# Presentation: 148604

## Measurement of thett production cross section in pp collisions at  s=1.8 TeV

**Measurement of the********tt production cross section in ********pp collisions at *********** *****s=1.8 TeV**

**Giorgio Apollinari**
**Fermilab**
**CDF Paper Seminar, January 2001**

## Plan of the Seminar

*Introduction *
*Data Samples*
*Tools Development *
*Simulation Calibration  *
*Tagging Algorithms*
*Tools Cross-Checks*
*Cross Section Measurement*

## In the SM, the top quark completes the third quark family
Measurement of         is of interest
as a test of QCD (                     )
as a landmark for beyond-SM searches
At the Tevatron, top quarks are pair produced viaqq annihilation (90%) or gluon fusion (10%)
In the SM framework,  tWb and when one of the W’s decay leptonically the final state is characterized by
High transverse momentum e or 
Four jets, some of which with heavy flavor content 
due to gluon radiation or jet merging, the actual number of jets may vary
Missing Et (undetected )

*In the SM, the top quark completes the third quark family*
*Measurement of         is of interest*
*as a test of QCD (                     )*
*as a landmark for beyond-SM searches*
*At the Tevatron, top quarks are pair produced via****qq annihilation (90%) or gluon fusion (10%)*
*In the SM framework,  t****Wb and when one of the W’s decay leptonically the final state is characterized by*
*High transverse momentum e or ***
*Four jets, some of which with heavy flavor content *
*due to gluon radiation or jet merging, the actual number of jets may vary*
*Missing Et (undetected ****)*

***Introduction***

***Focus of this analysis***

## Introduction

***Introduction***

* **Measurement Plan*
*follow guidelines used in all previous CDF measurements **1,2** of the M**top** and production cross section and revise/expand many details of the latest analysis **3*
*Use tagging techniques to enhance the relative fraction of events coming from top decays relative to background by selecting heavy flavor decays*
*Secondary Vertex Tagging **	**(SECVTX)*
*Semileptonic Decay Tagging**	**(SLT)*
*Displaced Tracks Tagging**	**	**(JPB)*
*Calculate and calibrate all background contributions to the tagged W+jet, with emphasis on the understanding of the major background sources*
*Tagging techniques efficiencies*
*Non-heavy flavor (Mistag) rates*
*Heavy Flavor production rate in Monte Carlo simulation*
*Attribute the excess over background in the W+ ****3 jet events with at least one tag to****tt production and derive ******tt*
*1**	** *F. Abe* et al., *Phys. Rev. Lett.* 74, 2626 (1995)*
*2  *F. Abe* et al., *Phys. Rev. Lett.* 80, 2767 (1998)*
*3  *F. Abe* et al., *Phys. Rev. Lett.* 80, 2773 (1998)*

***Focus of this Seminar (Paper) ***

## Data Collection
Integrated Luminosity 
105.1 ± 4.0 pb-1  (tot =80.03 ±  2.24 mb)
Data were accepted by a three-level trigger
L1: Single Calorimeter Towers and Muon Chamber track segments
L2: Jet-like clustering and Central Tracker information
L3 Full event reconstruction

*Integrated Luminosity *
*105.1 ± 4.0 pb**-1**  (****tot** =80.03 ±  2.24 mb)*
*Data were accepted by a three-level trigger*
*L1: Single Calorimeter Towers and Muon Chamber track segments*
*L2: Jet-like clustering and Central Tracker information*
*L3 Full event reconstruction*

*Physics Objects Reconstruction*
*e and **** selected with standard quality cuts*
*Isolation*
*Track and EM-Calorimeter/Muon Detector matching*
*Calorimeter Information*
***  **** **ee are removed using tracking information*

***Data Collection and Reconstruction***

## Data Collection and Reconstruction

*Physics Objects Reconstruction (cont.)*
*jets reconstructed using a cone of R=0.4 in ****space*
***(E**T**)/E**T  **~ 1/**** E**T*
*Uncertainty in large-angle gluon emission implies a 10% systematic uncertainty on the jet energy scale.*
*E**T** and neutrino reconstruction*
*Transverse missing energy defined as*
*when a **** is present, the E**T**  is calculated as*

## Data Samples Selection

*W+jets samples *
*This sample contains the****tt signal. W****l**** are selected from high-p**T** inclusive lepton (primary lepton) and large missing energy*
*E**T** **** 20 GeV (p**T** **** 20 GeV/c for ****)*
*E**T** **** 20 GeV*
*at least one jet with E**T **** **15 GeV and |****| **** 2*

