Transcript Physics results from ALEPH (Summer Conferences 2002)

Physics results from ALEPH
(Summer Conferences 2002)
Andrea Venturi
INFN Pisa and CERN
On behalf of the ALEPH Collaboration
LEP Physics Jamboree Jul 22nd 2002
Outline
LEP II
Standard
LEP I
t’s branching ratios
•Two photons
•ee  Zee  mmee
• Colour reconnection studies
Charm gluon splitting
Only g’s final states
as from event shape
Searches for new physics
•“Complete” LEP II or LEP I
datasets used for (almost) all the
results
•Results are preliminary unless
published
• single top production
• LSP limits
•stop into gluino LSP
• non-standard Higgs
•Exclusion limits at 95% CL
Jul 22nd 2002
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LEP I: t Branching Ratios
• New results with the full LEPI
statistics: ~330k tt pairs
• Classification of each t decay
according to number of tracks, p0’s
and particle id: 13 classes
(e,m,h,hp0,h2p0,…,3h,3hp0,…)
• Improved treatment of MC
corrections and systematic
evaluation, especially g’s and p0’s
• Results corrected for the t decays
into K’s,w’s and h’s using previous
analyses (ALEPH and CLEO)
Jul 22nd 2002
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LEP I: t Branching Ratios
T itle:
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T itle:
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Lepton universality: Bm and Bp
translated into electron BR
WA t, m and p lifetimes and t mass
used
T itle:
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T itle:
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Lepton universality tested
within 2-3 per mille
Jul 22nd 2002
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LEP I: t Branching Ratios
• Vector spectral functions
from pp0, 3pp0, p3p0 BR’s and
mass distributions
Hadronic contribution to
g-2 radiative corrections
An example:
ee p+p- cross
section from
BR(pp0)
Jul 22nd 2002
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LEP I: gluon splitting into charm
N ( Z  q qg, g  c c)
g cc 
N ( Z  hadrons)
• 3 jets events with a lepton in the
least energetic jet
• NN with 6 variables to increase
signal purity: ~25% e, ~18% m
•
Main systematics:
– Lepton id
– Charm jet simulation
– BR(c  l)
• gcc(e)=(2.990.280.41) %
gcc(m)=(2.900.380.74) %
gcc=(2.98  0.48) %
WA: (2.96  0.38)%
Jul 22nd 2002
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LEP I + LEP II: as from event-shape variables
• Results from the full LEP I+LEP
II ALEPH data set
• 6 event-shape variables used:
T, MH2, BW, BT, C, -log y3
• Fit with O(as2) + NLLA
• Good agreement with as
running
running to MZ and combining:
as(MZ)=0.12110.0047
Jul 22nd 2002
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LEP II: gg  p+p- and gg  K+K• Measurements with LEP II data
Prediction
Rescaled x2
Angular distributions
pp
pp
Wgg distributions
KK
Jul 22nd 2002
Physics results from ALEPH - Andrea Venturi - INFN Pisa / CERN
KK
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LEP II: gg  D* X
•
•
•
•
D* from D0 + soft pion
Measurement “direct” and “singleresolved” contributions
D* cross sections vs pt and h
s(ee  ee cc)
direct
Single-resolved
Rapidity
Frixione et al.
(2000)
Jul 22nd 2002
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gg  D* X and s(eeeecc)
Transverse
momentum
Jul 22nd 2002
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LEP II: 2 fermions production: HF results
• New results: AbFB, QudscFB and Rc
ECM (GeV)
205
SM
AbFB
207
205
QudscFB
207
0.620  0.338  0.138
0.571
-0.256  0.232  0.057
0.572
0.00770.00510.0018
0.0070
0.01430.00390.0020
0.0069
ECM (GeV)
Rc
SM
196
0.2870.033 0.022
0.251
200
0.2620.035 0.014
0.252
205
0.2960.037 0.016
0.253
207
0.2870.029 0.021
0.253
Jul 22nd 2002
Physics results from ALEPH - Andrea Venturi - INFN Pisa / CERN
all: 2.3 s
207: 3.5 s
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LEP II (4f): ee  Zee  eemm cross section
• New analysis
• Signal definition according to LEP
WG (phase space cuts):
– Mmm > 60 GeV
– Forw electron q < 12o
– bckw elect: E>3 GeV, 12o<q<168o
• Selection efficiency: (362)%
• 16 events selected (183-207
GeV) (1.9 expected bkg)
s(ee  Zee  eemm)=57  14  4 fb
(average from 183 to 207 GeV)
Jul 22nd 2002
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Looking for Colour Reconnection in WW4q
events: preliminary results
• Colour singlets can be created across decay products of different W’s: we
cannot ask ourselves which W a particle comes from.
