W D Run II

1
W _at_ DØ Run II
Carsten Magaß magass_at_fnal.gov
III. Physics Institute A RWTH Aachen
NP Meeting August 12, 2004
2
New Particles beyond Standard Model
(and SUSY)
Many ideas from theorists (? R. Mohapatra,
Unification and Supersymmetry, chap. 6. 8. )

• Search for new heavy gauge bosons
• Search for lepton compositeness

• In these analysis we use
• well defined electron identification
• isolated electrons with high transverse momenta

. . . just started . . . collecting ideas
3
Heavy Gauge Bosons
Heavy gauge bosons predicted by numerous
extensions to SM
e.g. Left Right symmetric model of weak
interactions
Many analyses on production ? consider
charged heavy boson

• Parameters
• mass, width

• Additional
• mixing (mass eigenstates ? group eigenstates)
• new fermion boson couplings
• new CKM matrix

Often Make assumptions to get rid
of new parameters
? No mixing, ,
(top quark)
4
Heavy Gauge Bosons (contd)
Run I ? Run II ./. ? new, better limits ?
SM background W, QCD
Excluded
_at_
Taken from Search for Heavy W Bosons in 1.8 TeV
pp Collisions, DØ, 1995
5
Monte Carlo What do we expect ? (1) Numbers
Finished
Production of MC
(Pythia full Detector Simulation)
Steps of 100 GeV, 5000 events each
Cross sections ? Pythia (LO) multiplied by fixed
K factor of 1.34
W ???
6
Monte Carlo What do we expect ? (2)
Comparison Impact of W Mass
500 GeV 700 GeV 900 GeV 1 TeV
W

• Increasing mass
• ? Cross sections drops rapidly
• Jacobian Peak is smeared (? even not visible)
• flat distribution over wide range (here pT,
  mT)

7
Monte Carlo What do we expect ? (3)
Comparison W and W
8
W maybe an explanation for this guy . . .
9
DATA and MC samples
Data Common Samples Skim EM1TRK

• badLBN (runrange_luminosity)
• badruns (CAL, JET/MET, SMT, CFT)
• tmb ? root with TopAnalyze Stradivarius
• additional skimming (MET and pT cut)

Actual part of pre-shutdown data used as
test-sample
(valid for all numbers and plots in this talk)
MC
New Phenomena Page WW, WZ, ZZ inclusive samples
from Ulla Top Page
Reconstruction efficiencies
.root - samples provided by the Top Group
10
Electron and Event Selection
(1) Electron candidate
Minimum quality requirements

• ID 10, 11
• iso lt 0.15
• emf gt 0.9
• CC hdetlt1.1
• infiducial
• pT gt 30 GeV

Tight selection

• hmx7 lt 50.
• lhood gt 0.5

QCD estimate (from DATA) hmx7 gt 50.
(2) MET

• MET gt 30 GeV

(3) Event

• not bad (LBN, runquality)
• triggered

OR of EM_HI_ trigger (v8 v11) OR of E_SH30,
E_SHT20 (v12)
11
Why gtCClt and gtinfiduciallt ?

• Well understood region, description in MC
  reasonable
• Cutflow

12
Preselection
13
QCD Fit to DATA
14
Nasty thing Efficiencies in DATA and MC
Standard procedure ( . . . not inventing the
wheel again . . . ) tag and probe method
using
Minimum requirement CC, infiducial, pTgt25 GeV,
80 GeVltmeelt100 GeV
? 0.93
Trigger efficiency ? not yet considered for MCs
BUT Because of high pT threshold should be
near 100 .
15
All Cuts Applied
16
All Cuts Applied
17
Statistical Method Binned Likelihood
e.g. DØ Note 4214 (Z ? ee)
Better Limit on
? Systematic incertainties cancel !!!
Poisson statistics gaussian fluctuation of
errors
Number of W events observed
Normalization
Signal background events in bin i
Limit
18
Proof of Principle

• Distribution transverse Mass
• binning 10 bins, whereas

Done automatically, only looking at Signal MC (of
course NOT looking at DATA ! ! !)
19
. . . it works !
CAUTION VERY PRELIMINARY !!!

• poor MC statistic in higher bins
• only statistical errors,
• NO systematic effects considered yet

20
Outlook
Just started to have a look at decaying in
the electron mode

• analysis tools prepared ? debugging !!!
• trigger efficiency (minor point)
• more MC ? tails in distributions
• expand to full (CS) dataset
• optimize topological cuts to enhance S/B
• later systematics (QCD background)

. . . Evidence for new physics or
give just new limits . . .