# Presentation: 438974

## Electroweak and Top physics  at the Tevatron and indirect Higgs Limits

**Electroweak and Top physics  at the Tevatron and indirect ****Higgs Limits**

- Sandra Leone
- (INFN Pisa)
- for the CDF and DØ Collaborations
- SUSY07 Karlsruhe, July 28th 2007

## Outline

- The Tevatron & the experiments
- W and Z boson physics:
-  W & Z Cross section
-  W Mass and Width
-  inputs to PDF from W/Z data
-  Diboson production
- Top quark physics:
- Pair production cross section
- Top mass measurements
- Single top production
- A global look at the Standard Model:
- Indirect limit on the Higgs Mass from EWK data

## The Tevatron Collider

-  Run II: s = 1.96 TeV
- Performances have kept improving since the start of Run II. So far, 3 fb-1 collisions have been delivered to CDF and D0

**2.8 x 10****32**

- Peak Luminosities above   2 x 1032 cm-2 s-1 now common
_**Current Record**_ initial lum: _2.92 x 10__32_ cm-2 s-1
- Record Integrated luminosity per week **~ **45 pb-1

- Peak luminosity

## CDF & DØ 

-  18 countries      89 institutions >600 authors

- CDF & DØ

- 2 General purpose detectors capable of many different physics measurements

## Integrated Luminosity

- Start of physics-quality data

-  delivered: ~ 3 fb-1

- Detectors running stably since Feb. ’02
- Data taking  efficiency L(recorded/L(delivered)              commonly  > 85%

- All results shown in the following based on datasets ranging from   ~200 pb-1 to ~1.7 fb-1

- on tape  ~2.5 fb-1

## W/Z Gauge Bosons Identification 

- W/Z Gauge Bosons Identification

- At Tevatron W and Z  hadronic decays are overwhelmed by QCD bckg
- Identification through leptonic decays
- W/Z identification is a key ingredient for top physics and searches
- Often background for rare processes
- fundamental tools for calibrations and detector checks
- CDF and D0 are using the millions of W and Z boson decays collected, to produce excellent measurements of electroweak observables

- We

- Z

- ET>25GeV

- PT>20GeV

- PT>20GeV

##  Inclusive W/Z Cross Sections

- • Overall good  agreement with the NNLO calculations                              ( Stirling, Van Neerven)                                                                               • Accuracy limited by the systematic effects: dominated by the luminosity error (~6%), followed  by PDF uncertainties (~2%) in e/, and tau algo in **** channels

- The cross section for inclusive W and Z boson production  measured in all leptonic final states* ****(W***->***e***ν, μν, τν; ***Z***->***ee***, μμ, ττ***) ***by CDF and D0

## dσ/dy  distribution of Drell-Yan Z/γ* -> e+e-

- dσ/dy  distribution of Drell-Yan Z/γ* -> e+e-

- Measurement of the rapidity distribution and differential cross section of Drell Yan pairs can provide a stringent test of QCD.
- NNLO calculation with NLO CTEQ6.1                                                        PDF theory prediction compared to data.
- Theory prediction scaled to measured σ (Z)
- σ = 263.34± 0.93(stat.)± 3.79(sys.) pb.
- the agreement with theory is good,
- this measurement -with increasing statistics- can be used to constrain PDFs.

**1.1 tb****-1**

- Boson Rapidity

## CDF published the first attempt to constrain PDFs using the ratio of W  boson cross sections measured  with central and forward electrons.
provide sensitivity to the  W  rapidity

The largest experimental uncertainty,                                     (luminosity), cancels in this ratio. 
Experimental ratio can be compared                                            with acceptance ratios predicted by                                              any set of PDFs.

