Top properties at tevatron isabelle ripp baudot iphc strasbourg top workshop grenoble october 2006
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Top properties at Tevatron Isabelle Ripp-Baudot 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 épé-Renaudin S. Sharry. -. p. p.

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Characterization of the top quark

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Top properties at tevatron isabelle ripp baudot iphc strasbourg top workshop grenoble october 2006

Top properties at TevatronIsabelle Ripp-BaudotIPHC StrasbourgTop Workshop Grenoble october 2006

I. Ripp-Baudot


Characterization of the top quark

Characterization of the top quark

electric charge

lifetime

n

spin

spin

W-

mass

-

-

t

P. Shieferdecker

b

S. Crépé-Renaudin

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. Ripp-Baudot


Top strong production

is a pair production

top strong production

Tevatron @ 1.96 TeV : 85 % qq / 15 % gg

-

stt = 6.7 ± 0.8 pb 1 tt event / 24 min @ 1032 cm-2.s-1

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 b-tagged jets

/

+ likelihood (kinematic and topological characteristics) to discriminate against W+n jets background.

+ constrained fit

I. Ripp-Baudot


Anomalous kinematics

Anomalous kinematics

So-called « top » observed sample could contain an admixture of exotic processes.

dilepton sample 193 pb-1 (13 events)

Method seeks to isolate the subset of events with the largest concentration of possible non-SM physics  Kolmogorov-Smirnov 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 1.0-4.5 %.

/

/

PRL 95, 022001, 2005

I. Ripp-Baudot


Br t wb br t wq

Br(tWb)

|Vtb|2

Br(tWb) / Br(tWq)

R = = = 1 if unitarity of CKM in S.M.

Deviation of R from 1 : 4th generation of quarks ? non-S.M. top decay ? exotic background ?

Br(tWq)

|Vtb|2 + |Vts|2 + |Vtd|2

ℓ+jets sample 230 pb-1

R = 1.03 (stat.) (syst.)

|Vtb|>0.64 @ 95 % C.L.

PLB 639, p. 616, 2006

+0.17 +0.09

-0.15 -0.07

ℓ+jets and dilepton sample 162 pb-1

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 b-tagged jets multiplicity bins (0, 1, ≥2 b-tag).

ebtag= f(R) systematics. But only relative rates  independent of stt.

3 bins  R is overdetermined

I. Ripp-Baudot


Br t wb br t wq reach at tevatron

Tevatron prospect for RunII

Br(tWb)/Br(tWq)reach at Tevatron

  • CDF quick estimation of reach

  • assuming 3 generations (R=1)

  • Examples of non B.S.M. physics :

    - |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. Ripp-Baudot


W helicity in t w b

sz

t

p

W+-

mt2

F0 ≈

≈ 0.70

mt2 + 2 MW2

 Weak interaction : only V-A 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.

Whelicity in t  W b

 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. Ripp-Baudot


W helicity cont d

W helicity (contd)

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 (V-A) + 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. Ripp-Baudot


W helicity cont d1

W helicity (contd)

Angular distribution (unpolarized top) of the down-type 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. Ripp-Baudot


W helicity estimators

To measure w(q)  need to boost to top and W rest frames ( ET resolution, missing n…).

Several ideas of estimators :

1) Mℓb2 approximation :

/

W helicity estimators

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. Ripp-Baudot


W helicity estimators cont d

W helicity estimators (contd)

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 :

  • - used in mtop measurement.

  • sensitivity improved by using both W in each event.

  • the whole information and all combinationsof the charged lepton and the 4 jets in 2 W bosons and 2 top quarks are used.

  • efficient discrimination between the tt signal and the background.

  • problem of precision : gluon radiations, order of the computation (L.O. ?), inclusion of the 15 % gg  tt ?

I. Ripp-Baudot


W helicity studies at tevatron

W helicity studies at Tevatron

-0.34

PRD 73: 111103, 2006

PRD 72: 011104, 2005

submitted to PRL

summer 2006 conference

submitted to PRL

I. Ripp-Baudot


Outlook for w helicity

Outlook for W helicity

W helicity measurement will benefit from increasing stat

And decreasing error onMtop and JES.

Precision with 400 pb-1 : F+~ unconstrained(< 0.25 with F0 = 0.7 fixed)

DF0/F0 ≈ 30 %

1 fb-1 :sensitivity F+ < 0.1

DF0/F0 ≈ 20 %

Expected precision with 2 fb-1 : F+ < 0.05

DF0/F0 ≈ 5 – 6 %

And with 10 fb-1 (1 year at LHC) : DF+/F+~ 1 %

DF0/F0 ~ 2 %

I. Ripp-Baudot


Top electroweak production

is a single top production

top electroweak production

t-channel :

1.98 ± 0.21 pb

s-channel :

0.88 ± 0.07 pb

Associated production :

0.09 pb

Not discovered yet : smaller cross-section and higher background  only limits on this production mode.

Once it is observed :

 direct measurement of |Vtb| without the assumptionon unitarity of 3-generations CKM matrix : sa |Vtb|2

 sensitive to B.S.M. physics (Z’, H+, …)

 top spin physics (100 % polarized top quark). But not at Tevatron !

I. Ripp-Baudot


Characterization of the top quark

single top search at Tevatron

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. Ripp-Baudot


Characterization of the top quark

single top prospects at Tevatron

expected Tevatron Run II luminosity

Observation coming soon ?

We are here

I. Ripp-Baudot


Conclusion

Conclusion

  •  Top quark high mass  hope to open the window on the physics hiding B.S.M.

  •  Tevatron is currently the world’s only source of top quarks and will be until the successful beginning of LHC.

  •  Excellent performance of Tevatron Run II :

  • large top samples

     transition from the discovery phase to a new phase of precision measurements of the top quark properties.

I. Ripp-Baudot


Backups

backups

I. Ripp-Baudot


Top electric charge

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 pb-1 (17 double tagged events)

Two b-tagged jets

jet-parton assignement through kinematic fit.

Top charge estimation with a jet charge algorithm.

Likelihood to compare to exotic models.

top electric charge

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 pb-1

I. Ripp-Baudot


Top lifetime

top lifetime

Top is the heaviest known fundamental particle. Decays as a free quark t~ 10-25 s.

ℓ+jets sample 320 pb-1

≥ 3 jets + btagging

lifetime estimated with the lepton I.P.

first (and only one) direct measurement :

ct < 52.5 mm @ 95 % C.L.

(~ 1.8.10-13 s…)

(preliminary results Winter conf. 2006)

I. Ripp-Baudot


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