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The top quark at LHC: status and prospects
Marina Cobal-Grassmann“Journee ATLAS France”Londe Les Maure, 3-5 May, 2004
Marina Cobal - Londe Les Maure 2004
P 2 Motivations for Top Physics studies
Top quark exists and will be produced abundantly! In SM: top- and W-mass constrain Higgs mass
Sensitivity through radiative corrections Scrutinize SM by precise determination top mass
Beyond SM: New Physics? Many heavy particles decay in tt Handle on new physics by detailed
properties of top
Experiment: Top quark useful to calibrate the detector
Beyond Top: Top quarks will be a major source of background for almost every search for physics beyond the SM
direct
indirectEX
CLUDED
Summer 2003 result
Marina Cobal - Londe Les Maure 2004
P 3
1cos22
2
WZ
W
m
m
No observable directly related to mNo observable directly related to mHH. However the dependence can . However the dependence can appear through radiative correctionsappear through radiative corrections. tree level quantities changedtree level quantities changed
mH
, , r r = f [ln(m= f [ln(mHH/m/mWW), m), mtt22]]
By making precision measurements (already interesting per se):By making precision measurements (already interesting per se):• • one can get information on the missing parameter mone can get information on the missing parameter mHH• • one can test the validity of the Standard Modelone can test the validity of the Standard Model
SMmfermions (9)
mbosons (2)
VCKM (4)
GF (1)
s(1)
)1(sin2 2
2 rG
mFW
W
The uncertainties on mThe uncertainties on mtt, m, mWW are the dominating ones in the electroweak fit are the dominating ones in the electroweak fit
predictions
(down to 0.1% level)
lepteffcbl
bclFBcblhWZWZ AARm 2
,,,,,00
,,0
,, sin,,,,,,
tWW mm ,,
had
W2sin
WW CsQ 2sin)(
LEP+SLD:LEP+SLD:
UA2+Tevatron:UA2+Tevatron:
NuTeV:NuTeV:
APV:APV:
eeeeqq l.e.:qq l.e.:
What we know..
Marina Cobal - Londe Les Maure 2004
P 4
Top mass: Where we are
Marina Cobal - Londe Les Maure 2004
P 5
Tevatron only (di-lepton events or lepton+jet ) from W decays
Status of inputs (preliminary):mmtt=(178.0 =(178.0 2.7 2.7 (stat) (stat) 3.3 3.3 (syst)(syst)) GeV/c) GeV/c22
(latest Tevatron updated combination – RunI data)(latest Tevatron updated combination – RunI data) mmtt=(175 =(175 17 17 (stat) (stat) 8 8 (syst)(syst)) GeV/c) GeV/c22
(CDF di-leptons – RunII data)(CDF di-leptons – RunII data) mmtt=(178=(178+13+13
-9-9 (stat) (stat) 7 7 (syst)(syst)) GeV/c) GeV/c22
(CDF lepton+jets – RunII data)(CDF lepton+jets – RunII data)
Matter of statistics (also for the main systematics) and optimized use of the Matter of statistics (also for the main systematics) and optimized use of the available information. Each experiment expects 500 b-tagged tt l+jets events/fb available information. Each experiment expects 500 b-tagged tt l+jets events/fb Mtop ~ 2-3 GeV/cMtop ~ 2-3 GeV/c22 for the Tevatron combined (2-4/fb) for the Tevatron combined (2-4/fb)
mmt t 2.5 GeV ; 2.5 GeV ; mmW W 30 MeV 30 MeV mmHH/m/mH H 35% 35%
Near future of Mtop
In 2009 (if upgrade is respected) from Tevatron: Mtop = 1.5 GeV !!
Marina Cobal - Londe Les Maure 2004
P 6
What can we do at LHC?
LHC
TeVatron1034
1033
<1032
Luminosity
[cm-2s-1]
100
10
0.3
∫L
[fb-1/y]
14 LHC (high lum)
14 LHC (low lum)
2 TeVatron
√s
[TeV]
processprocess (pb)(pb) Events/sEvents/s Events/yEvents/y
bbbb 55101088 101066 10101313
ZZeeee 1.51.5101033 ~3~3 101077
WWℓℓℓ=e,μℓ=e,μ 33101044 ~60~60 101088
WWWWeeXX 66 1010-2-2 101055
tttt 830830 ~1.7~1.7 101077
HH(700 GeV/c(700 GeV/c22)) 11 221010-3-3 101044
--
--
Marina Cobal - Londe Les Maure 2004
P 7
Top production at LHC
Cross section determined to NLO precision Total NLO(tt) = 834 ± 100 pb Largest uncertainty from scale variation
Compare to other production processes:
Top production cross section approximately 100x Tevatron
Opposite @ FNAL
32121 10~ ; ˆ xxxsxs
~90% gg~10% qqProcess N/s N/year
Total collected before start LHC
W e 15 108 104 LEP / 107 FNAL
Z ee 1.5 107 107 LEP
tt 1 107 104 Tevatron
bb 106 1012-13 109 Belle/BaBar ?
