Proton TimeLike form factor measurements with PANDA B
Proton Time-Like form factor measurements with PANDA B. Ramstein, IPN Orsay, France on behalf of the PANDA collaboration Olympus workshop, Gatchina, July, 9 th , 2012
Outline • The PANDA@FAIR project • Electromagnetic channels with PANDA – – – pp e+e- at PANDA: proton time-like electromagnetic form factors pp π°e+e- reaction: time-like electromagnetic form factors in the unphysical region Transition Distribution Amplitudes and other measurements • Conclusion and outlook Gatchina, 9 July 2012 B. Ramstein (IPN Orsay) 2
The FAIR facility (1) FAIR at Darmstadt/Germany Facility for Antiproton and Ion Research • Hadron Structure and Dynamics • Nuclear and quark matter • Super-heavy elements • Nuclear Structure and Astrophysics • Atomic, Plasma and Material Physics • Radiobiology Antiproton ring High Energy Storage Ring 1. 5 – 15 Ge. V/c L = 2 x 1032 cm-2 s-1 σp/p = 10 -4 2 x 107 int. s-1 Gatchina, 9 July 2012 B. Ramstein (IPN Orsay) 3
The FAIR facility (2) Gatchina, 9 July 2012 B. Ramstein (IPN Orsay) 4
PANDA physics program ü Meson spectroscopy • D mesons • Charmonium • Glueballs, hybrids, tetraquarks, molecules, … ü Charmed and multi-strange baryon spectroscopy ü Single and double hypernuclei ü Hadrons in nuclear matter ü Proton structure Gatchina, 9 July 2012 B. Ramstein (IPN Orsay) 5
The PANDA experimental set-up Gatchina, 9 July 2012 B. Ramstein (IPN Orsay) 6
PANDA Barrel EMC • Barrel calorimeter: 11000 Pb. WO 4 crystals • Mechanical structure: carbon alveoles + Al inserts 1 slice= 1/16 barrel = 720 crystals = 720 kg • Proto 60 – 60 crystals cooled to -25° – tests with Bremsstrahlung photons at MAMI E/E = 1. 8% / √E + 0. 65% 7
The PANDA Collaboration At present a group of 500 physicists from 53 institutions of 16 countries Austria – Belaruz - China - France - Germany –India - Italy – Netherlands Poland – Romania - Russia – Spain - Sweden – Switzerland - U. K. – U. S. A. . Basel, Beijing, Bochum, IIT Bombay, Bonn, Brescia, IFIN Bucharest, Catania, Chicago, Cracow, IFJ PAN Cracow, Cracow UT, Dresden, Edinburg, Erlangen, Ferrara, Frankfurt, Genova, Giessen, Glasgow, GSI, FZ Jülich, JINR Dubna, Katowice, KVI Groningen, Lanzhou, LNF, Lund, Mainz, Minsk, ITEP Moscow, MPEI Moscow, TU München, Münster, Northwestern, BINP Novosibirsk, IPN Orsay, Pavia, Piemonte Orientale, IHEP Protvino, PNPI St. Petersburg, KTH Stockholm, U Torino, INFN Torino, Torino Politecnico, Trieste, TSL Uppsala, Tübingen, Uppsala, Valencia, SINS Warsaw, TU Warsaw, SMI Wien http: //www. gsi. de/panda 8
Time-Like and Space-Like electromagnetic form factors (1) Space-like SL e- e p p Real FFs e+p • Unphysical region p+p e++e- + X q 2<0 Time-like TL 0 3. 52 (Ge. V/c)2 p q 2>0 p e- Asymptotics • |GE, M(q²)| ~ (q²)-² e+ _ Constraints: • GEp(0)=1 • GMp(0)=μp • GEp(4 mp²)= GMp(4 mp²) _ Complex FFs p+p ↔ e++e- q 2 (Phragmén-Lindelhöf theorem) • Imaginary part of Time-Like form factors vanishes for q²→+∞
Time-Like and Space-Like electromagnetic electron scattering annihilation pp e e form factors (2) q > 4 m + - 2 e machines 100 2 Colliders (BES, Novosibirsk, PANDA) A 2/Mainz) Spacelike 10 -1 From S. Pacetti, ar. Xiv: 1012. 1232 v 1 Timelike unphysical p ( Jlab…. p GM/μp 10 -2 10 -3 -30 -20 -10 0 10 20 30 Dispersion relations: q 2 < 0 Gatchina, 9 July 2012 B. Ramstein (IPN Orsay) 10
