1. KLOE results on Hadronic cross section
Graziano Venanzoni
Laboratori Nazionali di Frascati
(for the KLOE collaboration)
Topical Workshop on (g-2)
Glasgow, Oct 2007

2. Outlook Motivation of s(e+e- ) at low energy
Reminder: KLOE published results on |F and awith 2001 data (normalization to Bhabha)
Update of |F and a with 2002 data, using two selection schemes (large and small angle)
Work in progress:
Extract |F via bin-by-bin normalisation to 
Use data collected at 1 GeV
Ccorreggere extract fpi …

3. a= (g-2)/2 =  aaaaa
had and the muon anomaly
Hadronic Cross Section & Muon-Anomaly
Motivation:
High Precision Test of the Standard Model
 Anomalous magnetic moment of the muon
 Fine structure constant at Z0-mass aQED (MZ)
Hadronic Vacuum Polarization
2nd largest contribution, pQCD not applicable
Error of hadronic contribution dominates total error of am! µ+ g* q
Muon-Anomaly
a= (g-2)/2 = 
aaaaa
theo
QED
had
weak
New physics
Dispersion-Relation
Channel  = s(e+ e )
gives >70% contribution to ahad!
K(s) = analytic kernel-function,
above typically 2…5 GeV, use pQCD
Alternative: Spectral function from
decay ( t  nt Hadrons) taking into
account isospin breaking corrections
amhad
shad (s)
M. Davier

4. (e+e-+-) with ISR:
Since DANE runs at fixed energy (1020 MeV), we measure the cross section
s(e+ e-  hadrons ) as a function of the hadronic c.m. energy M hadr by using
ISR (”radiative return”):
This method is a complementary approach to the standard
energy scan.
Rho - Resonanz
dds
0.1
0.3
0.5
0.7
0.9
Mpp2 [GeV2]
a.u.
S. Binner, J.H. Kühn, K. Melnikov, Phys. Lett. B 459, 1999
Neglecting FSR effects: = ) ( 2 s dM d M pp
ppg
H(s)
4mp2£ sp = M£ mf2
Mettere la seconda aprte come flash
Radiator
function H(s)
Luminosity, acceptance (and other normalizations) enter only once !
Requires precise calculations of the radiator H
 PHOKHARA MC NLO Generator
(H. Czyż, A. Grzelińska, J.H. Kühn, G. Rodrigo, Eur. Phys. J. C 27, 2003)
H. Czyz
0.1
0.3
0.5
0.7
0.9
Mpp2 [GeV2]

5. This talk is based on 240pb-1
DANE: A -Factory
e+e- - collider with =m GeV
Integrated Luminosity
Peak Luminosity Lpeak= 1.5 • 1032cm-2s-1
Total KLOE int. Luminosity:
L dt ~ 2500 pb1 ( )
DEAR,
This talk is based on 240pb-1
from 2002 data!
2006:
Energy scan with 4 points around m-peak
220 pb-1 at = 1000 MeV

6. KLOE Detector sp/p = 0.4% (for 900 tracks) sxy  150 mm, sz  2 mm
Drift chamber
sp/p = 0.4% (for 900 tracks)
sxy  150 mm, sz  2 mm
Excellent momentum
resolution

7. Excellent timing resolution
KLOE Detector
Electromagnetic Calorimeter
sE/E = 5.7% / E(GeV)
sT = 54 ps / E(GeV) 100 ps
(Bunch length contribution subtracted from constant term)
Excellent timing resolution

8. Extracting |F|2 from eve:
a) Via absolute Normalisation to VLAB Luminosity (as in 2001 analysis):
dsg(g)/dM2 is obtained by subtracting background from observed event spectrum, divide by selection efficiencies, and int. luminosity: 1)
Obtain s from (ISR) - radiative cross section dsg(g)/dM2 via theoretical radiator function H(s): 2)
Ccorreggere extract fpi … 3)
Relation between |Fp|2 and the cross section s(e+e-  +-)
b) Via bin-by-bin Normalisation to rad. Muon events (see later…)

9. Event Selection Pion tracks at large angles 50o< p <130o
a) Photons at small angles
 < 15o or  > 165o
 Photon momentum from kinematics:  
High statistics for ISR photons
Very small contribution from FSR
Reduced background contamination   

