K. Futatsukawa

Photoproduction of neutral kaons on a liquid deuterium target in the threshold region

The photoproduction process of neutral kaons on a liquid deuterium target is investigated near the threshold region, E{sub {gamma}}=0.8-1.1 GeV. K{sup 0} events are reconstructed from positive and negative pions, and differential cross sections are derived. Experimental momentum spectra are compared with those calculated in the spectator model using a realistic deuteron wave function. Elementary amplitudes as given by recent isobar models and a simple phenomenological model are used to study the effect of the new data on the angular behavior of the elementary cross section. The data favor a backward-peaked angular distribution of the elementary n({gamma},K{sup 0}){lambda} process, which provides additional constraints on current models of kaon photoproduction. The present study demonstrates that the n({gamma},K{sup 0}){lambda} reaction can provide key information on the mechanism of the photoproduction of strangeness.

γ-ray spectroscopy study of 11ΛB and 12ΛC

In this paper, a preliminary result from the latest hypernuclear γ-ray spectroscopy experiment (KEK-E566) is presented together with a short discussion. The experiment was performed at the KEK-PS K6 beam line in 2005. In this experiment, the 12C(π +,K +) Λ 12 C reaction was employed to populate Λ 12 C/ Λ 11 B hypernuclei. A germanium detector array, Hyperball2, was constructed to detect γ-rays emitted from the hypernuclei produced. Three hypernuclear γ-ray peaks were observed and assigned.

Neutral Kaon Photo‐Production in the Threshold Energy Region

We have been conducting an experimental program to study strangeness photoproduc‐tions on the deuteron by measuring K0 and Λ in the threshold energy region. The π−π+ from K0 and π−p from Λ are detected by use of large acceptance magnetic spectrometers. At the first stage of the program, we started with Neutral Kaon Spectrometer (NKS), which consisted of timing counters and tracking devices in the magnetic field. The NKS spectrometer was employed to measure K0 photoproductions from deuteron and carbon target for the first time. A newly constructed spectrometer (NKS2) has been employed for the second stage experiment. It consists of a 110 ton dipole magnet and a combination of detectors. The momentum distributions of K0 and A from γ+d process were observed, and compared with the calculations based on the isobar models. The NKS2 spectrometer has been upgraded by installing a three dimensional tracking device in the central region. This improvement enables to explore the simultaneous measurement of the K0‐A w...

Energy calibration of tagged photons by the d(γ,π−pp) reaction

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).

NEUTRAL KAON PHOTOPRODUCTION AT LNS, TOHOKU UNIVERSITY

The elementary photo-strangeness production process has been intensively studied based on the high-quality data of the charged kaon channel, γ + p → K+ + Λ(Σ0). However, there had been no reliable data for the neutral kaon channel γ + n → K0 + Λ(Σ0) and the theoretical investigations suffer seriously from the lack of the data. In order to have reliable data for the neutral kaon photo-production data, substantial effort has been made to measure the γ + n → K0 + Λ process in the π+π- decay channel, using a liquid deuterium target and a tagged photon beam (Eγ = 0.8-1.1 GeV) in the threshold region at the Laboratory of Nuclear Science (LNS), Tohoku University. We have taken exploratory data quite successfully with the use of Neutral Kaon Spectrometer (NKS) at LNS-Tohoku in 2003 and 2004. The data is compared to theoretical models and it indicates a hint that the K0 differential cross section has a backward peak in the energy region. The second generation of the experiment, NKS2, is designed to extend the NKS experiment by considerably upgrading the original neutral kaon spectrometer, fully replacing the spectrometer magnet, tracking detectors and all the trigger counters. The new spectrometer NKS2 has significantly larger acceptance for neutral kaons compared with NKS, particularly covering forward angles and much better invariant mass resolution. The estimated acceptance of NKS2 is three (ten) times larger for than that of NKS. The spectrometer is newly constructed and installed at the Laboratory of Nuclear Science, Tohoku University in 2005. The deuterium target data was taken with tagged photon beam in 2006-2007. We will report recent results of NKS2 in this paper. Additionally, a status of the upgrade project that gives us larger acceptance and capability of K0 + Λ coincidence measurement will be presented.

Neutral Kaon Spectrometer 2

Abstract 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.