proton electromagnetic form factors in Time-Like region - Cross-sections: pp → e+e- angular distributions: pp → e+e- FENICE+DM 2 (e+e-) - BABAR: (e+e- pp ) LEAR (pp) Geff - E 835 (pp) 4 mp 2 ü Geff : large error bars above 13 (Ge. V/c)2 ü- |GE/GM| : § Inconsistent data above threshold § Lack of precise data above 5 (Ge. V/c)2 Gatchina, 9 July 2012 B. Ramstein (IPN Orsay) 11
Goal of PANDA measurements Extract Time-Like |GE| and |GM| for proton up to 14 (Ge. V/c)2 - e+e- reaction from lepton angular distributions in pp and measure Geff up to 30 (Ge. V/c)2 Two major challenges: ü Decrease of sensitivity to GE with increasing q 2 - Gatchina, 9 July 2012 üHuge hadronic background - + -) / (pp e+e-) ~106 B. Ramstein (IPN Orsay) 12
Counting rate and sensitivity to |GE| ~120 days, L = 2. 1032 cm-2 s-1 = 2 fb-1 Statistical errors only GE=0 GE=GM GE=3 GM Ntot=1. 1 106 Ntot=64000 M. Sudol et al. EPJA 44 (2010) 373 Gatchina, 9 July 2012 B. Ramstein (IPN Orsay) Ntot=2000 13
- Hadronic background rejection for pp e+epion production Canaux chargés Background rejection takes advantage of : • Hermiticity of the detector • Particle Identification • Kinematical constraints Most problematic background is pp π+π- A. Dbeyssi Ph. D, Orsay for Gatchina, 9 July 2012 scale GEANT simulations -pp. Full - π+π- background e+e- and pp B. Ramstein (IPN Orsay) 14
- pp + - parametrization of CERN data for p p → + s < 6 (Ge. V/c)2 : Legendre polynomial fits s > 6 (Ge. V/c)2 : pp π+π- counting rules (Ong et Van de Wiele, IPNO-DR-08 -01) or Regge trajectories (idem, EPJA 46 (2010) 291). ( + -)/ (e+e- q 2 = 8. 21 (Ge. V/c)2 2. 4 10 6 ( + -)/ (e+e-) ) 1. 5 105 cosq. CM Gatchina, 9 July 2012 B. Ramstein (IPN Orsay) ? New measurements of p p → + will be provided by PANDA (also important for p. QCD mechanism studies) 15
Rejection of pp + Straw Tube Tracker DIRC(Cerenkov) Electro. Magnetic. Calorimeter Non-gaussian tails of truncated d. E/dx distribution 1) Use complementarity of e/ discrimination ( - , °) , ° 2 Edep/p ~ 1 EMC response to - p=1. 5 Ge. V/c capability of the different detectors 2) Use the different _ _ kinematical constraints of pp e+e- and pp + - reactions Electron momentum resolution (bremstrahlung ) Gatchina, 9 July 2012 B. Ramstein (IPN Orsay) T. Zerguerras, IPN Orsay 16
pp e+e- signal reconstruction - Sudol et al. EPJA 44 (2010) 373 q 2 [Ge. V/c]2 π + πcontamination 8. 2 0. 004 % 12. 9 0. 017 % 16. 7 0. 061 % contamination < 0. 1 % Ø Background suppression factor is at least of the order of 109 Ø Taking into account PID & kinematic fit contamination <<1% Gatchina, 9 July 2012 B. Ramstein (IPN Orsay) 17
Time-Like Form Factor measurement with PANDA : precision estimates L=2 fb-1 Courtesy of S. Pacetti Sudol et al. EPJA 44 (2010) 373 E. Tomasi-Gustafsson and M. P. Rekalo, PLB 504, 291 E. Tomasi-Gustafsson, ar. XIv: 0907. 4442 Geff PANDA BES < 1% ~10% p. QCD ? Gatchina, 9 July 2012 ~23% ~50% Phragmèn-Lindelöf theorem ? B. Ramstein (IPN Orsay) 18
