# Presentation: 214041

## Enough Bs.... Let’s Talk about Top

**Florencia Canelli**
***on behalf of the CDF Collaboration***

## Over the Top:Precision Top Quark Mass Measurements from CDF

**Florencia Canelli**
***on behalf of the CDF Collaboration***

## Outline

- State of the Art in CDF Mtop measurements
- CDF Mtop program
- New measurements
- New CDF combination
- Future

- Florencia Canelli - UCLA

## The Top Quark

**The Top Quark**

- The top quark was discovered only 10 years ago
- Existence is required by the SM, but striking characteristics: its mass is surprisingly large
- Studied only at the Tevatron

-  t     Z   W    b    c     s    d    u              e            e

- Particle Masses

- The Standard Model

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## Why measure the Top Quark Mass?

- Related to standard model observables and parameters through **loop diagrams**
- Consistency checks of SM parameters
- Precision measurements of the Mtop (and MW)  allow prediction of the MHiggs
- Constraint on Higgs mass can  point to physics beyond the standard model

- Summer 2005

- Florencia Canelli - UCLA

## Tevatron Performance in Mtop/Mtop

**Tevatron Performance in ********M****top****/M****top**

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## At Tevatron, mainly produced in pairs via the strong interaction

Decay via the electroweak interactions
	Final state is characterized by the decay of the W boson

			Dilepton 

			Lepton+Jets

			All-Jets

- Different sensitivity and challenges in each channel

- At Tevatron, mainly produced in pairs via the strong interaction
- Decay via the electroweak interactions
- 	Final state is characterized by the decay of the W boson
***	******	******	******Dilepton***
***	******	******	******Lepton+Jets***
***	******	******	******All-Jets***

**Production and Decay**

- 85%                                                                                                             15%

- Br(t Wb) ~ 100%

- Florencia Canelli - UCLA

## Dilepton Channel

- Branching fraction: 5%  (lepton = e or )
- Final state: 2 leptons, 2 b quarks, 2 neutrinos
- Combinatorial background: 2 combinations
- 2 neutrinos: under constrained, kinematically complicated to solve Mtop
- S:B = 2:1  and 20:1 requiring 1 identified b tag

- Final State from Leading Order Diagram

- What we measure

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## Lepton+Jets Channel

- Branching fraction: 30% (lepton = e or )
- S:B = 1:4  to 11:1 depending on the b-tagging requirement
- Combinatorial background: 12 (0 b tag), 6 (1 b tag), and 2 (2 b tags)
- 1 neutrino: over constrained
- Most precise Mtop measurements

- Final State from Leading Order Diagram

- What we measure

- Florencia Canelli - UCLA

## All Jets Channel

- Branching fraction: 44%
- Huge amount of background S:B = 1:8 after requiring at least 1 b-tag jet
- Combinatorial background: 90 combinations
- Backgrounds mainly from multi-jet QCD production

- Final State from Leading Order Diagram

- What we measure

- Florencia Canelli - UCLA

## Top Quark Mass at CDF

- Robust program of top quark mass measurements
- Many measurements in all the different channels -> consistency
- Different methods of extraction with different sensitivity -> confidence
- Combine all channels and all methods -> precision

- CDF Summer 2005 Results

- Florencia Canelli - UCLA

## Mtop

******M****top**

- Different statistical and systematical sensitivities in each channel
- Other sources arise from the assumptions employed to infer Mtop:
- Initial state and final state radiation
- Parton distribution functions
- b-jet energy scale
- Generators
- Background modeling and composition
- b-tagging efficiency
- MC statistics
- Systematics dominated by the uncertainty on parton energies (Jet Energy Scale, JES)

| CDF Measurement (~350pb-1) | Statistical (GeV/c2) | JES (GeV/c2) | Other  syst.
(GeV/c2) |
| --- | --- | --- | --- |
| Dilepton | 6 | 3 | 2 |
| Lepton+Jets | 4 | 2 | 1 |
| All Jets | 5 | 4 | 2 |

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## Jet Energy Scale

- Jet energy scale
- Determine the energy of the quarks produced in the hard scattered
- We use the Monte Carlo and data to derive the jet energy scale
- Jet energy scale uncertainties
- Differences between data and Monte Carlo from all these effects

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## Jet Energy Scale Uncertainties

- About 3% of Mtop when
- convoluted with ttbar
- pT spectrum

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## Additionally, we use Wjj mass resonance (Mjj) to measure the jet energy scale (JES)  uncertainty

- Additionally, we use Wjj mass resonance (Mjj) to measure the jet energy scale (JES)  uncertainty

***In-situ***** Measurement of JES**

- Mjj

- Measurement of JES scales directly with statistics!

