Barion Form Factors at FAIR P.Gianotti INFN Laoratori Nazionali Frascati

Form Factors: definitions Space Like Time Like q2<0 0. 4MN2 q2>0 Annihilation or reversed channel Electron scattering

Form Factors: definitions In the approximation of single g exchange ds/dW  [ |GM(q2)|2(1+cos2q)+4mN2/q2 |GE(q2)|2 sin2q)] Sachs and Pauli/Dirac FF in the Space-Like region  Fourier transform of charge and magnetization distributions At threshold (t=q2/4MN2=1)  |GE| = |GM| F1 and F2 are analytic functions of q2 real in Space-Like, but complex in Time-Like. Time-Like GE and GM FF are analytic prolongations of Space-Like non spin-flip (GE) and spin flip (GM) form factors. GE = F1 + t F2 GM = F1 + F2

Why measuring nucleon TL FF? FF are fundamental quantities of the nucleon (m, m, …) Understanding the Nucleon structure Comparison with Space-Like data that seems to show the non validity of the Born approximation Testing the hypothesis GE/GM= 1 Test different theoretical approaches

Form Factors: open questions Perturbative QCD (q2  ∞) F1(q2)  q-4 F2(q2)  q-6 q2F2/F1  constant exp data seems to indicate qF2/F1  constant limq2→∞ |GM|time like = |GM|space like exp data gives |GM|time like ≈ 2 |GM|space like

SL FF present situation Data on the ratio GE/GM for the proton including the older Rosenbluth separation data (crosses), most recent JLab Rosenbluth separation data (filled circles), and polarization transfer data (triangles) New Jlab data have been obtained with the recoil polarization method stating that: PRL 94 142301 (2005) The old assumption seems no more valid

FF TL: data extraction |GE| and |GM| in the Time-Like region can be determined by the reactions pp ↔ e+e- Presently statistics is limited  no real separation |GE|/ |GM| |GM| extracted assuming |GE| = |GM| (true at threshold) GE in Time-Like region is today unknown Recent data from BaBar  extraction of the ratio R = |GE|/ |GM| through the ISR method (e+e-  gpp) (q2<7 (GeV/c)2)

FF Time-Like: angular distribution In the approximation of single g exchange ds/dW  [ |GM(q2)|2(1+cos2q)+4mN2/q2 |GE(q2)|2 sin2q)]  is cross section isotropic? With PANDA we will have access to almost total angular range Direct access to |GM(q2)| and |GE(q2)| The sensitivity to |GE(q2)| decreases while energy increase (4mN2/q2 = 0.25 at 10 GeV, and only 0.14 at 15 GeV) 2g: odd cosq contributions in the cross-section. Are these an explanation? (PL B659 197)

FF Time-Like: present data A new bulk of data up to 20 GeV came from BaBar using the technique of ISR |GM|2 10-1 10-2 For E2 < 2.1 GeV2 the ratio |GE|/ |GM|has been found >1 in disagreement with previous LEAR data |GEp|/|GMp| E (GeV) 5 6 7 8 10 4 9 20 Ebeam (GeV) PRD 73 012005

Angular distributions BaBar data e+ e- → g p p Dashed: |GM| LEAR data p p → e+ e- Dot-dashed: |GE| Both data sets have big errors! Mpp=2.05 GeV/c2 Mpp=1.99GeV/c2 Mpp=1.96 GeV/c2 Dashed: |GE|/|GM| free Solid: |GE|=|GM| Mpp=1.92GeV/c2 Mpp=1.94GeV/c2 Mpp≈1.91 GeV/c2 Mpp≈1.99 GeV/c2 Mpp≈2.06 GeV/c2 Mpp≈2.15 GeV/c2 Mpp≈2.30 GeV/c2 Mpp≈2.70 GeV/c2 PLB 559 20 PRD 73 012005

Facility for Antiproton and Ion Research Primary Beams 2(4)x1013/s 30 GeV protons Secondary Beams Antiproton production target Antiprotons 3 - 30 GeV 100 m HESR High resolution mode dp/p ~ 10-5 (electron cooling) Luminosity = 1031 cm-2 s-1 Storage and Cooler Rings 1011 stored and cooled 0.8 - 14.5 GeV antiprotons High luminosity mode Luminosity = 2 x 1032 cm-2 s-1 dp/p ~ 10-4 (stochastic cooling)

PANDA: the detector calorimeter MVD DIRC STT/TPC Forward Spectrometer Forward tracking Solenoid target

PANDA: Physics program Charmonium and open charm spectroscopy; Charmed hybrids and glueballs: Meson mass modification in the nuclear matter; Double hypernuclei produced via Ξ-baryon capture; Wide angle compton scattering; Drell-Yan reactions; Baryon-Antibaryon production; CP-Violation (Λ,D). http://www-panda.gsi.de

Time-Like FF : world data |GM|2 10-1 10-2 in e+e- VEPP L=1032 Frascati L=2. 1032? BEPC/BES L=1033 Present typical errors 5% 20% 50% PANDA range : 5 to 30 (GeV/c)2 at L = 2. 1032 PANDA errors Belle ?? S=100 GeV2 ( centered on the upsilon 4S). ISR possible but far away from the « measurable «  region  los by at least a factor 1000 0.1% 1% 10%

