Report ofthe 2004 KEK PS External Review Committee
June 7-8, 2004
Seminar Room, Building 4, KEK, Tsukuba, Japan

Final ReportAugust 30, 2004
Satoshi Ozaki: Committee Chairman

Introduction
The 2004 External Review Committee of the KEK 12 GeV Proton Synchrotron (PS)
Program met on June 7-8, 2004 in the Seminar Room of Building 4 in the High Energy
Accelerator Research Organization (KEK). The members of the External Review
Committee and names of its Referees are listed in Appendix 1. The Committee
appreciates the valuable contribution by Referees, who, by mail, provided their expert
evaluation on specific experiments as well as general comments which have been
incorporated in this report. The agenda of the meeting is given in Appendix 2.
The charge to the Committee by the Director General of KEK is found in Appendix 3.
The completion of the 50 GeV proton synchrotron at the Japan Proton Accelerator
Research Complex (J-PARC), which is under construction in Tokai in a joint effort by
KEK and JAERI, has been delayed by one year and now its commissioning is anticipatedin 2008. Soon, KEK is compelled to dismantle some of the existing beam line equipment,
radiation shielding, as well as detector systems, refurbish them, and transfer them to JPARC in time for the commissioning in order to supplement the outfitting of theexperimental halls and beam lines. KEK also has to provide manpower to complete theaccelerator and experimental facility. These considerations, together with the natural
thought that the experimental programs at the 12 GeV PS will move to the new and more
powerful facility, lead to the inevitable conclusion that the operation of the 12 GeV PS at
KEK will have to be shut down in the near future.
With this backdrop, this review was called (1) to evaluate the contributions the 12 GeV
PS has made to the field of particle and nuclear physics since its commissioning morethan 25 years ago, (2) to evaluate the accomplishments and progress of physics research
programs at the PS during the past four years since the last review was performed in theyear 2000, and (3) to evaluate the performance of the 12 GeV PS and the timing of the
anticipated shut down. The Committee was also asked to comment on the transition planfor the experimental program and experimental facility from the 12 GeV PS at KEK to
the 50 GeV PS at J-PARC. The particular operative question is whether the PS can be
shut down, in the earliest case, at the end of the current Japanese Fiscal Year 2004 as has
been discussed occasionally, or should the shut down be delayed to accommodate various
programmatic needs.
Executive Summary
The KEK 12 GeV Proton Synchrotron (PS) Program since 1976:
Since its commissioning in 1976, the 12 GeV PS at KEK has successfully supported ahighly productive physics program in Japan. For more than 25 years, the PS has operated
well with good reliability in spite of the constraint of having limited aperture. This
limited aperture has prevented the PS from taking advantage of the steadily increased
booster intensity over the years. With many innovative steps the 12 GeV PS operations
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group recently succeeded in increasing the average intensity for the fast extraction from
4x1012 ppp to 6x1012 ppp, the improvement that was essential for the successful run of
the K2K experiment.
The experimental program of the 12 GeV PS can be divided into three periods, namely
1977 - 1984 (before TRISTAN), 1985 - 1998 (after the start of TRISTAN and before
K2K), and the period since 1999 (after the start of the K2K experiment). During the first
period, the PS was the only high-energy accelerator in Japan, and as such, it had
supported a wide range of particle and nuclear physics experiments. Notableaccomplishments in this period are an early determination of the upper limit for
K+→π+νν-bar and the rejection of the existence of barionium states.
During the second period (1985 – 1998), with the shift of emphasis in particle physics
research to TRISTAN, nuclear, in particular hypernuclear physics and kaon decay
physics dominated the PS program. The detection of double hypernuclei and success inthe hypernuclear gamma spectroscopy are the notable achievements. In the kaon decay
experiments, the committee noted the KL → µe study. Also noted is the observation of
the anti-protonic atom. This period also saw a considerable increase in the demand forthe test beams for detector R&D work related to TRISTAN experiments as well as
experiments at foreign laboratories.
The third period (1999 to date) is the subject of this External Evaluation, and is marked
by the K2K (KEK-to-Kamioka) experiment, the first accelerator based neutrino
oscillation program in the world and the first PS based large scale international
collaboration that placed the KEK 12 GeV PS on the map of the world. In order toachieve the goal of delivering 1020 protons on target as soon as possible, the PS-PAC
authorized the allocation of 2/3 of available beam time to K2K with fast extraction and
1/3 for other experiments with slow extraction. It was unfortunate that the accident at theSuperKamiokande detector after two and a half years of running shut the experimentdown. The detector was reconfigured and repaired within one year and it is now almost
reaching the original goal in the amount of data collected. Other experiments were runusing the remainder of the available time with significant accomplishments as detailed
later.
As a whole, the KEK 12 GeV PS has made significant contributions to the field ofparticle and nuclear physics as noted below:••••

Provided the foundation for the advancement of high energy physics in Japan.
Advanced frontier of strangeness nuclear physics, the unique accomplishment
worldwide.
Pioneered work on the accelerator based neutrino oscillation, providing
conclusive evidence with the disappearance experiment.
Established the best upper limit, some at the time of the measurements, on various
kaon decay modes and symmetry conservation.