Time-Like Form Factor measurement with PANDA : precision estimates L=2 fb-1 Sudol et al. EPJA 44 (2010) 373 Geff -VDM: F. Iachello et al. , PLB 43, 171 (1973) …extended VDM, PRC 66, 045501 (2002) Egle Tomasi-Gustafsson et al. , EPJA 24 (2005) 419 PANDA BES < 1% ~10% p. QCD ? Gatchina, 9 July 2012 ~23% ~50% PANDA will bring Precise determination of |GE| and | GM | up to 14 (Ge. V/c)2 Geff up to 30 (Ge. V/c)2 : transition towards perturbative QCD B. Ramstein (IPN Orsay) 19
2 contributions and radiative corrections Rosenbluth method Important role of 2 exchange and radiative corrections Polarization measurements ? No C-odd terms contribution • Advantage of annihilation reactions pp e+ e. The e+ and e- angular distributions are measured in the same experiment • PANDA measurements are sensitive to odd cos terms d /dcos e ~ A (1+ b cos esin 2 e + c cos 2 e+. . ) with b=5% or more (M. Sudol et al EPJA 44(2010) 373). Gatchina, 9 July 2012 B. Ramstein (IPN Orsay) 20
- 2 contributions in pp e+e • Model independent properties on cross sections and polarization observables : G. Gakh and E. Tomasi-Gustafsson NPA 761(2005)120. see E. Tomasi-Gustafsson’s talk • 2 contributions at large q 2 in a factorization approach J. Guttmann, N. Kivel, M, Vanderhaeghen PRD 83 (2011) 094021 see N. Kivel’s talk Distribution Amplitudes • resonant contribution: H. -Q. Zhou and B. S. Zou. ar. Xiv: 1112. 4615 v 2 Gatchina, 9 July 2012 B. Ramstein (IPN Orsay) 21
- radiative corrections for pp e+e. IPN Orsay et al. contributions: A. Ahmadov et al. , Phys. Rev. D 82: 094016, 2010 J. Van de Wiele and S. Ong, ar. Xiv: 1202. 1114 v 1 [nucl-th] Small contribution of box terms e+ angular distribution Born ~-15% for E cut=100 Me. V angle dependent effect Full calculation Important effect of interference between proton and lepton radiation Final state radiation only Charge asymmetry J. Van de Wiele ans S. Ong, ar. Xiv: 1202. 1114 v 1 [nucl-th] Gatchina, 9 July 2012 Event generators with photon emission for PANDA experiments B. Ramstein (IPN Orsay) 22
Time-Like form factors in the unphysical region (1) Dispersion relations q 2 < 0 pp e+e- annihilation q 2 < 0 p p Unphysical region p p → e+ e- π0 Space Like (SL) Time Like (TL) p p γ(q) Гμ(q) e+ e- q 2 = s q 2 > 4 mp 2 | FFs real Vector meson poles: q 2 = m 2 , m 2 Vector Meson Dominance (VMD) form factor models can be tested Gatchina, 9 July 2012 FFs complex 4 mp 2 B. Ramstein (IPN Orsay) q 2 23
Form factors in the unphysical region (2) Basic idea: reach q 2 < 4 mp 2 by giving 4 -momentum to another particle (e. g. π0) M. P. Rekalo, Sov. J. Nucl. Phys. , vol 1, 760 (1965) p e+ e- ° q 1 st calculation of d /dq 2 for p p → e+ e- π0 | p q 2 + exch. A. Dubnickova et al, . Z. Phys. C 70 (1996) 473 -482 C. Adamuščín et al. , Phys. Rev. C 75, 045205, 2007 q New investigations by J. Van de Wiele and J. Boucher in IPN Orsay to build an event generator for simulation studies ü d 5 / dq 2 d 0 d 0 d ed e ü constrained on existing data Armstrong et al. , PRD 56, (1997)2509 q Recent calculation of d 5 / dq 2 d 0 d 0 d ed e and polarization observables G. I. Gakh et al. ar. Xiv: 1206. 0929 data: Fermilab E 760 for -p p → 0 √s=3. 005 Ge. V
