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A. SidotiUniversity of Pisa - INFN
Pisa
W Cross Section Measurements at CDF
CDF
1
Italo-Hellenic School of PhysicsThe Physics of LHC:
theoretical tools and experimental challengesMartignano, Grecìa Salentina (Lecce, Italy)
May 20-25, 2004
Goals & Outline
Goals:
•Present a “high-PT” cross section measurement with
details and technicalities (that you will hardly find in articles: “Dusty corners” )
•W bosons are high-PT well known processes, present
in many decays of interesting particles -> better to know them!•Measuring (pp->W) x BF(W->e)
Outline:
Physics of hadron collisions
Tevatron collider and CDF detector
W cross section measurements
Physics Processes at hadron colliders
LHC
TeVatron1033
<1032
Luminosity
[cm-2s-1]
10
0.3
∫L
[fb-1/y]
14 LHC (low lum)
2 TeVatron
√s
[TeV]
--
--
Electron:EM CalorimetersHigh Pt Track
Neutrinos:Large Missing EnergyOnly Transverse ( Met)
Muons:Muon DetectorsHigh PT Track
W Signature: Isolated Lepton and MET
Z Signature: Two Isolated Leptons (opposite charge)
W and Z bosons at hadron collidersAt hadronic collider W and Z bosons:decaying hadronically are overwhelmed by QCD background-> identification trough leptonic decays Can be produced with additional jets
Z(W)
e/
e/ ()
p
p
q
q
Cross Section: Physics
For a given physical process: =N events-Nbkg
x L dt
= Total efficiency (Trigger x Acceptance x Selection)
L dt = integrated luminosity
Nevents = Number of events
Nbkg = Number of background eventsStrategy of the analysis:1. Identify a clean sample of We events (Estimate
background contamination)2. Evaluate efficiencies (Includes trigger, kinematics,
electron ID and acceptances)3. Evaluate integrated luminosity4. Evaluate systematics
Luminosity, L, is a measurement of the brightness of the interaction region
The event rate, R, for a given process of x-section s is given by R = L*
The luminosity is a major machine parameterHigh luminosity sensitivity to small x-section
Instantaneous luminosity at colliders:f: frequency of collisionsn1,2 = number of particles in bunchx,y = transverse (Gaussian) dimensions of beam
Luminosity at Colliders
Or:
x,y= beam emittance
*x,y = amplitude functionBeam quality: bunch preparation, from source to storage
Beam optics parameter: related to magnets configuration
(.10-9 rad.m)(m)
2.2-1.4
0.35
0.5
0.5
Tev LHC
x F(z/*)
x F(z/*)
Tevatron
For RunII: New Main Injector:
• Improve p-bar production
Recycler ring (commissioning):
• Accumulate p-bars Center of mass energy
increase s RunI = 1.8 TeVNow s RunII = 1.96 TeV
CDFDØ
Main Injector
TevatronBoosterRecycler
ChicagoWorld’s highest energy p pbar collider.First accelerator with SC dipole magnets•Started operations in 1983•RunI(1992/93 and 1994/95)•RunII(2001/xx)
Instantaneous and Integrated Luminosity increase
Tevatron: LuminosityIntegrated Luminosity is a key ingredient for Tevatron RunII success.Analysis presented here (Mar2002- Jan2003) is based on integrated luminosity (72pb-1)
Record Peak Luminosity (05/02/2004) 6.11031 cm-2 s-1
CDF Takes efficiency at >85%Silicon integrated most of runs
CDF and DØ are collecting 1pb-1/day
CDF● CDF II during silicon installation
0
= 2.0n
= 3.0n
COT
0
.5
1.0
1.5
2.0
0 .5 1.0 1.5 2.0 2.5 3.0
END WALL HADRON CAL.
