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

davier@lal.in2p3.fr

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

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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

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The Complete List of ALEPH Branching Ratios

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Backup Slides

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– –

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