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Debora Leone Institut für Experimetelle Kernphysik Universität Karlsruhe on behalf of KLOE collaboration. Tau04 Nara 14-17/09/2004. Measurement of the hadronic cross section at KLOE. a m theory vs. experiment. e + e - and t data differ for p + p - - PowerPoint PPT Presentation
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Debora LeoneInstitut für Experimetelle KernphysikUniversität Karlsruhe
on behalf of KLOE collaboration
Measurement of the hadronic cross section at KLOE
Tau04Nara 14-17/09/2004
D. Leone Hadronic cross section @ KLOE
a theory vs. experimentT
HE
OR
Y
‘03
e+ e - Data: 2.7 - Deviation
– Data: 1.4 - Deviation
Exp
erim
ent
’02/
‘04 Experiment BNL-E821
Values for +(2002) and -(2004)in agreement with each other.Precision: 0.5ppm
Dispersion integral for hadroniccontribution to a evaluated for:
a) CMD-2 (Novosibirsk/VEPP-2M) channel with 0.6% precision < 1 GeVb) -Data from ALEPH /OPAL/CLEO
e+e- and data differ for +-
channel in a specific energy window above 0.6 GeV2
(above the peak)
a-11659000(10-10)
Status up to July ’04
The standard method to measure (e+e- hadrons) is the energyscan, i.e. the syst. variation of c.m. energy of the machine.Since at DANE the collision energy is fixed,we use a complementary approach:looking for e+e- +- events, where the photon is emitted in the initial state (ISR),we have a continuous variation of s, theinvariant mass of the hadronic system
hadr
d(e+ e- hadrons + )d
hadrons
(e+ e- hadrons) H(hadr )
Precise knowledge of ISR processRadiator function H(Q2,,M2
)MC generator: PhokharaH. Czyz, A. Grzelinska, J.H. Kühn, G. Rodrigo
4m2< s < m
2
D. Leone Hadronic cross section @ KLOE
The Radiative Return
D. Leone Hadronic cross section @ KLOE
selection
Pion Tracks at large angles 50o < < 130o
Photons at small angles < 15o and > 165o
are masked byquadrupoles near the I.P.
(no photon tagging)
)pp(pp miss
High statistics for ISR Photons
Low relative contribution of FSR
Reduced background contamination
e+ e-
EM calorimeter
Drift chamber
D. Leone Hadronic cross section @ KLOE
dN()/dM2
after acceptance cutsEvent analysis:
Efficiencies and background
Normalize to Luminosity
Radiative CorrectionsCross section (e+e-
cross section
M2 [GeV2]
dN
(
)/
dM
2 [
nb
-1/G
eV
2] 141 pb-1
No acceptance at threshold region
50000
40000
30000
20000
10000
Differential cross sectiond()/dM
2
Divide by Radiator Function
signalregion
tail
Step 1: e+e-are separated from by means of a Likelihood method(signature of EmC-clusters and TOF of particle tracks)
D. Leone Hadronic cross section @ KLOE
Background Rejection 1/2
Mtr
k [
MeV
]M
2 [GeV2]
0|q||pp|)M|p|M|p|(M 2221
22trk
22
2trk
21
Step 2: and e+e-rejected by means “Trackmass ”
m
m
m
ee
D. Leone Hadronic cross section @ KLOE
Background Rejection 2/2
Step 3: fit data trackmass distributions with MC ones (signal + background) with free normalization parameters
M2 [0.32,0.37] GeV2 Mtrk [MeV]
Mtrk [MeV]
KLOE uses large angle Bhabha events for the luminosity evaluation:
)1( BkgMC
NdtL
Theory precision (radiative corr.)
•BABAYAGA event generator (Pavia group)• syst. comparison among other generators (Bhagenf, BHWIDE, VEPP-2M ); max. = 0.7 %uncertainty 0.5% =BABAYAGA error
Experimental precisionExcellent agreement data-MC
N = events with 55<<125
D. Leone Hadronic cross section @ KLOE
Luminosity Measurement
55o 125o
Polar Angle [°]
• data
MC
D. Leone Hadronic cross section @ KLOE
Analysis (e+e-)
EFFICIENCIES: Trigger + Cosmic Veto Tracking + Vertexing /e separation Reconstruction filter Trackmass cut Unfolding procedure Acceptance
BACKGROUND e+e- e+e- e+e-
LUMINOSITY Bhabha at large angles
0.9 %
0.3 % d(
e+e
-
)
/dM
[
nb
/GeV
2 ]
M [GeV2]
Interference
140 pb-1 of 2001 data1.5 millions events
0.6 %
D. Leone Hadronic cross section @ KLOE
FSR Contribution
Two kinds of FSRThere is no initial state radiation andthe e+ and the e- collide at the energy M the virtual has Q2 = M
2
Background
Simultaneous presence of a
initial and final photon
The cross section e+e- +- has to be inclusive with respect to NLO FSR events:
D. Leone Hadronic cross section @ KLOE
FSR Treatment
“FSR Inclusive” approach
(e+e- FSR )
Event analysis Phokhara ISR+FSR
Luminosity
(e+e- ISRFSR )
Radiator H
N(e+e- ISRFSR)add back missing FSR
Correction for unshifting
s
e
e} s
Invariant mass of thesystem , s invariant mass of thevirtual photon s
D. Leone Hadronic cross section @ KLOE
FSR uncertainty
“FSR Exclusive” approach
N(e+e- ISRFSR)
(e+e- ISR)
(e+e- )
Radiator H
Event analysisPhokhara ISRLuminosity
subtract FSR contributionestimated by MC
FSR
0.8 .. 0.9% Schwinger ‘90
= 0.2% ± 0.1%
Rel. difference inclusive - exclusive approach
0.4 0.5 0.6 0.7 0.8 0.9
1
1.04
1.02
0.98
0.97
0.96
0.95
0.99
1.01
1.03
1.05
1.
