Incoherent φ photo-production from deuteron in SPring-8/LEPS M. Miyabe for LEPS collaborators RCNP Osaka University Baryons’10

 Physics overview  Experiment  Result and discussion  Summary Contents 2010/12/7Baryons’10

Vector Meson Photo-production ● Vector Meson Dominance ● Pomeron Exchange ● Meson Exchange  N  q _q_q _ qq =  Decreasing with energy. Dominant at low energies Slowly increasing with energy Almost constant around threshold  N   (~ss) uud 2010/12/7Baryons’10

Titov, Lee, Toki Phys.Rev C59(1999) 2993 Data from: SLAC('73), Bonn(’74),DESY(’78) Natural parity exchange Unnatural parity exchange It is important to distinguish the natural parity exchanges from unnatural ones P 2 : 2 nd pomeron ~ 0 + glueball (Nakano, Toki (1998) EXPAF97)  =0 degree)  photo-production near threshold 2010/12/7Baryons’10

Polarization observables with linearly polarized photon Decay Plane //  natural parity exchange (-1) J (Pomeron, Scalar mesons) Polarization vector of  K+K+ K+K+ K-K- In  meson rest frame Decay Plane  unnatural parity exchange -(-1) J (Pseudo scalar mesons  )   Relative contributions from natural, unnatural parity exchanges Decay angular distribution of  meson 2010/12/7Baryons’10

Decay Angular distribution Prediction by A. Titov (PRC,2003) -- ρ 3 =-0.5 Pure unnatural parity exchange 0   P, glueball, , f 2 ’   p ρ 3 =0.5 for Pure natural parity exchange ~ ~ 2010/12/7 Baryons’10 Polarization angle of γ K decay plane angle

Result from LEPS with proton target Non monotonic behavior around 2GeV. Natural parity exchange is dominant → 0 + glueball ? Pseudo scalar meson exchange is not negligible. T. Mibe, et al. PRL (2005) ρ 3 =0.199+/ ρ 3 =0.189+/ E1 E2 ~ ~ 2010/12/7Baryons’10

 Is the bump structure candidate of the exotic process (2 nd 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 ρ 3.  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. Explore the exotic process ~ 2010/12/7Baryons’10

φ photo-production from Deuteron 1.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. 2.Incoherent production  Interact with proton or neutron in deuteron.  Estimation the neutron contribution. 2010/12/7Baryons’10

 Due to isospin effect,  g πnn = - g πpp → destructive  g ηnn = g ηpp → constructive π-η interference effect  Detailed Information for unnatural (π/η) exchange process Incoherent production g (π, η)NN g φγ (π, η) π,η φγ NN 2010/12/7Baryons’10

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. 2010/12/7Baryons’10

Decay asymmetry as a function of energy and η-exchange strength Decay asymmetry Σ φ =2ρ 3 Eγ=2 GeV if η-exchange contribution is large --> Large difference in decay asymmetry neutron proton neutron proton ~ 2010/12/7Baryons’10

EXPERIMENT 2010/12/7Baryons’10

The LEPS beamline  2010/12/7Baryons’10

LEPS spectrometer for charged particles 1m TOF wall MWDC 2 MWDC 3 MWDC 1 Dipole Magnet (0.7 T) Start counter Silicon Vertex Detector Aerogel Cerenkov (n=1.03)  K-K- K+K+ Eγ~2.4GeV Polarization ~95% > 1 Mcps 2010/12/7Baryons’10 Liq. D2

result 2010/12/7Baryons’10

Invariant mass K + K -  Fit with Gaussian convoluted breit-weigner  Resolution~1.5MeV Cut point for invariant mass is +/-10MeV from peak position Total Φ event ~ 17k. 2010/12/7Baryons’10

Minimum momentum P min spectator approximation P miss n p φ n p P CM γ P KK E KK Pγ Eγ P miss E miss In LAB system, the spectator momentum become minimum when the direction of proton and neutron is anti-parallel to p miss In quasi-free event, spectator nucleon has a small momentum such as fermi motion momentum n p P min = P min 2010/12/7Baryons’10

Characteristics of P min  Quasi-free process makes a peak around zero.  coherent process  P min ~  Dominant P min ≧ 0.1  Other inelastic events are distributed at large negative value. GeV MM D P min 2010/12/7Baryons’10 Deuteron Mass

Differential cross section  Differential cross section at t=t min  About 30% reduction from free proton  Not a simple nuclear density effect since deuteron is loosely bounded. Red : incoherent γN → φN Black: free proton Lower Histogram T d = (dσ/dt) N /2*(dσ/dt) p Eγ eff (GeV) dσ/dt(t=t min ) (μb) Transparency ratio 2010/12/7Baryons’10

