アクティブ標的を用いたΞハイパー核の精密分光 High … · 金築俊輔1,...

アクティブ標的を用いたΞハイパー核の精密分光High-resolution spectroscopy of Ξ-hypernucleus with an active target

越川亜美1, 天野宣昭1, 市川真也1, 市川裕大2, 江川弘行1,2, 加藤静吾5, 金築俊輔1, 後神利志3, 高橋俊行4, 高橋仁4, 竹中耕平1, 永江知文1,七村拓野1, 広瀬恵理奈4, 森津学6, and the J-PARC E05 collaboration

1 京大理 2 JAEA 3 阪大RCNP 4 KEK 5 山形大理 6 阪大理

ELPH研究会C015, Sendai, 02.Dec.2016

Motivation of spectroscopy of hypernuclei

• NN interaction Baryon-baryon interaction in SUf(3)

• Role of strangeness in high density hadronic matter

• Our knowledge of hypernuclei:- S=−1 Λ, Σ

‣ (K−,π−) (π+,K+) (e,e’K+)‣ γ-ray spectroscopy→ΛN, ΣN eff. interaction

- S=−2 Ξ, ΛΛ‣ limited experimental

information

generalization

S=0

−1

−2

N

Z

-∞ inner core of neutron stars??

Stra

ngen

ess

2

especially @short range

Previous Studies with Emulsions• “NAGARA” event

- uniquely identified as a production and decay of 6ΛΛHe

- ΔBΛΛ = 0.67±0.17 MeV

• “KISO” event- Ξ−+14N → 10ΛBe+5ΛHe- BΞ = (1.11 or 4.38) ±0.25 MeV

3

H. Takahashi et al., PRL 87 (2001) 212502

weakly attractive

PTEP 2015, 033D02 K. Nakazawa et al.

Fig. 1. A superimposed image from photographs and a schematic drawing of the KISO event.

Fig. 2. Close-up images around each vertex; see Fig. 1 for locations of points and tracks. (a) Points A and B.From point A, an Auger electron can be seen below track #2. (b) Point C. (c) point D.

Table 1. Range and angle data of related tracks. The ranges and angles for tracks #1 and #2 are discussed inthe text. The total range was measured to be 77.1 ± 0.3 µm from point B to C.

Track Range (µm) theta (deg.) phi (deg.) Comments

#1 8.0 ± 0.3 133.0 ± 3.0 13.2 ± 3.2 Single-hypernucleus#2 69.1 ± 0.5 40.4 ± 0.9 193.1 ± 1.2 77.1 ± 0.3 µm from B to C#3 13.3 ± 0.4 102.3 ± 2.3 340.4 ± 1.6#4 >4990.7 145.0 ± 0.9 85.4 ± 1.3 Out of the emulsion stack#5 6.7 ± 0.3 49.6 ± 4.2 132.6 ± 4.3 α from 8Be#6 5.8 ± 0.3 131.0 ± 4.5 318.9 ± 4.7 α from 8Be#7 2492.0 ± 3.9 43.1 ± 1.3 191.8 ± 1.5#8 37.3 ± 0.7 131.9 ± 1.3 29.2 ± 1.3

consistent with the decay of the hyperfragment at points B and C, respectively. This event topologyis consistent with an event of at-rest capture of a "− hyperon by a 12C, 14N, or 16O nucleus in theemulsion, followed by production of twin single-hypernuclei. In the case of "− hyperon capture bythese nuclei, the total A and Z numbers of the hyperfragments do not exceed 17 and 7, respectively.