- Constrain the invariant mass of the non-b-tagged jets to be 80.4 GeV/c2

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## Data and Monte Carlo

- b-jet pT

- ttbar pT

- W-jet pT

- Mttbar

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## In this Talk

**Dilepton:** Matrix Element
**Lepton + jets:** Template analysis
**Lepton + jets:** Matrix Element
**Lepton + jets:** Decay Length
**All Hadronic:** Ideogram

- Florencia Canelli - UCLA

## Mtop Dilepton Results

## Method  Overview

- Measurement with this method using 340 pb-1:
- hep-ex/0512070, PRL accepted, PRD to be submitted
- Wine and Cheese August, 2005
- Likelihood is a linear combination of signal and background hypothesis
- Optimizes the use of information in the event
- Description of dominant backgrounds: Drell-Yan, WW+jets, fakes (instrumental)
- Updated measurement
- 	using 750 pb-1

|  | Expected 
Events (750 pb-1) |
| --- | --- |
| DY, WW+jets, fakes | 15.7 4.3 |
| EW (WZ,WZ,ZZ) |  3.6  0.7 |
| Total background | 19.4  3.4 |
| tt (6.1 pb) | 36.1  1.2 |
| Data | 64 |

- Florencia Canelli - UCLA

## Results

**Results**

- Using 64 candidates events found in 750 pb-1 we measure
- Restrict sample to b-tagged events: Mtop = 162.7 ± 4.6 ± 3.0 GeV/c2
-         Comparable sensitivity to best lepton+jets Run I measurements

- Florencia Canelli - UCLA

## Mtop Lepton+Jets Results

## Template Analysis

- Measurement using this method with 318 pb-1:
- PRL 96, 022004; PRD 72, 032003
- Used for Run I measurements
- Wine and Cheese April, 2005
- Reconstructed mtop and mjj from data are compared to templates of various true Mtop and JES (jet energy uncertainty shift)  using an unbinned likelihood
- Uses four samples to increase sensitivity

|  | 2 b tags | 1 b tag (T) | 1 b tag (L) | 0 b tag |
| --- | --- | --- | --- | --- |
| Expected S:B | 10:1 | 4:1 | 1:1 | 0.6:1 |
| Expected Number of Events ( tt = 6.1pb) | 47 | 104 | 64 | no a priori estimate |
| Data (680 pb-1) | 57 | 120 | 75 | 108 |

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## Template Analysis Results

**Template Analysis Results**

- Using 360 candidate events in 680 pb-1 we measure
- Using in-situ JES calibration results in 40% improvement on JES

- Better sensitivity than the previous world average!

- Florencia Canelli - UCLA

## Matrix Element Analysis Technique

**Matrix Element Analysis Technique**

- CDF adaptation of method used by D0:
- Nature Vol 429, June 2004, D0 Run I
- Similar to the CDF Dynamical Likelihood Method PRL 96, 022004; PRD accepted, Wine and Cheese November, 2004
- D0 preliminary Run II result using 380 pb-1
- Optimizes the use of kinematic and dynamic information
- Build a probability for a signal and background hypothesis
- Likelihood simultaneously determines Mtop, JES, and signal fraction, Cs:

- Florencia Canelli - UCLA

## Matrix Element Analysis Technique

**Matrix Element Analysis Technique**

- For a set of set measured variables x:
- JES sensitivity comes from W resonance
- All permutations and neutrino solutions are taken into account
- Lepton momenta and all angles are considered well measured
- Background probability is similar, no dependence on Mtop