## Z+jets samples 
possible source of background to W+jets events
because of similar production mechanism in Z+jets and W+jets, the sample can be used to verify that all the backgrounds tott production are properly estimated
Second lepton selected according to relaxed criteria (loose leptons)
all events containing an identified Z decay  or a primary lepton and a loose lepton (dilepton events)  are removed from the W sample

*Z+jets samples *
*possible source of background to W+jets events*
*because of similar production mechanism in Z+jets and W+jets, the sample can be used to verify that all the backgrounds to****tt production are properly estimated*
*Second lepton selected according to relaxed criteria (loose leptons)*
*all events containing an identified Z decay  or a primary lepton and a loose lepton (dilepton events)  are removed from the W sample*

***Data Samples Selection (cont.)***

## Data Samples Selection (cont.)

*Generic jets samples *
*samples used to calibrate the Monte Carlo generators, mistag calculations and detector simulation.*
*7 samples selected requiring various thresholds on the calorimeter clusters energies *
*JET20, JET50, JET70, JET100, ****E**T** 175 , ****E**T** 300  and ****E**T** 125 4CL*
*Low-p**T **inclusive lepton sample*
*used to define a sample richer in****bb production to measure the efficiency of the b-tagging algorithms*
*low p**T** electrons (p**T  **** 7.5 GeV/c matched to E**T  **** 8 GeV calorimeter tower) is the main sample for the b-tagging algorithm efficiency measurement*
*results are cross-checked in a low p**T**  muon sample (p**T** ** **** 7.5 GeV/c)*
*Isolated photon sample*
*used to define a sample richer in c-quark jets*
*The final sample consist of approximately 3000  ****+ **** 1 jet candidates*

## Monte Carlo Generators

*Three Monte Carlo generators are used in this analysis: Herwig, Pythia and Vecbos*
*Pythia is used for****tt acceptance (also evaluated with Herwig)*
*Herwig is used to estimate the fraction of W+****1 jet with heavy flavor *
*Herwig (and Pythia) use tree-level matrix element calculations for the partons hard scattering, followed by a modeling of the parton showers accounting for color correlations between initial and final state hadrons and by a phenomenological hadronization when the partons invariant masses fall below a minimum QCD cutoff.*
*Vecbos is used to study the phase space region in which Herwig is not reliable, namely the W****cc and W****bb events in which the two b or c quarks produce two well separated jets. *
*Collinear singularities regulated by cut-off values P**T**min**=8 GeV/c and R**min**=0.4*
*Checked that Herwig and Vecbos provide the same prediction for the fraction of jets with heavy flavor at the Rmin threshold.*
*Use MRSD**0**’ structure functions and the CLEO Monte Carlo to model the decay of heavy hadrons*

## Detector Simulation

*A quick simulation (QFL) based upon parameterization and simple models  creates the detector response.*
*Central tracker simulation converts generator level tracks into reconstructed tracks using covariance matrices derived from data*
*no hit/patter recognition simulation*
*efficiency measured by a track-embedding procedure*
*density of hits/multiple interaction simulated by a track degradation parameterized as a function of the hit density around a track. *
*SVX simulation is a hit-level simulation*
*Covariance elements must be multiplied by factor 2 to reproduce the data*
*efficiency for reconstructing SVX track must be degraded too. *

## Tagging Algorithms (SECVTX)

*SECVTX*
*based on the determination of the event  Primary Vertex and the reconstruction of additional secondary vertices using displaced tracks associated to a jet*
*Primary Vertex*
*reconstructed in z (****z**~0.2 cm)*
*reconstructed in x-y (****x**~****y**~10-25 ****m)*
*Secondary Vertices*
*Positive Tags  (two stages process)*
*three or more tracks belonging to a common vertex (no K**s** and ****decays) *
*two or more tracks with more stringent requirements (p**T** or impact parameter significance).*
*L**xy**/****xy** > 3*
*Negative Tags*

*PV*

*Positive*
*Tag*

*Negative*
*Tag*

## Tagging Algorithms (JPB)

*Jet-probability (JPB)*
*used to cross-check SECVTX*
*algorithm compares track d**0** (impact parameters) to measured resolution (JET50), calculates a probability of being consistent with zero lifetime hypotesis*
*uniform  probability for light quarks and gluon jets*
*low probability for heavy flavor*
*parameterization done on data and MC  independently. *
*Probability*