      Rexp = 0.925 ± 0.033
The theoretical NLO predictions are: 
RCTEQ     = 0.924 ± 0.031
RMRST01E = 0.941  ± 0.012

- provide sensitivity to the  W * *rapidity
- The largest experimental uncertainty,                                     (luminosity), cancels in this ratio.
- Experimental ratio can be compared                                            with acceptance ratios predicted by                                              any set of PDFs.
-       Rexp = 0.925 ± 0.033
- The theoretical NLO predictions are:
- RCTEQ     = 0.924 ± 0.031
- RMRST01E = 0.941  ± 0.012

- Ratio of central-to-forward W ->e**** cross section

- “R” as a function of the ± 1**** eigenvalues of PDF sets.

- CTEQ6.1

**MRST01E**

- PRL **98, **251801 (2007)

**223 pb****-1**

## W Mass Measurement Strategy

- W mass fundamental parameter of SM
-  Radiative corrections: depends on Mtop and MHiggs
-  W propagator includes H, tb, hypothetical new particle loops

- Precise knowledge of MW (and Mtop) constrains SM Higgs mass

- W mass obtained from fit of                                transverse mass **M****T****(l********):**

**Lepton Momentum               ** calibrate from J/ and upsilons  cross check with Z  

**200 pb****-1**

- M****

## Mw : CDF Result

- MT

- MT

**M****W**** = 80413 ± 48 MeV**

- the best single-experiment result, now statistically limited

**200 pb****-1**

****

- e

- Submitted to PRL hep-ex/0707.0085

##  Direct measurement of W 

-  Direct measurement of ****W

-  Determine W width using the tail    of MT(l****) distribution
- D0 finds   Γ**W**** = 2011 ±142 MeV** (177 pb-1, e)
- CDF finds Γ**W**** = 2032 ±71 MeV **(350 pb-1, e,μ)

**signal region: 100-200 GeV/c****2**

**normalization**

- MT

**350 fb****-1**

**177 pb****-1**

- CDF result is the world'smost precise single direct measurement

## Summary for Mw and Γw

- CDF  has most precise single experiment measurements of the W boson mass and width.

- Reduces uncertainty on world average by 15%:
**29 ******** 25 MeV**

- Reduces uncertainty on world average by 22%
**60 ******** 47 MeV**

## Diboson production 

- Study of diboson production:
- Test Gauge Boson Self Interactions
-  Intermediate step towards SM Higgs searches
-  Both experiments measured inclusive cross sections for:
-  WW  (PRL 94, 151801(2005), hep-ex/0605066)
-  WZ –ZZ
-  W****
-  Z****(hep-ex/0705.1550)

## W : Radiation Zero

- The interference among the tree-level diagrams below creates a zero amplitude  for cos(*) = -( 1 + 2Qd )     ( measure  - lepton  , not * )
- Observing the (destructive) interference in W****** (**trilinear vertex**)** is a test of the SM gauge structure

**MC**

**DØ data**

- CDF σ(W+γ) = 18.0±2.8 pb  (1.1 fb-1)
-  D0(ET>7GeV, MT(l,,MET)>90 ):       σ (W+γ) = 3.2±0.5±0.2(lum)pb

**0.9 fb****-1**

- (Lepton charge) *(******** –****lepton)

## WZ Cross Section Measurement

- DO: 12 events (BG ~ 3.6)

- Significance** : 3.3 ******** (summer 06)**

- NLO:              =3.7±0.1 pb

**0.8 fb****-1**

- Require 3 e,μ leptons and missing tranverse energy

- CDF: Significant improvements in lepton acceptance by forming leptons from all the available information

- 16 candidates, (BG ~ 2.7) expected 12.5

- Observation** **** ~ ****6 ******

**1.1 fb****-1**

- PRL **98**, 161801 (2007)

## First hints of ZZ

- pp -> ZZ is the smallest  measured at the Tevatron: NLO=1.4 pb
- D0: 1 ee candidate, expected ~ 1.5:  < 4.3 pb (95%CL)
- CDF has combined 4**l** & **ll** channel:
- 1 ee candidate; expected ~ 2.5
- For **ll******use an event-by event  probability                                           and construct a discriminant  which is fit                                               to extract the signal
- Significance** : 3.0 ******
- CDF is updating the WZ and ZZ results                                         soon with 2 fb-1  “stay tuned ..."