The Performance of the 12 GeV PS Accelerator since the Year 2000:

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The KEK PS complex consists of a 750 keV Cockcroft-Walton H− ion source, a 40 MeV
linac, a 500 MeV rapid-cycling synchrotron (booster), and a 12 GeV synchrotron. It
provides a 500 MeV proton beam from the booster and 12 GeV protons to the users. The
complex was completed in 1976.
In order to meet the requirements of the K2K experiment (in total 1 x 1020 protons-ontarget), the performance was upgraded during 1998 to 1999. The integrated number ofprotons-on-target, recorded by the experiment, already has almost reached its goal infiscal year 2003. This is very impressive and the team should be congratulated on thisachievement.
The PS complex is operating efficiently with a fractional down-time which is less than
10%. This is comparable to the down-time of the 26 GeV CERN Proton Synchrotron(CERN PS) which is about 5%. The fraction of time used for setting-up and machinestudies is about 10% which is reasonable and nearly the same number as observed at the
CERN PS. The total time scheduled for operation per year is close to 6000 hours, whichis comparable to the 5000 to 6500 hours per year of the CERN PS, depending on thephysics program. The remaining 2800 hours allow for proper maintenance of theaccelerator complex, its infrastructure and official holidays. This time span includes thecool-down time after an extended running period which is required for the maintenanceof important components that have become radio-active due to unavoidable beam losses.
The performance goal of the KEK PS was achieved by a number of well-targetedmeasures to increase the intensity and the reliability, and to reduce the losses in theaccelerators. This quickly led to an increase of about a factor of 1.5 to 2 in the delivered
intensity of fast extracted beams when compared to the period before 1999.
These measures included well justified hardware upgrades of key booster components(magnet power supply, RF cavities and RF power amplifiers) and careful re-engineeringof the vacuum envelope of the PS, resulting in a reduction of the impedance seen by thebeam which significantly reduced the losses at transition. Furthermore, extensive
machine studies were made to improve the tuning of the accelerators and to raise beamstability limits. A prominent example is the introduction of white noise in the RF, which
produced an increase in the space charge threshold by bunch lengthening.
KEK PS Particle Physics Program since the Year 2000:
The recent KEK program in particle physics has addressed frontier issues in its neutrino
and kaon experiments. The results obtained are significant and the experience gained intheir pursuit will be extremely valuable for the next generation of neutrino and kaonstudies to be carried out at J-PARC. The much higher flux of neutrinos and kaonsattainable at J-PARC will improve the experimental sensitivity and could lead to major
discoveries. The neutrino and kaon experiments carried out at KEK in recent years
include: E362, E246, E470, and E391a.

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The above particle physics program is viewed as an outstanding success. The neutrino
experiment (E362), K2K, has pioneered an accelerator based long baseline neutrino
oscillation experiment. It made very important measurements regarding the neutrino
oscillations, confirming with a 99.99% confidence level the neutrino oscillation
discovered by SuperKamiokande. This is a major success of the KEK-PS experimental
program in recent years. The K2K experiment will also provide very useful neutrino
cross-section measurements. The kaon experiment, E246, searched for T-violation in Kµ3
decay using a precise measurement of transverse muon polarization, and obtained thebest bound to date. Another kaon experiment, E391a, is currently taking data, aiming at
searching for the CP violating KL→π0νν-bar decay with sensitivity at the level of 10-10.
These kaon experiments provide valuable information regarding backgrounds for some of
the most interesting future kaon experiments imaginable. The experience gained fromthose efforts will prove extremely valuable for J-PARC.
KEK PS Hadron and Hyperon Program since the Year 2000:
The physicists running strangeness physics experiments at the KEK 12 GeV PS havetaken full advantage of its capability to deliver an outstanding set of results over the past
five years even with limited beam availability. The Japanese physicists heading thiseffort are to be commended for taking a world leadership role in the field. The γ-ray
spectroscopy research was a giant step forward; the Hyper-ball is a superb technicalsuccess and the precision data obtained are of major importance in hypernuclear physics.
The Σ+-p scattering measurement and its relation of the spin-orbit potential plus the Σnucleus repulsive potential demonstration are important contributions to strangenessphysics and our effort to understand the baryon-baryon interaction. The non-mesonicweak decay of the Λ hypernuclei experiments have resolved a decade-long puzzle in
hypernuclear physics, suggesting that the kaon exchange plays a crucial role in the mesonexchange picture of the hyperon-nucleon interaction. The discovery of the Nagara event6ΛΛ He is considered by some the most significant result of the past 5 years in
hypernuclear physics. The observation of the excess dileptons in p-C and p-Cu reactions
gave a first hint of the medium modification of vector mesons in nuclei. The observationof possible signatures for deeply bound kaonic states in light nuclei and theirinterpretation is especially tantalizing; one would certainly urge additional time for an
experiment to provide clear confirmation prior to any permanent shutdown of the KEK
PS. In any case, the record at KEK in strangeness physics since 2000 is unequaled.
Conditionally Approved Experiments and Approved Experiments Awaiting for
Beam Time at 12 GeV PS:
Three experiments have been conditionally approved by PAC for future KEK beam time:1) E548: Study of Kaonic Nuclei by the (K−, p) Reactions and Search for the Kπbound state in Kaon Induced Reaction2) E549: Confirmation of Nuclear Kaonic State and Search for its Excited State
3) E559: High Resolution Spectroscopy of Pentaquark Θ+

