High PT Hadron Collider Physics

1
High PT Hadron Collider Physics

• Outline
• 1 - The Standard Model and EWSB
• 2 - Collider Physics
• 3 - Tevatron Physics
• QCD
• b and t Production
• EW Production and D-Y

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Backup Text
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Units
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Tools Needed
(will use both during lecture demonstrations)
( Google them all also Ghostview and Acrobat
reader )
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COMPHEP Models and Particles
Can edit the couplings e.g. ggH Use SM Feynman
gauge Watch for LOCK
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COMPHEP - Process
1-gt 2,3 1-gt 2,3,4 1,2 -gt3,4 1,2 -gt3,4,5 1,2-gt
3,4,5,6 (slow) x options No 2 -gt 1
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COMPHEP Simpson, BR
Find simple 2-gt2. Graphs (with menu) Results can
be written in .txt files Several PDF, p and
pbar, Check stability of results
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COMPHEP - Cuts
May be needed to avoid poles or to simulate
experimental cuts, e.g. rapidtiy or mass or Pt.
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COMPHEP - Cuts
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COMPHEP - Vegas
Full matrix element calculation interference.
Watch chisq approach 1. Setup plots, draw them
and write them.
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COMPHEP - Decays
Strictly tree level. Does not do loops or box
diagrams. Explore this very useful tool. If
there are problems bring them to the class and
well try to fix them.
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1 - The SM and EWSB

• 1.1 The Energy Frontier
• 1.2 The Particles of the SM
• 1.3 Gauge Boson Masses and Couplings
• 1.4 Electroweak Unification
• 1.5 The Higgs Mechanism for Bosons and Fermions
• 1.6 Higgs Interactions and Decays

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The Energy Frontier
Historically HEP has advanced with machines that
increase the available C.M. energy. The LHC is
designed to cover the allowed Higgs mass range.
Colliders give maximum C.M. energy.
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The Standard Model of Elementary Particle Physics

• Matter consists of half integral spin fermions.
  The strongly interacting fermions are called
  quarks. The fermions with electroweak
  interactions are called leptons. The uncharged
  leptons are called neutrinos.
• The forces are carried by integral spin bosons.
  The strong force is carried by 8 gluons (g), the
  electromagnetic force by the photon (?), and the
  weak interaction by the W Zo and W-. The g and ?
  are massless, while the W and Z have 80 and 91
  GeV mass respectively.

J 1
g,?, W,Zo,W-
Force Carriers
u d
c s
t b
2/3 -1/3
Quarks
J 1/2
Q/e
e ?e
? ???
? ??
1 0
Leptons
J 0
H
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Gravity Hail and Farewell
Ignore gravity. However, gravity is a precursor
gauge theory which is non-Abelian. The gauge
quanta are charged ? non-linearity. The gravity
field carries energy, or mass. Therefore,
gravity gravitates. This is also true of the
strong force (gluons are colored) and the weak
force (W,Z carry weak charge). The photon is the
only gauge boson which is uncharged.
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How do the Z and W acquire mass and not the
photon?

• Gravity - Physics is the same in any local
  general coordinate system --gt metric tensor or
  spin 2 massless graviton coupled universally to
  mass GN.
• Electromagnetism - Physics is the same regardless
  of wave function phase assigned at each local
  point --gt massless, spin 1, photon field with
  universal coupling e
• These are gauge theories where local invariance
  implies massless quanta and specifies a universal
  ( GN, e ) coupling of the field to matter.
• Strong interactions are mediated by massless
  gluons universally coupled to the color
  charge of quarks gs.
• Weak interactions are mediated by massive W,Z,W-
  universally coupled to quarks and leptons.
  gWsin?W e. How does this spontaneous
  electroweak symmetry breaking occur? (Higgs
  mechanism)

