Nucleon05 Frascati 1214 Octobre 2005

1
Nucleon05Frascati 12-14 Octobre 2005

• Morceaux choisis
• (D. Bettoni, M. Mirazita and V. Druzhinin)
• 
  S. Ong

2
(No Transcript)
3
C is the Coulomb correction factor, taking into
account the QED coulomb interaction. Important
at threshold.
? finite
There is no Coulomb correction in the neutron
case.
4
Form Factor Properties

• At threshold GEGM by definition, if F1 and F2
  are analytic functions with a continuous
  behaviour through threshold.
• GE (4mp2) GM (4mp2)
• Timelike GE and GM are the analytical
  continuation of non spin flip and, respectively,
  spin flip spacelike form factors. Since timelike
  form factors are complex functions, this
  continuity requirement imposes theoretical
  constraints.
• Two-photon contribution can be measured from
  asymmetry in angular distribution.

5
Proton Magnetic Form Factor GM
The first experiment to produce a positive
result for the proton timelike form factor was
carried out at ADONE in Frascati ee- ??pp The
measurement was based on 0.2 pb-1 of data at 4.4
GeV2 yielding 25 events.
6
Proton Magnetic Form Factor GM
The first measurement of the timelike form
factors at threshold is due to the ELPAR
experiment at CERN. They observed 34 events of
?pp annihilation at rest in a liquid H2
target. The measurement assumes GEGM
7
Proton Magnetic Form Factor GM
Various measurements of the proton form
factors were carried out at DCI in Orsay
using ee- ??pp The first experiment was DM1
which recorded 63 events in 4 data points.
8
Proton Magnetic Form Factor GM
At DCI in ORSAY the DM2 collected data in three
data taking runs for a total of 0.7 pb-1. With a
total of 112 events in 6 points they
attempted to measure the angular distribution,
from which they could fit GM/GE0.34, but
GEGM was still allowed.
9
Proton Magnetic Form Factor GM
The first high-statistics measurement of the
timelike form factors was carried out at LEAR by
the PS 170 collaboration. They recorded a total
of 3667 ?pp ? ee- events in 9 data points. The
angular distribution is compatible with
GEGM. First indication of steep rise near
threshold.
10
Proton Magnetic Form Factor GM
The E760 experiment at Fermilab produced the
first measurement of the form factors at high Q2
?pp ? ee- Very difficult measurement due to
very small cross section. They recorded 29
events. The measurement assumes GEGM.
11
Proton Magnetic Form Factor GM
The FENICE experiment at ADONE, primarily
devoted to the measurement of the neutron form
factor, produced also a measurement of the proton
magnetic form factor with 69 events in 4 points.
12
Proton Magnetic Form Factor GM
E835 at FNAL, continuation of E760, made further
measurements at high Q2 with a total of 206
events in 2 data taking runs.
13
Proton Magnetic Form Factor GM
A new measurement at high Q2 was recently
made by the CLEO at CESR in ee- ??pp. It assumes
GEGM. The measurement is based on 14 events.
14
Proton Magnetic Form Factor GM
Another measurement of the proton timelike
form factors has been reported by BES. The
measurement covers 9 data points from (2.0
GeV)2 to (3.07 GeV)2 using the hypothesis
GEGM.
15
Proton Magnetic Form Factor GM

• BaBar measurement using
• Initial State Radiation (ISR)
• ee- ???pp
• Advantages
• All energies at the same time
• ? fewer systematics
• CMS boost
• ? easier measurement at threshold
• Disadvantages
• Luminosity proportional to invariant mass bin L
  ???s
• More background

16
Asymptotic Behavior
The dashed line is a fit to the PQCD prediction
The expected Q2 behaviour is reached quite early,
however ...
17
Asymptotic Behavior
The dashed line is a fit to the PQCD prediction
The expected Q2 behaviour is reached quite early,
however ... ... there is still a factor of
2 between timelike and spacelike.
18
Threshold Q2 Dependence
Steep behavior near threshold observed by PS 170
at LEAR (2000 events).
19
BaBar Measurement using ISR
BaBar measurement very near threshold confirms
steep rise of Form Factor
20
Neutron Timelike Form Factor

• Only one measurement
• FENICE at ADONE

80 events
The neutron form factor is bigger than that of
the proton !!!
21
Why measure time-like FFs

• Proton FFs have been measured from threshold up
  to 15 GeV2
• 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
GEGM Space-like data showed that this
relation is valid only at threshold Different
hypothesis on GE/GM produce large changes in
the FF
22
Proposal for nucleon FF measurement at DAFNE2
A Letter of Intent has been already signed by
more than 70 physicist from 22 institution and 6
countries
23
Experimental requirements

