# Presentation: 685005

## Top Quark Mass Measurements at the TeVatron

** ****Two new (preliminary) results:**
** ****CDF      Run II (********s = 1.96TeV, 2001 - present)**
** ****D****Ø****        Run I  (********s = 1.8TeV, 1992 - 1996)**

**Florencia Canelli**
***University of Rochester***
**for the CDF and D****Ø**** **** collaborations**

## Top Quark Mass

- The top quark mass, Mtop, enters as a parameter in the calculation of
- radiative corrections to other Standard Model observables

-  Mtop is roughly 1⁄2 the
-    vacuum expectation
-    value of the Higgs field

-  better understanding
-    of EWSB mechanism?
-  to perform more precise
-     tests we need:
-            more data
-                  and
-           improved techniques

-  Mtop can be related, with
-    mW, to the Higgs mass

- Florencia Canelli - Rochester

## Top Quark Production and Decay

- In proton antiproton collisions at TeVatron energies, top quarks are primarly produced in pairs

- Single production via weak interaction: **not yet observed**

**PRODUCTION**

**DECAY**

- Each quark decays ~ 100% into a
- W-boson and a b-quark

**BR(t********Wb) @ 100%**

- 3 main experimental signatures  depending  on the decay of the W  boson:
-       **dilepton,  lepton+jets, all-hadronic**

- Florencia Canelli - Rochester

## ttbar Decay Signatures

- DILEPTON  BR(ee++e) = 5%
- Small background
- Small cross section
- 2 high-pT leptons, 2 b jets, large missing-ET
- LEPTON +JETS BR(e+jets,+jets) = 30%
- manageable backgrounds
- higher statistics
- 24 jet combinatorics
-  1high-PT lepton, 4 jets (2 b jets), large missing-ET
- ALL-HADRONIC BR(jets)=44%
- qcd background
-  jet combinatorics
- 6 jets (2 b jets)

- Tagging of b-quarks reduces background and combinatorics:
- 	**soft lepton tag (b->l **** c)****	****secondary vertex tag**

- Florencia Canelli - Rochester

## Run I Results

- Florencia Canelli - Rochester

## CDF Run II Top Mass Measurement

## Lepton + Jets Channel  

**Event selection (same as Run I)**
- Exactly one isolated high pT e or 
- Missing ET>20 GeV
- Jets ET>15 GeV & ||<2
- Z and cosmic veto

- Backgrounds
- W + jets (*measured from data and MC*)
- Non W background (fake lepton) (*measured from data*)
- Diboson, Drell-Yan, single top (small) (*measured from MC*)

- 72 pb-1     33 candidates

- Florencia Canelli - Rochester

## Lepton + jets Kinematics

** **
-  4 jets =>12 combinations
-  x2 depending on kinematics ambiguities
-  every combination has two solutions for pz
-  2-constraint kinematical fit → Mtop
***p*** unknown		–3
- Impose ***p****T* balance		+2
*M*(*q**1**q**2*) = *M**W**	*	+1
*M*(*l***)    = *M**W*		+1
*M*(*W*+*b*) = *M*(*W*–*b*)		+1

- 5 vertices
- 20 degrees
- of freedom

- Florencia Canelli - Rochester

## Outline of the Method

** **
-  2-constraint fit applied, combination with lowest 2 is chosen for top mass
- Reconstructed top masses from data are compared to *parameterized* templates of top and background Monte Carlo
-  Extract top quark mass and statistical uncertainty using maximum Likelihood
-  Mtop is the minimum of the log-likelihood distribution
-  top corresponds to a change of 0.5 units in the log-likelihood