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Lepton Colliders - LEP
Z peak L and R leptons have different
couplings to the Z. There is Z-photon
interference which leads to a F/B asymmetry. A
way to measure the Weinberg angle. gW measured
from muon decay.
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Field Theory
Classical Special Relativity Lagrangian density,
P is an operator Classical gauge
replacement Quantum gauge replacement
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WW in ee- Collisions
Test of self-coupling of vector bosons. There are
s channel Z and photon diagrams, and t channel
neutrino exchange. Test of VVV couplings. In
COMPHEP play with the Breit-Wigner option as s
dependence of the cross section depends crucially
on the W width i.e. technique to measure W
width..
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Simpson Angular Dist
Cross section without neutrino exchange in the t
channel. Note divergent C.M. energy dependence
voilates unitarity.
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WW Cross Section at LEP
COMPHEP point shown. Proof that the WWZ triple
gauge boson coupling is needed and that there are
interfering amplitudes that themselves violate
initarity.
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WW? at LEP
Probe of quartic couplings. LEP data confirms
SM WWAA, WWZA
Cross section in COMPHEP with all final state
bosons having Pt gt 5 GeV is 0.36 pb
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ZZ at LEP
SM has only the single Feynman diagram. There are
no relevant triple or quartic couplings in the
SM. Use the data to set limits on couplings
beyond the SM.
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ee- Cross Sections
WW, ZZ, and WW? are seen at LEPII. At even higher
C.M. energies, WWZ and ZZZ are produced -
indicating triple and quartic V couplings. New
channels open up at the proposed ILC. Try a few
(red dots) processes yourself..
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ILC Process - Example
Cross section 1 fb at 500 GeV in COMPHEP.
Approximate agreement with full calculation.
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The Higgs Boson Postulated
Potential
Lagrangian density Minimum
at a non-zero vev
cosmological term
This is Landau-Ginzberg superconductivity much
too simple?
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How the W and Z get their Mass

• Covariant derivative contains gauge fields W,Z.
  Suppose an additional scaler field ? exists and
  has a vacuum expectation value. Quartic couplings
  give mass to the W and Z, as required by the data
  V(r) e(exp(-r/?)/r) - weak at large r,
  strength e at small r.

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Numerical W, Z Mass Prediction

• The masses for the W and Z are specified by the
  coupling constants. G comes from beta decays or
  muon decay.

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Higgs Decays to Bosons

• Field excitations gt interactions with gauge
  bosons VVH, VVHH, VVV, VVVV

Higgs couples to mass. Photons and gluons are
massless to preserve gauge symmetry unbroken.
Thus there is no direct gluon or photon coupling.
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ZZH Coupling and ILC Production
ILC at 500 GeV C.M. Higgs production by off shell
Z production followed by H radiation, Z -gtZH.
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Higgs Coupling to Fermions

• The fermions are left handed weak doublets and
  right handed singlets. A mass term in the
  Lagrangian, is
  then not a weak singlet as is required.
• A Higgs weak doublet is needed, with Yukawa
  coupling,

Yukawa Mass from Dirac Lagrangian
density Fermion weak coupling constant
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Higgs Decay to Fermions

• The threshold factor is for P wave, ?2l1 since
  scalar decay into fermion pairs occurs in P wave
  due to the intrinsic parity of fermion pairs.
• The Higgs is poorly coupled to normal (light)
  matter
• gt gW (mt/ MW)/?2 1.0, so top is strongly
  coupled to the Higgs.

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The Higgs Decay Width
The Higgs decay width, ? scales as MH3. Thus at
low mass, the detector defines the effective
resonant width and hence the time needed to
discover a resonant enhancement. At high masses,
the weak interactions become strong and ??/M 1.
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Higgs Width - WW ZZ
Higgs decays to V V have widths ? M3 Try this
as a COMPHEP example
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Higgs Width Below ZZ Threshold
Below ZZ threshold, decays can occur in the tails
of the Breit Wigner Z resonance, with ? 2.5
GeV, M 91 GeV. This compares to the width to
the heaviest quark, b at a Higgs mass of 150
GeV. Means that WW is an LHC strategy.
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Early LHC Data Taking

• We have seen that the Higgs couples to mass.
  Thus, the cross section for production from
  gluons or u, d quarks is expected to be small.
• Therefore, it is a good strategy to prepare for
  LHC discoveries by establishing credibility. The
  SM predictions , extrapolated from the Tevatron,
  should first be validated by the LHC
  experimenters.