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Of these proposals, E549 is a clear follow-up to E471, and should run to confirm theexistence of deeply bound, narrow kaonic states before the KEK PS closes. E548 is aninteresting exploratory experiment, if time is available, although one cannot argue that its
need to run is as pressing as that of E549. Given the high profile nature of pentaquark
physics at this time, KEK should make a supreme effort to explore its production
mechanism and spectroscopy before the KEK PS closes. For both E549 and E559
experiments, their physics importance is very high and also the time is of the essence.
Test Beam Facility:
A test beam facility, no doubt, is indispensable in proving the principle of an innovative
detector, in finalizing a proposed detector component before mass production, and incalibrating completed detectors to confirm their performance characteristics. The KEK
PS has provided such an opportunity since its start in 1976 for the PS experimentalgroups, international collaboration groups and others. It has also contributed to
producing a number of scientific and technical papers for many years. This opportunity
will be lost when the impending shut down of the PS will take place. Although a test
beam facility is planned at J-PARC, commissioning of such a facility is some years away
and also the scope is rather limited.
The committee was informed that a plan exists to build an alternative test beam facility at
KEK by making use of the existing 8 GeV electron linac. The committee strongly
recommends that it be built in a timely manner.
General Consideration and Recommendations:
The KEK 12 GeV PS has played a critical role in advancing Japanese particle and nuclear
physics to international prominence. It provided opportunities to carry out pioneeringexperiments in particle physics, and to develop a unique and well instrumented hadronand hypernuclear physics program. Also the facility was instrumental in educating andtraining a large number of young physicists and students, many of them are now very
active in the international arena. The number of experiments successfully completed, thenumber of physics papers published in refereed journals, and in particular the number ofdoctoral degrees acquired, based on the program at an accelerator facility, are very
important measures for the success of the facility. In this regard, 12 GeV PS has an
outstanding record of completing 119 experiments, publishing 279 physics papers, andletting 135 students attain the doctoral degree. The detailed statistics on these accounts,
supplied to the Committee, are given in Appendix 4.
The J-PARC 50 GeV program is a natural continuation of the program at the KEK PS.
Therefore, the promising experimental programs that were developed using the KEK PS
must be transferred to J-PARC with further refinement. In addition, the new accelerator
facility, with expected performance much higher than the current PS capability, will
attract a new breed of experiments.

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Although the neutrino experimental results from the K2K experiment could be improved
with more statistics, considering that much higher fluxes, attainable at the J-PARC, will
significantly improve the sensitivity and extend its reach into a domain where
revolutionary discoveries are possible and that J-PARC will come on-line in 2008, thecommittee sees little need for a long extension of the program beyond the presently
planned runs. The committee, however, notes that there is a critical need to complete theproposed near term data taking before the impending shut down of the 12 GeV PS inorder to improve the systematic error on the present K2K experiment.
The 12 GeV PS is now at a very advantageous point to apply its power to a highly time
critical investigation such as the investigation of pentaquark states (E559) and theconfirmation of an interesting finding of the deeply bound kaonic nuclear states (E549).
For the pilot experiment like E391a, it is important to establish the feasibility of datataking with low background before the shut down so that further investment and planningfor the J-PARC experiment can be made with confidence. These considerations and anevaluation of the beam time needed to complete these critical experiments lead to therecommendation that the shut down of the 12 GeV PS should be delayed to the end of FY
2005 if not into FY 2006. It is the committee’s judgment that the benefits from thisextension clearly outweigh the pressure it might cause on the available resources.
A timely completion and commissioning of J-PARC with well equipped experimental
halls must be the top priority of the Project Director. Although outside the purview of the
J-PARC project, one hopes that a lot of thought has been given to maintaining thecapability of the physicists who will utilize this outstanding facility once it becomes
operational. One should not lose sight of the fact that it is the ingenuity and creativity ofJapanese physicists which has placed Japan at the forefront of neutrino and strangenessnuclear physics for the past decade. Such talent, if squandered while waiting for J-PARC,
will be next to impossible to restore.
Despite the overwhelming impression that J-PARC will be unmatched in the world, it is
not without significant competitors. Injector proton synchrotrons for hadron colliders at
BNL, CERN, and Fermilab have been upgraded in recent years to ensure a highperformance of the colliders, and are now becoming available for fixed target programs at
10’s to 100’s of GeV. For instance, BNL is working towards RSVP (Rare Symmetry
Violating Processes) program and CERN is organizing a large workshop this fall to study
its future fixed target program. As to the neutrino beam program, all three laboratories
have proposals for a high power proton driver in Mega-Watt range. Considering theworldwide situation, there is another reason to note that a timely completion of J-PARC
is of critical importance.

