/ hep-ex arXiv:1405.6377


Measurement of the charged-pion polarisability


Adolph, C. (Erlangen - Nuremberg U.) ; Akhunzyanov, R. (Dubna, JINR) ; Alexeev, M.G. (Turin U.) ; Alexeev, G.D. (Dubna, JINR) ; Amoroso, A. (INFN, Turin) ; Andrieux, V. (DAPNIA, Saclay) ; Anosov, V. (Dubna, JINR) ; Austregesilo, A. (Munich, Tech. U.) ; Badelek, B. (Warsaw U.) ; Balestra, F. (INFN, Turin) ; Barth, J. (Bonn U.) ; Baum, G. (Bielefeld U.) ; Beck, R. (Bonn U., HISKP) ; Bedfer, Y. (DAPNIA, Saclay) ; Berlin, A. (Ruhr U., Bochum) ; Bernhard, J. (Mainz U., Inst. Kernphys.) ; Bicker, K. (Munich, Tech. U.) ; Bieling, J. (Bonn U.) ; Birsa, R. (INFN, Trieste) ; Bisplinghoff, J. (Bonn U., HISKP) ; Bodlak, M. (Charles U.) ; Boer, M. (DAPNIA, Saclay) ; Bordalo, P. (Lisbon, IST) ; Bradamante, F. (INFN, Trieste) ; Braun, C. (Erlangen - Nuremberg U.) ; Bressan, A. (INFN, Trieste) ; Buchele, M. (Freiburg U.) ; Burtin, E. (DAPNIA, Saclay) ; Capozza, L. (DAPNIA, Saclay) ; Chiosso, M. (INFN, Turin) ; Chung, S.U. (Brookhaven) ; Cicuttin, A. (INFN, Trieste) ; Colantoni, M. (INFN, Turin) ; Crespo, M.L. (INFN, Trieste) ; Curiel, Q. (DAPNIA, Saclay) ; Dalla Torre, S. (INFN, Trieste) ; Dasgupta, S.S. (Matrivani Inst., Calcutta) ; Dasgupta, S. (INFN, Trieste) ; Denisov, O.Yu. (INFN, Turin) ; Dinkelbach, A.M. (Munich, Tech. U.) ; Donskov, S.V. (Kurchatov Inst., Moscow) ; Doshita, N. (Yamagata U.) ; Duic, V. (Trieste U.) ; Dunnweber, W. (Munich U.) ; Dziewiecki, M. (Warsaw U. of Tech.) ; Efremov, A. (Dubna, JINR) ; Elia, C. (INFN, Trieste) ; Eversheim, P.D. (Bonn U., HISKP) ; Eyrich, W. (Erlangen - Nuremberg U.) ; Faessler, M. (Munich U.) ; Ferrero, A. (DAPNIA, Saclay) ; Filin, A. (Kurchatov Inst., Moscow) ; Finger, M. (Charles U.) ; M. Finger jr (Charles U.) ; Fischer, H. (Freiburg U.) ; Franco, C. (Lisbon, LIFEP) ; von Hohenesche, N. du Fresne (CERN) ; Friedrich, J.M. (Munich, Tech. U.) ; Frolov, V. (CERN) ; Gautheron, F. (Ruhr U., Bochum) ; Gavrichtchouk, O.P. (Dubna, JINR) ; Gerassimov, S. (Munich, Tech. U.) ; Geyer, R. (Munich U.) ; Gnesi, I. (INFN, Turin) ; Gobbo, B. (INFN, Trieste) ; Goertz, S. (Bonn U.) ; Gorzellik, M. (Freiburg U.) ; Grabmuller, S. (Munich, Tech. U.) ; Grasso, A. (INFN, Turin) ; Grube, B. (Munich, Tech. U.) ; Grussenmeyer, T. (Freiburg U.) ; Guskov, A. (Dubna, JINR) ; Guthorl, T. (Freiburg U.) ; Haas, F. (Munich, Tech. U.) ; von Harrach, D. (Mainz U., Inst. Kernphys.) ; Hahne, D. (Bonn U.) ; Hashimoto, R. (Yamagata U.) ; Heinsius, F.H. (Freiburg U.) ; Herrmann, F. (Freiburg U.) ; Hinterberger, F. (Bonn U., HISKP) ; Hoppner, Ch. (Munich, Tech. U.) ; Horikawa, N. (Chubu U.) ; d'Hose, N. (DAPNIA, Saclay) ; Huber, S. (Munich, Tech. U.) ; Ishimoto, S. (KEK, Tsukuba) ; Ivanov, A. (Dubna, JINR) ; Ivanshin, Yu. (Dubna, JINR) ; Iwata, T. (Yamagata U.) ; Jahn, R. (Bonn U., HISKP) ; Jary, V. (Prague, Tech. U.) ; Jasinski, P. (Mainz U., Inst. Kernphys.) ; Jorg, P. (Freiburg U.) ; Joosten, R. (Bonn U., HISKP) ; Kabuss, E. (Mainz U., Inst. Kernphys.) ; Ketzer, B. (Bonn U.) ; Khaustov, G.V. (Kurchatov Inst., Moscow) ; Khokhlov, Yu. A. (Moscow, MIPT) ; Kisselev, Yu. (Dubna, JINR) ; Klein, F. (Bonn U.) ; Klimaszewski, K. (Warsaw, Inst. Nucl. Studies) ; Koivuniemi, J.H. (Ruhr U., Bochum) ; Kolosov, V.N. (Kurchatov Inst., Moscow) ; Kondo, K. (Yamagata U.) ; Konigsmann, K. (Freiburg U.) ; Konorov, I. (Munich, Tech. U.) ; Konstantinov, V.F. (Kurchatov