Study of Light Hypernuclei Study of Light Hypernuclei by Pionic Decay at JLABby Pionic Decay at JLAB

Liguang TangLiguang Tang

Other spokespersons:Other spokespersons:A. Margaryan, L. Yuan, S.N. Nakamura, J. ReinholdA. Margaryan, L. Yuan, S.N. Nakamura, J. Reinhold

Collaboration:Collaboration:From both Hall C and A hypernuclear programsFrom both Hall C and A hypernuclear programs

JLAB PAC 33, January 14-18, 2008JLAB PAC 33, January 14-18, 2008

IntroductionIntroductionNuclei Baryon-Baryon Interaction Neutron Stars

D.H.

D.H.D.H.

S.H.S.H.N.R.p

S.H.S.H.N.R.N.R.n

(uds)

(uds)

P(uud)

n(udd) The single and double The single and double

hypernuclei are the hypernuclei are the main sources of the main sources of the strange sector of strange sector of baryon-baryon baryon-baryon interactioninteraction

S=-1

S=-2

S=-0

Discovery of the first hypernucleus by pionic decay in Discovery of the first hypernucleus by pionic decay in emulsion produced by Cosmic Rays. Marian Danysz and emulsion produced by Cosmic Rays. Marian Danysz and

Jerzy Pniewski, 1952Jerzy Pniewski, 1952

• p + - (64%); n + 0 (36%)

• Remain effective even at medium A

Access rich information about Access rich information about hypernuclear and nuclear physicshypernuclear and nuclear physics

Used exclusively to determine the Used exclusively to determine the binding energy of light (A≤15) binding energy of light (A≤15) hypernuclei in emulsionhypernuclei in emulsion

Precision: ~50keVPrecision: ~50keV Resolution: ~0.5 – 1.0 MeVResolution: ~0.5 – 1.0 MeV Problems: Problems:

- Poor statistics- Poor statistics

- Calibrations- Calibrations

- Cannot resolve pure 2-body decay- Cannot resolve pure 2-body decay Was not interested in the past ~20 Was not interested in the past ~20

years – years – low energy and low yieldlow energy and low yield

New Opportunity at JLABNew Opportunity at JLAB

Combination the CEBAF beam and Combination the CEBAF beam and the HKS systemthe HKS system

High precision and high yieldHigh precision and high yield

Program features:Program features:

• Energy resolution: Energy resolution: ~130 keV FWHM~130 keV FWHM

• BB precision: precision: ~10 keV~10 keV

• Simultaneous lifetime measurement Simultaneous lifetime measurement (timing resolution ≤80ps)(timing resolution ≤80ps)

Wide range of physicsWide range of physics

Directly Produced Hypernuclei - Directly Produced Hypernuclei - ExampleExample

p

e’

e

12C

K+

12B

12Cg.s. -

Mesonic two body decay

1- 0.02- ~150 keV

Ground state doublet of 12

B

B and

Indirectly Produced Hypernuclei – Indirectly Produced Hypernuclei – ExampleExampleFragmentation ProcessFragmentation Process

p

e’

e

12C

12B

*

K+

4He

-

Mesonic two body decay (~10-10s)

Access to variety of light and exotic

hypernuclei, some of which cannot be

produced or measured precisely

by other means

4H

Fragmentation (<10-16s)

Physics Objectives – YN InteractionsPhysics Objectives – YN Interactions Emulsion data of light hypernuclei (primarily the ground Emulsion data of light hypernuclei (primarily the ground

states) were used to check theoretical models on YN states) were used to check theoretical models on YN interaction in the past 40 some years.interaction in the past 40 some years.

