Top properties at Tevatron Isabelle RippBaudot IPHC Strasbourg Top Workshop Grenoble october 2006. Characterization of the top quark. electric charge lifetime. ℓ. n. spin. spin. W . mass. . . t. P. Shieferdecker. b. S. Cr épéRenaudin S. Sharry. . p. p.
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
I. RippBaudot
electric charge
lifetime
ℓ
n
spin
spin
W
mass


t
P. Shieferdecker
b
S. CrépéRenaudin
S. Sharry

p
p
structure of the tWb coupling: W helicity
Vtb: single top
decay channels: Br(t Wb) / Br(t Wq) t t n q
productionratestt
production of something exotic ?new resonance
b
t
spin correlation
CP violation
CP violation
W+
rare channels : t Zc, gc susy t H+ b
rare channels : t Zc, gc susy t H+ b
Is this particle the S.M. top quark ?
I. RippBaudot
Tevatron @ 1.96 TeV : 85 % qq / 15 % gg

stt = 6.7 ± 0.8 pb 1 tt event / 24 min @ 1032 cm2.s1
7 kevt / year

tt final state selection (ℓ+jets) based on sequential cuts :
 one high pT lepton
 large ET
 4 high pT central jets
 ≥ 1 btagged jets
/
+ likelihood (kinematic and topological characteristics) to discriminate against W+n jets background.
+ constrained fit
I. RippBaudot
Socalled « top » observed sample could contain an admixture of exotic processes.
dilepton sample 193 pb1 (13 events)
Method seeks to isolate the subset of events with the largest concentration of possible nonSM physics KolmogorovSmirnov test with 4 variables : ET, lepton pT, angle(ET, lepton), proba to be tt.
Conclusion : no particular subset shows a significant discrepancy with S.M.
proba to observe a data sample less consistent with S.M. is 1.04.5 %.
/
/
PRL 95, 022001, 2005
I. RippBaudot
Br(tWb)
Vtb2
R = = = 1 if unitarity of CKM in S.M.
Deviation of R from 1 : 4th generation of quarks ? nonS.M. top decay ? exotic background ?
Br(tWq)
Vtb2 + Vts2 + Vtd2
ℓ+jets sample 230 pb1
R = 1.03 (stat.) (syst.)
Vtb>0.64 @ 95 % C.L.
PLB 639, p. 616, 2006
DØ
+0.17 +0.09
0.15 0.07
ℓ+jets and dilepton sample 162 pb1
R = 1.12 (stat.) (syst.)
Vtb>0.61 @ 95 % C.L.
PRL 95, 102002, 2005
+0.21 +0.17
0.19 0.13
ℓ + ≥4 jets
Likelihood fit on number of selected events in btagged jets multiplicity bins (0, 1, ≥2 btag).
ebtag= f(R) systematics. But only relative rates independent of stt.
3 bins R is overdetermined
I. RippBaudot
 Vts = 0.1 and 3 generations
R = 0.99
 Vtb = 0.5 and 4 generations
R = 0.96
will need combination of CDF and DØ analysis to be interesting…
Charles Plager @ PANIC 2005, October 2005
I. RippBaudot
sz
t
p
W+
mt2
F0 ≈
≈ 0.70
mt2 + 2 MW2
Weak interaction : only VA structure.
Introduced by hand to describe experimental observations.
Can be tested at high energy with top quarks by measuring the W polarization.
tWb structure can also be tested through the electroweak single top production, but with lower precision and of course not at Tevatron.
Relativistic limit : chirality helicity(observable !)when m/p 0
t W b decay : mb << Eb and bL b
bL
W+0
W++
t
t
bL
bR
In the S.M. : W++ (right) suppressed by a factor mb2/mt2 in the t W+ b decay :
2 MW2
F ≈
≈ 0.30
F+ ≈ 0
mt2 + 2 MW2
I. RippBaudot
In practice :
● measurement ofF+ quantification of a V+A contribution.
Would decrease F in benefit of F+ and let F0 unchanged.
F0 constrained to 0.7.
By comparing data to M.C. = a (VA) + b (V+A), neglecting interferences between the two contributions.