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Vector Bosons and Forces
The 4 forces appear to be of much different
strength and range. We will see that this view is
largely a misperception.
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2 - Collider Physics

• 2.1 Phase space and rapidity - the plateau
• 2.2 Source Functions - protons to partons
• 2.3 Pointlike scattering of partons
• 2.4 2--gt2 formation kinematics
• 2.5 2--1 Drell-Yan processes
• 2.6 2--gt2 decay kinematics - back to back
• 2.7 Jet Fragmentation

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Kinematics - Rapidity

• One Body Phase Space
• NR

Rapidity
Relativistic
Kinematically allowed range in y of a proton with
PT0
If transverse momentum is limited by dynamics,
expect a uniform distribution in y
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Rapidity Plateau
Monte Carlo results are homebuilt or COMPHEP -
running under Windows or Linux
Region around y0 (90 degrees) has a plateau
with width ?y 6 for LHC


LHC
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Rapidity Plateau - Jets
For ET small w.r.t sqrt(s) there is a rapidity
plateau at the Tevatron with ?y 2 at ET lt 100
GeV.
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Parton and Hadron Dynamics
For large ET, or short distances, the impulse
approximation means that quantum effects can be
ignored. The proton can be treated as containing
partons defined by distribution functions. f(x)
is the probability distribution to find a parton
with momentum fraction x.
Proceed left to right
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The Underlying Event
The residual fragments of the pp resolve into
soft - PT 0.5 GeV pions with a density 5 per
unit of rapidity (Tevatron) and equal numbers of
??o?-. At higher PT, minijets become a
prominent feature
s dependence for PT lt 5 GeV is small
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COMPHEP - Minijets
p-p at 14 TeV, subprocess gg-gtgg, cut on Ptggt 5
GeV. Note scale is mb/GeV
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Minijets - Power Law?
pp(gg) -gt g g
The very low PT fragments change to minijets -
jets at low PT which have mb cross sections at
10 GeV. The boundary between soft, log(s)
physics and hard scattering is not very
definite. Note log-log, which is not available in
COMPHEP must export the histogram
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The Distribution Functions

• Suppose there was very weak binding of the uud
  valence quarks in the proton.
• But quarks are bound, .
• Since the quark masses are small the system is
  relativistic - valence quarks can radiate
  gluons gt xg(x) constant. Gluons can decay
  into pairs gt xs(x) constant. The distribution
  is, in principle, calcuable but not
  perturbatively. In practice measure in
  lepton-proton scattering.

x 1/3, f(x) is a delta function
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Radiation - Soft and Collinear
?,k
The amplitude for radiation of a gluon of
momentum fraction z goes as 1/z. The radiated
gluon will be collinear - ? k gt ? 0.
Thus, radiated objects are soft and collinear.
P (1-z)P
Cherenkov relation
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COMPHEP, et-gtetA
Use heavy quark as a source of photons needed
to balance E,P. See strong forward
(electron-photon) peak.
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Parton Distribution Functions
In the proton, u and d quarks have largest
probability at large x. Gluons and sea
anti-quarks have large probability at low x.
Gluons carry 1/2 the proton momentum.
Distributions depend on distance scale (ignore).
valence sea gluons
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Proton Parton Density Functions
g dominates for x lt 0.2 At large x, x gt 0.2, u
dominates over d and g. sea dominates for x lt
0.03 over valence.
Points are simple xg(x) parametrization.
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2--gt2 Formation Kinematics
x1
x2
E.g. for top quark pairs at the Tevatron, M 2Mt
350 GeV. ltxgt ??350/1800 0.2 Top pairs
produced by quarks.
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Linux COMPHEP

• g g-gtg g with Pt of final state gluons gt 50
  GeV at 14 TeV p-p
• n.b. To delete diagrams use d, o to turn them
  back on one at a time
• Cross section is 0.013 mb (very large)
• Write out full events but no fragmentation.
  COMPHEP does not know about hadrons.

