT 32.1-GeV/c

CROSS-SECTION OF PARTICLE DIFFRACTIVE PRODUCTION IN ANTI-P P INTERACTIONS AT 32-GEV/C. (IN RUSSIAN)

STUDY OF ELASTIC anti-p p SCATTERING AT 32-GeV/c

Charged Particle Multiplicities in $\bar{p} p$ Interactions at 32-{GeV}/$c$

K+ p, K- p AND anti-p p ELASTIC SCATTERING AT 32.1-GeV/c

A Study of the Structure of the Events With the Multiparticle Diffraction Dissociation in $K^- p$ Exclusive Reactions at 32-{GeV}/$c$

Coherent diffractive photoproduction of $\rho^{0}$ mesons on gold nuclei at RHIC

K+ P AND K- P ELASTIC SCATTERING AT 32.1-GEV/C. FRANCE-SOVIET UNION AND CERN-SOVIET UNION COLLABORATIONS

Observation of color-transparency in diffractive dissociation of pions.