Polarisation-dependent differential cross sections σT associated with the target asymmetry T have been measured for the reaction γp→→pπ0 with transverse target polarisation from π0 threshold to photon energies of 190 MeV. The data were obtained using a frozen-spin butanol target with the Crystal Ball / TAPS detector set-up and the Glasgow photon tagging system at the Mainz Microtron MAMI. Results for σT have been used in combination with our previous measurements of the unpolarised cross section σ0 and the beam asymmetry Σ for a model-independent determination of S - and P -wave multipoles in the π0 threshold region, which includes for the first time a direct determination of the imaginary part of the E0+ multipole.
Target asymmetry T for c.m. cos(Theta_pi0)= 0.996
Target asymmetry T for c.m. cos(Theta_pi0)= 0.966
Target asymmetry T for c.m. cos(Theta_pi0)= 0.906
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The results on measuring polarization in charge exchange reaction π−+p→π0+n at 40 GeV/c are presented for the 4-momentum transfer range from 0 up to 2 (GeV/c)2. At |t|≦0.4 (GeV/c)2 the polarization has a positive sign. In the “crossover” region of π± elastic scattering a possible minimum in the polarization behaviour has been seen for the first time. the polarization is zero within the statistical accuracy near this point. In the “deep” region of the charge-exchange differential cross-section the polarization has a negative sign. The presented data are not in agreement with the modern theoretical models.
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We report final results on the polarization parameter P in elastic scattering of π − , K − and antiprotons at 40 GeV/ c incident momentum. The energy dependence of P (t) in π − p above 10 GeV/ c is well fitted by P (t) α s αR(t)-α P (t) where α R (t) are the effective Regge and Pomeron trajectories respectively. The data in K − p are compatible with exchange degeneracy. The results inp¯p show an important structure for |t|> 0.3 (GeV/c) 2 demonstrating the existence of a large helicity flip amplitude.
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The polarization parameter in the reactions π−p→ηn and π−p→η′n at 40 GeV/c with −t ranging from 0 to 2.6 (GeV/c)2 and 1.0 (GeV/c)2, respectively, was measured in experiments using a propanediol polarized target. Only gamma particles from the neutral meson decay were detected. The polarization parameter of the first reaction turns out to be negative in a widet interval (0.05<−t<1.6 (GeV/c)2) and probably changes its sign at larger values oft. The average value of the polarization parameter of the second reaction is equal to −17±8)% in the region 0.05<−t<0.5 (GeV/c)2.
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The paper presents results on measuring the polarization in the reaction π − p→ π 0 n at 40 GeV/ c in the 4-momentum transfer range 0<| t |⩽2 (GeV/ c ) 2 . The results based on the statistics of about 2.2 million recorded events made it possible to observe a noticeable value and complex structure in the polarization behaviour up to | t |⩽2 (GeV/ c ) 2 .
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We present experimental results on measuring a single spin asymmetry in η-meson production in the interaction of transversely polarized protons and antiprotons at p lab = 200 GeV / c with a proton target in the region 0.2 < x F < 0.7 for p ↑ p , 0.3 < x F < 0.7 for p ̄ ↑p and 0.7 < p T < 2.0 GeV / c . A comparison of single spin asymmetries in π- and η-meson production is made.
The true asymmetry for ETA production in proton-proton collisions.
The true asymmetry for ETA production in antiproton-proton collisions.
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.
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.
We have measured the polarization of $\Lambda$ hyperons produced inclusively by a $\Sigma^-$ beam of 340 GeV/c momentum in nuclear targets. From a sample of 9.5 millions of identified $\Lambda$ decays, polarizations were determined in the range $x_F \gt 0.1$ and $p_t\leq 1.6$ GeV/c . The polarization w.r.t. the production normal is mainly positive for $x_F \geq 0.3$. At fixed values of $x_F$, it increases with $p_t$ to a maximum between $p_t = 0.5$ and $p_t = 1$ GeV/c , and then decreases to zero or even negative values, in sharp contrast to the plateau above $p_t = 1$ GeV/c observed in inclusive $\Lambda$ production by protons.
Measured values of the LAMBDA polarization as a function of PT in the XL range 0.1 to 0.2.
Measured values of the LAMBDA polarization as a function of PT in the XL range 0.2 to 0.3.
Measured values of the LAMBDA polarization as a function of PT in the XL range 0.3 to 0.4.
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