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Achim Denig The Radiative Return: A Review of Experiments
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The Radiative Return:
Review of Experiments
The Radiative Return:
Review of Experiments
Achim DenigUniversität Karlsruhe
BINP NovosibirskFebruary 27, 2006
Achim Denig The Radiative Return: A Review of Experiments
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The Radiative Return:
How and Why?
F
ISR
Achim Denig The Radiative Return: A Review of Experiments
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Radiative Return - How?
Modern particle factories, as DANE or PEP-II/KEK-B are designedfor a fixed center-of-mass energy: s = m = 1.02 GeV in the case of DANE,
(4s) in case of B-factories: Energy-scan not possible!
New and completely complementary ansatz: Consider events with Initial State Radiation (ISR)
‘Radiative Return’ to -resonance: e+ e
S. Binner, J.H. Kühn, K. Melnikov, Phys.Lett. B459 (1999) 279
ISR
d(e+ e hadrISR)
dMhadr
for (2m2 < Mhadrs
dhadr +
dMhadr
=
MC- Generator PHOKHARA = NLO
J. Kühn, H. Czyż, G. RodrigoRadiator-Function H(s)
ISR
)(2
2 sdM
dM
H(s) Talk H. Czyż
Achim Denig The Radiative Return: A Review of Experiments
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Radiative Return at Particle Factories
[m
bar
n]
1 10
s [GeV]
DANE
Using the method of the Radiative Return one can study the entire energy region below ca. 4 GeV!
PEP-II
s=1.02 GeV
s=10.6 GeV
Experiment KLOE:
Energy region < 1 GeV,
dominated by -channel
(-resonance)
ExperimentBaBar:
Energy region1 ... 3 GeV,
dominated byhigher multi-
plicities (esp. ),up to recently data
with 20 ... 50% systematic errors!
(4s)
pQCD
Achim Denig The Radiative Return: A Review of Experiments
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Why Precision Cross Section Measurements?
ahad
<1.8 GeV
Davier, Eidelman, Höcker, Zhang
2m4
had3had ds)s(K)s(
4
1
a
12 - 5 - 12 (+)3.7 - 5 (+J/, )1.8 - 3.743 (+,)2 > 4 (+KK)
• Cross section measurements are of utmost importance for hadronic contribution to muon anomaly ahadr and for knowledge of fine structure constant at s=mZ
2!
Experimental inputinto dispersion integral
2 needed with ca.1% precision!
• Great potential to study the spectrum of vector resonances (J PC = 1 ) above -peak - this region is very poorly known BaBar discovery of Y(4260) resonance (m=42608 MeV, =8823 MeV )
• Production of resonance pairs with limited choice of quantum numbers
Talk J. Izen
Achim Denig The Radiative Return: A Review of Experiments
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Results from KLOEat the phi-factory DANE:
The Pion FormfactorHigh Precision needed!
Achim Denig The Radiative Return: A Review of Experiments
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Selection ISR
Pion tracks at large angles 50o < < 130o
a) Photons at small angles < 15o and > 165o
No photon tagging
• High statistics for ISR photons• Negligible contribution of FSR• Reduced background
< 150
)pp(pp miss
b) Photons at large angles50o < < 130o
Photon tagging possible• Measurement of threshold region • Increased contribution of FSR • Contribution f0(980)
> 500
The KLOE Detector
Achim Denig The Radiative Return: A Review of Experiments
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Small Angle Analysis
ee
m
220
200
180
160
140
120
100
m
0.4 0.5 0.6 0.7 0.8 0.9 1.0.3
MTRK (MeV)
M2 (GeV2)
• Experimental challenge: fight hughe background from ande+ereduced by means of kinematic cuts (trackmass), and likelihood function (e--separation)
• Background from LO-FSR negligible (reduced by acceptance cuts: small ), NLO-FSR not reduced and not a background, efficiency has to be known
• Normalisation to integrated luminosity, which is obtained from large-angle- Bhabha events (clean exp. selection)
LO-FSR NLO-FSR
Achim Denig The Radiative Return: A Review of Experiments
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Result Small AnglesAcceptance 0.3%
Trigger 0.3%
Tracking 0.3%
Vertex 0.3%
Reconstruction filter 0.6%
Particle ID 0.1%
Trackmass cut 0.2%
Background 0.3%
Unfolding effects 0.2%
Total experimental Error 0.9%Luminosity ( LA Bhabhas ) 0.6%
Vacuum polarization 0.2%
FSR corrections 0.3%
Radiator function 0.5%
Total theoretical Error 0.9%
TOTAL ERROR 1.3%
(e+e- ) nb
0.4 0.5 0.6 0.7 0.8 0.90.3
200
400
600
800
1000
1200
1400
M2 (GeV2)
KLOE2001 Data
140pb-1
Phys. Lett. B606 (2005) 12
Statistics negligible (1.5 Million events)
Acceptance 0.3%
Trigger * 0.3%
Tracking 0.3%
Vertex 0.3%
Reconstruction Filter * 0.6%
Particle ID 0.1%
Trackmass Cut 0.2%
Background 0.3%
Unfolding Effects 0.2%
Total experimental Error 0.9%Luminosity * 0.6%
Vacuum Polarization 0.2%
FSR Corrections 0.3%
Radiator Function 0.5%
Total theoretical Error 0.9%
*Goal 2002 data: Error < 1%
Normalisatio
n
to µµ
Talk F. Nguyen
Achim Denig The Radiative Return: A Review of Experiments
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a [10-10 ]
KLOE (‘05)
SND (’05)
CMD-2 EPS (‘05) preliminary
CMD-2 (‘04)
MM22 (GeV (GeV22))
/
KL
OE -
1
• CMD-2 (‘04) and KLOE agree @ high M
• some disagreement btw. KLOE and CMD-2/SND on the peak
• fair agreement btw all 4 data sets CMD-2 and KLOE agree within 0.5 • disagreement btw KLOE and SND ca.1.5
interpolation of 60KLOE data points from
0.35 to 0.95 GeV2
Comparison with recent e+e Data
Comparison of e+e- experiments 2 contribution to ahadr
[0.3
7-0.