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Detailed Evaluation of the KEK PS Program
Neutrino Sector
E362: K2K Experiment
Known as K2K, this search for neutrino oscillation using neutrino beams form the KEK
PS and the SuperKamiokande detector has been a flagship experiment of the KEK
program, and has been a pioneering neutrino oscillation experiment with a long baselineof 250 km. Based on accumulated data samples taken in June 1999 to February 2004,
K2K has observed 108 neutrino events contrary to the 150.9 (+11.6-10.0) expected
events, and found the energy distortion characterized by neutrino oscillations. The null
oscillation probabilities are found to be 0.33% in the νµ disappearance and 1.1% in the Eνenergy distortion. Combining both results, K2K has confirmed the neutrino oscillation
discovered in the SuperKamiokande atmospheric neutrino observation with a 99.99 %confidence level. The K2K results provide important information regarding the patternof neutrino masses and mixing. The high priority given by KEK to this experiment waswell justified.
During the upcoming data-taking runs, it is quite important to improve the understandingof systematic errors and to increase the significance of the K2K results. Therefore, thefollowing proposals should be finalized: at least 6 months normal run in 2004; at least 4months more of beam exposure for more data in SciBar; beam alignment runs; and ananti-neutrino operation study. These runs can also provide more measurements of low
energy neutrino interactions with Eν < 1 GeV where the neutrino oscillation parameters
give a strong distortion in the energy spectrum.
In addition to its outstanding physics results, the experience gained will be extremely
valuable for the next generation T2K (Tokai-to-Kamioka) experiment that will use amuch more intense neutrino beam and the well understood and tested SuperKamiokande
detector. That effort will significantly advance neutrino physics and should get underway
as soon as possible.
K-decay Sector
E246: Search for T-Violating Transverse Muon Polarization in K+µ3 Decay using
Stopped Kaons
E470: Branching Ratio Measurement of K+ → π+π0γ Direct Emission
This experiment searched for T-violation in Kµ3 decays via a transverse muonpolarization measurement. Such an effect is extraordinarily small in the Standard Model,
but could be induced in interesting extensions that provide new sources of CP violation.
The experiment improved the bound on such an effect by a factor of 3 which is theworld-record to date. On top of that, it should be noted that E246 has established aprecise measurement for transverse muon polarization in K+ → π0µ+ν. This experimental