Inner silicon6 layers
30
30
SOLENOID
Intermediate silicon1 or 2 layers
= 1.0
EN
D P
LUG
EM
CA
LOR
IMETER
EN
D P
LUG
HA
DR
ON
CA
LOR
IMETERn
m
m
Time of Flight
Larg
e v
olu
me w
ire-c
ham
ber
96
layers
ISL1m
SVXII
L00
Wedge of Central Calorimeter(CEM)(courtesy D. Lucchesi)
Pseudorapidity = -log tan (/2)
Looking for W->e Candidates
• W selection:– High energy electron– Electron is isolated
– Large missing ET
• MET = |vector sum of all calorimeter energy in transverse plane| ~ ET
– Jacobian peaks:
• Both lepton ET and MET peak at about ½ the W mass
– Expect correlation between ET of lepton and neutrino
W->e candidates are selected matching:•Calorimetric information Electron Cluster energy,•Track information from tracking detectors (COT and Silicon)
Cone() r=0.4
Variables(I)
Variables used for selecting events:
•ET: calorimetric energy of EM cluster with all corrections
and considering as event vertex in z the z0 of the track associated.•MET: Missing transverse energy -> Unbalance of energy in
the transverse plane MET = - ET
•Relative Calorimetric Isolation:
•Had/Em: Energy in Hadronic Calorimeter/ Energy in EM
Calorimeter
•E/P: ratio Calorimetric energy/total momentum of track•Lshr: Lateral shower profile of adjacent calorimetric towers, comparison with test beam data to electron•Track quality selection: number of hits in the COT
•|z0|: z coord. of closest approach of track with beam axis
EM energy in cone R()=0.4 around EM clusterEM cluster energy
Variables (II)Variables based on ShowerMax detector: a anode cathode strip detector plane inserted inside the EM calorimeter
Trackx
z
•Charge x X: Distance
between shower deposit
and track extrapolation
in x direction (local) times
the charge of the particle
• z: Distance between
shower deposit and track
extrapolation in z
direction
Selecting electrons(“Tight” Selection)
Variable||
Em Cluster ET
Relative Calo. Isolation (R=0.4)Ehad/Eem
E/P OR PT<50 GeV/c#Stereo COT SuperLayers#Axial COT SuperLayers
Track PT
|z0|Lshr
Charge x X2
strip
|z|Fiduciality
Cut<1.1 (CEM)>25 GeV
<0.1<0.055+0.00045 . E
<2.0≥3 with ≥7hits≥3 with ≥7hits
>10 GeV/c<60 cm
<0.2>-3.0 cm AND <1.5 cm
<10<3.0 cm
Energy Corrections
Energy Corrections
Other corrections need to be applied to electron-magnetic cluster energy:•Tower-to-tower gain corrections•Time dependent gain corrections•“Face” corrections dependent on the position of the EM shower (from Test beam data)
Check of overall energy scales are made requiring that the invariant mass of dielectron pairs peaks at the Z mass value Overall Energy scale is OK
Time Dependent CorrectionsTime-Dependent corrections are evaluated calculating the average E/P (E from calorimeter, P from track momentum measurement) as a function of run number. E/P is averaged for 0.9<E/P<1.1
Tower to Tower Corrections<
E/
P>
Tower Number
For each calorimetric tower E/P average is measured.A correction factor (corr)is evaluated to bring the <E/P> close to 1.For each tower tEE’ = E/corrt
Improvement on dielectron invariant mass resolution: 5.4 GeV/c2 4.0 Gev/c2
CES-x corrections A variation (max variation ~7%) in the energy scale is found as a function of the local x position of the CES.The <E/P> distribution is flattened using f(x).
f(x
)
After corrections
<E
corr/
Pco
rr>
Conversion RemovalElectrons coming from photon conversion are removedConversion algorithm looks for couple of opposite sign tracks with |xy|<0.2 cm AND |cot|<0.04
Transverse plane
xy Conversion radius distribution
But don’t throw the baby with the dirty water
These events (Trident) are good!