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gg -gt gg in Linux COMPHEP
Note the kinematic boundary, where ltxgt 0.007 is
the y0 value for x1x2 for M 100, C.M.
14000.
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CDF Data DY Electron Pairs
DY Plateau x1,x2 at Z mass 0.045
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The Fundamental Scattering Amplitude
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Pointlike Parton Cross Sections
Pointlike partons have Rutherford like
behavior ? ?(?1?2)A2/s s,t,u are
Mandelstam variables. A2 1 at y0.
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Hadronic Cross Sections
To form the system need x1 from A and x2 from B
picked out of probability distributions with the
joint probability PAPB to form a system of mass M
moving with momentum fraction x. C is a color
factor (later). The cross section is ??
(d?/dy)y0?y. The value of ?y varies only slowly
with mass ln(1/M)
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2--gt2 and 2--gt1 Cross Sections
scaling behavior depends only on ? and not M
and s separately
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DY Formation 2 --gt 1
At a fixed resonant mass, expect rapid rise from
threshold - ?? (1-M/?s)2a - then slow
saturation. ?W 30 nb at the LHC
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DY Z Production F/B Asymmetry
CDF Run I
The Z couples to L and R quarks differently -gt
parity violating asymmetry in the photon-Z
interference.
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F/B Asymmetry
Coupling of leptons and quarks to Z specified in
SM by gauge principle.
Coupling to L and R fermions differs gt P
violation R-L coupling. Predict asymmetry , A
I3/Q. Thus, A for muons 1, that for u quarks is
3/2, while for d quarks it is 3.
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COMPHEP
At 500 GeV the asymmetry is large and positive
here not p-p but u-U
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COMPHEP - Assym
Option in Simpson to get F/B asymmetry in
COMPHEP
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DY Formation of Charmonium
Cross section ? ?2?(2J1)/M3 for W, width
2 GeV, ? 47 nb. For charmonium, width is
0.000087 GeV, and estimate cross section in gg
formation as 34 nb. The PT arises from ISR and
intrinsic parton transverse momentum and is only
a few GeV, on average. Use for lepton momentum
scale and resolution.
g
?
g
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Charmonium Calibration
Cross section in ylt1.5 is 800 nb at the LHC.
Lepton calibration mass scale, width?
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Upsilon Calibration
Cross section BR about 2 nb at the LHC. Resolve
the spectral peaks? Mass scale correct?
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ZZ Production vs CM Energy
VV production also has a steep rise near
threshold. There is a 20 fold rise from the
Tevatron to the LHC. Measure VVV coupling. ZZ has
2 pb cross section at LHC.
Not much gain in using anti-protons once the
energy is high enough that the gluons or sea
quarks dominate.
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WWZ Quartic Coupling
Not accessible at Tevatron. Test quartic
couplings at the LHC.
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Jet-Jet Mass, 2 --gt 2
Expect 1/M3 behavior at low mass. When M/?s
becomes substantial, the source effects will be
large. E.g. for M 400 GeV, at the Tevatron,
M/?s0.2, and (1-M/?s)12 is 0.07.
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Jets - 2 TeV- ylt2


1/M31-M/?s12 behavior
ET M/2 for large scattering angles.
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COMPHEP Linux
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Scaling ?
Tevatron runs at 630 and 1800 GeV in Run I. Test
of scaling in inclusive jet production. Expect a
function of
only in lowest order.
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Direct Photon Production
Expect a similar spectrum with a rate down by
ratio of coupling constants and differences in u
and g source functions. ?/?s14 u/g6 at x0.
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D0 Single Photon
Process dominated by q g a la Compton
scattering.
COMPHEP 2 TeV p-p
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2--gt 2 Kinematics - Decays