Already indirectly limited to a few % by b s g measurements(CLEO, BaBar, Belle). But based on theoretical assumptions (penguins, QCD).
● measurement ofF0without hypothesis on physics beyond S.M.
F+ constrained to 0.
Deviation from its S.M. predicted value would question the EWSB by the Higgs mechanism, responsible for the longitudinal degree of freedom of massive W bosons.
I. RippBaudot
Angular distribution (unpolarized top) of the downtype decay products of the W+ :
w(cos q) = (1 + cos q)2 F+ + (1 – cos q)2 F + sin2q F0
3
3
3
8
4
8
ℓ+
R*top
b
q
W+
R*W
t
n
Helicity fractions F+ and/or F0 and/or F will be measured from the angular distribution w (cos q).
I. RippBaudot
To measure w(q) need to boost to top and W rest frames ( ET resolution, missing n…).
Several ideas of estimators :
1) Mℓb2 approximation :
/
2 Mℓb2
cos q ≈
1
with mb~ 0
mt2 – MW2
Depends on Dmtop and b JES.
2) Charged lepton pT spectrum :
Relies on M.C. templates.
b
p
ℓ+
top
W++
n
ℓ+
W0+
W
ℓ+
n
W+
n
I. RippBaudot
3) Constrained kinematic fit :
W and top masses are constrained.
Resolutions on E and p from lepton, jets and ET have to be known.
(~ 60 tt / 25 bkg)
/
4) Matrix element method :
I. RippBaudot
0.34
PRD 73: 111103, 2006
PRD 72: 011104, 2005
submitted to PRL
summer 2006 conference
submitted to PRL
I. RippBaudot
W helicity measurement will benefit from increasing stat
And decreasing error onMtop and JES.
Precision with 400 pb1 : F+~ unconstrained(< 0.25 with F0 = 0.7 fixed)
DF0/F0 ≈ 30 %
1 fb1 :sensitivity F+ < 0.1
DF0/F0 ≈ 20 %
Expected precision with 2 fb1 : F+ < 0.05
DF0/F0 ≈ 5 – 6 %
And with 10 fb1 (1 year at LHC) : DF+/F+~ 1 %
DF0/F0 ~ 2 %
I. RippBaudot
tchannel :
1.98 ± 0.21 pb
schannel :
0.88 ± 0.07 pb
Associated production :
0.09 pb
Not discovered yet : smaller crosssection and higher background only limits on this production mode.
Once it is observed :
direct measurement of Vtb without the assumptionon unitarity of 3generations CKM matrix : sa Vtb2
sensitive to B.S.M. physics (Z’, H+, …)
top spin physics (100 % polarized top quark). But not at Tevatron !
I. RippBaudot
Observed(expected) limits
st (pb)
ss (pb)
0.88 ± 0.07
1.98 ± 0.21
S.M. (NLO) prediction
PRD 71, 012005, 2005
PLB 622, p. 265, 2005
Summer 2005 conferences
Summer 2006 conferences
I. RippBaudot
single top prospects at Tevatron
expected Tevatron Run II luminosity
Observation coming soon ?
We are here
I. RippBaudot
transition from the discovery phase to a new phase of precision measurements of the top quark properties.
I. RippBaudot
I. RippBaudot
Top discovered by CDF and DØ twofold ambiguity in the pairing W/b
B.S.M. theories heavy quark with q =  e mixed with the actual top (mass 270 GeV)
Compatible with experimental data (Rb, AFBb).
ℓ + jets sample 370 pb1 (17 double tagged events)
Two btagged jets
jetparton assignement through kinematic fit.
Top charge estimation with a jet charge algorithm.
Likelihood to compare to exotic models.
4
3
S q pT0.6
qtop = qℓ +
S pT0.6
Sample of quark pairs with charge 4e/3 excluded @ 94 % C.L.
submitted to PRL
results coming soon with 955 pb1
I. RippBaudot
Top is the heaviest known fundamental particle. Decays as a free quark t~ 1025 s.
ℓ+jets sample 320 pb1
≥ 3 jets + btagging
lifetime estimated with the lepton I.P.
first (and only one) direct measurement :
ct < 52.5 mm @ 95 % C.L.
(~ 1.8.1013 s…)
(preliminary results Winter conf. 2006)
I. RippBaudot