3/11

at Kyoto U

niversity on April 28, 2016

http://ptep.oxfordjournals.org/D

ownloaded from

VOLUME 87, NUMBER 21 P H Y S I C A L R E V I E W L E T T E R S 19 NOVEMBER 2001

n, and L baryons [10]. Double-L hypernuclei are closelyrelated to the existence of the H dibaryon [11]. If themass of the H dibaryon, MH , was less than twice the Lhyperon mass in a nucleus, two L hyperons in the nucleuswould be expected to form the H. With this assumption,the lower limit of the mass of the H dibaryon can becalculated from the following relation:

MH . 2ML 2 BLL , (2)

where ML is the mass of a L hyperon in free space.In order to study such systems, an emulsion/

scintillating-fiber hybrid experiment (E373) has beencarried out at the KEK proton synchrotron using the1.66 GeV!c separated K2 meson beam [12,13]. Theschematic view around the target is given in Fig. 1. J2

hyperons were produced via the quasifree "K2, K1# reac-tions in a diamond target [14] and brought to rest in FujiET-7C emulsion. The "K2, K1# reactions were taggedby a spectrometer system. The positions and angles ofentry of the J2 hyperons at the emulsion were measuredwith a scintillating microfiber-bundle detector [15] placedbetween the diamond target and the emulsion stack. Thetracks of the J2 hyperons were scanned and traced in theemulsion by a newly developed automatic track scanningsystem [16]. An emulsion stack consisted of a thin emul-sion plate located upstream followed by eleven thickemulsion plates [17]. The thin plate had 70-mm-thickemulsion gel on both sides of a 200-mm-thick acrylic basefilm, and each thick plate had 500-mm-thick emulsion gelon both sides of a 50-mm-thick acrylic film.

Although we have analyzed only 11% of the total emul-sion, we have found an event of seminal importance, amesonically decaying double hypernucleus emitted froma J2 capture at rest [18]. A photograph and schematicdrawing of the event are shown in Fig. 2. We named thisevent “NAGARA.” A J2 hyperon came to rest at point

FIG. 1. Schematic view of the experimental setup.

A, from which three charged particles (tracks No. 1, No. 3,and No. 4) were emitted. One of them decayed into a p2

meson (track No. 6) and two other charged particles (tracksNo. 2 and No. 5) at point B. The particle of track No. 2decayed again to two charged particles (tracks No. 7 andNo. 8) at point C.

The measured lengths and emission angles of thesetracks are summarized in Table I. The particle of trackNo. 7 left the emulsion stack and entered the downstreamscintillating-fiber block detector (D-Block) [19]. TrackNo. 5 ended in a 50-mm-thick acrylic base film. The tracksof the three charged particles emitted from point A arecoplanar within the error as are the three tracks from pointB. The kinetic energy of each charged particle was calcu-lated from its range, where the range-energy relation wascalibrated using a decays of thorium series in the emul-sion and m1 decays from p1 meson decays at rest.

The single hypernucleus (track No. 2) was identifiedfrom event reconstruction of its decay at point C. Mesonicdecay modes of single hypernuclei were rejected becausetheir Q values are too small. The decay mode of thesingle hypernucleus is nonmesonic with neutron emission.If either track No. 7 or No. 8 has more than unit charge,the total kinetic energy of the two charged particles ismuch larger than the Q value of any possible decay modebecause of the long ranges of tracks No. 7 and No. 8.Therefore, both tracks No. 7 and No. 8 are singly charged,and only LHe isotopes are acceptable.

The kinematics of all possible decay modes of the dou-ble hypernucleus (track No. 1) which decays into LHe(track No. 2) and p2 (track No. 6) were checked, andBLL and DBLL were calculated. Since track No. 5 endedin the base film, only the lower limit of the kinetic energy

FIG. 2. Photograph and schematic drawing of NAGARAevent. See text for detailed explanation.

212502-2 212502-2

K. Nakazawa et al., PTEP (2015) 033D02

10ΛBe 5ΛHe

1.03±0.18 or 3.87±0.21

Previous Spectroscopic Study• BNL-AGS E885

Missing-mass spectroscopy via the 12C(K−,K+) reaction @1.8 GeV/c- dσ/dΩ (−20 MeV < E < 0 MeV)

‣ θK+<14°: 67 events, 42±5 nb/sr‣ θK+< 8°: 42 events, 89±14 nb/sr‣ Indication of existence of

Ξ bound state- Mass resolution: 14 MeV (FWHM)

‣ no clear peak‣ shape analysis VΞ = −14 MeV ?