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group has also explored a number of other kaon physics topics including direct photon
emission in K+ → π+π0γ.
In most of its measurements, E246 was statistics limited. Additional kaon flux would
have improved the results significantly. The experiment really requires a much more
intense beam. However, in order to access PT ~ 10-4 which is the goal at J-PARC,
obtaining a systematic uncertainty of δPT < 10-4 is essential. Having demonstrated theirability to reduce systematic backgrounds, this experiment is ideal for the high flux thatwill be provided at J-PARC. The possible order of magnitude sensitivity improvement in
the muon transverse polarization attainable at that facility will explore interesting
potential new sources of CP violation beyond the Standard Model.
E391a: Study of KL → π0νν-bar
This experiment was designed to search for KL → π0νν-bar with sensitivity O(10-10), i.e,
about three orders of magnitude beyond existing bounds. Even at that level, it falls short
by about an order of magnitude of Standard Model expectations. For that reason, it has
been viewed as a pilot program to search for new physics and to better understandbackgrounds. The latter point is very important, since measurement of this rare decay
will be extremely difficult; but the payoff for eventually measuring it is very high. It will
provide the cleanest known manifestation of CP violation in the Standard Model andtogether with B physics studies could unveil new sources of CP violation. The expertise
obtained in this endeavor will be very valuable for future pursuits at Brookhaven (theKOPIO experiment) and an envisioned higher statistics study at J-PARC.
Hadron Sector
E325: Study of Chiral Property of Dense Nuclear Matter through Measurements of
Meson Mass Modification in Medium
This experiment addresses the issue of meson mass modification within the nuclear
medium – the partial restoration of QCD chiral symmetry in dense nuclear matter – bybombarding nuclear targets of different atomic mass with 12 GeV protons to produce π, ρ,and ω mesons within the nucleus and then measuring their spectral shape by detecting
electron-positron pairs from the decaying mesons. The data taken in 2000-2002 withhigh statistics strengthen their previous results published in 2001, indicatingthe excess of
e+e− pairs below the ω-meson peak in carbon and copper nuclei. A possible origin of thisexcess is the modification of the ρ-meson inside the nucleus. Detailed analyses of thedispersion relation of the in-medium ρ-meson and of the in-medium properties of the φmeson are under way. The data would be the best experimental evidence of the medium
modification of mesons in nuclei among other attempts in hadron-nucleus and nucleusnucleus collisions. Judgment on the implication of the experiment must await final
analysis of the full data set and the consequent interpretation of the data, which should bemade the experimental team’s top priority.
Nuclear Physics with Strangeness Sector
9E373: Double Strange Nuclei by Emulsion Hybrid Method
E522: Search for H-dibaryon Resonance via 12C(K−, K+ΛΛ and Study of Ξ−NInteractions
This experimental group constructed a hybrid system of Scintillating-fiber bundle tracker
and emulsion, which is highly sensitive, precise and has been productive in finding
double strange nuclei and a possible H-dibaryon candidate. E373 addresses thecharacterization of the hyperon-hyperon interaction by stopping Ξ's in a nuclear emulsion
to form ΛΛ hypernuclei. The existence of such bound systems indicates an attractive
interaction, and the size of the binding energy provides information about the strength of
the interaction. There was no unique interpretation for the first event, the so-called
Demachi-Yanagi event, but the second event, Nagara-event does have a uniqueinterpretation as 6ΛΛHe; the production and decay of a double-Λ hypernucleus (6ΛΛHe)
were confirmed from kinematical analysis. The results give a mass for the nucleus
indicating a weakly attractive Λ-Λ interaction. The reported result has excited theorists
around the world. Despite suggestions by many that such an experiment was not an
optimum means to search for ΛΛ hypernuclei, a truly important result was obtained. In
E522, they have measured the invariant mass spectrum of ΛΛ in 12C(K−, K+ Λ Λ)
reactions and observed an enhancement (2.7 standard deviations) near the threshold,which may be the unstable H-dibaryon. No clear distinction between evidence for an
unstable H dibaryon and an attractive final-state ΛΛ interaction was established. One
awaits the final result from the experiment and its interpretation.
E419: Measurement of B(E2) in 7ΛLi
E509: γ-ray Spectroscopy of Hyperfragments using Stopped K Method
E518: γ-ray Spectroscopy of 11ΛB
Hyper-ball, a large-acceptance germanium detector array, was constructed anddemonstrated that high-precision gamma spectroscopy of hypernuclei is feasible. It
solved the technical problems associated with the severe background in such an
experiment and obtained ~three orders of magnitude improvement in the energy
resolution. In E419 and E518, gamma rays from 7Li(π+, K+γ)7ΛLi and 11B (π+, K+γ)11ΛB
have been measured with dramatic improvement in resolution compared with theconventional methods and the level structure of the 7ΛLi has been determined. Energy
spacing of the ground state doublet of 7ΛLi, which provides a measure of the strength of
the spin-spin interaction between Lambda and a nucleon, has been investigated. Precise
gamma ray measurement enabled Doppler shift analysis for the life-time of the excitedstate, suggesting possible modification of the core nucleus in 7ΛLi. This finding may
validate the theoretically based assertion from the 1960s that the addition of a Λ to ahelium isotope should compress the nuclear core and increase the magnitude of the
Coulomb energy in the hypernucleus relative to that in the associated core nucleus. The
Hyper-ball has proven to be a major technical success. Additional efforts with otherhypernuclei to confirm spin dependence of the Λ-N interaction obtained from 7ΛLi arebeing carried out by the same group.

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In E509, the feasibility of gamma ray spectroscopy also has been demonstrated for the
stopped K− method, which can produce a wide variety of hyperfragments with a higher
rate. Moreover, the stopped K− experiments are very relevant in investigating theimportant question of charge symmetry breaking through the production of mirror
hypernuclei. The strength of the E2 7ΛLi (5/2)+ → (1/2)+ transition γ-ray was determined,
which contains information regarding the hypernuclear production mechanism. A new γray was observed which does not match any known γ-ray from light nuclei.
Unfortunately, the beam time provided has not been sufficient to obtain definitive physics
results, although it seems clear that the method does hold the promise of being a useful
tool as advertised in the proposal. If beam time can be found for this experiment before
the shutdown of the KEK PS, then these measurements are deserving of the additional
shifts originally requested.
The first application of high-precision gamma ray spectroscopy with “Hyper-ball” hasprovided a vivid picture of Λ's in nucleus and has opened a new era of hypernucleus
physics. It is strongly recommended to continue their efforts with the "Hyper-ball-2" andalso at J-PARC.
E438: Study of Σ-Nucleus Potential by the (π−, K+) Reaction
E521: Production of Neutron-Rich Λ-Hypernuclei by the (π−, K+) Double-Charge
Exchange Reaction
Inclusive (π−, K+) spectra with various target nuclei have been measured with very highprecision using the SKS magnetic spectrometer. From distorted-wave impulse
approximation analysis, a strongly repulsive Σ− nucleus potential with a non-zero size ofthe imaginary part has been demonstrated, which is consistent with the potential extracted
from the former study of Σ-atom x-rays. This result will provide a strong constraint onparameterization of models of the Σ-nucleon interaction, whether one works within theframework of the OBE model or constituent quark model. Furthermore, theinterpretation of these data in terms of the Σ-nucleus interaction in normal nuclear mattersuggests that it is unlikely that Σ− would appear within the core of a neutron star. This
exploratory experiment was quite successful. An extension of this physics at J-PARC isencouraged.
From a missing mass analysis of the (π−, K+) reaction, the neutron-rich Λ hypernucleus
10+−ΛLi has been observed in this pilot experiment E521. The Λ production rate for (π , K )++was found to be about 3 orders of magnitude smaller than that for (π , K ). No discrete10
ΛLi peak was observed, probably due to the limited statistics obtained. Additional
investigation is required to understand the reaction mechanisms. This is the first attempt
to produce hypernuclei in the region of exotic nuclei, which opens a new region of
nuclear physics.
E452: Spin-dependent Interaction in Σ+p Scattering