***W(x,y)*** is the probability that a parton level set of variables ***y*** will be measured as a set of variables ***x *****(parton level corrections)**

***d******n************ ***is the differential cross section: LO Matrix element

***f(q)*** is the probability distribution than a parton will have a momentum ***q***

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## Monte Carlo Tests

- Calibrate method against MC samples
- Shows unbiased measurement
- Extracted errors are found to be underestimated by 6%

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## Event Selection

- Exactly 4 jets with with ≥ 1 b tags
- 1-b tag: 4 jets ET>15 GeV (S:B=5:1)
- 2-b tags: 4 jets ET>15 GeV (S:B=13:1)

|  | Expected 
Events (680 pb-1) |
| --- | --- |
| W+4 jets (Mistags) | 4.39  0.91 |
| Non-W (QCD) | 3.75   1.86 |
| Wbb | 3.35  1.54 |
| Wcc | 1.60  0.76 |
| Wc | 1.00  0.45 |
| Single top | 0.81  0.19 |
| EW (WZ,WZ,ZZ) | 0.77  0.17 |
| Total background | 15.67  2.54 |
| tt (6.1 pb) | 78.89  2.74 |
| Data | 118 |

- Florencia Canelli - UCLA

## Results

**Results**

- Using the 118 candidates in 680 pb-1 our Mtop is:

- with  JES = 1.019  0.022  (stat)

- Better sensitivity than the previous world average!

- Florencia Canelli - UCLA

## Results

**Results**

- Compare Data and Monte Carlo calculating the invariant mass of 2 and 3 jets
- Signal probability evaluated at Mtop=174.5 GeV/c2 and JES=1 and using the most probable configuration

- Excellent agreement found between data and Monte Carlo

- Florencia Canelli - UCLA

## Decay Length Overview

- The method has been published by C. Hill *et al.* at PRD 71, 054029
- B hadron decay length  b-jet boost  Mtop
- Uses the average transverse decay length of the b-hadrons <Lxy>

- Relies on tracking, no JES and uncorrelated with other measurements

- Florencia Canelli - UCLA

## Selection and Tests

- Event selection used to maximize the amount of signal in the sample:
- 3 or more jets
- 1 ≤ b tag jet
- 375 events with S:B = 3:1

|  | Expected 
Events (695 pb-1) |
| --- | --- |
| Total background | 111.6  12.5 |
| Data | 375 |

- Requires accurate simulation of Lxy
-  Enriched heavy-flavor samples
-  <Lxy> (data/Monte Carlo) = 0.992  0.012
-  Major systematic uncertainty

- Data and Monte Carlo comparison in control sample

- Florencia Canelli - UCLA

## Results

- Using the 375 candidates in 695 pb-1 our top quark mass measurement is:
- <Lxy> = 0.5808 ±0.0227 cm

- Will carry more weight by the end of Run II

- Florencia Canelli - UCLA

## Mtop All Jets Results

## All Jets

- Main challenges in this channel:
- Small signal fraction S:B = 1:8 after requiring at least 1 identified b-jet
- Large combinatorial background: 90 combinations
- Selection and events
- ET/  ( ET) < 3 (GeV)1/2
-  ET   280 GeV
- nb-tag   1
- Exactly 6 jets
- Ideogram method from the Delphi experiment for the W mass measurement, used in a Run II preliminary D0 for top mass measurement in lepton+jets channel

|  | Expected 
Events (310 pb-1) |
| --- | --- |
| Multi-jets (light) | 182 |
| Multi-jets (heavy flavor) | 68 |
| Total background | 240  |
| tt (6.1 pb) | 40 |
| Data | 290 |

- Florencia Canelli - UCLA

## Ideogram Overview

**Ideogram Overview**

- Define a 2D event likelihood as
- Weight each combination with kinematical and b-tagging information: wi
- Extract from kinematical fit to mtop and manti-top  m1, m2, 1,2, 2

- Scomb combinatorial background from Monte Carlo

- Sm calculated convoluting Briet-Wigners and Gaussian resolution functions

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## Template Shapes

- Template for combinatorial background

- Signal, correct combination

- Template for background

- Using the two fitted masses
- gives a good separation
- between
- signal and background