4

be found in the recent references !2,9" in which the(K!,K") cross sections for the 12C and 16O targets havebeen estimated for pK!#1.6 GeV/c .The calculation was performed for 0°$#K"$16° and a

series of Woods-Saxon $! well depth parameter values:V0$#12, 14, 16, 18, and 20 MeV. The radius and skin depthof the $ potential were fixed at R#1.1A1/3 fm and a$#0.65 fm. The proton wave function in the 12C target wasgenerated using a Woods-Saxon potential with V0N#50 MeV, R#1.1A1/3 fm, and aN#0.65 fm. The elemen-tary $! production cross section was set to 35 %b/sr to becompatible with the normalization of our experimental data.The kinematic factor & , which accounts for the transforma-tion between the two-body and A-body frames, was set to0.73.As a typical example of the angular dependence of the

differential cross section, the dashed line in Fig. 3 shows thecase of the ground state for V0$#14 MeV. In order to makea comparison between the theory and the data, we calculatethe angle-averaged differential cross sections,'(d2(/d)dE)(E)* and fold the results with the experimen-tal resolution. However, we first present theoretical12C(K!,K")$

12Be spectra which have not been folded by theexperimental energy resolution but have been angle-averaged over 0°$#K"$14°. As shown in Fig. 5, the resultfor V0$#20 MeV +dashed line, has two bound-state peaks,corresponding to the $!s- and p-orbitals. The widths ofthese peaks are determined using a one-boson-exchangemodel to estimate the rate for the $N→-- conversion. Forthe case of V0$#14 MeV, the p state is not bound but it iscalculated as a resonance state in the continuum; therefore asudden rise is seen just above the threshold in Fig. 5.Figure 6 shows experimental excitation energy histograms

for 12C(K!,K")X for two different limits on the scatteringangle of the outgoing K", #K"$14°, and #K"$8°. The dataclearly show an enhancement around zero excitation energywhen compared to a Monte Carlo simulation based on qua-sifree $ production which has been normalized to the totalnumber of 12C(K!,K")X events +curve QF,.

In the same figure, the $12Be production theoretical curves

for several $ potential well depths, folded with the 6.1 MeVrms experimental resolution, are shown for comparison withthe data. The expected location of the ground state of --

12 Be+assuming a total binding energy of the -’s, B-- , of 25MeV, and the thresholds for -

11 Be"- and 11B"$! pro-duction are indicated. The normalization calculation for thecase #K"$8° is less sensitive to the model of angular de-pendence because the spectrometer acceptance is fairly flatover this region but drops rapidly for #K"%8° as shown inFig. 3; we present the results for both the entire acceptanceand for #K"$8° in Fig. 6.Visual inspection shows that the theoretical curve for the

value of the $-nucleus potential well depth V0$#14 MeVagrees with the data reasonably well in the region of excita-tion energy !20 MeV$E$0 MeV and much better thanthe curve for V0$#20 MeV. If any of the observed signalresults from direct two-- production without an intermediate$12Be state, the discrepancy between the V0$#20 MeV re-sults and the remaining experimental signal becomes even

FIG. 5. Results of DWIA calculations, before folding by theexperimental energy resolution, for the 12C(K!,K")$

12Be reactionfor V0$#14 MeV and 20 MeV. The cross section has been aver-aged over the kaon angular range 0$#K"$14°.

FIG. 6. Excitation-energy spectra from E885 for 12C(K!,K")Xfor #K"$14° +top figure, and #K"$8° +bottom figure, along with$12Be production theoretical curves for V0$ equal to 20, 18, 16, 14,and 12 MeV. The results of a quasifree $ production calculationare also shown +curve QF,. The expected location of the groundstate of --

12 Be and the thresholds for -11 Be"- and 11B"$! pro-

duction are indicated with arrows.

