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Incoherent φ photo-production from deuteron in SPring-8/LEPS

Incoherent φ photo-production from deuteron in SPring-8/LEPS. M. Miyabe for LEPS collaborators RCNP Osaka University Baryons’10. C ontents. Physics overview Experiment Result and discussion Summary. q. _ q. . . N. Vector Meson Photo-production. Vector Meson Dominance

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Incoherent φ photo-production from deuteron in SPring-8/LEPS

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  1. Incoherent φphoto-production from deuteron in SPring-8/LEPS M. Miyabefor LEPS collaborators RCNP Osaka University Baryons’10

  2. Contents Baryons’10 Physics overview Experiment Result and discussion Summary

  3. q _ q   N Vector Meson Photo-production • Vector Meson Dominance • Pomeron Exchange • Meson Exchange _ qq =  Slowly increasing with energy Almost constant around threshold    (~ss) Decreasing with energy. Dominant at low energies N Baryons’10 uud

  4. Natural parity exchange Unnatural parity exchange P2: 2ndpomeron ~ 0+glueball (Nakano, Toki (1998)EXPAF97) photo-production near threshold Titov, Lee, Toki Phys.Rev C59(1999) 2993 =0 degree) Data from: SLAC('73), Bonn(’74),DESY(’78) It is important to distinguish the natural parity exchanges from unnatural ones Baryons’10

  5. Decay Plane //  natural parity exchange (-1)J (Pomeron, Scalar mesons) Decay Plane  unnatural parity exchange -(-1)J (Pseudo scalar mesons ) Polarization observables with linearly polarized photon In  meson rest frame K+  Polarization vector of  K-  K+ Relative contributions from natural, unnatural parity exchanges Decay angular distribution of  meson Baryons’10

  6.  P, glueball,  , f2’ p Decay Angular distribution ~ ρ3=0.5 for Pure natural parity exchange K decay plane angle Polarization angle of γ ~ ρ3=-0.5 Pure unnatural parity exchange 0   Baryons’10 - Prediction by A. Titov (PRC,2003)

  7. Result from LEPS with proton target E1 E1 E2 ~ ρ3=0.199+/-0.052 E2 ~ ρ3=0.189+/-0.030 • Non monotonic behavior around 2GeV. • Natural parity exchange is dominant 　→　0+ glueball? Pseudo scalar meson exchange is not negligible. T. Mibe, et al. PRL95 182001(2005) Baryons’10

  8. Explore the exotic process ~ Baryons’10 • Is the bump structure candidate of the exotic process (2nd Pomeron (glueball))? • The model based on Pomeron exchange and pseudo scalar exchange failed to explain such a non-monotonic behavior. This suggests that unknown natural parity process exist. • But natural parity exchange process is comparable to pseudo scalar exchange process from the value of ρ3. • To extract the natural parity process, detailed study for pseudo scalar π-η exchange is important. Study of incoherent photo-production from deuteron is unique tool for this purpose.

  9. φ photo-production from Deuteron • Coherent production • Interact with deuteron itself. Deuteron is iso-scalar target • Iso-vector π exchange is forbidden. • Pure natural parity exchange except for η-exchange process. • Incoherent production • Interact with proton or neutron in deuteron. • Estimation the neutron contribution. Baryons’10

  10. Incoherent production γ φ gφγ (π, η) π,η N N g(π, η)NN Baryons’10 • Due to isospin effect, • gπnn = - gπpp→ destructive • gηnn = gηpp→ constructive π-η interference effect • Detailed Information for unnatural (π/η) exchange process

  11. Differential cross section as a function of energy and angle. Due to πη interference effect, cross section from neutron decrease as low energy and forward angle. Baryons’10

  12. Decay asymmetry as a function of energy and η-exchange strength Eγ=2 GeV neutron neutron proton proton ~ Decay asymmetry Σφ=2ρ3 if η-exchange contribution is large --> Large difference in decay asymmetry Baryons’10

  13. Experiment Baryons’10

  14.  The LEPS beamline Baryons’10

  15. Dipole Magnet (0.7 T) TOF wall Start counter  Aerogel Cerenkov (n=1.03) MWDC 3 Silicon Vertex Detector MWDC 2 MWDC 1 LEPS spectrometer for charged particles K+ K- • Eγ~2.4GeV • Polarization ~95% • > 1 Mcps Liq. D2 1m Baryons’10