Differential cross section in KKp mode  Similar degree of reduction such as incoherent process  reduction of incoherent process is not only neutron.  π-η interference is small Red : exclusive KKp event Black: free proton Lower Histogram T d = (dσ/dt) KKp /(dσ/dt) free p Td 2010/12/7Baryons’10 n p K+K+ K-K- detect Not detect

Spin density matrix element  ρ 3 N is little bit higher than free proton.  Theoretical prediction of ρ 3 n is 0.25~0.30.  ρ 3 N is 0.23~0.25 good agreement  Small difference ρ 3 p and ρ 3 n  η-exchange is small Red : γ+N → φ+N Black : γ+p → φ+p Eγ eff (GeV) ρ 3 as a function of Eγ ~ ~ ~ ~ ~~ 2010/12/7Baryons’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 Eγ eff estimation.  From analysis for exclusive KKp event,  Reduction is not only neutron but also proton in deuteron.  π-η interference is small.  Decay asymmetry ρ 3 is similar with free proton one  η exchange component is weak.  Bump like structure around Eγ= 2GeV for γ+p → φ+p → Another natural parity process candidate to cancel out the increasing pseudo-scalar π.  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. Summary ~ 2010/12/7Baryons’10

Backup 2010/12/7Baryons’10

Differential cross section  Differential cross section at t=t min  About 30% reduction from free proton  Not a simple nuclear density effect since deuteron is loosely bounded. Red : incoherent γN → φN Black: free proton Lower Histogram T d = (dσ/dt) N /2*(dσ/dt) p Eγ eff (GeV) dσ/dt(t=t min ) (μb) Td 2010/12/7Baryons’10

 p  p  p  p M.A. Pichowsky and T.-S. H. Lee PRD 56, 1644 (1997) Prediction from Pomeron exchange Prediction from meson exchange Data from: LAMP2('83), DESY('76), SLAC('73), CERN('82), FNAL('79,'82), ZEUS('95,'96) Prediction : dominant contribution from pseudo scalar meson exchange near threshold Vector Meson Photo-production 2010/12/7Baryons’10

 K+ K+K+ K-K-  p’  meson rest frame (Gottfried-Jackson(GJ) frame)  K+ K+K+ K-K-   pol Production plane z Decay plane z-axis  K+ -  pol    direction of linear polarization Decay angular distribution of  meson 2010/12/7Baryons’10

Coherent production with deuteron  Deuteron is iso-scalar target  Iso-vector π exchange is forbidden.  Pure natural parity exchange except for η-exchange process. 2010/12/7Baryons’10

Result of coherent production off deuterons from LEPS Differential cross sectionDecay asymmetry Differential cross section at t=t min shows increasing with energy. Dashed line shows theoretical calculations. Decay asymmetry shows natural parity exchange is dominant W. Chang et al., Physics Letter B 658, 209 (2008). 2010/12/7Baryons’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-exchange is weak? Additional natural parity process is required! Summary of results of coherent production 2010/12/7Baryons’10

Linearly polarized Photon Backward Compton scattering by using UV laser light Intensity (typ.) : 2.5 * 10 6 cps Tagging Region : 1.5 GeV< E  < 2.4 GeV Linear Polarization : 95 % at 2.4 GeV E  (Tagger) (GeV) E  (GeV) Counts Linear polarization 2010/12/7Baryons’10

Check for coherent exclusion  Without p min cut.  Reduction is significant  Eγ< 2.0 GeV, coherent contamination is small. 2010/12/7Baryons’10

Exclusive KKp event in LH2 Eγ dσ/dt t=tmin (μb) 2010/12/7Baryons’10

|dσ/dt| N and |dσ/dt| KKP |dσ/dt| N /|dσ/dt| KKP |dσ/dt| N -|dσ/dt| KKP Eγ eff (GeV) |dσ/dt| KKP 2010/12/7Baryons’10

Spin density matrix elements 1-dimensional projections Relations to standard definition 2010/12/7Baryons’10

Alvin Kiswandhi Phys. Lett. B(2010) 2010/12/7Baryons’10

Comparison with proton 2010/12/7Baryons’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 φ photo-production from free protons. The objectives of this thesis 2010/12/7Baryons’10

Nuclear transparency ratio  T A =σ A /(A*σ N ) (=P out )  Mass number dependence is larger than theoretical calculation.  Large σ φN in nuclear medium.  How about deuteron case? T. Ishikawa et al, Phys. Lett. B 608, 215 (2005) 2010/12/7Baryons’10

