The Search for Exotic Mesons in Photoproduction. Diane Schott

Transcription

1 The Search for Exotic Mesons in Photoproduction Diane Schott

2 Purpose The constituent quark model gives initial set of mesons formed by qq pairs. It is described by simplest QCD bound state. QCD allows for additional states known as exotics: qqḡ, qq qq, ggg,... Production of exotics is fundamental to low-energy QCD.

3 Purpose Constituent Quark Model accounts for qq pairs. Allowed states: J PC = 0 ++, 0 -+, 1 ++, 1 +-, 2 ++, Forbidden states: J PC = 0 --,0 +-,1 -+,1 --,2 +-,...

4 Partial Wave Analysis Maximum Likelihood fit of the intensity: X I( ) = X, 0 V A V 0 A 0 α is the set {J, P, M, L, I, λ, S} used to describe the resonance X. γ ε Vα ε Aα re-scattering X η π ε is the reflectivity is + or - and is related to the sign of M, where M is the projection of J in z direction. A = (M)(A M P ( 1) J M A M ) N N

5 Partial Wave Analysis The reaction is a series of 2 body reactions with no re-scattering. Decays resulting in more than 2 final states are expressed as a series of 2 body decays π ε Aα = ε Aα (X Iπ) ε Aα (I ππ) γ ε Vα ε Aα I π X π N N

6 PWA: Quantities of Interest From the PWA we get a set of complex ε Vα and have the normalization integral. From this the yield (N) can be calculated for a given wave or wave set. tan( )= Im( V V 0 ) Re( V V 0 ) Phase differences will show interferences between 2 waves with no dependence on the strength of the waves. N = N 0 N r N X,, 0 V V 0 0

7 Previous Results: π1(1400) π1 At Brookhaven, E852 collaboration: π - p π - η p (18.3 GeV) M = 1370 ±16 MeV a2 Γ = 385 ± 40 MeV Published a mass and width of the π1(1400). This was followed by the ηπ 0 analysis but no consistent set of amplitude parameters were found.

8 Previous Results: π1(1600) At Brookhaven, E852 collaboration: π - p ρ π - p (18.3 GeV) M = 1593 ±8 MeV Γ = 168 ± 20 MeV Published a mass and width of the π1(1600).

9 Previous Results: π1(1600) At Brookhaven, E852 collaboration: π - p ρ π - p (18.3 GeV) M = 1593 ±8 MeV Γ = 168 ± 20 MeV Published a mass and width of the π1(1600).

10 Previous Results: Summary Other states π1(2000) seen in b1π, f1π * C. Amsler. Mesons beyond the naive quark model. Physics Reports, 387:61 117, (2004).

11 Photoproduction Beams of photons may be a more natural way to create hybrid mesons. Simple QN counting leads to the exotic mesons quarksj PC gluonicflux J PC =0 +, 1 +, 2 +,... quarksj PC gluonicflux J PC =1, 1 ++

12 g12 Is a photoproduction experiment Ran in 2008 for 3 months A 5.7 GeV e - beam was used to get a maximum of 5.45 GeV photons. Triggers: 26 billion (68 pb -1 )

13 PWA in G12 Finished: π + π + π (by Craig Bookwalter) ηπ - (by Diane Schott) Pending analysis: π 0 π + π (by FSU) K + K - (by FSU and CNU)

14 π + π + π g12 - π + π + π γ X = a 2 (1320),π 2 (1670)... Y = ρ(770),f 2 (1270)... X π + π + Y π π, ρ p n

15 π + π + π PWA: Mass Independent Fit The allowed wave set is M( + + )(GeV/c 2 ) Entries: quark model - J PC = 0 ++, 2 ++ exotic wave - J PC = 1 -+ Counts per 5 MeV/c M( + + )(GeV/c 2 )

16 π + π + π PWA: Mass Independent Fit ± [ (770) ] Intensity D Events per 20 MeV/c a D M( + + )(MeV/c 2 )

17 π + π + π PWA: Mass Independent Fit ± [ ] S Intensity S Events per 20 MeV/c a S M( + + )(MeV/c 2 )

