The Next Generation of Hypernucleus and Hyperatom Experiments

1
The Next Generation ofHypernucleus and Hyperatom
Experiments

• GSI, 18.10.2000
• Josef Pochodzalla
• Univ. Mainz

2
Quark Structure of Hyperons
Nucleons
Hyperons
3
Present Status of s-1 Nuclei

• Until few years ago hypernuclear studies focused
  on (p,K) or (K-,p-) reaction
• New tools
• ee- ? F1020 ? KK tagging (FINUDA _at_ DA?NE)
• g-spectroscopy with Ge (BNL, KEK, GSI)
• (e,eK)YX (TJNAF, MAMI-c)
• Topics
• YN interaction
• non-mesonic weak decay
• Lp ? pn
• Ln ? nn
• unique chance to study baryon-baryon
• weak interaction !

Weak decays...
4
Hypernuclei and Deconfinement
Question...

• Manifestation of the Pauli priciple on the quark ?

5
Status of Multi - Hypernuclei

• Multi-Hypernuclei are a terra incognita...
• ...but they exist !

6 candidates for LL-hypernuclei are
observed 1963 Danysz et al. 10Be 1966
Prowse 6He 1991 KEK-E176
10Be or 13Be 1991 KEK-E176 3 non-mesonic
decays
LL
LL
LL
LL
(K-,K) X-
6
LL-Nuclei as a Laboratory

• Hyperon-hyperon interaction
• H-particle
• R.L. Jaffe
• (1977)

Sakai et al (nucl-th/9912063)...
The situation in a finite nucleus will be that
the low-lying states have the character of LL
bound states, but that some of excited states may
have strong admixture of the H-nuclear states.
7
The s-3 Challange
-

• W hypernuclei by WW production
• Electric quadrupole moment of the W by hyperfine
  splitting in W-atoms)
• tensor forces between quarks
• expectation QW (0 - 3.1) 10-2 fm2
• DE(l10 ?l9) 515 keV
• DEQ few keV for Pb

QW 0.02 fm2
QW - 0.02 fm2
spin-orbit DEls (aZ)4 lmW quadrupole DEQ
(aZ)4Q33m3W
) C.J. Batty (1995)...
The precision measurements of X-rays from W- Pb
atoms will certainly require a future generation
of accelerators and probably also of physicists.
8
Production of s-2 Hypernuclei

• relativistic HI collisions
• coalescence of hyperons
• Bodmer (1971), Rufa et al. (1989), Schaffner et
  al. (1991)...
• X- capture X- p ? LL 28 MeV
• (K-,K)
• KEK-PS E373, BNL-E906...
• pp annihilation at rest
• K. Kilian (1987), DIANA coll.
• X X threshold

_
_
pp ? KK p(K) 285 MeV/c ? KN ? K X- p d
? KKp X-
_
-
-
_
p
9
X- capture

• X-atoms x-rays
• conversion
• X-(dss) p(uud) ? L(uds) L(uds)
• DQ 28 MeV

Conversion probability...

• ...approximatly 5-10

10
Hyperon Production
_
X X-
2.6 GeV/c
For example...

• with L21032 cm-2s-1 ? 700 s-1 for a C
  target

11
X- Properties

• X- mean life 0.164 ns

Consequence...

• minimize distance production capture
• initial momentum 100-500 MeV/c ? range few
  g/cm2

12
Setup

• beam 3 GeV/c, ? ? 1mm no halo (roman pots?)
• internal gas target e.g. Ne, width 1mm
• Tracking detector for X-
• 2-3 cm thick
• diamond strip
• Si strip
• capillary fiber

gas jet
readout
13
Capillary Detector

• Glascapillaries filled with szintillator

• - interaction (CHORUS)

Problem...

• fast readout
• possible solution Hybrid Phototube ALICE
  pixel chip Needs RD !

14
Gamma Spectroscopy

• Ge box based on VEGA type detectors
• segmented Clover
• 7 cm ?, 14 cm long
• 4 seg. clover, ePH 0.13 _at_ 1.33 MeV
• resolution 0.5
• fast electronics
• under development

beam
-
p
crucial point...
15
Count Rate

• luminosity 21032 cm-2s-1
• XX- cross section 2mb for pp ? 700 Hz
• p(100-500 MeV/c) p500? 0.0005
• X reconstruction probability 0.5
• stopping and capture probability pCAP? 0.20
• total stopped X- ? 3000 / day
• X- to LL conversion probability pLL ? 0.05
• total LL hyper nucleus production ? 4000 /
  month
  
• gamma emission/event, pg ? 0.5
• g-ray peak efficiency pGE? 0.1

-
total single line g-rate

• 5/day golden events (X trigger)
• 500/day with KK trigger

16
Competition
device
status
beam/ target
reaction
experiment
20000 stopped X-
K- beam, diamond target
neutron detector arrays
(X--,12C) ? 12B n
BNL-AGS E885
LL
few tens 2p decays of 4LLH
K- beam line
Cylindrical Detector System
2p decays
BNL-AGS E906
several hundreds stopped X-
(K-,K)
emulsion
(K-,K)X
KEK-PS E373
Observed captured X- per day
beam/ target
device
reaction
facility
spectrometer, DW 30 msr
lt7000
8106/sec 5 cm 12C
(K-,K)X
JHF



vertex detector
2000
106 stopped p per sec
p p ? KK KN ? X K
cold anti-protons


vertex detector g-spectrometer
3000 golden events 300000 KK trigger
L21032, thin target, production vertex ?
decay vertex
p p ? X X
GSI-HESR

17
Conclusion

• The anti-proton storage ring HESR _at_ GSI can
  provide a unique facility to study strange
  hyperatoms and hypernuclei.
• Key points
• highest luminosity possible
• moderate beam quality
• micro tracking device
• high rate Germanium array
• Detailed spectroscopic studies of multi-strange
  systems will be possible. hyperon laboratory