Tevatron Physics

1
Tevatron Physics

• 4.1 QCD - Jets and Dijets, ?s determination
• 4.2 Prompt Photons
• 4.3 b Production at Fermilab
• 4.4 t Production at Fermilab
• 4.5 D-Y and Lepton Composites
• 4.6 EW Production
• W Mass and Width
• Pt of W and Z
• bb Decays of Z, Jet Spectroscopy
• 4.7 Higgs Mass from Precision EW Measurements

2
Kinematics
Initial State
3
Kinematics - II
Final State
4
Jet Et Distribution and Composites
Simplest jet measurement - inclusive jet ET . Jet
defined as energy in cone, radius R. Classical
method to find substructure. Look for wide angle
(S wave) scattering. Limits are ? ?s.
5
CDF Run II Data reach
6
Dijet Et Distribution Run I
As ?3 - ?4 increases MJJ increases and the
cross section decreases. The plateau width
decreases as ET increases (kinematic limit)
7
Dijet Mass Distribution
Falls as 1/M3 due to parton scattering and (1-
M/?s)12 due to structure function source
distributions. Look for deviations at large M
(composite variations or resonant structure due
to excited quarks).
8
Initial, Final State Radiation
The initial state has no transverse momentum.
Thus a 2 body final state is back-to-back in
azimuth. Take the 2 highest Et jets.
9
2 and 3 Jets and ?s
running of the coupling constant (later). As Q2
--gt? ?s(Q2) --gt 0. Gluons have color charge
unlike photons, so they mutually
interact JJJ to JJ cross section depends on
the strong coupling constant
Coupling strength decreases as mass increases
10
Running of ?s
Energy below which strong interaction is strong
11
Precision ?s Measurement
Tevatron
12
Excited Quark Composites
q
q
g
Look for resonant JJ structure, with a limit
C.M. energy
13
t Channel Angular Distribution
If t channel exchange describes the dynamics,,
then ? distribution is flat - as in Rutherford
scattering. Deviations at large scattering angles
would indicate composite quarks.
14
Prompt Photons Run I
2--gt 2 processes similar to jets. Down by
coupling and source factors Also useful in jet
balancing for calibration. Important SM
background in Higgs searches. ug--gtu? uu-
-gt??
15
Diphoton, CDF Run II
16
Comphep Tree Only
Tevatron, 2 TeV ?lt1, ETgt10 GeV
17
B Production _at_ FNAL
d?/dPT 1/PT3 so ?(gt) 1/PT2 Spectrum is as
expected with PT M/2, gg --gt b b.
Adjustment in b -gt B fragmentation function
resolves the discrepancy
18
B Production - II
Note rapidity plateau which extends to ?y 5 at
this low mass, 2mb scale.
19
B Lifetimes
Use Si tracker to find decay vertices and the
production vertex. ?(B) ?(b). For Bc both the b
and the c quark can decay gt shorter lifetime
20
CP Violation - Unitary Triangle
The mass scale is 10 GeV, so the cross section
is large at LHC, 0.1 mb, and the Tevatron.
Therefore high statistics data can be obtained at
CDF, D0, BTeV, LHCb as well as at ee- machines
such as Belle and Babar
In the SM all CP violation is due to a single
complex phase in the quark mixing matrix too
small to explain the baryon asymmetry -gt
leptogenesis?
21
Weak Decay Widths
Fermi theory
Standard Model
m?
W
G2
2 body weak decay
t -gt W b
22
Top Mass and Jet Spectroscopy
D0 - lepton jets t--gtWb W--gtJJ, l?
23
Jet Spectroscopy - Top
CDF - Lepton jets (Si or lepton tags) t--gtWb so
2 bs in the event
24
tt --gt WbWb, W--gt qq or l?
CDF D0 Top quark mass from data taken in the
twentieth century
25
Top Mass _at_ FNAL
Run I Run
II
26
Top Production Cross Section
gt 100x gain in going to the LHC
Are the mass and the cross section consistent
with a quark with SM couplings?
27
Run II Top Cross section
No evidence for deviation from SM coupling of a
heavy quark.
28
DY and Lepton Composites
Drell-Yan Falls with the source function. For
