Моделирование электромагнитного форм-фактора протона во времени-подобной области в среде PandaRoot

1. Моделирование электромагнитного форм-фактора протона во времени-подобной области в среде PandaRoot Д. Морозов ИФВЭ (Протвино)

2. Outline • Introduction • Experimental setup • FSC PandaRoot Development • Generators • What is also needed • Near term plans • Conclusions

3. Introduction • The electromagnetic probe is an excellent tool to investigate the structure of the nucleon • GE and GM of the proton parametrize the hadronic current in the ME for e-p → e-pand in its crossed processp+p- → e+e-

4. Introduction • Matrix element for elastic electron proton scattering in the frame of one-photon exchange: • k1(p1), k2(p2) - four-momenta of the initial and final electron (nucleon) • u(k) ,u(p) – spinors • q = k1 - k2, q2 < 0 • Annihilation - k2(p2) change sign and q2 = s

5. Introduction • Annihilation process - access positive q2 (time-like) from q2 = 4m2p • Unitarity of ME: • space-like FFs are real functions of q2 • time-like - complex functions • In the Breit frame, space-like FFs have concrete interpretations, they are the Fourier transforms of the spatial charge (GE) and the magnetization distribution (GM) of the proton • slope at q2 = 0 gives the charge and magnetization radius of the proton • In time-like region, FFs reflect the frequency spectrum of the electromagnetic response of the nucleon • two complementary aspects of nucleon structure can be studied • complete description of the electromagnetic FF over full q2 range.

6. Introduction • Estimation: PANDA will be able to get |GE|and|GM| in time-like domain from ~5 (GeV/c)2 up to ~14 (GeV/c)2by measuring angular distribution of p+p- → e+e-. GM up to 22 (GeV/c)2by measuring total cross section • Unpolorized diff. cross section: where τ = q2/4m2p • independent measurements of |GE|and|GM| • Only BABAR and LEAR had enough statistics to extract |GE|and|GM| independently, but accuracy on R= |GE|/|GM| is ~ 50%. • PANDA aim is few % in 107 sec

7. FF in space-like region (JLab) JLAB arXiv:1102.2463 [nucl-ex]

8. Introduction • The challenge is to suppress the huge background from hadronic channels. It’s ~106 times higher in cross section then signal e+e- • π+π-, K+K- • EMC is ~20X0 ~ λ0: 30% of hadronic interactions, charge exchange is the most harmful • can produce deposition as e with same momentum • π0π0 • one(two) Dalitz decay e+e-γ with 1% branching still big enough • direct decay then conversion in material • e+e-X, where X – mesons, lepton pairs, photons • direct e+e-X • produced γ materializes in detector material • a good e/pion separation is mandatory up to ~15 GeV/c • PID from each detector and kinematical constrained have to be exploited

9. Experimental setup • Pipe • Central spectrometer • Solenoid Magnet • TPC (STT) → PID, tracking • MVD → vertex, tracking • EMC: Barrel, Endcaps → PID • TOF → c PID (0.3 – 1 GeV) • MDT → PID muon • GEM → tracking • DIRC → charged PID • Forward spectrometer • Dipole Magnet • EMC: FSC → PID • Forward DIRC(DSK)→ c PID • DCH → tracking • FTOF → charged PID • FTS: straw tubes→tracking

10. FSC PandaRoot Development • Geometry • emc_module5_fsc.root in 16 and 17 GeometryVersions • 1496 modules (54x28 with 4x4 spacing) • cell 5.5 x 5.5 x 67.5 cm3 consists of 380 lead (0.275 mm ) scintillator (1.5 mm ) layers • wrapped by tyvek and black paper • 6x6 optical fibers 1.4 mm thick docked to PMT photocathode by a single bunch • Macro to create geometry • PndEmc class modified to load geometry • PndEmcStructure class modified to transform the cells coordinates to the global system of geometrical indexes (for fast searching and cluster formation) • PndEmcHit and PndEmcHitProducer updated to collect the hits from transport code at VMC level

11. FSC PandaRoot Development • Digitization model • Hit → electronics signal shape (Waveform): PndEmcHitsToWaveform • Signal shape: analytic function of RC-CR circuit with • Tint = 5nsec — integration time, • Tdiff = 20 nsec — differential time and • Tsig = 15 nsec — time of raising the signal in shashlyk module • For each hit discrete signal shape simulating SADC was built up • Nsamples = 20 — the number of SADC counts • SampleRate = 180 Mhz — ADC rate • NPhotonsPerMev = 21 — N of photons per 1 MeV of deposited energy • ENF = 1.3 – excess noise factor for PMT • Gaussian incoherent electronics noise with 3 MeV width added to each ADC bin • the signal was converted to the integer value in each bin • Waveform → ADC digitized signal in energy units: PndEmcWaveformToDigi • maximum was searched inside each digitized signal shape: magnitude → value, position→ time of signal arrival • Absolute value normalization by 1 GeV delta function signal as input • Cells with Edigi > EdigiThreshold= 8 MeV are stored for the following analysis

12. FSC PandaRoot Development • Energy resolution for Digi hits • σE/E = (3.0 ± 0.1)%/√E + (0.6 ± 0.1)% • Compare to test beam • σE/E = (2.8 ± 0.2)%/√E + (1.3 ± 0.1)% • Utilize the algorithms for cluster finding and bumps splitting already implemented in EMC code • Absent: • e PID → shower shape analysis (it’s different compare to PWO) • E1/E9 (E1/E25) • lateral moment of the cluster • a set of zernike moments (radial and angular dependent polynomials) • parameters are partially correlated • Multilayer Perceptron (MLP) may be applied (for PWO as well). The training of the MLP requires big set of single tracks for e, μ, π, K and p • Leakage correction for FSC

13. MLP output example • PWO in BABAR framework

14. Generators • Signal channel – exist in PandaRoot • Background – absent but in preparation • Extrapolationof experimental data

15. What is also needed • Forward tracking? • CPU/Storage • About 5∙108 events need to be simulated • Requires at least 30 TB of disk space • Now: local cluster (400 CPU, no space) is not sufficient. PANDA Grid can be used? • In a ~1 year: the hope is to have ~50 TB and cluster will be helpful for PANDA • IHEP cluster can be incorporated to PANDA Grid

16. Near term plans • Finish FSC reco code • Shower shape parameters for shashlyk modules • MLP training? • Leakage • Generator issues • Production of MC data • Background suppression • PID cuts • Kinematical constrains • Efficiencies

17. Conclusions • FSC in PandaRoot is implemented • Some tuning and e PID required • Time like form-factor could be interesting but challenging • High hadronic background • Huge amount of events → storage • IHEP might be a part of Panda Grid