**1.5 fb****-1**

- 1 - Likelihood ratio for ll****

## Top quark physics

- The top quark is a very special particle:
- Heavier than all known particles
- Decays before hadronizing:                                                              Γtop=1.5 GeV > ΛQCD
- Top discovery 12 years ago, since                     then many top studies performed to                   answer the question:                                                          is what we call “top quark”                                     adequately described by                                                 the Standard Model?
- Still many open questions:
- Why is the top mass so large ?
- Why is its Yukawa coupling ~ 1?
- Does top play a special role in EWSB?

- (see _S. Cabrera talk_ for a review of top properties studies and search for new physics in the top samples)

## Top Quark Production at Tevatron

- ~85%

- ~15%

- _QCD pair production_
- NLO = 6.7 pb (for mTop= 175 GeV)

- s-channel

- t-channel

-  smaller than top pair production, but ➡ allows direct access to Vtb  CKM matrix element: cross section   |Vtb|
-  Single top identification is challenging ➡  huge background

**Notes:**
Single top Associated production tW  too small at the Tevatron 

## Top Quark  Decay

- SM  predicts: BR( *t **→ **Wb*) ≈ 100%

- Event topology determined by the decay modes of the  2 W’s in final state. Always  b jets are  present

- Dilepton (ee, μμ, eμ)
- BR = 5%, 2 high-PT leptons + 2 b-jets + large missing-ET
- Lepton (e or μ) + jets
- BR = 30%, single lepton + 4 jets (2 from b’s) + missing-ET
- All Hadronic:
- BR = 44%, six jets, no missing-ET
-  ****had +X
- BR = 21%

- For ttbar pairs decay:

## Measurements of tt

- Measurements of tt

- The top pair production cross section error ~ 12%  similar to the theoretical one
-  high-precision test of perturbative QCD calculations (now at NNLO – Cacciari, Kidonakis)
- The cross section is measured in all final states:          it is the first step of any analysis studying the top quark properties.

## Lepton +jets tt  & R

- b-jet identication technique based on a neural network, to count the number of events with 0, 1 and at least 2 b-jets.
- R = B(t->Wb)/B(t->Wq)  can be extracted simultaneously from the distribution of the observed events between  the three categories
- likelihood discriminant based on the kinematic properties of tt events is used to further constrain the number of tt events without tagged jets.

- Lepton +jets tt  & R

**912 pb****-1**

- |Vtb| > 0.901 @ 95% CL assuming CKM unitarity
- |Vtb| > 0.096 @95% CL  without CKM unitarity

- R > 0.812 @95%

## Lepton +jets tt & R

- Lepton +jets tt & R

- Predicted and observed number of events in the 0,1 and 2 b-tag samples, for events with at least 4 jets

- Zero-tag sample in bins of topological discriminant

- Summary of R at the Tevatron

**912 pb****-1**

## Top Quark Mass Measurements

- Top mass is a fundamental SM parameter
- Measured by kinematic reconstruction, fit to invariant mass distribution
- Need to relate the reconstructed  jets back to parton level:
- _Jet Energy Scale is crucial!_
- Many Methods exist, most precise top mass
- from_ Matrix Element Method in __**l**__+__jets:                          _
- Use four-vectors of reconstructed objects
- Calculate a probability per event to be signal                             or background as a function of the top mass
- Product of event probabilities used to extract                                   the most likely mass
- The mass of the jet pair from Wjj is used to obtain an _internal constraint to the jet energy scale_(JES).