H (130) 0.02 105 ?
LHC is a top factory!
Low lumi
Marina Cobal - Londe Les Maure 2004
P 8
Top decay In the SM the top decays to W+b
All decay channels investigated Using ‘fast parameterized’ detector
response Checks with detailed simulations
1. Di-leptons (e/) BR≈4.9% 0.4x106 ev/y No top reconstructed Clean sample
2. Single Lepton (e/) BR=29.6% 2.5x106 ev/y One top reconstructed Clean sample
3. Fully Hadronic BR≈45% 3.5x106 ev/y Two tops reconstructed Huge QCD background Large combinatorial bckgnd
Marina Cobal - Londe Les Maure 2004
P 9
MTop from lepton+jet
Br(ttbbjjl)=30%for electron + muon
Golden channel Clean trigger from isolated lepton
The reconstruction starts with the W mass: different ways to pair the right jets
to form the W jet energies calibrated using mW
Important to tag the b-jets: enormously reduces background
(physics and combinatorial) clean up the reconstruction
Lepton side
Hadron side
Typical selection efficiency: ~5-10%:
•Isolated lepton PT>20 GeV
•ETmiss>20 GeV
•4 jets with ET>40 GeV
•>1 b-jet (b40%, uds10-3,
c10-2)
Background: <2%
W/Z+jets, WW/ZZ/WZ
Marina Cobal - Londe Les Maure 2004
P 10
Lepton + jet: reconstruct top
Hadronic side W from jet pair with closest invariant mass
to MW
Require |MW-Mjj|<20 GeV
Assign a b-jet to the W to reconstruct Mtop
Kinematic fit Using remaining l+b-jet, the leptonic part is
reconstructed |mlb -<mjjb>| < 35 GeV Kinematic fit to the tt hypothesis,
using MW constraints
j1
j2
b-jet
t
Selection efficiency 5-10%
Marina Cobal - Londe Les Maure 2004
P 11
Top mass systematics
Method works: Linear with input Mtop
Largely independent on Top PT
Biggest uncertainties: Jet energy calibration FSR: ‘out of cone’ give
large variations in mass B-fragmentation
Verified with detailed detector simulation and realistic calibration
Source of uncertainty
Hadronic
Mtop
(GeV)
Fitted Mtop (GeV)
Light jet scale
0.9 0.2
b-jet scale 0.7 0.7
b-quark fragm
0.1 0.1
ISR 0.1 0.1
FSR 1.9 0.5
Comb bkg 0.4 0.1
Total 2.3 0.9
Challenge:
determine the mass of the top around 1 GeV accuracy in one year of LHC
Marina Cobal - Londe Les Maure 2004
P 12 Alternative mass determination
Select high PT back-to-back top events: Hemisphere separation
(bckgnd reduction, much less combinatorial) Higher probability for jet overlapping
Use the events where both W’s decay leptonically (Br~5%) Much cleaner environment Less information available from two ’s
Use events where both W’s decay hadronically (Br~45%) Difficult ‘jet’ environment Select PT>200 GeV
Mtop
Various methods all have different systematics
Marina Cobal - Londe Les Maure 2004
P 13
Uncertainty On b-jet scale: Hadronic 1% Mt = 0.7 GeV5% Mt = 3.5 GeV10% Mt = 7.0 GeV
Uncertainty on light jet scale: Hadronic 1% Mt < 0.7 GeV10% Mt = 3 GeV
Jet scale calibration
Calibration demands: Ultimately jet energy scale calibrated within 1%
Uncertainty on b-jet scale dominates Mtop: light jet scale constrained by mW
At startup jet-energy scale known to lesser precision
Scale b-jet energyScale light-jet energy
MTop MTop
±10%
Marina Cobal - Londe Les Maure 2004
P 14
Alternative methods
Continuous jet algorithm Reduce dependence on MC Reduce jet scale uncertainty
Repeat analysis for many cone sizes R
Sum all determined top mass:robust estimator top-mass
Determining Mtop from (tt)? huge statistics, totally different systematics
But: Theory uncertainty on the pdfs kills the idea 10% th. uncertainty mt 4 GeV Constraining the pdf would be very precious… (up to a few % might not be a dream !!!)
