SIDIS Dihadron Beam Spin Asymmetry

Spokespersons

C. Dilks, T. Hayward, A. Vossen

Year

2020

Abstract

The observation of beam spin asymmetries in two-pion production in semi-inclusive deep inelastic scattering off an unpolarized proton target is reported for the first time. The data presented here were taken in the fall of 2018 with the CLAS12 spectrometer using a 10.6 GeV longitudinally spin-polarized electron beam delivered by CEBAF at JLab and correspond to an integrated luminosity of 58.3~fb$^{-1}$ delivered on target. The measured asymmetries provide a first signal sensitive to the PDF $e(x)$ in the collinear framework and constitute the first observation of helicity-dependent two-pion fragmentation described by the fragmentation function $G_1^\perp$.

Comment

Process: ep→eπ⁺π^-X
Data tables have the following columns:

1. mean Q²
2. mean x
3. mean M_h, the dihadron invariant mass
4. mean z, of the pion pair
5. mean P_T, more commonly written P_h^⊥, is the component of the total dihadron momentum, transverse to q
6. A_LU amplitude, for a particular modulation
7. statistical uncertainty
8. systematic uncertainty

For each of the 7 asymmetry modulations, there are 4 tables, one for each binning scheme: (1) binned by x, (2) binned by M_h, (3) binned by z and M_h, and (4) binned by P_T and M_h.

Publication

1. T.B. Hayward, C. Dilks, A. Vossen, H. Avakian Observation of Beam Spin Asymmetries in the Process ep→eπ+π-X with CLAS12 // (submitted to PRL)

Quantities

A_LU^sin φ_h   A_LU^sin φ_R   A_LU^{sin (φ_h−φ_R})   A_LU^{sin (2φ_h−φ_R})   A_LU^{sin (2φ_h−2φ_R})   A_LU^{sin (−φ_h+2φ_R})   A_LU^{sin (3φ_h−2φ_R})

Measurements