Achim Denig Radiative Return @ DANE MENU 2004 Measurement of the Hadronic Cross Section via Radiative Return at DANE Achim Denig for the KLOE Collaboration MENU 2004 September 3 rd Beijing, IHEP Universität Karlsruhe Institut für Experimentelle Kernphysik
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Measurement of the Hadronic Cross Section via Radiative Return at DA F NE
Measurement of the Hadronic Cross Section via Radiative Return at DA F NE. MENU 2004 September 3 rd Beijing, IHEP. Universität Karlsruhe Institut für Experimentelle Kernphysik. Achim Denig for the KLOE Collaboration. hep-ex/0407048, sent to Phys. Lett. B. Outline: Muon Anomaly - PowerPoint PPT Presentation
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Achim Denig Radiative Return @ DANE MENU 2004
Measurement of the Hadronic Cross Section
via Radiative Returnat DANE
Achim Denig for the KLOE Collaboration
MENU 2004September 3rd
Beijing, IHEP
Universität KarlsruheInstitut für Experimentelle Kernphysik
Achim Denig Radiative Return @ DANE MENU 2004
hep-ex/0407048, sent to Phys. Lett. B
Outline:
Muon Anomaly Radiative Return at KLOE
Results & Outlook
Further KLOE-Results: St. Müller (Session B2)
Achim Denig Radiative Return @ DANE MENU 2004
...2/2/)2g(a
newweakhadQEDtheor aaaaa
Motivation: Determination of Hadronic Vacuum Polarization = High Precision Test of the Standard Model
• Anomalous magnetic moment of the muon a = (g2)• Running fine structure constant at Z0-mass QED (MZ)
Dirac-Theory: (g 2 ) = 0Quantum corrections: (g 2 ) 0 due to corrections of: - electromagnetic interaction - weak interaction - strong interaction (and maybe NEW PHYSICS ???)
Hadronic Vacuum Polarization
hadrons
+ +
B field
q
q
2nd largest contrib., cannot be calculated in pQCDError of hadronic contribution is dominating total error !
Muon - Anomaly
Achim Denig Radiative Return @ DANE MENU 2004
Hadronic contribution to a can be estimated by means of a dispersion integral:
- K(s) = analytic kernel-function, almost flat in s- above 2…5 GeV, use pQCD
Hadronic Cross Section
Input Dispersion Integral:
a) hadronic electron-positron cross section data, e.g. e+e + b) hadronic - decays (CVC-theorem, taking into account isospin breaking corrections), e.g. 0
2m4
2
2had
s
)s(K̂)s(Rds
3
ma
)*ee(
)hadronsqq*ee()s(R
tot
tot
H
1 / s2 makes lowenergy contributionsespecially important:
eein the range < 1 GeVcontributes to 70% !
Achim Denig Radiative Return @ DANE MENU 2004
Muon-Anomaly: Theory vs. Experiment
a 11 659 000 ∙ 1010
TH
EO
RY
’20/
‘03
Exp
erim
ent
’20/
‘04 Experiment BNL-E821
Values for +(2002) and -(2004)in agreement with each other.Precision: 0.5ppm
Dispersion integral for hadronic contribution to aevaluated for:
a) e+ e-Data ONLY CMD-2 (VEPP-2M) measured channel with 0.6% precision < 1 GeV 2.7 – Deviation
b) -Data ONLY (if available) ALEPH /OPAL/CLEO 1.4 – Deviation
Theoretical values taken fromDavier, Eidelman, Höcker,
Zhang: hep-ex/0308213
a 11 659 000 ∙ 1010
e+e data and data differ for + channel in a specific energy window
above 0.6 GeV2 (above the -peak)!
Status u
p
to July ‘04
Achim Denig Radiative Return @ DANE MENU 2004
Radiative Return• Standard method for cross section measurement is the energy scan, i.e. the systematic variation of the c.m.s.-energy of the accelerator
• DANE is a - factory and therefore designed for a fixed c.m.s.-energy: s = m = 1 019 MeV; a variation of the energy is not foreseen in near future
Complementary approach:Take events with Initial State Radiation (ISR)
Cross section as a function of the 2-Pion invariant mass s=M
“Radiative Return” to -resonance:
e+ e
d(e+ e )dM
ISR
MC- Generator PHOKHARA = NLO
J. Kühn, H. Czyż, G. RodrigoRadiator-Function H(s)
)(2
2 sdM
dM
H(s)
s
Achim Denig Radiative Return @ DANE MENU 2004
L
1
1
M
NN
dM
d
..2
bkgobs
2
AcceptSelect
Background Signal
Selections-Efficiency
Luminosity
Acceptance
Analysis
• Final state e+e- relatively easy signature, however cross section measurement on percent level is a challenging task (normali- zation, efficiencies, background)
• KLOE Detector designed for CP – violation, we are having a high resolution tracking chamber ideal for the measurement of M!
Analysis-Items:
Achim Denig Radiative Return @ DANE MENU 2004
Selection
500< < 1300
< 150 > 1650
Pion tracks at large angles 50° < < 130°
• High statistics for ISR events• Reduced background contamination• Low relative contribution of FSR
Photons at small angles < 15° and > 165°
are shadowed byquadrupoles near the I.P.
Drift ChamberEM Calorimeter
)pp(pp miss NO PHOTON TAGGING
Achim Denig Radiative Return @ DANE MENU 2004
Background
ee
signalregion
MTRK (MeV)
m
tail
1) Pion-Electron-Separation Rad. Bhabhas e+ee+eare separated by means of a Likelihood- Method (Signature of EmC-Clusters and TOF of particle tracks)
m
M GeV2 2( )m
0)( 2221
222
222
1 qppMpMpM trktrk
2) Kinematic Separation e+e
using „Trackmass“-variable
M – dependent MTRK-Cut
3) Residual BackgroundFit Trackmass-Spectra for signal and background with free normalization parameters (shape from MC)