A measurement of the single-spin asymmetry A N in p↑ + p→ π 0 + X at 200 GeV with x F = 0 shows a transition in the production process from a “ low -x T ” regime with A N = 0, through an intermediate region of negative asymmetry, to a “ high -x T ” regime with A N > 0.3. This transition occurs at x T ≈ 0.4 and is consistent with x T -scaling of A N in pion production using polarized beams or targets from √− s =5.2 to 19.4 GeV. Results for A N in η production by polarized protons and in π 0 production by polarized antiprotons are also presented.
Statistical errors only.
The Brookhaven Alternating Gradient Synchrotron polarized proton beam incident on a beryllium target was used for inclusive Λ production at beam momenta of 13.3 and 18.5 GeV/c. The beam polarization was transverse to the beam direction with magnitude 0.63 at 13.3 GeV/c and 0.40 at 18.5 GeV/c. The Λ polarization was measured and found to be in agreement with results from earlier experiments which used unpolarized proton beams. Analyzing power AN and spin transfer DNN of the Λ’s were both measured and compared with a hyperon-polarization model in which the polarization arises from a Thomas-precession effect. There is good agreement with its predictions: AN=0 and DNN=0. In particular, our measurement of 〈DNN〉=-0.009±0.015 supports the idea that the valence quarks carry all of the hadron spin, since this assumption is implicit in the model’s use of SU(6) wave functions to form final-state hadrons from beam fragments and sea quarks. The presence of substantial KS samples at both beam momenta and Λ¯’s at 18.5 GeV/c prompted a measurement of their analyzing powers, which yielded AN(KS)=-0.094±0.012 at 13.3 GeV/c beam momentum and -0.076±0.015 at 18.5 GeV/c, and AN(Λ¯)=0.03±0.10.
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Surprisingly large polarizations in hyperon production by unpolarized protons have been known for a long time. The spin dynamics of the production process can be further investigated with polarized beams. Recently, a negative asymmetry AN was found in inclusive Λ0 production with a 200GeV/c transversely polarized proton beam. The depolarization DNN in p↑+p→Λ0+X has been measured with the same beam over a wide xF range and at moderate pT. DNN reaches positive values of about 30% at high xF and pT∼1.0GeV/c. This result shows a sizable spin transfer from the incident polarized proton to the outgoing Λ0.
Errors are statistical only. The systematic errors are estimated to be negligible.
Errors are statistical only. The systematic errors are estimated to be negligible.
Errors are statistical only. The systematic errors are estimated to be negligible.
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.
We have measured the analyzing power in π+, π−, and KS0 production by a polarized proton beam at 13.3 and 18.5 GeV/c. The data cover the central and the beam fragmentation region, in the transverse-momentum range up to 2 GeV/c. The results indicate that sizable effects are present at high xF and also persist into the hard-scattering region for KS0 and π+. A zero value of the analyzing power was observed for π− production.
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The considerable polarization of hyperons produced at high xF has been known for a long time and has been interpreted with various theoretical models in terms of the constituents' spin. Recently, the analyzing power in inclusive Λ0 hyperon production has also been measured using the 200GeV/c Fermilab polarized proton beam. The covered kinematic range is 0.2≤xF≤1.0 and 0.1≤pT≤1.5GeV/c. The data indicate a negative asymmetry at large xF and moderate pT. These results can further test the current ideas on the underlying mechanisms for hyperon polarization.
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Ratio of the spin averaged invariant cross section for PI0 production in p p and pbar p interactions.
We present the first measurement of the form factor ratios g1/f1 (direct axial-vector to vector), g2/f1 (second class current) and f2/f1 (weak magnetism) for the decay Xi0 -> Sigma+ e- anti-nu/e using the KTeV (E799) beam line and detector at Fermilab. From the Sigma+ polarization measured with the decay Sigma+ -> p pi0 and the e- - anti-nu/e correlation, we measure g1/f1 to be 1.32 +0.21-0.17(stat.) +/- 0.05(syst.), assuming the SU(3)f (flavor) values for g2/f1 and f2/f1. Our results are all consistent with exact SU(3)f symmetry.
Vector(F1) to axial(G1) formfactor ratio. Total systematic error is 0.054.
The analyzing power AN in inclusive π0 production has been measured with use of the new 185-GeV/c Fermilab polarized proton beam. We obtain the value AN=0.10±0.03 for π0's in the kinematic region 0.2<xF<0.8 and 0.3<pT<1.2 GeV/c. In certain models of particle production this suggests that the spin of the proton is carried by its valence quarks.
The invariant double-differential cross section, E 1 E 2 d 6 σ / d p 3 1 d p 3 2 , and the double-spin asymmetry, A LL , for inclusive multi-γ pair production in which γ-rays came from neutral mesons were measured with a 200 GeV / c longitudinally-polarized proton beam and a longitudinally-polarized proton target. Most of the multi-γ pairs comes from two-jet type events which are sensitive to partonic interaction. The A LL values were found to be consistent with zero. The invariant double-differential cross section for inclusive π 0 π 0 production was also measured. These measured cross sections are consistent with LUND Monte Carlo simulations. Using the LUND Monte Carlo simulation package with the Carlitz-Kaur model of spin dependent distribution functions of valence quarks, the A LL values have been compared with theoretical predictions of gluon polarization, ΔG / G . The results put restrictions on the size of ΔG / G in the region of 0.05 ⪅ x ⪅ 0.35.
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