latest physics results from aleph paolo azzurri cern - july 15, 2003

Latest Physics Results from ALEPH

Paolo Azzurri

CERN - July 15, 2003

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 2

What’s new ?

• QCD Studies

• Four fermions & Gauge Couplings

• Jet reconstruction & radiative Z peak

• SUSY searches

• Conclusions & Prospects

QCD studies

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 4

αS @ 91-209 GeV

NLO + NLL TheoryTheory syst error evaluated with the lepwg method

(uncertainty band method)

Consistent analysis at all energies using six event shape variables

in hadronic events

)hadr(0011.0

)pert.th.(0045.0

(exp)0011.0

)stat(0009.0

1214.0

LEP2LEP1

ZS m

FINAL !

CMES

CME

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 5

Two-dimensional BE correlations

Selection of two-jet events with large thrust

q

q

2

1

String = Pion source

Q= p= p1 - p2

QL : longitudinal component of pQT : transverse component of p

Data/MC double ratio of the distribution of like-sign tracks to reference samples

Reference of mixed pionsfrom different events

Reference of unlike-sign pionsfrom the same event

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 6

Two-dimensional BE correlations

Lund Model

predicts RT<RL

Fit double ratio to:

source size source size andand strengthstrengthdepend on the depend on the

reference sample !reference sample !

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 7

Rapidity gaps in gluon jets

From OPAL proposal

to test CR at Z peak

rapidity gap withno charged particles

rapidity gap

q

q

gluon – jet(softest)

High purity quark jets :data/mc agreement

Jets with 1.5 rapidity gap

MC with CR (GAL)

MC without CR

The charge of the third softest jet (most likely gluon)

is sensitive to CR models

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 8

Rapidity gaps in gluon jets

New ALEPH measurement

as a function of the rapidity gap

Tested CR models not in agreement

with data at all rapidity gaps

(overestimate of CR effects)

Models with no CR agree with data only at zero rapidity gap :

data shows an effect !

(data-MC)/MC

Four fermions & Gauge Couplings

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 10

Zee production

New analysis of the hadronic decay channeleeqq: 4f signal defined by lepwg convention

Selection efficiency=24%, purity =82%

10%at SMwith agreement

pb )syst(01.0(stat)05.053.0qqeeZee

section cross Average

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 11

W-pair production

Consistent event selections at all energies 183-207 GeV

More stringent evaluationsof systematic uncertainties

Latest data reprocessingand event reconstructions

FINAL !

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 12

W decay couplings

019.0014.1(syst)07.0(stat)32.020.11WB

020.0018.1(syst)07.0(stat)25.089.10WB

018.0004.1(syst)07.0(stat)27.080.10eWB

gg

gg

gg

e

e

Lepton non-universality

(syst)007.0(stat)017.0958.0V

009.0992.0(syst)13.0(stat)38.014.67qqWB

cs

ggq

Lepton universality

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 13

BE correlations in W pairs

W pairs Double ratio: four jet decays compared to two mixed hadronic

parts of semileptonic decays

BEIMC,,

q22,

q4

data,q22

,q4(Q)D'

NN

NN

MC BEI = BE Inside W decayMC BEB = BE Between W decays

4q

2q2q

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 14

BE correlations in W pairs

006.00.077 : BEB JETSET

(syst)014.0(stat)015.0001.0

level) BEB MCat (fixed GeV 61.2

disfavoured at the 3.7 sigma level

Fit double ratio to:

unlike –sign pairs

like –sign pairs

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 15

BE correlations in W pairs

055.00.720' :BEB JETSET

(syst)200.0(stat)148.0124.0'

Integral of the BE enhancement

disfavoured at the 3.3 sigma level

Double differenceComplementary measurement:

BEIMC,,q22

,q4

data,q22

,q4Q'

NNNN

like –sign pairs

unlike –sign pairs

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 16

Triple Gauge Couplings

Z1g

New multi-parameter fits with correct O(α) treatment in W-pair analysis

W pairs, single W and single photonscombined

1-D, 2-D & 3-D95% CL contour limits

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 17

Generic Triple Gauge Couplings

NEW ! updated

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 18

Generic Triple Gauge Couplings

Form Factor for Vector Resonance Enhancement of L Le e W W

2

2T

M i M

M s i MF

,M mass & width of technirho

T.L.Barklow et al. hep-ph/9704217

( )M GeV

M

excludedat 95% CL

For at 95% C.L. 1M 625M GeV

NEW !