*Negative JPB calculated with tracks having a negative d**0** *

## Tagging Algorithms (JPB)

*Tag defined for JPB < 0.05*

*	**Data-Simulation comparison for impact parameter significance (d/****d**)*

*	**Distribution of positive and negative JPB in a mixture of JET50 and JET140 data.*

## Tagging Algorithm (SLT)

*The Soft Lepton Tagging algorithm tags b quarks by searching for an electron or **** from a semileptonic decay.*
*in this analysis we search for SLT candidates only in a cone of radius 0.4 around the axis of a jet with E**T** **** 15 GeV ( as opposed to the previous ******tt** measurement)*
*selection criteria based on tracking-calorimetry or tracking-muon detectors matching. Additional requirement (preradiator, dE/dx) also used.*
*events with Z candidates from primary-SLT combination are removed.*
*Mistags (fake SLT)*
*parameterized in data as function*
*	**of p**T** and track isolation *
*removal heavy flavor from a fit of*
*	**the SLT d**0** distribution*
*Simulation does not need to rely on*
*	**detector QFL modeling for efficiencies*
*	**estimation*
*generator tracks weighted by data -measured ***

## SECVTX & JPBTagging Efficiencies

***SECVTX & JPB******Tagging Efficiencies***

*In the simulation, 94% of the events with a tag on the a-jet are due to****bb production*
*99% of double tag events are due to****bb production *
*In the data we remove the a-jet tags due to “QCD” processes to obtain the analog equation*

*Measure tagging efficiency in data (****b**) and simulation (****b**MC**) using the low-p**T** electron sample (dijet sample enriched in****bb decays)*
*Define Scale Factor (SF) as*

## SECVTX & JPBTagging Efficiencies (cont.)

***SECVTX & JPB******Tagging Efficiencies (cont.)***

*Iterative procedure fits both SF and F**hf** (fraction of events in which the e-jet contain hadrons with heavy flavor)*
*The F**hf** is in agreement with previous CDF measurements **1*
*1**	** *F. Abe* et al., *Phys. Rev. Lett.* D50, 2966 (!994)*

## SECVTX & JPBTagging Efficiencies (cont.)

*Verify agreement between the tagging efficiencies as function of transverse energy in the data and simulation *

*Single tags*

*Double tags*

***SECVTX & JPB******Tagging Efficiencies (cont.)***

## Many cross-check and systematic studies are performed to check the validity of the SF calculation
Cross-check the validity of using “QCD” tagging rate to describe the a-jet tags in events where the e-jet does not contain heavy flavor
Cross-check on the sensitivity of c-jets modeling
Cross-check on the sensitivity to gluon splitting
Cross-check of the SF dependence on ET
Cross-check of the SF calculation on the low-pT  sample
Cross-check of the SF in events with double tags
Scale Factor Origin 

*Many cross-check and systematic studies are performed to check the validity of the SF calculation*
*Cross-check the validity of using “QCD” tagging rate to describe the a-jet tags in events where the e-jet does not contain heavy flavor*
*Cross-check on the sensitivity of c-jets modeling*
*Cross-check on the sensitivity to gluon splitting*
*Cross-check of the SF dependence on E**T*
*Cross-check of the SF calculation on the low-p**T** **** sample*
*Cross-check of the SF in events with double tags*
*Scale Factor Origin *

***Tagging Efficiencies ******Cross-checks***

## Tagging Efficiencies Cross-checks (cont.)

*In events where the e-jet does not contain heavy flavor, a-jet tags are predicted using the probability of tagging jets with heavy flavor as measured in generic jet data*
*assumption tested on a sub-sample of events where the electron in e-jets is due to a **** conversion*
*Heavy flavor purity is 8.7 % from the number of e-jets with a SECTVTX or JPB tag*
*in the remaining 91.3% of the events, tagged a-jets are predicted using the parameterization derived from generic jets*

***Tagging Efficiencies ******Cross-checks (cont.)***

## Tagging Efficiencies Cross-checks (cont.)

***Tagging Efficiencies ******Cross-checks (cont.)***

*To check the sensitivity of the SF to the modeling of the c-jets, we select a sample with a different relative fraction of b and c-jets.*
*In events where the a-jet is tagged by JPB, the fraction of****cc production increases to 11% (from 5%) according to the simulation.*
*If the SECVTX and JPB SF are determined using a-jets tagged by JPB instead of SECVTX, the SF changes by less than 1%*
*As shown later, the gluon splitting cross section (g ****bb or****cc) requires a 40% correction.*
*The SECVTX Scale Factor changes by less than 2%.*