W->e eventsAfter applying the selectionNumber of observed Events: 37584
Some kinematical distributions:
Electron ET Missing Transverse Energy
Transverse MassTransverse Mass:
MT = √2(ET . MET(1-cos ))Some good properties: invariant under W boson PT (if cut not applied) -> used for W mass measurement
Digression: Z->ee Sample•One of the most useful calibration sample for high PT objects (other calibration samples are J/ee, ee):•Clean sample of electron from Z->ee is obtained.•Will be used to evaluate efficiencies
Selection criteria:•At least one “Tight” electron selection•At least one “Loose” electron
•ET>25 GeV•Opposite sign track pointing to EM Cluster•PT>20 GeV/c•|z0|<60 cm
•Invariant mass of dielectron pair 75 GeV/c2<Mee<105 GeV/c2
Backgrounds
Two sources of backgrounds:•“EWK” Electroweak processes like Z->ee and W->that mimick a genuine W->e event
Evaluated from MC•“QCD” Dijet events where one jet is lost (cracks) and the other fakes an electron
Evaluated from data
Three methods for QCD bkg evaluation:•Relative Isolation vs Missing ET •Fake Rate•Angular Correlation
EWK BackgroundZ->ee cross section is related to W->e through R:
R=x BF(We)xBF(Zee)
One can use R from theory (Stirling et al.): R = 10.67 ±0.15
Therefore NZ, number of bkg events from Z->ee:
NZ = NWC – NOther-NZ
R(W/Z)
NOther = NQCD+N
R(W/Z) = R x (W->e)/(Z->ee)
Same idea for N
N = NWC – N’Other-N
R(e/)
N’Other = NQCD+NZ
R(e/) = (W->e)/(W->)
Iterative process to determine N and NZ
“QCD” Background: “IsoRel vs MET”
The simplest and most discriminating characteristics between an “isolated” electron as the one coming from the W decay and a jet is the Isolation.There is NO correlation between Missing Transverse Energy and Isolation for dijet events faking a W->e candidate.”Isorel vs MET” method
Bkg QCD = B x C
A
IsoRel vs MetContributions of signal and “EWK” bkg in regions A, B and Cshould be subtracted from region population.
Also consider possible trigger effects
SystematicsSystematic uncertainties are evaluated measuring the number of QCD events obtained modifying the Relative Isolation and MET cut.
Relative Isolation Cut
MET Cut
Red: # QCD evts RawBlue: # QCD evts after EWK processes removal
Systematic uncertainty is evaluated ~50%
#QCD = 587±52(stat)±294(syst)
QCD Bkg: Fake Rate methodFake Rate : Probability that jet fakes an electron (events collected by a trigger requiring at least one jet with ET>20 GeV)Parameterized as a function of ET
Denominator: Events with at least two jets with ET>15 GeV MET>15 GeV and not more than one “loose” electronNumerator: Denominator && one “tight” electron
Integrating the MET spectrum for MET>25 GeV and weighting for the “prescale” trigger factor one gets:
#QCD = 800±300 evts
QCD Bkg: Angular Correlation Method
Reconsider IsoRel vs Met method.Subtraction of signal and other EWK bkg is MC based.One can use a “data-driven” methodUse angular distributions to separate QCD from W->e signal
In QCD Bkg events jet faking an electron recoils against the jet
Jet faking an electron
“Genuine Jet”
In W->e Signal events W boson recoils against the jet
Jet
uncorrelated
“True” electron
Neutrino
Angular correlationsOperative method:O-jet events are assumed “background free”Calculate between sum of jet momenta and electron
QCD Bkg
W->e signal
MET distributions for:
QCD Bkg W->e Signal
for “Non Isolated” electron sample
Subtraction
“Pure QCD Bkg” MET distributionis used on isolated sample to estimate the number of QCD events:#QCD = 594±80(stat)
Background summary
All methods to evaluate QCD background are in agreementTotal number of W->en candidates: 37574
Backgrounds
QCD
Z->ee
W->
Total
587±29
9
317±14
752±17
1656±3
00Total background contamination less than 5%
Acceptance:Evaluated using MonteCarlo W->e ( generated with Pythia)
Efficiencies:Electron ID:
Evaluated from Data Z->ee sampleTrack Matching
Evaluated using a combination of Data and MC(Z->ee CC) EM Cluster Reconstruction
Evaluated using a combination of Data and MC (Z->ee CC) Trigger
Evaluated using back up triggers from data
3333
Acceptance and Efficiencies
Acceptance Measurement
•Acceptance is calculated using MC•W->e are simulated using Pythia MC (6.203) using CTEQ5L Parton Distribution Function•A full detector simulation is used to model the behavior of the CDF detector
It is crucial to tune MC to best match Data and MC
Selection cut considered:•ET>25 GeV•MET>25 GeV•||<1.1
Acceptance: Systematic Uncertainties
Systematic to acceptance are due to uncertainties in the simulation:
Energy Scale and Resolution
W Boson Transverse momentum
Material Estimate
Recoil Energy (Modeling energy deposition in the
Calorimeters)
Parton Distribution Function Uncertainties
Pythia ParametersSeveral “knobs” in Pythia are used to modify the Z Boson PT for tuning data to MC.
