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SUMMARY:The pion-nucleon sigma term from pionic atoms
DTSTART;VALUE=DATE-TIME:20190624T144000Z
DTEND;VALUE=DATE-TIME:20190624T150500Z
DTSTAMP;VALUE=DATE-TIME:20260731T064455Z
UID:indico-contribution-66@indico.koza.if.uj.edu.pl
DESCRIPTION:Speakers: Avraham  Gal (Racah Institute of Physics\, The Hebre
 w University of Jerusalem)\nEarly work suggested that the in-medium pion-n
 ucleon threshold isovector amplitude b1 gets renormalized in pionic atoms 
 by about 30% away from its free-space value [1]. Weise attributed such ren
 ormalization to the leading low-density decrease of the in-medium quark co
 ndensate and the pion decay constant in terms of the pion-nucleon sigma te
 rm [2]. Subsequent work triggered by data from `deeply bound states' in pi
 onic atoms supported this idea [3]. Accepting the validity of this approac
 h\, we extracted the pion-nucleon sigma term from a large-scale fit of pio
 nic-atom level shift and width data across the periodic table. Our fitted 
 value for sigma is (57+/-7) MeV and is robust with respect to variation of
  pion-nucleon interaction terms other than b1 [4]. This value of sigma agr
 ees with values obtained in several recent studies based on near-threshold
  pion-nucleon phenomenology [5]\, but sharply disagrees with values obtain
 ed in recent direct lattice QCD calculations [6]. \n\n[1] Reviewed by C.J.
  Batty\, E. Friedman\, A. Gal\, Phys. Rep. 287 (1997) 385. \n[2] W. Weise\
 , Acta Phys. Pol. B 31 (2000) 2715\, Nucl. Phys. A 690 (2001) 98c. \n[3] R
 eviewed by E. Friedman\, A. Gal\, Phys. Rep. 452 (2007) 89. \n[4] E. Fried
 man\, A. Gal\, Phys. Lett. B 792 (2019) 340. \n[5] Reviewed by J. Ruiz de 
 Elvira\, et al.\, J. Phys. G 45 (2018) 024001. \n[6] Reviewed by N. Yamana
 ka\, et al. (JLQCD)\, Phys. Rev. D 98 (2018) 054516.\n\nhttps://indico.koz
 a.if.uj.edu.pl/event/1/contributions/66/
LOCATION:Collegium Maius
URL:https://indico.koza.if.uj.edu.pl/event/1/contributions/66/
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