EVIDENCE OF $ HYPERNUCLEAR PRODUCTION IN . . . PHYSICAL REVIEW C 61 054603

054603-5

Bound region

P. Khaustov et al., PRC 61 (2000) 054603

a better resolution @J-PARC

J-PARC E05 Experiment• Spectroscopic study of Ξ−-hypernucleus

via the 12C(K−,K+)12ΞBe reaction (T. Nagae et al.)- missing-mass spectroscopy- observe Ξ-hypernucleus bound state(s)

as a peak structure‣ better mass resolution; ΔM < 2 MeV→deduce the information of ΞN interaction

• Pilot run in Nov. 2015 w/ SKS spectrometer- mass resolution: 6 MeV (FWHM)- beam intensity:

6x105 K−/spill (5.52 sec, Acc. 39 kW)

5

Target

Inc. K−1.8 GeV/c

Scat. K+

~1.4 GeV/cD1

Q1Q2SDC3,4

TOF

J-PARC E05 Experiment• Spectrometers

- Inc. K−: Beam Spectrometer‣ Δp/p < 1.0x10-3 (FWHM)

- Scat. K+: S-2S Spectrometer‣ Δp/p = 6.0x10-4 (FWHM)‣ Magnet construction has been completed.‣ will be installed in FY2018

• Beam intensity: 1.2x106 K−/spill (4 sec, Acc. 80 kW) in 2018?

6

Target

Inc. K-1.8 GeV/c

Scat. K+

~1.4 GeV/cD1

Q1Q2

TOF

WC,AC

SDC3,4

Expected Spectra• Black line: DWIA calculation for ESC08a interaction

Nuclear core excitations are fully taken into account.

• Colored lines: the calculation folded with the experimental resolution

• A high missing-mass resolution (< 2 MeV) is essential to resolve discrete hypernuclear states

7

1-1

1-21-3

2+

12C(K-,K+)12ΞBe, pK = 1.7 GeV/c (θlab = 0°)

T=1

-Binding Energy [MeV]

T. Motoba and S. Sugimoto, NPA 835 (2010) 223

Future Extension• A variety of targets

- light targets: 7Li→7ΞH (αnnΞ), 10B→10ΞLi (ααnΞ)‣ αΞ− interaction→spin and isospin independent term of ΞN potential

‣ + information derived from the 12C(K−,K+)12ΞBe →dependence

- heavy targets: 89Y→89ΞRb‣ A-dependence of the single-particle potential of Ξ−

‣ Coulomb-assisted states

8

S-2S Spectrometer• Composed of

- three magnets QQD - four drift chambers: σx=250 µm

Δp/p = 6.0x10-4 (FWHM)

• K+ trigger = TOF∧AC∧WC

9

Review

22

KEK-PS E549 experiment to look for K−pnn/K−ppn sys-tems. In these high-statistic inclusive spectra, no narrow structures ⩽40 MeV/c2 were observed. In the case of K−pnn, the upper limits of the formation branching ratio with an assumed width of 0, 20, 40 MeV/c2 were determined to be (0.4– ) × −6 10 4, (0.2– ) × −6 10 3 and (0.06– ) × −5 10 2/(stopped K−), respectively, with 95% confidence level, in the mass range 3000 < M < 3200 MeV/c2. In the case of K−ppn, the upper limits at 95% confidence level with the width of 0 and 20 MeV/c2 were at most 1%.

The OBELIX Group analyzed their data of p4He annihilations at rest [244, 245]. In the invariant mass of the π −−p p coming from Λp, a narrow peak with a width <( ±33.9 6.2) MeV was observed with the binding energy of (− ± ±151.0 3.2 1.2stat syst) MeV for K−pp (or K

2H) with a statistical significance of 4.7 σ. There were some dif-ficulties in clearly identifying the Λ and the peak width meas-urement was limited due to the detector resolution.

