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W-Boson Transverse Single-Spin Asymmetries in Run 17
Updated on Fri, 2024-11-22 09:26. Originally created by oleg on 2024-11-06 16:06.
Intended journal: Physical Review D
Abstract:
Figure 2: The limited detector acceptance, mainly in pseudorapidity, leads to a loss of information of the hadronic recoil measurement. The resulting uncertainty in the azimuthal angle introduces a dilution of the measured transverse-spin asymmetries, which can be corrected. The dilution factor, D, is transverse momentum dependent. The average dilution is similar in all rapidity bins of the reconstructed recoil, <D>=0.75 and a minimum pt_recoil is used for the asymmetry determination.
Figure 3: The accuracy of the hadronic recoil method has been studied in embedded simulation. The rapidity migration is affected by the smeared reconstruction of the hadronic recoil and the choice of the quadratic solution of the longitudinal momentum of the neutrino. The bin-migration is the dominant contribution to the correlation of measured and real rapidity. It is more pronounced in W+ bosons (left) than W- bosons (right) due to the decay kinematics and the detector acceptance.
Figure 4: Transverse single-spin asymmetries A_N and A_S as functions of the W-boson rapidity based on the hadronic recoil method. The data are compared to theory predictions which have been smeared according to the rapidity bin-migration from Fig. 3. All asymmetries have been corrected for beam polarization and the dilution of the azimuthal angle.
Figure 5: Transverse single-spin asymmetries A_N as functions of the unfolded W-boson rapidity. The moderate correlation, especially for W+ bosons, leads to a significant increase of the statistical uncertainty of the unfolded asymmetries. The data are compared to the most recent results from global fits, which include the sign-change predicted for the Sivers effect between SIDIS and hadronic collisions.
Analysis Note:
- version 1
Paper draft:
- draft version 0
Presentations:
PWGC preview
Final results
Preliminary request
Measurement of Transverse Single-Spin Asymmetries of W-bosons in p+p Collisions at sqrt(s)=510 GeV
PAs: Elke Aschenauer, Oleg Eyser, Salvatore FazioIntended journal: Physical Review D
Abstract:
We present the measurement of the transverse single-spin asymmetries of weak boson production in
polarized proton-proton collisions sqrt(s)=510 GeV by the STAR experiment at RHIC.
The measured observables A_N and A_S are sensitive to transverse momentum dependent parton
distribution functions, specifically the Sivers function f^⊥q_1T and the transversal helicity distribution
g^q_1T.
The current data with an integrated luminosity of 340 pb-1 improve upon the figure-of-merit of previous
results by about a factor of five for A_N.
The A_S data are the first of their kind.
The results are shown for the reconstructed kinematics based on the hadronic recoil and A_N
is unfolded to the W-boson kinematics to allow direct comparison with theory predictions.
The Sivers effect is of special interest due to a predicted sign-change when compared to deep inelastic
lepton-proton scattering.
Comparison with global fits exhibits a discrepancy with growing rapidity which is expected to inform our
knowledge of the sea-quark Sivers function.
Figure 1: Comparison of high-pT electrons and positrons in data, embedded simulation, and data-driven background methods. The pT-dependence shows good agreement between data and the summed contributions from simulated signal and various backgrounds. For the selection of W-boson events, a pT-threshold of 25 GeV/c is used, as in previous publications.polarized proton-proton collisions sqrt(s)=510 GeV by the STAR experiment at RHIC.
The measured observables A_N and A_S are sensitive to transverse momentum dependent parton
distribution functions, specifically the Sivers function f^⊥q_1T and the transversal helicity distribution
g^q_1T.
The current data with an integrated luminosity of 340 pb-1 improve upon the figure-of-merit of previous
results by about a factor of five for A_N.
The A_S data are the first of their kind.
The results are shown for the reconstructed kinematics based on the hadronic recoil and A_N
is unfolded to the W-boson kinematics to allow direct comparison with theory predictions.
The Sivers effect is of special interest due to a predicted sign-change when compared to deep inelastic
lepton-proton scattering.
Comparison with global fits exhibits a discrepancy with growing rapidity which is expected to inform our
knowledge of the sea-quark Sivers function.
Figure 2: The limited detector acceptance, mainly in pseudorapidity, leads to a loss of information of the hadronic recoil measurement. The resulting uncertainty in the azimuthal angle introduces a dilution of the measured transverse-spin asymmetries, which can be corrected. The dilution factor, D, is transverse momentum dependent. The average dilution is similar in all rapidity bins of the reconstructed recoil, <D>=0.75 and a minimum pt_recoil is used for the asymmetry determination.
Figure 3: The accuracy of the hadronic recoil method has been studied in embedded simulation. The rapidity migration is affected by the smeared reconstruction of the hadronic recoil and the choice of the quadratic solution of the longitudinal momentum of the neutrino. The bin-migration is the dominant contribution to the correlation of measured and real rapidity. It is more pronounced in W+ bosons (left) than W- bosons (right) due to the decay kinematics and the detector acceptance.
Figure 4: Transverse single-spin asymmetries A_N and A_S as functions of the W-boson rapidity based on the hadronic recoil method. The data are compared to theory predictions which have been smeared according to the rapidity bin-migration from Fig. 3. All asymmetries have been corrected for beam polarization and the dilution of the azimuthal angle.
Figure 5: Transverse single-spin asymmetries A_N as functions of the unfolded W-boson rapidity. The moderate correlation, especially for W+ bosons, leads to a significant increase of the statistical uncertainty of the unfolded asymmetries. The data are compared to the most recent results from global fits, which include the sign-change predicted for the Sivers effect between SIDIS and hadronic collisions.
Analysis Note:
- version 1
Paper draft:
- draft version 0
Presentations:
PWGC preview
Final results
Preliminary request
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