Search

We have investigated a prototype triggerless data acquisition (DAQ) system for charmed-baryon spectroscopy at J-PARC. A special time-to-digital converter (TDC) dedicated to continuous timing measurement without any external trigger was developed. A high dynamic range of the order of 1010 for the timing measurement was realized by introducing the heartbeat method, which periodically generates a delimiter datum. DAQ software receiving and filtering the data stream from the TDCs was also developed based on a message-queue application programming interface (API), FairMQ. We tested the prototype DAQ system with detectors using electrons and positrons converted from a bremsstrahlung photon beam with a rate condition of up to 1.9 MHz/1-mm detector segment. The DAQ received a 5.4 Gbps data stream from six TDCs and merged them to a complete data set. After sorting a certain portion of the data, the software searched for a set of corresponding data fragments in response to the penetration of a positron or electron using time separation between detector hits in the time axis and removed unnecessary hits. Around 25 GB RAM and 25 CPU threads were required for the online computing power under the test conditions. No silent data drop in the DAQ software was observed.

Coherent photoproduction of the neutral pion and eta meson on the deuteron, $$\gamma {d}$$ $$\rightarrow $$ $$\pi ^0\eta {d}$$ , has been experimentally studied at $$E_\gamma

An internal radiator made of a carbon wire is employed to produce bremsstrahlung-photon beams for meson photoproduction experiments from circulating electrons in a synchrotron at the Research Center for Electron Photon Science, Tohoku University. The horizontal electron-beam size at the radiator location is determined from the decay rate of the resultant photon intensity as a function of the distance between the fixed position of the radiator and the centroid of the electron beam. The horizontal beam size at the radiator location is determined to be 0.74 mm with a statical error less than 0.01 mm for 1.3-GeV circulating electrons. The horizontal correlation between the position and momentum direction of the electron beam is also measured. The horizontal size and correlation are well-reproduced by the design values of the parameters of the synchrotron.

Coherent double neutral-pion photoproduction on the deuteron, γ d → π 0 π 0 d , has been experimentally studied at incident photon energies ranging from 0.75 to 1.15 GeV. The total cross section as a function of the γd center-of-mass energy shows resonance-like behavior, which peaks at approximately 2.47 and 2.63 GeV. The measured angular distribution of deuteron emission is rather flat, which cannot be reproduced by the kinematics of quasi-free π 0 π 0 production with deuteron coalescence. In π 0 d invariant-mass distributions, a clear peak is observed at 2.14 ± 0.01 GeV / c 2 with a width of 0.09 ± 0.01 GeV / c 2 . The spin-parity of this state is restricted to 1 + , 2 + or 3 − from the angular distributions of the two π 0 s. The present work shows strong evidence for the existence of an isovector dibaryon resonance with a mass of 2.14 GeV / c 2 . The 2 + assignment is consistent with the theoretically predicted D 12 state, and also with the energy dependence of the πd partial-wave amplitude P 2 3 for the π ± d → π ± d and π + d → p p reactions.

We have measured the differential cross-sections and analyzing powers for ($p,2p$) reactions at an incident energy of 392 MeV on $^{12}$C, $^{16}$O, $^{40}$Ca, and $^{208}$Pb nuclei, leading to discrete states of the residual nuclei. The data are compared with two kinds of distorted-wave impulse approximation (DWIA) calculations, a standard calculation using a global optical potential and a calculation using wave functions generated in a relativistic Hartree model. The spectroscopic factors deduced from these two calculations agree with those determined in ($e,e'p$) studies mostly within 15% in the case of the lighter three target nuclei. However, those for the $^{208}$Pb target are overestimated compared with the ($e,e'p$) results. In the heavy target case, the DWIA results are very sensitive to the radius parameter of the bound-state potential and thus a careful treatment is required. Regarding the analyzing powers of the present measurement, we confirmed that the $j$-dependence is sufficient for practical spectroscopic use.

