Observation of a New Narrow Axial-Vector Meson a1(1420).

C Adolph,F Balestra,A Lehmann,L Dhara,J Pretz,K Kondo,E Burtin,A Sandacz,C Quintans,S Takekawa,S Grabmüller,R Beck,A Amoroso,B Ketzer,R Joosten,D Panzieri,S Levorato,A Austregesilo,M Chiosso,S Huber,K Königsmann,J.-C Peng,A Nagaytsev,M Bodlak,A Magnon,L Sinha,J Barth,P Kremser,S Uhl,P Schiavon,R Birsa,M Ziembicki,F Tessarotto,W Meyer,N Horikawa,A Guskov,Q Curiel,S Tessaro,J Lichtenstadt,W Eyrich,G Reicherz,C Regali,W Dünnweber,M Büchele,M Stolarski,F Thibaud,R Akhunzyanov,J Bisplinghoff,R Jahn,M Faessler,P Sznajder,G Meshcheryakov,S Schopferer,M Quaresma,A Zink,C Santos,T Iwata,D Von Harrach,C Riedl,N Du Fresne Von Hohenesche,B Parsamyan,K Kurek,J Pochodzalla,S Platchkov,S Wallner,M Gorzellik,M Zavertyaev,H Schmieden,T Szameitat,J Ter Wolbeek,K Bicker,Y Bedfer,A Maggiora,F Hinterberger,S Dasgupta,T Weisrock,H Fischer,F Krinner,L Silva,T Schlüter,G Sbrizzai,D Hahne,N Kuchinski,Y Miyachi,F Sozzi,E Zemlyanichkina,T Michigami,A Bressan,F Kunne,M Levillain,B Grube,P Bordalo,K Schönning,A Efremov,V Duic,M Wilfert,V Andrieux,M Ostrick,S Paul,S Ishimoto,S Sirtl,A Rychter,I Konorov,P Jörg,F Klein,V Tskhay,T Grussenmeyer,Yu Kisselev,M Finger,T Matsuda,A Grasso,A Srnka,F Nerling,Yu Ivanshin,S Ramos,D Neyret,T Nagel,N Makke,M Virius,A Cicuttin,S Gerassimov,W.-D Nowak,N D’Hose,O Kouznetsov,F Gautheron,M Pešek ,O.p Gavrichtchouk ,C.-Y Hsieh ,O.yu Shevchenko ,И Орлов ,E.r Bielert ,Yu.a Khokhlov ,I Savin ,V Jarý ,G.k Mallot ,S Torre ,К Заремба ,R Kurjata ,J.f.c.a Veloso ,Hiromasa Suzuki ,Hiroki Matsuda ,M Šulc ,M Alexeev ,S.v Donskov ,В.ф Константинов ,А.g Оlshevsky ,V.n Kolosov ,M Boër ,A.m Kotzinian ,А Иванов ,Claude Marchand ,V.a Polyakov ,G D Alexeev ,Jan Friedrich ,V.d Samoylenko ,Florian Haas ,D.v Peshekhonov ,F H Heinsius ,G.v Khaustov ,I J Choi ,Ryo Hashimoto ,В Аносов ,Stephan Schmeing ,J H Koivuniemi ,A S Nunes ,M.l Crespo ,A.a Lednev ,V Nikolaenko ,C.d.r Azevedo ,Yu.v Mikhailov ,P.d Eversheim ,О Денисов ,W C Chang ,Z.v Kroumchtein ,S U Chung ,Jan Matoušek ,D I Ryabchikov ,M Slunečka ,J Nový ,N.s Rossiyskaya ,V V Frolov ,M Grosse‐Perdekamp ,M Dziewiecki,A Szabelski,I Gnesi,N Makins,F Bradamante,B Badełek,E Kabuß,J Marzec,F Herrmann,C Franco,A Ferrero,A Martin,F Pereira,N Doshita,M Krämer,A Selyunin,K Klimaszewski,C Braun,S Sarkar,E Rocco,J Bernhard,K Schmidt

doi:10.1103/physrevlett.115.082001

Abstract

The COMPASS Collaboration at CERN has measured diffractive dissociation of 190 GeV/c pions into the π(-)π(-)π(+) final state using a stationary hydrogen target. A partial-wave analysis (PWA) was performed in bins of 3π mass and four-momentum transfer using the isobar model and the so far largest PWA model consisting of 88 waves. A narrow peak is observed in the f0(980)π channel with spin, parity and C-parity quantum numbers J(PC)=1(++). We present a resonance-model study of a subset of the spin-density matrix selecting 3π states with J(PC)=2(++) and 4(++) decaying into ρ(770)π and with J(PC)=1(++) decaying into f0(980)π. We identify a new a1 meson with mass (1414(-13)(+15)) MeV/c2 and width (153(-23)(+8)) MeV/c2. Within the final states investigated in our analysis, we observe the new a1(1420) decaying only into f0(980)π, suggesting its exotic nature.

Highlights

The COMPASS Collaboration at CERN has measured diffractive dissociation of 190 GeV=c pions into the π−π−πþ final state using a stationary hydrogen target
far largest partial-wave analysis (PWA) model consisting of 88 waves
A narrow peak is observed in the f0ð980Þπ channel with spin

Summary

Introduction

The COMPASS Collaboration at CERN has measured diffractive dissociation of 190 GeV=c pions into the π−π−πþ final state using a stationary hydrogen target.

Results

Conclusion