Flavor dependent azimuthal asymmetries in unpolarized semi-inclusive DIS at HERMES
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lavor Dependent Azimuthal Asymmetries in Unpolarized SemiInclusive DIS at HERMES1 F. Giordano for the HERMES Collaboration University of Illinois at UrbanaChampaign, Department of Physics, 1110 West Green Street, Urbana, IL 618013080, USA email: [email protected] Abstract—The azimuthal cosφh and cos2φh modulations of the distribution of hadrons produced in unpolar ized semiinclusive deepinelastic scattering of electrons and positrons off hydrogen and deuterium targets have been measured in the hermes experiment. For the first time these modulations were determined in a 4Dimensional kinematic space for positively and negatively charged pions and kaons separately, as well as for unidentified hadrons. These azimuthal dependences are sensitive to the transverse motion and polariza tion of the quarks within the nucleon via, e.g., the Cahn, Boer–Mulders and Collins effects. DOI: 10.1134/S1063779614010353 1
In leptonnucleon deepinelastic scattering (DIS), the structure of the nucleon is probed by the interac tion of a high energy lepton (l) with a target nucleon (N), via, at HERMES kinematics, the exchange of one virtual photon. If at least one of the produced had rons (h) is detected in coincidence with the scattered lepton, the reaction is called semiinclusive deep inelastic scattering (SIDIS): l + N → l' + h + X, where X is the target remnant. If unintegrated over the hadron momentum com ponent transverse to the virtual photon direction Ph⊥ (Fig. 1), the cross section can be written as [1]: 2
1. MULTIDIMENSIONAL UNFOLDING cos φ h
In order to study the new structure functions F UU cos 2φ
and F UU h defined in Eq. (2), a measure of the azi muthal modulation of the unpolarized cross section is needed, which can be extracted via the socalled 〈cosnφh〉moments:
∫
cos nφ h dσdφ h 〈cosnφh〉 = dσ dφ h
2
dσ α γ dσ ≡ = 2 ⎛ 1 + ⎞ { A ( y )F UU, T 2 ⎝ 2x⎠ dxdydzdP h⊥ dφ h xyQ (1) + B ( y )F UU, L + cos φ
cos φ C ( y ) cos φ h F UU h
+
∫
(2)
with n =1, 2 and dσ defined in Eq. (2). The extraction of these cosine moments from data is challenging because they couple to a number of experimental sources of azimuthal modulations, e.g. detector geometrical acceptance and higherorder QED effects (radiative effects). Moreover, in the typi cal case, the event sample is binned only in one vari able (1dimensional analysis), and integrated over the full range of all the other ones, but the mentioned structure functions and the instrumental spurious contributions depend on all the kinematic variables x, y, z and Ph⊥ simultaneously. These experimental con tributions have been corrected for in a fully differential
cos 2φ B ( y ) cos 2φ h F UU h },
cos 2φ
where F UU h and F UU h are azimuthally dependent structure functions, and are related respectively to cosφh and cos2φh modulations, with φh the azimuthal angle of the hadron production plane around the vir tualphoton direction (Fig. 1). Among the possible mechanisms, two are expec
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