93 G
eV2 ]
JETP, Vol. 101, No 6 (2005) 1053 PLB 578 (2004) 285
Achim Denig The Radiative Return: A Review of Experiments
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Analysis 2002 Data: Large Angles
important cross-checkthe threshold region is accessible photon tagging is possible (4-momentum constraints) lower signal statistics large background large FSR (charge asymmetry!)irreducible bkg. from decays
PRO & CONTRA
Talk D. Leone
50o<<130o
50o<<130o
L = 240 pb-1
preliminary
MM22 (GeV (GeV22))
MC MC
By means of dedicated selection
cuts it is possible to fight thedominant background
Threshold region non-trivial due to irreducible FSR-effects,which have to be cut from MCusing phenomenological models(interference effects unknown)
ff
FSR f0
Achim Denig The Radiative Return: A Review of Experiments
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• Run at s = 1.00 GeV started on Dec. 16
Good machine performance off-peak:
Status off-peak running Feb. 24, 2006: 167pb-1 written on tape!
DANE - Run Off - Resonance
Dec. 16 Feb. 24Jan. 6
167pb-1
Off-Peak-Performance:
> 5pb-1/day
Intg
erat
ed L
um
inos
ity
/ pb
-1
Feb. 1
XMas
Run-Nr.
• We hope to continue up to end of March and to acquire > 200pb-1
Trackmass [MeV]
Nu
mb
er o
f E
ven
ts /
MeV
10pb-1 ONPEAK
OFFPEAK
Physics Case:• background-free Radiative Return 200pb-1 allow to be statistically com- petitive with VEPP-2000 at threshold
• a -scan allows to study the model- dependence in desciption of f0(980)
• background-free - program
Achim Denig The Radiative Return: A Review of Experiments
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Results from BaBarat the B-factory PEP-II
Higher Multiplicities at higher Energies (so far)I have chosen highlights from published Analyses
3,4,6 Hadrons + pp
Achim Denig The Radiative Return: A Review of Experiments
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Radiative Return at BaBar• Center-of-mass energy of machine PEP-II (s=m(4s)=10.6 GeV) far from mass range of interest (ca. < 4 GeV ) requires high energy photon- 5.3) GeV requires high integrated luminosity of PEP-II (Run1-4: ca. 240 fb-1, Goal 2008: 1000fb-1) • Hard ISR-photon back-to-back to hadrons only acceptance for large angle photons photon tagging!
1 muon ID
2 muon IDs
e+e
• Normalisation: to integrated luminosity and radiator function to radiative muon pairs, which are selected with high precision
Event-Display of an ISR-Event in transversal plane
Achim Denig The Radiative Return: A Review of Experiments
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• Mass resolution of hadronic system improved by means of a kinematic fit Input to the fit: Momentum and direction of ISR-photon (not energy!) Constraints: energy and momentum conservation (and 0 mass)
• 2-distribution of kinematic fit is the main tool for background subtraction long tail due radiative corrections (NLO) remaining background obtained from MC (for qq events) or from data with sideband technique (for ISR events)
Data +
MC
Radiative Return at BaBar
• Background from (4s) and from B-decays is very small (E > 3 GeV) main backgroud from other ISR-events background from continuum processes e+eqq
Example for 2 distribution from 3 analysis
Achim Denig The Radiative Return: A Review of Experiments
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3 Hadrons: e+e
Spectrum dominatedby , , J/ resonances
• Coverage of wide mass region in one experiment: systematic error ca. 5% < 2.5 GeV
• Inconsistency found with DM2 results > 1.4 GeV
• Fit of the mass spectrum up to 1.8 GeV M() = 13502020 MeV/c2 PDG: 1400 - 1450 () = 4507070 MeV 180 - 250 M() = 1660102 MeV/c2 1670 30 () = 2303020 MeV 315 35 M, and phases between and , ’, ’’ fixed in the fit
DM2
BaBar
SND
BR(J/3) = (2.18±0.19)% PDG: (1.50 ±0.20)% BES: (2.10±0.12)%
N=920±34
PRD 70 (2004) 07200489fb-1
Achim Denig The Radiative Return: A Review of Experiments
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4 Hadrons: e+e E
vent
s/0.
