Deeply Virtual Scalar Produc2on

Transcription

1 Exclusive Meson Producon Workshop - 4 Jan 015, Jefferson Lab Deeply Virtual Scalar Producon Charles Hyde Old Dominion University Mirror Image Symmetry Breaking

2 Global GPD program GPD program DVCS Deep Virtual Vector Mesons: ρ, φ, ω, K*, J/Psi Deep Virtual Pseudo Scalars: pions, kaons, eta What about Scalars? Orphan parcle σ, f 0, etc

3 Deep Virtual Hadron Producon (DVHP) Factorizaon of DVHP does not require isolaon of a resonant final state (Deep Virtual Meson Producon): DVMP DVMP Consider Deep Virtual ππ producon at ππ mass threshold Dominated by scalar channel sigma - meson, Higgs parcle of nuclear physics Connecon to ππ sca^ering amplitude

4 Example of CLAS data (cf. M.Guidal) rho(770) f 0 (980) f (170) Phase space ππ Δπ ππ at threshold High Luminosity needed High resolu3on mass & angular distribu3ons for J p = 0 +, 1, π + π and π 0 π 0 Isospin= 0, 1, ππ threshold

5 Why Scalars? channel has a gluon Distribuon amplitude What is the gluon content of the σ- meson? Near ππ threshold: the dependence of the intensity on m ππ is related to the effecve chiral Lagrangian (EChL) describing the interac3on of sob pions with gravity. Therefore one can use data on hard exclusive pion pair producon to probe this yet unknown part of the EChL. (Lehmann- Dronke, Schaefer, Polyakov, Goeke, PRD, 63, )

6 Experimental Opportunies/Opons Deep Virtual π π producon at large Q, W : Near ππ threshold and at small t Min t. Approximate - body kinemacs: Both pions parallel to q- vector, correlated with (e,e ) Performance: Hall A: Super Bigbite Spectrometer (SBS) for π + π pair, HRS or BigBite for e. New ECal in SBS for π 0 π 0 pair? Or thin Shower max in front of HCal? SBS: Luminosity /(cm sec)

7 Super Bigbite (SBS), Sample parameters Acceptance (θ SBS = 15 ) 70 msr ~ (±5 H) x (±1 V) (±50%) Δp/p Charged parcle resoluon δp/p = 0.3% %GeV/p σ θ = [ GeV/p] mrad PbGlass Calorimeter for electron arm Operate at 50 C for connuous annealing of Rad damage Need to add large (6.5 m ) ECal or PreShower detector in front (or instead) of HCalo in SBS. Assume 15%/ E γ and ±mr 5m) resoluon.

8 Extracting J π I = Channel charged pions m ππ dependence: Angular Moments <P 0 >, <P 1 >,... Isospin separaon via π + π / π 0 π 0 J π Ι = 1 1 channel vanishes for π 0 π window ρ f 0 +f <P 1 > π + π <P 3 > ρ [f 0 +f ] interference ρ f interference σ ρ interference FIG. 4. P 1 (cos ) as a function of x Bj and m. FIG. 5. P 3 (cos ) as a function of x Bj and m.

9 BigBite(e ) SuperBigbite(ππ) A single sexng Mass resoluon: Charged Channel: δ(m ππ ) ~ 0.00 GeV Neutral Channel: δ(m ππ ) ~ 0.09 GeV ) (GeV Q θ q Kinematic Limit 11 GeV (SBS) BB SBS Acceptance W = 4.0 GeV BigBite 16 deg 1 deg x Bj

10 ππ Threshold Behavior ππ Distribuon Amplitude C = 1 +b m π + Chiral Lagrangian C 1 [4L 11 +L 1 L 13 ]8m π /f π Gravitaonal coupling of pion field. L (4) il 9 Tr F U U L 11 R Tr U U L 1 R Tr U U L 13 R Tr mu U m. 79 Here F is the field strength of the photon field, R and R are the Ricci tensor and the curvature scalar of an external gravitational field, and U exp(i a a /f ) is the non-linear pseudo-goldstone field. The ellipsis stands for the terms of the EChL that are not relevant for us here. Now we can use the results of the calculations in Refs. 36,37 to express the constant C and the near threshold behavior of the functions F, f 0, and f in terms of the constants L i in the EChL 79.

11 Conclusions The scalar ππ channel of DVHP offers novel physics Gluon DA Gravitaonal terms in Chiral Lagrangian An exploratory program seems feasible with equipment currently under construcon in Halls A & B. Assistance in developing a cross secon code for Monte Carlo simulaons would be greatly appreciated.

12 ππ Mass resoluon θ/ = 0.05 rad = ½ opening angle of pion pair. ν = 5 GeV: p π =.5 GeV M = 4m π + (p π sin(θ/) 4m π + (p π θ) M = 0.08 GeV GeV = 0.14 GeV M = 0.38 GeV Charged Parcle δ(m) ~ M δp/p p δθ δ(m) = GeV 0.00 GeV Neutral δp/p = 15%/sqrt(p) δθ = 1cm/5m = e- 3 δ(m)= (0.4)(0.1) + (.5)(0.00) = 0.09 GeV