https://doi.org/10.1140/epja/i2008-10735-x
Regular Article - Experimental Physics
A new analysis improving the evidence of a narrow peak in the invariant-mass distribution of the 
p system observed in the 
annihilation at rest on 4He
1
Dipartimento di Fisica Nucleare e Teorica, Università di Pavia, and Istituto Nazionale di Fisica Nucleare, Sezione di Pavia, Pavia, Italy
2
Dipartimento di Fisica Sperimentale, Università di Torino, and Istituto Nazionale di Fisica Nucleare, Sezione di Torino, Pavia, Italy
3
Dipartimento di Fisica Nucleare e Teorica and Dipartimento di Chimica Generale, Università di Pavia, Pavia, Italy
* e-mail: Paola.Salvini@pv.infn.it
Received:
29
October
2008
Revised:
4
February
2009
Accepted:
19
February
2009
Published online:
31
March
2009
The presence of a narrow peak in the
p invariant-mass distribution observed in the annihilation reaction at rest 
is discussed again through an analysis procedure which improves the ratio signal/background in comparison with the previous analysis. The peak is centred at 2223.2±3.2stat±1.2syst MeV and has a statistical significance of 4.7
, values compatible with those published previously. If interpreted as the result of the decay into
p of a 
bound system, the corresponding binding energy should be B = - 151.0±3.2stat±1.2syst MeV and the width 
< 33.9±6.2 MeV. The production rate has a lower limit of 1.2 10-4. Data on the annihilation reaction at rest
4He 
p
p
p
s
X , analyzed for the first time, lead to a result in qualitative agreement with the previous one.
PACS: 13.75.Ev Hyperon-nucleon interactions – / 13.75.Jz Kaon-baryon interactions – / 36.10.-k Exotic atoms and molecules (containing mesons, antiprotons and other unusual particles) – / 21.80.+a Hypernuclei –
© SIF, Springer-Verlag Berlin Heidelberg, 2009