025
GeV
ISRBackground
Non-ISR Background MC
Average BG fractions
data
Comparison with world data
Systematic errors: – 12% for m4 < 1 GeV,
– 5% for 1 < m4 < 3 GeV, 16% above best measurement above 1.4 GeV
Coverage of wide region in one experiment no point-to-point normalization problems when evaluating (g-2)hadr
PRD 71 (2005) 05200189fb-1
Achim Denig The Radiative Return: A Review of Experiments
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Substructures in e+e
J/+-+-
(2S)J/+-
a1(1260)
J/(770)
f0(1370)?
Comparison with Monte-Carlo (Czyż, Kühn): – assumes a1(1260) contribution dominant
– assumes additional f0(1370) contribution confirmed by experiment?!
EPJ C18(2000)497
No J/ in MC
BR (J/ ++)=(3.610.26 0.26)10-3 PDG: (4.0 1.0) 10-3BR ((2S) +J/ )=( 36.11.5 3.7) % PDG: (31.0 2.8) %
Extract J/ , (2S) Branching Ratios:
Channel in preparation!
Achim Denig The Radiative Return: A Review of Experiments
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e+e The K+K+ final state The K+KK+K final state
• Large improvement in precision and mass range, in agreement with DM-1
• Systematic error: 15%, domin. Kaon-ID
• Substructures: - dominant K*(892)K - substantial andK+K
• First measurement ever, which benefits from good PID-capabilities
• Systematic error: ca. 25%, few backgr.
BR (J/ K+K+) =(6.090.50 0.53)10-3 PDG: (7.2 2.3) 10-3BR (J/ K+KK+K) = ( 6.71.0 3.1 )10-4 PDG: - no entry -
Achim Denig The Radiative Return: A Review of Experiments
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6 Hadrons: e+e 3(The 3(+ final state The 2(+0 final state
• Large improvement in precision • Systematic error: 20%, bkg. dominated • very little substructure: ~1 /event• Dip near 1950 MeV, already seen by FOCUS in diffractive photoproduction
Also first measurement of 2(+K+K
• Hughe improvement in precision and mass range, differences to world data • Systematic error: 20%, bkg. dominated • Very rich substructure: - seen - f0(980), .... present• Dip near 1950 MeV also in this mode
hep-ex/062006 accepted by PRD232fb-1
Achim Denig The Radiative Return: A Review of Experiments
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m6=1.88±0.03 GeV
6=130±30 MeV
6=21±40 deg
m420=1.86±0.02 GeV
420=160±20 MeV
420=-3±15 deg
Resonance
Continuum
M3(+-) M2(+-)00
Continuum
Resonance
• Combined fit of continuum and resonance good agreement between charged and partly neutral mode width significantly larger than FOCUS
e+e 3(
2
2
2
2/3
24cont
i
Asims
egm
s
a
msb
contms
eccA
20
)/(
10)(
0
Achim Denig The Radiative Return: A Review of Experiments
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2
E2
2p2
M2
2
Gm
m2G
m3
C4)ppee(
2 Protons: e+e p pCross section parametrized by magnetic and electric formfactors GM and GE
• Experimental challenge: fight KK, , bkg. with
10-100 higher cross section• Require 2 good proton
tracks (dE/dx, DIRC)• Perform 3C kinematic fit 4000 pp Events
• Can measure |GE/GM| by fitting the distribution of the cosine of helicity angle• See rise, then fall of |GE/GM|• In disagreement with LEAR data PS170, agreement only at threshold GE and GM equal at high masses
PRD 73 (2006) 012005240fb-1
2pp
pp
K+K
KK
Cut
Mpp
MC from Czyż, Kühn EPJ C35(2004) 527
Achim Denig The Radiative Return: A Review of Experiments
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e+e p p
2
2pp
2p
2pp
2
F)m
m21(
m3
C4
Defining the effective proton form factor:
Sharp dips at 2.25 and 3.0 GeVGood agreement
with pQCD-prediction at high Q2
Peak at threshold
Complicated structure is observed:
allows comparisonwith other experiments(ppe+e, e+e pp)
Talks NN
Achim Denig The Radiative Return: A Review of Experiments
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Conclusionsand
Outlook
Achim Denig The Radiative Return: A Review of Experiments
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Conclusions
• Feasibility of the Radiative Return for high-precision measurement (Pion Formfactor @ 1%) proven at KLOE
• Dedicated DANE-run off-resonance (s=1.00 GeV) with integrated luminosity >200pb-1 will substantially improve precision for tagged and untagged analyses
• Many exclusive ISR channels already measured at BaBar more in progress (K…), welcome BELLE!
