The Tevatron Program Marching Toward the Higgs

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The Tevatron ProgramMarching Toward the Higgs

• Robert Roser
• Fermi National Accelerator Laboratory

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Why Does One Do High Energy Physics?

• The Experiments are large -- many operating
  experiments EACH have 700 physicists. The LHC
  experiments will have many more (gt2000/each)
• Author list might take more pages in a journal
  than the actual article
• Physicists have to travel great distances to get
  to their experiments
• Startup times for experiments are large already
  working on experiments and accelerators that
  wont run till 2018 or beyond
• The apparatus is far from being table top in size
• A single experimenter does not have total control
  over his or her environment

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One Persons Answer My Answer

• We want to understand some of the most
  fundamental questions in nature
• We want to understand how the universe was
  created
• We, as physicists have an insatiable curiosity
  for the world we live in and how it works
• We enjoy working with a large group of smart
  people toward a common goal
• The variety of physics topics that these new
  experiments can address means life is never
  boring
• BECAUSE ITS FUN

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An Introduction to Particle Physics

• The Standard Model of Particle Physics
  statesThe world is comprised of Quarks and
  Leptons that interact by exchanging Bosons
• There are three differet types of leptons
• Mass Me lt M? lt M? M ? ? 0
• Each particle has an antiparticle (electrons ?
  positrons)

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The Standard Model Quarks

• Quarks (u, d, s) were postulated by Gell Mann in
  1964
• Quarks are unusual in that they have fractional
  charge
• Each Quark has its own antiparticle
• Mass Mu Md lt Ms lt Mc lt Mb ltlt Mt
• The Charm Quark was discovered in 1974 at BNL
  SLAC
• The Bottom and Top Quarks was discovered at
  Fermilab in 1977 and 1994 respectively

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The Forces that tie things together

• Four known forces in the universe
• Electromagnetism
• Batteries, chemical reactions, refrigerator
  magnets
• Strong
• Holds protons and neutrons together in nuclei ?
  stable
• Weak
• Responsible for nuclear ß decay
• Gravity
• Familiar to us all but
• Not accommodated in Standard Model

?
g
W
Z0
??

• Each force is mediated by its own particle
• mediated meaning exchange of force particle
  between participating matter particles
• Useful diagrams

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An example Water!

• H20

H
H
O
U
U
U
d
d
d
Proton
Neutron
2/32/3-1/3
2/3-1/3-1/3
8e
28 Up Quarks 26 down quarks 10 electrons
e
8P
H2O
P
8N
Hydrogen
Oxygen
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Tying it all together!
The Standard Model of Particle Physics

• Good description of particles and their
  interactions
• Extensively tested
• But need explanation of W, Z, fermion masses
• This cant be the entire story

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Electroweak Symmetry Breaking

• We know the W and Z have nonzero masses
• Its what makes the Weak force so weak!
• Symmetry must be broken
• Enter the Higgs Mechanism
• Introduces new field for particles to interact
  with
• Interaction strength mass of particle
• Consequences
• MW, MZ ? 0 in model
• Matter particles have mass
• Existence of Higgs boson
• but no prediction for its mass

Understanding the origin of masses is one of the
priorities at the Tevatron and LHC.
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Higgs Mechanism
Popularity ? Mass
Analogy by Prof. David Miller University College
of London
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How does one search for the Higgs boson?(or
anything else for that matter)
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Making Particle X
Thanks to Einstein we know that a high energy
collision of particle A and B can result in the
creation of particle X
E mc2

Energy
particle beam energy
anti-particle beam energy
Ea
Eb
Mx
As long as Ea Eb gtgt Mxc2
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Its a bit more complicated
Proton
Anti-Proton
d
u
u
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The Tevatron P Pbar Collider

• E proton E antiproton 980 GeV
• Ecm 1.96 TeV

Wrigley Field
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Colliding Beam Detectors

• Detector design is always a compromise
• available space
• technological risk
• readout time and construction time
• Goal is to completely surround collision with
  detectors
• Arrange detectors in layers based on
  functionality
• Measure particles position, momentum and charge
  first
• Type and kinetic energy second

CDF II Detector cross section
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The Life of an Experimentalist