Problem of inconsistency and model of choice existProblem of inconsistency and model of choice exist

Recent Recent -spectroscopy program has been successful for -spectroscopy program has been successful for spin dependent interactions but unable to measure spin dependent interactions but unable to measure BB

Recent successful mass spectroscopy programs cannot Recent successful mass spectroscopy programs cannot reach a precision on reach a precision on BB exceeding emulsion dataexceeding emulsion data

YN B (3H) B (4

H) B (4H* ) B (4

He) B (4He* ) B (5

He)

SC97d(S) 0.01 1.67 1.2 1.62 1.17 3.17

SC97e(S) 0.10 2.06 0.92 2.02 0.90 2.75SC97f(S) 0.18 2.16 0.63 2.11 0.62 2.10

SC89(S) 0.37 2.55 Unbound 2.47 Unbound 0.35

Experiment 0.13 ± 0.05 2.04 ± 0.04 1.00 ± 0.04 2.39 ± 0.03 1.24 ± 0.04 3.12± 0.02

The wealth of information coming from this poor The wealth of information coming from this poor statistics emulsion experiment is solely attributable statistics emulsion experiment is solely attributable to the technique's inherent good energy resolution, to the technique's inherent good energy resolution, ~50 keV~50 keV in this instance, and forcefully emphasizes in this instance, and forcefully emphasizes the need to strive for comparable energy resolution the need to strive for comparable energy resolution in counter experiments.in counter experiments.

- - D. Davis, 1992D. Davis, 1992

As it turns out, binding energies of light hypernuclei As it turns out, binding energies of light hypernuclei are highly correlated from calibrations to are highly correlated from calibrations to 1212

C for C for example, and most likely incorrect. example, and most likely incorrect. - D. - D. Davis, HYP2006Davis, HYP2006

Replace emulsion data with a new set of Replace emulsion data with a new set of data that has a factor of 2-5 times better data that has a factor of 2-5 times better precision on Bprecision on B to check current and future to check current and future theories with stringent limitstheories with stringent limits

Separate small ground state doubletsSeparate small ground state doublets

Study charge symmetry breaking in YN Study charge symmetry breaking in YN interaction, such as interaction, such as BB((44

HHg.s.g.s.) - B) - B((44HeHeg.s.g.s.))

YN Interactions – YN Interactions – cont.cont.

Search for and measure precisely the Search for and measure precisely the BB of the of the exotic hypernuclei is another effective way for exotic hypernuclei is another effective way for exotic nuclear physicsexotic nuclear physics

Many hypernuclei with unstable nuclear core Many hypernuclei with unstable nuclear core exist, e.g. exist, e.g. 66

HeHe, , 77BeBe, , 88

HeHe, , 99Be. Be. Other exotic Other exotic

hypernculei may exist, e.g. hypernculei may exist, e.g. 66H, H, 77

HH, , 88HH, , 1010

HeHe, , and and 1111

LiLi through fragmentation processthrough fragmentation process

Search for Highly Exotic HypernucleiSearch for Highly Exotic Hypernuclei

Bound hypernucleu

s

Search for light Search for light hypernuclei toward hypernuclei toward nucleon drip-lines: nucleon drip-lines: hypernuclei with hypernuclei with extreme isospinsextreme isospins

Other programs:Other programs:Heavy ion collisionHeavy ion collision

JINR, HypHI JINR, HypHI

This program – high This program – high precision on Bprecision on B

Hypernuclei at:

* -stability line* Neutron rich* Nucleon drip-lines

Pion decays offer insights into the hypernuclear Pion decays offer insights into the hypernuclear and nuclear structure, and the momentum and nuclear structure, and the momentum dependence of the single particle wave functionsdependence of the single particle wave functions

Impurity Nuclear Physics Impurity Nuclear Physics Hypernuclear and nuclear structureHypernuclear and nuclear structure

Nucleus at g.s.

-

Hypernucleus w/ hyperfine g.s. doublet

E < 100 keV

Decay pion can be used to determine the spin ordering of the doublet

Hypernucleus at g.s.