The 2 methods are in excellent agreement Higher order FSR corrections negligible Proof of Factorization Ansatz
FSR systematic = 0.3%, coming from 2 contributions0.2% difference incl-excl correctionupper limit of 20% for scalar QED model
(point-like pions): 20% 1% = 0.2%
D. Leone Hadronic cross section @ KLOE
Cross Section (e+e-+-)
Final spectrum: after the correction for vacuum polarization2
bare )sα(
α(0)σ(s)(s)σ
had(s) from F. Jegerlehner, July 2003
s[GeV2]
Total error = 1.3 %
D. Leone Hadronic cross section @ KLOE
2 contribution to ahadr
We have evaluated the dispersion integral for 2 channel in the energy range 0.35 <s<0.95 GeV2
2
2
)()(4
13
0.95GeV
0.35GeV
sKds
eea
Comparison with CMD-2 in the energy range 0.37<s<0.97 GeV2
KLOE (375.6 0.8stat 4.8syst+theo) 1.3% ErrorCMD-2 (378.6 2.7stat 2.3 syst+theo) 0.9% Error
At large values of s (>m2) we are consistent with CMD-2 and
we confirm the deviation from -data.
• CMD-2• KLOE
s [GeV2]
|F(s)|
a= (388.7 0.8stat 3.5syst
3.5theo) 10-10
D. Leone Hadronic cross section @ KLOE
Conclusion
KLOE has proven the feasibility to use initial state radiation to measure hadronic cross section (hep-ex 0407048)
We expect to reduce the systematic error below 1% by repeating the analysis with 2002 data. Improvements from theory are also expected.
The analysis at large photon angle to study the region near the threshold is going on.
Evaluation of ratio R – the analysis has already begun
D. Leone Hadronic cross section @ KLOE
= data
= MC
preliminary
Polar angle []A
sym
metr
y Test of sQED model: at large photons angles the amount of FSR is large. Here it is possible to study the charge asymmetry. It comes out from the interference between ISR (C-odd) and FSR (C-even)
))
)))
(θN(θN
(θN(θNA(θ
ππ
ππ
[]
+
-
Outlook
Integrating asymmetrywe get a difference data-MC of (8.5 1.2)%
Large angle photon analysis to explore the threshold region tagged measurement
D. Leone Hadronic cross section @ KLOE
Backup slices
D. Leone Hadronic cross section @ KLOE
Unfolding the Mass Revolution
s (true) [GeV2]
s (
obs)
[G
eV
2]
Trackmass [MeV]
The smearing matrix “almost” diagonalInversion of smearing matrix possibleA more sophisticated unfolding techniqueis obtained by means of the unfoldingpackage GURU (A. Höcker et.al./ALEPH).
Issues: - Reliability of MC simulation - Correct choice of the regularization parameter
Systematics studied by varying meaningful values of the regularization parameter:
Due to nature of the dispersion integral the effect on a is almost negligible
D. Leone Hadronic cross section @ KLOE
Terms not included in Phokhara
Unshifting correction
D. Leone Hadronic cross section @ KLOE
Relative contribution of LO-FSR Relative contribution of NLO-FSR
D. Leone Hadronic cross section @ KLOE
MTRK
e e
before cutting on particle ID
after cutting on particle ID
m
Likelihood effect on Mtrk distribution
F=1
wit
h F
=1
s (GeV2)
Radiator Function
D. Leone Hadronic cross section @ KLOE
D. Leone Hadronic cross section @ KLOE
reconstructedkine
M2 [GeV2]
M2 [GeV2]
D. Leone Hadronic cross section @ KLOE
KLOE & DANE
e+e- collider @ S = M = 1019.4 MeV
achieved peak Luminosity: 8 1031cm-2 s-1
2000-2002 data set: 500 pb-1
KLOE detector designed for CP violation studies good time resolution t= 57 ps /E(GeV) 54 psin calorimeter andhigh resolution drift chamber (p/p is 0.4% for > 45°), ideal for the measurement of M.
pb
-
1
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