Luminosity uncertainty then plays the game (5%?)
Luminosity uncertainty then plays the game (5%?)
Marina Cobal - Londe Les Maure 2004
P 15
Use exclusive b-decays with high mass products (J/) Higher correlation with Mtop Clean reconstruction (background free) BR(ttqqb+J/) 5 10-5 ~ 30% 103 ev./100 fb-1
(need high lumi)
Top mass from J/
Different systematics (almost no sensitivity to FSR)
Uncertainty on the b-quark fragmentation function becomes the dominant error
M(J/+l) Pttop
MlJ/
M(J/+l)
Marina Cobal - Londe Les Maure 2004
P 16
Search for resonances
Many theoretical models include the existence of resonances decaying to top-topbar SM Higgs (but BR smaller with respect to the WW and ZZ decays) MSSM Higgs (H/A, if mH,mA>2mt, BR(H/A→tt)≈1 for tanβ≈1) Technicolor Models, strong ElectroWeak Symmetry Breaking, Topcolor, “colorons”
production, […]
Study of a resonance Χ once known σΧ, ΓΧ and BR(Χ→tt) Reconstruction efficiency for semileptonic channel:
20% mtt=400 GeV 15% mtt=2 TeV
1.6 TeV resonance
Mtt
xBR required for a discovery
mtt [GeV/c2]
σxB
R [
fb]
30 fb-1
300 fb-1
1 TeV
830 fb
Marina Cobal - Londe Les Maure 2004
P 17
Couplings and decays
Does the top quark behaves as expected in the SM? Yukawa coupling to Higgs from ttbarH events Electric charge Top spin polarization CP violation
According to the SM: Br(t Wb) 99.9%, Br(t Ws) 0.1%, Br(t Wd) 0.01%
(difficult to measure)
Can probe t W[non-b] by measuring ratio of double b-tag to single b-tag Statistics more than sufficient to be sensitive to SM expectation for
Br(t W + s/d) need excellent understanding of b-tagging efficiency/purity
Marina Cobal - Londe Les Maure 2004
P 18
In the SM the FCNC decays are highly suppressed (Br<10-13-10-10) Any observation would be sign of new physics
Sensitivity according to ATLAS and CMS studies :
t Zq (CDF Br<0.137, ALEPH Br<17%, OPAL Br<13.7%) Reconstruct t Zq (l+l-)j Sensitivity to Br(t Zq) = 1 X 10-4 (100 fb-1)
t q (CDF Br<0.032) Sensitivity to Br(t q) = 1 X 10-4 (100 fb-1)
t gq Difficult identification because of the huge QCD bakground One looks for “like-sign” top production (ie. tt) Sensitivity to Br(t gq) = 7 X 10-3 (100 fb-1)
Rare decays: FCNC
Marina Cobal - Londe Les Maure 2004
P 19
Top Charge determination
Can we establish Qtop=2/3? Currently cannot exclude exotic possibility Qtop=-4/3
Assign the ‘wrong’ W to the b-quark in top decays tW-b with Qtop=-4/3 instead of tW+b with Qtop=2/3 ?