10. Event Selection Pion tracks at large angles 50o< p <130o
a) Photons at small angles
 < 15o or  > 165o
 Photon momentum from kinematics:  
High statistics for ISR photons
Very small contribution from FSR
Reduced background contamination  
b) Photons at large angles
50o <  < 130o  
Photon is explicitly measured in the detector!
Threshold region accessible
Increased contribution from FSR
Contribution from
f0(980)

11. Published result, 2001 data Published KLOE Result:
Acceptance
0.3%
Trigger
Tracking
Vertex
Reconstruction filter
0.6%
Particle ID
0.1%
Trackmass cut
0.2%
Background
Unfolding effects
Total experimental Error %
Luminosity ( LA Bhabhas )
Vacuum polarization
FSR corrections
Radiator function
0.5%
Total theoretical Error %
TOTAL ERROR 1.3%
Acceptance
0.3%
Trigger
Tracking
Vertex
Reconstruction filter
0.6%
Particle ID
0.1%
Trackmass cut
0.2%
Background
Unfolding effects
Total experimental Error %
Phys. Lett. B606 (2005) 12
s ( e+e-  p+p- ) nb
KLOE
2001 Data
140pb-1
Statistical error negligible
(1.5 Million events)
Phys. Lett. B606 (2005) 12
app( GeV2) = (388.7  0.8stat4.9syst) · 10-10

12. C. M. Calame et al., Nucl. Phys. B758 (2006) 227
2002 data: improvements wrt 2001
Larger data set allows for more refined evaluation of systematic errors
associated with selection efficiencies; evaluate all contributions again
2002 data less effected by pile-up events from machine background
additional online software trigger level introduced to recover cosmic veto
inefficiency in 2002 (that gave an inefficiency of up to 30% in 2001)
Improved offline-event filter reduces its systematic uncertainty to <0.1%,
was the largest contribution (0.6%!) to the error in published result
Trigger issue in 2001 data resolved (see below)
New event generator - theoretical error of Bhabha
effective cross section decreases from 0.5% to 0.1% - Bhabha cross section
lowered by 0.7%; therefore pion form factor decreases by 0.7%
C. M. Calame et al., Nucl. Phys. B758 (2006) 227

13. 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 app by 0.4%

14. Small angle analysis 2002  Preliminary r-w Interference
Statistics: 242pb-1 of 2002-data
3.4 Million Events
qMiss<150 or
qMiss>1650 
r-w Interference
M2 (GeV2)
M2 (GeV2)

15. Small Angle Analysis Experimental challenge: Fight
background from  ,ee  , ,
reduced by means of kinematical
cuts in (trackmass), and likelihood
function
signal region
Normalization to integrated luminosity,
which is obtained from large-angle-
Bhabha events (clean exp. selection) mp
Background from LO-FSR negligible
(reduced by acceptance cuts: small qg),
NLO-FSR not reduced and not a
background, efficiency has to be known mm
mr2
Surviving background evaluated by
MC and subtracted
LO-FSR
NLO-FSR

16. Background: ppp events only fitted below 0.6 GeV2
Main backgrounds estimated from MC shapes fitted to data distribution in MTrk
(ppg/mmg, ppp, eeg)
Data
S MC
g
, eeg
Data
S MC
g
eeg
0.42< M2 < 0.44 GeV2
0.68< M2 < 0.7 GeV2
MTrk [MeV]
MTrk [MeV]
Bhabha contamination small
ppp events only fitted below 0.6 GeV2
ppp-peak is cut by event streaming and elliptical Cut in MTrk
Excellent agreement on TRK mass spectrum
Between data and MC

17. Luminosity: Quoted theor. accuracy: 0.1%
At KLOE, Luminosity is measured using „Large angle Bhabha“ events (55o<qe<125o)
KLOE is its own Luminosity Monitor!
F. Ambrosino et al. (the KLOE Coll.) Eur.Phys.J.C47: ,2006
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.
Generator used for Bhabha cross section:
BABAYAGA (Pavia group):
seff = (428.00.3stat) nb
C. M. Calame et al., Nucl. Phys. B758 (2006) 227
Systematics on Luminosity
Theory
0.10 %
Acceptance
0.25 %
Background (ppg)
0.08 %
Tracking+Clustering
Energy Calibration
0.13 %
Knowledge of s run-by-run
TOTAL % theo  0.32% exp = 0.34 %
New version of generator gives 0.7% decrease in cross section
compared to previous version
Quoted theor. accuracy:
0.1%

