3-10 August 2016
Chicago IL USA
US/Central timezone
There is a live webcast for this event.

First observation of π-K+ and π+K- atoms, their lifetime measurement and πK scattering lengths evaluation. (12' + 3')

6 Aug 2016, 15:15
Ontario ()


Oral Presentation Strong Interactions and Hadron Physics Strong Interactions and Hadron Physics


Leonid Afanasyev (Joint Inst. for Nuclear Research (RU))


The Low Energy QCD allows to calculate the π-π and π-K scattering lengths with high precision. There are accurate relations between these scattering lengths and π+-π-, π-K+, π+K- atoms lifetimes. The experiment on the first observation of π-K+ and π+K- atoms is described and results are presented. The atoms were generated on Ni and Pt targets hit by the PS CERN proton beam with momentum P=24 GeV/c. Moving in the target, part of atoms break up producing characteristic π-K pairs (atomic pairs) with small relative momentum Q in their c.m.s. In the experiment, we detected na=345+-61 (5.7 standard deviations) π-K+ and π+K- atomic pairs. The main part of π-K pairs are produced in free state. The majority of particles in these pairs are generated directly or from short-lived sources as rho, omega and similar resonances. The electromagnetic interactions in the final state create Coulomb pairs with a known dependence on Q of the number of pairs. This effect allows to evaluate the number of these Coulomb pairs. There is a precise ratio (~1%) between the number of π-K+ (π+K-) Coulomb pairs with small Q and the number of produced π-K+ (π+K-) atoms. Using this ratio, we obtained the numbers of generated π-K+ and π+K- atoms Na=1200+-80 in total. The breakup probability Pbr=na/Na depends on the atom lifetime. Using for Ni and Pt targets this dependence, known with a precision about 1%, the πK atom lifetime was measured and from its value the πK scattering lengths were evaluated. The presented analysis shows that the π-K+ and π+K- atoms production in the p-nucleus interactions increases by 16 and 38 times respectively if the proton momentum P is increased from 24 GeV/c up to 450 GeV/c.

Primary authors

Leonid Afanasyev (Joint Inst. for Nuclear Research (RU)) Prof. Leonid Nemenov (JINR)

Presentation Materials

Your browser is out of date!

Update your browser to view this website correctly. Update my browser now