The shad measurement at DAFNE collider

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The shad measurement at DAFNE collider
DAFNE ee- collider on f - mass ? s 1.02 GeV
61 of a?had is covered by the r -
resonance region 0.5 GeV
lt ?s lt 0.9 GeV
DAFNE can contribute with the
s(ee- ? hadrons) measurement from the threshold
up to the f mass
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The radiative return method
Standard way energy scan of the beams
Alternative Approach ee-?
hadrons g at ?sMf where
g is emitted in the initial state (ISR)
the invariant mass of the hadronic system
M2had Mf2-2 MfEg changes
continuously in 4mp2 lt M2had lt Mf2
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Radiative return vs Energy scan

• errors on luminosity and on the center of mass
  energy of ee-
• 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

• define acceptance cuts
• use a description with
• 1 radiative photon
• e e - ? p p - g

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Radiation description ISR and FSR
EVA Montecarlo generator S. Binner,
J.H. Kühn, K. Melnikov Phys. Lett. B 459
(1999)
ISR (signal) enhanced by the ?-resonance
Eg gt10 MeV

peaked at small angle
5lt ?gCMlt21 55lt ?p lt125 (pTgt200 MeV)

ISR/(ISRFSR)gt99
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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 lt qg lt40
Comparison Data/MC looks good EVA -MC
describes FSR on the some - level
60 lt qg lt120
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The background f ? f0 g ? p p - g
The direct decay ? ? ? ? - ? affects the
region M2had gt 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 lt qg lt120
Contribution in that region at the few level
K. Melnikov, F. Nguyen, B. Valeriani, G.
Venanzoni 2000
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The shad measurement at KLOE
Superconducting Coil B0.6 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 / 52140 sense / total
wires all stereo wires
Be beam pipe (0.5 mm thickness) permanent Quads
instru- mentation (32 PMTs)
sp / p lt 0.4 sz 2 mm
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II. The strategy
e e - ? p p - ?
- the acceptance efficiency eacc is evaluated
from MC - the global selection efficiency
esel is evaluated from DATAMC - 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 0 (BR 15.5
)

• the Luminosity is measured using Bhabha
  scattering at large angles

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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
?(x2vtx y2vtx ) lt 8 cm zvtx lt 15 cm
5 lt ?gCM lt 21 55 lt ?p lt 125 ( pTgt200
MeV)
- Use drift chamber for p tracks detection
and vertex reconstruction - Use calorimeter for
p identification no explicit g
detection needed !
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IV. Bhabha rejection
cut Log(rL) 0 for each bin
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Before Likelihood ( Rad. Bhabhas )
Mtrk is defined by
After Likelihood
Mtrack (MeV)
V. The residual backgrounds
p p-g
ee-g
m m-g
cut 2s around the ppg peak
p p-po
Mtrack (MeV)
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VI. f ? p p - p 0 rejection
p p- p0
p p- g
Mtrack (MeV) vs M2pp (GeV2)
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VII. The measurement of the luminosity

• Use Large Angle Bhabhas ( seff 425nb )
• 55 lt q - lt 125
• Acoll. lt 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 lt 1
C.M.C. Calame et.al. Nucl. Phys., B 584
(2000)
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Preliminary results
I. ds/dM2pp spectrum
16.4 pb-1 of Nov./Dec. 2000 Data
Acceptance cuts
5 lt ?gCM lt 21 55 lt ?p lt 125 ( pTgt200
MeV)
data 3.72 0.14 (stat.) nb
MC 3.55 0.07 (stat.) nb systematic ?
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II. The pion form factor
Fpp 2
theoretical function (superimposed) from
Gounaris-Sakurai parametrization? ? with
mr 770 MeV mw 782 Mev
Gr 150 MeV Gw 8.5
MeV
?s (MeV)
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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 qg0