Technique: Hard radiation from top quarks
Radiative top production, pptt cross section proportional to Q2top
Radiative top decay, tWb
On-mass approach for decaying top: two processes treated independently
Matrix elements havebeen calculated and fed intoPythia MC
Radiative top production
Radiative top decay
Marina Cobal - Londe Les Maure 2004
P 20
Top Charge determination
Yield of radiative photons allows to distinguish top charge
Q=2/3 Q=-4/3
pptt 101 ± 10 295 ± 17
pptt ; tWb 6.2 ± 2.5 2.4 ± 1.5
Total background 38 ± 6
Determine charge of b-jet andcombine with lepton Use di-lepton sample Investigate ‘wrong’ combination
b-jet charge and lepton charge
Effective separation b and b-bar possible in first year LHC
Study systematics in progress
i
κ
i
i
κ
ii
bjet
pj
pjqq
pT()
events
10 fb-1
One year low lumi
Marina Cobal - Londe Les Maure 2004
P 21
Top spin correlations
In SM with Mtop175 GeV, (t) 1.4 GeV » QCD
Top decays before hadronization, and so can study the decay of ‘bare quark’ Substantial ttbar spin correlations predicted in pair production
Can study polarization effects through helicity analysis of daughters Study with di-lepton events Correlation between
helicity angles + and -
for e+/+ and e-/-
e+/+
top+
With helicity correlationNo helicity correlation
<CosΘ+ · CosΘ-> <CosΘ+ · CosΘ->
leptons)for 1 :qualityanalyser (spin
base)helicity in n correlatiospin of (degree 34.0
4
coscos1
coscos
1 2
C
C
dd
d
Marina Cobal - Londe Les Maure 2004
P 22
Top spin correlations
Also study spin correlations in hadronic decays (single lepton events) Least energetic jet from W
decay: ~ 0.5
Ratio between ‘with’ and ‘without’ correlations
Able to observe spin correlations in asymmetry C 30 fb-1 of data:
± 0,035 statistical error ± 0,028 systematic error
10 statistical significance for a non-zero value with 10 fb-1
30 fb-1<CosΘ+ · CosΘ->
Marina Cobal - Londe Les Maure 2004
P 23
Single top production
Direct determination of the tWb vertex (=Vtb)
Discriminants:- Jet multiplicity (higher for Wt)
- More than one b-jet (increase W* signal over W- gluon fusion)- 2-jets mass distribution (mjj ~ mW for the Wt signal only)
Three production mechanisms:
Main Background [xBR(W→ℓ), ℓ=e,μ]: tt σ=833 pb [ 246 pb] Wbb σ=300 pb [ 66.7 pb] Wjj σ=18·103 pb [4·103 pb]
Wg fusion: 245±27 pbS.Willenbrock et al., Phys.Rev.D56, 5919
Wt: 62.2 pbA.Belyaev, E.Boos, Phys.Rev.D63, 034012-3. 7
+16.6 W* 10.2±0.7 pbM.Smith et al., Phys.Rev.D54, 6696
Wg [54.2 pb]
Wt [17.8 pb]
W* [2.2 pb]
1) Determination of Vtb
2) Independent mass measurement
Marina Cobal - Londe Les Maure 2004
P 24
Signal unambiguous, after 30 fb-1:
Complementary methods to extract Vtb
With 30 fb-1 of data, Vtb can be determined to %-level or better(experimentally)
Single top results
Detector performance critical to observe signal Fake lepton rate b and fake rate id Reconstruction and vetoing of
low energy jets Identification of forward jets
Each of the processes have different systematic errors for Vtb and are sensitive to different new physics heavy W’ increase in the
s-channel W* FCNC gu t increase in the
W-gluon fusion channel
ProcessVtb
(stat)Vtb
(theory)
Wg fusion 0.4% 6%
Wt 1.4% 6%
W* 2.7% 5%
Process Signal Bckgnd S/B
Wg fusion 27k 8.5k 3.1
Wt 6.8k 30k 0.22
W* 1.1k 2.4k 0.46
Marina Cobal - Londe Les Maure 2004
P 25
Undergoing analyses CP violation in top events (K. Martens, University of Toronto ) Top spin polarization in di-lepton events (V. Simak et al., Prague) Top spin polarization in single lepton events (E. Monnier, P. Pralavorio,
F. Hubaut, CPPM) Single top studies (M. Barisonzi, NIKHEF) Optimization of kinematic reconstruction in the single lepton channel (V.
Kostioukhine, University of Genova)
Commissioning studies (S. Bentvelsen, NIKHEF) New MC validation (S. Bentvelsen, E. Monnier, P. Pralavorio) Full simulation studies of detector effects (A. Etienvre, J. Schwindling,
JP Meyer, Saclay) Full simulation studies of b-tagging (S. Moed, University of Geneva) Top mass and calibration studies (D. Pallin, F. Binet, Clermont-
Ferrand) Ttbar resonances (E. Cogneras, Clermont-Ferrand)
Marina Cobal - Londe Les Maure 2004
P 26 What is left before the LHC starts?
Cover topics still open: cross section, couplings, exotic, resonances,
Define a strategy for validation of the MC input models (e.g: UE modeling and subtraction, jet fragmentation properties, jet energy profiles, b-fragmentation functions..)see M. Mangano talk at IFAE 2004
Explore the effects of changing detector parameters in evaluating the top mass.