Continuous coverage from threshold to Ecm~4.5 GeV Precisions ( 5% ) considerably improved > 1.4 GeV Some channels measured for the first time ever Many J/ψ BR’s better than world average
Clarify confusing situation of Pion Formfactor < 1GeV;Energy region 1 - 3 GeV more and more important for a!
Radiative-Return-Program started in 2000 as work-around
energy scan impossible ! Today established:
complementary & competitive!
Achim Denig The Radiative Return: A Review of Experiments
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Reserve
Achim Denig The Radiative Return: A Review of Experiments
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140pb-1 Statistics used forthe published analysis(Small angle analysis)
250 pb-1 Data analysis in preparation (small angles & large angles)
Radiative Return at DANE
2004 – 2005 -Run: 2 fb-1
Achim Denig The Radiative Return: A Review of Experiments
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dN(/ dM2
after acceptance cuts
Divide by Radiator-function
Radiative corrections
Extract from the Measurement
Differential cross section d()/dM
2
Event-analysis: efficiencies, background
as a function of M
Normalization with Luminosity 10 000
20 000
30 000
40 000
50 000
M [GeV2]
Cross section (e+e- )
Event- Analysis
Excellent mass-resolution
-
Achim Denig The Radiative Return: A Review of Experiments
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Ausblick: KLOE • Untersuche Ereignisse bei großen Photonwinkeln, um den Bereich M
2 < 0.35GeV2 zu vermessen, bisher kinematisch unterdrückt!
• Photon Tagging möglich! Komplementäre Analyse mit vollkommen verschiedenen systemat. Fehlern!
• Anteil der FSR groß bei großen Photonwinkeln (bis zu >10%)
Untersuche FSR-Parametri- sierung (z.B. skalare QED) durch Messung der Ladungs-Asymmetrie:
Die Ladungsasymmetrie ergibt sich aufgrund unter-schiedlicher C-Parität der ISR- und FSR-Amplitude
))
)))
(θN(θN
(θN(θNA(θ
ππ
ππ
M2 (GeV2)
P R E L I M I N A R Y
-20K L O E
P R E L I M I N A R Y
Polarwinkel [°]
-10
0
15
10
5
-5
-15
50 70 90 110 130
• KLOE Daten• MC (skalare QED)
Ladungs-Asymmetrie [%]20
-20
Achim Denig The Radiative Return: A Review of Experiments
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Komplementäre KLOE-Analyse bei großen Photonwinkeln: 50° < < 130°
• Interferenzterm zwischen ISR und FSR asymmetrisch unter Austausch führt zu einer nicht vernachlässigbaren Asymmetrie zwischen und- :
KLOE: AFB und f0(980), f0(600)
• AFB ist ein sensitiver Parameter auf die Präsenz von skalaren Mesonen f0(980) f0(600) (?)Czyż et al., MC Phokhara, hep-ph/0412239
Vorwärts-Rückwärts-Asymmetrie:
)90(θN)90(θN
)90(θN)90(θN
ππ
FBA
• Dies führt zu einer Ladungs- bzw. Vorwärts-Rück-Asymmetrie für – - Ereignisse
Möglichkeit zum Test der Modell- abhängigkeit der Kopplungen und zum Studium der Natur von f0(980) bzw. Existenz von f0(600)!
0.3
0.2
0.1
0
-0.1
-0.2
0.4 0.6 0.8 1.0M [GeV]
F-B
-Asy
mm
etri
eMC: Nur ISR+FSR+Interferenz, kein f0
KLOE Daten preliminary
MC: Kaon Loop Modell
nur f0(980)f0(980)
Achim Denig The Radiative Return: A Review of Experiments
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Hadronischer Beitrag zu a12 - 5 - 12 (+)3.7 - 5 (+J/, )1.8 - 3.743 (+,)2 > 4 (+KK)
< 1.8 GeV
ahad
2[ahad]
<1.8 GeV
<1.8 GeV
Calculations based on hep-ph/0308213Davier, Eidelman, Höcker, Zhang
e+e- data only!
