# Presentation: 547203

## Christophe Clément
University of Stockholm
For CDF and DØ Collaborations

*University of Stockholm*
*For CDF and D**Ø** Collaborations*

**Flavor Physics and CP Violation**
**Vancouver 2006**

**Tevatron Top Results**

## Top and the Tevatron

- Speculated to be related to EWSB,
-       its mass is important SM parameter.
- As close as we can get to a free quark:
-      Top decays in 0.5×10-24s, before hadronizes
-  Only a handful of top candidates in Run I,
-     but is it standard model top quark?
-   Run II: measure detailed properties
-     with much larger data sets.
-  Test production and decay mechanisms, does it
-     have SM quantum numbers...
- Heavy enough to decay to exotic particles (H+, W’...)

- April 11, 2006                           C.Clément   FPCP 2006                                             2/18

**Top and the Tevatron**

**Tevatron**
**√****s=1.96 TeV, L~10****32****cm-2s-1**

## Top Quark Production and Decay

- Single top production via electroweak interaction
**    ****expected but not yet observed ****(coming back to this topic)**

- April 11, 2006                           C.Clément   FPCP 2006                                             3/18

- SM predicts FCNC decays are tiny, *t**→**Wq* is dominant
- 3 quark generations + direct measurements of Vub and Vcb predict Vtb, *B(t****Wb)~1*

**Top Quark Production and Decay**

- σtt=6.8±1.2pb (theory)

## Top Pair Final States

- Used for all measured top quark properties so far

- April 11, 2006                           C.Clément   FPCP 2006                                             4/18

**Top Pair Final States**

## Top Pair Cross Section

- April 11, 2006                           C.Clément   FPCP 2006                                             5/18

- Test of  pQCD at high energy, prediction for σtt (6.8±1.2)pb, non-SM production?
- Exotic top decays (tH+b,...): compare σtt in various channels
- l+jets/ll  and*τ*/non- *τ* ratios: so far weak constraints.

**l****+****track**
**D****Ø**** dilepton**
**370pb****-1**

**Top Pair Cross Section**

**Notes:**
Already many published results, improved techniques: l+track, 0,1,2 tags,Charged higgs search

## B(t→Wb) and Vtb

- Count       events with 0, 1, 2 b-tagged jets

- April 11, 2006                           C.Clément   FPCP 2006                                             6/18

**CDF Published 160 pb****-1**** PRL 95, 102002, 2005 ***B(t**→**Wb)=* 1.12+0.27 -0.23 (stat + syst)
- |Vtb|>0.61 @95%C.L.
**D****Ø**** 240 pb****-1** **hep-ex/0603002**  (submitted to PRL)
*B(t**→**Wb)=*1.03+0.19-0.17 (stat+syst)
- |Vtb|>0.61 @95%C.L.

**B(*****t******→******Wb*****) and V****tb**

**Within standard model**
- |Vtb| = √*B(t**→**Wb)* +h.o.
- 0.9990<|Vtb|<0.9992
-      at 90% C.L.

- Estimate Ntt in 0-tag
-           sample

## Top Quark Decay: W helicity

**f****-****~30%**

- April 11, 2006                           C.Clément   FPCP 2006                                             7/18

**If right handed W then:**
-   1) angular momentum is not conserved OR
-   2) b is right handed (suppressed)
**⇒ ****no W****R**

**f****0****~70%**

**f****+****~0%**

**Top Quark Decay: W helicity**

## W helicity

- April 11, 2006                           C.Clément   FPCP 2006                                             8/18

**t**

**l****+**

**v**

**b**

**W****+**

- θ

**W rest frame**

**W****L**

**W****R**

**W****0**

**Longitudinal polarization W****0**
-      leptons emitted ⊥ to W boost
**Left handed polarization W****L**
-      leptons emitted antiparellelle to W boost
-      **⇒**lower lepton pT

- θ = angle between the **l****+** and the direction of **t**

- 70% W0 + 30%WL

**W helicity**

## W helicity

- April 11, 2006                           C.Clément   FPCP 2006                                             9/18

- Measurement of f+ by DØ in **lepton+jets**
- and **dilepton** events:
**fit cos ****θ**** templates to data**

**D****Ø**** 370 pb****-1** **preliminary **
- f+=0.08± 0.08(stat)±0.05(syst) (for f0=0.7)

- CDF: f+ and fo in **l+jets** and **dilepton**
**i)   fit cos ****θ**** templates**
**ii)  use lepton p****T**

**CDF**** 200 pb****-1 ****(hep-ex/0511023)**
- f0=0.74+0.22-0.34
- f+<0.27 @ 95% C.L.

**W helicity**

## Top Quark Charge

- April 11, 2006                           C.Clément   FPCP 2006                                            10/18

**OR**

**?**

**D****Ø**** 370 pb****-1** **preliminary **
- Qtop is not 4e/3 at 94%CL

**Top Quark Charge**

**Notes:**
Beautiul mirror...

## The Mass of the Top Quark

- April 11, 2006                           C.Clément   FPCP 2006                                            11/18