Formation System
Decay CM Decay
The measured values of y3, y4 and ET allow one to
solve for the initial state x1 and x2 and the
c.m. decay angle.
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COMPHEP - Linux
gg-gt g g, in pp at 14 TeV with cut of Pt of
jets of 50 GeV. See a plateau for jets and the t
channel peaking. Want to establish jet cross
section, angular distributions and to look at jet
balance missing Et distribution in dijet
events. MET angle jet azimuthal angle and no
non-Gaussian tails.
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Parton--gtHadron Fragmentation
For light hadrons (pions) as hadronization
products, assume kT is limited (scale ?. The
fragmentation function, D(z) has a radiative
form, leading to a jet multiplicity which is
logarithmic in ET
Plateau widens with s, ltngtln(s)
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CDF Analysis Jet Multiplicity
Different Cone radii
Jet cluster multiplicity within a cone increases
with dijet mass as ln(M).
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Jet Transverse Shape
There is a leading fragment core localized at
small R w.r.t. the jet axis - 40 of the energy
for Rlt 0.1. 80 is contained in R lt 0.4 cone
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Jet Shape - Monte Carlo
Simple model with zD(z) (1-z)5 and ltktgt 0.72
GeV. Leading fragment with ltzmaxgt 0.24. On
average the leading fragment takes 1/4 of the
jet momentum. Fragmentation is soft and
non-perturbative.
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Low Mass LHC Rates
For small x and strong production, the cross
section is a large fraction of the inelastic
cross section. Therefore, the probability to find
a small Pt minijet in an LHC crossing is not
small.
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V V Production - W ?
The angular distribution at the parton level has
a zero. The SM prediction could be confirmed with
a large enough event sample. pp at 2 TeV with
Pt gt 10 GeV, 0.6 pb
Asymmetry somewhat washed out by the contribution
of sea anti-quarks in the p and sea quarks in the
anti-proton.
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3 Tevatron -gt LHC Physics

• 3.1 QCD - Jets and Di - jets
• 3.2 Di - Photons
• 3.3 b Pair Production at Fermilab
• 3.4 t Pair Production at Fermilab
• 3.5 D-Y and Lepton Composites
• 3.6 EW Production
• W Mass and Width
• Pt of W and Z
• bb Decays of Z, Jet Spectroscopy
• 3.7 Higgs Mass from Precision EW Measurements