  16. result Baryons’10

  17. Invariant mass K+K- • Fit with Gaussian convoluted breit-weigner • Resolution~1.5MeV Cut point for invariant mass is +/-10MeV from peak position Total Φevent ~ 17k. Baryons’10

  18. Minimum momentum Pmin spectator approximation In quasi-free event, spectator nucleon has a small momentum such as fermi motion momentum φ γ Pγ Eγ PKK EKK Pmiss Emiss n n p In LAB system, the spectator momentum become minimum when the direction of proton and neutron is anti-parallel to pmiss p Pmiss Pmin n p PCM = Pmin Baryons’10

  19. Characteristics of Pmin • Quasi-free process makes a peak around zero. • coherent process • Pmin ~ +0.15 • Dominant Pmin≧0.1 • Other inelastic events are distributed at large negative value. MMD Deuteron Mass GeV GeV Pmin Baryons’10

  20. Differential cross section Red : incoherent γN→φN Black: free proton • Differential cross section at t=tmin • About 30% reduction from free proton • Not a simple nuclear density effect since deuteron is loosely bounded. dσ/dt(t=tmin) (μb) Transparency ratio Eγeff (GeV) Baryons’10 Lower Histogram Td = (dσ/dt)N/2*(dσ/dt)p

  21. Differential cross section in KKp mode Red : exclusive KKp event Black: free proton • Similar degree of reduction such as incoherent process • reduction of incoherent process is not only neutron. • π-ηinterference is small Td K- K+ n Not detect p detect Baryons’10 Lower Histogram Td = (dσ/dt)KKp/(dσ/dt)free p

  22. Spin density matrix element ~ ρ3as a function of Eγ ~ • ρ3N is little bit higher than free proton. • Theoretical prediction of ρ3n is 0.25~0.30. • ρ3N is 0.23~0.25 good agreement • Small difference ρ3p and ρ3n • η-exchange is small ~ ~ ~ ~ Eγeff (GeV) Red : γ+N→φ+N Black : γ+p→φ+p Baryons’10

  23. Summary ~ Baryons’10 • Non monotonic structure in cross section with Eγ increase at Deuteron target. • Differential cross section for incoherent φ photo-production shows a significant reduction from free proton • Some effect other than nuclear density is necessary. • Reduction is significant independent with coherent exclusion cut and Eγeff estimation. • From analysis for exclusive KKp event, • Reduction is not only neutron but also proton in deuteron. • π-η interference is small. • Decay asymmetry ρ3 is similar with free proton one • ηexchange component is weak. • Bump like structure around Eγ= 2GeV for γ+p→φ+p →Anothernatural parity process candidate to cancel out the increasing pseudo-scalarπ. • More statistic and new data is ready. • 2006~7 about 3 times event for proton and deuteron target. • 2009 ~10 maximum ~2.9GeV photon beam for proton. • detail analysis and extrapolate the energy region.

  24. Backup Baryons’10

  25. Differential cross section Red : incoherent γN→φN Black: free proton • Differential cross section at t=tmin • About 30% reduction from free proton • Not a simple nuclear density effect since deuteron is loosely bounded. dσ/dt(t=tmin) (μb) Td Eγeff (GeV) Baryons’10 Lower Histogram Td = (dσ/dt)N/2*(dσ/dt)p

  26. p p p p Vector Meson Photo-production M.A. Pichowsky and T.-S. H. Lee PRD 56, 1644 (1997) Prediction from Pomeron exchange Prediction from meson exchange Prediction : dominant contribution from pseudo scalar meson exchange near threshold Data from: LAMP2('83), DESY('76), SLAC('73), CERN('82), FNAL('79,'82), ZEUS('95,'96) Baryons’10

  27. Decay angular distribution of  meson  meson rest frame (Gottfried-Jackson(GJ) frame)  K+ K+ K+-pol p’ pol K+ z-axis Production plane K+ z  K- K- Decay plane direction of linear polarization Baryons’10

  28. Coherent production with deuteron • Deuteron is iso-scalar target • Iso-vector π exchange is forbidden. • Pure natural parity exchange except for η-exchange process. Baryons’10

  29. Result of coherent production off deuterons from LEPS Decay asymmetry Differential cross section W. Chang et al., Physics Letter B 658, 209 (2008). Differential cross section at t=tmin shows increasing with energy. Dashed line shows theoretical calculations. Decay asymmetry shows natural parity exchange is dominant Baryons’10

  30. Summary of results of coherent production Baryons’10 • Differential cross section • Increase with energy • Model prediction including Pomeron and η-exchange is under estimate. • No bump structure. • Decay asymmetry • Pure natural-parity exchange • η-exchangeis weak? Additional natural parity process is required!