ud the W is prominent, while for uu the Z is the
main high mass feature. Above that mass there is
no SM signal, and searches for composite leptons
or sequential W, Z are made.
Run I
29
Extract V,A Coupling to Fermions
F/B asymmetry allows an extraction of the A and V
couplings, gA, gV of fermions to the Z at high
mass compare to SM.
30
Run II DY High Mass
31
Run II DY High Mass
Whole zoo of new Physics candidates all still
null.
32
W - High Transverse Mass
Run I
Search DY at high mass for sequential W. Mass
calculated in 2 spatial dimensions only using
missing transverse energy.
33
W - SM Mass and Width Prediction
Mass
W
Width
Color factor of 3 for quarks. 9 distinct dilepton
or diquark final states.
34
Comphep W BR
Check that the naïve estimates are confirmed in
Copmhep.
35
W,Z Production Cross Section
36
Lumi with W, Z ?
At present in Run II, using W,Z is more accurate
than Lumi monitor
37
W and Z - Width and Leptonic B.R.
Expect 1/9 0.11
Expect 9 (0.21 GeV) 1.8 GeV
38
Direct W Width Measurement
Far from the pole mass the Breit Wigner width
dominates over the Gaussian resolution
decay widths of 1.5 to 2.5 GeV
Monte Carlo
39
W Transverse Mass
D0 and CDF transverse plane only. Use Z as a
control sample. At large mass dominated by the BW
width, since falloff is slow w.r.t the Gaussian
resolution.
40
W Mass Colliders, Run I
Hadron
WW production near threshold (Chpt. 1 )
41
W Mass - All Methods
Direct
Precision EW measurements
42
I.S.R. and PTW
u d
W
g
2--gt1 has no F.S. PT. Recall Chpt.1 - charmonium
production. There are F.S. radiation modes where
W or Z radiates a H (Chpt. 5) Higgs
Bremmshtrahlung
43
Comphep - PTW
Basic 2 --gt 2 behavior, 1/PT3. . Gluon radiation
from either initial quark.
44
Lepton Asymmetry at Tevatron
45
CDF Lepton Asymmetry
Positron goes in antiproton direction Electron
goes in proton direction ? Charge asymmetry,
constrains PDF
46
Comphep - Asymmetry
Comphep generates the asymmetry. Can use the PDF
that Comphep has available to check PDF
sensitivity
47
Z --gt bb
Dijets with 2 decay vertices (b tags). Look for
calorimetric JJ mass distribution. Mass
resolution, dM 15 GeV. This exercise is
practice for searches of JJ spectra
48
Run II Mass resolution
Using tracker information to replace distinct
energy deposit in the calorimetry for charged
particles with the tracker momentum which is
more precisely measured. Seems to gain 20.
This is important for Higgs searches (Chpt. 5)
49
VV at Tevatron - W? from D0
The WW ? vertex as measured at Run II is
consistent with the SM, as it is at LEP II.
50
WW at D0 Run II
Look at dileptons plus missing transverse energy.
Tests the WWZ and WW ? vertex as at LEP - II
51
WW Cross Section Measured at CDF
Extrapolate to LHC energy. COMPHEP gives a D-Y
WW cross section at the LHC of 72 pb.
52
W mass Corrections due to Top, Higgs
Klein-Gordon Dirac
W mass shift due to top (m) and Higgs (M)
53
2 - What is MH and how do we measure it?

• The Higgs mass is a free parameter in the current
  Standard Model (SM).
• Precision data taken on the Z resonance
  constrains the Higgs mass. Mt 176 - 6 GeV, MW
  80.41 - 0.09 GeV. Lowest order SM predicts
  that MZ MW/cos?W.. Radiative corrections due to
  loops.
• Note the opposite signs of contributions to mass
  from fermion and boson loops. Crucial for SUSY
  and radiative stability. (Chpt. 6)

b t H W
W W
W W
54
CDF D0 Data Favor a Light Higgs
55
Top and W Mass and Higgs
1 s.d contours all precision EW data A light H
mass seems to be weakly favored.
56
Precision EW Data and Higgs Mass
More data from Run II at the Tevatron will help
to test the low mass Higgs region.