The non-strange \(B=2\) system (dibaryon) has been studied using coherent neutral-meson photoproduction from the deuteron, \(\gamma d\rightarrow \pi ^0\pi ^0d\) and \(\gamma d\rightarrow \pi ^0\eta d\), measured with the FOREST detector at the ELPH facility. A rather flat angular distribution of deuteron emission and a peak in the \(\pi ^0d\) invariant-mass distribution give evidence for the 2.15-GeV isovector dibaryon. The excitation function of the total cross section as a function of the \(\gamma d\) center-of-mass energy for the former reaction shows the evidence for the existence of 2.47- and 2.63-GeV isoscalar dibaryons.

Although the ω meson is one of the best established hadrons, its fundamental properties such as the interaction with the nucleon is not known yet due to the difficulties in realizing scattering experiments. Recently, we have performed high-precision photoproduction experiment of the ω meson from the proton near the threshold. The total cross sections are determined at incident energies ranging from 1.08 to 1.15 GeV. The 1/2 and 3/2 spin-averaged scattering length aωN and effective range rωN between the ω meson and nucleon are extracted from the excitation function of the total cross section using a model with the final-state ωN interaction based on the Lippmann-Schwinger equation. The obtained values are aωp=(−0.97−0.16+0.16)+i(0.07−0.14+0.15) fm and rωp=(+2.78−0.54+0.68)+i(−0.01−0.50+0.46) fm, suggesting a strong repulsion force.

The J-PARC Hadron Experimental Facility was constructed with an aim to explore the origin and evolution of matter in the universe through experiments with intense particle beams. In the past decade, many results from particle and nuclear physics experiments have been obtained at the present facility. To expand the physics programs to as yet unexplored regions, the extension project of the Hadron Experimental Facility has been extensively discussed. This contribution presents the physics of the extension of the Hadron Experimental Facility to resolve issues related to strangeness nuclear physics, hadron physics, and flavor physics.

A transmittance monitor has been developed for the second tagged-photon beamline at the Research Center for Electron Photon Science, Tohoku University, Japan. In this beamline, an internal radiator is employed to produce the bremsstrahlung photon beam out of circulating electrons in a synchrotron. The transmittance, which is defined as the probability of finding a photon coming to the target position when an electron is detected with a photon-tagging counter, should be determined to deduce cross sections for photo-induced reactions. The developed monitor consists of a telescope of thin plastic scintillators with a positron and electron converter, and a dedicated circuit implemented in a field-programmable gate array chip. The transmittance can be measured with this monitor for high-intensity photon beams corresponding to 20 MHz tagging signals. The measured transmittance is found to be constant with respect to the photon intensity for each photon-tagging channel.

A di-quark correlation has been proposed to describe the internal structure of hadrons, especially those of exotic ones. Nevertheless it lacks a conclusive experimental evidence. The J-PARC E50 experiment performs charmed baryon spectroscopy at J-PARC high-momentum beam line to investigate the role of di-quark correlations in baryons. The energy levels of the excited sates are measured by a missing-mass technique for the first time, and the production rates and decay branching ratios are also measured.

We study $\eta$ photoproduction off the deuteron ($\gamma d\to\eta pn$) at a special kinematics: $\sim 0.94$ GeV of the photon beam energy and $\sim 0^\circ$ of the scattering angle of the proton. This kinematics is ideal to extract the low-energy $\eta$-nucleon scattering parameters such as $a_{\eta N}$ (scattering length) and $r_{\eta N}$ (effective range) because the $\eta$-nucleon elastic scattering is significantly enhanced. We show that if a ratio $R$, the $\gamma d\to\eta pn$ cross section divided by the $\gamma p\to\eta p$ cross section convoluted with the proton momentum distribution in the deuteron, is measured with 5% error, ${\rm Re}[a_{\eta N}]$ (${\rm Re}[r_{\eta N}]$) can be determined at the precision of $\sim\pm$0.1 fm ($\sim\pm$0.5 fm), significantly narrowing down the currently estimated range of the parameters. The measurement is ongoing at the Research Center for Electron Photon Science (ELPH), Tohoku University., Comment: 4 pages, 5 figures, Contribution to the Proceedings for 8th International Conference on Quarks and Nuclear Physics (QNP2018), November 13-17, 2018, Tsukuba, Japan