Nucleus w/ hyperfine g.s. doublet

E < 100 keV

Example: Example: 77Li w/ g.s. doublet 1/2Li w/ g.s. doublet 1/2++ & 3/2 & 3/2++

Impurity Nuclear Physics – Impurity Nuclear Physics – cont.cont. Probing nuclear structure with Probing nuclear structure with

Impurity Nuclear Physics – Impurity Nuclear Physics – cont.cont. Probing nuclear structure with Probing nuclear structure with

Example: Example: 1010B w/ g.s. doublet 1B w/ g.s. doublet 1-- & 2 & 2--

Spin order is not knownSpin order is not known

transition (transition (22-- 1 1--) was not found) was not found

Success competition by weak mesonic decaySuccess competition by weak mesonic decay

Assumed order could be wrongAssumed order could be wrong

Decay pion may provide clearificationDecay pion may provide clearification

1010Be Be may be the candidate at JLABmay be the candidate at JLAB

Impurity Nuclear Physics Impurity Nuclear Physics Role and effect of Role and effect of in Nucler Medium in Nucler Medium

E2

Precise Precise BB allows separation of those low lying states which allows separation of those low lying states which have sufficient long lifetime (i.e. have sufficient long lifetime (i.e. decay competes with weak decay competes with weak decay) decay)

Lifetime of these separable states allows to extract transition Lifetime of these separable states allows to extract transition probabilities probabilities B(E2)B(E2) and B(M1) which provide information about and B(M1) which provide information about the medium effect to baryon or the medium effect to baryon or to the core medium to the core medium

5/2+

3/2+

1/2+

E20 (MeV)

~1 .7

5/2+ and 3/2+ states are from unbound 2+ state of 6He core

7He

-

7Li

E2

1/2+

5/2+7/2+

0 (MeV)~0 .26

~1 .48

11B

-

11C

Tagged-Weak Pi-Method of B(E2) and Tagged-Weak Pi-Method of B(E2) and B(M1) Measurement B(M1) Measurement

By measuring both of PBweak(t) and PAweak(t) and fitting them together to the

equations above, , and m can be determined.λWA λW

B

If states can be separated and statistics is sufficient to measure lifetimes, then

Technique & Exp. LayoutTechnique & Exp. Layout

Pre-Chicaned Electron Beam

Hall C Z-axis

To Hall Dump To low power local dump

dump

Schematic Top View of New Hypernuclear

Decay Tagging System at Jlab

Standard Splitter and Standard Splitter and HKS for KHKS for K++

Enge & target moved Enge & target moved upstream for decay upstream for decay pionspions

Tilted TGT (25mg/cmTilted TGT (25mg/cm22) ) Eff. TGT (50mg/cmEff. TGT (50mg/cm22))

Standard pre-chicane Standard pre-chicane beam line (E05-115)beam line (E05-115)

Local dump for photonsLocal dump for photons Similar luminosity as Similar luminosity as

E05-115 (HKS/HES)E05-115 (HKS/HES)

Need calibration for Need calibration for the absolute Hthe absolute HS S

central momentum central momentum

Configuration Enge Split-Pole (or HES) spectrometer and detector package

Central momentum 115 MeV/c

Momentum acceptance ± 40%

Momentum resolution (r.m.s.) 10-4 without multiple scattering

Momentum resolution (r.m.s.) 4.9 10-4 with multiple scattering

Dispersion 1.28 cm/%

Time-zero precision < 100 ps (~80 ps)

Pion detection angle ~60 degree relative to the incident beam

Flight path length 309 cm

- survival rate ~ 60%

Solid angle ~20 msr

Total efficiency of the detector package

 

~80%

Parameters of the Parameters of the HHSS spectrometer spectrometer

Example of Possible G.S. of Light Hypernuclei Example of Possible G.S. of Light Hypernuclei from from 1212C TargetC Target

4H

8Li

12B

3H

7Li

11B

5He

8Be

9Be

Background:• ~97.5% QF decay• ~2.5% (K+ & -) accidentals

G.S. only (doublet structures are not shown)G.S. only (doublet structures are not shown) Estimated based on emulsion data thus may Estimated based on emulsion data thus may

under-estimated for some of the hypernucleiunder-estimated for some of the hypernuclei Additional hypernuclei may appear Additional hypernuclei may appear

