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Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 1
ALEPH Results on Branching Ratios and Spectral Functions
Michel Davier
Laboratoire de l’Accélérateur Linéaire, Orsay
Tau Workshop 2004
September 14 - 17, 2004, Nara, Japan
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 2
Final ALEPH Analysis
• only 91-93 data published for branching ratios, 91-94 for spectral functions
• 94-95 statistics x1.5 91-93
• selection efficiencies obtained from data for each topology
• improved photon ID better separation between good and fake photons
• new method to correct the number of fake photons (hadron interactions in ECAL
and splitting of EM showers) in MC simulation
• reduced feedthrough in low BR channels
• improved methods for the estimation of systematic uncertainties
Final analysis of the complete LEP 1 data sample
Detailed publication available shortly
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 3
Event Selection and non- Background
events selected by vetoing backgrounds
• total energy: Bhabhas, -pairs
• pT balance, low visible energy: -induced processes
• high multiplicity: Z qq
Break-mix method to determine efficiency on data for every selection cut
• tag one hemisphere to get sample unbiased/cut
• keep opposite hemisphere as unbiased decay
• construct event sample with pairs of selected hemispheres
• apply cut and measure efficiency (small correlations taken from MC)
event selection efficiency 79% (92% in polar acceptance, 5% / modes)
Non- background measured on data sample for leptonic channels,
from MC for hadronic channels (-induced, 4-fermion, qq)
kept relatively high (1.2%) to retain large efficiency
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 4
Photon ID
Collimated decays granularity
- transverse: 75,000 ECAL cells
- 3-fold longitudinal segmentation
Large improvement compared to
published results on 91-93 data
Likelihood method probability to be
a good photon, discriminating variables
to distinguish good/fake photons
data
MC good
fake photons
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 5
Decay Classification
• e e ID, not in ECAL cracks
• ID, P2 GeV
• hadronic channels
- 0 reconstruction: 2 resolved photons + kimenatic fit
merged photons (energy-weighted moments)
single photons (single,radiative, collinear; fake)
- track (1 - 2,3,4 – 5) and 0 (1 – 4 for 1-pr, 1 – 3 for 3-pr ) multiplicities
- low BR channels: 3 tighter tracks required for 3h 2-3 0, only resolved
0’s for h 4 0 and 3h 3 0
• ‘garbage can’ for rejected hemispheres (‘class 14’) 3.6%
e in cracks: 21% with P2 GeV: 27%
1-pr hadronic (mostly P2 GeV): 41%
3,5-pr hadronic: 11%
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 6
Sample
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 7
Global BR Analysis
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 8
Systematic Uncertainties
• method: identify sources of systematics, for each one
- link systematic source to relevant variables
- study data/MC distributions of these variables
- characterize and measure systematic bias stat error syst error
- correct MC for measured bias and keep total error as quoted syst uncertainty
• main sources
- / 0 reconstruction
- non- backgrounds
- event selection efficiency
- particle ID efficiency matrix
- secondary interactions
- tracking
- MC dynamics
- MC statistics
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 9
/ 0 Systematic Sources
- efficiency at low-energy (threshold)
- efficiency at high energy (track overlap)
- conversions
rate
h misID in multiprong environment
p misID in secondary interactions
- ID efficiency (good/fake probability)
- fake photon rate correction
- energy calibration
- 0 efficiency
- Dalitz decays
- radiative photons
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 10
Systematic Errors 94-95
(B in %)
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 11
Particle Spectra (leptons)
non- background
Data/MC comparison
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 12
Particle Spectra (hadrons)
Data/MC comparison
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 13
Mass spectra
Data/MC comparison
All multihadrons h 0
non-
feedthrough
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 14
Exclusive BR‘s
• topological BR’s defined by charged-track and 0 multiplicities
• class 14 (removed decays) consistent with 0
B14 = (0.065 0.027 0.028) %
consistent with standard decays
• dedicated analysis found no ‘invisible’ decay (efficiency=0 in our selection)
