Measurement of the Collins and Sivers asymmetries on transversely polarised protons

The COMPASS collaboration Alekseev, M.G. ; Alexakhin, V.Yu. ; Alexandrov, Yu. ; et al.
Phys.Lett.B 692 (2010) 240-246, 2010.
Inspire Record 856645 DOI 10.17182/hepdata.55141

The Collins and Sivers asymmetries for charged hadrons produced in deeply inelastic scattering on transversely polarised protons have been extracted from the data collected in 2007 with the CERN SPS muon beam tuned at 160 GeV/c. At large values of the Bjorken x variable non-zero Collins asymmetries are observed both for positive and negative hadrons while the Sivers asymmetry for positive hadrons is slightly positive over almost all the measured x range. These results nicely support the present theoretical interpretation of these asymmetries, in terms of leading-twist quark distribution and fragmentation functions.

36 data tables

The COLLINS asymmetry for positively charged hadrons as a function of X.

The COLLINS asymmetry for positively charged hadrons as a function of Z.

The COLLINS asymmetry for positively charged hadrons as a function of PT.

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Polarization of Sigma+ hyperons produced by 800-GeV/c protons on Cu and Be.

The SELEX collaboration Pogodin, P. ; Alkhazov, G. ; Atamantchouk, A.G. ; et al.
Phys.Rev.D 70 (2004) 112005, 2004.
Inspire Record 629483 DOI 10.17182/hepdata.42834

We show that Σ+ hyperons produced by 800 GeV/c protons on targets of Be and Cu have significant polarizations (15–20%). These polarizations persist at values of pt≈2  GeV/c and a wide range of xF. The polarizations from the Cu target are consistently less than from Be. The average ratio of the Σ+ polarization from Cu to that from Be is 0.68±0.08.

2 data tables

Measured values of the SIGMA+ polarization as functions of PT and XL for proton CU collisions.

Measured values of the SIGMA+ polarization as functions of PT and XL for proton BE collisions.


A precise measurement of the tau polarisation at LEP-1.

The DELPHI collaboration Abreu, P. ; Adam, W. ; Adye, T. ; et al.
Eur.Phys.J.C 14 (2000) 585-611, 2000.
Inspire Record 511443 DOI 10.17182/hepdata.49001

The$\tau$polarisation has been studied with the${\rm e^+e^-}\to \tau^+\tau^-$data collected by the DELPHI detector at LEP in

2 data tables

The errors are statistical and systematic combined in quadrature.

No description provided.


Precision measurement of charge symmetry breaking in n p elastic scattering at 347-MeV

Zhao, J. ; Abegg, R. ; Berdoz, A.R. ; et al.
Phys.Rev.C 57 (1998) 2126-2141, 1998.
Inspire Record 484066 DOI 10.17182/hepdata.25692

A nonzero difference of the analyzing powers due to charge symmetry breaking has been measured with high precision in np elastic scattering at a neutron beam energy of 347 MeV. The neutron beam and proton target were alternately polarized for the measurements of An and Ap. A mirror-symmetric detection system was used to cancel geometry-related systematic errors. From fits of the measured asymmetry angular distributions over the range of 53.4°<~θcm<~86.9°, the difference in the zero-crossing angles of the analyzing powers was determined to be 0.438°±0.054°(stat.)±0.051°(syst.) in the center-of-mass system. Using the experimentally determined slope of the analyzing power dA/dθ=(−1.35±0.05)×10−2 deg−1 (c.m.), this is equivalent to ΔA≡An−Ap=[59±7(stat.)±7(syst.)±2(syst.)]×10−4. The shape of ΔA(θ) in the vicinity of the zero-crossing angle has also been extracted. Predictions of nucleon-nucleon interaction models based on meson exchange agree well with the results.

1 data table

(C=N) or (C=P) stands for polarized beam or target.


The Zero crossing angle of the n - p analyzing power

Davis, C.A. ; Abegg, R. ; Berdoz, A.R. ; et al.
Phys.Rev.C 53 (1996) 2052-2067, 1996.
Inspire Record 402498 DOI 10.17182/hepdata.26459

The angles at which the n-p elastic scattering neutron analyzing power A00n0 crosses zero were measured with precision at four TRIUMF energies below 300 MeV. The mean interaction energies are also measured with greater precision than in previous experiments. The results are En=175.26±0.23 MeV, θzx=98.48°±0.28°; En=203.15±0.20 MeV, θzx=91.31°±0.18°; En=217.24±0.19 MeV, θzx=87.64°±0.18°; and En=261.00±0.16 MeV, θzx=80.18°±0.19°. After correction for charge symmetry breaking effects, the energy where the averaged neutron-proton analyzing power crosses zero at θzx=90° is found to be En=206.8±0.6 MeV. © 1996 The American Physical Society.

4 data tables

Polarized beam and target.

Polarized beam and target.

Polarized beam and target.