We have developed a charge-to-time converting (QTC) leading-edge discriminator for plastic-scintillator signals, which is packaged in a NIM-standard double-width module. The pulse width of the discriminator output is approximately proportional to the charge integration of input signals up to 40–50 pC. The non-linearity is 20%, 10%, 4%, and 2% at maximum for the input charges below 7 pC, for 7–10 pC, for 10–20 pC, and above 20 pC, respectively, for the minimum input charges larger than 2 pC. The discriminator could be suitable in the measurement of the timing and charge of plastic-scintillator signals together with a multi-hit time-to-digital converter (TDC) module.

An electromagnetic calorimeter, BGOegg, composed of 1320 BGO crystals, has been constructed at the Research Center for Electron Photon Science, Tohoku University to study the structure of hadrons in detail using photo-induced reactions. The design of the new electromagnetic calorimeter and the basic characteristics of the manufactured BGO crystals are described. A performance test has been conducted for the prototype, which consists of 25 crystals arranged in a 5×5 matrix, using positron beams at energies ranging from 100 to 800 MeV. The obtained energy resolution is ( σ E / E ) 2 = ( 0.63 % ) 2 + ( 1.15 % ± 0.04 % ) 2 / ( E / GeV ) + ( 0.42 % ± 0.03 % ) 2 / ( E / GeV ) 2 at room temperature. The energy resolution corresponds to 1.38 % ± 0.05 % for 1-GeV positrons. The position resolution is found to be σ r / mm = ( 3.07 ± 0.03 ) ( E / GeV ) − 0.202 ± 0.008 which corresponds to an angular resolution of approximately 1 ° for 1-GeV positrons.

An electromagnetic calorimeter complex, FOREST, has been constructed for meson photoproduction experiments at the Research Center for Electron Photon Science, Tohoku University. It consists of three types of calorimeters, which are made of pure cesium-iodide crystals, lead scintillating-fiber modules, and lead glass Cherenkov counters. Each calorimeter is equipped with a plastic scintillator hodoscope to identify charged particles. The design and performance of FOREST are described. The energy responses of test calorimeters have been investigated by using 100–800 MeV positron beams. The energy resolutions of the three calorimeters are found to be approximately 3%, 7%, and 5% for 1-GeV photons, respectively. A cryogenic hydrogen/deuterium target system fitted to the FOREST experiments and a newly developed data acquisition system are also presented.

Dasatinib treatment markedly increases the number of large granular lymphocytes (LGLs) in a proportion of Ph+ leukemia patients, which associates with a better prognosis. The lymphocytosis is predominantly observed in cytomegalovirus (CMV)-seropositive patients, yet detectable CMV reactivation exists only in a small fraction of patients. Thus, etiology of the lymphocytosis still remains unclear. Here, we identified NK cells as the dominant LGLs expanding in dasatinib-treated patients, and applied principal component analysis (PCA) to an extensive panel of NK cell markers to explore underlying factors in NK cell activation. PCA displayed phenotypic divergence of NK cells that reflects CMV-associated differentiation and genetic differences, and the divergence was markedly augmented in CMV-seropositive dasatinib-treated patients. Notably, the CMV-associated highly differentiated status of NK cells was already observed at leukemia diagnosis, and was further enhanced after starting dasatinib in virtually all CMV-seropositive patients. Thus, the extensive characterization of NK cells by PCA strongly suggests that CMV is an essential factor in the NK cell activation, which progresses stepwise during leukemia and subsequent dasatinib treatment most likely by subclinical CMV reactivation. This study provides a rationale for the exploitation of CMV-associated NK cell activation for treatment of leukemias.