Achim Denig The Radiative Return: A Review of Experiments
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Radiative Korrekturen
Radiative Korrekturen:
ii) FSR - Korrekturen Wirkungsquerschnitt inkl. in FSR:
Im Falle des Radiative Return:betrachte - Events mit ISR- und FSR-Photonen = NLO-FSR
i) “Nackter“ Wirkungsquerschnitt dividiere durch Vakuumpolarisation
Vernach-lässigbar!
2 Verfahren für FSR Korrekturen:
• Approach 1: “exklusive NLO-FSR“ - Korrigiere gemessenes für FSR - Benutze MC mit reiner ISR in Analyse - Add. FSR-Beitrag zu (ca. 0.8%)
• Approach 2: “inklusive NLO-FSR“ - Benutze MC mit ISR+FSR in Analyse - korrigiere für Verschiebung in s
Achim Denig The Radiative Return: A Review of Experiments
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FSR KorrekturenZwei komplementäre Prozeduren für die FSR-Korrekturen:
“FSR Exklusiver” Ansatz “FSR Inklusiver” Ansatz
N(e+e- ISRFSR)
(e+e- ISR)
(e+e- )
(e+e- ISRFSR )
(e+e- FSR )
Radiator H
Event AnalysePhokhara ISR
Luminosity
Event Aanalyse Phokhara ISR+FSR
Luminosity
Radiator H
FSR
Addiere FSR 0.8 .. 0.9% Schwinger ‘90
subtrahiere FSR Anteil
Wie gut stimmen diese beiden Prozeduren überein?
N(e+e- ISRFSR)
Achim Denig The Radiative Return: A Review of Experiments
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FSR-Korrekturen gut verstanden FSR-Beiträge höherer Ordnung vernachlässigbar Faktorisierungs-Ansatz richtig
Pion Formfaktor (KLOE)
= 0.2% ± 0.1%
Unterschied inklusiver -exklusiver Ansatz
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.
FSR Korrekturen
Achim Denig The Radiative Return: A Review of Experiments
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Comparison with CMD-2 and - Data
CMD-2KLOE
0.4 0.5 0.6 0.7 0.8 0.9
45
40
35
30
25
20
15
10
5
0
s (GeV2)
Overall good agreement,some deviations in peak?
|F(s)|2 Relative difference e+e- vs.
s (GeV2)
e+e - and – data completely incompatible! Isospinbreaking effects?!
– Data (ALEPH, OPAL, CLEO)error band
differences 10% ... 20%
s (GeV2)0.2 0.4 0.6 0.8 1.0
20%
10%
0%
- 20%
-10%
A. Höcker @ ICHEP04
Pion form factor
Achim Denig The Radiative Return: A Review of Experiments
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Muon Anomaly: 2 Contribution to ahadr
= (388.7 0.8stat3.5syst3.5theo) · 10-10
Dispersion integral for 2-channel in energy interval 0.35 <M2<0.95 GeV2
2
2
GeV95.0
GeV35.0
3 )()ππ(π4/1 sKeedsa
Our measurement allows us to compute the contribution of the 2-channel a
in the dispersion integral for the anomalous magnetic moment of the muon.
Comparison with CMD-2 in energy interval 0.37 <M2<0.93 GeV2 :
(375.6 0.8stat 4.9expt+theo) 10-10
(378.6 2.7stat 2.3expt+theo) 10-10
KLOE:
CMD2:
365 370 375 385380
a·1010
Very good agreement in the disperion integral !
Achim Denig The Radiative Return: A Review of Experiments
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Muon Anomaly: Theory vs. Experiment
a 11 659 000 ∙ 10-10
Experiment E821
DEHZ’03 [e+e- based]
DEHZ’03 [based]
a 11 659 000 ∙ 1010140 150 160 170 180 190 200 210
a 11 659 000 ∙ 1010
DEHZ‘03
hadrweakQEDtheo aaaa
KLOE- and CMD-2 measurements of the pion form factor are used for a new evaluation of the hadronic contribution and therefore of the muon anomaly!
Comparison experiment - theory allows a precision test of the standard model
Standardmodel prediction: New KLOE measurement Phys. Lett. B606 (2005) 12• New 4th order QED calculation (Kinoshita, Nio) Phys.Rev.D70 (2004) 113001• New ‘Light-by-light’ calculation (Melnikov, Vainshtein) Phys.Rev.D70 (2004) 113006
Theory (SM) - Experiment aexp - atheo = ( 25.2 ± 9.2 ) ·10-10
2.7 standard deviations difference !