Inst., Moscow) ; Kotzinian, A.M. (INFN, Turin) ; Kouznetsov, O. (Dubna, JINR) ; Kramer, M. (Munich, Tech. U.) ; Kroumchtein, Z.V. (Dubna, JINR) ; Kuchinski, N. (Dubna, JINR) ; Kuhn, R. (Munich, Tech. U.) ; Kunne, F. (DAPNIA, Saclay) ; Kurek, K. (Warsaw, Inst. Nucl. Studies) ; Kurjata, R.P. (Warsaw U. of Tech.) ; Lednev, A.A. (Kurchatov Inst., Moscow) ; Lehmann, A. (Erlangen - Nuremberg U.) ; Levillain, M. (DAPNIA, Saclay) ; Levorato, S. (INFN, Trieste) ; Lichtenstadt, J. (Tel Aviv U.) ; Maggiora, A. (INFN, Turin) ; Magnon, A. (DAPNIA, Saclay) ; Makke, N. (INFN, Trieste) ; Mallot, G.K. (CERN) ; Marchand, C. (DAPNIA, Saclay) ; Martin, A. (INFN, Trieste) ; Marzec, J. (Warsaw U. of Tech.) ; Matousek, J. (Charles U.) ; Matsuda, H. (Yamagata U.) ; Matsuda, T. (Miyazaki U.) ; Meshcheryakov, G. (Dubna, JINR) ; Meyer, W. (Ruhr U., Bochum) ; Michigami, T. (Yamagata U.) ; Mikhailov, Yu. V. (Kurchatov Inst., Moscow) ; Miyachi, Y. (Yamagata U.) ; Moinester, M.A. (Tel Aviv U.) ; Nagaytsev, A. (Dubna, JINR) ; Nagel, T. (Munich, Tech. U.) ; Nerling, F. (Mainz U., Inst. Kernphys.) ; Neubert, S. (Munich, Tech. U.) ; Neyret, D. (DAPNIA, Saclay) ; Nikolaenko, V.I. (Kurchatov Inst., Moscow) ; Novy, J. (Prague, Tech. U.) ; Nowak, W.D. (Freiburg U.) ; Nunes, A.S. (Lisbon, LIFEP) ; Olshevsky, A.G. (Dubna, JINR) ; Orlov, I. (Dubna, JINR) ; Ostrick, M. (Mainz U., Inst. Kernphys.) ; Panknin, R. (Bonn U.) ; Panzieri, D. (INFN, Turin) ; Parsamyan, B. (INFN, Turin) ; Paul, S. (Munich, Tech. U.) ; Peshekhonov, D. (Dubna, JINR) ; Platchkov, S. (DAPNIA, Saclay) ; Pochodzalla, J. (Mainz U., Inst. Kernphys.) ; Polyakov, V.A. (Kurchatov Inst., Moscow) ; Pretz, J. (Aachen, Tech. Hochsch.) ; Quaresma, M. (Lisbon, LIFEP) ; Quintans, C. (Lisbon, LIFEP) ; Ramos, S. (Lisbon, IST) ; Regali, C. (Freiburg U.) ; Reicherz, G. (Ruhr U., Bochum) ; Rocco, E. (CERN) ; Rossiyskaya, N.S. (Dubna, JINR) ; Ryabchikov, D.I. (Kurchatov Inst., Moscow) ; Rychter, A. (Warsaw U. of Tech.) ; Samoylenko, V.D. (Kurchatov Inst., Moscow) ; Sandacz, A. (Warsaw, Inst. Nucl. Studies) ; Sarkar, S. (Matrivani Inst., Calcutta) ; Savin, I.A. (Dubna, JINR) ; Sbrizzai, G. (INFN, Trieste) ; Schiavon, P. (INFN, Trieste) ; Schill, C. (Freiburg U.) ; Schluter, T. (Munich U.) ; Schmidt, K. (Freiburg U.) ; Schmieden, H. (Bonn U.) ; Schonning, K. (CERN) ; Schopferer, S. (Freiburg U.) ; Schott, M. (CERN) ; Shevchenko, O.Yu. (Dubna, JINR) ; Silva, L. (Lisbon, LIFEP) ; Sinha, L. (Matrivani Inst., Calcutta) ; Sirtl, S. (Freiburg U.) ; Slunecka, M. (Dubna, JINR) ; Sosio, S. (INFN, Turin) ; Sozzi, F. (INFN, Trieste) ; Srnka, A. (Inst. Sci. Instruments, Brno) ; Steiger, L. (INFN, Trieste) ; Stolarski, M. (Lisbon, LIFEP) ; Sulc, M. (Liberec Tech. U.) ; Sulej, R. (Warsaw, Inst. Nucl. Studies) ; Suzuki, H. (Chubu U.) ; Szabelski, A. (Warsaw, Inst. Nucl. Studies) ; Szameitat, T. (Freiburg U.) ; Sznajder, P. (Warsaw, Inst. Nucl. Studies) ; Takekawa, S. (INFN, Turin) ; Wolbeek, J. ter (Freiburg U.) ; Tessaro, S. (INFN, Trieste) ; Tessarotto, F. (INFN, Trieste) ; Thibaud, F. (DAPNIA, Saclay) ; Uhl, S. (Munich, Tech. U.) ; Uman, I. (Munich U.) ; Virius, M. (Prague, Tech. U.) ; Wang, L. (Ruhr U., Bochum) ; Weisrock, T. (Mainz U., Inst. Kernphys.) ; Wilfert, M. (Mainz U., Inst. Kernphys.) ; Windmolders, R. (Bonn U.) ; Wollny, H. (DAPNIA, Saclay) ; Zaremba, K. (Warsaw U. of Tech.) ; Zavertyaev, M. (Lebedev Inst.) ; Zemlyanichkina, E. (Dubna, JINR) ; Ziembicki, M. (Warsaw U. of Tech.) ; Zink, A. (Erlangen - Nuremberg U.)