A fast beam-profile monitor has been developed for high-energy photon beamlines at the Research Center for Electron Photon Science, Tohoku University. The position of the photon converted into an electron–positron pair in a 0.5 mm-thick aluminum plate is measured with two hodoscopes made of scintillating fibers with cross-sections of 3 × 3 mm 2 . Events in which charged particles are produced upstream are rejected with a charge veto plastic scintillator placed in front of the plate, and pair-production events are identified with a trigger plastic scintillator placed behind the plate. The position is determined by a developed logic module with a field-programmable gate array. The dead time for processing an event is 35 ns, and a high data acquisition efficiency ( ~ 100 % ) can be achieved with this monitor for high-intensity photon beams corresponding to 20 MHz tagging signals.

The B = 2 bound/resonance state (dibaryon) is an interesting object, which can be a molecule consisting of two baryons or a spatially compact hexaquark hadron object. The yd ^ n°n°d reaction has been experimentally investigated at incident energies ranging from 0.58 to 1.15 GeV to study non-strange dibaryons. The angular distributions of deuteron emission in the yd center-of-mass energy cannot be reproduced by quasi-free production of two neutral pions followed by deuteron coalescence. Additionally a 2.14-GeV peak is observed in the n°d invariant mass distribution. These suggest a sequential process such as yd ^ RIS ^ n°RIV ^ n°n°d with an isoscalar dibaryon RIS and an isovector dibaryon RIV. Since the mass of the observed isoscalar dibaryons are close to the sum of the nucleon (N) and nucleon resonance (N*) masses, an S-wave NN* molecule may play a role as a doorway to a dibaryon.

We theoretically investigate a possibility of an $\eta ^{\prime} d$ bound state and its formation in the $\gamma d \to \eta d$ reaction. First, in the fixed center approximation to the Faddeev equations we obtain an $\eta ^{\prime} d$ bound state with a binding energy of 25 MeV and width of 19 MeV, where we take the $\eta ^{\prime} N$ interaction with a coupling to the $\eta N$ channel from the linear $\sigma$ model. Then, in order to investigate the feasibility from an experimental point of view, we calculate the cross section of the $\gamma d \to \eta d$ reaction at the photon energy in the laboratory frame around 1.2 GeV. As a result, we find a clear peak structure with the strength $\sim$ 0.2 nb/sr, corresponding to a signal of the $\eta ^{\prime} d$ bound state in case of backward $\eta$ emission. This structure will be prominent because a background contribution coming from single-step $\eta$ emission off a bound nucleon is highly suppressed. In addition, the signal can be seen even in case of forward $\eta$ emission as a bump or dip, depending on the relative phase between the bound-state formation and the single-step background.

We report the measurement of the $\gamma p \rightarrow K^{+}\Lambda$ and $\gamma p \rightarrow K^{+}\Sigma^{0}$ reactions at SPring-8. The differential cross sections and photon-beam asymmetries are measured at forward $K^{+}$ production angles using linearly polarized tagged-photon beams in the range of $E_{\gamma}=1.5$--3.0 GeV. With increasing photon energy, the cross sections for both $\gamma p \rightarrow K^{+}\Lambda$ and $\gamma p \rightarrow K^{+}\Sigma^{0}$ reactions decrease slowly. Distinct narrow structures in the production cross section have not been found at $E_{\gamma}=1.5$--3.0 GeV. The forward peaking in the angular distributions of cross sections, a characteristic feature of $t$-channel exchange, is observed for the production of $\Lambda$ in the whole observed energy range. A lack of similar feature for $\Sigma^{0}$ production reflects a less dominant role of $t$-channel contribution in this channel. The photon-beam asymmetries remain positive for both reactions, suggesting the dominance of $K^{*}$ exchange in the $t$ channel. These asymmetries increase gradually with the photon energy, and have a maximum value of +0.6 for both reactions. Comparison with theoretical predictions based on the Regge trajectory in the $t$ channel and the contributions of nucleon resonances indicates the major role of $t$-channel contributions as well as non-negligible effects of nucleon resonances in accounting for the reaction mechanism of hyperon photoproduction in this photon energy regime.

