References - Bogoliubov Laboratory of Theoretical Physics - JINR

As is seen in Fig. 1 values of the elements of classes A and B from the ρ0 are close to
those from the φ meson. If the SCHC approximation is valid, only elements of classes A
and B may be nonzero. There is no statistically significant violation of SCHC observed
in the φ meson elements, while elements of class C from the ρ0 meson deviate from zero
with factors of from 3 to 10 of the total uncertainties σtot. SinceT01 ≡ 0 in the absence of
longitudinal quark motion [7], this could meanthatthequarkmotioneffectsintheρ0are stronger than in the φ meson due to the heavier valence quarks (s¯s) compared to those of
the ρ0 meson (uū and d ¯ d). Note however that the H1 Collaboration has observed a small
violation of SCHC [8] for the φ meson.
As was shown in [9], contributions to the azimuthal target spin asymmetry A sin(φ−φs)
UT
of u and d quarks cancel for the ρ0 and have the same sign for the ω meson. This makes
the ω meson an excellent candidate for studying the GPD E. HERMES accumulated 429
ω production events from the transversely polarized proton. The results show that the
is negative, in agreement with the prediction of Ref. [9], and deviates
sign of A sin(φ−φs)
UT
from zero at −t ′ =0.12 GeV2 by twice the total uncertainty σtot.
4 Direct Extraction of Helicity Amplitude Ratios
Fitting the angular distribution of decay pions in correlation with the scattered lepton
provides the parameters of the amplitude ratios A1 − A9 for ρ 0 production if the
SDMEs are expressed in terms of these amplitudes. The Q 2 dependence of Re{T11/T00}
(Im{T11/T00}) is shown in left (right) panel of Fig. 2 both for the hydrogen and deuterium
targets.
Re(T 11 /T 00 )
1.5
1
0.5
HERMES preliminary
ep(d)→e´ρ 0 p(d)
Proton
Deuteron
Q 2 [GeV 2 1 2 3
]
Im(T 11 /T 00 )
1
0
HERMES preliminary
ep(d)→e´ρ 0 p(d)
Proton
Deuteron
Q 2 [GeV 2 1 2 3
]
Figure 2: The Q 2 dependence of A1 =Re(T11/T00) andA2 =Im(T11/T00) for hydrogen and deuterium
targets. The inner error bars show the statistical uncertainties while the outer ones indicate statistical
and systematic uncertainties added in quadrature. The parameterization of the curves is given in text.
The solid lines are calculated with mean values of the fit parameters; dashed lines correspond to a one
standard deviation change in the curve parameters.
The parameterization A1 = a/Q, A2 = bQ describes the Q 2 dependence well in the
HERMES kinematic region for both targets. Since the angular distributions for production
on the proton and deuteron are compatible within the experimental accuracy, a fit
to the combined data was performed. The results a =(1.129 ± 0.024) GeV with χ 2 per
degree of freedom χ 2 /Ndf =1.02, b =(0.344±0.014) GeV −1 , χ 2 /Ndf =0.87 correspond to
the curves presented in Fig. 2; the solid lines are calculated using the mean values of the
242