Perform commissioning studies with top events Contribute to simulation validation …
Marina Cobal - Londe Les Maure 2004
P 27
Commissioning the detectors Determination MTop in initial
phase Use ‘Golden plated’ lepton+jet
Selection: Isolated lepton with PT>20 GeV Exactly 4 jets (R=0.4) with
PT>40 GeV Reconstruction:
Select 3 jets with maximal resulting PT
Signal can be improved by kinematic constrained fit Assuming MW1
=MW2 and MT1
=MT2
PeriodStat Mtop (GeV)
Stat /
1 year 0.1 0.2%
1 month 0.2 0.4%
1 week 0.4 2.5%No background
included
Calibrating detector in comissioning phase
Assume pessimistic scenario:
-) No b-tagging
-) No jet calibration
-) But: Good lepton identification
Marina Cobal - Londe Les Maure 2004
P 28
Commissioning the detectors
Signal plus background at initial phase of LHC
Most important background for top: W+4 jets Leptonic decay of W, with 4 extra ‘light’ jets
Alpgen, Monte Carlo has ‘hard’ matrix element for 4 extra jets(not available in Pythia/Herwig)
ALPGEN:
W+4 extra light jets
Jet: PT>10, ||<2.5, R>0.4
No lepton cuts
Effective : ~2400 pb
With extreme simple selection and reconstruction the top-peak should be visible at LHC
L = 150 pb-1
(2/3 days low lumi)
measure top mass (to 5-7 GeV) give feedback on detector performance
Marina Cobal - Londe Les Maure 2004
P 29
Top in DC2 Tier test
The 10M tier1 events in light of top: Generation/simulation of 106 top events, inclusive decays, using
MC@NLO Using Herwig for MC + UE Simulation with full geometry
Simulation 500K top events with displaced ID Same truth generated top events as above 1 cm displacement of ID – check tracking performance
Simulation of 106 W+jet events MC@NLO For W+2 jet background
Simulation of 250K W+4jet events with AlpGen pT>15 GeV approximately
Marina Cobal - Londe Les Maure 2004
P 30
What is still missing?
Top production is ‘over-weighted’ in 10M sample Unrealistic to ask for more in this sample
One of priorities in ‘post-production’: Regenerate half of the top MC@NLO sample Now using Jimmy UE (much more activity), after tuning
Still on the wish-list: Top events with spin correlations
TopRex available, perhaps AcerMC? Single top events
also TopRex Dedicated samples single- and dilepton top events Top events with PYTHIA (cross check with DC1)
Marina Cobal - Londe Les Maure 2004
P 31
Conclusions
Precise determination of Mtop is waiting… Challenge to get Mtop ~ 1 GeV
Confirmation that top-quark is SM particle Measure Vtb, charge, CP, spin, decays
Top quarks for commissioning the detectors Top peak should be visible with eyes closed
Today’s signal, tomorrow’s background Top quarks as main background
for many new physics channels
LHC is top factory
(tt)~830 pb-1
107 events in first year
Marina Cobal - Londe Les Maure 2004
P 32
Rare SM top decays
Direct measurement of Vts, Vtd via decays tsW, tdW
Decay tbWZ is near threshold
(mt~MW+ MZ+mb)
BRcut(t bWZ) 610-7
(cut on m(ee) is 0.8 MW)
Decay tcWW suppressed by GIM
factor BR(t cWW) ~ 110-13
If Higgs boson is light: tbWH FCNC decays: tcg, tc, tcZ (BR: 510-11 , 510-13 , 1.310-13 ) Semi-exclusive t-decays tbM
(final state 1 hadron recoiling against a jet:
BR(t b) 410-8, BR(t bDs) 210-7)
2 2b Wm M
Marina Cobal - Londe Les Maure 2004
P 33
Top mass from di-leptons
Use the events where both W’s decay leptonically (Br~5%) Much cleaner environment Less information available due to two neutrino’s
Sophisticated procedure for fitting the whole event, i.e. all kinematical info taken into account (cf D0/CDF) Compute mean probability as function of top mass hypothesis