Count rate predictions for pp π0 e+e. Iachello VMD form factor model Phys. Rev. C 69, 055204, 2004 Incident energy dependence ρ, ω and φ resonances |GM| |GE| q 2 (Ge. V/c 2) p- q 2 (Ge. V/c 2) e+ e- p Luminosity =2 fb-1 T=1 Ge. V q²=2. ± 0. 25 (Ge. V/c)² ° at T=1 Ge. V , q 2=2 (Ge. V/c)2 172000 events for q 2=0. 5 (Ge. V/c)2, 4000 events for =1° ( =20°) J. Boucher Ph. D Orsay dec. 2011 3/02/2011 Orsay, PANDA meeting 25
- + e- π 0 ? How hadronic to extract tensors GE and Gto in p p → e From form factors M p p q 2 e+ e+ * e- ° + exch. e e- d /d e J. Boucher Ph. D Orsay dec. 2011 In the one nucleon exchange model : d /d e For fixed θπ0 and q², Fit of lepton angular distributions in * frame R=|GE/GM| and cos( E- M) e+ (deg) General result: the angular distribution in θe* and φe* in * frame gives access to 4 Hμν at fixed θπ0 and q² d /d e e+ (deg)
- Background for pp π0 e+e. Background rejection takes advantage of : • Hermiticity of the detector • Particle Identification • Kinematical constraints Most problematic background is pp π+π- 0 + - 0 q pp Calculation for T=1 Ge. V J. Van de Wiele, IPN Orsay Effective lagrangians: 9 graphs in total + + … at T=1 Ge. V , q 2=0. 6 (Ge. V/c)2 B/ S=3 -5. 103 q 2=2 (Ge. V/c)2 B/ S=3. 106 -3. 107 → input for simulations - N. B. PANDA will provide new measurements of pp π+π- 0 Gatchina, 9 July 2012 B. Ramstein (IPN Orsay) 27
Expected precision on |GE|/|GM| and the phase difference σR/R [%] | p p → e + e- π0 q²=0. 605 ± 0. 005 (Ge. V/c²)² q²=2. 0 ± 0. 125 (Ge. V/c²)² |GE|/|GM| q 2=2 Signal contamination <1 % at q²=0. 6 < 10% at q 2=2. 0 For the first time cos(φE-φM) can be extracted with 10 -30% precision σcos(δφ) /cos(δφ) [%] ~ 1% precision close to the ω resonance ~ 10% precision at q 2 =2 (Ge. V/c²)² ~ 20% precision at q 2= 4 Mp 2 =3. 52 (Ge. V/c²)² q 2=0. 605 q 2=2 q 2=0. 6 cos( E- M) T. Hennino, J. Boucher, IPN Orsay Gatchina, 9 July 2012 B. Ramstein (IPN Orsay) 28
Form factor measurement in the unphysical region: outlook q The measurement of electromagnetic form factors moduli and phase difference below 4 mp 2 threshold in pp π0 e+e- , following the one nucleon exchange model is feasible q However: there are open questions: ü off-shell effects on form factor p p ü Validity of the nucleon exchange model , § role of exchange § importance of s-channel terms q 2 e+ e- ° E. A. Kuraev et al. ar. Xiv: 1012. 5720 v 2 [hep-ph] - π0γ measurement at PANDA can be checked with pp Gatchina, 9 July 2012 B. Ramstein (IPN Orsay) 29
- Another approach for the pp e+e-π0 reaction : Transition Distribution Amplitudes Hard sub-process : Distribution Amplitude = 3 -quark operator matrix element <0|uud|p> Signature: Angular distribution of the e+/e- in the * frame ~ (1+ cos 2 ) q 2>>1 Transition Distribution Amplitude = 3 -quark operator matrix element =00 or = 1800 ‘ ’ at rest in p or pbar rest frame t=(pp/p-p )t=0 3 TDA < |uud|p> J. P. Lansberg et al, PRC 76, 111502(2007) New window on the sea quarks in proton wave function complementary to corresponding quantities from CLAS/JLAB Gatchina, 9 July 2012 B. Ramstein (IPN Orsay) 30
