Evidence for πK-atoms with DIRAC

B Adeva,A Lamberto,M Chiba,A Penzo,S Constantinescu,K Gritsay,Z Hons,C Curceanu,D Dumitriu,A Anania,T Trojek,M Hansroul,C Mariñas,G Caragheorgheopol,J Gerndt,C Guaraldo,M Pentia,A Lanaro,T Vrba,A Kulikov,O Vázquez Doce,P Zrelov,A Ryazantsev,V Brekhovskikh,S Sugimoto,S Trusov,Y Allkofer,C Amsler,V Olchevskii,J.L Fungueiriño,L Kruglova,V Yazkov,L Tauscher,A Sidorov,D Drijard,V Lucherini,P Chliapnikov,C Regenfus,M Pló,J Saborido,M Zhabitsky,Y Yoshimura,P Levi Sandri,J Rochet,L Afanasyev,M Kobayashi,C Ciocarlan,A Dudarev,S Horikawa,I Kurochkin,A Benelli,I Manuilov,M Iliescu,J Schacher,A Romero,M Gugiu,M Nikitin,C Detraz,A Gorin,A López Agüera ,A.v Kuptsov ,A.v Tarasov ,T Čechák ,V M Ronjin ,V.g Lapshin ,V.i Komarov ,V.i Rykalin ,V.v Karpukhin ,V.v Kruglov ,Victor A Utkin ,J Klusoň ,J Smolík ,L.l Nemenov ,M Dūma ,R Lednický ,Kenji Okada ,Diego Dreossi ,O.e Gorchakov ,F Takéutchi ,G F Rappazzo

doi:10.1016/j.physletb.2009.03.001

Abstract

We present evidence for the first observation of electromagnetically bound π±K∓-pairs (πK-atoms) with the DIRAC experiment at the CERN-PS. The πK-atoms are produced by the 24 GeV/c proton beam in a thin Pt-target and the π± and K∓-mesons from the atom dissociation are analyzed in a two-arm magnetic spectrometer. The observed enhancement at low relative momentum corresponds to the production of 173±54πK-atoms. The mean life of πK-atoms is related to the s-wave πK-scattering lengths, the measurement of which is the goal of the experiment. From these first data we derive a lower limit for the mean life of 0.8 fs at 90% confidence level.

Highlights

The study of electromagnetically bound hadronic pairs is an excellent method to probe QCD at very low energy
We have presented the first evidence for the production of π K -atoms by detecting 173 ± 54 atomic-pairs
The evidence is strengthened by the observation of correlated π K

Summary

Introduction

The study of electromagnetically bound hadronic pairs is an excellent method to probe QCD at very low energy. A measurement of the π K -atom ( Aπ K ) lifetime was proposed already in 1969 [7] to determine the difference |a1/2 − a3/2| of the s-wave π K -scattering lengths, where the indices 1/2 and 3/2 refer to the isospin of the π K -system. Pairs of oppositely charged mesons may interact and form electromagnetically bound systems Their subsequent ionization in the production target leads to mesons emerging from the target with low relative momentum (thereafter called atomic pairs). The mean life of the π K -atom can be calculated from the number of observed low-momentum pairs. This method was first proposed in 1985 [12]. In this Letter we report on the observation of π K -atoms from the first data with DIRAC-II

Experimental setup

Tracking and calibration

Data analysis

Conclusions