Erratum: Exclusive photoproduction of a γ ρ pair with a large invariant mass

: An unfortunate misprint in our numerical code has led to an overestimate of the cross section for the exclusive photoproduction of a γ ρ L pair in the kinematics where the pair has a large invariant mass and the ﬁnal nucleon has a small transverse momentum, described in the collinear factorization framework. The rates are thus expected to be smaller but the possibility to disentangle the transversity GPDs through the process where the ρ − meson is transversely polarized is enhanced.

(pb · GeV −6 ) Figure 6. Differential cross section for a photon and a longitudinally polarized ρ meson production, for the proton (left) and the neutron (right), at M 2 γρ = 4 GeV 2 . Both vector and axial GPDs are included. In black the contributions of both u and d quarks, in blue the contribution of the u quark, and in green the contribution of the d quark. Solid: "valence" model, dotted: "standard" model. This figure shows the dominance of the u-quark contribution due to the charge effect. Note that the interference between u−quark and d−quark contributions is important and negative.
Figure 7. Differential cross section for a photon and a longitudinally polarized ρ meson production, for the proton (left) and the neutron (right), at M 2 γρ = 4 GeV 2 . Both u and d quark contributions are included. In black the contributions of both vector and axial amplitudes, in blue the contribution of the vector amplitude, and in green the contribution of the axial amplitude. Solid: "valence" model, dotted: "standard" model. This figure shows the dominance of the vector GPD contributions. There is no interference between the vector and axial amplitudes.
In our published paper [1], an unfortunate misprint in our numerical code has led to an overestimate of the cross section for the exclusive photoproduction of a γ ρ pair, in the case where the final ρ-meson is longitudinally polarized. The corrected plots corresponding to figures 6-11, 16 and 22 are displayed below, and can be obtained from the previous figures by a division by a factor of 36. The total rates are thus expected to be smaller but the possibility to disentangle the transversity GPDs through the process where the ρ−meson is transversely polarized is enhanced.    Figure 9. Differential cross section for a photon and a longitudinally polarized ρ meson production, for the proton (left) and the neutron (right), as a function of −u ′ , for M 2 γρ = 3, 4, 5, 6 GeV 2 (resp. in black, red, blue, green). Solid: "valence" model, dotted: "standard" model. We use here the "valence" scenario. σ even (pb) Figure 11. Integrated cross section for a photon and a longitudinally polarized ρ meson production, on a proton (left) or neutron (right) target. The solid red curves correspond to the "valence" scenario while the dashed blue curves correspond to the "standard" one. Additional corrections (the modifications on the equations have no effect on our estimates), are: • Equation (4.11) should be replaced by • In equations (4.10) and (A.10)-(A.18), T A 5 should be replaced by −T A 5 .

JHEP10(2018)029
• The first sentence of subsection 5.5 should be: For S γN = 20 GeV 2 , the integration over M 2 γρ of our above results within our allowed kinematical region, here 2.10 GeV 2 < M 2 γρ < 9.47 GeV 2 (see appendix D), allows to obtain the cross sections σ proton odd ≃ 0.54 pb and σ proton even ≃ 21 pb for the proton, and σ neutron odd ≃ 0.42 pb and σ neutron even ≃ 2.3 pb for the neutron.
• The last sentence of section 6 should read: With an expected luminosity L = 100 nb −1 s −1 we obtain for 100 days of run: 7.5 10 3 ρ T and 1.9 10 5 ρ L .
• In the conclusion, the beginning of the last but one paragraph should read: To conclude, the cross section of our process is a factor 10 more than the γP → P e + e − process, for similar values of the hard scale, for which experimental proposals have been approved at JLab. • Equation (D.11) should read • Equation (E.2) and (E.6) should read (E.2) and tan θ = − 2M s(1 + ξ)α p t −α 2 (1 + ξ) 2 s 2 + p 2 t M 2 .
(E.6) JHEP10(2018)029 • The last sentences of the paper should read: Putting additional cuts on M 2 γρ , like M 2 γρ > 6 GeV 2 , allows to increase the ratio odd versus even from ∼ 1/25 to ∼ 2/3, keeping about 3% of the chiral-odd contribution, for typically S γN between 18 GeV 2 and the maximal value 21.5 GeV 2 . This in principle would lead, dealing with observables sensitive to the interference between the chiral-odd and the chiral-even contributions, to a relative signal of the order of 80%.
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