DA  NE-2 plans for the study of Nucleon Form Factors Marco Mirazita INFN Laboratori Nazionali di Frascati Workshop on Nucleon Form Factors Frascati, October 2005

Why measure time-like FFs Proton FFs have been measured from threshold up to ~15 GeV 2 in e + e - → p pbar (ADONE, DM1-2, FENICE, BaBar) p pbar → e + e - (PS135 and PS135 at CERN, E760 and E835 at FNAL) TOTAL CROSS SECTION PLUS THE ASSUMPTION |G E |=|G M | Space-like data showed that this relation is valid only at threshold Different hypothesis on |G E |/|G M | produce large changes in the FF See talk by S. Pacetti on DR analysis of proton FFs Time-like FFs are basically unknown -Poor knowledge of the absolute values -Phases never measured

Proposal for nucleon FF measurement at DA  NE2 A Letter of Intent has been already signed by more than 70 physicist from 22 institution and 6 countries Accurate measurement of pp and nn cross section  model-independent extraction of proton and neutron FFs First measurement of outgoing proton (neutron) polarization  relative phase between G E and G M First measurement of  (  ) baryon production (including polarization)  strange baryon FF Study of angular asymmetry in pp (nn) distributions  look for 2-photon contribution Measurement of e + e - →hadrons and other exclusive multipion processes  sub-threshold NN resonance … and many other processes

Experimental requirements Beam requirements: beam energy > 1 GeV high luminosity ~10 32 cm -2 s -1 (cross section ~ nb) beam polarization not required (but could help) Detector requirements: high detection acceptance for charged and neutral particles identification of exclusive final state - protons  momentum+TOF - high neutron efficiency - detection of antinucleons  converter installation of a polarimeter - carbon analyzer + 2 tracking systems

Possibility of upgrading the energy in DA  NE up to 2.4 GeV

DAΦNE energy upgrade Minimal modifications to reach 1.2 GeV per beam interaction region (only one) vacuum chambers dipoles (normal conducting) control system diagnostic Injection at 510 MeV keeping the present injection system ramp up time ~ minutes beam life time ~ hours Peak luminosity at the  mass (cm -2 s -1 )

DAΦNE parameters for 1.2 GeV operation

The DA  NE detectors FINUDA KLOE 1 m

The FINUDA detector 1 cm vertex region OSIM nuclear targets TOFino ISIM 10 cm TOFone straw tubes drift chambers Two series of 8 drift chambers, 6 cm thick each 6 layers of straw tubes (total thickness  16 cm) TOFone (72 scintillators, 10 cm thick) Beam pipe (Be, 0.5 mm thick) TOFino (12 scintillators, 0.2 cm thick) ISIM (8 modules, 300  m thick) Nuclear targets OSIM (10 modules, 300  m thick)

Track reconstruction with FINUDA Number of hits per particle Inner region: TOFino 1 ISIM 1 OSIM1 Vertex region DC2 straw1 TOFone1 7 total hits per particle, at least 4 hits for the track fit Back-to-back events  use hits of both nucleons E p = 1.2 GeV p p = 748 MeV/c

Antinucleon converter 1 cm vertex region TOFino OSIMISIM Two possible otpions Between inner and outer regions 8 carbon “targets” before DCbeyond vtx region Carbon seems to be the best choice (  proton polarimeter)

e+e-  pp with FINUDA Low energy protons: annihilation can help  s = 1890 MeV, B = 0.2 T

Efficiency and resolution for pp tracks E=1.0 GeV E=1.1 GeV E=1.2 GeV B=10 kgauss PRELIMINARY MC STUDY proton efficiency For comparison in real data: - Muons in K+ →  +  /p<1% for P  =235 MeV/c

Proton angular distributions Projected data assuming |G E | = |G M | Integrated luminosity L =100 pb -1 Constant detection efficiency  =80% fit of angular distributions in the FINUDA coverage F(  )=A(1+cos 2  )+Bsin 2  |G E ||G M | FINUDA Max sensitivity to |G E |

e+e-  nn with FINUDA  s = 1890 MeV, B = 0.2 T 1.5 cm carbon converter strong  background reduction if N tracks > 2 neutron TOF signal in coincidence A. Filippi, INFN Torino

Neutron efficiency E beam Expected efficiency for antineutron annihilation (1.5 cm carbon converter) PRELIMINARY Neutron efficiency in 10 cm of scintillators (TOFone)  = % The two techniques can be combined to increase the efficiency - close to threshold  antineutron detection - higher energy  antineutron OR neutron