11This experiment addresses the physics of the Σ+-proton interaction, in particular thestrength of the spin-orbit interaction compared with that of the Λ-proton interaction,
which is known to be very weak. The SCITIC (Scintillating Track Image Chamber)detector developed during the course of this experiment, appears to have been very
successful. Analysis of the data is in progress, but preliminary results show a large
left/right asymmetry in the Σ+-P scattering experiment. Complete analysis of the full data
set from E452 is awaited.
E462: Exclusive Measurement of the Non-Mesonic Weak Decay of 5ΛHe
E508: Coincidence Measurement of the Weak Decay of 12ΛC
These experiments address the non-mesonic (Λ+N → N+N) weak decay of Λ hypernuclei,
a baryon-baryon strangeness changing weak interaction processes. There has been along standing puzzle where simple one-pion-exchange (OPE) model calculations
predicted Γn << Γp, where Γx = Γ(Λ + x → n + x), while earlier experiments gave Γn/Γp_1. A definitive experimental measurement was demanded.
The experiment made use of most of the SKS magnetic Spectrometer, i.e. its large
acceptance and fine resolutions for K+ mesons in (π+, K+) reactions. They used 6Li and12
C as the target in order to obtain some information on the A dependence of the process.
By requiring “back-to-back” configuration of produced nucleon pairs together with anappropriate energy cut, they have succeeded in measuring the Γn/Γp ratio to be close to
0.5 with small statistics and systematic errors. The results clearly exclude the naïve OPEmodel. There are two theoretical approaches in predicting the Γn/Γp ratio. One is a moresophisticated meson exchange model where the kaon and other heavier mesons areincluded. The other is based on a direct quark scattering model. Both predict Γn/Γp _ 0.5,agreeing with the data. Further study is needed to distinguish the two approaches. The
proposed J-PARC experiment addresses this problem trying to measure the spin andisospin dependence in high statistics by comparing non-mesonic decays of 4ΛHe and 4ΛH.
Other results with high statistics, such as the lifetimes of 5ΛHe and 12ΛC Hypernuclei andthe branching fraction to the pion (or Γπ/ΓΛ), began to constrain theoretical models.
These results are to be published in 5 letter papers and 1 full paper. The committee ispleased to see the group’s high activity in this field and strongly recommends an earlystart on the proposed experiment at J-PARC.
E471: Search for Strongly bound Kaonic System
It has been proposed theoretically that K− could form a deeply bound state with lightnuclei and even change the structure of the nucleus in a qualitative manner. The aim of
this experiment is to search for such an exotic K-nucleus bound system with (K−, n) and(K−, p) reactions with stopping K− in the 4He target. In the former reaction, an indicationof the deeply bound K−ppn system with a binding energy of 174 ± 4 MeV with the width< 25 MeV is observed. In the latter reaction, surprisingly a proton peak that corresponds12to a missing mass of around 3120 MeV was observed, giving a stronger indication of abound K−pnn system. If the results are verified, they will have a great impact on nuclear
and hadron physics because it would open a new field of the dense multi-hadron/quark
system with the strangeness as a catalyzer. Therefore, it is of great importance to carryout the confirmation experiment, the conditionally approved E549, before closing theKEK 12 GeV PS.
J-PARC Project
J-PARC Accelerator Overview
Generally the construction of the J-PARC accelerator complex is proceeding on schedulewith the linac commissioning with beam in FY 2006. Namely, the civil construction ismaking good progress at the Tokai site with the target completion date in April 2005, intime for the beginning of the Linac and Rapid Cycling Booster Synchrotron installation.
Development and fabrication of technical components for these accelerators also appear
to be in good shape. As to the Main Ring, civil construction is scheduled to be completed
in the summer of 2006 with partial beneficial occupancy available already in FY 2005.
This will allow the installation of the ring components to begin in the fall of 2005. The
Main Ring components are in various states of fabrication and proceeding very well. All
together, there is no apparent technical concern that may impact the schedule ofcommissioning the 50 GeV PS in FY 2008.
The Committee was informed that the beam simulation through the accelerator systemstill takes a long time. Since the sound operations of the accelerator as well as theunderstanding of the beam loss, which can be caused by an accumulation of small errors,
rely heavily on the beam simulation, a way must be found to speed up the beamsimulation program. The beam loss is particularly critical for the high intensity
accelerator at J-PARC because it can activate the accelerator components, making
maintenance more difficult, and can lead to radiation damage if it becomes severe. Good
beam simulation and good instrumentation, as most modern accelerators have practiced,
are also the key to speedy commissioning of the accelerator system.
Facilities for Experiments at the J-PARC 50 GeV Accelerator
The highest priority experiment for particle physics at J-PARC, of course, is the long
baseline neutrino oscillation experiment “T2K”. The committee is pleased to hear thatthe budget for the neutrino beam line was restored, almost enabling an on schedule startof the experiment.
Budgetary constraints will limit initially the scale of the experimental hall. Constructionof only one primary beam line with one target station will be possible even with amaximum recycling of existing beam line components from the KEK 12 GeV facility.
Taking this into an account, the planned strategy for other nuclear and particle physics
experiments, presented for the Day 1 program is well justified. The final decision13