## Top quark mass measurement: l +jets

-  166 W + 4 jets (>=1 b-tag)
- tt candidates

**940 pb****-1**

- Mtop =170.9  2.2(stat. + JES)  1.4(syst.) GeV
- = 170.9  2.6 GeV

- Mjj

- Mjjj

## Top quark mass measurement : l +jets

- Top quark mass measurement :** ****l**** **+jets

**l**** **+    + 4 jets
- Psig = sum over all 24 possible object-parton assignments, weighted with b-tagging event probabilities

- Mtop =170.5  2.4(stat. + JES)  1.2(syst.) GeV
- = 170.5  2.7 GeV

**913 pb****-1**

- Mtop

- JES

## Summary of top mass measurements

****M/M  ~ 1.1%                               of the order of the top natural width                  be careful in interpreting the meaning of the measurement
-                                                                           both exp.s are addressing a number of effects that, too small to have an impact in the first measurements, can now become important.
-                                                                           reconsider which theoretical aspects are relevant, at the 1 GeV level, and whether they are sufficiently well under control.

- The top quark mass is known with a precision that was  thought unreachable at the Tevatron only a few years ago*:*

## Top properties: W Helicity

- W helicity in top decays is fixed by Mtop, MW, and V-A structure of the tWb vertex. It is reflected in kinematics of W  decay products.
_**W helicity states:**_

- left-handed
- fraction: f-

- longitudinal
- fraction: f0

- right-handed
- fraction: f+

_**In Standard Model:**_          **~30%                      ~70%                         ~0.036%**

-  Measure angular distribution of  charged     lepton wrt. top in W rest frame: cos*

## W Helicity Measurement

- D0 uses **l**+jets and  **ll**** **events
-  With F0 fixed to the SM value (1par):
-  F+ = 0.017 ± 0.048(stat) ± 0.047(syst)
-  F+ < 0.14 @ 95% CL

**1 fb****-1**

**1.7 fb****-1**

- CDF uses **l**+ ≥ 4 jets, ≥  1b tag
-  1 parameter fit:
-     F+ (F0=0.7)= 0.01 ± 0.05 ± 0.03
-      F0  (F+=0)  = 0.65 ± 0.10 ± 0.06                  F+ < 0.12 @ 95% CL
-  2 parameter fit:
-     F0 = 0.38 ± 0.22 ± 0.07                     F+  = 0.15 ± 0.10 ± 0.04

## Evidence for single top production 

- D0 searched for single top  with three methods: decision trees (DT), matrix element (ME), and a neural network (NN).
- Discriminants are constructed with a large number of kinematic observables (DT, NN) or by evaluating the differential probability of signal with single top ME.
- A product over all bins                           (Njets, Ntags, lepton type) of                the  discriminant outputs is fit         with a likelihood.

*Signal enriched sample     signal depleted sample*
*(high discriminant region)   (W+jets dominated) *

**0.9 fb****-1**

## All Single Top Results

-     Expected significance: 2.3

- DØ Combination: 3.6

**0.9 fb****-1**

## Future Prospects

- For Mw & Mtop Tevatron has done better than expected
- with >4 fb-1 and CDF+D0 together may get to:                   ****M_top** = 1.0-1.2 GeV. **
- By the end of Run II, Mw will be known with close to 0.02%  (M_W = **20-25 MeV** )precision!

## Indirect bounds on the Higgs

- the ****2 curve is derived from  precision ewk measurements, as a function of the Higgs-boson mass, assuming the SM to be the correct theory of nature.
- The recent improvements in top and W  push the most likely value of the Higgs boson mass deep down into the excluded region

- 114 GeV < mH < 182 GeV @ 95% C.L.

-  mH < 144 GeV @ 95% C.L.