In the DISTO experiment at the SATURNE accelerator at Saclay, the exclusive reactions of → Λ +pp p K at 2.85 GeV and 2.50 GeV were investigated to search for the K−pp [246, 247]. Both missing-mass and invariant-mass distributions were obtained. A broad enhancement was found at 2.85 GeV by selecting the emission angles of K+ and p, while a very small cross section was observed at 2.50 GeV. From the observation, a binding energy of ( ± ±103 3 5stat syst) MeV and a width of ( ± ±118 8 10stat syst) MeV were obtained.

In-flight (K−, n/p) reactions at the K− incident momentum of 1 GeV/c were used to produce kaonic nuclei in KEK-PS E548 experiment [248]. The inclusive spectra of the 12C(K−,n) and 12C(K−, p) reactions were measured. While they observed a significant number of events in the K− bound region, they were not able to observe any clear peak structures correspond-ing to bound states. From the spectrum shape analysis, they estimated the K− potential depths of −190 MeV and −160

MeV for 12C(K−,n) and 12C(K−,p), respectively, which sug-gests that the K nucleus potential is deep.

At LEPS/SPring-8 facility, the K−pp bound state was searched for in the γ π→ + −d K X reaction at =γE 1.5–2.4 GeV [249]. The inclusive π+ −K photo-production of deuterium was measured for the first time in this energy range. There was no peak in the mass region of 2.22–2.36 GeV/c2.

During the phase of the final editing of this review article, the J-PARC E27 experiment has reported the observation of a ‘K−pp’-like structure in the π( )+ +d K, reaction [250]. The experiment was carried out at the K1.8 beam line in the had-ron experimental hall of J-PARC by using the π+ beam at 1.69 GeV/c. In this reaction, Λ(1405) would be produced as a door-way to the K−pp formation [251]. However, large backgrounds due to hyperon and hyperon resonance production processes affect the inclusive π( )+ +K, missing-mass measurement. In order to suppress such backgrounds, two-proton coincidence was requested in a range counter array system surrounding the deuterium target. A broad bump structure in the K−pp mass distribution around 2.27 GeV/c2 was observed in the Σ p0 decay mode, which corresponds to a K−pp binding energy of ( )−

+−+95 17

18stat 21

30syst MeV and to a width of ( )−

+−+162 45

87stat 78

66syst

MeV.

9. Future perspectives

9.1. Strangeness nuclear physics at J-PARC

At the J-PARC hadron experimental hall, two experiments are currently scheduled to run in 2015. One experiment is E15 to search for the K−pp bound state in the 3He(K−, n) reaction at 1 GeV/c. In this experiment, the K−pp signals will be obtained not only in the missing-mass of the (K−, n) spectrum but also in the invariant mass of the Λ-p pairs from the non-mesonic decay of the K−pp. A large neutron detector system in the for-ward direction and a cylindrical detector system surrounding the liquid 3He target are installed in the K1.8BR area. The other experiment is E13 to measure hypernuclear γ-rays with the Hyperball-J detector system [16]. The γ-ray transitions of

Λ4 He( →+ +1 0 ) and several new ones in Λ

19F will be measured. The NΛ spin–spin interaction will be studied in an sd-shell hypernucleus for the first time.

A new hybrid-emulsion experiment, E07, ‘Systematic study of double strangeness system with an emulsion-counter hybrid method’ is in preparation at the K1.8 beam line. They aim to stop about ten times more Ξ−s (∼103 Ξ−s) in emulsion compared with the previous E373 experiment. The KURAMA spectrometer system will be used for the forward K+ detection. In order to speed up the emulsion analysis, a high-speed auto-matic scanning system has been developed. By replacing the emulsion system with the Ge detector system, Hyperball-J, an experiment, E03, to measure the x-rays from the Ξ−-atom, can be carried out at the same beam line.

As for the Ξ-hypernuclei, the E05 experiment ‘Spectroscopic study of Ξ-hypernucleus, Ξ

12Be, via the 12C(K−, K+) reaction’ is constructing a new high-resolution spectrometer S-2S (see

Figure 10. Schematic view of the S-2S spectrometer for the (K−, K+) reaction. It consists of three magnets QQD (two quadrupole magnets and one dipole magnet).

