Meson Photoproduction at Intermediate and High Energies Messina 10-11 November 2011 Photoproduction of vector mesons Valentina Vegna
Vector Mesons quark content: " 0 : uu # dd 2 " + : ud " # : u d quark content: " : ss quark content: " : uu + dd 2 Particle Data Group, J. Phys. G 37, 075021 (2010)
Total Cross Section Vector Mesons 10 2 thresholds Erbe (1968) @ DESY ABBHHM (1968) @ DESY Ballam (1973) @ SLAC 10! 0 + p $ & + p " (µb) Klein (1998) @ SAPHIR 1! + p $ # + p ABBHHM (1968) @ DESY Ballam (1973) @ SLAC Barth (2003) @ SAPHIR ABBHHM (1968) @ DESY! + p $ % + p Ballam Barth (1973) @ SLAC (2003) @ SAPHIR 0 1 2 3 4 5 6 (GeV) E!
γ + p φ + p Status of the experimental results
Differential Cross Sections Diffractive behaviour Exchange in the t-channel SAPHIR: Barth et al., Eur. Phys. J. A 17, 269-274 (2003) LEPS: Mibe et al., PRL 95, 182001 (2005)
Energy dependence of (dσ/dt) t=- tmin nonmonotonic behavior LEPS: Mibe et al., PRL 95, 182001 (2005)
Decay Angular Distributions The quantization axis z is defined as the direction of the photon in the Φ rest frame The G-J system is used to test the t-channel helicity conservation which implies that the spin of Φ is aligned along the direction of the photon.
Decay Angular Distributions The quantization axis z is defined as the direction of the photon in the Φ rest frame The G-J system is used to test the t-channel helicity conservation which implies that the spin of Φ is aligned along the direction of the photon. The quantization axis z points into the direction of Φ in the CMS The H system is used to test the s- channel helicity conservation.
Decay Angular Distributions SAPHIR: Barth et al., Eur. Phys. J. A 17, 269-274 (2003) (Helicity frame) LEPS: Mibe et al., PRL 95, 182001 (2005) (Gottfired Jackson frame)
Decay Angular Distributions SAPHIR: Barth et al., Eur. Phys. J. A 17, 269-274 (2003) (Helicity frame) Dominant contribution of natural parity exchange Pomeron exchange
Decay Angular Distributions SAPHIR: Barth et al., Eur. Phys. J. A 17, 269-274 (2003) (Helicity frame) Not negligible contribution of unnatural parity exchange π 0 exchange
Decay Angular Distributions SAPHIR: Barth et al., Eur. Phys. J. A 17, 269-274 (2003) (Helicity frame) LEPS: Mibe et al., PRL 95, 182001 (2005) (Gottfired Jackson frame) Not additional unnatural parity processes
Decay Angular Distributions SAPHIR: Barth et al., Eur. Phys. J. A 17, 269-274 (2003) (Helicity frame) LEPS: Mibe et al., PRL 95, 182001 (2005) (Gottfired Jackson frame) Not additional unnatural parity processes No explanation for the energy dependent behavior
γ + p ω + p Status of the experimental results
Theoretical motivations Searching for the missing resonances Width = 8.49 MeV I = 0 Clean detection of the ω over the background Filter of resonances: N*
Differential Cross Sections SAPHIR (1998) SLAC (1973) R.W. Clifft et al. (1977) Y.Oh, A.I.Titov and T.-S.H.Lee arxiv:nucl-th/0104046 v2 16 Apr 2001 pseudo-scalar Pomeron Born term N* excitation
Beam Asymmetry: experimental results GRAAL A.Ajaka et al. Phys. Rev. Lett 96, 132003 (2006) CBELSA/TAPS F.Klein et al. Phys. Rev. D 78, 117101 (2008)
Beam Asymmetry: theoretical results GIESSEN (2002) PRC 66 055212 GIESSEN (2002) PRC 66 055212 GIESSEN (2005) PRC 71 055206 Zhao (2005) PRC 71 054004 Bonn-Ga (2008) PRD 78 117101 Paris (2009) PRC 79 025208
Decay Angular Distributions SAPHIR: Barth et al., Eur. Phys. J. A 18, 117-127 (2003)
Decay Angular Distributions Adair Frame: The quantization axis z is defined as the direction of the photon in the CM frame SAPHIR: Barth et al., Eur. Phys. J. A 18, 117-127 (2003) CLAS: Williams et al., PRC 80, 065208 (2009)
φ Perspectives for φ
Perspectives for φ φ γ + p φ + p New measurement of dσ/dt at 2 GeV
Perspectives for φ φ γ + p φ + p New measurement of dσ/dt at 2 GeV γ + n( p) φ + n(p) Measurement of: dσ dt decay angular distribution
Perspectives for ω φ Measurement of dσ dt t =t min and of its energy dependence
Perspectives for ω φ γ + p ω + p Study of the decay angular distribution with a polarized photon beam (Gottfried-Jackson frame) Measurement of dσ dt t =t min and of its energy dependence
Perspectives for ω φ γ + p ω + p Study of the decay angular distribution with a polarized photon beam (Gottfried-Jackson frame) Measurement of dσ dt t =t min γ + n( p) ω + n(p) No published results! and of its energy dependence
Vector meson photoproduction @ BGO-OD φ K + K forward spectrometer (O.D. + Drift Chambers + ToF) ω π 0 γ ω π + π π 0 BGO detector forward spectrometer (O.D + Drift Chambers + ToF)