Photo-production of hadrons is experimentally studied using 0.8 – 1.2 GeV photon beams at the Research Center for Electron Photon Science, Tohoku University, Japan. Photons areproduced at the bremsstrahlung process by inserting a carbon fiber into the circulating electrons in the 1.3 GeV electron synchrotron. The energy of each photon is determined from the trajectory of the corresponding recoil electron. The energy resolution and time resolution of the current photontagging system is not enough high for the next-generation physics program. We have developed a new system called TaggerIIs. The angular resolution should be higher than 5° to reject the background particles coming from other points than the carbon fiber. The time resolution is required to be less than 200 ps to identify the bunch corresponding to a produced photon. We have adopted a combined system of a multi wire drift chamber and plastic-scintillator hodoscope for the new system. The wire chamber has a frame with length of 1000 mm along pole shape of a bending magnet and consists of 3 sense wire planes (X, X’, X) of wire length of 116 mm. A shape of the cell is hexagonal andthe spacing of the sense wires is 6 mm. The hodoscope consists of 60 plastic scintillators (EJ212) of 30 mm height and 5mm thickness. The width of each scintillator is designed from 5 mm to 30 mm. A performance of the new system has been tested using positron beams. As a result, weachieved that the detection efficiency of the wire chamber was 99%, the angler resolution was 0.60\ensuremath{\unicode{0x25E6 \textbf{and the timing resolution of the hodoscope was 165.8 ps.

We have measured the cross sections for $\pi^0\pi^\pm$ photoproduction on the nucleon in the deuteron with an electromagnetic calorimeter system, FOREST, at the Research Center for Electron Photon Science, Tohoku University, Japan. The incident photon energy ranges from 570 to 1150 MeV, corresponding to the $\gamma N$ center of mass, $W_{\gamma N}$, from 1400 to 1750 MeV. The baryon resonances coupling to $\rho^+ n$ and $\rho^-p$ are observed as intermediate states together with $\Delta$-Kroll-Ruderman background components. The angular distributions for the produced $\rho^+$ and $\rho^-$ mesons are convex downward and upward at high energies ($W_{\gamma N}\sim 1720$ MeV), respectively.

A large-acceptance spectrometer, Neutral Kaon Spectrometer 2 (NKS2), was newly constructed to explore various photoproduction reactions in the gigaelectronvolt region at the Laboratory of Nuclear Science (LNS, currently ELPH), Tohoku University. The spectrometer consisted of a dipole magnet, drift chambers, and plastic scintillation counters. NKS2 was designed to separate pions and protons in a momentum range of less than 1 GeV/$c$, and was placed in a tagged photon beamline. A cryogenic H$_{2}$/D$_{2}$ target fitted to the spectrometer were designed. The design and performance of the detectors are described. The results of the NKS2 experiment on analyzing strangeness photoproduction data using a 0.8--1.1 GeV tagged photon beam are also presented., Comment: 62 pages, 29 figues. Submitted to Nucl. Instrum. Meth. A

We have proposed an experiment for studying charmed baryons via the p ( π − , D ⁎ − ) reaction at the J-PARC high-momentum beam line. Charmed baryons will be measured by a missing mass method. Scattered D ⁎ − will be reconstructed by detecting its decay chain of D ⁎ − → D ¯ 0 π − → K + π − π − . We designed a Ring Imaging Cherenkov (RICH) counter with two radiators, aerogel and C 4 F 10 of refractive indices 1.04 and 1.00137, respectively, in order to identify pions and kaons in a wide momentum range from 2 to 16 GeV/ c . Spherical mirrors will be used to focus Cherenkov photons to the photon sensor alloys. The performance of the designed RICH counter is evaluated by a Monte-Carlo simulation based on GEANT4. Detection efficiency for scattered particles averaged over π and K is found to be 99%. Wrong particle identification ratios of pions and protons to kaons are 0.1% and 0.14%, respectively. The background level in the inclusive p ( π − , D ⁎ − ) spectrum increases only 5% due to the wrong identifications.