• Our camera is not fast enough to take a picture
  of say a top quark! We have to infer based on
  the information provided!
• What do we know?
• Conservation of Energy
• Conservation of Momentum
• Emc2
• What do we want to identify?
• Electrons
• Muons
• Quarks
• Neutrinos
• b quarks

(Helps!)
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Particle Signatures

• Electrons - deposit all their energy in
  electromagnetic calorimeter which can be matched
  to a track
• Photons - no track

• Muons Match signal in muon chambers to track

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Particle Signatures (2)

• Quarks - fragment into many particles to form a
  jet
• Leave energy in both calorimeters

• Neutrinos - pass through material
• Measured indirectly by imbalance of transverse
  energy in calorimeters

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Identifying b quarks
A Top Quark Event
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Collecting the Data You Want!

• Tevatron
• 36 p x 36 p bunches
• collisions every 396 ns
• 1.7 MHz of crossings
• CDF Detector
• Very complicated with lots of information
  available on each collision
• The problem
• You cant write out each collision to tape!
• The Solution
• A Device called a trigger
• Examines every event in real time and identifies
  the most interesting

• CDF 3-tiered trigger
• L1 accepts 25 kHz
• L2 accepts 800 Hz
• L3 accepts 150 Hz
• (event size is 250 kb)
• Accept rate 112,000
• Reject 99.991 of the events

Level-1/2 Triggers
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The CDF Experiment
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The CDF Collaboration
Europe ? 21 institutions
North America ? 34 institutions
Asia ? 8 institutions
The CDF Collaboration ? 15 Countries ? 63
institutions ? 635 authors
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Taking data happily
lt85gt efficient since 2003
As of today about 4.8 fb-1 delivered, 4 fb-1
recorded
About 80 of Delivered Luminosity is available
for physics analysis
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Physics Highlights from CDF

• Observation of Bs-mixing
• ?ms 17.77 - 0.10 (stat) - 0.07(sys)
• Observation of new baryon states
• ?b and ?b
• WZ discovery (6-sigma)
• Measured cross section 5.0 (1.7) pb
• ZZ observation
• 4.4-sigma
• Single top Observation (4.4-sigma) with 2.7 fb-1
  
• cross section 2.2 pb
• Vtb 1.02 0.18 (exp.) 0.07 (th.)?
• Measurement of Sin(2?_s)

Precision W mass measurement Mw_cdf 80.413 GeV
(48 MeV) Precision Top mass measurement Mtop_cdf
172.2 (1.7) GeV W-width measurement 2.032
(.071) GeV Observation of new charmless Bgthh
states Observation of Do-Dobar mixing Constant
improvement in Higgs Sensitivity S.M. Higgs
Exclusion at 170 GeV at 95 C.L. when combined
with D0results
A Goldmine of Physics Opportunities
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The road to the (SM) Higgs
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Where is the Higgs Hiding?
MH lt 154 GeV at 95 C.L. Preferred
MH 8736-27 GeV
Mw vs Mtop
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CDFs Latest W Mass Result
Mw 80.413 ? 0.048 GeV
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Summary of Top Mass
Mt 172.4 ? 1.0 ?1.3 GeV lt1 Precision
We now know the mass of the top quark with better
precision than any other quark 12 short years
from discovery to this.
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A Roadmap to discovery
Harder to Produce
?
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Harder to Observe
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Higgs Production and Decay
Higgs are produced in several diferent
ways Higgs decay into different final states
depending on the mass of the Higgs To find it,
we need to look at all these final decay states
and combine the results
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The Challenge
These are production numbers trigger,
acceptance etc not yet factored in
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Can we use the strategy for the top quark to
find the Higgs?

• Namely just count events that look like top
• Estimate a top signal the number of events that
  might mimic
• The difference between the two is the signal

NO!
From the previos page. we expect to make 50-70
Higgs events inside our detector for each 1/fb of
data We now have 3 /fb of data so we expect to
have made 150-200 Higgs If our efficiency for
finding them is a few percent, we are trying
locate a handful of events out of billions of
collisons!
This is Hard!!!
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First Step.