Z PT Distribution for data (points) and MC (histo)
2 between Z boson PT distribution data and MC
Generator level W boson PT variations shifting one of the Pythia parameter
Pythia Parameters: Summary
To evaluate the systematic uncertainty from tuning the Pythia parameters, MC generated with 3variation are used to evaluate acceptance.A relative systematic uncertainty is evaluated to be:A/A = 0.043 %
Material EstimateCorrect amount of material in the detector should be considered. Check material budget:E/P distribution is a good observableThe ratio of the number of events in the E/P peak (0.9<E/P<1.1) to the number of events in the tails of the distribution (1.5<E/P<2.0, 2.0<E/P<2.5).The amount of material (in X0) needed is evaluated in order to have the same ratio for Data and MC
~4±2% X0 of additional material (copper) has to be added
A/A = 0.73 %
Recoil Energy
Need to tune the MC model of energy deposition in We events to have the best possibile match of MET with data.•Hadronic showering•W boson recoil energy•Underlying event•Multiple interactionsCan be inaccurate for MC and need to be tuned.
leptonneutrino
U = -(ET + MET)
U
Compare projection parallel and perpendicular to electron and tune them.
UparU’par =Kpar x Upar + Cpar
UperpU’perp =Kperp x Uperp + Cperp
Recoil EnergyShift and scale parameters are obtained after minimizing the 2 for the distributions of U for data and MC.
Before tuning After tuning
MET is then recalculated using the tuned recoil energy U’:
MET’=-(ET+U’)
A/A = 0.25 %
PDF Uncertainties•Momentum distributions of quarks and gluons are required as an input for MC simulation•We will use the CTEQ6 PDF•CTEQ6 are determined after minimizing a 2 for global data.•After diagonalization of the covariance matrix a new set of CTEQ6 with “errors” can be extracted
20 sets of PDFs with ±1- are available
PDF systematic uncertainties are extracted from relative changes in the acceptances
It is not necessary to run the whole simulation.Can stop at generator level
A/A = +1.2/-1.4 %
Systematic Uncertainties for Acceptance: Summary
Source
Energy scale
Energy Resolution
Recoil Energy
W Boson PT
Material
Total
A/A (%)
0.34
0.03
0.25
0.04
0.73
+1.2/-1.4
+1.43/-1.64
A(%)
0.08
0.01
0.06
0.01
0.17
+0.28/-0.34
+0.34/-0.39
Total Acceptance = 23.96%
Efficiencies
Need evaluate efficiencies for:ID: electron ID (E/P, Lshr, etc…)Tracking: reconstructing the track of the high-pT lepton in the COTReconstructing: reconstructing EM cluster (calorimeter)TriggerAll these efficiencies are “conditional” efficiencies: i.e. provided that the requirements above are matched
In this way we are taking correctly into account correlations among variables
Order matters!
