1. The shad measurement at DAFNE collider
DAFNE: e+e- collider on f - mass  s = 1.02 GeV
61% of ahad is covered
by the r - resonance region:
0.5 GeV < s < 0.9 GeV
DAFNE can contribute with
the s(e+e-  hadrons) measurement from the threshold
up to the f mass
Anna Ferrari - KAON 2001, June

2. The radiative return method
Standard way: energy scan of the beams
Alternative Approach:
e+e- hadrons + g at s=Mf
where g is emitted in the initial state (ISR)
the invariant mass of the hadronic system:
M2had = Mf2-2 MfEg
changes continuously in 4mp2 < M2had < Mf2
Anna Ferrari - KAON 2001, June

3. Radiative return vs Energy scan
Radiative return: a direct, pure QED, alternative method
to measure s (e+e-  hadrons)
errors on luminosity and on the center of mass energy of e+e-
are the same for the full energy range
by-product of the standard research program of KLOE
BUT:
accurate knowledge of the photon emission including radiative corrections
is needed
In practice, since there are regions with
ISR strongly enhanced:
- use a description of e+e-  hadrons + n g
(all radiative corrections included)
- fold with the detector description
- fit the experimental data
The most precise way is
the inclusive approach
define acceptance cuts
use a description with
1 radiative photon:
e + e -  p + p - g
Anna Ferrari - KAON 2001, June

4. + = Radiation description: ISR and FSR EVA * Montecarlo generator qg
* S. Binner, J.H. Kühn, K. Melnikov Phys. Lett. B 459 (1999)
Eg (MeV) qg
FSR
(background):
enhanced
at small energies
follows pion
angular distribution
ISR (signal):
enhanced by
the -resonance
Cut in Eg-qg-plane :
Eg >10 MeV +
peaked at
small angle
5°< gCM<21°
55°< p <125°
(pT>200 MeV) =
ISR/(ISR+FSR)>99%
Anna Ferrari - KAON 2001, June

5. Comparison Data/MC looks good
Test of FSR/ISR simulation
An efficient test of the MC model of FSR
is the check of the charge asymmetry
of pion pairs:
20° < qg <40°
Comparison Data/MC looks good
EVA -MC describes
FSR on the some % - level
60° < qg <120°
Anna Ferrari - KAON 2001, June

6. The background f  f0 g  p + p - g
The ‘direct’ decay   +  -  affects the region: M2had > 0.8 GeV2
Problem: the parameters of the f0 -meson through which the decay
proceeds:  f0  +  -  are poorly known.
constructive or destructive interference with FSR?
Solution: study interference from 0 0  decay:
study the charged decay experimentally at large photon angle:
complementary analysis to hadronic cross section
BR(f0  p0p0 )Exp = (0.80.090.06)•10-4 KLOE coll
1999 data
60° < qg <120°
Contribution in that region at the few % level*
*K. Melnikov, F. Nguyen, B. Valeriani, G. Venanzoni 2000
Anna Ferrari - KAON 2001, June

7. The shad measurement at KLOE
Superconducting Coil B=0.6 T
I. The KLOE detector
Iron Yoke
Electromagnetic Calorimeter
Pb / Scintillating Fibres
(4880 PMTs)
Endcap - Barrel - Modules
sE /E = 5.7% /E(GeV)
s t= 57 ps /E(GeV)  50 ps
Cylindrical Drift Chamber
4 m , 3.3 m Length
90% Helium, 10% Isobutane
12582 / sense / total wires
all stereo wires
Be beam pipe
(0.5 mm thickness)
permanent Quad’s instru-
mentation (32 PMTs)
sp / p < 0.4%
sz = 2 mm
Anna Ferrari - KAON 2001, June

8. e+ e -  e+ e -  (radiative Bhabha) e+ e -  m+ m - 
II. The strategy
e+ e -  p+ p - 
- the acceptance efficiency eacc is evaluated from MC
- the global selection efficiency esel is evaluated from DATA+MC
- the trigger efficiency etrig is evaluated from DATA
the experimental Backgrounds come from:
e+ e -  e+ e -  (radiative Bhabha)
e+ e -  m+ m - 
e+ e -  f  p+ p - p (BR = 15.5 %)
the Luminosity is measured using Bhabha scattering at large angles
Anna Ferrari - KAON 2001, June