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 19

Quartic Gauge Couplings

Wc

W aa ,0

Zc

Z aa ,0

Analysis of acoplanar photon pairs with high transverse momentum

(ννγγ final state)

Limits @ 95% CL:

2ΛaZ

c

2ΛaW

c

2

0 ΛaW

2

0 ΛaZ

Jet reconstruction improvements& radiative Z peak

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 21

Rescaled di-Jet mass

1

2

1

2

Jet 1

Jet 2

Radiative Z event:

sinsinsin

sinsinsin

:mass rescaledjet -di

sinsinsin

sinsinsin

:massangular jet -di

21212211

2121221112

2121

212112

sm

sa

Jet angles and jet velocities are the fundamental ingredients ofradiative Z and W mass measurements with kinematic fits

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 22

Jet velocity & mass

Last jet reconstruction(with ECAL cleaning)

Z peak jets boost

(T>0.8)

jetjet Mlog

)log(

P

MeV 20180M

%2.05.1)(: DATA/MC

jet MeV 205M %2.00.0)(: DATA/MC jet

Jet boost (and mass) now well calibrated !

Removing low energy neutrals(<1.5 GeV , and <2 GeV if mixed)

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 23

Simulation of forward charged tracks

Loss of forward tracks in data(nuclear interactions in Vdet material)

Year 2000 Z peak hadronic eventsAffects regions with at low polar angle(4% max deficit in forward directions)

Deficit parametrized as a functionof the track cosθ and PT

Monte Carlo tracks corrected

cos

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 24

Radiative Z peak

MeV 54Total

MeV 24anglePolar

MeV 16 tracksForward

MeV 12stat MC

MeV 16background

MeV 7ISR

MeV 20methodFit

MeV 30rsCalorimete

MeV 19ionFragmentat

effect mSource 12

MeV (syst) 58 (stat) 3243E

MeV (syst) 54 (stat) 3040m

b

Z

Systematic uncertainties

Unbinned likelihood fit to a pdf built with a fit to the MC reference

2GeV/cZm

SUSY searches final results

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 26

Constraints on the MSSM

Improvement of the selectron searchin the gaugino region

New scan of low tanβ with stau mixing(without Higgs constraints)

2

20

2

TeV/c4 4545

TeV/c 1

TeV/c 1

50tan1

A

m

limits on the LSP mass

Combination of searches for charginos, neutralinos, sleptons, higgs

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 27

Limits on the LSP mass with stau mixing

LSP limit at 95% CLwith any stau mixing

GeV 42.6 GeV 36.8mixingstau

GeV 5.43GeV 39.6many

GeV 49.5 GeV 39.6sfermionsheavy

sconstraint higgs tanallC.L. @95%limit )m(

0

01

NEW ! improved

Summary of LSP limits

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 28

Conclusions & Prospects

ALEPH is coming to an end …

☼ Searches for new physics completed with the LSP limits Many Standard Model analyses completed

or close to being published

Archiving of ALEPH data and Monte Carlo (~3Tb)

for long term analysis completed (June 2003)

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 29

Two-dimensional BE correlations

Comparison with other LEP experiments

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 30

BE correlations in W-pairs

Fit results without fixing the source radius

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 31

Triple Gauge Couplings

W-pairs, single W and single photonscombined

@95% C.L.

O(α) correction sytematic now evaluated as the difference

between schemes

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 32

Quartic Gauge Couplings

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 33

Jet velocity & mass

Z peak jets boost

(T>0.8)

jetjet Mlog

)log(

P

MeV 20180M

%2.05.1)(: DATA/MC

jet

MeV 2030M %2.03.0)(: DATA/MC jet

Jet boost (and mass) calibrated !

ECAL cleaningwith full egs simulation:

Last jet reconstructionwith ECAL cleaning

CERN - July 15, 2003 P.Azzurri - Latest physics results from ALEPH 34

Radiative Z peak

ncalibratiofit on error includes

4.05.03.05.03.07.05.03.14.09.04.06.0(%)

4.08.13.05.03.03.04.05.04.00.04.05.0(%)

462745474218456141563735)(

40493737362641336253240)(

charged50.075.021std

2

1

12

12

MeVa

MeVm

coneconeGeVpGeVp

sinsinsin

sinsinsin

:massangular jet -di

sinsinsin

sinsinsin

:mass rescaledjet -di

2121

212112

21212211

2121221112

sa

smMain effective changes

wrt observation large data/MC shift :

•Strict cut on beam background •ECAL cleanning in jets

•Removal of low energy neutrals•Correction of forward tracks