18. Radiative corrections
Radiator-Function H(s) (ISR):
Fp=1
s (ppg) with Fp=1 [nb]
ISR-Process calculated at NLO-level
PHOKHARA generator (Czyż, Kühn et.al)
Precision: 0.5%
H(s)
Radiative Corrections:
i) Bare Cross Section
divide by Vacuum Polarisation
 from F. Jegerlehner:
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)

19. Correcting for FSR energy:
Go from M2  M2g*
The presence of FSR results in a shift of the measured quantity M2towards lower values:
M2g*
M2
g* [GeV2]
Use special version of PHOKHARA which allows to determine whether photon comes from initial or final state  build matrix which relates pp to g* .
MonteCarlo
ISR only:
 = M2
FSR photon present:
 = M2g(FSR)
pp [GeV2]

20. Small angle result from 2002 data:
Preliminary
Systematic errors on ampp:
Offline Filter
negligible
Background
0.3%
Trackmass/Miss. Mass
0.2% (prelim)
p/e-ID
Vertex
0.5%
Tracking
0.4%
Trigger
0.2%
Acceptance ()
Mpp2 Mg* (FSR corr.)
0.3% (prelim)
Software Trigger
0.1 %
Luminosity
0.3%
Acceptance (Miss)
0.1%
Radiator H
0.5%
Vacuum polarization
negligible
STotal = 1.1%

21. Comparison :
(updated)

22. Evaluating ampp with small angle
Dispersion integral for 2p-channel in energy interval <Mpp2<0.95 GeV2
2001 published result (Phys. Lett. B606 (2005) 12):
app( GeV2) = (388.7  0.8stat4.9syst) · 10-10
Applying update for trigger eff. and change in Bhabha-cross section used for luminosity evaluation:
app( GeV2) = (384.4  0.8stat4.9syst) · 10-10
2002 preliminary:
app( GeV2) = (386.3  0.6stat3.9syst) · 10-10

23. Large angle analysis: Preliminary FSR f0 rp
important cross check with small
angle analysis
threshold region is accessible
photon is explicitly required
(allows 4-momentum constraints)
lower statistics for signal
FSR not negligible
large   p+p-p0 background
irreducible bkg. from f decays
240 pb-1
2002 Data
Nr. of events / 0.01 GeV2
Mpp2 [GeV2]
Threshold region non-trivial
due to irreducible FSR-effects, to be computed from MC using phenomenological models (interference effects unknown) f f0 g p
 important!
f, r p g
 small! f r p g
&
&
FSR f0 rp

24. Apply specific selection cuts:
Large angle analysis (cont‘d):
Apply specific selection cuts:
Preliminary
Exploit kinematic closure of the event
 Cut on angle  btw. ISR-photon and missing momentum
Kinematic fit in p+p-p0 hypothesis using 4-momentum and p0-mass as constraints
FSR contribution added back to
cross section (estimated from PHOKHARA
generator)
2002 Data L = 240 pb-1 p+ p- W g
LA stat.+syst.
error
Error on LA dominated by syst. uncertainty on f0 contr.
Reducible background from p+p-p0
and µ+µ-g well simulated by MC
Mpp2 [GeV2]
Model dependence of irreducible background from f f0g p+p-g is the dominating uncertainty. Computed
using different models for f0-decay and input from dedicated KLOE f f0g analyses (with f0 decaying to charged and neutral pions).

25. (60% (=3.110-10) of systematical error due to f0-uncertainty)
Comparison SA-LA 2002:
Preliminary  
(sLA-sSA)/sSA
Range of comparison
LA stat.+syst.
error
Range of comparison
app between GeV2:
Small angle:
app( GeV2) =
(255.4  0.4stat  2.5syst) · 10-10
Large angle:
app( GeV2) =
(252.5  0.6stat  5.1syst) · 10-10
(60% (=3.110-10) of systematical error due to f0-uncertainty)

