Accessing the Sivers TMD function in proton + proton collisions through the measurement of transverse single spin asymmetries (TSSAs) in Drell-Yan and weak boson production is an e ff ective path to test the fundamental QCD prediction of the non-universality of the Sivers function. Furthermore, it provides data to study the spin-flavor structure of valence and sea quarks inside the proton and to test TMD evolution of parton distributions. The TSSA amplitude, ANA_NAN , has been measured at STAR in proton+proton collisions at ssqrt{s}s = 500 GeV, with a recorded integrated luminosity of 25 pb−1^{−1}−1. Within relatively large statistical uncertainties, the current data favor theoretical models that include a change of sign for the Sivers function relative to observations in SIDIS measurements, if TMD evolution effects on the ANA_NAN are small. RHIC plans to run collisions of transversely polarized proton+proton beams at ssqrt{s}s = 500 GeV in 2017, delivering an integrated luminosity of 400 pb−1^{−1}−1 . This will allow STAR to perform a precise measurement of TSSAs in both Drell-Yan and weak boson production, as well as other observables sensitive to the non-universality of the Sivers function via the Twist-3 formalism, e.g. the TSSA of prompt photons.
Transverse Single-Spin Asymmetries of Weak Boson, Drell-Yan and Prompt Photon Production at STAR
Fazio, S.
2017-01-01
Abstract
Accessing the Sivers TMD function in proton + proton collisions through the measurement of transverse single spin asymmetries (TSSAs) in Drell-Yan and weak boson production is an e ff ective path to test the fundamental QCD prediction of the non-universality of the Sivers function. Furthermore, it provides data to study the spin-flavor structure of valence and sea quarks inside the proton and to test TMD evolution of parton distributions. The TSSA amplitude, ANA_NAN , has been measured at STAR in proton+proton collisions at ssqrt{s}s = 500 GeV, with a recorded integrated luminosity of 25 pb−1^{−1}−1. Within relatively large statistical uncertainties, the current data favor theoretical models that include a change of sign for the Sivers function relative to observations in SIDIS measurements, if TMD evolution effects on the ANA_NAN are small. RHIC plans to run collisions of transversely polarized proton+proton beams at ssqrt{s}s = 500 GeV in 2017, delivering an integrated luminosity of 400 pb−1^{−1}−1 . This will allow STAR to perform a precise measurement of TSSAs in both Drell-Yan and weak boson production, as well as other observables sensitive to the non-universality of the Sivers function via the Twist-3 formalism, e.g. the TSSA of prompt photons.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
