Evaluation of a m pp between 0.35 and 0.95 GeV 2 with data from the KLOE detector. Stefan E. M üller Laboratori Nazionali di Frascati. (f or the KLOE collaboration). 2007 Europhysics Conference on High Energy Physics Manchester, 19-25 July 2007. Dispersion integral :. .
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Evaluation of ampp between 0.35 and 0.95 GeV2 with data from the KLOE detector
Stefan E. Müller
Laboratori Nazionali di Frascati
(for the KLOE collaboration)
2007 Europhysics Conference on High Energy Physics
Manchester, 19-25 July 2007
Dispersion integral:
ahadr can be expressed in terms of
(e+e- hadrons) by the use of a
dispersion integral:
(e+e-+-) with ISR:
Mhadr
ds(e+ e- hadrons +g)
dMhadr
=s(e+ e- hadrons) H(Mhadr)
Particle factories have the opportunity to measure the cross section
s(e+ e- hadrons) as a function of the hadronic c.m. energy M hadr by using
the radiative return:
This method is a complementary approach to the standard energy scan.
Neglecting FSR effects:
Requires precise calculations of the radiator H
EVA + PHOKHARA MC Generator
(S. Binner, J.H. Kühn, K. Melnikov, Phys. Lett. B 459, 1999)
(H. Czyż, A. Grzelińska, J.H. Kühn, G. Rodrigo, Eur. Phys. J. C 27, 2003)
DANE: A -Factory
e+e--collider with =m1.0195 GeV
Integrated Luminosity
Peak Luminosity Lpeak= 1.4 • 1032cm-2s-1
Total KLOE int. Luminosity:
L dt ~ 2500 pb1 (2001 - 05)
DEAR,
This talk is based on 240pb-1
from 2002 data!
KLOE Detector
Driftchamber
sp/p = 0.4% (for 900 tracks)
sxy 150mm, sz 2 mm
Excellent momentum
resolution
KLOE Detector
sE/E = 5.7% /E(GeV)
sT= 54 ps /E(GeV) 50 ps
(Bunch length contribution subtracted from constant term)
Excellent timing resolution
Electromagnetic Calorimeter
Event Selection
Pion tracks at large angles
50o< p <130o
a) Photons at small angles
< 15oor > 165o
No photon detection!
Event Selection
Pion tracks at large angles
50o< p <130o
a) Photons at small angles
< 15oor > 165o
No photon detection!
b) Photons at large angles
50o< < 130o
detector!
Event selection
MTrk (MeV)
220
200
p+p-p0
180
p+p-g(g) signal
region
160
140
120
m+m-g(g)region
(+ e+e-g(g)
100
80
0.4
1.0
0.5
0.6
0.7
0.8
0.9
0.3
Mpp2(GeV2)
and Missing Mass Mmiss
(defined by 4-momentum conservation
under the hypothesis of e+e-+-x
To further clean the samples from radiative Bhabha events, a particle ID estimator for each charged track based on Calorimeter Information and Time-of-Flight is used.
Published result with 2001 data
Published KLOE Result:
Improvements/updates with respect to 2001:
Phys. Lett. B606 (2005) 12
s (e+e- p+p- ) nb
30% cosmic veto inefficiency
recovered in 2002 by introducing additional software trigger level
KLOE
2001 Data
140pb-1
Improved offline-event filter reduces its systematic uncertainty to <0.1%
New generator [email protected] - theoretical error of Bhabha reference cross section goes from 0.5% to 0.1% - Bhabha cross section value is lowered by 0.7%
Trigger efficiency correction had to be updated due to a doublecounting of
efficiencies.
Mpp2 (GeV2)
app(0.35-0.95 GeV2) =
(388.7 0.8stat4.9syst) · 10-10
Trigger 2001 update
Impact of update on trigger correction on 2001 cross section:
KLOE 2001 TRG updated
KLOE 2001 published
KLOE 2001 TRG updated
KLOE 2001 published
Changes published value on app by 0.4%
Small angle analysis 2002
Preliminary!!!
Statistics: 242pb-1 of 2002-data
3.4 Million Events
qMiss<150 or
qMiss>1650
r-w Interference
M2(GeV2)
M2(GeV2)
Luminosity:
At KLOE, Luminosity is measured using „Large angle Bhabha“ events (55o<qe<125o)
KLOE is its own Luminosity Monitor!
The luminosity is given by the number of Bhabha events divided for an effective cross section obtained by folding the theory with the detector simulation.
New version of generator gives 0.7% decrease in cross section
compared to previous version
Quoted accuracy:
0.1%
Radiative corrections
Fp=1
s (ppg) with Fp=1 [nb]
H(s)
Radiator-Function H(s) (ISR):
Radiative Corrections:
i) Bare Cross Section
divide by Vacuum Polarisation
from F. Jegerlehner:
http://www-com.physik.hu-berlin.de/~fjeger/
ii) FSR - Corrections
Cross section spp must be incl. for FSR
FSR corrections have to be taken into account
in the efficiency eval. (small angle acceptance, MTrk) and in the passage M2
Net effect of FSR is ca. 0.8%:
FSR contr. (sQED)
Small angle result from 2002 data:
Preliminary!!!
Systematic errors on ampp:
STotal= 1.1%
Comparison 2001-2002:
(updated)
Evaluating amppwith small angle
Dispersion integralfor2p-channel in energy interval 0.35 <Mpp2<0.95 GeV2
2001 published result (Phys. Lett. B606 (2005) 12):
app(0.35-0.95GeV2) = (388.7 0.8stat4.9syst) · 10-10
Applying update for trigger eff. and change in Bhabha-cross section used for luminosity evaluation:
app(0.35-0.95GeV2) = (384.4 0.8stat4.9syst) · 10-10
2002 preliminary:
app(0.35-0.95GeV2) = (386.3 0.6stat3.9syst) · 10-10
Large angle analysis:
p
g
f, r
p
g
f
p
p
f
g
f0
r
p
p
small!
important!
Preliminary!!!
angle analysis
(4-momentum constraints)
240 pb-1
2002 Data
Nr. of events / 0.01 GeV2
Mpp2 [GeV2]
Threshold region non-trivial
due to irreducible FSR-effects, to be estimated from MC using phenomenological models (interference effects unknown)
&
&
f0
FSR
rp
Large angle analysis (cont‘d):
p+
g
p-
W
Apply dedicated selection cuts:
Preliminary!!!
2002 Data L = 240 pb-1
LA stat.+syst.
error
Error on LA dominated by syst. uncertainty on f0 contr.
Mpp2 [GeV2]
Comparison SA-LA 2002:
Preliminary!!!
(sLA-sSA)/sSA
Range of comparison
LA stat.+syst.
error
Range of comparison
app between 0.5 - 0.85 GeV2:
Small angle:
app(0.50-0.85GeV2) =
(255.4 0.4stat 2.5syst) · 10-10
Large angle:
app(0.50-0.85GeV2) =
(252.5 0.6stat 5.1syst) · 10-10
(60% of systematical error due to f0-uncertainty)
ampp Summary:
Summary of the small angle results:
Preliminary!!!
Jegerlehner (hep-ph/0703125):
Using new KLOE result would increase difference from 3.2s to 3.4s
ampp Summary:
Comparison withamppfrom CMD2 and SND in the range 0.630-0.958 GeV :
Phys. Lett. B648 (2007) 28
Preliminary!!!
Conclusions:
KLOE results also agree with recent results on app from the CMD2 and SND experiments at VEPP-2M in Novosibirsk
Outlook:
(outside the f resonance)