• Select Events with high Pt Leptons (e,u,tau)
• Select Events with Missing Energy (neutrinos)
• Select events with jets from b-quarks
• Details of each decay channel slightly different

B-tagging is about 50-70 efficient. Depends on
Et and ?? of jet
S/B now 1400(So the first factor of 1 billion
is easy!)
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Second step

• Use other distinguishing features
• Simplest Approach fit a kinematic distribution
• Low M(H) Fit the dijet Mass
• Use More Sophisticated Approaches (multivariate)
• Artificial neural networks
• Matrix elements
• Other discriminants

H
Mbb MH
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Step 3 -- Optimization

• Ongoing Intense Optimization Efforts (improving
  your efficiency for identifying them.)
• Basic Selection
• Maximize Trigger Configuration
• Identify as many high pt leptons as possible
• Improve b-tagging
• New ideas
• Neural network algorithms
• Improved background rejection
• Improved MET and Jet resolution
• Critical for Mjj resolution
• Multivariate inputs

Improved Mjj
Very Hard and painstaking Work!!!
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An Example -- Higgs ?WW

• H?WW?l?l? - signature Two high pT leptons and
  Missing Energy
• Primary backgrounds WW and top in di-lepton
  decay channel
• Key issue Maximizing lepton acceptance
• Most sensitive Higgs search channel at the
  Tevatron

s x BR (H?WW) expected limit 1.66 times SM for
a Higgs mass of 165 GeV Observed 1.63
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Step 4 Combine Channels
No single channel has the power to reach SM
prediction for MH lt 160 GeV/c2
With 3/fb
MH 115 GeV/c2
?
170 GeV/c2
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Step 4 Channel Combination

• Statistically combine channels
• Use a procedure to account for correlated
  uncertainties

Factor away in sensitivity from SM
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Step 5 Combine Experiments
Neither experiment has sufficient power to span
the entire mass range using the luminosity we
expect to acquire in Run II
Exp. 1.2 _at_ 165, 1.4 _at_ 170 GeV
Obs. 1.0 _at_ 170 GeV
Factor away in sensitivity from SM
SM Higgs Excluded mH 170 GeV
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Future Prospects

• We can extrapolate into the future
• With current analysis and just add more data
• Extend the sensitivity for anticipated
  improvements

We continue to make significant progress
95 CL
95 CL
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Tevatron Higgs reach with FY10 run
Tevatron Projected Sensitivity CDFD0 combined

• With 7 fb-1 analyzed
• exclude all masses !!! except real mass
• 3-sigma sensitivity 155170
• LHCs sweet spot

We find this very compelling
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Reaching for the Higgs Horizon
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Conclusions

• We are making great strides in the search for the
  Higgs
• The accelerator WILL provide data sets of
  sufficient size to give us a chance!
• We know what to do in terms of analysis
• If the Higgs is there, we have a chance to find
  it!
• These next two years will be a very exciting time
  as we conclude our search and the LHC starts
  theirs.

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Backup
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WH ?l?bb Channel an example

• High Pt Lepton
• Missing Et
• 2 Jets
• Split by number of btags
• Examine Figures of Merit
• Features
• Good Acceptance
• Final state similar to single top production
• 2-3 events/fb

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WH ?l?bb Channel
Inputs Mjj, Pt(b), Pt(sys), Ml?j(min), ?R l?,
Et(jets)

• Figure of Merit Advanced Neural Network

Results at mH 115GeV 95CL Limits/SM
7.8 produced 5.6 Expected Limit 5.7 Observed
8.3 (7.2 exp)
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How Does a Rolex Work?

• HEP experimentalist would do the following
• Purchase many watches -- ten of thousands!
• One at a time, throw them at
• a brick wall (fixed target)
• or another watch (colliding beams)
• After each collision observe the remaining
  pieces
• Statistically collect information for all the
  collisions
• Draw conclusions on how the watch works.

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Physics at High Luminosity
Muon ID efficiency
Electron ID efficiency
Efficiency
b-tagging efficiency
Inst lum
Inst lum
Number of reconstructed vertices
3e32
Inst lum
Inst lum
Electron L1 trigger eff.
Muon L1 trigger eff.
Physics at high luminosity is under control
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Top Quarks at CDF
b-jet
Muon
Jet
Jet
b-jet
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The Challenge

• Higgs production is a low rate process at the
  tevatron
• Backgrounds are many orders of magnitude larger
• ChallengeSeparate the signal from the
  background
• Start S/B before any cuts is 11011

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Decoding Limit Plots 101
Factor away in sensitivity from SM