Münster 2002 – scientific programme
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HK: Physik der Hadronen und Kerne
HK 26: Electromagnetic and Hadronic Probes III
HK 26.6: Talk
Wednesday, March 13, 2002, 12:30–12:45, D
First results from the new pionic hydrogen experiment — •M. Hennebach1, D. F. Anagnostopoulos2, W. Breunlich3, H. Fuhrmann3, D. Gotta1, A. Gruber3, P. Indelicato4, Y.-W. Liu5, B. Manil4, V. Markushin5, N. Nelms6, A. J. Rusi El Hassani7, L. M. Simons5, and H. Zmeskal3 — 1IKP, FZ Jülich — 2Dept. of Mat. Science, Univ. of Ioannina — 3IMEP, Österr. Akademie der Wiss., Wien — 4Lab. Kastler-Brossel, UPMC Paris — 5PSI, Villigen — 6Univ. of Leicester — 7Dept. de Phys., Tanger, Morocco
A new high–precision measurement of the strong–interaction shift (є1s) and broadening (Γ1s) of the ground state in pionic hydrogen (π H) has been started at PSI. This experiment constitutes a direct measurement of the π N scattering lengths and is an important test of the methods of chiral perturbation theory (χPT).
Pions from the πE5 beam at PSI are slowed down into a cryogenic gas target installed inside the cyclotron trap to form pionic atoms. Resultant x–rays are reflected onto a large area CCD array by a Bragg spectrometer. є1s is derived by comparing the measured energy with a pure QED calculation; Γ1s is obtained after deconvolution of the crystal response function. Collision processes during the cascade of the pion through the atomic levels could skew the measured values - molecular formations of the form [(π−pp)p]ee could shift the measured energy, and Coulomb deexcitation will increase the width of the line. The possible influence of these collision processes is investigated by varying the target density. During the first production run, conducted in spring 2001, measurements ranged from 3 bar to liquid hydrogen (eqv. pressure ∼700 bar).