26. Asymmetry:
In case of non-vanishing FSR contribution, the interference term
between ISR and FSR is odd under exchange p+  p- .This gives rise
to a non-vanishing forward-backward asymmetry:
Binner, Kühn, Melnikov, Phys. Lett. B 459, 1999
KLOE  Data
MC [ISR + FSR]
MC* [ISR+FSR+f0(980)]
 check the validity of the FSR model
(Phokhara uses sQED, i.e. pointlike pions)
radiative decays of the
 into scalar mesons decaying to + -
contribute to the charge asymmetry
Czyz, Grzelinska, Kühn, hep-ph/
*G. Pancheri et. al., arXiv:
Possibility to study the properties of scalar mesons with charge asymmetry

27. ampp KLOE summary: Preliminary Jegerlehner (hep-ph/0703125):
Using the new KLOE result increases difference from 3.2s to 3.4s

28. ampp Summary: Preliminary
Comparison with ampp from CMD2 and SND in the range GeV :
Phys. Lett. B648 (2007) 28
Preliminary

29. Conclusions:
KLOE has extracted app in the range between GeV2 using cross section data obtained via the radiative return with photon emission at small angles.
The preliminary result from 2002 data agrees with the updated result from the published KLOE analysis based on 2001 data
Data from an independent and complementary KLOE measurement (Large angle analysis) of the 2p-cross section yelds app in the range between GeV2
All three KLOE results are in good agreement
KLOE results also agree with recent app results from the CMD2 and SND experiments at VEPP-2M in Novosibirsk

30. Outlook: See next slides…
Refine the small angle analysis by unfolding for detector resolution, to release the  cross section table
Continue evaluation of resonance contributions in the large angle analysis to decrease model dependence from f0(980) contribution
Measure the pion form factor via bin-by-bin ratio of pions over muons (Normalization to radiative muon pairs)
Obtain pion form factor from data taken at s = 1000 MeV
(off-peak data)
See next slides…

31. Extracting |F|2 from norm. to 
(exact only in the absence of FSR)
Some Effects cancel out in the ratio:
Luminosity ( LA Bhabhas )
0.6%
Vacuum polarization
0.2%
FSR corrections
0.3%
Radiator function
0.5%
Total theoretical Error %
needs to select µµg events with similar precision as ppg x
0.3%
In presence of FSR:
Corr. due to FSR
„Observed“ cross sections

32. p-m separation:
p-m separation is achieved in the analysis by a rigid cut in MTrk:
Data


ppg
No man‘s land
mmg
MTrk[MeV]
mmg
MTrk< 115 MeV
ppg
MTrk> 130 MeV
Additional tool used in evaluation of efficiencies: p-m ID by means of a Neural Network (NN):
ppg
mmg
NN >0.7 for mmg
NN <0.2 for ppg
Data
-- MC

33. Spectra after SMA selection:
The spectra of selected events for the small angle analysis from pb-1 of data taken in 2002:
Pions
3.42 Mio events
Muons
0.87 Mio. events

34. Forward-Backward-Asymmetry
DAFNE Off-peak data:
Run-Nr
s ( MeV ) F
s = 1023
s = 1030
s = 1018
s = 1010
s = 1000
It allows to extract |F|2 down to thresh. in a background-free enviroment
220 pb-1, competitive with
VEPP-2M at threshold
Study model-dependence of f0(980) (in connection with on-peak data)
Forward-Backward-Asymmetry
MC Phokhara
Data 2006 off-peak
Tagged photons
Preliminary
Run at √s=1000 MeV between
Dec and March 2006
 220 pb-1 on tape
Energy scan around -peak
 4 scan points, 10 pb-1 each
Mpp2 (GeV2)

36. Backup slides

37. Reminder: Comparison with e+e- - and t - Data
Relative difference btw. published
KLOE (2001) and CMD-2, SND
Plot from I. Logashenko using
non-published data from
CMD-2 and SND!
KLOE published
SND hep-ex/
CMD-2 published
CMD-2 prel.
ALEPH t-data •
•••
Relative difference btw. e+e- Data
and t-spectral function from ALEPH
s / sKLOE - 1
interpolation of 60
KLOE data points from 0.35 to 0.95 GeV2
s [GeV2]
s [GeV]
KLOE confirmed the CMD-2 discrepancy with tau data and “...invalidates the use of t-data until a better understanding of the discrepancies is achieved” (A. Höcker ICHEP-04)
Some disagreement btw. KLOE and SND/CMD-2 seen at low and high masses
aµhad from all recent e+e- experiments agree now within 0.5s
Waiting for new results from KLOE (this talk), Babar, and t data (Belle)