Rep. Prog. Phys. 78 (2015) 096301

Aerogel:n=1.06 π+ veto

Water:n=1.33 p veto

WC

ACTOF

DC3, 4

D1

Q2Q1

Acceptance [mSr] Target Yields ΔM [MeV]

(FWHM)BNL-E885 50 C 16 g/cm2 42 14

E05 w/ SKS 110 C 9.3 g/cm2 39 (10 days) 6E05 w/ S-2SActive target 60 CH 10 g/cm2 120 (20 days) <2



Δp/p = 6.0x10-4 (FWHM)


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+−+95 17

18stat 21


+−+162 45

87stat 78

66syst

MeV.










Rep. Prog. Phys. 78 (2015) 096301


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ACTOF

DC3, 4

Q2Q1

Figure 6: DWIA spectra with NHC-D and Ehime. Figure 7: DWIA spectra with ESC04d and ESC08a.

4. DWIA (K−, K+) reaction spectra predicted by typical Ξ-N interactions

The (K−,K+) reaction cross sections for the T = 1 Ξ-hypernuclear states of 12Ξ Be have been

calculated in DWIA. The Ehime result (dotted line in Fig. 6) shows an ‘easy-to-understand’ spec-trum in the sense of formal similarity to the (π+,K+) reaction: three 1− states and a substantial2+ state are excited. In the NHC-D case (solid line), the strongly excited 2+ state comes downsharply in direct consequence of the strong p-state attraction nature of NHC-D. It is notable inNHC-D that the J = 1−1 (T=1) state is excited strongly. The two cases in Fig. 6 suggest a pos-sibility of observing a Ξ-hypernuclear peak in the bound state region, if the Ξ-state width is notlarge (e.g. less than about 5 MeV FWHM).

Figure 7 shows the ESC04d case (solid line) together with the ESC08a case. As the ESC04dspin-spin interaction is very strong (even stronger than the N-N case), the spin structure of theΞ-hypernuclear wave functions is mixed up, so that (K−,K+) cross sections are scattered overseveral high-lying J = 1− states. The 1−1 state gets only a small cross section. The reductionof the spin-spin strength by a factor of 0.3 leads to two pronounced 1− states at lower energypositions [20]. The most recent Ξ-N interaction, ESC08, gives the similar spectra as of themodified ESC04d. One may refer to Ref. [24] for an idea of using spin-isospin saturated nuclearcores (α’s) so as to be ‘free’ from the uncertainty of the sΞ · sN strength.

In conclusion, we have tested three available Ξ-N interactions in the structure calculationsand compared the DWIA outcome for the (K−,K+) reaction spectra. Being different from theprevious ‘frozen core’ treatment, the nuclear core excitations are fully taken into account. As wedo not have any experimental firm basis for the existing Ξ-N model interactions, we await the(K−,K+) experiment to be done at J-PARC. It will not only discriminate between the existing Ξ-N potentials, but also provide us with good opportunities of understanding hypernuclear systemswith S = −2.

The authors are grateful to Y. Yamamoto and Th.A. Rijken for providing the YNG-type Ξ-Ninteractions and to E. Hiyama for discussion.

References

[1] H. Bando, T. Motoba, and J. Zofka, Int. J. Mod. Phys. A 21, 4021 (1990).

T. Motoba, S. Sugimoto / Nuclear Physics A 835 (2010) 223–230 229


(FWHM)BNL-E885 50 C 16 g/cm2 42 14


WC

D1

Expected spectrumESC08

ESC08

T.Motoba and S.Sugimoto, NPA 835 (2010) 223-230

In the simulation, the conversion width was not taken into account.

In the case of BNL E885

ESC08

J-PARC E05Expected spectrumESC08

ESC08


In the simulation, the conversion width was not taken into account.