Summary of data taking ● Trigger condition : TAG*UpVeto*STA*AC*TOF ● Run period (150mm-long LH 2 )2002,May July (150mm-long LD2) 2002,July – 2003 Feb, Apr-Jun ● Total number of trigger 2.26*10 8 trigger 4.64*10 8 trigger 2010/12/7Baryons’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 → φ X events. φ Event selection 2010/12/7Baryons’10

Particle identification and 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 Decay in flight cut 2010/12/7Baryons’10

Vertex cut < Vertex z < < Vertex(x,y) < /12/7Baryons’10

Missing Mass cut  Missing mass distribution for γ + p → φ X (MMp)  Smearing due to the fermi motion effect.  Cut region for MMp with LD 2 is 80 MeV. 2010/12/7Baryons’10

Summary of φ selection 2010/12/7Baryons’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. Procedure analysis for quasi-free like Incoherent γ+N → φ+N production 2010/12/7Baryons’10

Energy Definitions For cross section 100MeV step For decay asymmetry 200MeV step 2010/12/7Baryons’10

Minimum momentum spectator approximation P miss n p n p φ n p P CM n p γ P KK E KK Pγ Eγ P miss E miss In lab system, the missing momentum become minimum when the direction of proton and neutron is anti-parallel to p miss The momentum of pn system as In quasi-free event, spectator nucleon has a small momentum such as fermi motion momentum 2010/12/7Baryons’10

Coherent production  P cm ～ 0  P min ～ γβM pn ～ 0.5 P miss  Positive momentum around > 0.1 GeV/c 2010/12/7Baryons’10

P min by Monte-Carlo simulation  Peak due to the quasi-free process is symmetric around zero. σ ～４４ MeV  Coherent process  Dominant at P min > 0.1GeV  cut point is P min ~ 0.1GeV. P min distribution in MC GeV 2010/12/7Baryons’10

Effective photon energy  Due to Fermi-motion, total energy of KKN system was smeared.  P min strongly correlated to z- component of fermi momentum inside deuteron.  P min could be used for estimating Fermi momenta of target nucleons.  Total center of mass energy s of KKN system Pmin vs. Fermi momentum z GeV P min Fermi momentum 2010/12/7Baryons’10

Conversion Eγ eff from Eγ  Effective photon energy Eγ eff as s is the center of mass total energy of KKN system.  Resolution for Eγ is improved. (~50%) Eγ resolution GeV 2010/12/7Baryons’10

Contamination of coherent process into incoherent process Real data(black) MC(blue/red) Contamination ratio of coherent to incoherent Contamination of coherent process is large at High energy region. less than 10% at P min ≦ 0.09 P min cut P min 2010/12/7Baryons’10

Validity check of P min cut-point for incoherent process slopeDifferential cross section Distributions are flat at |Pmin|=<0.09 except for E1 and E2. about 10% fluctuation from the tighter cut. P min cut E9 E8E7 E6E5 E4 E3E2 E1 E2 E1 E3 E4E5 E6 E7E8 2010/12/7Baryons’10

Conversion to effective photon flux Photon flux ω γ for each Eγ as ω γ (Eγ)=Frac(Eγ) ＊ N tag Frac(Eγ) : photon fraction for Eγ N tag : corrected tagger scalar count In nucleon at rest frame, At one specific Eγ eff, it depends on some Eγ which spread over because of fermi motion. Conversion ratio from each Eγ bin is calculated using Monte-Carlo. Eγ eff Eγ eff (GeV) P min <0.09 P min : all ωγωγ 2010/12/7Baryons’10

Conversion ratio  At one specific Eγ eff Conversion ratio from each Eγ bin  10 MeV bining for each Eγ eff and Eγ  Eγ resolution ~ 10MeV 2010/12/7Baryons’10

Estimate the Final state interaction  Momentum of outgoing nucleon is small, and FSI effect is enhanced near threshold.  Strength of FSI is enhanced in small relative momentum p and n. (similar kinematics in coherent) n p n φ γ p FSI enhancement factor pn relative momentum k k = |p n – p p |/2 2010/12/7Baryons’10

Monte Carlo simulation  Real data are fitted by distributions of coherent, inciherent and FSI processes produced by MC.  FSI contribution is very weak at all energy bin. << 1% Missing Mass distribution MM D Black :real, red coherent green: incoherent, blue: FSI GeV 2010/12/7Baryons’10

P-N relative momentum fit Data were fitted by results FSI and coherent prodeced by MC. χ2/ndf distribution as a function of FSI strength χ2 is better with smaller FSI effect. weak  FSI effect is negligible small GeV 2010/12/7Baryons’10