Pages: 9

Abstract: The COMPASS collaboration at CERN has investigated pion Compton scattering, $\pi^-\gamma\rightarrow \pi^-\gamma$, at centre-of-mass energy below 3.5 pion masses. The process is embedded in the reaction $\pi^-\mathrm{Ni}\rightarrow\pi^-\gamma\;\mathrm{Ni}$, which is initiated by 190 GeV pions impinging on a nickel target. The exchange of quasi-real photons is selected by isolating the sharp Coulomb peak observed at smallest momentum transfers, $Q^2<0.0015$ (GeV/$c$)$^2$. From a sample of 63000 events, the electric pion polarisability is determined to be $\alpha_\pi\ =\ (\,2.0\ \pm\ 0.6_{ stat}\ \pm\ 0.7_{ syst}\,)\ \times 10^{-4}\,\mbox{fm}^3$ under the assumption $\alpha_\pi=-\beta_\pi$ that relates the electric and magnetic dipole polarisabilities. This result is in tension with previous dedicated measurements, while it is found in agreement with the expectation from chiral perturbation theory. An additional measurement replacing pions by muons, for which the cross-section behavior is unambigiously known, was performed for an independent estimate of the systematic uncertainty.

Web-Page: http://inspirehep.net/record/1298026/files/fig1a.png; http://inspirehep.net/record/1298026/files/fig1b.png; http://inspirehep.net/record/1298026/files/fig1c.png; http://inspirehep.net/record/1298026/files/fig1d.png; http://inspirehep.net/record/1298026/files/fig2.png; http://inspirehep.net/record/1298026/files/fig3.png; http://inspirehep.net/record/1298026/files/arXiv:1405.6377.pdf


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