ID Efficiencies
ID efficiency are measured using the second leg of a Z->ee decay.•One leg is required to be tight•The other (probe electron) is required to pass:
•ET>25 GeV•Opposite sign track pointing to the EM Cluster with PT>10 GeV/c and |z0|<60 cm
•Invariant mass 75 GeV/c2<Mee<105 GeV/c2
NCC = #events passing cuts aboveNTT = #events with both electrons tightNTi = #events with one tight, one probe an passing i-th ID cutFor a single selection cut (i-th):
iID= NTi+NTT
NCC + NTT
Eff = 81.8±0.8 %
ID Distributions
ID Distributions
Track ReconstructionEfficiency is measured on a un-biased sample with respect to COT tracks.•Data collected with W_NOTRACK•MET>25 GeV AND ET>25 GeV•No extra jet in the event•Had/Em<0.05, Lshr<0.2, 2
strip<10,•Only Silicon reconstructed track pointing to EmCluster
Trk=#events passing above cuts
#events passing selection cut + COT track pointing to EM Cluster
Eff = 99.7±0.2 %
EMCluster reconstruction
The EM cluster reconstruction efficiency is defined as the efficiency to reconstruct a EMcluster corresponding to a high-pT electron. Possible inefficiencies in this procedure might come from:•Detector failures (dead towers, proton beam splashes)•Code inefficiencies (bugs)
Efficiency measured on sample obtained requiring a “very tight track” (high quality track)
Eff = 99.0±0.4 %
Physics Processes at hadron colliders
LHC
TeVatron1033
<1032
Luminosity
[cm-2s-1]
10
0.3
∫L
[fb-1/y]
14 LHC (low lum)
2 TeVatron
√s
[TeV]
--
--
Triggers ad CDF
Analyzed events have been collected by a three level trigger:•L1_CEM8_PT8: single central EM calorimetric tower with ET>8 GeV and a track with PT>8GeV/c pointing to it•L2_CEM16_PT8: Central EM clusters are clustered. Energy of cluster > 16 GeV and Had/Em<0.125•L3_CEM18_PT8: Reconstructed offline clusters with Energy>18 GeV and Had/Em<0.125 + other requirements (Analysis selection cuts).
Trigger Efficiency: Strategy
•Use data collected by trigger paths different from the one used for the analysis (backup triggers)•Apply offline selection cuts•Measure efficiency:
= #Events Triggers Fired (Data AND Backup) AND Offline cuts
#Events Trigger Fired (Backup) AND Offline cuts
Need to evaluate trigger efficiencies.We have a trigger simulation but prefer to evaluate trigger efficiencies from data.What we need is the “conditional trigger efficiency” i.e. Trigger efficiency provided that analysis selection passed:(Trigger|Analysis selection)
Track Trigger EfficienciesTrack Trigger Efficiencies:Evaluated using the W_NOTRACK trigger pathW_NOTRACK has no track requirement at trigger level but requires MET>25 GeV.
L1_PT8 efficiency vs L3_PT8 efficiency vs |
Calorimetric Trigger EfficienciesUse “prescaled” backup trigger paths with some “missing” trigger primitives
L1_EM8 efficiency vs Highest EM Tower ET L2_CEM16 Trig Eff. vs ET
Efficiency Summary
Selection
Tracking
EM Reco
ID
Trigger
Eff (%)
99.7±0.2
99.0±0.4
81.8±0.8
96.6±0.1
Luminosity at CDFII
Howto Measure Luminosity
Different methods have been used since ISR times.Will focus on CDF RunII method
For a defined physical process:
Nint = L x
Where:L is the instantaneous luminosityNint is the interaction rate for the process with cross section
Measuring Luminosity at CDFII
For RunII CDF build the CLC (Cherenkov Luminosity Counter) to measure instantaneous luminosity
For a defined selection criteria {}: x fBC = int x CLC x LWhere: = <# Interactions/Bunch Xing>fBC = Frequency of collisionsL = Inst. Luminosityint = cross section of physical processCLC = CLC efficiency{} Defines a collision (thresholds, timing, etc…)
Measuring Luminosity at CDFIIPhysics process is inelastic ppbar scattering.Operationally can be computed as: (other possibilities: no interactions / bunch Xing, etc.)