Background from non-resonant KK events  Backgrounds under the KK invariant mass spectrum are mainly from non-resonant KK events.  Estimate the background contamination into phi events by using the side band region Non-resonant K + K - invariant mass GeV 2010/12/7Baryons’10

Differential cross section t dependence. Fitting function : dσ/dt = C*exp(-b*t) (red curve) Slope parameter b as a function of Eγ eff nonmonotonic behavior of slope, Slope b = / (free proton b=3.38+/-0.23) GeV Eγ eff t (GeV 2 ) dσ/dt (μb) 2010/12/7Baryons’10

Energy dependence of differential cross section at t=t min  Cross section does not simply increase with energy at Eγ ～ 2.2 GeV dσ/dt at (t=t min ) with Constant slope b= /12/7Baryons’10

Differential cross section with tighter P min cut nonmonotonic behavior of slope, Slope b = / (free proton b=3.38+/-0.23) dσ/dt at (t=t min ) with b=3.45 t dependence P min ≦ 50 Cross section decreases at E1~E3 Eγ eff (GeV) dσ/dt(t=t min ) (μb) Black histogram : 90MeV, Red : 50MeV 2010/12/7Baryons’10

3-particle KKp mode  All particles (KKp) in the final state were detected to select the exclusive proton events.  The statistics is very limited but, the bump-like structure is seen as well as the results from free- proton target. dσ/dt at (t=t min ) with Constant slope b=3.38 dσ/dt(t=t min ) (μb) 2010/12/7Baryons’10

Decay angular distribution ρ 1~5 as a function of EγDecay angular distribution 2010/12/7Baryons’10

Differential cross section at Eγ  In the original Eγ, similar reduction appeared  Eγ ～ 1.9GeV  Photon flux is similar for both Eγ and Eγ eff. 2010/12/7Baryons’10

Eγ eff at KKp mode Eγ eff (KK) : calculated with K+K- Eγ eff (KKp) :calculated with K+K- p Estimation of Eγ eff works well. Eγ eff (KK) Eγ eff (KKp) 2010/12/7Baryons’10

Tighter P min cut Differential cross section at t=t min Red : incoherent γN → φN Black: free proton Red : γ+N → φ+N Black : γ+p → φ+p ρ 3 as a function of Eγ Decrease in Highest energy region Eγ eff (GeV) ρ3ρ3 Td dσ/dt(t=t min ) (μb) 2010/12/7Baryons’10

Backup figures 2010/12/7Baryons’10

Nuclear transparency ratio 2010/12/7Baryons’10

Eγ vs. Eγ(n) Eγ Eγ(n) 2010/12/7Baryons’10

Spin density matrix HorzVert 2010/12/7Baryons’10

Spin density matrix 2010/12/7Baryons’10

ρ Horz, VertHorz+Vert 2010/12/7Baryons’10

Spin density matrix element 2010/12/7Baryons’10

Spin density matrix element Vert Horz 2010/12/7Baryons’10

P min dependence slopeDifferential cross section 2010/12/7Baryons’10

Photon flux 2010/12/7Baryons’10

Photon flux 2010/12/7Baryons’10

Comparison to LEPS result 2010/12/7Baryons’10

Pmin<50MeV 2010/12/7Baryons’10

Tagger cut 2010/12/7Baryons’10

Coherent contamination 2010/12/7Baryons’10

Lambda(1520) 2010/12/7Baryons’10

Non-resonant BG 2010/12/7Baryons’10

2010/12/7Baryons’10 Experiment at Spring-8 8GeV electron storage ring Harima Hyogo

2010/12/7Baryons’10

Liquid hydrogen target 150mm 2010/12/7Baryons’10

Drift Chamber calibration  Depth of the multi hit TDC ~3 (before 8)  High Voltage value of sense wire is large.  Threshold for discri-amp is low.  Noisy level is high 2010/12/7Baryons’10

t 0 calibration  Large fluctuation in TDC offset value t 0.  Every 10 run calibration. DC-t 0 run dependence run tdc 2010/12/7Baryons’10

xt-calibration  X drift = c 1 t+c 2 t 2 +c 3 t 3 +c 4  Correct the origin-point  Calcurate parameters when resolution and efficiency are down 2010/12/7Baryons’10

Result of calibration Number of outlier Χ^2 probability LH2(short) LH2(long) 2010/12/7Baryons’10

2010/12/7Baryons’10

Decay angular distribution ● W 0,W 1,W 2 are parameterized by the 9 spin density matrix elements.     Re(    )                    Im(    ) and  Im(    ) Unpolarized part Polarized part K.Schilling et al. Nucl. Phys. B15(1970) /12/7Baryons’10

Final state interaction 2010/12/7Baryons’10