Photoproduction of the neutral kaon on the deuteron has been investigated at the Research Center for Electron Photon Science, Tohoku University. We constructed the Neutral Kaon Spectrometer-2 for the detection of charged particles from the decay of the neutral kaon and the hyperon. We obtained a momentum distribution of K 0 with the inclusive measurement. It was consistent with the previous measurement. The total cross section of γ + d → K 0 + Λ + p was estimated from the measured integral cross section of γ + d → Λ + X. The total cross section with respect to the photon energy was compared with the theoretical calculations. It favored the Saclay-Lyon A model calculation with the ratio of the neutral to charged coupling constants of the axial-vector meson, K 1, as ~ −1.5. The energy dependence and the magnitude of the total cross section were similar to the total cross section of γ + p → K + Λ.

A beam profile monitor for 1-GeV region gamma-ray beams has been developed using an X-ray flat panel sensor. In order to increase its sensitivity to gamma-rays, a converter plate was placed on the input window. We tested its sensitivity to input gamma-ray photons with various types of converter plates. The output brightness of the pixels was found to be correlated to the number of electrons and positrons converted from the gamma-ray photons. A measured profile of the 1-GeV region gamma-ray beams obtained with a 1-mm thick lead plate was consistent with the beam profile measured with plastic scintillator hodoscopes. It suggested that the X-ray flat panel sensor was sufficiently applicable to the beam profile monitor for 1-GeV region gamma-ray beams.

Several beam-profile monitors have been developed for high-energy photon beamlines at the Research Center for Electron Photon Science, Tohoku University, Japan. The position of the photon converted into an electron-positron pair in a metal plate is measured in these monitors. In the current monitor, two layers of 16 scintillating-fiber hodoscopes with a cross section of a 3-mm square have been adopted for the position measurement. The effective area is a 48 mm square. Events in which charged particles are produced upstream are rejected with a charge veto plastic scintillator placed in front of the plate, and pair-production events are identified with a trigger plastic scintillator placed behind the plate. The position is determined by a logic circuit with a field-programmable gate array. The dead time for processing an event is several tens of ns, and a high data acquisition efficiency can be achieved with these monitors for high-intensity photon beams (approximately 400 MHz). In the new developing monitor, the scintillating-fiber hodoscopes are planned to be replaced with a multi-anode metal-packaged photomultiplier tube. The secondary emission electrons produced at the photoelectric surface by the electron-positron pair are utilized for the position measurement. In this contribution, the overview of the developed monitor and prospects of the developing monitor will be discussed.

We have developed an event mixing technique to observe Bose-Einstein correlations (BEC) between two identical neutral pions produced in photo-induced reactions in the non-perturbative QCD energy region. It is found that the missing-mass consistency cut and the pion-energy cut are essential for the event mixing method to effectively extract BEC observables. A Monte Carlo (MC) simulation is used to validate these constraints and confirms the efficiency of this method. Our work paves the way for similar BEC studies at lower energies where the multiplicity of emitted bosons is limited.