Transition Distribution Amplitudes in pp e+e-π0 reaction : estimates for PANDA J. P. Lansberg et al, PRC 76, 111502(2007) Tp-=0. 788 Ge. V Tp-=3. 5 Ge. V Estimates for PANDA: ( Mainz/Orsay collaboration M. C. Mora Espi, B. Ma) including acceptance and efficiency L= 2 fb-1 , Q 2 < 1 Ge. V 2 Feasible at s=W 2=5 (Ge. V/c)2, but probably not at W 2=10 (Ge. V/c)2 also - to be studied • pp J/ 0 (same TDA’s) • Possible generalization to h and (more TDAs) Gatchina, 9 July 2012 B. Ramstein (IPN Orsay) 31
Nucleon structure and p. QCD with PANDA Panda Physics Performance ar. Xiv: 0903. 3905 [hep-ex] • More about electromagnetic Time-Like proton form factors – pp + - (collaboration with Torino) – pd n e+e- H. Fonvieille and V. Karmanov, EPJA 42 (2009)287 – Polarization in pp e+e- → relative phase of GE and GM • Other electromagnetic processes: – pp , pp ° (GDA, Giessen) – pp e+e- ° (Transition Distribution Amplitude p ) – pp + - X ( Drell-Yan, Torino/Ferrara) 3/02/2011 Orsay, PANDA meeting 32
Conclusion and outlook The PANDA detector at FAIR will allow for a variety of QCD studies, from 2018 q Electromagnetic channel measurements : • pp e+e- Proton Time-like Form factors : GE and GM up to q 2=14 (Ge. V/c)2 , , Geff up to 30 (Ge. V/c)2 and pp π0 e+e- : access to form factors in the unphysical region • pp e+e- 0, pp J/ 0 , pp e+e- (TDA) • pp 0, General Distribution Amplitudes complementary to JLAB/CLAS • pp µ+µ-X Drell-Yann q Simultaneous measurement of hadronic channels: ( + -, + - 0, …. ) • background for electromagnetic channels • Interest for p. QCD mechanisms Gatchina, 9 July 2012 B. Ramstein (IPN Orsay) 33
Thanks PANDA/IPN Orsay team: J. Boucher, A. Dbeyssi, M. Gumberidze, T. Hennino, R. Kunne, T. Liu, B. Ma, D. Marchand, S. Ong, E. Tomasi-Gustafsson, J. Van de Wiele in collaboration with Mainz/GSI Thank you for your attention ! Gatchina, 9 July 2012 B. Ramstein (IPN Orsay) 34
From experimental to physical information Tp=1 Ge. V ; q²=2. 0 ± 0. 125 (Ge. V/c²)² ; 10°<θπ°<30°; Nth=18 486 H 11+H 22 -2 H 33 Predicted e+ distribution in * Corrected experimental distribution Projection and fit Full simulation chain Determination of R=|GE|/|GM| and cos(φE-φM) from the shapes only Gatchina, 9 July 2012 B. Ramstein (IPN Orsay) H 11 -H 22 and H 13 35
Hadronic channels understand the reaction mechanism and the transition towards p. QCD - - - pp + - , pp K+K- , pp + - 0 q only low quality data exist from CERN q High statistics expected at PANDA, easy to measure q pp + - , pp + - 0 needed anyway to control the background for proton form factor measurements in pp e+e- and pp e+e- 0 reactions q theoretical work: J. Van de Wiele and S. Ong EPJA 46 (2010) 291: models checked on existing data to be used as generators for simulations Possibility to explore up to -t=30 (Ge. V/c)2 With PANDA 3/02/2011 Orsay, PANDA meeting 36
Hadronic tensor extraction: proof of principle • Tp=1 Ge. V • q²=2. 0 ± 0. 125 (Ge. V/c²)² H 11 • Lint = 2 fb-1 • d 2σ/dΩe* generated in the γ* rest frame (θe*, φe* in 10°/bin) Theoretical value Reconstructed value • Reconstructed value from the fit of d 2σ/dΩe* in each θπ0 interval (Δθπ0=1°) Direct access to Hμν via the angular distribution valid whatever the model is 12/15/2021 H 22 H 33 H 13 Only statistical errors without acceptance nor efficiency T. Hennino (IPN Orsay) 37
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