Measurement of Azimuthal Asymmetries in Inclusive Production of Hadron Pairs ine+e−Annihilation at Belle

Abstract

The Collins effect connects transverse quark spin with a measurable azimuthal dependence in the yield of hadronic fragments around the quark's momentum vector. Using two different reconstruction methods, we find evidence of statistically significant azimuthal asymmetries for charged pion pairs in e(+)e(-) annihilation at a center-of-mass energy of 10.52 GeV, which can be attributed to a transverse polarization of the primordial quarks. The measurement was performed using a sample of 79 x 10(6) hadronic events collected with the Belle detector.

Measurement of Collins asymmetries in inclusive production of charged pion pairs ine+e−annihilation atBABAR

“…Our data are also consistent with the previous measurements performed by the Belle Collaboration [18,19], with the exception of the bins where the highest fractional energies are involved. In particular we measure an asymmetry about three standard deviations higher in the highest (z 1 ; z 2 ) bin.…”

“…The first efforts to measure Collins asymmetries in e þ e − annihilation, by studying Z 0 → 2 jets events, were performed by the DELPHI Collaboration [17], while the first observation was obtained by the Belle Collaboration [18][19][20], from a study of inclusive production of charged pion pairs at a center-of-mass (c.m.) energy of approximately 10.6 GeV.…”

Longitudinal and transverse spin asymmetries for inclusive jet production at mid-rapidity in polarizedp+pcollisions ats=200 GeVAdamczyk1, Agakishiev2, Aggarwal3 et al. 2012Phys. Rev. DSelf Cite805380View full textAdd to dashboardCite

“…Semi-inclusive deep-inelastic scattering experiments have also measured a broad range of transverse spin asymmetries (see for example [31][32][33][34][35][36]), including asymmetries sensitive to the Collins and Sivers effects. The Collins effect involves the convolution of quark transversity with the transverse-spin-dependent Collins fragmentation function, which has been measured in e þ e À scattering [37,38]. The Sivers effect ascribes a spin-dependent transverse momentum to the partons in a transversely polarized proton.…”

Measurements of fragmentation functions and implications for semi-inclusive deep-inelastic scattering

“…In particular, when studying the transversemomentum structure of the nucleon through semi-inclusive DIS it will be unavoidable to also know the transverse-momentum structure of hadronization as the transverse momentum of the hadrons in semi-inclusive DIS arises through convolutions of the transverse-momentum dependence of both the parton distribution and fragmentation functions. Fragmentation functions are mainly constrained through measurements of semi-inclusive DIS [2,3,4,5] and of hadron production in electron-positron annihilation, especially the very precise data from the B factories [6,7,8,9,10,11,12]. [In case of transverse-momentum integrated fragmentation functions, data on hadron production in proton-proton collision is also used in global analyses.]…”