The total cross sections were measured for coherent double neutral-pion photoproduction on the deuteron at incident energies below 0.9 GeV for the first time. No clear resonance-like behavior is observed in the excitation function for $W_{\gamma d}=2.38$--2.61 GeV, where the $d^*(2380)$ dibaryon resonance observed at COSY is expected to appear. The measured excitation function is consistent with the existing theoretical calculation for this reaction. The upper limit of the total cross section is found to be $0.034$~$\mu$b for the dibaryon resonance at $W_{\gamma d}=2.37$~GeV (90\% confidence level) in the $\gamma d \to \pi^0\pi^0 d$ reaction., Comment: submitted to Physics Letters B

Although fluoroquinolones or other antibiotics are commonly used to prevent bacterial infections after hematopoietic cell transplantation (HCT), because of the growing presence of multidrug-resistant microorganisms, it is important to identify patients who are more likely to benefit from antibacterial prophylaxis. To evaluate risk factors for early bacterial infection after allogeneic HCT, we retrospectively analyzed clinical data for 112 consecutive adult patients with hematological malignancies who received transplants without any antibacterial prophylaxis. The cumulative incidence of bacterial infection at 30 days after transplantation was 16%. Among various pre-transplant factors, only high serum ferritin (>700 ng/mL, 47 patients) and high C-reactive protein (CRP) (>0.3 mg/dL, 28 patients) levels were significantly associated with the development of bacterial infection in a multivariate analysis (hazard ratio (95% confidence interval): ferritin, 4.00 (1.32–12.17); CRP, 3.64 (1.44–9.20)). In addition, septic shock and sepsis with organ failure were exclusively observed in patients who had high ferritin and/or high CRP levels. These results suggest that pretransplant serum ferritin and CRP levels can be useful markers for predicting the risk of early bacterial infection after allogeneic HCT. It may be prudent to limit antibacterial prophylaxis to patients with predefined risk factors to ensure the safety of HCT with the use of fewer antibiotics.

The second GeV bremsstrahlung photon beamline has been constructed for meson photo-production experiments at Research Center for Electron Photon Science, Tohoku University, where a 1200 MeV electron synchrotron called STretcher Booster (STB) has been in operation primarily for Quark Nuclear Physics. An internal radiator is employed to produce the bremsstrahlung photon beam out of circulating electrons in the STB ring. A photon tagging system is placed inside one of the bending magnets of the ring. The tagged energy of the photon beam ranges from 740 to 1150 MeV for 1200 MeV operation of the STB synchrotron. The details of the tagging system and the characteristics of the photon beam are described.

Photoproduction of the K 0 from the deuteron and the carbon nucleus has been investigated at the Laboratory of Nuclear Science, Tohoku University in Sendai. The Neutral Kaon Spectrometer and the Neutral Kaon Spectrometer 2 were developed to detect π + π − pairs coming from the decay of the K S 0 . The resulting K 0 momentum spectra for inclusive K 0 photoproduction were compared with theoretical calculations based on isobar models for γ + n → K 0 + Λ , utilizing the spectator hypothesis. An upgrade of the inner detectors to enhance the acceptance for the coincidence measurement of the K S 0 and Λ is underway. We expect that the exclusive and kinematically complete measurement of the reaction will provide us with direct access to the center-of-mass observables that are important for further understanding the mechanism for strangeness photoproduction.

The energy of tagged photons, which were provided from the internal photon tagging system of the Laboratory of Nuclear Science, Tohoku University, has been calibrated using the d(γ,π−pp) reaction. Charged pions and protons in the final state were detected with the Neutral Kaon Spectrometer (NKS2). Photon energies were obtained from the reaction of d(γ,π−pp). The derived photon energy was consistent with the design of the tagger system and the previous measurement using electron-positron pair production. The consistency demonstrates the performance of NKS2 and the capability of the photon energy calibration using d(γ,π−pp).

A large solid angle γ-ray detector system, FOREST, has been constructed at LNS-Sendai to study the π0 and η photo-production reactions. The FOREST detector consists of three electro-magnetic calorimeters: pure CsI crystals, Lead/SciFi blocks and Lead Glass Cherenkov counters. It covers about 90% of the total solid angle. A new data acquisition system for the FOREST detector has been developed to handle high rate trigger events with a high efficiency. To investigate performances of FOREST and the DAQ system, a test experiment has been conducted. The π0 and η mesons are clearly observed. A DAQ efficiency of 76% has been obtained at a 2 kHz trigger request.

