Leading-twist single-transverse-spin asymmetries: Drell-Yan and deep-inelastic scattering

John C. Collins

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865 Scopus citations


Recently, Brodsky, Hwang and Schmidt have proposed a new mechanism that gives a transverse spin symmetry at leading twist in semi-inclusive deep-inelastic scattering. I show that the new mechanism is compatible with factorization and is due to a transverse-spin asymmetry in the kT distribution of quarks in a hadron (the "Sivers asymmetry"). An earlier proof that the Sivers asymmetry vanishes because of time-reversal invariance is invalidated by the path-ordered exponential of the gluon field in the operator definition of parton densities. Instead, the time-reversal argument shows that the Sivers asymmetry is reversed in sign in hadron-induced hard processes (e.g., Drell-Yan), thereby violating naive universality of parton densities. Previous phenomenology with time-reversal-odd parton densities is validated.

Original languageEnglish (US)
Pages (from-to)43-48
Number of pages6
JournalPhysics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
Issue number1-2
StatePublished - May 30 2002

All Science Journal Classification (ASJC) codes

  • Nuclear and High Energy Physics


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