CMD-2 and KLOEare averaged in
hadronic contribution
New
Achim Denig The Radiative Return: A Review of Experiments
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e+e e+e ISR Y(4260) ISR
In ISR-events in 2005 a new vector resonance was discovered at BaBar:
m = 4260 8 MeV = 88 23 MeV
Why? Hadron Spectroscopy
J/
X = Vector Resonance J PC = 1
125 ± 23 Events
• Direct production allowed only for vector resonances• Resonances with different quantum numbers in decays of vector resonances or in production of vector resonance together with pseudoscalar / scalar
Y(4260)
Achim Denig The Radiative Return: A Review of Experiments
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How? Initial-State-Radiation
Rho - Resonanz
0.1 0.3 0.5 0.7 0.9M
[GeV2]
Radiative cross section
a.u
.
Rho - Resonanz
-Resonance
0.1 0.3 0.5 0.7 0.9 s [GeV2]
Non-radiativecross section
a.u
.
MC- Generator PHOKHARAH.Czyż, H.Kühn, G.Rodrigo
Correct for ISR-process
Rho - Resonanz
Radiator function H(s)0.1 0.3 0.5 0.7 0.9
M [GeV2]
a.u
.
Achim Denig The Radiative Return: A Review of Experiments
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Background
Mmiss[MeV]
0.6 < M2<0.64 GeV2
DataMC
MC
MC
0.3 < M2<0.34 GeV2
Data
Mmiss[MeV]
Bkg.: Missing Mass
0.62 < M2<0.67 GeV2
Data
MC
MC
MTrk[MeV]
0.32 < M2<0.37 GeV2
Data
MC
MC
MTrk[MeV]
Muon Bkg.: Trackmass
Achim Denig The Radiative Return: A Review of Experiments
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DANE - Run Off - Resonance• In Dec.’05 DANE has gone off-resonance
• Scientific Committee of LNF recommends to run at s = 1.00 GeV up to 31/03/06 acquire an integegrated luminosity of 200pb-1
• In addition it was recommended to perform a -scan of 4 points, 10pb-1 each
s (
MeV
)
s = 1023s = 1023
s = 1030s = 1030
s = 1018s = 1018
s = 1010s = 1010
s = 1000s = 1000
Run-Nr.
{
on-peakData 2002
KaonLoop fitNo-Structure fit
(900-1000 MeV), f0(980) dependence on s
Achim Denig The Radiative Return: A Review of Experiments
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Overview of (e+e- hadrons)
• CMD-2, KLOE measured (e+e- → -) at <1%.
• Precise (6%) measurements from BES for 2< s < 5 GeV, CLEO data point at 7 GeV.
• No recent data for 1<s<2 GeV, errors ~10-15%.
• CMD-2, KLOE measured (e+e- → -) at <1%.
• Precise (6%) measurements from BES for 2< s < 5 GeV, CLEO data point at 7 GeV.
• No recent data for 1<s<2 GeV, errors ~10-15%.
• R(s) is defined as
• Crucial input for hadronic contributions to – Muon anomalous magnetic moment (a) – Running of QED (for SM fits, Higgs Mass).
• R(s) is defined as
• Crucial input for hadronic contributions to – Muon anomalous magnetic moment (a) – Running of QED (for SM fits, Higgs Mass).
)(
)Hadrons()(
0
ee
eesR
magnitude errors
Burkhardt & Pietrzyk
2001Contributions to
had
Davier et al., 2003
s [GeV/c2]
Achim Denig The Radiative Return: A Review of Experiments
43
BaBar/PEP-II• PEP-II is an asymmetric e+e- collider with a CM energy of 10.58 GeV.
• Peak luminosity = 9.2 1033 cm-2s-1
• Integrated luminosity = 273 fb-1
BaBar EMC:• 6580 CsI(Tl) crystals• Covers 91% of solid angle• Resolution ~2 % at high E.
Cherenkov Angle(Kaon from D*+ D0 ,
D0 K- + sample)BaBar DIRC•Quartz Cherenkov radiator•Covers 80% of solid angle•Particle ID up to 4-5 GeV/c
Achim Denig The Radiative Return: A Review of Experiments
44
• Can measure |GE/GM| by fitting the distribution of the cosine of the helicity angle.
• See rise, then fall of |GE/GM|• Not in agreement with LEAR data, except at threshold
1.877<mpp<1.950 GeV
2.100<mpp<2.200 GeV
1.950<mpp<2.025 GeV
2.200<mpp<2.400 GeV
2.025<mpp<2.100 GeV
2.400<mpp<3.000 GeV
pp
M
d
Gd
2cos1~cos
)(
pp
E
d
Gd
2sin~cos
)(
• GE, GM give Different angular distributions:
GE component
GM component
Data + Fit
|GE/GM|
Proton Helicity Angle
Achim Denig The Radiative Return: A Review of Experiments
45
• Efficiency Corrections– Dependence on |GE/GM|– 2 shape– Nuclear interactions with detector material– PID– photon detection– Triggering
• Cross Section:– No dip at threshold– Sharp dips at 2.25 GeV, 3 GeV
• J/, (2S) signals.• Normalize to e+e- +-
Cross Section
(pb)
PDG
(2.170.08).10-3
(2.36±0.24).10-4
4
3
10)9.03.3())2((
10)16.022.2()/(
ppSB
ppJB
J/ (2S)
Efficiency ME
ME
Achim Denig The Radiative Return: A Review of Experiments
46
• Define “Effective” form factor by
• Peak at threshold, sharp dips at 2.25 GeV, 3.0 GeV.