= <NH>
<N1H>
Average Number of hits in CLC per bunch Xing
Average Number of hits in CLC per single ppbar interaction
L = fBC . <NH>
in . CLC. <N1H>
Uncertainties:Efficiency of CLC (based on MC) Measuring average number of hits (PMT gains, detector stability)Inelastic ppbar cross section (2.8 between CDF and E811)Overall Luminosity uncertainty(~6%)
Luminosity at CDFII
59
For a high luminosity environment measurements based on Cherenkov radiators have advantages over Beam-Beam Counters (RunI):
•Can discriminate between particles from primary interaction and secondary interaction (beam-halo,…)•Can count number of hits Increased precision measuring multiple interactions•Insensitive to low momentum particles (Cerenkov threshold 2.2 GeV/c for )•Excellent time resolution (t~100ps) (can identify in-time collisions)
Luminosity Region CorrectionThe requirement that the event vertex fall within ±60 cm of the center of CDF limits the event acceptance to a portion of the full luminous region of p p collisions while the luminosity reported by the CLC detector is over the full luminous region in z.
Efficiency is measured on events collected by “Minimum bias” trigger.
pp beam luminosity function (~ z vertex distribution)
= 95.0±0.4 %
Z Vertex distribution
Measured Zvtx Distribution fit to the luminosity function n = 100 bins, 2 = 119
Summary
Other EWK measurement:Extension in the “Forward Region”
Extension of acceptance in the higher h region.EM cluster from “Plug” calorimeters.Larger role played by tracks reconstructed only with silicon (silicon standalone tracking algorithm)
Extended pseudorapidity electron coverage+Forward Tracking1.1<||Ele<2.8
Small background contamination (QCD, W,Z ee) (~6% e, ~11 % )Systematics from PDF, energy scales, material description
xBF = 2.874± 0.034 (stat) ±0.167(syst) ± 0.172(lum) nb
Z and W cross section x BR(W/Z->l/ll)
20 years of W and Z at hadronic colliders!
CDF Run II Electron 1.1<||<2.8
Measuring Ratio R of x BF
R BF(p p
_
W lv)
BF(p p_
Z ll )
(p p_
W )
(p p_
Z) (Z)
(Z ll)(W l l )
(W )
(W) can be extracted indirectely.
From LEP
From Theory:Rosner et al.
From Theory: Van Neerven
R Measurements:R e-channel:R -channel:R Combined(W)(MeV)
10.860.18 0.1611.100.27 0.1710.940.150.132071 40
10.340.5911.320.76
2187128
CDF
DØ Theory
10.66 0.05
2092 ± 40 World Average
2150 ± 90 LEP Direct
From R to W width Measurement
Lepton UniversalityFrom W decaying in e and :
2
2
)(
)(
We
W
e g
g
eW
W
R
RU
From W decaying in :
2
2
)(
)(
We
W
e g
g
eW
W
R
RU
g/ge
CDF measurement0.990.040.07
g/ge
CDF measurementWorld Average
1.0110.0180.9930.025
Z Forward Backward Asymmetry
...cos)cos1(
)0(cos)0(cos
)0(cos)0(cos
2
BA
dd
ddAFB
Probing (Unique at Tevatron):
• Z/* Interference in High Invariant
Mass Region (far from Z-pole)
Consistent with SM
Constraints on non-SM Z Couplings
soon!
SM Contributions
Beyond SM(Z’,New Interactions)
W gammaZ gamma
Non SM!
•DiBoson Coupling Measurements:•Probe ewk boson self-coupling•Sensitivity to physics BSM(Anomalous Couplings)
Triple Boson coupling
DiBoson Production
W- Z-
DiBoson Production
Non SM
W-gamma
Selection Cuts
•One High-PT lepton(e,)
•One Photon(R(,l)>0.7)
•Large Missing ET
SM @s=1.96TeV19.3 ± 1.4
19.7±1.7stat±2.0sys±1.1lum29%259e+
•B(Wl) (pb)BackEvents
Consistent with SM
ET()
probing anomalous couplings
5.5±1.7stat±0.6sys±0.3lum6.8%69
•B(Z-->ll) (pb)Back.
