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Expectations from LHC and LC for Top Physics. Top Mass Couplings and decays Top spin polarization Single top production. Marina Cobal Hadron Collider Physics 2004 Michigan State University, 14-18 June. Top quark mass is a fundamental parameter of the EW theory - PowerPoint PPT Presentation
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1
Expectations from LHC and LC for Top Physics
Marina CobalHadron Collider Physics 2004Michigan State University, 14-18 June
Top Mass
Couplings and decays
Top spin polarization
Single top production
Marina Cobal - HCP2004
P 2 Motivations for Top Physics studies
Top quark mass is a fundamental parameter of the EW theory By far has the largest mass of all known fundamental particles In SM: top- and W-mass constrain Higgs mass
Sensitivity through radiative corrections Scrutinize SM by precise determination top mass
Top quark exists and will be produced abundantly ! window for new physics Many heavy particles decay in tt Handle on new physics by detailed properties of top
And in addition…
Experiment: Top quark useful to calibrate the detector (LHC) Beyond Top: Top quarks will be a major source of background for
almost every search for physics beyond the SM (LHC)
Marina Cobal - HCP2004
P 3
TOTEM
ALICE : heavy ions,p-ions
ATLAS and CMS :pp, general purpose
LHCb : pp, B-physics
27 km ring 1232 dipoles B=8.3 T
LHC and experiments
pp (mainly) at s = 14 TeV Startup in April 2007
Initial/low lumi L1033 cm-2 s-1
2 minimum bias/x-ing “Tevatron-like” environment
10 fb-1 /year Design/high lumi L=1034 cm-2 s-1
after ~ 3 years ~ 20 minimum bias/x-ing
fast ( 50 ns) radhard detect 100 fb-1 /year
Marina Cobal - HCP2004
P 4
LC machine
Maybe some years after the LHC startup
ECM of operation 200-500 GeV, possible upgrade to 1 TeV
80% Polarization of e- beam
Luminosity: 300 fb-1/year
Marina Cobal - HCP2004
P 5
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 of 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 - HCP2004
P 6
The ttbar cross section is ~103 smaller than at LHC, but higher L ~0,85 pb at max, around 390 GeV, and falls down with energy as 1/s
..and at LC?
~200000 tt/year at TESLA parameters
Marina Cobal - HCP2004
P 7
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 - HCP2004
P 8
Top mass: Where we are
Marina Cobal - HCP2004
P 9
Tevatron only (di-lepton events or lepton+jet ) from W decaysStatus 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 - HCP2004
P 10
What is the Top Mass?
Problem for the top: what is the mass of a colored object? The top pole mass is not IR safe (affected by large long-distance
contributions), cannot be determined to better than O(QCD)
Measurement of mt: At Tevatron/LHC: kinematic reconstruction, fit to invariant mass dist.
at the LHC: accuracy 1-2 GeV (limited by FSR)
At the LC, mainly from threshold behavior Measurement comparison data – Monte Carlo: involves transition from actually
measured quantity to suitably defined (short-distance) top mass ‘Threshold mass’ at the LC: accuracy 20 MeV [M. Martinez, R. Miquel ’03] Transition to MS mass: m 100 MeV [A. Hoang et al. ’00]
Marina Cobal - HCP2004
P 11
LHC: 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 - HCP2004
P 12 LHC: 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 constraintsj1
j2
b-jet
t
Selection efficiency 5-10%
Marina Cobal - HCP2004
P 13
LHC: MTop 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 - HCP2004
P 14 LHC: 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 - HCP2004
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 - HCP2004
P 16
Mtop at LC
Scan of the threshold for e+e-ttbar Very precise measurements (< 20 MeV)
To perform this analysis with small systematic errors need to study:
beam spread
beamstrahlung
initial state radiation
Simultaneous measurements of 3 physical observables: tt
Pt of top
Forward-Backward asimmetry of top AtFB
Multiparameter fit up to 4 parameters Mt (1S)
s(MZ)
t
gtH
Theoretical uncertainties to relate the 1S to the MS mass is ~ 100 MeV
)(GeVs(
pb)
Marina Cobal - HCP2004
P 17
Georg Weiglin, LCWS04 Paris
Marina Cobal - HCP2004
P 18
LHC: 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) at LHC 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 - HCP2004
P 19
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
At the LHC Yukawa coupling can be measured to < 20% from t-tbar H production
@ the LC, the precision of the measurement of the top Yukawa coupling will be better than ~ 10 % if mH ≤ 190 GeV/c2
For a light Higgs (mH ~120 GeV/c2): Precision ~ 5-6 %
Marina Cobal - HCP2004
P 20
LHC: Couplings and decays
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 - HCP2004
P 21
The Wtb vertex can be probed and measured using either top pair production or single top production Total tt rate depends weakly from Wtb vertex structure C and P asymmetries, top polarization, spin correlations can provide
interesting info The single top production rate is instead directly proportional to the square
of the Wtb coupling
LHC could rivale the reach of a high L (500 fb-1) 500 GeV LC
Search for anomalous Wtb couplings
)(2
)(2
22WWWW
RWWWW
L ihfM
FandihfM
F
Marina Cobal - HCP2004
P 22
In the SM the FCNC decays are highly suppressed (Br<10-13-10-10) Any observation would be sign of new physics FCNC can be detected through top decay or single top production
Sensitivity according to CMS studies (of top decays) :
t Zq (CDF Br<0.137, ALEPH Br<17%, OPAL Br<13.7%) Reconstruct t Zq (l+l-)j Sensitivity to Br(t Zq) = 1,6 X 10-4 (100 fb-1)
t q (CDF Br<0.032) Sensitivity to Br(t q) = 2,5 X 10-5 (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) = 1,6 X 10-3 (100 fb-1)
LHC: FCNC Rare decays
Marina Cobal - HCP2004
P 23
In general, the LHC will improve by a factor of at least 10 the Tevatron sensitivity to top-quark FCNC couplings
LC has smaller statistics but also smaller background For anomalous interactions with a gluon the LHC has an evident
advantage
FCNC
Marina Cobal - HCP2004
P 24
Studied at LHC:
Interesting: BR 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)
LHC: tWbZ rare decay
Marina Cobal - HCP2004
P 25 LHC: 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 - HCP2004
P 26 LHC: 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 - HCP2004
P 27
LHC: 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 - HCP2004
P 28
Top spin correlations
Able to observe spin correlations in parameter 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->
For the LC case one can find a top spin quantization axis in which there will be very strong spin correlations . Detailed studies, both at the ttbar threshold and in the continuum region remain to be done.