In the case of BNL E885

ESC08

J-PARC E05

(w/o natural width)NPA 835 (2010) 223



Δp/p = 6.0x10-4 (FWHM)


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+−+95 17

18stat 21


+−+162 45

87stat 78

66syst

MeV.










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Q2Q1








References




ESC08


In the simulation, the natural width was not taken into account.

J-PARC E05


(FWHM)BNL-E885 50 C 16 g/cm2 42 14





Δp/p = 6.0x10-4 (FWHM)


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+−+95 17

18stat 21


+−+162 45

87stat 78

66syst

MeV.










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Q2Q1








References




ESC08



J-PARC E05


ESC08



J-PARC E05


(FWHM)BNL-E885 50 C 16 g/cm2 42 14



Current Status• Electromagnets

- Q1, Q2: ready- D1: field measurement

• Existing detectors- DC1, DC3, DC4- AC: ready

• New detectors- TOF- DC2- Water Čerenkov

T. Gogami et al., NIM A 817 (2016) 7013

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+−+95 17

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66syst

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WC

ACTOF

DC3, 4

D1

Q2Q1

- + Active target

D1 magnet• Measurement with an NMR✓ long-term stability: ΔB/B = 1.6x10-6✓ hysteresis effect: <1.8 mT

• Field distribution measurement with a Hall probe- measurement and analysis in progress at KEK- to check consistency

between a measured and a calculated field maps

- accuracy 0.1%

14

used for momentum analysis

Active Target• Missing-mass resolution

• 12ΞBe production (120 counts, 1.2x106 K−/spill (4 sec))

- how to realize a good mass resolution with enough statistics?→direct measurement (ΔE < 1 MeV) of the energy-loss fluctuation event-by-event

15

Target ΔM [MeV] (FWHM) Irradiation time

C 3 g/cm2 2 65 daysC 10 g/cm2 >4 20 days

Active target10 g/cm2 <2 20 days

�M2 =

✓@M

@pK��pK�

◆2

+

✓@M

@pK+

�pK+

◆2

+

✓@M

@✓�✓

◆2

+�E2tgt

1.67 0.62 0.04[MeV2] ?

Active Target• Scintillating fiber:

scintillation light output → correction of the energy of kaons event-by-event

• Energy losses of - incident K-s

- scattered K+s- decay charged-particlesshould be separately measured event-by-event.→The target must be divided into segments.

16

K- K+

12ΞBe

π0n Λ Λ

pπ-

E0K+ = ES-2S

K+ +�EATK+

E0K+ = ES-2S

K+ +�EATK+

ΔEAT

# of γ

E0K+ = ES-2S

K+ +�EATK+ΔEK-

AT

Active Target• Scintillating fiber bundle

- 3x3 mm square or 3 mmφ round cross-section (~1000 fibers) - MPPCs attached on the both ends of each fiber- requirement: ΔEAT < 1 MeV

• Performance test (single fiber)- @RCNP Grand Raiden

with p@392 MeV‣ study of the correlation

between the energy loss & light output

- source test‣ to be performed

17

Summary• J-PARC E05 Experiment

- spectroscopic study of Ξ-hypernucleus via the 12C(K-,K+)12ΞBe- aims to observe a clear peak of the 12ΞBe bound state- will provide us information of the ΞN interaction

(binding energy, Ξ-p→ΛΛ conversion strength)

• Further studies with high intensity K- beams- light targets: spin and isospin dependence- heavy targets: UΞ in nuclear matter

• New experimental devices- S-2S D1 magnet: field measurement- Active target: performance test of scintillating fibers

18

Backup

20

A dependanceTable 2: Energies, widths and mean radii, r =

√< r2 >, predicted by NHC-D, Ehime

and ESC04d∗. The Ξ−-nucleus potentials are obtained by folding the ΞN G-matrixinteractions. The results for the Woods-Saxon potential with V 0

Ξ = −14 MeV are alsolisted.