Binvisible 0.11% (95% CL)
assume that all considered modes add to 100% and proceed to
the determination of exclusive BR’s
• modes with kaons (KS, KL, K) have been measured separately
(complete study with full LEP 1 ALEPH data up to 4 hadrons/mode),
subtracted on a statistical basis
• correct for EM modes (all decays, , 0) using measured
channels with and
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 15
Non-strange Branching Ratios
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 16
Leptonic modes
( )
)(
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 17
Hadronic modes (1-prong)
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 18
Hadronic modes (3,5-prong)
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 19
Lepton Universality in the Charged Current
Beuni = (17.810 0.039) %
Be and B
g / ge = 0.9991 0.0033
Be , B and WA (290.6 1.1) fs
g / g = 1.0009 0.0023 0.0019 0.0004
g / ge = 1.0001 0.0022 0.0019 0.0004
(Be , B) ( ) (m)
B and WA
g / g = 0.9962 0.0048 0.0019 0.0004
0.0007 (radiative corrections)
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 20
The Hadronic Sector
CVC + isospin breaking ee ALEPH
B0 24.52 0.31 25.47 0.13 0.95 0.33
(%) B30 1.09 0.08 0.98 0.09 -0.11 0.12
B30 3.63 0.21 4.59 0.09 0.96 0.23
a1 decays
B3 / B20 = 0.979 0.018
to be compared to 0.985 CLEO (PWA + isospin breaking / masses)
V,A separation
R = 1 Be – 1.9726 = 3.642 0.012
R,S = 0.160 0.006 R,V+A = 3.482 0.014
R,V = 1.782 0.011 0.002
R,A = 1.700 0.011 0.002 R,VA = 0.081 0.018 0.005
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 21
Spectral Functions
• hadronic mass spectra corrected by kinematic factor and scaled by Bi Be
• unfolding from detector effects by regularized inversion of 140x140 detector
response matrix (Höcker-Kartvelishvili)
• specific systematic studies using full analysis for every syst. source,
constructing corresponding covariance matrices
- and 0 reconstruction
- energy calibration and resolution (charged particles and 0‘s)
- tracking and secondary interactions
- unfolding procedure (test distributions)
• spectral functions obtained for the leading channels 0, 20, 30,
3, 30
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 22
Spectral Functions: Results
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 23
Spectral Functions: V, A
V A
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 24
Spectral Functions: V A
V + A V A
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 25
Spectral Functions: QCD analysis
• changes since 1998 published analysis: full LEP1 statistics for BR
re-analysis of spectral functions
• analysis now even more limited by theoretical uncertainties
some progress in the calculation of the S4 term (Chetyrkin-Kühn et al)
but not complete yet: favours Kataev-Starshenko estimate K430
• use R,V, R,A, R,V+A, and the mass-weighted moments (shapes)
• results soon available
- very close to published ones with smaller experimental and slightly
smaller theoretical errors
- some evidence for OPE problems, except in the V+A case where
it does not matter (non-perturbative contributions below 1%)
• recall published results S(m2) = 0.334 0.007exp 0.021th
S(MZ2) = 0.1202 0.0008exp 0.0024th 0.0010ext
from Z width (EW fit) S(MZ2) = 0.1183 0.0027
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 26
The Complete List of ALEPH Branching Ratios
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 27
Backup Slides
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 28
– –
0: Comparing ALEPH, CLEO, OPAL
Good agreement observed between ALEPH and CLEO
ALEPH more precise at low s
CLEO better at high s
Shape comparison only. SFs normalized to WA branching fraction (dominated by ALEPH).
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 29
Testing CVC
Infer branching fractions from e+e– data:
2
20
CVC 20
SU(2)-corrected(6 | |
BR kin( ) )m
ud EWV Sds s
ms
Difference: BR[ ] – BR[e+e – (CVC)]:
Mode ( – e+e –) „Sigma“
– – 0 + 0.94 ± 0.32 2.9
– – 3 0 – 0.08 ±
0.110.7
– 2 – + 0 + 0.91 ± 0.25 3.6
leaving out CMD-2 : B0 = (23.69 0.68) % (7.4 2.9) % relative discrepancy!
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 30
New Precise e+e –+
– Data from KLOE Using the „Radiative Return“
...
Overall: agreement with CMD-2
Some discrepancy on peak and above ...
Tau Workshop, Nara, Sept 14-17, 2004 M. Davier – ALEPH Results 31
The Problem (revisited)
Relative difference between and e+e – data:
zoom
No correction for ± –
0 mass (~ 2.3 ± 0.8 MeV) and width (~ 3 MeV) splitting applied
Jegerlehner, hep-ph/0312372Davier, hep-ex/0312064