Neutron angular distributions Projected data assuming |G E | = |G M | (black) or |G E | = 0 (red) Integrated luminosity L =100 pb -1 Constant detection efficiency  =15% fit of angular distributions in the FINUDA coverage F(  )=A(1+cos 2  )+Bsin 2  FINUDA |G E ||G M |

FF measurement: projected accuracy Integrated luminosity  pb -1 KLOE in last 12 months: 1800 pb -1 at  mass prototne protonneutron

Induced polarization non negligible polarization P y maximal at 45° and 135° high discriminating power between theories extraction of FF relative phase Polarization normal to the scattering plane No beam polarization

Polarization measurement The polarization is measured through secondary scattering in a strong interaction process The spin-orbit coupling causes an azimuthal asymmetry in the scattering tracking system  analyzer pp ss e+e+ e-e- p p P PCPC z’ drift chambers straw tubes TOFone Vertex region OSIM Analysing power

Proton polarimeter Multiple scattering cut Angular cut  5° is required MAIN BACKGROUND SOURCE: multiple scattering at small angles Mainz polarimeter data E p ~ 1.1 ÷ 1.2 GeV scatterer thickness: 7 cm Moliere radius:  m 1.5 o

Fits of exp. data T=60 MeV T=100 MeV T=260 MeV Carbon analysing power A c known from few tenths of MeV up to some GeV Average values  =5°-20° Multiple scattering cut

Polarization measurement Polarization is extracted by measuring asymmetries y  + - x For example, for P y pol (  cos  ) Averaged analysing power ~ 50 % Polarization ~ 15% max (pQCD model) Expected effect of the order of few % at E BEAM = 1.2 GeV For Δ R/R  30 %: total luminosity  2500 pb -1 (1 year with average cm -2 s -1 )

Integrated luminosity protonneutron s [GeV 2 ]E beam [MeV] L [pb -1 ] cross (100)section (100) (100) (100) polarization

Hyperon Form Factors Hyperons can also be produced in e + e - interactions ( , , …) energy threshold: √s ~ 2 M  ~ 2.23 GeV 2 From u-spin invariance: G M n ~ 2 G M  Smaller cross section as for nucleon production  TOT ~ 0.1 nbarn Production rates comparable with N N are expected Y Y final state could be identified by detecting the decay of one hyperon Angular distributions  moduli of FF For weakly decaying hyperons ( ,  ± (1189)) the polarization measurement does not require a polarimeter

angular distribution of the proton Weak decay does not conserve parity A  A S + A P P-wave, parity conserving S-wave, parity non conserving  polarization To measure normal  polarization: asymmetry of proton angle with respect to the normal to the scattering plane high efficiency is expected (~ 50 %)

Conclusions The increase of DAΦNE energy above the nucleon-antinucleon threshold is possible with minor changes in the machine FINUDA is well suited for the Nucleon FF measurement - good proton resolution - adequate neutron detection - easy implementation of a polarimeter Possibility to improve the neutron detection - two (or more) converters - new array of scintillators just before the end-cap - neutron polarimeter

Momentum reconstruction E beam = 1.2 GeV - P p = 748 MeV/c  =6.4%  =2.5%  =3.7%  =1.9% For comparison in real data: Electrons from Bahba scattering  =3.2% for P e =510 MeV/c Muons in K+ →  +  <1% for P  =235 MeV/c PRELIMINARY

Angular distributions LEAR data p p → e + e - BaBar data e + e - →  p p M pp =2.1 M pp =1.91 M pp =2.05 M pp =1.98M pp =1.96 DR analysis

Anomalous behavior in total cross section BaBar found steps in total cross section at  s =2.2 and 2.9 GeV

Resonance below ppbar threshold? Some anomaly found close to the physical threshold multihadronic cross section Proton FF Combined fit M=1870±10 MeV  =10±5 MeV

6  production DM2 experiment Anomaly close to NN threshold e + e - → 3  + 3  - Same structure in diffractive pion photoproduction FNAL M = ± ± GeV  = 29 ± 11 ± 4 MeV J PC = 1 -- I G = 1 +  p → p 3  + 3  - Mass and width consistent with  (mhad) and proton FF fit Results confirmed by BaBar (unpublished yet) new vector meson? NN bound state?

Stat. error on FF measurement PROTON NEUTRON E BEAM =942 MeV/c E BEAM =1067 MeV/c E BEAM =1178 MeV/c Assuming G E =G M

Total cross section Full lines