Maximal probability corresponds to top massSource of uncertainty
Di-lepton Mtop (GeV)
statistics 0.3
b-jet scale 0.6
b-quark fragm 0.7
ISR 0.4
FSR 0.6
pdf 1.2
Total 1.7
80000 events
(tt) = 20 %
S/B = 10
Mea
n pr
oba
bilit
y
mass
Selection:
2 isolated opposite sign leptons
Pt>35 and Pt>25 GeV
2 b-tagged jets
ETmiss>40 GeV
Marina Cobal - Londe Les Maure 2004
P 34
Top mass from hadronic decay
Use events where both W’s decay hadronically (Br~45%) Difficult ‘jet’ environment
(QCD, Pt>100) ~ 1.73 mb (signal) ~ 370 pb
Perform kinematic fit on whole event b-jet to W assignment for combination
that minimize top mass difference Increase S/B:
Require pT(tops)>200 GeV
Source of uncertainty
Hadronic Mtop
(GeV)
Statistics 0.2
Light jet scale 0.8
b-jet scale 0.7
b-quark fragm 0.3
ISR 0.4
FSR 2.8
Total 3.0
3300 events selected:
(tt) = 0.63 %
(QCD)= 2·10-5 %
S/B = 18
Selection
6 jets (R=0.4), Pt>40 GeV
2 b-tagged jets
Note: Event shape variables like HT, A, S, C, etc not effective at LHC (contrast to Tevatron)
Marina Cobal - Londe Les Maure 2004
P 35
High Pt sample
The high pT selected sample deserves independent analysis: Hemisphere separation (bckgnd reduction, much less combinatorial) Higher probability for jet overlapping
Use all clusters in a large cone R=[0.8-1.2] around the reconstructed top- direction Less prone to QCD, FSR,
calibration UE can be subtracted
j1
j2
b-jet
t
Statistics seems OK and syst. under control
R
Mtop Mtop
P 36
Uncertainty On b-jet scale: Hadronic 1% Mt = 0.7 GeV5% Mt = 3.5 GeV10% Mt = 7.0 GeV
Uncertainty on light jet scale: Hadronic 1% Mt < 0.7 GeV10% Mt = 3 GeV
Jet scale calibration
Calibration demands: Ultimately jet energy scale calibrated within 1%
Uncertainty on b-jet scale dominates Mtop: light jet scale constrained by mW
At startup jet-energy scale known to lesser precision
Scale b-jet energyScale light-jet energy
MTop MTop
±10%
Marina Cobal - Londe Les Maure 2004
P 37
Interesting: branching ratio depends strongly on Mtop
Since Mtop~MW+Mb+MZ
With present error mt 5 GeV, BR varies over a factor 3
B-jet too soft to be efficiently identified “semi-inclusive” study for a WZ near
threshold, with Z l+l- and W ->jj Requiring 3 leptons reduces
the Z+jets background
Sensitivity to Br(t WbZ) 10-3 for 1 year at low lumi. Even at high L can’t reach Sm predictions ( 10-7 - 10-6)
G. Mahlon hep-ph/9810485
M(top) (GeV)
(t
WbZ
)/(t
Wb)
Rare decays: topWbZ
Marina Cobal - Londe Les Maure 2004
P 38
Various approaches studied Previously: ttbarHq Wb(b-bbar)j(lb)
for m(H) = 115 GeV Sensitivity to Br(t Hq) = 4.5 X 10-3
(100 fb-1)
New results for: t tbarHq WbWW*q Wb(l lj) (lb)
≥ 3 isolated lepton with pT(lep) > 30 GeV pTmiss > 45 GeV ≥ 2 jets with pT(j) > 30 GeV, incl. ≥ 1 jet con b-tag Kinematical cuts making use of angular correlations
Sensitive to Br(t Hq) = 2.4 X 10-3
for m(H) = 160 GeV (100 fb-1)
Signal
ttH
tt
Signal
ttH
tt
topHq
Marina Cobal - Londe Les Maure 2004
P 39
Non-SM Decays of Top 4thfermion family
Constraints on Vtqrelaxed:
Supersymmetry (MSSM) Observed bosons and fermions would have superpartners 2-body decays into squarks and gauginos (t H+ b )
Big impact on 1 loop FCNC two Higgs doublets
H LEP limit 77.4 GeV (LEP WG 2000) Decay t H+ b can compete with t W+ b 5 states (h0,H0,A0,H+,H-) survive after giving W & Z masses H couples to heaviest fermions detection through breakdown of e / m / t
universality in tt production
at ( ( )) ~ 3bBR t W b W c 10 m 100GeV
, , 01 1 1 1 1t t g t b t t