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Kinematics - Review
Initial State
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Review Kinematics - II
Final State
86
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.
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CDF Run II Data Reach
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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)
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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). Limits at Tevatron and LHC
will increase as C.M. energy.
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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 in the 2 J or
more sample. At the higher Pt scales available at
the LHC ISR and FSR will become increasingly
important determined by the strong coupling
constant at that Pt scale.
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Running of ?s - Measure in 3J/2J
Energy below which strong interaction is strong
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Excited Quark Composites
q
q
g
Look for resonant J - J structure, with a limit
C.M. energy
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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.
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Diphoton, CDF Run II
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. Must establish SM
photon signals ug--gtu? (Lecture 2) uu--gt??
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COMPHEP Tree Only
Tevatron, 2 TeV ?lt1, ETgt10 GeV
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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. Establish a b jet
signal and b tagging efficiency using 1 tag to 2
tag ratio. Many LHC searches and SM backgrounds
(e.g. top pairs) require b tagging.
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B Production Rapidity Distribution
Note rapidity plateau which extends to ?y 5 at
this low mass, 2mb scale. At the LHC tracking
and Si vertexing extends to y lt 2.5.
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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.
At LHC establish lifetime scale.
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Weak Decay Widths
Fermi theory
Standard Model
m?
W
G2
2 body weak decay
t -gt W b
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Top Mass and Jet Spectroscopy- Run I
D0 - lepton jets t--gtWb W--gtJJ, l?
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Jet Spectroscopy - Top
CDF - Lepton jets (Si or lepton tags) t--gtWb so
2 bs in the event
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tt --gt WbWb, W--gt qq or l?
CDF D0 Top quark mass from data taken in the
twentieth century
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Top Mass _at_ FNAL
Run I
Run II
104
Top Production Cross Section
gt 100x gain in going to the LHC. The discovery at
the Tevatron becomes a nasty background at the
LHC. However, W-gt JJ in top pair events sets the
calorimeter energy scale at the LHC.
Are the mass and the cross section consistent
with a quark with SM couplings?
105
Run II Top Cross section
No evidence for deviation from SM coupling of a
heavy quark. At the LHC top pair events have
jets, heavy flavor, missing energy and leptons.
They thus serve as a sanity check that the
detector is working correctly in many final state
SM particles. The LHC experiments must establish
a top pair sample before contemplating, for
example, SUSY discoveries.
106
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
107
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. If a Z is seen at the LHC,
use the F/B distribution to try to extract the A
and V couplings.
108
Run II DY High Mass
109
Run II DY High Mass
Whole zoo of new Physics candidates all still
null. At LHC establish muon and electron
momentum scale and resolution with Z mass and
width. Explore tail when backgrounds are under
control.
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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.
111
W - SM Mass and Width Prediction
Mass
W
Width
Color factor of 3 for quarks. 9 distinct dilepton
or diquark final states.
112
COMPHEP W BR
Check that the naïve estimates are confirmed in
COMPHEP for W and Z into 2x.
113
W,Z Production Cross Section
Cross section x BR for W is 4 pb for Tevatron
Run II
114
Lumi with W, Z ?
At present in Run II, using W,Z is more accurate
than Lumi monitor. Use W and Z at LHC as
standard candles. Test of trigger and reco
efficiencies cross-check minbias trigger
normalization.
115
W and Z - Width and Leptonic B.R.
Expect 1/9 0.11
Expect 9 (0.21 GeV) 1.9 GeV
116
Direct W Width Measurement
Far from the pole mass the Breit Wigner width
(power law) dominates over the Gaussian resolution
decay widths of 1.5 to 2.5 GeV
Monte Carlo
117
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.
118
W Mass Colliders, Run I
Hadron
WW (LEP II) production near threshold (Lecture 1 )
119
W Mass - All Methods
Direct
Precision EW measurements
120
I.S.R. and PTW
u d
W
g
2--gt1 has no F.S. PT. Recall Lecture 2 -
charmonium production. Scale is set by the FS
mass in 2 -gt 1.
121
COMPHEP - PTW
Basic 2 --gt 2 behavior, 1/PT3. . Gluon radiation
from either initial quark.
122
Lepton Asymmetry at Tevatron
123
CDF Lepton Asymmetry
Positron goes in antiproton direction Electron
goes in proton direction ? Charge asymmetry,
constrains PDF. Recall u gt d at large x.
124
COMPHEP - Asymmetry
COMPHEP generates the asymmetry in pbar-p at 2
TeV. Can use the PDF that COMPHEP has available
to check PDF sensitivity. Generate your own
asymmetry and look for deviations.
125
Z --gt bb, Run I
Dijets with 2 decay vertices (b tags). Look for
calorimetric J-J mass distribution. Mass
resolution, dM 15 GeV. This exercise is
practice for searches of J-J spectra such as Z
decays into di-jets, or H decays into b quark
pairs.
126
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 quite hard at LHC we will use W-gtJJ in
top pair events.
127
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. Transverse mass in leptonic W decays with
additional photon.
128
WW at D0 Run II
Look at dileptons plus missing transverse energy.
Tests the WWZ and WW ? vertex as at LEP - II
129
WW Cross Section Measured at CDF
Extrapolate to LHC energy. COMPHEP gives a D-Y
WW cross section at the LHC of 72 pb. At LHC will
be able to begin to explore W-W scattering
independent of Higgs searches.
130
W Mass Corrections Due to Top, Higgs
Klein-Gordon Dirac
W mass shift due to top (m) and Higgs (M)
131
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.

b t H W
W W
W W
132
CDF D0 Data Favor a Light Higgs
133
Top and W Mass and Higgs
1 s.d contours all precision EW data A light H
mass seems to be weakly favored.