• Beam requirements
• beam energy gt 1 GeV
• high luminosity 1032 cm-2 s-1 (cross section
  0.1-1 nb)
• beam polarization not required (but could help)

• Detector requirements
• high detection acceptance for charged and
  neutral particles
• identification of exclusive final state
• - protons ? momentumTOF
• - high neutron efficiency
• - detection of antinucleons ? converter
• installation of a polarimeter
• - carbon analyzer 2 tracking systems

24
Possibility of upgrading the energy in DAFNE up
to 2.4 GeV
25
DAFNE 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

26
The DAFNE detectors
FINUDA
27
The FINUDA detector

• 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)

drift chambers
straw tubes
TOFone
10 cm

• 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)

28
Proton angular distributions

• Projected data assuming GE GM
• Integrated luminosity L100 pb-1
• Constant detection efficiency e80
• fit of angular distributions in the FINUDA
  coverage
• F(q)A(1cos2q)Bsin2q

29
ee-?nn with FINUDA
A. Filippi, INFN Torino
?s 1890 MeV, B 0.2 T

• strong gg background reduction if Ntracks gt 2
• neutron TOF signal in coincidence

30
Neutron angular distributions

• Projected data assuming GE GM (black) or
  GE 0 (red)
• Integrated luminosity L100 pb-1
• Constant detection efficiency e15
• fit of angular distributions in the FINUDA
  coverage
• F(q)A(1cos2q)Bsin2q

31
FF measurement projected accuracy
prototne
Integrated luminosity ? 700-1000 pb-1
KLOE in last 12 months 1800 pb-1 at F mass
32
Induced polarization
33
Polarization measurement
34
Carbon analysing power
Ac known from few tenths of MeV up to some GeV
35
Polarization measurement
Expected effect of the order of few at EBEAM
1.2 GeV
For ?R/R ?30 total luminosity ?2500 pb-1 (1
year with average 1032 cm-2 s-1)
36
Integrated luminosity
37
Anomalous behavior in total cross section
BaBar found steps in total cross section at ?s
2.2 and 2.9 GeV
38
Resonance below ppbar threshold?
Combined fit M187010 MeV G105 MeV
39
6p production
40
Conclusions

• The increase of DAFNE 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

41
ISR m
Mass spectrum of pp system in the ee- ? pp?
reaction is related to cross section of ee- ? pp
reaction at Em.
ee- ? pp cross section depends on two form
factors, electric GE and magnetic GM.
The ratio of form factors GE/GM can be obtained
from the analysis of the proton angular
distribution. The terms corresponding GM and GE
have angular dependence close to 1cos2? and
sin2?, respectively.
42
BaBar detector

• DIRC
• Quartz Cherenkov radiator
• Covers 80 of solid angle
• Particle ID above 600 MeV/c

• DCH
• 40 layers, axial and stereo wires.
• Covers 92 of solid angle
• dpt/pt 0.5 -1.5
• Particle ID up to 600 MeV/c

• EMC
• 6580 CsI(Tl) crystals
• Covers 91 of solid angle
• E resolution 2 at high E.

43
Event selection
Data 232 fb-1 collected during 1999-2004

• At least 2 tracks with

• Rxy lt 2.5 cm
• ?z lt 6cm
• p? gt 0.1 GeV/c
• 0.45 lt ? lt 2.4

• A photon with ECM gt 3 GeV and 0.375 lt ? lt 2.4
• Two tracks must pass proton selector
• The kinematic fit is applied imposing energy and
  momentum conservation under different mass
  hypotheses

44
KK-, ??-, ??-, ee- background
data
K
?
?
45
Background subtraction
N1 and N2 are numbers of events with ?2 lt 30 and
30 lt ?2 lt60, respectively. ?N1/N2
Since the result of JETSET for rare processes
requires confirmation we use the method of
background subtraction based on the difference of
?2 distributions for signal and background
events.
pp?
Nbkg5020 is in an agreement with the
estimation from simulation, 395.
pp?0?
pp?0
46
Mass spectrum
47
GE/GM ratio
BaBar GE/GM measurements vs previous ones
and dispersion relation prediction (yellow) based
on JLab space-like GE/GM and analyticity
DM2FENICE

• BaBar
• LEAR
• hep-ph/0507085

E835
48

• The ee-? pp cross section and proton form factor
  have been measured from threshold up to 4.5 GeV.
• The form factor have complex mass dependence. We
  confirm near-threshold enhancement observed in
  LEAR experiment. There are also two mass regions,
  near 2.25 and 3 GeV, with the rapid decrease of
  the form factor.
• The GE/GM ratio has been measured from
  threshold to 3GeV. We have observe noticeable
  deviation of this ratio from unity, in
  disagreement with previous LEAR measurement.