H. Funahashi

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.

Experimental signature of medium modifications for rho and omega mesons in the 12 GeV p+A reactions.

The invariant mass spectra of e+e- pairs produced in 12 GeV proton-induced nuclear reactions are measured at the KEK Proton Synchrotron. On the low-mass side of the meson peak, a significant enhancement over the known hadronic sources has been observed. The mass spectra, including the excess, are well reproduced by a model that takes into account the density dependence of the vector meson mass modification, as theoretically predicted.

Evidence for in-medium modification of the phi meson at normal nuclear density.

Invariant mass spectra of e(+) e(-) pairs have been measured in 12 GeV p + A reactions to detect possible in-medium modification of vector mesons. Copper and carbon targets are used to study the nuclear-size dependence of e(+) e(-) invariant mass distributions. A significant excess on the low-mass side of the phi meson peak is observed in the low betagamma(= beta/square root(1-beta(2))) region of phi mesons (betagamma < 1.25) with copper targets. However, in the high betagamma region (betagamma > 1.25), spectral shapes of phi mesons are well described by the Breit-Wigner shape when experimental effects are considered. Thus, in addition to our earlier publications on rho/omega modification, this study has experimentally verified vector meson mass modification at normal nuclear density.

Observation of rho/omega meson modification in nuclear matter.

We measured the invariant mass spectra of electron-positron pairs in the target rapidity region of 12-GeV p+A reactions. We have observed a significant difference in the mass spectra below the omega meson between p+C and p+Cu interactions. This difference indicates that the spectral shape of mesons is modified at normal nuclear-matter density.

Photoproduction of Lambda(1405) and Sigma0(1385) on the proton at E(gamma) = 1.5-2.4-GeV

Differential cross sections for {gamma}p{yields}K{sup +}{lambda}(1405) and {gamma}p{yields}K{sup +}{sigma}{sup 0}(1385) reactions have been measured in the photon energy range from 1.5 to 2.4 GeV and the angular range of 0.8<cos({theta})<1.0 for the K{sup +} scattering angle in the center-of-mass system. This data is the first measurement of the {lambda}(1405) photoproduction cross section. The line shapes of {lambda}(1405) measured in {sigma}{sup +}{pi}{sup -} and {sigma}{sup -}{pi}{sup +} decay modes were different with each other, indicating a strong interference of the isospin 0 and 1 terms of the {sigma}{pi} scattering amplitudes. The ratios of {lambda}(1405) production to {sigma}{sup 0}(1385) production were measured in two photon energy ranges: near the production threshold (1.5<E{sub {gamma}}<2.0 GeV) and far from it (2.0<E{sub {gamma}}<2.4 GeV). The observed ratio decreased in the higher photon energy region, which may suggest different production mechanisms and internal structures for these hyperon resonances.

Photoproduction ofΛ(1405)andΣ0(1385)on the proton atEγ=1.5−2.4GeV

Differential cross sections for {gamma}p{yields}K{sup +}{lambda}(1405) and {gamma}p{yields}K{sup +}{sigma}{sup 0}(1385) reactions have been measured in the photon energy range from 1.5 to 2.4 GeV and the angular range of 0.8<cos({theta})<1.0 for the K{sup +} scattering angle in the center-of-mass system. This data is the first measurement of the {lambda}(1405) photoproduction cross section. The line shapes of {lambda}(1405) measured in {sigma}{sup +}{pi}{sup -} and {sigma}{sup -}{pi}{sup +} decay modes were different with each other, indicating a strong interference of the isospin 0 and 1 terms of the {sigma}{pi} scattering amplitudes. The ratios of {lambda}(1405) production to {sigma}{sup 0}(1385) production were measured in two photon energy ranges: near the production threshold (1.5<E{sub {gamma}}<2.0 GeV) and far from it (2.0<E{sub {gamma}}<2.4 GeV). The observed ratio decreased in the higher photon energy region, which may suggest different production mechanisms and internal structures for these hyperon resonances.

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 .

(K−, K+) reaction on nuclear targets at PK = 1.65 G

Abstract The forward-angle cross sections of the (K − , K + ) reaction on nuclear targets of C, Al, Cu, Ag and Pb have been measured at the K − incident momentum of 1.65 GeV/ c in a side range K + momentum. The obtained K + momentum spectrum for each target nucleus is characterized by a peak in the high-momentum region ( p K + > 0.95 GeV/ c ) and a broad bump in the low-momentum region ( p K + c ). A comparison of the measured spectrum with a DWIA calculation indicates that the quasifree process, K − (p) → K + Ξ − , is dominant in the high-momentum region. The target mass-number dependence of the cross section is well fitted with A α , where α is 0.38 ± 0.03 for the high-momentum region and 0.56 ± 0.02 for the low-momentum region. The result indicates that the quasifree process takes place at the peripheral of the target nucleus, whereas the two-step processes are dominant in the low-momentum region.

Enhanced ΛΛ production near threshold in the 12C(K−,K+) reaction

Abstract Enhanced production of ΛΛ pairs, above levels predicted by a two-step process model, has been observed near threshold (in the mass range 2.23-2.26 GeV/c2) in the 12C(K−,K+) reaction at 1.66 GeV/c using a scintillating fiber target. The differential cross section for ΛΛ production in the momentum region 0.95≤pK+≤1.3 GeV/c averaged over the range 2.3o≤θK+≤14.7o was found to be 7.6±1.3 ±0.9 μ b/sr, and that for the enhancement was found to be approximately 3 μ b/sr.

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.