Observation of a new ηπ0π0 resonance at 1900 MeV/ c2 in two-photon scattering

K Karch,K Wachs,K Fairfield,B Lurz,P Zschorsch,R Lekebusch,F Messing,I Kirkbride,U Volland,R Cowan,W Koch,D Antreasyan,R Cabenda,K Brockmüller,A Compagnucci,J Irion,U Strohbusch,P Schmitt,W Maschmann,D Gelphman,D Besset,K Wacker,R Hofstadter,A Fridman,K Strauch,V Stock,B Monteleoni,D Sievers,H Marsiske,G Folger,A Engler,W Walk,S Keh,M Scheer,T Kloiber,R Nernst,T Kiel,G Conforto,J Gaiser,Z Jakubowski,J Schotanus,C Rippich,B Van Uitert,H Wegener,S Leffler,B Renger,B Muryn,K Königsmann,M Reidenbach,G Landi,C Peck,H G Kilian ,E D Bloom ,D Williams ,I Brock,S Lowe,D G Coyne ,H W Bartels ,H Vogel,M Kobel,F H Heimlich ,K.j De Graaf ,A M Litke ,W J Metzger ,S Krüger,F H Heinsius ,P Mcbride,A S Schwarz ,J Tompkins,G Glaser,B Pollock,H Janßen ,H Meyer,J K Bienlein ,B Niczyporuk,A Bizzeti,R W Kraemer ,H J Trost ,R T Van De Walle ,P N Ratoff ,F C Porter ,A.f Voigt ,A M Cartacci ,A C König ,W S Lockman ,J Schütte,D Prindle,D Marlow,R Lee,T Skwarnicki,P G Pelfer ,S Cooper,C Bieler ,G Godfrey,M Cavalli‐Sforza ,G Nowak,R Clare

doi:10.1016/0370-2693(90)91268-g

Abstract

Using the Crystal Ball detector at the DORIS II e +e − storage ring, we measure the ηπ 0 π 0 mass spectrum in the reaction e +e −→e +e − ηπ 0 π 0→e +e −6 γ from the ηπ 0 π 0 threshold to about 2500 MeV/ c 2. The spectrum is dominated by the η′, for which we determine Γ γγ ( η′)BR( η'→6 γ)=0.36±0.02±0.03 keV. In addition, we observe an enhancement in the cross section near 1900 MeV/ c 2 which we attribute to the two-photon production of a new resonance X(1900). The angular distributions and the invariant mass distribution of the ηπ 0 subsystem are consistent with those expected for the hypothetical η 2 meson with J PC =2 −+. For this J P assignment the resonance parameters are M(X) = 1876 ±35±50 MeV/ c 2, Γ tot(X)=228±90±34 MeV/ c 2 and Γ γγ (X)BR(X→ ηππ) = 0.9±0.2±0.3 keV.

Highlights

We report on an investigation of the reaction 27,~n°n °, observed in the six-photon final state ~t
We improve the measurement of FvrOI' )BR0q'-,6y) and report for the first time on an enhancement in the cross section of "y~rln°n ° at an invariant mass of about 1900 M e V / c 2. We interpret it as the production of a new resonance X(1900)
The X(1900) is the first new resonance to be discovered in 27 collisions

Summary

Introduction

We report on an investigation of the reaction 27-,~n°n °, observed in the six-photon final state ~t. Candidate events for the six-photon final state are selected by requiring six energy depositions in the calorimeter.

Results

Conclusion