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Systematic Study of Double Strangeness System by an Emulsion-Counter Hybrid Method

Experimental motivation. 0 . Previous experiment E373 (KEK-PS) [97% scanned]. Ⅰ. Making a S=-2 nuclear chart.Ⅱ. Study of H-resonance or dibaryon state.Ⅲ. First measurement of X-ray from -atom

Outline of E964R and Development since 2001Ⅰ. Double-sided Si Strip Detector (DSSD).Ⅱ. Nuclear Emulsion.Ⅲ. Hyperball2

Summary Conditions

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Phys. Dept., Gifu Univ.K.Nakazawa

Current status of AGS-E964

Dept. of Phys., Tohoku Univ.H.Tamura

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＊two body case at point AΞ - +

12C → 10Be + t or 10Be* + tΛΛ ΛΛ

Δ BΛΛ ： -1.14± 0.19 or +1.86± 0.19MeVBΛΛ ：12.29± 0.17(excited) MeV 15.29± 0.17(ground) MeV

＊three body case at point A1) Ξ - + 14N → 13B + p + n

Δ BΛΛ ： +1.47 MeV+2.4- 0.7

Λ Λ

::

protonA

CΞ

B

Demachi-yanagi event

2001

Double- hypernuclei from E373(KEK-PS)

“ the most significant result of the past 5 years in hypernuclear physics. ”

Final Report of the 2004 KEK PS External Review Committee (August 30, 2004),p5.

5

6ΛΛHe

4He

t

Ξ -

p

π -

ΛHe

10μm500

10

5

2001

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Comparison with past results

inte

ract

ion

en

ergy

12

or or

or

or

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interaction is weakly attractive.Our knowledge for int. until now.

E373

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B & nuclear medium effect

To know int. independent on the nuclear medium effect, we need to measure A-dependence of B.

B:

b

ind

ing

en

erg

y in

nu

cleu

s

S=-2 nuclear system

‘H’

B depends on A

B may NOT depend on A

Theoretical prediction

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Candidate events of double-hypernucleus

from E373

preliminary

20023rd double- hypernucleus

Nuclear species of the double- can be , or .

He He

Be

2003

2004

2003

Analysis in progress

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Nuclear Chart with Strangeness

　

Experimental motivation Ⅰ

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Strange matter Our goal is making a S=-2 nuclear chart, by observing so many nuclei with S=-2 as possible.

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H-dibaryon resonance (?) near the threshold

KEK-PS E522

Experimental motivation Ⅱ

What is the ground state of S=-2 nucleus?

Recent result

2. A-dependence of B3. Decay branching ratio [S=-2] => p, n

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M()thres.

1. Confirm this enhancement by several times higher statistics.

or H-dibarion state in nucleus?|H> √a √b N> - √c |mixing?

‘H’

E373 data : Br(=>p) < 12%, by 1/4 data and assumption P (

stop=>Z)~20% result of KEK-E176

E964 can achieve Br(=>p) < 0.3% Br(=>n) < 3 %

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The first measurement of X-ray of -atom-nucleus potential can be seen.

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H.Tamura will introducethis with the developmentof Hyperball 2, later.

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Nuclear Physics with double strangeness (S=-2)

KEK-E373 => AGS-E964

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6 countries16 institutes34 staffs+ Graduate stu.

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Outline of E964R

# Beam : K- (1.7GeV/c), 2 x 105 => 4 x 105 K-/spill with K-/->9 at D6-line

# Detectors : Nuclear Emulsion, Double-sided Si strip Detector (DSSD),

Ge-Detector (Hyperball), KURAMA magnet carried from Japan# Time requested :

300 =>150 hours for detector tune1100 =>600 hours for beam exposure

# Trigger : (K-, K+) => 104 - stopping events (10 times higher stat. than E373)

We request Beam time in FY2006

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Experimental setup of E964Sep.09,2004

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Development #1Double-sided Si Strip Detector (DSSD)

1st Surface 2nd Surface

・ Two sets in the 4mm gap between the Target & Emulsion.

・ DSSDs have already been ordered to HAMAMATSU Photo Co.Ltd.

Precise tracking of hyperons for the top emulsion plate. => Reduction of background tracks, which are picked up in the plate. => Speeding up of emulsion scanning.