• Good fit to pQCD prediction for high mpp.
,3
4 2
2
2
Fm
C
pp
.2 2
2
22
E
pp
pM G
m
mGF
2
2
24 log)( pp
pp
ppM
m
m
CmG
Eff
ecti
ve F
orm
Facto
r
Form Factor
Eff
ecti
ve F
orm
Facto
r
Eff
ecti
ve F
orm
Facto
r
Achim Denig The Radiative Return: A Review of Experiments
47
e+e- 3(+-)• Same method, Require Ntrk=6• Use 1C Fit, require 2
6 < 20• Same method, Require Ntrk=6• Use 1C Fit, require 2
6 < 20
DataISR Bkg
Efficiency
J/
(2S)
(3(+-)) (nb)
• Efficiency relatively flat in m6, ~20%• Structure at ~1.9 GeV, already in DM2 data.• J/, (2S) signals.• Main source of uncertainty: Bkg subtraction.
• Efficiency relatively flat in m6, ~20%• Structure at ~1.9 GeV, already in DM2 data.• J/, (2S) signals.• Main source of uncertainty: Bkg subtraction.
Non-ISR Bkg
Log Scal
eCovers entire
spectrum up to 4.5 GeV/c2
Achim Denig The Radiative Return: A Review of Experiments
48e+e- 3(+-) Structures• Simple MC model: only 1 0+-
• Excellent (and suprisingly good!) overall agreement with MC:
– Presence of 0 peak– No other structures in 2, 3, 4 spectra
• Signal from J/ S[not in MC]
3.15 < m6 < 4.5 GeVm(+-)
m(+-
)
m(2+2-
)
J/
(2S), including +- J/
Data MC
Charmonium
states not
included in M
C
GeV/c2
GeV/c2
GeV/c2
Achim Denig The Radiative Return: A Review of Experiments
49e+e- 2(+-) 00Data ISR
Bkg
Non-ISR Bkg
Cross Section (nb)
Efficiency
Shape similar to 3(+-); differs sharply from DM2 above 1.9 GeV/c2
but other measurements very imprecise.
Shape similar to 3(+-); differs sharply from DM2 above 1.9 GeV/c2
but other measurements very imprecise.
• Require E > 50 MeV, cut on helicity• Require Kaon veto for charged pions• Use 5C fit (impose 0 masses, exclude
Energy)
Log Scal
e
Achim Denig The Radiative Return: A Review of Experiments
50e+e- 2(+-) 00 Structures• Rich resonance structure:
–
– f0– f2(1270)/f0(1370)?– J/2(+-) 00
Data in Red, MC in Blue
f
in Red, ½(
in Blue
f(1270) or f(1370)
J
m()
No f0
Achim Denig The Radiative Return: A Review of Experiments
51e+e- 2(+-) 00 Structures (2)
A signal for e+e- , is visible
A signal for e+e- , is visible
Select
in other
combination
2
02
02
2/32
0 )(
)(
sims
m
mF
sF
s
m
F(s) = 2-body P-wave
phase-space
Fit Results:
0 = 3.08±0.33 nbm = 1645 ± 8 MeV= 114 ± 14 MeV
Fit Results:
0 = 3.08±0.33 nbm = 1645 ± 8 MeV= 114 ± 14 MeV
(1680) ?
(1650) ?
J/
J/
(2S)
(e
+e
-
)
(n
b)
Fit a resonance shape: Fit a resonance shape:
m = 1680 ± 20 MeV, = 150 ± 50 MeVm = 1670 ± 30 MeV, = 315 ± 35 MeV
Achim Denig The Radiative Return: A Review of Experiments
52
e+e- K+K-2(+-)• Same as before, + Require 2 Kaons.• Clear signals for K*0, J/and (2S)• signal in K+K- spectrum, some from J/
decays.
• Same as before, + Require 2 Kaons.• Clear signals for K*0, J/and (2S)• signal in K+K- spectrum, some from J/
decays.J/
(2S)
J/
(2S)
K*0
J/
K*0
(K+K-2(+-)) (pb)
Band
Achim Denig The Radiative Return: A Review of Experiments
53
J/ Results for 6h Modes
But for 3(), only 1excess, not enough for BF value. But for 3(), only 1excess, not
enough for BF value.