The total cross sections for the π+π− photoproduction on the deuteron were measured in an energy range of 0.8 to 1.1 GeV. The obtained total cross section for the quasi-free π+π− photoproduction on the deuteron was about 60 % of those on the free proton. The cross section for Δ++Δ− photoproduction was derived from the non-quasi-free π+π− photoproduction events. It was smaller than the previous data.

Differential and total cross sections of the D(γ, η)pn reaction have been measured for photon energies between 600 and 1150 MeV. The data provide the information of the γn → ηn reaction above Eγ ≥ 800 MeV. The total cross section shows a narrow resonance structure peaked at Eγ = 1020 MeV. The angular distribution coefficients together with the total cross section are compared with the calculation of the isobar model by using the impulse approximation. Although the spin and parity of the resonance cannot be determined unambiguously, a negative parity assignment gives better fit to the data.

The heavy quark baryon spectroscopy is an essential ways to understand the hadron structure. In the case of the charmed baryon, two light quarks are isolated and form the diquark correlation due to the small color-magnetic interaction between the charm and lighter quarks. The excitation modes from the diquark correlation are reflected to the structure of the excited spectrum and the decay modes of excited states. In addition, by measuring the ratio of the cross section between the ground state Λc + and excited states, the information of the inside structure such as the configuration of the diquark correlation and the spin/isospin of excited states can be obtained [1]. From the systematic study of charmed baryons, the diquark correlation which is expectedly a degree of freedom to describe hadrons can be revealed. We propose a spectroscopy experiment [2] to investigate excited states of charmed baryons at the J-PARC high-momentum beam line. The high-intensity secondary pion beams of more than 10 7 per pulse are used with a momentum of 20 GeV/c. The beam momentum can be measured with the resolution of 0.1% by using the momentum-dispersive optics. The excitation energy, width and production cross section are measured by the missing mass technique. The charmed baryons are produced via the π − + p -> Yc* + + D* − reaction. The decay particles of the D* − meson are detected by the forward magnetic spectrometer system which has a large acceptance and a high-momentum resolution. Due to the forward large acceptance of the spectrometer, the decay measurements of the produced charmed baryons can also be performed for determining the absolute decay branching ratio and the spin/parity of the excited states. The systematic measurement of the excitation energy, production rate and decay properties of charmed baryons are performed at J-PARC.

Ultrafast optical response of organic metal (TMTTF)2AsF6 induced by 1.5 cycle (7 fs) infrared pulse was investigated. Intense coherent oscillation of correlated charge (18 fs) grows in the time scale of 50 fs, reflecting the spontaneous-formation of the electronic coherence before the electronic thermalization.

A beam test has been performed on a prototype electromagnetic calorimeter of bismuth silicate BSO crystals for the first time using electrons of 0.5–3.0 GeV. The calorimeter consists of nine BSO crystals, 22 mm × 22 mm × 180 mm (15.6 radiation lengths), arranged in a 3 × 3 array. Each crystal is coupled to a small photomultiplier tube of 20 mm in diameter. The obtained energy resolution is σ E / E = ( 0.023 ± 0.003 ) / E ( GeV ) ⊕ ( 0.017 ± 0.002 ) for incident electrons of the energy E in GeV. The position information for an electron injected onto the center crystal of the calorimeter array is given with energy deposit signals from nine BSO crystals. The RMS position resolution σ x is parameterized as σ x = [ ( 3.2 ± 0.1 ) / E ( GeV ) ⊕ ( 1.3 ± 0.1 ) ] mm at the center of the crystal. Misidentification probability of pions to electrons is found to be ∼ 10 - 3 for the pion momentum ranging from 1.0 to 3.0 GeV/c.