・ Effective area : 30x60mm2 / Thickness : 0.3mm / pitch : 50m

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Development #2 Automatic Scanning

Current systemSurface & Grid : 22 sec.Track_scan : 15 sec.

Images are shown: 1. Surface detection => Grid measurement for position calib.2. Track scanning

Developing systemSurface & Grid : 9 sec.Track_Scan : 6 sec.

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x3 faster

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Development #3 Production method of emulsion

Production method of Emulsion gel will be changed.For E964, amount of emulsion gel => 2.4 tonsFuji-film needs one year or more by conventional way.

Emulsion costwill be saved

50%

by the product ion lines for commercial f ilms

Conventional way by hand

Using the production lines for commercial films

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Stopping power and physicalcharacteristic has been tested,and the result showed no problem.

Budget approved

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E373 emulsion (ET-7C,D)

200nm

Size of AgBr crystals

Size 40nmRMS 9nm

Development #4 Fine crystal emulsion

NIT(Nano Image Tracker) developed by Nagoya U.

SEM Micrographs of AgBr crystalsSEM Micrographs of AgBr crystals

Dark Field Image of Light MicroscopeDark Field Image of Light Microscope

Tracks due to 5MeV α - Tracks due to 5MeV α - particlesparticles

Merit1) get better position resolution.

2) insensitive for beam track => higher dense exposure.

Under development

We will use this as possible.

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High accuracy Ge resolution

< 1.5 keV (FWHM) at 0.3 MeV

-> Accuracy of X-ray energy

~ 0.2 keV (FWHM)

< Expected energy shift

0.3 － 3 keV

(Friedman, Gal)

The first measurement of --atomic X rays employing “Hyperball” (Ge detector array)

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> 100 counts for each

Quite low background

Take clear - stopping events only

identified in emulsion.

Energy shift -> - nucleus potential -> -N interaction

H.Tamura

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Revised

9Be (K-, -) 9Be

Observed “Hypernuclear Fine Structure”

AGS E930: Precision spectroscopy of

Hypernuclei for N interaction (‘98,‘01)

N tensor force: T= 0.03 MeV N spin-orbit force: S= - 0.01 MeV

43±5 keV 26.1±2.0 keV

16O (K-, -) 16O

E(keV)E(keV)

Ukai et al.,submitted to PRL.

Akikawa et al.,PRL 88 (2002) 082501.

Hyperball (Ge array) E ~ 3 keV (FWHM)

+ D6 line

M. Ukai won a RHIC-AGS thesis award this year.

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Add six new “Clover” Ge detectors

-> efficiency doubled (6 Clover + 8 single detectors)

eff.~ 6% at 0.3 MeV

much higher than the proposal (~ 4%)

K-single Ge detector

= 60%]

x 14

“Clover” Ge detector= 125%]

x 6

K+

All new detectors working fine. In-beam test of Clover Ge OK.

Construction completed by November, 2003

Development #5

Hyperball2

E964 setup

to BNL

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Summary

Physics :1) making a S=-2 nuclear chart by ~102 Z via 104 -stopping events.

=> at least several nuclides will provide us B definitive information. 2) confirm production enhancement.

obtain the information about the component of H-dibaryon state in S=-2 system by A-dependence of B & decay of Z.

3) the First measurement of X-ray of -atom => may give us -nucleus potential. Preparation of the E964 experiment :

1) cutdown in requested beam time : 1400 => 750 hours 2) #1 DSSDs has been ordered. #2 Development of emulsion scanning system is in progress. #3 Mass-production of emulsion has been ready. #4 Test of fine crystal emulsion is in progress.

#5 Hyperball2 will be ready soon.

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Conditions

# Experimental budget : $3M by JPN Gov. (’03~’07)

[necessary time before running after its decision]

at least 10 months

# 6 months : from order to delivery of emulsion 4 months : emulsion plate making[Budget profile]: # emulsion : ~$0.8M in JFY2004 & 2005 => hope to run in the beginning of 2006 it will be spoiled in ~one year, we can’t keep it for a long time

(ex.2yrs).

We will pay for everything except beam time. We are able to run in FY2006 and hope that.

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