Y. Yoshimura

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.

Nuclear-matter modification of decay widths in the phi-->e+e- and phi-->K+K- channels.

The invariant mass spectra of phi-->K+K- are measured in 12 GeV p+A reactions in order to search for the in-medium modification of phi mesons. The observed K+K- spectra are well reproduced by the relativistic Breit-Wigner function with a combinatorial background shape in three betagamma regions between 1.0 and 3.5. The nuclear mass number dependence of the yields of the K+K- decay channel is compared to the simultaneously measured e+e- decay channel for carbon and copper targets. We parameterize the production yields as sigma(A)=sigma0Aalpha and obtain alphaphi-->K+K- -alphaphi-->e+e- to be 0.14+/-0.12. Limits are obtained for the partial decay widths of the phi mesons in nuclear matter.

Nuclear mass number dependence of inclusive production of {omega} and {phi} mesons in 12 GeV p+A collisions

The inclusive production of {omega} and {phi} mesons is studied in the backward region of the interaction of 12 GeV protons with polyethylene, carbon, and copper targets. The mesons are measured in e{sup +}e{sup -} decay channels. The production cross sections of the mesons are presented as functions of rapidity y and transverse momentum p{sub T}. The nuclear mass number dependences (A dependences) are found to be A{sup 0.710{+-}}{sup 0.021(stat){+-}}{sup 0.037(syst)} for {omega} mesons and A{sup 0.937{+-}}{sup 0.049(stat){+-}}{sup 0.018(syst)} for {phi} mesons in the region of 0.9

STUDY OF IN-MEDIUM MESON MODIFICATION IN 12 GeV p + A REACTIONS

Invariant mass spectra of low-mass vector mesons in the e+e- channel are measured in 12 GeV p + C and p + Cu reactions at the KEK Proton Synchrotron. Significant excess is observed at the low-mass side of ω meson peak over the known hadronic sources both in the C and Cu target data. Also below the ϕ meson peak, an excess is found in the Cu target data for slowly moving mesons whose βγ is less than 1.25. They can be interpreted as signatures of the spectral modification of vector mesons in cold nuclear matter.

Medium modification of vector mesons observed in 12 GeV p+A reactions

The invariant mass spectra of e + e - pairs produced in 12 GeV p+A reactions are measured at the KEK Proton Synchrotron. We observed a significant enhancement over the known hadronic sources on the low-mass side of the ω meson peak for C and Cu data. The 95% CL allowed parameter regions for ρ/ω) ratio are obtained as ρ/ω < 0.15 and ρ/ω < 0.31 for C and Cu targets, respectively. As for the Φ meson, the data obtained with a Cu target revealed a significant excess on the low-mass side of the Φ meson peak mainly in the βγ Φ < 1.25 region.

Nuclear production of χ meson at KEK

Publisher Summary In quantum molecular dynamics, hadrons are described as a bound state of confined valence quarks which obtained the effective mass due to the spontaneous breaking of the chiral symmetry. This mechanism determines the properties of hadrons in free space, such as the mass and the decay width. This chapter presents an experiment, which is the first attempt to measure the production and decay of Ф mesons in the kinematical region where the effect of nuclear media should play an important role. The experiment E325 is being performed at the primary beam-line EP1B at the KEK Proton Synchrotron. The data from the first physics run in 1997 are reported. The kinematical region of the observed Ф mesons covers 1 to 3 in βγlab where modification of Ф meson in nuclear matter is expected to be visible. The shape of the invariant mass spectra of the observed Ф mesons are consistent with that observed in free space within the statistics which are presently available.

Fluctuations in number of molecules in several liquids including water. The role of attractive intermolecular interactions in anomalies of water

Abstract The temperature dependence of fluctuation in number expressed by 〈(ΔN)2〉 / 〈N〉 has been examined for water, hexane, toluene, carbon disulfide under isochoric conditions. The fluctuation in water is four to six times larger than that in the other molecular liquids because of the attractive forces. At a low liquid density, the fluctuation has a minimum against temperature in water and hexane, but it increases monotonically in toluene and carbon disulfide. Upon compression the temperature dependence of the fluctuation becomes positive for all liquids except water. It is verified that the negative temperature dependence is caused by the attractive intermolecular interactions. The minimum appears in systems where attractive interactions are important as a result of a relatively low molecular packing. Water is anomalous in the sense that the attractive nature of the molecular field cannot be lost easily by an increase in density which may be absorbed by the open structure.