- Originally used EW measurements to predict mtop
**                   ****Derive m****Higgs**** from EW measurements and m****top**
- Future (if we know mHiggs): does EW, mHiggs and mtop fit together

- Quadratric
- dependence
- in mtop

- Log
- dependence
- in mH

- Why mtop is hot

**The Mass of the Top Quark**

## Template Method + in situ calibration

- Split lepton+jet sample in 4 depending on 0/1/2 tags and jets pT
- Extract mrecot and mjj for each event by minimizing χ2:
- Compare **observed** **m****reco****t**** and m****jj** to templates at various mass and JES

- April 11, 2006                           C.Clément   FPCP 2006                                            12/18

**Idea:** Constrain **jet energy scale** using the known W mass and the observed mjj

- Largest systematic error

- l*, jet resolutions*

**CDF 680 pb****-1**
- Mtop=173.4±2.5(stat+JES) ±1.3(syst) GeV

**Template Method + *****in situ***** calibration**

## Matrix Element Method + in situ calibration

- April 11, 2006                           C.Clément   FPCP 2006                                            13/18

- Constrain jet energy scale using the
-    known W mass and the observed mjj
- Combine 0, 1 and 2 tag events

**D****Ø**** 370 pb****-1**
- Mtop=170.6 +4.0-4.7(stat+JES)± 1.4(syst)

- Vector of kinematic observables

- Transfer from parton to measured kinematics

- Probability of the parton config **y** (ME)

**Jet energy scale**

**Top quark mass**

- Attempts to use maximum of information

**y**=Parton kinematics

**Matrix Element Method + *****in situ***** calibration**

**Main systematics on top quark mass**
- b-jet energy scale
- Jet energy scale
- ISF & FSR
- Background shapes
- Signal fraction

## More on Top Quark Mass

- April 11, 2006                           C.Clément   FPCP 2006                                            14/18

- Many mass analyses techniques, various
-    channels,
- Dilepton mass: low statistics but promising
-    because less sensitive to JES and smaller
-    background.
- Consistent with precision EW?

**More on Top Quark Mass**

## Electroweak Top Production

- April 11, 2006                           C.Clément   FPCP 2006                                             15/18

*s*-channel, ”*tb”*
- σs~0.9 pb

*t*-channel, ”*tqb”*
- σt~2.0 pb

- Measure directly the Vtb CKM matrix element, σs, σt ∝|Vtb|2
**Experimentally challenging** because not too different from W+2 jets
- Use events with Wev or W v
- Signature: 1 isolated lepton, MET, 2 or more jets
*s*-channel: 1,2 b-tagged jets   *t*-channel: 1 *b*-tagged jet + 1 light jet
- Major backgrounds: W+jets, top anti-top pairs, fake leptons
**Not yet observed!**

**Electroweak Top Production**

## Search for Single Top

**Precuts**
- 1 isolated electron/muon,
- high MET,
- 1 or 2 b-jets, (*s channel*)
- 1 b- and ≥1 light-jet (*t*-channel)
**2. Discriminate against**
-     W+jets and
**3. Build 4 discriminants**
- W+jets  / *s-channel*
- ttbar      / *s-channel*
- W+jets  / *t-channel*
- ttbar      / *t-channel*

- April 11, 2006                           C.Clément   FPCP 2006                                            16/18

- e.g. used in
- tqb/Wbb and
- tqb/ttbar discriminant

**D****Ø**** Preliminary 370 pb****-1  ****exp/obs**
*s-channel*   3.3/5.0 pb
*t-channel*    4.3/4.4 pb
**Published 230 pb****-1****  ****(Phys. Let. B 622)**
*s-channel*   4.5/6.4 pb
*t-channel*    5.8/5.0 pb

**Search for Single Top**

## Search for Single Top

- On 695 pb-1 CDF carries out 2 analyses:
- likelihood discriminant based
- ANN based

- April 11, 2006                           C.Clément   FPCP 2006                                            17/18

- Extrapolation to larger dataset

- Eg. of variable used in
- discriminant , here
- ”top-mass like” variable

**Search for Single Top**

## Conclusions

**Now an order of magnitude more data is available thanks to run II**, CDF and DØ are providing a series of precision measurements of the top quark properties,
**Precision tests of SM prediction** for production (pQCD), decay vertex
-      (V-A, Vtb), electric charge, single top production are performed
**Many more measurements not mentionned here**: search for t ́ quark, t→W ́b, Z’→       , anomalous couplings, FCNC decays, decays with tau-leptons...
**Single top searches** are getting closer to expected cross sections
- Precise measurement of the top quark mass, already
-      **outperforming expected performance of 3 GeV,**
**Put constraints on the SM,**
-      realistically aiming at Δmtop=2 GeV for entire Run II

**Conclusions**

**Notes:**
>1fb-1 available now...