Marina Cobal - HCP2004
P 29
LHC: 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 at LHC:
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
3) Opportunity to measure top spin pol.
4) May probe FCNC
Marina Cobal - HCP2004
P 30
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)
LHC: 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 - HCP2004
P 31
Single top at LC e+ e- e+bt, ebt
Cross section calculated to LO at e+e-, and e collision modes, including various beam polarizations
Recently calculated NLO corrections in the e case, well under control
Production in e collisions is of special interest Rate is smaller than the top pair rate in e+e- only by a factor of 1/8 at
500-800 GeV energies. It becomes the dominant LC process for top production at a multi-TeV LC
Direct Vtb measurement:
Same precision as LHC in the e+e- option. Can arrive to 1% for a polarized e collider.
Improved accuracy in |Vtb| could be input for LHC Measure b-quark distribution function in proton
(or be used as consistency check for new interactions)
Marina Cobal - HCP2004
P 32
Few final thoughts…
LHC pp collision at 14 TeV
Kinematics:
can use PT conservationComposite nature of protons
Underlying events, not fixedStrongly interacting particle
Large QCD background Under construction
s
e+-e- collisions at 0.5-1 TeV
Kinematics:
can use momentum conservationBetter defined initial stateBackground smaller than LHCNot sure yet IF, WHEN, WHERE it will be built
Marina Cobal - HCP2004
P 33
Interplay between LHC and LC
Not much interaction between the LHC and LC communities up to short time ago
In 2002 a LHC/LC study group was formed first in Europe and then soon it took a worldwide character
Working Group contains 116 members from among Theorists, CMS, ATLAS, Members of all the LC study Groups + Tevatron contact persons.
Document in preparation: www.ippp.dur.ac.uk/~georg/lhclc
Electroweak and QCD precision physics
E. Boos, A deRoeck, S. Heinemeyer, W.J. Stirling.
Marina Cobal - HCP2004
P 34
CMS yoke
LHC is a reality now:
Huge construction activities going on!!
ATLAS cavern
Marina Cobal - HCP2004
P 35 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 - HCP2004
P 36 LHC: 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 - HCP2004
P 37LHC: 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 - HCP2004
P 38
Conclusions
Precise determination of Mtop is crucial for EW physics: Precision tests, constraints on Higgs sector, sensitivity to new physics Challenge to get Mtop ~ 1 GeV with LHC, and ~ 100 MeV with LC
Confirmation that top-quark is SM particle and search for deviation from SM Measure Vtb, charge, CP, spin, decays Many precision measurements from LC
Use top quark for the LHC detectors commissioning
Interplay between LC and LHC could be as useful as it was for LEP+SLC+Tevatron
39
BACKUP SLIDES
Marina Cobal - HCP2004
P 40
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 - HCP2004
P 41
.
Graphically summarizedby Jae Yu
LC Timeline
Marina Cobal - HCP2004
P 42
BASELINE MACHINEo ECM of operation 200-500 GeV
o Luminosity and reliability for 500 fb-1 in 4 yearso Energy scan capability with <10% downtimeo Beam energy precision and stability below about 0.1%o Electron polarization of > 80%o Two IRs with detectorso ECM down to 90Gev for calibration
UPGRADESo ECM about 1 TeV
o Allow for ~1 ab-1 in about 3-4 years
http://www.fnal.gov/directorate/ icfa/LC_parameters.pdf
LC Machines
Marina Cobal - HCP2004
P 43
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 - HCP2004
P 44
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 - HCP2004
P 45
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
Marina Cobal - HCP2004
P 46
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 - HCP2004
P 47
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 - HCP2004
P 48
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 - HCP2004
P 49
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
Marina Cobal - HCP2004
P 50
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 - HCP2004
P 51
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
LHC: 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%
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