• Interesting to better understand non-perturbative QCD, worrying for the W
mass measurement
• Larger effects at the end of the parton shower and in the non-perturbative
part  MC models
• ALEPH preliminary results from:
– Charged particle multiplicity and momentum spectrum analysis
• Real data are compared to different MC models using WW4q and WW lnqq events
– Particle flow analysis in WW4q (started by L3)
• Particle multiplicity between jets from the same and different W’s are compared to MC
models with and without Colour Reconnection
– Variation of the W mass measurement when soft particle (momentum cut) are
discarded from jet reconstruction
Jul 22nd 2002
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DMW with CR models
Mass shift in MeV
SKI model predictions
Model
DM (MeV)
Herwig CR
~30
Ariadne 2 CR
70-80
Rathsman (GAL)
30-40
% of reconnected events
In SKI model Preco is controlled
by the parameter Ki
Jul 22nd 2002
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CR: Charged Particle spectra
JETSET
vs
others
Xp=p/Ebeam
10 GeV
Jul 22nd 2002
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1GeV
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CR: Particle flow between W’s
•
•
•
In WW  4q events
particles are projected to
the closest inter-jet plane
and angles w.r.t. jet are
measured
Inter-jet angles are
normalized to 1
Distribution is folded and
binned ratio is done:
Rn = one bin from 0.2
to 0.8
3
(A+B)/
(C+D)
0=4
1
2
Rn=1.0950.014(stat)
0.006(syst)
0.006(extrap)
extrapolated to 189 GeV
Jul 22nd 2002
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CR: Particle flow between W’s
•
Rn measured in data is compared with MC
predictions from different models with
and without CR
•
Rn(data)= 1.0950.014(stat) 0.006(syst)
0.006(extrap)
SKI model
DR/stot
ki=2.3
Model
parameter
Ki
• Background, BE and detector
systematics are included.
Fragmentation is not included
Bias induced by MC tuning
has not been evaluated yet
Jul 22nd 2002
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CR from the W mass
• CR is expected to affect mainly
low momentum particles and
particles away from the jet
core
•
Measure the variation of the W
mass obtained removing
progressively low momentum
particles (pcut analysis) or “far
away” particles (cone analysis)
Mass shift
•
The following results have been
obtained with the pcut analysis
•
The slope of the W mass
measurement is compared to the
MC predictions.
Jul 22nd 2002
Physics results from ALEPH - Andrea Venturi - INFN Pisa / CERN
Momentum
cut
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CR from the W mass
•Very preliminary results:
•conservative systematics and bias
•improved “calibration” studies to be done
Semileptonic events
control sample
D 2  1 KI  1.3 Preco  42%
Fully hadronic events
•
Jul 22nd 2002
Ariadne2 (CR) model predicts a fairly
large mass shift (~70-80 MeV) but
quite insensitive to momentum and
cone cuts
Physics results from ALEPH - Andrea Venturi - INFN Pisa / CERN
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CR from the W mass statistical error
• VERY preliminary study
• Relative error variation wrt no
Pcut analysis
• It is sensitive to CR
• It can differentiate models
– In particular AR2
Jul 22nd 2002
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From SM to new physics: g’s final states
• Final results
(CERN-EP/2002-033):
•Acoplanar photons
•ee  XX  YYgg: s < 0.1 – 0.04 pb
~~
•ee o1 o1  GG gg: M > 98.8 GeV
•Single photon
•Nn = 2.86  0.09
•ee  XY  YYg: s < 0.25 – 0.05 pb
•Super-light gravitino > 1.3 10-5 eV
•Gravity with extra dimension:
graviton mass limit:
MD > 1.26 – 0.57 TeV (d=2-6)
•Collinear photons
•Gravity with extra dimension: string scale
•Contact interactions:
L6 > 1.35 TeV, L7 > 0.74 TeV , L8 > 21.4 GeV
•Excited electron: M > 213 GeV (fg = 1)
Jul 22nd 2002
Physics results from ALEPH - Andrea Venturi - INFN Pisa / CERN