9. III. The event selection
1 charged vertex close to IR
with 2 connected tracks +
acceptance cuts:
Likelihood method for p/e discrimination
kinematical cuts for residual
background suppression
Event Display DIDONE p+ p- g
(x2vtx +y2vtx ) < 8 cm
|zvtx | < 15 cm
5° < gCM < 21°
55° < p < 125°
( pT>200 MeV)
- Use drift chamber for p tracks detection
and vertex reconstruction
- Use calorimeter for p identification
no explicit g detection needed !
Anna Ferrari - KAON 2001, June

10. IV. Bhabha rejection elik - A Likelihood method based on:
- ToF of ‘charged ’ clusters in EmC
- shape and energy deposition of the charged cluster
- +  - 0 are used for Pion information
- e+ e - g are used for Electron information
- We use two data samples:
- A relative likelihood function is defined for different bins in momentum e
|p| [MeV]
elik
 98%
Log(rL)
cut:
Log(rL) = 0
for each bin
Anna Ferrari - KAON 2001, June

11. V. The residual backgrounds p+ p-g
Before Likelihood
( Rad. Bhabhas )
Mtrk is defined by:
After
Likelihood
Mtrack (MeV)
V. The residual backgrounds
e+e-g
p+ p-g
cut:
2s around the ppg peak
m+ m-g
p+ p-po
Mtrack (MeV)
Anna Ferrari - KAON 2001, June

12. VI. f  p + p - p 0 rejection
p+ p- p0
These events are separated at the streaming level
by applying a cut in the ( Mtrack , Mpp ) plane
we look at the events that fall
in the ppg selection cut
p+ p- g
6.5 pb-1
60°<Qg<120°
5°<Qg<21°
p+ p- p0
Background in
p+ p- p0 is dominating
the very low Mpp2 - region
p+ p- p0 background
is almost negligible
21°<Qg<60°
Mtrack (MeV) vs M2pp (GeV2)
Anna Ferrari - KAON 2001, June

13. VII. The measurement of the luminosity
Use Large Angle Bhabhas ( seff = 425nb ):
55° < q + - < 125 °
Acoll. < 9 °
E+ -  400 MeV
* Data
BABAYAGA*
- Berends/Drago/Venanzoni
Track - Energy (MeV)
LAB - Candidates
(Systemat., Accept.)
Background
(gg, ppg, ...)
Theoret. Generators
with rad. corrections
Track - Polar angle
Berends/Drago/Venanzoni
BABAYAGA*
Luminosity- Measurement on % Level
agreement with independent gg-Counter < 1%
* C.M.C. Calame et.al.
Nucl. Phys., B 584 (2000)
Anna Ferrari - KAON 2001, June

14. Preliminary results I. ds/dM2pp spectrum
16.4 pb-1 of Nov./Dec Data
dspp/dM2pp (nb/GeV2)
M2pp (GeV2)
Acceptance cuts:
5° < gCM < 21°
55° < p < 125°
( pT>200 MeV)
data:
3.72 ± 0.14 (stat.) nb
MC:
3.55 ± 0.07 (stat.) nb
systematic  2%
Anna Ferrari - KAON 2001, June

15. |Fpp |2 II. The pion form factor s (MeV)
theoretical function (superimposed)
from Gounaris-Sakurai parametrization
 with:
mr = 770 MeV mw = 782 Mev
Gr = 150 MeV Gw = 8.5 MeV
s (MeV)
Anna Ferrari - KAON 2001, June

16. Conclusions and Outlook
A method for the hadronic cross section measurement using the radiative
return coming from ISR, has been tested at KLOE with 16.4 pb-1.
The agreement with the EVA MC prediction (Kühn et.al.) is good
(at the level of few %)
Efficiencies, Systematics effects, Background and Luminosity
are under control at the level of few %
future:
- refine the evaluation of all the effects, from data
- work out the possibility to perform an inclusive measurement
- measure shad at the level of 1% with an integrated Lumi. of 200pb-1
Input from theory: NLO generator from Kühn et.al.
 increases statistics and reduces systematics, going down to qg=0
Anna Ferrari - KAON 2001, June