S. Yamashita

Analyzing power in inclusive π+ and π− production at high xF with a 200 GeV polarized proton beam☆

The analyzing power in inclusive charged pion production has been measured using the 200 GeV Fermilab polarized proton beam. A striking dependence in x(F) is observed in which A(N) increases from 0 to 0.42 with increasing x(F) for the pi+ data and decreases from 0 to -0.38 with increasing x(F) for pi- data. The kinematic range covered is 0.2 less-than-or-equal-to x(F) less-than-or-equal-to 0.9 and 0.2 less-than-or-equal-to p(T) 2.0 GeV/c. In a simple model our data indicate that at large x(F) the transverse spin of the proton is correlated with that of its quark constituents.

Search for the H dibaryon in (K−, K+) reaction with scintillating fiber active target

Abstract We have studied ( K − , K + ) reactions at P K − = 1.66 GeV/c by using a newly developed active target made of plastic scintillating fibers. The H dibaryon ( S = −2, I ( J π ) = 0(0 + )) has been searched for through the direct process, K − + C → K + + H + X , by the analysis of the K + momentum spectrum with the help of visual data of the scintillating fiber target. No evidence for the H production was observed. Upper limits for the differential cross section for the H production in the forward direction of the K + is 0.04–0.6 μb/sr at the 90% confidence level for the H mass range from 1850 to 2215 MeV/c 2 .

Large-xF spin asymmetry inπ0 production by 200-GeV polarized protons

The spin asymmetryAN for inclusive π0 production by 200-GeV transversely-polarized protons on a liquid hydrogen target has been measured at Fermilab over a wide range ofxF, with 0.5<pT<2 GeV/c. AtxF>0.3, the asymmetry rises with increasingxF and reaches a value ofAN=0.15±0.03 in the region 0.6<xF<0.8. This result provides new input regarding the question of the internal spin structure of transversely-polarized protons.

Σ+p elastic scattering in the region of 300 ⩽ pΣ ⩽ 600 MeV/c with a scintillating fiber target

Abstract We have performed a hyperon-proton scattering experiment with a scintillating fiber active target. The Σ − p, Λ p and Σ + p scattering have been studied with the same experimental setup. In this paper, we present the differential cross sections of the Σ − p elastic scattering in the momentum region from 400 to 700 MeV /c . This is the first measurement of the Σ − p elastic scattering in the momentum region where the P- and higher waves contributions are important. The present data are in good agreement with the one boson exchange model (Bonn–Julich model A) and the quark cluster model (FSS of Kyoto–Niigata model).

High-xT single-spin asymmetry in π0 and η production at xF=0 by 200 GeV polarized antiprotons and protons☆☆☆

A measurement of the single-spin asymmetry A(N) in P up + P --> pi-0 + X at 200 GeV with x(F) = O 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) almost-equal-to 0.4 and is consistent with x(T)-scaling of A(N) in pion production using polarized beams or targets from square-root -s = 5.2 to 19.4 GeV. Results for A(N) in eta-production by polarized protons and in pi-0 production by polarized antiprotons are also presented.

Measurement of single spin asymmetry in η-meson production in p↑p and p̄↑p interactions in the beam fragmentation region at 200 GeV/c

We present experimental results on measuring a single spin asymmetry in η-meson production in the interaction of transversely polarized protons and antiprotons at plab = 200 GeV/c with a proton target in the region 0.2 < xF < 0.7 for p↑p, 0.3 < xF < 0.7 for p↑p and 0.7 < pT < 2.0 GeV/c. A comparison of single spin asymmetries in π- and η-meson production is made.

Scalar and vector meson production and two-step processes in the (K-, K+) reaction on 12C

Abstract The double strangeness exchange reaction ( K − , K + ) is investigated with respect to the sub-threshold production of scalar and vector mesons ( f 0 / a 0 / φ ) decaying into K + K − and the two-step processes induced by intermediate mesons and Ξ − hyperons at p k − = 1.66 GeV/ c using a scintillating fiber active target. The differential cross section ( 〈 dσ dΩ L 〉) averaged over the angular interval (2.3° ⩽ θ K + L ⩽ 14.7°) for the sub-threshold f 0 / a 0 / φ meson production with the K + K − decay is 11 ± 6 μ b/sr at 0.6 ⩽ p K 1 c . The present result differs significantly from the theoretical calculation which predicts the contribution of the f 0 / a 0 / φ meson production to be predominant in the ( K − , K + ) reaction below p K + = 0.95 GeV/ c . We found a sizable contribution from two-step ( K − , K + processes, characterized by production of two S = −1 hyperons, consistent with the result of the intra-nuclear cascade (INC) model calculation with respect to the meson-induced hyperon (or hyperon resonance) pair production in the momentum region 0.6 ⩽ p K + c . The observed enhancement of the cross section for the two-step ΛΛ production beyond the prediction of the INC model at p K + ⋍ 1.1 GeV /c could be due to the Ξ − p → ΛΛ reaction in 12 C.

Search for H dibaryon by scintillating fiber track detector

The H dibaryon search experiment using a scintillating-fiber target was performed at KEK-PS. The preliminary results are reported. No evidence of the H production via C(K−, K+) reaction has been found. The upper limit of the ratio of the H production to the quasi-free process, K−+(p)→K++Ξ− is 0.05–0.6% forMH⩽2200 MeV/c2. For 2200 MeV/c2⩽MH⩽2230 MeV/c2, the upper limit for the production of the H which decays into Σ−+p is 0.6–07%.

Hyperon-proton scattering experiments with a scintillating fiber detector at KEK

Abstract Hyperon-proton scattering is being studied at KEK in order to obtain a better understanding standing of the baryon-baryon interaction. A scintilating fiber (SCIFI) block detector has been used as a production target of hyperons as well as a target for hyperon scattering on hydrogen. The pilot experiment (E251) for Σ + p scattering has been completed, and the next experiment (E289) for Σ + p, Σ − p and Λp channels has finished its data taking and is now uder analysis.

Enhanced production of ΛΛ pairs near threshold in the (K-,K+) reaction on 12C

Abstract Enhanced production of ΛΛ pairs, above the prediction of a two-step process model, is observed near threshold (around the masses of 2.23 – 2.26 GeV/c2) in the12C(K−,K+) reaction at PK− = 1.66GeV/c using a scintillating fiber target. The differential cross section for the ΛΛ production averaged over 2.3° ≤