NHC-D Ehime ESC04d∗ W.S.Target E Γ r E Γ r E Γ r E

[MeV] [MeV] [fm] [MeV] [MeV] [fm] [MeV] [MeV] [fm] [MeV]12C [12Ξ Be]

s −4.4 0.5 3.2 −4.5 0.3 3.1 −4.6 4.6 3.3w/o Coulomb −1.9 0.5 3.7 −1.9 0.2 3.7 −2.1 3.9 3.7 −2.227Al [27Ξ Na]

s −14.9 0.7 2.0 −13.4 0.2 2.3 −10.1 5.7 3.0w/o Coulomb −8.4 0.7 2.2 −7.3 0.2 2.6 −4.7 4.7 3.4 −5.1

p −7.1 0.4 3.4 −5.9 0.2 3.6 −5.2 2.8 4.1w/o Coulomb −2.0 0.3 4.0 −1.1 0.1 4.5 −0.8 1.9 5.140Ca [40Ξ Ar]

s −19.7 0.6 2.2 −18.7 0.2 2.4 −14.1 5.9 3.0w/o Coulomb −10.8 0.6 2.4 −9.9 0.2 2.6 −6.2 4.9 3.4 −6.5

p −13.7 0.5 3.0 −11.5 0.2 3.3 −9.3 3.3 3.9w/o Coulomb −5.7 0.4 3.3 −3.9 0.2 3.7 −2.4 2.5 4.5 −1.289Y [89Ξ Rb]

s −31.4 0.6 2.3 −29.8 0.2 2.5 −22.4 6.5 3.0w/o Coulomb −16.4 0.6 2.5 −15.0 0.2 2.8 −8.5 5.2 3.7 −9.0

p −26.2 0.5 3.0 −23.6 0.2 3.3 −17.8 3.9 4.0w/o Coulomb −12.0 0.4 3.2 −9.8 0.2 3.6 −5.3 2.8 4.6 −4.6

d −20.6 0.4 3.5 −17.3 0.2 3.9 −13.3 2.4 4.7w/o Coulomb −7.3 0.3 3.9 −4.6 0.1 4.4 −2.0 1.7 5.5 −0.2

f −14.8 0.3 4.1 −11.0 0.1 4.6 −8.7 1.6 5.4

potentials; three Ξ-nucleus potentials obtained from the ΞN G-matrix interaction and asimple Woods-Saxon type potential with the depth of −14 MeV. It should be noted thatNHC-D and Ehime models predict deep UΞ and strong mass-number (A) dependencefor Ξ energies. This is owing to the strong odd-state attractions which come from thelack of space-exchange terms in one-boson-exchange potential picture. On the otherhand, ESC04d∗ model predicts the energies very close to those with the Woods-Saxonpotential, when the Coulomb interactions are switched off. Therefore, the experimentaldata on not only the Ξ-binding energies but also the their A-dependence have valuableinformation to probe the ΞN interaction. It should be also noted that the conversionwidths for ESC04d∗ and NHC-D/Ehime are very different from each other.

For s- and light p-shell systems, NHC-D and Ehime give rise to almost no Ξ boundstate because of their weak even-state attractions, when the Coulomb interactions are

9

21

Long-term stability

σ= 1.6μTΔB/B = 1.6x10-6

22

Excitation curve

By~1.5 T @2500 A1.8

Excitation curve Hysteresis effect[mT]

11

23

Performance Estimation

Momentum resolution Solid angle

pK [GeV/c]

p(K−

,K+ )Ξ

−

hype

rnuc

lear

prod

uctio

n

24

Angular acceptance

applox. 55 msr

25

Angular acceptance

4°

18°8°

pK=1.35 GeV/cT2-Q1= 55 cm

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Kinematics

Scattered K+ momentumRecoil momentum

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Expected Spectra

-B [MeV]-10 -8 -6 -4 -2 0 2 4 6 8

[Cou

nts /

0.5

MeV

]

0

5

10

15

20

25

-B [MeV]-10 -8 -6 -4 -2 0 2 4 6 8

[Cou

nts /

0.5

MeV

]

0

10

20

30

40

50

60

70

20 days 60 days








References



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