regarding which beam line will be constructed has to be left to the future PAC and will bebased upon final approval of the Day-1 experiment.
Neutrino Experiment at J-PARC
T2K, the subsequent generation neutrino oscillation experiment using J-PARC andSuperKamiokande is the most advanced proposal to date. Although they use the same
technology as conventional beams, several improvements in the neutrino beam line
components and the front detector complex are required. The goal of the T2K proposal,
establishing the framework of 3 flavor-mixing and searching for CP violation in the
lepton sector, offers the physics potential of long baseline neutrino experiments for the
coming ten years. Here the main focus is the sensitivity limit to the small mixing angle
θ13. This proposal is of high priority in J-PARC since the experiment is in competition
with the US NuMi and the French Double-Chooz. The committee notes that if the JPARC construction and the T2K detector construction are performed on schedule thenthe first neutrino beam will arrive at the SuperKamiokande in 2009 as planned in the
proposal.
Kaon Decay and Muon Experiment at J-PARC
The kaon program will be at the forefront of CP violation searches, both within theStandard Model framework and beyond it. The muon program also holds great promise.
Building on the MECO effort at BNL, J-PARC studies of rare muon processes could
extend the search for a muon number violation or study it in detail (if discovered by
MECO). In addition, searches for a muon electric dipole moment (edm) (or deuteronedm), using storage ring technology, could nicely expand the J-PARC program. Having
a world class set of particle physics experiments at J-PARC will also be important for its
applied physics program. The particle physics experiments are very demanding and force
human ingenuity to its limits, developing new technology and ideas. Thoseadvancements should greatly help in any applied muon and neutron beam program at JPARC.
Hadron Physics Experiments at J-PARC
The operation of J-PARC for hadron physics experiments remains several years in the
future. Nonetheless, the hadron physics community responded enthusiastically to theProject Director's call for Letters of Intent in July 2002. Seven LOI’s have been received,
including those from internationally recognized spokespersons from around the world.
The 50 GeV PS is clearly an attractive facility. One anticipates additional exciting
proposals as the time for J-PARC operation approaches.
There are many subjects to be studied in the hadron physics at the J-PARC 50 GeV PS,
ranging from hadron spectroscopy to dense hadronic matter and to the perturbative QCD.
The recent discovery of the pentaquark and the ample data at RHIC on hot QCD matter
let us anticipate new surprises in hadron physics in coming years, and the J-PARC 50

14

GeV PS should prepare for them. An appropriate selection of the experiments for Phase1 will become a non-trivial but highly important issue.
Hypernuclear Physics at J-PARC
It is the ingenuity and creativity of Japanese physicists which has placed Japan
at the forefront of strangeness nuclear physics for the past decade. This important
activity should be and will certainly be continued in the 50 GeV PS right from the Day-1
experiments. New generation spectroscopy of the hypernuclei and the search for a newform of dense matter with strangeness are two of the key directions to be explored in the
new facility.
As is the case with the hadron physics experiments, the operation of hypernuclear physics
experiments at J-PARC is several years in the future, mid JFY 2008. Nonetheless, thestrangeness physics community responded enthusiastically to the Project Director's callfor Letters of Intent in July 2002. Six LOI’s have been received, all of which appear toform a natural extension of the highly successful KEK 12 GeV PS program. One cananticipate new and even more exciting proposals as the time for operating J-PARC
approaches.

15

Appendix 1

KEK-PS External Review 2004
June 7-8, 2004
List of Committee Members and Referees(Titles and affiliations to be added)
The Committee Members
Satoshi Ozaki: chairman

BNLozaki@bnl.gov

Tetsuo Hatsuda:

U. Tokyohatsuda@phys.s.u-tokyo.ac.jp

Ken-ichi Hikasa:

Tohoku U.

hikasa@phys.tohoku.ac.jp

Yasuo Miake:

U. Tsukuba

miake@tac.tsukuba.ac.jp

Atsuto Suzuki:

Tohoku U.

neutrino@mx1.phys.tohoku.ac.jp

Yasushi Watanabe:Tokyo Inst. of Technology
watanabe@hp.phys.titech.ac.jp

Referees
Benjamin Gibson:

LANL

bfgibson@lanl.gov

William Marciano:

BNL

marciano@bnl.gov

Stephen Myers:

CERN

stephen.myers@cern.ch

16

Appendix 2
KEK-PS External Review 2004
June 7-8, 2004
Seminar Hall, Building 4
Monday, June 7
8:30
9:00
9:05
9:40
10:15
10:35
11:10