Targets: Targets: 1212C and C and 77Li (Optimized combination)Li (Optimized combination)

• 1212C – Heaviest in p-shell; reliable yield rates on variety of light C – Heaviest in p-shell; reliable yield rates on variety of light hypernuclei but not too crowdedhypernuclei but not too crowded

• 77Li – Best chance for the lightest and highly exotic Li – Best chance for the lightest and highly exotic hypernuclei, such as hypernuclei, such as 66

HH

Beam energy: 1.8 – 2.2 GeVBeam energy: 1.8 – 2.2 GeV

Beam current and acq. timeBeam current and acq. time

• 1212C, 60C, 60A (100 Max.), 20 daysA (100 Max.), 20 days

• ~1000 counts for ~1000 counts for 44H (physics w/ moderate yield)H (physics w/ moderate yield)

• ~6000 counts for ~6000 counts for 55He (physics and calibration)He (physics and calibration)

• 77Li, 30Li, 30A (50 Max.), 20 days A (50 Max.), 20 days

Primary: Primary: 77He, He, 66

He, He, 55He; He; Questionable:Questionable: 44

He, He, 66H, H, 55

H, H, 44HH

Trigger rate: ~ few hundred HzTrigger rate: ~ few hundred Hz

Beam Parameters and Beam TimeBeam Parameters and Beam Time

SummarySummary CEBAF beam and HKS provide unique CEBAF beam and HKS provide unique

opportunity for a new counter type opportunity for a new counter type high precision decay pion program – high precision decay pion program – Producing data that replaces emulsion Producing data that replaces emulsion data in the role of checking theoriesdata in the role of checking theories

It can study a wide range of physics It can study a wide range of physics that either not accessible by other that either not accessible by other means or complementary to other means or complementary to other programsprograms

International Hypernuclear NetworkInternational Hypernuclear Network

PANDA at FAIR• 2012~• Anti-proton beam• Double -hypernuclei• -ray spectroscopy

MAMI C• 2007~• Electro-production• Single -hypernuclei• -wavefunction

JLab• 2000~• Electro-production• Single -hypernuclei• -wavefunction

FINUDA at DANE• e+e- collider• Stopped-K- reaction• Single -hypernuclei• -ray spectroscopy (2012~)

J-PARC• 2009~• Intense K- beam• Single and double -hypernuclei• -ray spectroscopy for single

HypHI at GSI/FAIR• Heavy ion beams• Single -hypernuclei at extreme isospins• Magnetic moments

SPHERE at JINR• Heavy ion beams• Single -hypernuclei

JLab, HπS• Electro-production• Single -hypernuclei at normal and extreme isospins• Binding energies•π - decay spectroscopy•Impurity nuclear physics

Basic map from Saito, HYP06

Introduction – Introduction – cont.cont.

ExampleExample

H. Outa et al., “Lifetime measurement of 4H hypernucleus”, INS-Rep.-914 (1992)

Decay Decay -- is used even in modern studiesis used even in modern studies

In the last 20 years or so, mesonic decay has not In the last 20 years or so, mesonic decay has not been really interested in study of the been really interested in study of the hypernuclear/nuclear structure, because of its low hypernuclear/nuclear structure, because of its low momentum and the difficulty to reach high momentum and the difficulty to reach high precision with unavoidable thick targets using precision with unavoidable thick targets using msonic beamsmsonic beams

Emulsion: cannot resolve two body decay Emulsion: cannot resolve two body decay and typical resolution is 0.5 – 1.0 MeVand typical resolution is 0.5 – 1.0 MeV

Counter type: resolution is 1.0 – 2.0 MeVCounter type: resolution is 1.0 – 2.0 MeV

Time delayed

The proposed project capable to provide precise binding values of known hypernuclei and have a

great potential to extend this landscape

Exotic HypernucleiExotic Hypernuclei

Different decay channels of excited 7He* hypernucleus (Majling,

2006).