P. Pile

Studies of hypernuclei by associated production

Abstract The spectroscopy of hypernuclei across a wide range of mass number has been studies by the associated production (π+, K+) technique. The energies of Λ single particle states in the s, p, d, and f shells have been determinedas a function of A. It is demonstrated that the (π+, K+) reaction is the method of choice for studying Λ-bound levels of hypernuclei.

γ-ray spectroscopy in Λ hypernuclei

Abstract The present status of hypernuclear γ -ray spectroscopy with Hyperball is summarized. We observed two γ transitions of 16 Λ O( 1 − → 1 − , 0 − ) and obtained the strength of the ΛN tensor force. In 10 B( K − , π − γ ) data, we did not observe the spin-flip M1 transition of 10 Λ B( 2 − → 1 − ), but γ rays from hyperfragments such as 7 Λ Li( 7 / 2 + → 5 / 2 + ) and 9 Λ Be( 3 / 2 + → 1 / 2 + ) were observed. In 11 B( π + , K + γ ) data, we observed six γ transitions of 11 Λ B. We also attempted an inclusive γ -ray measurement with a stopped K − beam.

First Measurement of Proton-Proton Elastic Scattering at RHIC

Abstract The first result of the pp2pp experiment at RHIC on elastic scattering of polarized protons at s =200 GeV is reported here. The exponential slope parameter b of the diffractive peak of the elastic cross section in the t range 0.010⩽|t|⩽0.019 (GeV/c)2 was measured to be b=16.3±1.6(stat.)±0.9(syst.) (GeV/c)−2.

Kaon-Nucleus Interaction Studied through the In-Flight (K^-, N) Reaction

K-nucleus interaction by the 12 C(K � ,N ) reaction. Missing mass spectra were derived from the momenta of both neutrons and protons from the reaction. An appreciable strength was observed below the ¯ K-nucleus threshold, which indicates that the ¯ K-nuclear potential is strongly attractive. The missing mass spectra are compared with the results of theoretical calculations. It is found that a potential depth of approximately �190 MeV best reproduces the spectrum of the 12 C(K � ,n ) reaction and approximately �160 MeV best reproduces that of the 12 C(K � ,p ) reaction. Our data show that the ¯ K-nucleus potential is sufficiently deep to realize kaon condensation in the core of neutron stars.

The influence of the nuclear medium on K+ total cross sections

Abstract The study of the K+ total cross sections on a wide range of nuclei has revealed important modifications of the free-space K+-nucleon interaction when the nucleon is embedded in a nucleus. Data indicating such an effect were first obtained in a comparison of the total cross sections on carbon and deuterium. In this letter we report new measurements on 6Li, silicon, and calcium, and demonstrate that the previously reported modifications occur quite generally.

Search for double-Λ hypernuclei and the H-dibaryon in the (K−,K+) reaction on 12C

Abstract A search for double- Λ hypernuclei ( 12 ΛΛ Be) and H -dibaryons using the 12 C( K − , K + ) reaction was performed at the BNL-AGS using a high-intensity 1.8 GeV/ c K − beam. A missing-mass analysis below the end point of the quasi-free Ξ − production was used to investigate these S =−2 systems. The upper limit obtained for the forward-angle cross section of 12 ΛΛ Be production is 6 to 10 nb/sr. This is the first search for the direct production of double- Λ hypernuclei to reach the sensitivity required to observe the signal predicted by theoretical calculations. For the H -production cross section, we have obtained an upper limit in the range of a few nb/sr to 10 nb/sr for the H mass below 2100 MeV/ c 2 . This upper limit is the most sensitive H search result to date for a tightly bound H .

Weak decays of He-4(Lambda)

We measured the lifetime and the mesonic and non-mesonic decay rates of the 4He-Lambda hypernucleus. The hypernuclei were created using a 750 MeV/c momentum K- beam on a liquid 4He target by the reaction 4He(K-,pi-)4He-Lambda. The 4He-Lambda lifetime was directly measured using protons from Lambda p -> n p non-mesonic decay (also referred to as proton-stimulated decay) and was found to have a value of tau = 245 +/- 24 ps. The mesonic decay rates were determined from the observed numbers of pi-s and pi0s as Gamma_pi-/Gamma_tot = 0.270 +/- 0.024 and Gamma_pi0/Gamma_tot = 0.564 +/- 0.036, respectively, and the values of the proton- and neutron-stimulated decay rates were extracted as Gamma_p/Gamma_tot = 0.169 +/- 0.019 and Gamma_n/Gamma_tot <= 0.032 (95% CL), respectively. The effects of final-state interactions and possible 3-body Lambda N N decay contributions were studied in the context of a simple model of nucleon-stimulated decay. Nucleon-nucleon coincidence events were observed and were used in the determination of the non-mesonic branching fractions. The implications of the results of this analysis were considered for the empirical Delta I = 1/2 rule and the decay rates of the 4H-Lambda hypernucleus.

Optics design and performance of LESB3, a two-stage separated 800-MeV/c kaon beamline

Abstract The optics design and the measured performance are described for LESB3, the 800-MeV/ c kaon beamline at the Brookhaven AGS used by E787 to search for rare K + decays. The beamline provides a flux of ∼5×10 5 K + /10 12 protons on target, with a K/π ratio of >3.

First measurement of A N at s = 200 GeV in polarized proton–proton elastic scattering at RHIC

We report on the first measurement of the single spin analyzing power (A_N) at sqrt(s)=200GeV, obtained by the pp2pp experiment using polarized proton beams at the Relativistic Heavy Ion Collider (RHIC). Data points were measured in the four momentum transfer t range 0.01 < |t| < 0.03 (GeV/c)^2. Our result, averaged over the whole t-interval is about one standard deviation above the calculation, which uses interference between electromagnetic spin-flip amplitude and hadronic non-flip amplitude, the source of A_N. The difference could be explained by an additional contribution of a hadronic spin-flip amplitude to A_N.

A large acceptance, high-resolution detector for rare K+-decay experiments

Abstract The detector of the E865-collaboration at the Brookhaven-AGS described here combines a magnetic spectrometer for the charged decay products of 6 GeV /c K + with excellent electromagnetic calorimetry and efficient particle identification for electrons and muons. Its high-resolution, large acceptance and high rate capability made it well suited for the study of extremely rare or forbidden decays with multi-leptonic final states such as K+→π+μ+e−, K+→π+l+l−, K+→l+νle−e+ and K+→π+π−e+νe down to branching ratios below 10−11 in an intense K+ beam (≈108 per AGS spill).