M. Kobayashi
K. Nakamura
K. Satoh
K. Nishikawa
J. Imazato

11:35
12:00

T. Inagaki
J. Imazato

13:50
14:20
14:50

T. Kobayashi
T. Komatsubara
K. Nakazawa

15:15
15:35

S. Okada

16:00

H. Noumi

16:25

H. Tamura

16:50
17:15
19:00

M. Ieiri

Closed Session
Opening address
Overview of KEK-PS Experiments
Overview of KEKPS Accelerator
Coffee
E362
K2K Experiment
E246
Search for T-Violation in Kµ3 Decay
E470
Branching Ratio Measurement of K+→π+π0γ
E391a Study of KL →π0νν-bar
Facilities for Experiment at the J-PARC 50 GeV Accelerator
Lunch
Neutrino Experiment at J-PARC
Kaon Decay Experiments at J-PARC
E373
Double Strange Nuclei by Emulsion Hybrid
Method
E522
Search for H-dibaryon Resonance via
12C(K−,K+ΛΛ) and Study of Ξ−N interactions
Coffee BreakE462
Exclusive Measurement of the Non-Mesonic Weak
Decay of 5ΛHe
E508
Coincident Measurement of the Weal Decay of
12
ΛC
E438
Study of Σ-Nucleus Potential by the (π−, K+)
Reaction
E521
Production of Neutron-Rich Λ-Hyper-nuclei by the(π−, K+) Double-Charge Exchange Reaction
E419
Measurement of B(E2) in 7ΛLi
E509
γ-ray Spectroscopy of Hyperfragments using
Stopped K Method
E518
γ-ray Spectroscopy of 11ΛB
Test Experiments
Closed Session
Reception

17

Tuesday, June 8
8:30
9:00
9:30
9:55
10:15
10:40

S. Nagamiya
Y. Yamazaki
K. NakaiM. Iwasaki
H. En’yo

11:05 T. Nagae
11:35 H. En’yo
14:00

J-PARC Project Overview
J-PARC Accelerator Overview
E452
Spin-dependent Interaction in Σ+p Scattering
Coffee BreakE471
Search for Deeply Bound Kaonic Nuclear State
E325
Study of Chiral Property of Dense Nuclear Matter
through Measurement of Meson Mass Modificationin Medium
Hypernuclear Physics at J-PARC
Hadron Physics Experiments at J-PARC
Lunch
Closed Session

18

Appendix 3

19

Appendix 4
Statistics on the Number of Experiments, Publications, and Doctorates
In Table 1, the number of experiments are summarized for each category of (High Energy
Physics, Nuclear Physics, and Chemistry), and for each period (first period, second
period, and third period). Hadron physics experiments in the first and second periods areclassified as High Energy Physics, because mostly those people belonging to high-energy
physics community conducted these experiments, while in the third period hadron
physics experiments are classified as Nuclear Physics because mostly those people
belonging to the nuclear physics community conducted these experiments.
In the second set of four tables (Table 2), the number of Doctoral degrees, physics papers,
and technical papers from High Energy Physics, Nuclear Physics, and Chemistry areclassified. Then, each of the categories is further divided into three periods.
In Table 3, the number of Doctoral degrees, physics papers, and technical papers fromeach of the experiments, reviewed by the Committee, are presented.
Table 1
Number of Experiments by Category
High Energy Physics
Total
First period
Second period
Third period

Nuclear Physics

36
25
7
4

72
13
42
16

20

Chemistry

11
3
5
3

Table 2
Doctoral Degrees, Physics and Technical Papers Produced in the KEK PS Program
DoctoralDegrees
Total
High Energy Physics
Nuclear Physics
Chemistry

Physics Papers published inrefereed Journal

135
72
60
3

279
109
149
21

Technical Papers

114
63
48
3

High Energy Physics
DoctoralDegrees
Total
First period
Second period
Third period

Physics Papers published inrefereed Journal

72
43
8
21

109
74
20
15

Technical Papers

63
45
6
12

Nuclear Physics
DoctoralDegrees
Total
First period
Second period
Third period

Physics Papers published inrefereed Journal

60
11
35
14

149
28
97
23

Technical Papers

48
4
35
9

Chemistry
DoctoralDegrees
Total
First period
Second period
Third period

Physics Papers published inrefereed Journal

3
1
1
1

21
3
8
10

21

Technical Papers

3
0
3
0

Table 3
Experiments Reviewed by this Committee
DoctoralDegrees

Physics Papers published inrefereed JournalTechnical Papers

Neutrino Physics
E362

8

4

3

K Decay Experiment
E246/E470
E391a

12
8
1
3
Hadron Physics and Neutron Physics (Except Hypernuclear Physics)
E325
4
2
E443
2
7
Hypernuclear Physics
E373
2
4
E419
1
4
E438
1
1
E452
3
2
E462/E508
1
2
E471
0
1
E518
0
0
E521
0
0
E522
0
0
Kaonic Hydrogen X-Ray Experiment
E546
1
10

22

8
1
2
3
2
0
0
1
0
1
0
0
0
0