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
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