Manabu Moritsu(Kyoto Univ.)
for the J-PARC E05 (AXiS) Collaboration
2010/12/02 @ KEK-WS “Strangeness2010”

Introduction1.
J-PARC E05 Experiment
Recent discussion on experimental plan

2.
3.
4.

X-hypernuclei

Setup modification for low intensity beam

Summary2



So far, we know L-N interaction well
extracted from structure of L-hypernuclei,including spin component.
 (p,K) reaction with SKS
 g-ray spectroscopy with Hyperballsuccessful theoretical understanding.

Information is very limited.
LL-hypernuclei => weakly attractive L-L interactionex.) NAGARA event : unique ID of species, 6LLHe

X-hypernuclei :

No definite evidence for a bound state.
There were several experiments using (K-,K+) reaction.

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BNL-E885
12C (K-, K+)

DM=14 MeV(FWHM)

 Previous experiment : BNL-E885

P.Khaustov et al., PRC61(2000)054603

 not clear evidence of X-hypernuclear bound state.
 because of limited mass resolution

 suggest weakly attractive potential of -14 MeV depth.
 by shape analysis of QF-tail almost unique information on X-hypernuclei up to now4 Various B-B interaction models exist.

 Their predictions are quite different for X-N int.

Experimental information is strongly awaited.
DWIA spectra with various int. (T=1)

T.Motoba et al., NPA835(2010)223

5 Strangeness in dense nuclear matter Inspect into the core of neutron stars
 Strangeness will take the key role
If X-N is attractive (UX ~-18MeV),
X will appear next to L in neutron stars.

r0F.Waber, PPNP54(2005)193

J.Schaffner-Bielich, NPA804(2008)309

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Spectroscopic study of X-hypernucleus
 using 12C(K-, K+) reaction ; -> 12XBe Missing mass spectroscopy measure momentum of both incident K- and outgoing K+ with high-resolution (~3MeV) and enough statistics
 Only J-PARC can do this experiment. <= 1.4 x 106 K-/spill

Goal observe peaks of X-hypernuclei for the first time.
 Binding energy => potential depth (real part) Width => XN->LL conversion width (imaginary part)7

 K1.8 beam line + SksPlus

 K- : 1.8 GeV/c, Beam Spectrometer (Dp/p ~10-4)
 K+ : 1.3~1.4 GeV/c, SksPlus (Dp/p ~2 x 10-3)
 New D-mag. is added to obtain stronger mag. field.
 prior momentum resolution than acceptance(40msr)
SksPlus
J-PARC Hadron Hall

Dp/p ~ 0.2%(FWHM)

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Setup modification for low intensity beam

Accelerator intensity is very limited.
 now, ~% of design value (270kW)

In original E05 plan, statistics are miserable. => not realistic
 need more acceptanceSksZero2
SksZeromodify SKS configuration
 SksZero → SksZero2


only move normal SKS
downstream detectors
to high-momentum side9

Momentum AcceptanceAngular Acceptancep = 1.3 GeV/c

SksZero2
SksMinus
SksZero2
SksPlus

SksPlus

SksMinusq±1⁰p [GeV/c]
X-hyp.
Acceptance is larger.
 SksZero2 > SksPlus
80 msr
40 msr @1.4GeV/c



100%-coverage angle
 SksZero2 < 5⁰
 SksPlus < 3⁰10

Triggered scattering particle profile @ SDC1YSksPlus

YSksZero2

0 - 5⁰ 10 - 15⁰

0 - 5⁰ 10 - 15⁰

5 - 10⁰ 15 - 20⁰

5 - 10⁰ 15 - 20⁰zz
X

can increase vertical angular acceptance.

X11Momentum Resolution

K- + 12C → K+ + X
Missing Mass
Resolution

in FWHM
Dp [MeV/c]

Dp/p [%]DM [MeV]

SksPlus

2.86

0.20

3.3

SksZero2

3.31

0.24

3.7

SksMinus

3.78

0.27

4.0

DEstrag=2MeV is included.
(5.4g/cm2 12C target)

Dp/p =DM =Resolution is just a little worse, but acceptable level.

SksZero2: 0.24 % ,SksPlus: 0.20 %SksZero2: 3.7 MeV , SksPlus: 3.3 MeV
12

Y(12XBe) = Nbeam x Ntarget x ds/d x ∆ x fdecay x fanalysis= 1.4x106[/spill] x 2.4x104[spill/day] x 5.4 x 6.02x10-7/12[/µb]x 0.06[µb/sr] x 0.04[sr] x 0.5 x 0.7= 7.6 events/day~ 230 events/month13Y(12XBe) = Nbeam x Ntarget x ds/d x ∆ x fdecay x fanalysis= 1.4x106[/spill] x 2.4x104[spill/day] x 5.4 x 6.02x10-7/12[/µb]30/270 x 5/3
x 0.06[µb/sr] x 0.04[sr] x 0.5 x 0.7(in case of Pt T1-target)
0.08= 7.6 events/day
2.8~ 230 events/month84
We can take~80/month statistics at 30kW
as the first step of E05.

Now planning….
14 J-PARC E05 is planed to observe X-hypernuclei via(K-,K+) missing mass spectroscopy.
 It provides essential information to S=-2.
 X-N interaction are extracted from B and G.
 Resolution and statistics are important at theexperimental point of view.
 We are preparing modified experimental plan for
low intensity version. Larger acceptance andacceptable resolution are achieved.
 We want to start exp. at 30kW as the first step.
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