3H

lifetime: an open issue in hypernuclear physics
M. Agnello1,2, E. Botta2,3, T. Bressani2, A. Feliciello2, T. Nagae4, T. Takahashi5, H. Tamura6
1Politecnico
4Kyoto
2INFN
5IPNS,
di Torino, Dept. of Applied Science and Technology, Torino, Italy
– Sezione di Torino, Torino, Italy
3Università di Torino, Dept. of Physics, Torino, Italy
University, Dept. of Physics, Kyoto, Japan
KEK, Tsukuba, Japan
University, Dept. of Physics, Sendai, Japan
6Tohoku
The physics case: which value for 3H lifetime?
The naive expectation
He bubble
chambers
photographic
emulsions
p
(heavy) ions
collisions
B ( Λ3 H)  0.13  0.05 MeV
n
Λ
unexpected?
surprising?
40
w.a.  20331
ps
n
 ( H)   ( free )
3
Λ
supported by several theoretical predications, e.g.: M. Rayet, R.H. Dalitz, NCA 46 (1966) 786
H. Kamada et al., PRC 57 (1998) 1595
15
w.a.  19313
ps
28
w.a.  18523
ps
The 4H situation
~20 years
photographic
emulsions
counter
experiments
large error bars ↔ small data samples
A new (3,4H) measurement @
w.a.  247 85
54 ps
original idea: K0 spectroscopy
 -  3, 4 He  K 0 
3,4

H
14
w.a.  177 14
ps
@ p  1.0  1.1 GeV / c
p
Λ
 π  π
n
n
B ( Λ4 H)  2.12  0.01 MeV
delayed time spectrum technique  (AZ)
>>
B ( Λ3 H)
(tdecay – tproduction)
Experimental
concept layout (not to scale)
He

4
Λ
p p
n
Reaction kinematics:
modular design
SKS
spectrometer
(liquid
S
K
S
a
c
c
e
p
t
a
n
c
e
3,4He)
 
(1.05 ÷ 1.10 GeV/c)
 Ks0
700 MeV/c → ~2 cm range
3,4He
3b
 to SKS

2b
 3,4H
350 ÷ 400 MeV/c → few mm range 
  to K0 spectrometer
(range detector)
 to range detector
Design performances:
 MM
 time
 
≤ 3 MeV (FWHM)
≤ 100 ps (FWHM)
≈ 2  sr
Selection criteria:
≤ 3 MeV
≤ 100 mrad
T(prongs)
 
  p >650 MeV/c, 2° <  < 14°  10 < p < 120 MeV/c, 60° <  < 100°
  0 < p < 133 MeV/c, 0° <  < 180°
Expected rates
yield(4 H)  N beam 
N target
d
time
 NA 
  sp   sp   an 
d
Tcycle
4
N beam  109  / spill
d
 10 b/sr
d
4H

N target  1 g/cm 2

[ d / d ] 3 H

[ d / d ] 4 H

 sp  0.02 sr
=1
 sp  BR( K 0  K s0     )   rc (   )  0.03
 an  0.5
time
 3.4 s/spill
Tcycle
Educated guess
3H

yield(4 H)  1.14  10 4 / d
yield( H  π  He)  yield( H)  BR        an  yield( H)  0.2
4

-
4
H. Tamura et al., PRC 40 (1989) 479
4

   1  an  0.8
  0.5
0.49
4 [d / d] 3 H
yield(3 H)  yield(4 H)  
3 [ d / d ] 4 H

4

[d / d]
[d / d]
3

4

H

H
?
H. Kamada et al., PRC 57 (1998) 1595
0.40
  0.5
   1  an  0.4

educated
guess
educated guess on the beam intensity improvement
 (0.1  1)
yield(3 H   -  p  d )  yield(3 H)  BR  Ωπ      an  yield(3 H)  0.1
= 0.1
Further readings:
1) E. Botta et al., RNC 38 (2015) 387
2) M. Agnello et al., NPA 954 (2016) 176