- Taking the LEP bound into account:

## Indirect bounds on the Higgs: SM vs MSSM

- Prediction for MW in the SM and the MSSM as a function of Mtop

- S. Heinemeyer, W. Hollik, D. Stockinger,
- A.M. Weber, G. Weiglein '06

- MSSM band:
- scan over SUSY mass parameters
- overlap:
- SM is MSSM-like
- SM band:
- variation of MH  in SM

- slight preference for non-zero SUSY contributions

## Conclusions

- Tevatron experiments have in their hands a gold mine of more than 2fb-1 of data
- The accelerator is performing well and the two detectors are well-understood
- CDF and D0 are bringing the tests of the Standard Model at a level of precision which meets or exceeds that of electron-positron colliders
- _The top mass is known with __**1.1% precision**__, the W mass with __**0.04% precision**_
- CDF and D0 will continue to produce excellent physics through 2009, and possibly after that
- Expect 6-8 fb-1 by the end of Run II
- _Expect 0.7% precision on top mass, 0.02% on W mass_
- The Higgs boson hunt is under way
- Surprises may be just around the corner

## Backup

## Tevatron Collisions & Cross Sections

- Cross sections for various physics processes vary over many orders of magnitude:
- processes of interest are often buried under heavy background
- need good rejection factors, selection and analysis strategies
- As luminosity increases experiments are forced to deal with new challenges
- Trigger and analyses being retuned to match the changes

## Electroweak physics with 

- Electroweak physics with ****

- _D__Ø__ __ _separates taus into 3 categories based on final state particles,      **** identified with  Neural Network

- _CDF_ uses cut based tau identification
- defines signal and isolation cone around seed track direction
-  0 information is added
- Require track & 0 isolated

- Type 1: 1 track

- Type 2: 1 track with EM en. Type 3: more than 1 track

- Z    is irreducible background to Higgs   search

## Z  eh

- Use channel ****1   e + ****2  had : isolated electron (ET>10 GeV/c) and hadronic tau (pT>15 GeV/c)
- Event topology cuts to reject qcd and W+jet backgrounds
- Cross section consistent with SM expectation

- L = 350 pb-1

## W Charge Asymmetry

-  W boson exhibit a production asymmetry due to the different PDF of u and d quarks in the proton:
- We measure a lepton charge asymmetry (convolution of production and V-A decay)

**230 pb****-1**

- CDF presented  a new analysis method which reconstructs the W rapidity (using a weighted iterative estimate).               To be updated soon with 1 fb-1

**343 pb****-1**

- Lepton rapidity

## AFB Above Z pole

- Statistics limited but ultimately sensitivity to Z’ beyond SM Distributions consistent with SM predictions

- L= 177 pb-1

## Dilepton tt

- _Signature_: events with  ee+2 jets, +2 jets,  e+1 jet
- _Observed data events:_ 73
- 16 ee, 9 
- 32 e+2 jets, 16 e+1jet
- _Expected background_**:** 23.5
- No requirement on b-jet identification

**1.05 fb****-1**

## Dilepton tt

- _Signature__**:**_ isolated high pT ee, , e,       2 jets
- _Observed data events_: 77:  16 ee, 26 , 35 e
- _Main Backgrounds__**: **_WW( ee,,em ) + jets, Z/***** ( **** e ) + jets, Z/g* ( ee, ) + jets, W + jets (jet fakes isolated e,) (~ 25.6 events)

- tt = 6.2  1.1 (stat.)  0.7 (syst.)  0.4 (lumi) pb

**1.2 fb****-1**

- ttbar   signal bin

## Lepton +jets tt 

- _Event Samples:_
- 1 b-tags Signal fraction ~80%
- 2 b-tags Signal fraction ~90%
- _Main Backgrounds:_
- Multijet production with fake lepton,
- W production + ≥ 3 jets
- Most top properties measurements use  4 jets events. Yields: 231 (1 b-tag), 101 (2 b-tags)

- Lepton +jets tt

**≥****1  b-tag:**

**≥****2  b-tag:**

**1.12 fb****-1**

## Lepton +jets tt

- _Signature:_ isolated high pT lepton, ≥3 jets
- 1 jet is required to be b-tagged by a very performant Neural Network b-tagging algorithm (****= 54%, fake rate =1%)
- Event yields are fit in 8 categories (e/; 3/ 4 jets; 1/ 2 b-tags) to derive the final result:

**= 1 b-tag**

- ** ****2 b-tags**

**pure ttbar sample!**

**913 pb****-1**

## Top Quark Mass: Matrix Element Method

- Use four-vectors of reconstructed objects
- Calculate a probability per event to be signal or background as a function of the top mass
- Product of event probabilities used to extract the most likely mass
- The mass of the jet pair from Wjj is used to obtain an _internal constraint to the error on the jet energy scale_(JES).