PAX program Plans for the TL FF Separate measurement of |GE| et |GM| Precisions on the ratio R=|GE|/|GM| and sR DR/R <1% at low Q2 DR/R = 10% at Q2=10 (GeV/c)2 Separation possible up to Q2=15 (GeV/c)2 Test of the 1 g hypothesis (symmetry of the angular distribution) Measure |GM| up to Q2=25 (GeV/c)2 Possibility to measure the phase difference j(GE) - j(GM) in case of transverse polarization pp↑ ↔ e+e- Double spin asymmetry will allow the independent measurements of GE and GM PAX program

Experimental challenge ≈106 2 μb/8pb at q2=9 (GeV /c)2 106 times higher background Thanks to PANDA PID capabilities we expect to reach a pion rejection power at the level of 10-8 Cherenkov radiation: above 1 GeV Radiators: quartz, aerogel, C4F10 Energy loss: below 1 GeV Tracking devices: best accuracy with a TPC Electromagnetic processes: EMC for e/g Time of flight Problem: no start detector, huge material

PANDA PID To allow electron-pion separation at 10-8 level PANDA must have excellent PID capability MVD PID capability Beam Space resolution 50μm Low material 5% X/X0 dE/dx capability High rate 107 ev/s

PANDA tracking system Two options Straw Tube Tracker Space resolution: r < 150µm z ~ few mm Momentum resolution: pt / pt ~ 1.2 % Material budget: X/X0 ~ 1.0-1.3% dE/dx capability Two options Straw Tube Tracker Time Projection Chamber

dE/dx performances, stt vs tpc supposing the particles are hitting 22 tubes Gaussian distribution ( ~ 6 %): probability of misidentified pion 3% at 1 GeV/c , 10% at 6 GeV/c stt tpc [Panda TPR]

DIRC Concept Detection of Internally Reflected Cherenkov light 2.05 Different Cherenkov angles give different reflection angles PANDA DIRC similar to BaBar 96 Fused silica bars, 2.6m length Water tank & 7000 PMTs Alternative readout: (x,y,t), mirrors Momentum (GeV/c) e - (deg) Fraction of misidentified pions (DIRC) (εelectron=90%) 0.5 2.05 2-3 10-3 0.8 0.01 1.5 % 1.0 0.52 12% 1.5 0.23 27% Schwiening Schwiening

Electromagnetic Calorimeters Forward Endcap 4000 PWO crystals High occupancy in center Readout LA APD or vacuum triodes Backward Endcap 800 Crystals Worse resolution due to service lines of trackers Needed for hermeticity Barrel Calorimeter 11000 PWO Crystals LA APD readout σ(E)/E~1.5%/√E + const. 1.0 GeV/c  e Energy deposit in EMC Forward Shashlyk (after dipole magnet) 350 channels Readout via PMTs σ(E)/E~4%/√E + const. Alternative Designs: Spiral Shashlyk Segmented composite Shashlyk-Sandwich for for (e/h/µ)

Pion rejection is OK 1. 5.4 2.5 8.2 5. 12.9 10. 22.3 MPtot 2particles Tp_bar (GeV) Q2 (GeV/c)2 qCM qlab plab (GeV/c) Misident. Probability ECAL×DIRC×dE/dx MPtot 2particles 1. 5.4 20° 13° 2.2 0.001 × 0.5 ×0.05 = 2.5 10-5 0.1 10-9 132° 0.57 0.033 × 0.003 ×0.03 = 3.0 10-6 90° 54° 1.43 0.001 × 0.3 ×0.03 = 9. 10-6 0.001 × 0.3 × 0.03 = 9. 10-6 2.5 8.2 10° 3.7 0.001 × 1. ×0.05 = 5. 10-5 0.3 10-9 117° 0.7 0.014 × 0.014 × 0.03 = 6. 10-6 41° 0.001 × 1. × 0.03 = 3. 10-5 0.9 10-9 5. 12.9 7.4° 6.1 0.001 × 1. × 0.1 = 10-4 0.6 10-9 102° 0.8 32° 3.4 0.001 × 1. × 0.05 = 5. 10-5 2.5 10-9 10. 22.3 5.4° 10.9 0.001 × 1. × 0.3 = 3. 10-4 5.4 10-9 85° 1.0 0.005 × 0.12 × 0.03 = 1.8 10-5 24° 5.95 0.001 × 1. × 0.1 = 1. 10-4 10. 10-9 Pion rejection is OK

ds/dW  [ |GM(q2)|2(1+cos2q)+4mN2/q2 |GE(q2)|2 sin2q)] FF Time-Like : GE et GM ~100 days, L = 2. 1032 cm-2s-1 ds/dW  [ |GM(q2)|2(1+cos2q)+4mN2/q2 |GE(q2)|2 sin2q)] - en 10 7 s Nb of counts for pp→e+e- cos(cm) 106 counts 3000 counts 6 104 counts Nb of counts for pp→e+e- Nb of counts for pp→e+e- - 10 B. Ramstein J. Van de Wiele 6 104 counts 5 106 counts 3000 counts 80 counts Q²=22.3 (GeV/c)² cos R=|GE|/|GM| s=q2=5.4 (GeV/c)2 q2= 8.2 (GeV/c)2 q2=12.9 (GeV/c)2 q2=22.3 (GeV/c)2 Ntot=106 Ntot=66000 Ntot=2750 Ntot=82 Elab=1 GeV Elab=2.5 GeV Elab=5 GeV Elab=10 GeV DR=0.6% DR=3% DR=25% DR= 100% 09/03/2007 B. Ramstein EM working group

Summary - electromagnetic form factors: fundamental property of nucleon - poorly known in time-like region - PANDA offers a unique possibility to measure in time-like domain up to q2 = 20 GeV2 - crucial: high luminosity & excellent particle ID