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Measurements of the tau polarization in Z0 decays

The DELPHI collaboration Abreu, P. ; Adam, W. ; Adye, T. ; et al.
Z.Phys.C 67 (1995) 183-202, 1995.
Inspire Record 393793 DOI 10.17182/hepdata.47961

A sample of Z0→τ+τ− events observed in the DELPHI detector at LEP in 1991 and 1992 is analysed to measure the τ polarisation in the exclusive decay channels\(ev\bar v\),\(\mu v\bar v\), πν, ρν and a1ν. The τ polarisation is also measured with an inclusive hadronic analysis which benefits from a higher efficiency and a better systematic precision than the use of the exclusive decay modes. The results have been combined with those published on the 1990 data. A measurement of the τ polarisation as a function of production angle yields the values for the mean τ polarisation 〈P〉τ=−0.148±0.022 and for the Z0 polarisationPZ=−0.136±0.027. These results are used to determine the ratio of vector to axial-vector effective couplings for taus\(\bar v_\tau/\bar a_\tau= 0.074 \pm 0.011\), and for electrons\(\bar v_e /\bar a_e= 0.068 \pm 0.014\), compatible with e-τ universality. With the assumption of lepton universality, the ratio of vector to axial-vector effective couplings for leptons\(\bar v_l /\bar a_l= 0.072 \pm 0.008\) is obtained, implying a value of the effective weak mixing angle sin2θefflept=0.2320±0.0021.

10 data tables

Results are for both TAU+ and TAU- decay.

The systematic error contains a systematic error of 0.003 common to all channels.

Errors are statistical only.

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Measurements of angular distributions of differential cross-sections and analyzing powers of the reaction polarized p p ---> d pi+ between 1.3-GeV and 2.4-GeV

Yonnet, J. ; Abegg, R. ; Boivin, M. ; et al.
Nucl.Phys.A 562 (1993) 352-364, 1993.
Inspire Record 353857 DOI 10.17182/hepdata.36568

We have measured angular distributions of differential cross sections and analyzing powers ( A y ) of the reaction p p → d π + at six incident proton energies between 1.3 and 2.4 GeV. They confirm the rapid variations at √ s = 2.65 GeV suggested by earlier experiments. Deviations from a monotonic behavior are also found in the excitation functions of the differential cross section at t = 0 or where Θ π + (c.m.) = 0°. Structures clearly appear at √ s = 2.4 and 2.65 GeV, in some coefficients of the associated Legendre function expansions of A y .

12 data tables

No description provided.

No description provided.

No description provided.

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Test of spin dependence in charm-quark fragmentation to D*.

The TPC/Two-Gamma collaboration Aihara, H. ; Alston-Garnjost, M. ; Avery, R.E. ; et al.
Phys.Rev.D 43 (1991) 29-33, 1991.
Inspire Record 316132 DOI 10.17182/hepdata.22830

We have measured the polarization of D*, the energy dependence of the polarization, and the spin-density matrix of D* in e+e− annihilation at a center-of-mass energy of 29 GeV using the Time Projection Chamber detector at the SLAC storage ring PEP. In 147 pb−1 of data we see no strong evidence for polarization, alignment, or final-state interactions in this fragmentation process.

2 data tables

Polarization is the factor alpha(z) in the expression d width (D*-->D pi)/domega = C(1+alpha(z)cos(theta)**2).

Spin density matrices for D* --> D0 pi+.


High precision measurement of A in large P(T)**2 spin polarized 24-GeV/c proton proton elastic scattering

Crabb, D.G. ; Kaufman, W.A. ; Krisch, A.D. ; et al.
Phys.Rev.Lett. 65 (1990) 3241-3244, 1990.
Inspire Record 299843 DOI 10.17182/hepdata.19939

We measured the analyzing power A out to P⊥2=7.1 (GeV/c)2 with high precision by scattering a 24-GeV/c unpolarized proton beam from the new University of Michigan polarized proton target; the target’s 1-W cooling power allowed a beam intensity of more than 2×1011 protons per pulse. This high beam intensity together with the unexpectedly high average target polarization of about 85% allowed unusually accurate measurements of A at large P⊥2. These precise data confirmed that the one-spin parameter A is nonzero and indeed quite large at high P⊥2; most theoretical models predict that A should go to zero.

1 data table

Errors quoted contain both statistical and systematic uncertainties.


Proton proton bremsstrahlung at 280-MeV

Michaelian, K. ; Kitching, P. ; Hutcheon, D.A. ; et al.
Phys.Rev.D 41 (1990) 2689-2704, 1990.
Inspire Record 304884 DOI 10.17182/hepdata.23001

A proton-proton bremsstrahlung experiment has been carried out at TRIUMF using a 280-MeV polarized proton beam impinging on a liquid-hydrogen target. All three outgoing particles were detected: the higher-energy proton in a magnetic spectrometer, the lower-energy proton with plastic scintillators, and the photon in lead-glass Cherenkov detectors. The experiment shows the first unambiguous evidence for off-shell effects in the free nucleon-nucleon interaction, in that the analyzing powers disagree strongly with the predictions of the soft-photon approximation (which incorporates only on-shell information) but are consistent with the results of calculations using the Bonn and Paris potentials.

8 data tables

Estimated scale uncertainty is 1.5 pct.

Estimated scale uncertainty is 1.5 pct.

Estimated scale uncertainty is 1.5 pct.

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