## Top quark mass measurement : l l +jets

- Top quark mass measurement :** ****l l**** **+jets

- Measurement  sensitive to the kinematics of the events and observed number of events. The unconstrained system of dilepton events is solved using the top-antitop  longitudinal momentum, and the top quark mass is reconstructed for each event.

**M****top** =**170.7 ****+4.2****-3.9****(stat.) ±2.6(syst.) ±2.4(theory) GeV**

**1.2 fb****-1**

- The hatched areas mark the dilepton ttbar  and the template top mass measurement using Pzttbar(without cross section dependence).

****(tt)

- Mtop

- 70 dilepton events passing event selection and  mass reconstruction

## Forward-backward charge asymmetry                       in top pair production

- NLO calculations predict forward-backward asymmetries of 5-10%  but recent NNLO calculations predict large corrections.
- asymmetry arises from interference between contributions symmetric and antisymmetric under the exchange top -> anti-top, and depends strongly on the region of phase space being probed
- The low asymmetries expected in the SM  makes this a sensitive probe for new physics.

- Where:****
****y = yt -ytbar

- Forward events                          Backward events

-  = (12 ± 8(stat) ±  1(syst))%

**Notes:**
We provide functional
forms that allow the comparison of any model to the measured asymmetry. We use the measurement
to place limits on tt production via a Z0 resonance

## BKP - Upgrades at Tevatron

## Top mass: All-hadronic channel

- the combination of a dynamical likelihood
- and LO matrix elements allows a precise measurement.
*The selection requires 6 jets (E**t**>15 GeV, |****|<2) and uses*
*kinematical cuts now “standard” on aplanarity : ****E**t**3**, *
*centrality C>0.78,  ****E**t**>280 GeV, and a cut on the*
*matrix element –based “top likelihood” L<10.  *
- Templates of Mtop and Mjj are then used in a combined fit
- to Mtop and the jet energy scale. The result is:

## Consistency check of CDF single top analyses

*Matrix element:*
****** **(t-chan.)  = 2.7 +1.5 -1.3 pb
*Neural Network:*
****** **(t-chan.)  = 0.2 +1.1 -0.2 pb
****** **(s-chan.) = 0.7 +1.5 -0.7 pb
*2-D Likelihood discriminant:*
****** **(t-chan.)  = 0.2 +0.9 -0.2 pb
****** **(s-chan.) = 0.1 +0.7 -0.1 pb
**Consistency at 1%  **
- CDF expects to observe at 5 single top production with 4/fb

| Method | Neural Networks |  | Matrix Elements | Likelihood Function |
| --- | --- | --- | --- | --- |
|  | 1D | 2D | 1D | 2D |
| Expected p-value | 0.5% 2.6  | 0.4% 2.6  | 0.6% 2.5  | 2.5% 2.0  |
| Observed p-value | 54.6% | 21.9% | 1.0% | 58.5% |

## Ongoing effort

- Last update in mid March (new CDF result on WW, ZH  and from D0 on WH, ZHnew)

- 

- 

- 

- Data used: less than 50% of what on tape by now!

- 

- New, April 6 2007
- (post Winter Conferences)

## Non SM Higgs

- Non SM Higgs(es) have sizeable decay rate to  pairs
- Large efforts to bring up efficiency to trigger on tau events (and to detect tau)

- R. Strohemer