## Tagging Efficiencies Cross-checks (cont.)

***Tagging Efficiencies ******Cross-checks (cont.)***

*Scale Factor E**T** dependence*

*SECVTX Scale Factor in 4 different bins of e-jet E**T*
*Compare fraction of tagged jets in JET50 and JET100 data and corresponding simulation as a function of E**T** (simulation corrected for SF and increased gluon cross section)*

## Tagging Efficiencies Cross-checks (cont.)

***Tagging Efficiencies ******Cross-checks (cont.)***

*The low-p**T** **** sample (p**T** ****10 GeV/c) provides an independent data set to check the tagging efficiency Scale Factor.*
***-jets without heavy flavor are due to non-interacting hadrons or K/**** in-flight decays*
*To avoid the assumption that Herwig models correctly the yield   of jets with heavy flavor as a function of E**T** (E**T** dependence study) we compare rates of double SECVTX to double JPB tags in data (JET50 and JET100 with only two jets) and in simulation*
*from which we measure SF**SEC**/SF**JPB**=1.24 (vs. 1.28 measured in the low-p**T** electron sample)*

## Tagging Efficiencies Cross-checks (cont.)

*	**A SF of 1.25 for SECVTX indicates an efficiency of tagging in data which is 25% higher than the efficiency for tagging in the simulation*
*Scale Factor Origin*
*a significant fraction of the difference from unity is due to outdated CLEO decay table and outdated B-lifetimes in the CDF particle database*
*These two inaccuracies account for ~40% of the difference from unity*
*small inaccuracies in the implementation of the SVX detector geometry account for an additional 16% of this difference*
*If corrected for the two effect mentioned above, the scale factor would be 1.09 **** 0.11, with a 3% uncertainty due to the error on the b-lifetime and an additional ~8% uncertainty due to the CDF tracking system.*

***Tagging Efficiencies ******Cross-checks (cont.)***

## SECVTX and JPB Mistags 

*Mistags are tags in jets without heavy flavor caused by detector resolution effects *
*Positive and negative tagging rates  *
*measured in data (JET20, JET50, JET70, JET100 and SET300) *
*parameterized as a function of E**T** and N**TRK**SVX*
*Mistags derived from rate of Negative tags*
*Removal of negative tags produced by heavy flavor (i.e. rate of negative tags is different for jets originating from quarks and gluon splitting)*
*Recipy*
*Use jets above the trigger threshold and away from calorimeter cracks*
*94% of the leading jets contains just one heavy flavored hadron*
*Use “third jet” to map region below 30 GeV*
*96% tagged jets contain two hadrons produced by gluon splitting*
*Estimate the number of negative tags (as function of E**T**) due to heavy flavor by the difference P-N between positive and negative tags*
*correct, in the generic jet sample, for the presence of multiple interactions*

***SECVTX and JPB Mistags ***

## SECVTX and JPB Mistags 

*Tagging rates as a function of E**T** and track multiplicity*

***SECVTX and JPB Mistags ***

*Comparison between all tagged jets and prediction obtained using only jets away from calorimeter cracks*

## SECVTX and JPB Mistags 

*The ratio*
*	**can be empirically described by *
*	**for E**T ****30 GeV and E**T **<30 GeV respectively. *
*	**Then the negative tagging (or mistag) rate is given by:*
*	**	**	**	**	**for E**T** **** 30 GeV*
*	**	**	**	**	**for E**T **< 30 GeV*

***SECVTX and JPB Mistags ***

## SECVTX and JPB Mistags 

*In generic jet samples, ~70% of the events contain additional interactions and the negative tagging rate depends on the number of interactions.*
*The mistag rate is parameterized as a function of ****p**T**V** (sum of all transverse momenta for tracks displaced by more than 5 cm in z from the Primary Vertex) as*
*	**	**	**	**	**	**	**for ****p**T**V** < 60 GeV/c*
*	**	**	**	**	**	**	**for ****p**T**V  ****60 GeV/c*

***SECVTX and JPB Mistags ***

*	**The mistag rate in jets without heavy flavor is (50****5)% lower than previously estimated*

## SECVTX and JPB MistagsCross-check 

*Capability of the model to predict the rate of negative tags is tested in all available generic jet samples*
*compare measured negative tags to the sum of predicted mistags and predicted heavy flavors with negative tags *
*assumption (corroborated by simulation) that all jets below trigger threshold are gluon jets and all jets above trigger threshold are quark jets*