Events
•Two High-PT Leptons(Opposite
sign)
•One Photon (R(l,) >0.7)
Process:
pp->Z->ll
Consistent with SM•B(Z-->ll)SM= 5.4 ± 0.3pb
e+
Z-gamma
Two complementary approaches:
•Sensitive to WWγ and WWZ vertex•Higgs discovery channel•Right place to look for new Physics
14.3 +5.6 –4.9 (stat) 1.6 (sys) 0.9(lum) pb
Data 39
WW signal
16.3 ± 0.4
Bkg 15.273.55
BR(WWℓ+ℓ- )Th = 12.50.8pb(NLO)
Ldt=200pb-1
19.1 5.0 (stat) 3.6 (sys) 1.1(lum) pb
Dilepton selection (l+l-) (small yield and background)
Tight Lepton + Isolated Track selection(larger yield and background)
WW Production
Data 17
WW signal
11.3 ± 1.3
Bkg 4.8 ±0.8
Consistent with SM
W Mass measurement: RunIThe Tevatron Run 1 combined W mass measurement was ready six years after end of RunI
In Run I larger uncertainties coming from:StatisticsDetector Energy responseW Transverse MomentumPDF (correlated between experiments)
Method: fit Transverse Mass distributions to MC varying MW, including:•detectors effects,•W decay•W production model
W Mass measurement: RunI
Run I Tevatron
New Run I Top Mass Combined Measurement
W Boson mass SM key parameter and for SM Higgs mass constraints
W Mass measurement: Run II Prospects
direct extractio
n of (W)(W)
Almost all systematic uncertainties will decrease with statistics(control samples)Goal for Run II (with 250 pb-1) CDF Run II estimate (μμ)): = X±55(stat)±80(sys) MeV/c2
We need to improve uncertainties:•Radiative corrections (electrons)•QCD effects in W/Z production
Tevatron Run II Predictions
Thanks!
I would like to thank the organizers of this first LHC School whishing many others and successful future editions!
Backup Slides
ID FormulaN: number of Z->ee eventsT: efficiency of one leg passing tight cutsi: efficiency for one probe leg passing i-th ID cutNCC = (2.T(1-T)+T
2) x NNTT = T
2 x NNTi = (2 T i – T
2) x N
Solving for T and i:
i=NTi+NTT
NCC + NTT
T= 2NTT
NCC + NTT
79
Met
(G
eV)
Et (GeV)
Starting dataset
After Selection
10461 Events
Background ~5%79
MET vs Electron EtAll candidatesSelected by trigger MET_PEM
After whole selection chain
W->e candidates
Transverse Mass
8080
Kinematical Distributions
81
Electron ET Missing Transverse Energy
81
Xsection: ResultsCDF RunII Preliminary result:
xBF = 2.874 0.034 (stat) 0.167(syst) 0.172(lum) pb-1
82
For comparison, measurements in Central region are:
xBF(W->e) 2.782 0.014 +0.061-0.056 0.167 nb
xBF(W-> )2.772 0.014+0.064-0.060 0.166 nb
First CDF measurement of W cross section in PLUG region
xBFTHeory
= 2.687 0.054 pb-1 (Stirling, NNLO)
82
Conclusions
83
Result for 64pb-1 was blessed on March 18
Analysis of 200 pb-1 already started
(will be used for publication)
Basic work to select a ttbar enriched sample started (T.Staveris)
Stay tuned for more physics to come from large eta
83
References
84
Some References:
Measurement of the s x BF(W->enu) in the Plug Region using Calorimetric and Forward Tracking (CDF Note 6535)
Trigger Efficiencies for Plug Electrons in Run II (CDF Note 6864)
Face energy corrections
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