- Florencia Canelli - Rochester

## ttbar l+jet candidate

**tt l + jet candidate:**** **
**Nov 02 2002 run: 153693 event: 799494**
****** ****(CMUP) + 4 jets**

- Florencia Canelli - Rochester

## Result  

**CDF Run I combined:**
** ****M****top**** = 176.1 ± 6.5 GeV/c****2**

**Will improve with**
**detector understanding **
**Run I was 4.4 GeV**

**M****top**** = 171.2 ******** 13.4****stat**** ******** 9.9****sys**** GeV/c****2**

- Florencia Canelli - Rochester

## Using b-tagging

- Cleaner sample: smaller
- combinatorics, smaller
- background
-  3 or more jets
-  at least 1 b-tagged jet
-  11 candidates

- Work in progress

**Event tagging efficiency ******** = ****45 ****± 1 ± 5 %****(from data + MC)**

- Florencia Canelli - Rochester

## DØ Run I Top Mass Measurement

## Outline of the method

**Likelihood**

**Signal & Background**

**Detector Acceptance**

-  The values of c1 and c2 are optimized, and the likelihood is normalized
- automatically at each value of 

**Likelihood method using most available information**

- Florencia Canelli - Rochester

##         Signal and Background Probabilities

- resolutions,
- reconstruction effects

- Matrix Element

- PDF’s

- Measured, reconstructed
- objects in the event

- to be estimated

- Only in terms of the  main background (*W*+jets, 80%)
-  Calculated using VECBOS subroutines for *W*+jets

**Signal Probability**

**Background Probability**

- where

- Florencia Canelli - Rochester

## Event Selection

- D**** Statistics Run I (125 pb-1)
**Standard Selection:**
**Lepton:** ET>20GeV, |e|<2, ||<1.7
**Jets:** 4,  ET>15 GeV,  ||<2
**Missing E****T** > 20 GeV
- “ETW ’’> 60 GeV ; |W |<2
**           ****91 events**
*       **Ref.  PRD 58 (1998), 052001*
*                                                                                               *
**Additional cuts for this analysis :**
- 4 Jets only -> LO ME is used in
- probability calculation
** ****71 events**
- Background probability
- -> to improve purity
**22 events     =>   estimated 12 signal + 10 background****        **

- log(P W+jets)

- Florencia Canelli - Rochester

## Result

**This new technique improves the statistical error on M****t**** from 5.6 GeV **
**[****PRD 58 52001, (1998)****] to 3.6 GeV. **
_**This is equivalent to a factor of  2.4 in the number of events.**_** **

**M****top**** = 180.1 ******** 3.6****stat**** ******** SYS GeV**

- Florencia Canelli - Rochester

##      Check of Mw with DØ Run I Data

- Expect a substantial improvement in the JES systematic, and the application
- of this technique to many measurements

- Can help reduce the uncertainty in the jet energy scale (JES)

- Florencia Canelli - Rochester

##      Monte Carlo studies with 12s+10b

- The MC simulations show that the results obtained are consistent with expectations (Mtop =175 GeV)

- Mtop
- most probable
- value

- Mtop

- S/(S+B)

- Pull

- Florencia Canelli - Rochester

## Total Uncertainty

**I. ****Determined from MC studies with large  event samples:**

| Signal model | 1.5 GeV |
| --- | --- |
| Background model | 1.0 GeV |
| Noise and multiple interactions PRD 58 52001, (1998) | 1.3 GeV |

- II. **Determined from data:**

**                            ****Total systematic:****	****4.0 GeV**

| Jet Energy Scale | 3.3 GeV |
| --- | --- |
| Parton Distribution Function | 0.2 GeV |
| Acceptance Correction | 0.5 GeV |

**M****top**** = 180.1 ****±**** 5.4 GeV  (preliminary)**

- Florencia Canelli - Rochester

## Conclusions 

- Improved top mass measurement from Run I (D, 2003)

- TeVatron Top Mass Run I Measurement (CDF, D 1999)
- (new result not included)

- Top Mass from Run II (CDF, 2003)

- Improvements for Run IIa:
- Improved b-tagging
- Jet Energy Scale
- Improved Techniques
- Expected Mtop 2-3 GeV/c2

- Florencia Canelli - Rochester