***SECVTX and JPB Mistags******Cross-check ***

*JET100*

## SECVTX and JPB MistagsCross-check 

***SECVTX and JPB Mistags******Cross-check ***

*Rates of negative tags in various JET samples*

## SECVTX and JPB MistagsCross-check 

*Summary*

***SECVTX and JPB Mistags******Cross-check ***

## SECVTX and JPB MistagsCross-check 

*The same procedure is followed to check the JPB mistag parameterization*

***SECVTX and JPB Mistags******Cross-check ***

## Calibration of Heavy Flavor Content in the Simulation

*W****cc  and W****bb are the largest sources of backgrounds to****tt production*
*in this analysis, the fraction of W+jets with h.f. is estimated from Herwig*
*Herwig uncertainty in gluon splitting is estimated between 25% and 40%*
*Simulation needs to be calibrated*
*JET50 and JET100 data sets are compared  Herwig*
*g splitting production comparable to other mechanisms*

***Calibration of Heavy Flavor Content in the Simulation***

## Calibration of Heavy Flavor Content in the Simulation

*Use intuitive kinematical differences to distinguish gluon splitting from other h.f. production mechanisms.*

***Calibration of Heavy Flavor Content in the Simulation***

*Use ****R (in **** space) to separate direct production and flavor excitation from gluon splitting *
*Use large jet multiplicity since relative rate of gluon splitting increases with jet multiplicity*
*Fit simulation to data for*
*tagged jets in events with one taggable jet*
*tagged jets in events with one taggable jet and three or more jets*
*events with two tagged jets*
*tagged events with a companion jet within ****R<1.2*
*double tagged events with a companion jet with ****R < 1.2*

*Contributions and distances between 2 tagged SECVTX jets in JET50 MC*

*Contributions and distances between 1 tagged SECVTX jet and the closest jet with E**T**> 10 GeV in JET50 MC*

## Calibration of Heavy Flavor Content in the Simulation

*Fit results*
*b,c direct production+flavor excitation**	**	**** weight 1.11 **** 0.16*
*gluon splitting**	**	**	**	**	**** weight 1.36 **** 0.22*

***Calibration of Heavy Flavor Content in the Simulation***

*SECVTX*

*JPB*

*	**The fraction of g****bb and g****cc in the Herwig simulation needs to be increased by (39****19)% and (35****36)% respectively*

## Calibration of Heavy Flavor Content -Cross-Check

***Calibration of Heavy Flavor Content -Cross-Check***

## Composition of W+1 jet sample

***Composition of W+************1 jet sample***

*The contribution of each background to the****tt production is determined using the data or the simulations calibrated as shown previously.*
*The****tt production cross section is determined by attributing the excess of W+****3 tagged jet events completely to****tt production.*
*The following sources of background have been considered for this analysis:*
*non-W background*
*Z ***************
*single top production*
*diboson production*
*mistags in the W+jet sample*
*W +****bb and W +****cc production *
*Wc production*
*Z + heavy flavor production*

## Composition of W+1 jet sample

*Non-W background*
*determined directly from data by studying the isolation of the primary lepton in the low (E**T** **** 10 GeV) and high (E**T **** 20 GeV) E**T** regions*
*The number of non-W and tagged non-W is given by*
*	**where P**tag** is the tagging probability in region A*

***Composition of W+************1 jet sample***

## Composition of W+1 jet sample

*Z  **************  *
*background contribution evaluated using the Pythia generator and normalizing the simulation to the same number of  Z **** e**+**e**-** and Z **** ****+****-** seen in the data*
*Single Top *
*background contribution evaluated using ****= 1.5 **** 0.4 pb and the Herwig generator for the W-g fusion process, and ****= 0.74 **** 0.05 pb and the Pythia generator for the annihilation process.*
*Diboson production*
*the ZZ, WW and WZ background contributions are estimated using the Pythia generator with ****(WW)=9.5 pb, ****(WZ)=2.6 pb and ****(ZZ)=1.0 pb*
*Mistags*
* **For SECVTX and SLT the mistags are calculated weighting each jet by the mistag probability described previously. *
*In the SECVTX case, this re-evaluation reduces the background estimate by 50% compared to previous estimates. *
*The JPB mistags are included in the simulation.*

***Composition of W+************1 jet sample***

## Composition of W+1 jet sample

*W****bb + W****cc*
*the fraction of W+jet events in which only one jet contains heavy flavor is estimated with the Herwig generator*
*the fraction of W+jet events in which two different jets contains heavy flavor is estimated with the Vecbos generator*
*the tagging efficiencies are determined with the detector simulation. The number of tagged W****bb and W****cc events is:*
*	**where N**W** is the number of W events after removing the predicted number of non-W, dibosons, single top, unidentified Z and****tt events*

