Study of Light -Hypernuclei by Spectroscopy of Two Body Weak Decay Pions

Liguang TangDepartment of Physics, Hampton University

Jefferson National Laboratory (JLAB)JLab PAC40, June 18, 2013

Fragmentation of Hypernuclei and

Mesonic Decay inside Nucleus

Free: p + -

2-B: AZ A(Z + 1) +

-

This previous PR12-10-001 is now proposed as a part of combined experiments that can run at same time to maximize physics outcome

HRS – HKS: (e, e’K+) experiments for mass spectroscopyHKS – Enge or HKS – HES: New decay - spectroscopy experiment

Future Project: Super Hypernuclear Physics Experiment at JLab

Unified collaboration from the previous Hall A and C collaborations

Enge ()

HES () HKS (K)

HRS (e’)Septum

Septum

Combine the features of previous Hall A and C experiments, create an optimized future program w/ the CEBAF CW beam

Decay Pion Spectroscopy to Study -Hypernuclei

12C -

Weak mesonic two body decay

1- 0.02- ~150 keV

Ground state doublet of 12

BB and

Direct Production

p

e’

e12C K

+

Example:

Hypernuclear States:s (or p) coupled to low lying core nucleus

12Bg.s.

E.M.

*

12B

Decay Pion Spectroscopy for Light and Exotic -Hypernuclei

Fragmentation Process

p

e’

e 12C

Example: K +

*

s12B*

Highly Excited Hypernuclear States:s coupled to High-Lying core nucleus, i.e.particle hole at s orbit

4H

Fragmentation (<10-16s)

4Hg.s.

4He

-

Weak mesonic two body decay (~10-10s)

Access to variety of light hypernuclei, some of

which cannot be produced or measured

precisely by other means

e e

* K+

p

AZ

A(Z-1)

A1Z1 stop

A2Z2

(Z-1) = Z1+Z2; A=A1+A2

-

A1(Z1+1)

SPECTROSCOPYe e

* K+

,(-) p(n)

AZ (A-1)Z’

-

N

BACKGROUND

VS

Comparison of Spectroscopic and Background - Production

(b)

3B background

20 Ex

10 Ex 10 Ex 10 Ex

2-

3/2+

5/2+1/2+

9Li8

HeJp=? 1-

8Li

7H

1/2+

3/2+

7Li

1- ?

6Li

Additions from 9Li and its

continuum

(Phase II: 9Be target)

A

p

1 2 3 4 5 6 7 8 9 10 11 12

1

2

3

4

5

6

3H 4

H 5H 6

H 7H 8

H

6He 7

He 8He 9

He

6Li 7

Li 8Li 9

Li 10Li

11Be9

Be 10Be8

Be

11B9

B 10B8

B 12B

Light Hypernuclei to Be Investigated

Previously measured

Mirror pairs

Study of Light Hypernuclei by Pionic Decay at JlabIllustration on the Main Features

(a)2-B decay from 7He

and its continuum

(Phase I: 7Li target) 1/2+

PMaxPMin 0 2Ex Ex0 2

4H

0+

7He

1/2+

3/2+5/2+

3H

6He

1- ?6H

5H

90.0 100.0 110.0 120.0 130.0 140.0- Momentum (MeV/c)

3B background

(b)

3B background

20Ex

10Ex 10

Ex 10Ex

2-

3/2+

5/2+

1/2+

9Li

8He

1-

8Li

7H

1/2+

3/2+

7Li

1- ?

6Li

Additions from 9Li and its

continuum

(Phase II: 9Be target)

(c) Additions from 12B and its

continuum

(Phase III: 12C target)

12B1-

11Be

11B 10

Li

10Be

5/2+Jp=?10B

9He

9Be

9B

8H

8Be

8B 3B background

Illustration of Decay Pion Spectroscopy

• Precise measurement of ground state B (20keV) for a series of light hypernuclei with high resolution (130keV), spin-parity determination of g.s., charge symmetry breaking (CSB) from mirror pairs

• Neutron rich light hypernuclei (- coupling) and neutron drip line limit (6

H and 8H)

• Formation of quasi free continuum and fragmentation mechanism

Physics Goal of Decay Pion Spectroscopy

Provide precise input for theoretical description of -N interaction. Since B and excitation are the only sources of experimental information, study wide range of hypernuclei is needed.

Preliminary Results from MAMI-C

4H

2011 RunPartial

2012 RunPartial

KID affected by huge rate of e+ at 0

• Added 10cm Pb curtain

• Luminosity increased• KID was still a problem• K+ singles increased

just a little

KAOS – SPEC-C2A beam

20A beam

We are convinced at least on 4

H observation

• Higher production rate (~9 times)• Excellent PID for both K+ and -

• Less background (accidental or real)• Full coverage of the interested - momentum

range• Can take data together with the (e, e’K+)

experiment

Advantages of Jlab Experiment

Summary• High intensity CW beam at JLAB and the characters of

electro-production make possible for high precision hypernuclear programs, among which the decay pion program is unique.

• The decay pion spectroscopy program is able to provide precise and fundamental information needed to understand the YN and Y-Nucleus interactions.

• We are convinced from the MAMI-C test runs that the technique works.