Photoproduction of vector mesons

Transcription

1 Meson Photoproduction at Intermediate and High Energies Messina November 2011 Photoproduction of vector mesons Valentina Vegna

2 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, (2010)

3 Total Cross Section Vector Mesons 10 2 thresholds Erbe DESY ABBHHM DESY Ballam SLAC 10! 0 + p $ & + p " (µb) Klein SAPHIR 1! + p $ # + p ABBHHM DESY Ballam SLAC Barth SAPHIR ABBHHM DESY! + p $ % + p Ballam Barth SLAC SAPHIR (GeV) E!

4 γ + p φ + p Status of the experimental results

5 Differential Cross Sections Diffractive behaviour Exchange in the t-channel SAPHIR: Barth et al., Eur. Phys. J. A 17, (2003) LEPS: Mibe et al., PRL 95, (2005)

6 Energy dependence of (dσ/dt) t=- tmin nonmonotonic behavior LEPS: Mibe et al., PRL 95, (2005)

7 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.

8 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.

9 Decay Angular Distributions SAPHIR: Barth et al., Eur. Phys. J. A 17, (2003) (Helicity frame) LEPS: Mibe et al., PRL 95, (2005) (Gottfired Jackson frame)

10 Decay Angular Distributions SAPHIR: Barth et al., Eur. Phys. J. A 17, (2003) (Helicity frame) Dominant contribution of natural parity exchange Pomeron exchange

11 Decay Angular Distributions SAPHIR: Barth et al., Eur. Phys. J. A 17, (2003) (Helicity frame) Not negligible contribution of unnatural parity exchange π 0 exchange

12 Decay Angular Distributions SAPHIR: Barth et al., Eur. Phys. J. A 17, (2003) (Helicity frame) LEPS: Mibe et al., PRL 95, (2005) (Gottfired Jackson frame) Not additional unnatural parity processes

13 Decay Angular Distributions SAPHIR: Barth et al., Eur. Phys. J. A 17, (2003) (Helicity frame) LEPS: Mibe et al., PRL 95, (2005) (Gottfired Jackson frame) Not additional unnatural parity processes No explanation for the energy dependent behavior

14 γ + p ω + p Status of the experimental results

15 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*

16 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/ v2 16 Apr 2001 pseudo-scalar Pomeron Born term N* excitation

17 Beam Asymmetry: experimental results GRAAL A.Ajaka et al. Phys. Rev. Lett 96, (2006) CBELSA/TAPS F.Klein et al. Phys. Rev. D 78, (2008)

18 Beam Asymmetry: theoretical results GIESSEN (2002) PRC GIESSEN (2002) PRC GIESSEN (2005) PRC Zhao (2005) PRC Bonn-Ga (2008) PRD Paris (2009) PRC

19 Decay Angular Distributions SAPHIR: Barth et al., Eur. Phys. J. A 18, (2003)

20 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, (2003) CLAS: Williams et al., PRC 80, (2009)

21 φ Perspectives for φ

22 Perspectives for φ φ γ + p φ + p New measurement of dσ/dt at 2 GeV

23 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

24 Perspectives for ω φ Measurement of dσ dt t =t min and of its energy dependence

25 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

26 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

27 Vector meson 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)