***Composition of W+************1 jet sample***

## Composition of W+1 jet sample

*Wc *
*the gs **** Wc and gd **** Wc contributions are evaluated in Herwig. The uncertainty is dominated by the uncertainty in the strange sea content of the proton*
*Z + heavy flavor*
*the Pythia generator is used to estimate the fraction of unidentified Z decays passing our selection after normalizing the simulation to the Z**** e**+**e**-** and Z **** ****+****-** observed in the data.*
*The fraction of Z+ heavy flavor is derived by rescaling the fraction of W+jets events with heavy flavor*
*0.3 Zc for every Wc event*
*1 Z****cc for every W****cc*
*2 Z****bb for every W****bb *

***Composition of W+************1 jet sample***

## Composition of Z+1 jet sampleCross-checks

*Since the production mechanisms of W and Z bosons in association with jets are very similar, the Z+jet sample offers a unique opportunity to check the validity of all the background calculations described previously.*

***Composition of Z+************1 jet sample******Cross-checks***

*SECVTX*

## Composition of Z+1 jet sampleCross-checks

***Composition of Z+************1 jet sample******Cross-checks***

*A Poisson probability can be calculated for each “bin prediction”  to fluctuate to the observed number of events.*
*Monte Carlo simulation shows that the probability of observing such fluctuation strongly support the conclusion that the prediction agree with the observed tagged data in the Z+jets sample. *

*SLT*

## Composition of W+1 jet sampleNegative Tags Cross-checks

*Rates of W with negative tags will check the mistag rate prediction and offer a complementary test of the method used to determine the background contributions. *

***Composition of W+************1 jet sample******Negative Tags Cross-checks***

*Data and predictions agree within the estimated uncertainties*

*SECVTX*

## Measurement of tt

***tt Cross section derived using*
*Integrated Luminosity: **	**105.1 **** 4.0 pb**-1*
*Efficiency:**	**	**7.8 **** 1.3 % for M**top**=175 GeV/c**2*
*Errors:**	**14%**	**lepton ID and trigger efficiency*
*	**	**	**5%**	**jet energy scale*
*	**	**	**5%**	****tt Monte Carlo modeling*
*Tagging efficiencies:**	**0.505 ****  0.051 **	**(SECVTX)*
*	**	**	**	**	**0.455 **** 0.46**	**(JPB)*
*	**	**	**	**	**0.157 **** 0.016**	**(SLT)*
*Since the rate of W + h.f. is estimated from the W+jet production using the fraction of heavy flavor determined above, the****tt contribution is removed from the data through an iterative procedure.*

***Measurement of ******************tt***

## Measurement of tt

*A ****5 GeV/c**2** uncertainty in M**top** introduces a **** 1.8% change in the SECVTX and JPB cross-sections and a ****2.3% change in the SLT cross-section*

***Measurement of ******************tt***

*SECVTX*

*JPB*

*SLT*

## Measurement of tt

***Measurement of ******************tt***

*SECVTX*

*JPB*

## Measurement of tt

***Measurement of ******************tt***

*SLT *

## Measurement of tt

*Combine this measurement, the dilepton and the all-hadronic measurements to obtain the best CDF measurement of ******tt**  *
*The dilepton measurement does not require b-tagging and therefore is unchanged by the revision presented here*
*The all-hadronic measurement is revised due to the new b-tagging efficiency value*
*The resulting combined ******tt**  is*
*	**	**	*

***Measurement of ******************tt***

## Prospects for Run II

***Prospects for Run II***

*The main motivations for the ******tt** measurement in Run II remain the same:*
*precision test of QCD*
*search for non-standard model production mechanisms for****tt*
*calibration of the****tt background for new physics*
*In Run I, ****/****~30% (in SECVTX) , with ~25% statistical and ~17% systematical errors. With 2 fb**-1**:*
*statistical error will decrease:*
***1.30 pb **** **** 0.30 pb or lower for the increased SVX coverage  (~ 6% of the theoretical value)*
*systematical error*
***L/L **** ****tot**/****tot** ~ 3%   (presently ****L/L ~ 4%)*
*** **presently at ~ 17%*
*Lepton ID/trigger simulation at 14%, rest (gluon radiation,MC modeling, etc.) at ~9%*
***/****~ 12 % (in SECVTX)*
*	**	**	**  **Expected RunII error ****/****~9-10% (TDR)*