18 Events per 20 MeV/c 2 PWA: Mass Dependent Fit Mass-Dependent Fit to S A =1.4e+05 ±51.4 M =1198 ±0.1 =289.8 ±0.201 Inital 2 : 1.42e+07 Final 2 : 9.61e+05 Total events: 1.25e+08 PDG: radians per 20 MeV/c 2 a1 M = 1230 ± 40 MeV Γ = MeV Mass-Dependent Fit: S D M( + + )(MeV/c 2 ) Events per 20 MeV/c Mass-Dependent Fit: D Intensity A =4.79e+05 ±88.2 M =1309 ± =108.7 ± Inital 2 : 1.42e+07 Final 2 : 9.61e+05 Total events: 1.62e+08 PDG: π + π + π a2 M = 1316 MeV Γ = 107 MeV M( + + )(MeV/c 2 ) M( + + )(MeV/c 2 )

19 π + π + π PWA: Mass Independent Fit [f 2 (1270) ] S Intensity S Events per 20 MeV/c S S π2(1670) M( + + )(GeV/c 2 )

20 π + π + π PWA: Mass Independent Fit [ ] P Intensity Events per 20 MeV/c M( + + )(MeV/c 2 )? Events per 20 MeV/c [ ] P Intensity? M( + + )(MeV/c 2 )

21 π + π + π PWA: Mass Independent Fit No evidence for exotic 1 -+ phase motion Phase motion consistent with resonating 2 -+

22 ηπ - g12 - ηπ- η γ X π π p ++ π + p

23 ηπ - PWA: Mass Independent Fit The allowed wave set is M(ηπ - ) 200 Entries = qqḡ quark model - J PC = 0 ++, 2 ++ qq a 2 exotic wave - J PC = 1 -+ Bin Width = 0.05 GeV a M(ηπ )(GeV) M(ηπ-)

24 ηπ - PWA: Mass Independent Fit J PC m= , J PC m = M(ηπ-) The strongest contribution is from the D wave. M(ηπ-) The S wave shows a broad background with 1/2 the intensity of the D wave. The P waves shows no bump and is roughly 1/5 of the D wave.

25 ηπ - PWA: Mass Independent Fit J PC m= , J PC m = a2 M(ηπ-) The strongest contribution is from the D wave. M(ηπ-) The S wave shows a broad background with 1/2 the intensity of the D wave. The P waves shows no bump and is roughly 1/5 of the D wave.

26 ηπ - Mass Dependent Fit Used relativistic BW amplitudes to fit the partial wave intensity and phase together using a χ 2 fit. Includes error matrix calculated from PWA. mass: 1.32 ± 0.01 GeV a2 width: 0.14 ± 0.01 GeV PDG values: mass: ± GeV width: ± GeV

27 ηπ - Mass Dependent Fit Included π1 with a2 a2 mass: ± GeV a2 a2 width: ± GeV π1 mass: 1.39 ± 0.23 GeV π1 width: 0.58 ± 0.05 GeV

28 ηπ - Mass Dependent Fit included π1 with a2 a2 mass: ± GeV a2 width: ± GeV π1 mass: 1.39 ± 0.23 GeV π1 width: 0.58 ± 0.05 GeV Results of the fit varied greatly. The best fit for the π1 resulted in large errors for the mass and a width broader than the pion production value.

29 ηπ - Ratio of π1 to a2 From yields using E852 mass and width: Na2: Nπ1: (fit + 2 sigma) ( p! ++ 1 ) = 0.35 (CL of 95.4 %) ( p! ++ a 2 ) From the sum of the partial wave intensity, over the mass range: Na2: 49,518 ±7090 ±2652 Nπ1: 14,686 ±4674 ±9008 Where first is the statistical uncertainty is calculated by the sum of the squares of the error bars of the yields and second is the systematic uncertainty is calculated from the results of multiple PWA results ( p! ++ 1 ) = 0.30 (±0.21) ( p! ++ a 2 )

30 ηπ - Summary Theory has predicted photoproduction of π1 to be comparable to the a2. The PWA of the M(ηπ - ) resulted in: The wave set to be dominated by the 2 ++ partial wave coinciding with the a2 The 1 -+ partial wave intensity shows no structure The phase difference between 1 -+ and 2 ++ shows a shift The fits of the PWA intensity and phase difference resulted in the fit of the a2 but not of the π1.

31 Conclusion CLAS-g12 acquired photoproduction data for 3π and ηπ Performed mass independent PWA from GeV/c 2 Fit PWA yields and phases for resonance masses. Cleanly observe 1 ++, 2 ++, and 2 -+ well known resonance features. π1(1400) and π1(1600) exotic signal is not observed in charged exchanged photoproduction. Currently analyzing neutral exchange channel. Future meson spectroscopy experiment with greater luminosity and beam energy is a planned with GlueX.