Beam-Loss Monitoring Signals of Interlocked Events at the J-PARC Linac

It is important to understand why the beam loss occurs during user operation. It is understandable that the beam loss results from RF cavities failure. However, it would be still useful to study the beam loss detailed mechanism and to know which beam loss monitor (BLM) experiences the highest loss or is most sensitive. This may lead a reduction in the number of interlocked events and a more stable accelerator operation. The J-PARC Linac BLM has a simple data recorder that comprises multiple oscilloscopes. Although its functionality is limited, it can record events when an interlock is triggered. Of particular interest here are the events associated with only the BLM Machine Protection System (MPS). These may reveal hidden problems with the accelerator. INTRODUCTION The Japan Proton Accelerator Research Complex (J-PARC) is a high-intensity proton accelerator facility with three experimental hall, Materials and Life Science Experimental Facility (MLF), Hadron Experimental Facility (HD) and Neutrino Experimental Facility (NU). The accelerator parts are a 400-MeV linac, a 3-GeV Rapid-Cycling Synchrotron (RCS) and the Main Ring (MR), which is operated with 30 GeV. The designed beam power and intensity of the RCS at repetition rate of 25 Hz are 1 MW and 8.3 × 1013 protons per pulse (ppp), respectively. On a one-shot basis, this goal was achieved in early 2015 [1]. That same year, there were two MLF target failures at 500 kW. Since then, the nominal operational beam power and intensity of the RCS have been limited to 200 kW and 1.8 × 1013 ppp, respectively, for the MLF. The MR is operated with cycles of 2.48 and 5.52 s for the NU and HD, respectively. While most of the RCS beam is supplied to the MLF, four consecutive batches of two bunches each are injected from the RCS to the MR within either of these cycles. Operational MR beam powers of over 425 kW and 42 kW are achieved for the NU and HD. The designed linac beam current and macro-pulse length are 50 mA and 500 �s, respectively. However, the peak current of the linac has been kept to 40 mA so far in 2016. The linac bunch structure has also been changed at the request of users. The typical bunch structure for the MLF is 300 �s macro-pulses in the linac and one bunch in the RCS. For the HD, the macro-pulse length is the same as that for the MLF, but the intensity is typically 1.2 × 1013 ppp. For the NU, the macro-pulse is the designed 500 �s length and a typical RCS intensity is 5 × 1013 ppp. ∗ naoki.hayashi@j-parc.jp It is important to understand the over-all accelerator behavior, performance and characteristics, particularly in relation to the beam loss. The Machine Protection System (MPS) is usually triggered when a machine or instrument mal-functions or a beam loss monitor (BLM) hits its predeined threshold. The consequence in either case is that the beam is automatically stopped by the MPS. It is certainly the case that failure of a RF cavity can cause a beam loss. Hence, it is useful to study the detailed correlation between RF cavity failures and the beam-loss pattern. This requires event data from many recorders with time identiication. Sometime, a BLM will trigger the MPS without any sign of machine failure. This could be because of beam instability, accidental beam loss, or some other sources. Understanding beam losses and the entire machine characteristics further would help to reduce the number of MPS events and improve accelerator operation. LINAC AND BEAM MONITORS The linac comprises various sub-systems. Its front end is an RF-driven H− ion source [2] and a 3-MeV RFQ [3]. Three drift-tube-linac (DTL) and 16 separated drift-tubelinac (SDTL) cavities then follow, and the H− beam reaches 190 MeV at this point. After that, 21 annular-ring coupled structure (ACS) cavities that were added in 2013 accelerate the beam up to 400 MeV [4]. The linac-to-3 GeV RCS beam transport line (L3BT) has a length of 190.5 m1 and includes a 90 degree arc section in between two straight sections. The inal ACS cavity, is showing in Fig. 1, along with debunchers 1 and 2, and 0-degree and 30-degree beam dumps. There are two more beam dumps (100-degree and 90-degree) downstream of the second straight section. These four beam dumps are used during beam tuning. The arc section contains six bending magnets from the marked BM01 to BM06 in Fig. 1. A proportional chamber type BLM (BLMP) is adapted as the main BLM [5]. Its pre-ampliier is placed either in the sub-tunnel (B1F) or in the machine tunnel (B2F). The signal unit is in the klystron gallery (1F). Its high voltage (HV) is set to 2 kV. The maximum raw output is < 5 V. There are many BLMs distributed all over the linac. In particularly, after 7�h SDTL, each SDTL and ACS cavity has its own BLMP. In total, 79 BLMPs are connected to the MPS. The number of BLMP is 31 and 5 in the L3BT and in the beam dump area, respectively. ����14, ����18, and ����21 are located between the debuncher cavity 1 1 It comprises four subsections. Straight section before arc is 33.0 m, Arc section is 44.9 m, Straight section after arc is 59.1 m, and Injection section (to the RCS) is 53.5 m. Figure 1: Downstream section of the linac after the inal RF cavity ACS21. Locations of SCT and BLMP are indicated. and the beginning of the arc-section. ���12 (Slow Current Transformer, monitors the beam current) is also located at the right after the debuncher 1. ����33 is in front of BM04 and ����39 is in front of BM05. ���45 and ����55� are in the second straight section. In contrast to the RCS or MR BLMP, the linac BLMP MPS is triggered by the raw waveform and not by a signal integral. Although the integrated value might be more stable, the response time would be longer. The MPS for the linac is designed to stop the beam within 5 �s. The MPS thresholds can be changed using EPICS, most are set to 1.3 or 1.6 V. Inside the MPS unit, a comparator and two PLCs judge whether the raw BLMP signal is too wide. Presently, the threshold width is set to 340 ns. Description about the MPS and a MPS unit can be found in references [6, 7]. WAVEFORM ARCHIVING SYSTEM The raw BLM waveform archiving system comprises multiple oscilloscopes2. There are more than 50 oscilloscopes for the entire linac. At present, 12 of these actively archive the data when the MPS is triggered. The sampling rate is 100 Msample/s (10 ns/step), the record length is 100 ksample, and the sampling time is 1 ms. The scope parameters are monitored and can be modiied through EPICS. During a communication between the EPICS IOC and the oscilloscopes, the system is locked, no trigger is accepted and the data are not archived for about a second. This interrupt occurs every several seconds and this dead time is a problem of this system. The MPS stops the beam within several �s. However, the associated beam trigger from the timing system has an inherent delay. Several triggers are ired even after the MPS event, usually leading to some empty BLM data being recorded. That is why the archive system records 20 con2 Yokogawa, DL1640. secutive waveforms. The archive system records not only the BLM signals but also some SCT and fast current transformer (FCT, monitors the beam phase) waveforms.

Precise determination of Λ12C level structure by γ-ray spectroscopy

Level structure of the

Precise determination of Λ12C level structure byγ-ray spectroscopy

^{12}_{\Lambda}

Upgrade and Operation of J-PARC Linac

C hypernucleus was precisely determined by means of