Mode BaBar BF (232 fb-1) PDG 2004
J33 (4.40±0.29±0.29)10-3 (4.0±2.0)10-3
J22 (1.65±0.10±0.18)10-2 n/a
J (1.47±0.41±0.15)10-3 (1.58±0.16)10-3
JK+K-22 (5.09 ±0.42±0.35)10-3 (3.1±1.3)10-3
J22 (1.77 ±0.35±0.12)10-3 (1.60±0.32)10-3
Mode BaBar BF (89.3 fb-1) PDG 2004
(2S)22 (5.3±1.6±0.6)10-3 n/a
(2S)K+K-22 (2.1 ±1.0±0.2)10-3 n/a
33
K+K-22
22
Can remove J/(4), get direct signal. Can remove J/(4), get direct signal.
Achim Denig The Radiative Return: A Review of Experiments
54
e+e- +-+-• Perform 1C kinematic fits with m = 0 for 4, 2K2, 4K hypotheses
• Identify kaons using Cherenkov angle and dE/dx.
even
ts/0
.025
GeV
(~60K evts)
ISRBackgroun
d
e+e- +-+- Cross Section
(89.3 fb-1)
Non-ISR Background MC
Average BG fractions
data
Achim Denig The Radiative Return: A Review of Experiments
55
Resonant Structures in e+e- +-
+-
M(GeV/c2)
Charmonium
states n
ot
included in
MC
Data MC
J/+-+-
(2S)J/+-
(2S) excluded from these plots
f2(1270) or f0(1370) ?
MC
M4 = 2.3-3.0 GeV
MC
Data
f2(1270) or f0(1370) ?
Achim Denig The Radiative Return: A Review of Experiments
56
e+e- K+K-+-• Require 1 or 2 Kaon IDs• Negligible background• Good agreement with
DM1, much higher ECM reach.
• Systematics: Kaon ID, Efficiency.
• Require 1 or 2 Kaon IDs• Negligible background• Good agreement with
DM1, much higher ECM reach.
• Systematics: Kaon ID, Efficiency.
e+e- K+K-+-
Cross Section (89.3 fb-1)
Achim Denig The Radiative Return: A Review of Experiments
57
e+e- K+K-+-Resonant Structures
• K*(892) K dominates
• No K*K*, DD signals.
• , in K+K- and spectra with K*(892) bands excluded
• K*(892) K dominates
• No K*K*, DD signals.
• , in K+K- and spectra with K*(892) bands excluded
Excluding the K*(892) bands
band
K*0
No obvious structure in +-
when selecting K+K-
No obvious structure in +-
when selecting K+K-
Achim Denig The Radiative Return: A Review of Experiments
58
B((2S) J(36.1±1.5±3.7)B((2S) J(36.1±1.5±3.7)
• (2S) in 2+2- mode is signal is actually J/, no direct signal seen.
• Assuming PDG value of (2S)e+e-) and B(J/ ),
Assume PDG value of Je+e-): Assume PDG value of Je+e-):
PDG: 31.02.8 %)%8.25.11.36()/)2(( JSB
Would be interesting to compare with 00J/ BF from e+e- +-
00... Work in progress!
Mode BaBar BF (89.3 fb-1) PDG 2004
J (3.61±0.26±0.26)10-3 (4.0±1.0)10-3
JK+K- (6.09±0.50±0.53)10-3 (7.2±2.3)10-3
J2K+2K- (6.7 ±1.0±1.1)10-4 n/a
Achim Denig The Radiative Return: A Review of Experiments
59
e+e- +-0
NJ/ = 92034
Cross-Section:• Overall normalization error
~5% below 2.5 GeV.• Consistent with SND data
for M3 < 1.4 GeV.
• Inconsistent with DM2 results.• Structures at 1.25 and 1.65 GeV,
fit to and ’’, assuming:•(’) – () = 1800.•(’’) – () = 00
Cross-Section:• Overall normalization error
~5% below 2.5 GeV.• Consistent with SND data
for M3 < 1.4 GeV.
• Inconsistent with DM2 results.• Structures at 1.25 and 1.65 GeV,
fit to and ’’, assuming:•(’) – () = 1800.•(’’) – () = 00
M3[GeV/c2]
SND
J/
DM2
BaBar PDG 2004 BES 2003
B(J/) (2.18±0.19)% (1.50±0.20)% (2.10±0.12)%
PDG: 1400-1450 MeV/c2
PDG : 180-250 MeV
PDG: 1670 ± 30 MeV/c2
PDG: 315 ± 35 MeV
MeV 2030230
MeV/c 2101660
MeV 7070450
MeV/c 20201350
''
2''
'
2'
M
M
MeV 2030230
MeV/c 2101660
MeV 7070450
MeV/c 20201350
''
2''
'
2'
M
M
BaBar124 fb-1