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## Background Simulation

- Region 1

- Region 2

- Region 3

- Background is well understood

-  • Data
-  - Background MC

-  • Data
-  - Background MC

-  • Data
-  - Background MC

- Florencia Canelli - UCLA

## Monte Carlo Tests

- From 290 observed events we estimate S/B by measuring the sample purity in data
- From data we fit a signal fraction Cs=0.21  0.07
- Results in 61  20 signal events
- Compatible with all hadronic  cross section measurements with 310 pb-1

-   The Monte Carlo fitted purity is consistent with the purity obtained from data and independent of Mtop

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## Monte Carlo Tests 

- Estimation of the expected error is underestimated by 17%
- We understand that this is caused by the background
- Inflate errors to take into account this effect
- Expected statistical errors 4 - 5 GeV/c2

- Florencia Canelli - UCLA

## Results

- Using 310 pb-1 and 290 candidates we measure
- First Tevatron Run II all jets Mtop measurement
- Systematically limited!

- Similar statistical sensitivity as the lepton + jets channel

- Florencia Canelli - UCLA

## Summary of  Mtop Results

**Summary of  M****top**** Results**

| CDF Measurement | Extracted value (GeV/c2) | Statistical (GeV/c2)
 | JES (GeV/c2)
 | Other  syst (GeV/c2)
 |
| --- | --- | --- | --- | --- |
| Lepton+Jets: Template (680pb-1) | 173.4 | 1.7 | 1.8 | 1.3 |
| Lepton+Jets: ME(680pb-1) | 174.1 | 2.0 | 1.5 | 1.3 |
| Lepton+Jets: Decay Length (750pb-1) | 183.9 | +15.7
-13.9 | 0.3 | 5.6 |
| Dilepton: Matrix Element (750pb-1) | 164.5 | 4.5 | 2.6 | 1.7 |
| All Jets:
Ideogram (310pb-1) | 177.1 | 4.7 | 4.3 | 1.9 |

- We compare (confidence and consistency) and combine (precision)

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## Combining Mtop Results

- Excellent results in each channel
- Combine them to improve precision
- Include Run-I results
- Account for correlations
- Use BLUE (*NIM ****A270**** 110, ****A500**** 391)*
- Matrix Element analysis in lepton+jets not yet included. Working to understand statistical correlations with Template analysis

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## Combining Mtop Results

**Combining M****top ****Results**

- Are the channels consistent?
**	****	**
**	**
- We compare them taking into
- 	account their correlated
- 	systematics
- Discrepancy might reveal
- 	missing systematic?
- 	*or New Physics?*

-  **M****top****(All Jets) = 178.7 ******** 5.5 GeV/c****2**
** ****M****top****(Dilepton) = 164.8 ******** 4.8 GeV/c****2**
** ****M****top****(Lepton+Jets) = 173.5 ******** 2.8 GeV/c****2**

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## Future

**Future**

- We surpassed our Run II goal of measuring to 3 GeV/c2 precision
- Have made extrapolations based on present methods
- Upper limit: Only (stat) improves with luminosity
- Lower limit: Everything improves with luminosity
- Reality: likely somewhere in between

- With full Run-II dataset CDF should measure Mtop to < 1%

- Florencia Canelli - UCLA

## Conclusions

**Conclusions**

-  CDF has robust program of Mtop measurements
- First Run-II determination in all-jets channel
- Multiple methods and channels
- Observed consistency builds confidence
-   CDF combined
-  CDF should reach 1% precision with full Run-II data set
-   Tevatron combination better still

- Florencia Canelli - UCLA

## Conclusions

**Conclusions**

- Present uncertainties on Mtop and MW help constrain MHiggs to about 40% MHiggs/ MHiggs
- Best fit favors light MHiggs
- where CDF/D0 are sensitive
- where difficult for LHC
-  Mtop will continue to shrink
- New CDF/D0 MW expected soon...
-  MW will also shrink

- Florencia Canelli - UCLA