J. Tojo

Single transverse-spin asymmetry in very forward and very backward neutral particle production for polarized proton collisions at s=200 GeV

Abstract In the 2001–2002 running period of the Relativistic Heavy Ion Collider (RHIC), transversely polarized protons were accelerated to 100 GeV for the first time, with collisions at s = 200 GeV . We present results from this run for single transverse-spin asymmetries for inclusive production of neutral pions, photons and neutrons of the energy region 20–100 GeV for forward and backward production for angles between 0.3 mrad and 2.2 mrad with respect to the polarized proton direction. An asymmetry of A N = ( − 0.090 ± 0.006 ± 0.009 ) × ( 1.0 −0.24 +0.47 ) was observed for forward neutron production, where the errors are statistical and systematic, and the scale error is from the beam polarization uncertainty. The forward photon and π 0 , and backward neutron, photon, and π 0 asymmetries were consistent with zero. The large neutron asymmetry indicates a strong interference between a spin–flip amplitude, such as one pion exchange which dominates lower energy neutron production, and remaining spin–non-flip amplitudes such as reggeon exchange.

Production of twin λ-hypernuclei from ξ- hyperon capture at rest

Abstract A hybrid emulsion experiment was carried out to study double-strangeness nuclei produced via Ξ− hyperon capture at rest with the expectation of ten times larger statistics than previous experiments. We have analyzed 5% of the total emulsion and found one “twin-hypernuclei” event involving the emission of two single-Λ hypernuclei and a nuclear fragment from a Ξ− hyperon stopping point. The event is interpreted as the decay of a Ξ − + 14 N atomic system to 5 Λ He + 5 Λ He + 4 He + neutron . The species of the Ξ−-atom and the fragmentation products are uniquely identified for the first time for twin-hypernuclei events. Combined with the results from a past hybrid-emulsion experiment, one double-Λ hypernucleus and three twin-hypernuclei events have been found from Ξ− captures on light emulsion nuclei. The ratio of the detected rate of double-Λ hypernuclei to that of twin-hypernuclei is compared with theoretical estimates.

Doubly strange nuclei by a hybrid-emulsion experiment E373 at KEK

A hybrid emulsion experiment E373 at KEK has been carried out to study doubly strange nuclear system. By the 8% data analysis of all, one twin single-Λ hypernuclei event and two events of double-Λ hypernucleus have been successfully detected. The twin single-Λ event is uniquely interpreted as Ⅺ−+14N→Λ5He+Λ5He+4He+n for the first time. In the first double-Λ hypernucleus event, “Demachi-Yanagi,” it is interpreted as Ⅺ−+12C→ΛΛ10Be* (or ΛΛ10Be*)+t. The second double-Λ hypernucleus event, “NAGARA,” shows a clearly recognized topology and the interpretation is unique as Ⅺ−+12C→ΛΛ6He+4He+t, ΛΛ6He→Λ5He+π−+p, Λ5He→p+d+2n etc. By the preliminary result of the ΛΛ6He, the attractive ΛΛ interaction has been confirmed with the ΔBΛΛ∼1u2009MeV.

Measurement of Single Transverse‐spin Asymmetry in Forward Production of Photons and Neutrons in pp Collisions at s = 200 GeV

The Relativistic Heavy Ion Collider (RHIC) at the Brookhaven National Laboratory (BNL) was commissioned for polarized proton‐proton collisions at the center of mass energy su2009=u2009200u2009GeV during the run in 2001–2002. We have measured the single transverse‐spin asymmetry AN for production of photons, neutral pions, and neutrons at the very forward angle. The asymmetries for the photon and neutral pion sample were consistent with zero within the experimental uncertainties. In contrast, the neutron sample exhibited an unexpectedly large asymmetry. This large asymmetry will be used for the non‐destructive polarimeter for polarized proton beams at the collision points in the RHIC interaction region.

Observation of double-hypernuclei and Λ-Λ interaction

Abstract A hybrid-emulsion experiment has been carried out at KEK-PS to study S = −2 nuclei. With the analysis of about 35% of total emulsion, we have successfully found three events of sequential weak decay of a double-hypernucleus. The results of these E373 events are summarized together with those of past experiments. The first experimental study of the branching ratios of weak decay modes of double-hypernuclei has been performed.

RHIC pC CNI Polarimeter: Experimental Setup and Physics Results

Acceleration of polarized proton beams and experiments with them at RHIC require fast and reliable measurements of the polarization. The polarimeter presented here uses very high figure of merit of the elastic pC scattering at very low momenta transfer since the cross section is large. Small (a few percent) analyzing power of the reaction makes it necessary to collect about 10{sup 7} events per measurement. A deadtimeless DAQ system for the polarimeter is discussed in this paper. It is based on the waveform digitizer modules with on-board event analysis, resulting in typical polarization measurement times of several tens of seconds. During winter 2001/2002 RHIC polarized run several dedicated data runs were taken by the polarimeter to extract the form of the analyzing power dependence as a function of the momentum transferred at beam energies 24 and 100 GeV. This dependence is extremely important for the theoretical understanding of the CNI process including the contribution of the spin-flip hadronic amplitude. The new data may become an input to some theoretical models predicting the energy dependence of the analyzing power.

Scintillating-fiber-block detector for studying double-strangeness nuclei

Abstract Scintillating-fiber-block detectors have been constructed using 0.5 mm square fibers for the KEK-PS E373 experiment, which searches for double-strangeness nuclei. The main aim of the detector is to measure the energies of protons and pions produced from decay of double- or single-hypernuclei using their ranges. It is also used to detect Λ hyperons or the H -dibaryon, and to make event selection. The performance of the detectors was studied with low-energy proton and pion beams as well as minimum-ionizing particles. The energy resolution determined by the range measurements was 0.86 MeV for 37 MeV π − s and 1.4 MeV for 47 MeV protons. The excellent capability of π/p separation has been also demonstrated.

Commissioning of RHIC p-carbon CNI polarimeter.

An innovative polarimeter based on proton carbon elastic scattering in the Coulomb Nuclear Interference (CNI) region has been installed and commissioned in the Blue ring of RHIC during the first RHIC polarized proton commissioning. The polarimeter consists of ultra-thin carbon targets and four silicon detectors. All elements are in a 1.6 meter target chamber. It worked very well as a pivotal tool during the commissioning. It demonstrated that the RHIC snake magnets rotate spin to the expected direction. The results also show that polarized proton beam has been accelerated in RHIC and the polarization is maintained up to 29 GeV.

Study of double-strangeness nuclei with hybrid-emulsion method (KEK-PS E373)

Abstract An experiment to search for double-strangeness nuclei in nuclear emulsion is now being carried on as KEK-PS E373. Preliminary results of the data analysis for the K + spectrometer and the scintillating fiber detectors are presented. Status of the automatic track finding method for the emulsion is reported.