  31. Linearly polarized Photon • Counts • Linear polarization • E(GeV) • E(Tagger) (GeV) • Backward Compton scattering by using UV laser light • Intensity (typ.) : 2.5 * 106 cps • Tagging Region : 1.5 GeV< E < 2.4 GeV • Linear Polarization : 95 % at 2.4 GeV Baryons’10

  32. Check for coherent exclusion • Without pmin cut. • Reduction is significant • Eγ< 2.0 GeV, coherent contamination is small. Baryons’10

  33. Exclusive KKp event in LH2 dσ/dt t=tmin (μb) Eγ Baryons’10

  34. |dσ/dt|N and |dσ/dt|KKP |dσ/dt|N /|dσ/dt|KKP |dσ/dt|N -|dσ/dt|KKP |dσ/dt|KKP Baryons’10 Eγeff (GeV)

  35. Spin density matrix elements 1-dimensional projections Relations to standard definition Baryons’10

  36. Baryons’10 Alvin KiswandhiPhys. Lett. B(2010)

  37. Comparison with proton Baryons’10

  38. The objectives of this thesis Baryons’10 Measure the Incoherent φ photo-production from deuteron target γ+N→φ+N. • Differential cross section(bump structure) • (π、η)-interference • Decay asymmetry • η-exchange process magnitude • Extract quasi-free γ+N→φ+N events clearly. • Explore in the bump structure observed in φphoto-production from free protons.

  39. Nuclear transparency ratio • TA=σA/(A*σN) (=Pout) • Mass number dependence is larger than theoretical calculation. • Large σφN in nuclear medium. • How about deuteron case? T. Ishikawa et al, Phys. Lett. B 608, 215 (2005) Baryons’10

  40. Summary of data taking • Trigger condition : TAG*UpVeto*STA*AC*TOF • Run period • (150mm-long LH2) 2002,May - 2002.July • (150mm-long LD2) 2002,July – 2003 Feb, Apr-Jun • Total number of trigger • 2.26*108 trigger • 4.64*108trigger Baryons’10

  41. φ Event selection Baryons’10 Number of reconstructed track ≧2 Particle identification of K+ and K- particles(PID) Decay in flight cut (DIF) Vertex cut to select events produced at the deuteron target. Tagger cut to select reconstructed track at Tagger Invariant Mass K+K- to select phi events Missing Mass cut to select γ + N → φX events.

  42. Particle identification and decay in flight cut Decay in flight cut • Consistency of TOF hit position • Difference of y-position of TOF ≦80mm • Difference TOF slat number ≦1 • Number of outlier • Noutl ≦ 6 • χ2 probability • Prob(χ2)≧0.02 Kaon identification is 4σ Baryons’10

  43. Vertex cut -1120. < Vertex z < 880. -30< Vertex(x,y) < 30 Baryons’10

  44. Missing Mass cut • Missing mass distribution for γ + p → φX (MMp) • Smearing due to the fermi motion effect. • Cut region for MMp with LD2 is 80 MeV. Baryons’10

  45. Summary of φselection Baryons’10

  46. Procedure analysis for quasi-free like Incoherent γ+N→φ+N production Baryons’10 • LEPS spectrometer has designed for forward φ→K+K- event • Exclusive γ+n→φ+n event can’t be accepted. • Precise analysis for • Coherent process • Final State Interaction(FSI) • Fermi motion effect • Fortunately, we have acceptance of exclusive γ+p→φ+p→K+K-p too.

  47. Energy Definitions For decay asymmetry 200MeV step For cross section 100MeV step Baryons’10

  48. Minimum momentum spectator approximation γ In quasi-free event, spectator nucleon has a small momentum such as fermi motion momentum Pγ Eγ PKK EKK φ Pmiss Emiss n n p p The momentum of pn system as Pmiss p In lab system, the missing momentum become minimum when the direction of proton and neutron is anti-parallel to pmiss n n p PCM Baryons’10

  49. Coherent production • Pcm ～　0 • Pmin～ γβMpn ～ 0.5 Pmiss • Positive momentum around > 0.1 GeV/c Baryons’10

  50. Pmin by Monte-Carlo simulation Pmin distribution in MC • Peak due to the quasi-free process is symmetricaround zero. σ～４４MeV • Coherent process • Dominant at Pmin > 0.1GeV • cut point is Pmin ~ 0.1GeV. GeV Baryons’10

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