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Single top production limits
ALEPH
limits
• Final results with full LEPII data
•
•
– CERN-EP/2002-042
Multijet (with one b) final state (with or
without leptons)
e ~ 3% (lepton) , ~ 13.5% (hadron)
including BR’s
•24 candidates in data (20.1 expected)
•BR(tZc)+BR(tZu)<14% (95% CL)
(no g coupling, mtop=174 GeV)
Jul 22nd 2002
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Charginos nearly degenerate with neutralino
• Small mass differences with mass
unification only if M2 very large
• More “natural” with AMSB
Gaugino
region
• Dedicated analysis to cover the
hole between:
– Long-lived charginos: search for
heavy stable charged particles
– Chargino’s decay products can
trigger DAQ
• Search for ISR g plus soft tracks
compatible with g+- production
and decay
M > 88 GeV (heavy sfermions)
Higgsino
region
(Phys. Lett B533 (2002) 223)
Jul 22nd 2002
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Jul 22nd 2002
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LSP mass: toward an absolute limit
• Framework : MSSM
– LSP = 01
– Mass unification
• “Standard” analyses:
– Chargino and Neutralino searches
– Squarks and sleptons
– Higgs Boson
• If stau mixing ft is let free
–  t~n, 0 t~t can be dominating
– Dm(t~- 0) can be small: soft t’s in
final state
• Additional searches:
~ ~
ee+ - t nt n  tn0tn0 acoplanar t’s pairs (large Dm), ISR g+soft tracks
ee 01 02 t~t 0  t0t0
single t (small Dm)
ee 02 02 t~tt~t  tt0tt0 2-4 t’s final state
Jul 22nd 2002
Physics results from ALEPH - Andrea Venturi - INFN Pisa / CERN
(small Dm)
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An example:m=-1000 GeV
tanb=35: ft  0 - 40
m1/2 vs m0
LSP limit
I – chargino
3-bodies
II – chargino
2 - bodies
tanb=35
ft  0
Standard analyses
New t analyses
ISR g analysis
III - t’s final
states
Charginos +
ISR
Selectrons
MLSP > 41.6 GeV
tanb=35
ft  40
Jul 22nd 2002
Physics results from ALEPH - Andrea Venturi - INFN Pisa / CERN
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s-top decays into gluino LSP
•
•
•
•
Very preliminary Y2K data only
Gluino is LSP
~
t~
t can be produced at LEP II
e+ e-  ~
t~
t  cg~cg~
• R-parity conserved  R-hadrons
• MC simulation
– gluino parton shower in PYTHIA
– R-hadrons interact as heavy pions
• Missing energy is not always
present
• Selection of acoplanar jets
– depends on DM
– efficiencies: 10-22 %
– 4f background is subtracted
Jul 22nd 2002
Physics results from ALEPH - Andrea Venturi - INFN Pisa / CERN
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Search of Higgs boson with non-standard decays
• Flavour-independent Higgs
boson search (CERN-EP/2002-027)
• Only HZ  qqqq analysis has been
modified with respect to the
standard Higgs boson search
BR(had)+ BRtt= 1 : MH > 109.1 GeV
MH > 110.6 GeV
MH > 112.4 GeV
– No b-tagging + estimators of WW
and HZ hypothesis
BR(had)*s/sSM
BRtt*s/sSM
Hadronic
final state
limits
MH GeV
Jul 22nd 2002
Physics results from ALEPH - Andrea Venturi - INFN Pisa / CERN
tt
final state
limits
MH GeV
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Search of Higgs boson with non-standard decays
• Search for gg decays of a Higgs
boson (CERN-EP/2002-044):
– LEP I + LEP II
• Looking for events with two g’s +:
– Missing energy (Hnn)
– 2-4 charged tracks (Hll)
– > 5 tracks (Hqq)
Fermiophobic
Higgs: M>105.4 GeV
Jul 22nd 2002
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Summary and conclusions
• ALEPH is still obtaining interesting results from LEP I data
• Exclusion limits from searches are becoming more and more
general
• More exotic models have been explored
• Progress in understanding the main systematics of the W
mass measurement (LEP-wide joint effort)
• See you in Winter 2003 with other (final) results: 4f cross
sections, searches, W mass, …
Jul 22nd 2002
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