J-PARC E15J-PARC E15 実験の今後の展実験の今後の展望望

平岩聡彦京都大学On behalf of the J-PARC E15 collaboration

OutlineOutlineIntroduction

◦experiment & theory of K-ppJ-PARC E15 experiment

◦method◦setup◦background

Possibility of E15 exp. @ 30kWSummary & outlook

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IntroductionIntroduction

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Low-energy KN interactionLow-energy KN interactionK-nucleon interaction

◦Low energy Kp scattering ◦Kaonic hydrogen level shift (KEK-PS

E228)

Kaonic nuclei◦Kaon bound states with a few nucleons◦Extract the information about KN

interaction below KN threshold

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M.Iwasaki et al. , PRL 78, 3067(1997)Attractive (I=0)

How strong?

•DISTO

▫ pp K+X+, X+ p▫ B = 105±2(stat)±5(syst) MeV

= 118±8(stat)±10(syst )MeV

Experimental results on KExperimental results on K--ppppFINUDA

◦ Invariant mass of back-to-back p pairs in K- absorptions

◦ B = 115±6(stat)±4(syst) MeV = 67±14(stat)±3(syst) MeV

2010/12/2-4 ストレンジネス研究会 2010 5M.Agnello et al. , PRL 94, 212303 (2005)

T.Yamazaki et al. , PRL 104, 132502 (2010) 　

Theoretical study on KTheoretical study on K--pppp

KK--pp bound states should exist!pp bound states should exist!◦ A deep state or shallow state?◦ Decay width is sufficiently narrow?

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B.E [MeV] [MeV] Method

Yamazaki and Akaishi 48 61

(mesonic)Variational Method (ATMS)

Shevchenko, Gal, and Mares

55-70 90-110

(mesonic)Coupled ChannelFaddeev Calculation

Ikeda and Sato 60-95 45-80

(mesonic)Coupled ChannelFaddeev Calculation

Nishikawa and Kondo ~126 Skyrme Model

Dote, Hyodo, and Weise

20±3 (s-wave)

40-70 (mesonic)

Chiral SU(3)Variational Method

Arai, Oka, and Yasui depend on gΛ*Λ*σVariational Method(as Λ*p state)

Formation spectra : in-flight Formation spectra : in-flight 33He(KHe(K--,n),n)

2010/12/2-4 ストレンジネス研究会 2010 7T.Koike and T.Harada. , PLB652 (2007) 262

quasi-freebound

K- escape

K- conversion

KK-- + + 33He He “K “K--pp” + n @ Ppp” + n @ PKK=1GeV/c, =1GeV/c, =0º=0º

YA potential Signal can be

clearly seen!

Integrated production cross section amounts to 3.5 mb/sr.

Search for KSearch for K--pp bound states at pp bound states at J-PARCJ-PARC

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E15 experiment via in-flight (K-, n) reaction 　 on 3He. E27 experiment via d(+, K+) reaction.

J-PARC E15 collaborationJ-PARC E15 collaboration

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J-PARC E15 experimentJ-PARC E15 experiment Experimental search for KExperimental search for K--pp bound pp bound

states usingstates usingin-flight (Kin-flight (K--, n) reaction on , n) reaction on 33HeHe

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K-3He Formation K-pp

clusterneutron

p

p

-

Mode to decay charged particlesDecay

Missing

mass

Spectroscop

y

via neutron

Invariant

mass

reconstructio

n

We can observe both the“Formation” and “Decay” of K-pp bound state

1 GeV/c

Experimental SetupExperimental Setup

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J-PARC K1.8BRNeutron counter

Beam sweep magnet

Cylindrical Detector System

Beamline Spectrometer

1.0 GeV/c K-

NeutronTOF length 15mMissing mass resolusion for

K-pp (B.E. 100

MeV ) ~ 9.2 MeV/c2 (Pn~1.3GeV/c,

TOF=150ps)

Invariant mass resolution

for K-pp (B.E. 100 MeV)

~ 13 MeV/c2 (CDC=200m,

B=0.7T)

Identification of Identification of pn final state pn final state by CDS & NCby CDS & NC

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Possible background- 0pn final state + missing- QF- + missing- QF-, conv. + missing

Other processes can be clearly separated!!

Background?? : two nucleon Background?? : two nucleon absorptionabsorption

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2NA + N rescattering / conversion looks like a “signal” ??

(2NA itself is not a problem.)

2NA is very small

12C(K-,n) @ 1GeV/c

12C(K-,p)

T. Kishimoto et al., Prog.Theor.Phys. 118(2007)181.

De Broglie wave length @ 1 GeV/c ~ 1.2 fmNN distance in 3He ~ 2.25 fm

Proc. Jpn. Academy,Series B83 (2007) 144.

These probabilities are expected to be very small ...Anyway, let’s see how they look like!

Signal(DISTO) vs Background(2NA+Signal(DISTO) vs Background(2NA+ conv.)conv.)

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2NA and - conversion

(B.E.=100MeV =100MeV)

Signal(DISTO) vs Signal(DISTO) vs Background(2NA+rescattering)Background(2NA+rescattering)

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2NA and s-wave scattering

2NA and s-wave scattering

Possibility of the E15 Possibility of the E15 experiment with 30kW PS experiment with 30kW PS

operationoperation

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Yield estimation (1week run Yield estimation (1week run @30kW)@30kW)

Yield = NKaon x t x (d/d)=0º x R x r x A x e x ◦ Nkaon : kaons per spill (@30kW) 300k /spill

◦ t : target 0.08 [g/cm3] / 3 [g/mol] x 6.02x1023 [mol-1] x 9.3 [cm] ~ 1.4 x 1023 [cm-2]

◦ (d/d)=0º : differential cross section @ =0º 3 [mb/sr]

◦ R : Kpp decay branch (p) 0.5◦ r : branching ratio ( -p) 0.63◦ A : acceptance (NC + CDS) 5.3 [msr]◦ e : NC efficiency 0.3◦ : overall efficiency (trigger, detector, ana etc...) 0.7

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4.5 x103 signals can be collected in 1 week run with 30kW operation.

PLB 652 (2007) 262.PRC80 (2009) 055208

Missing mass of Missing mass of 33He(KHe(K--, n), n)

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pp // 00pp decay branches stand on same decay branches stand on same mass!mass!

4,500 signals (p) + 4,500 signals (0p) ~ Total 9,000 signals ( [p] : [0p] = 0.5 :

0.5 )

Improvement of statisticsImprovement of statistics

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Statistical improvement can be achieved by “one proton missing”. Missing proton resolution: 28 0.3 MeV/c2 ()Acceptance (NC+CDS)

◦ 3body phase space 0.079% (all detected) 0.12% (one proton missing)

◦ K-pp (B=100MeV, =100MeV) 0.042%(all detected) 0.098% (one proton missing)

pn final state still can be identified!

x2

SummarySummary & outlook & outlookJ-PARC E15 experiment

◦search for a K-pp bound state using in-flight (K- n) reaction on 3He

◦measure the missing mass in (K-, n) reaction and the invariant mass via the decay of K-pp, simultaneously.

E15 experiment @ 30kW operation◦Enough statistics for the first physics data

can be collected within a week if the cross section is ~ 3 mb/sr. (2% of the requested beam time)

We wish to start E15 exp. as soon as possible . (after E17)

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