Observation of a new narrow axial-vector meson $a_1(1420)$

C Adolph,R Akhunzyanov,M Alexeev,G D Alexeev,A Amoroso,V Andrieux,V Anosov,A Austregesilo,C D R Azevedo,B Badelek,F Balestra,John A Barth,R Beck,Y Bedfer,J C Bernhard,K Bicker,E R Bielert,R Birsa,J Bisplinghoff,Martin Bodlak,M Boer,P Bordalo,F Bradamante,C Braun,Alessandro Bressan,M Buechele,E Burtin,W C Chang,M Chiosso,Ikseon Choi,S U Chung,A Cicuttin,M L Crespo,Q Curiel,S Dalla Torre,S S Dasgupta,O Yu Denisov,L Dhara,S V Donskov,N Doshita,W Duennweber,V Duic,M Dziewiecki,Anatoli Vasilievich Efremov,P D Eversheim,W Eyrich,M A Faessler,A Ferrero,M Finger,H M Fischer,C Franco,N Du Fresne Von Hohenesche,J M Friedrich,V Frolov,F Gautheron,O P Gavrichtchouk,S G Gerassimov,I Gnesi,M Gorzellik,S Grabmueller,A Grasso,M Grosseperdekamp,B Grube,T Grussenmeyer,A Guskov,F Haas,D Hahne,D Von Harrach,Ronaldo Fumio Hashimoto,F H Heinsius,F H Herrmann,F Hinterberger,N Horikawa,N Dhose,C Yu Hsieh,Stefan M Huber,S Ishimoto,Andrew Ivanov,Yu I Ivanshin,T Iwata,R Jahn,V Jary,P Joerg,R Joosten,E M Kabuss,B Ketzer,G V Khaustov,Yu A Khokhlov,Yu Kisselev,F J Klein,K Klimaszewski,J H Koivuniemi,V N Kolosov,K Kondo,K Koenigsmann,I Konorov,V F Konstantinov,A M Kotzinian

PHYSICAL REVIEW LETTERS（2015）

Cited 101|Views102

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Abstract

The COMPASS Collaboration at CERN has measured diffractive dissociation of 190 GeV/c pions into the pi(-) pi(-) pi(+) final state using a stationary hydrogen target. A partial- wave analysis (PWA) was performed in bins of 3 pi 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 f(0)(980)pi 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 3 pi states with J(PC) = 2(++) and 4(++) decaying into rho(770)pi and with J(PC) = 1(++) decaying into f(0)(980)pi. We identify a new a 1 meson with mass (1414(-13)(+15)) MeV/c(2) and width (153(-23)(+8)) MeV/c(2). Within the final states investigated in our analysis, we observe the new a(1)(1420) decaying only into f(0)(980)pi, suggesting its exotic nature.

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Key words

meson<mmlmath xmlnsmml=http//wwww3org/1998/math/mathml,axial-vector

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