hybrids

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Some recent results from CDF
David Stuart U.C. Santa Barbara
October 24, 2005
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Tevatron
.
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Integrated Luminosity
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CDF is pursuing a broad physics program

• QCD
• Top
• B
• EWK
• New physics

My interest is (mostly) in searches for new
physics
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Searching for new phenomena

• Why?
• SM is incomplete
• What?
• Higgs
• Supersymmetry
• Extra generations
• Extra forces
• Extra dimensions
• How?
• SM

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Searching for a Z
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Electron Identification
A typical di-jet event
Atypical Z?ee event
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Electron Identification
Require little energy in hadron calorimeter
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Electron Identification
Require little energy around the EM cluster
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Electron Identification
Require a matching track
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Electron Identification
Require a matching track
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Electron Identification
Require a matching track
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Electron Identification
using a likelihood
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Electron Identification
using a likelihood
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In fact, the electron id differs
between central and forward electrons.
Reduced tracking in the forward region calls for
new techniques.
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Particle Tracking Coverage
proton
antiproton
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Intermediate Silicon Layers
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B
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Forward Electron Tracking Algorithm

• Form 2 seed tracks,
• one of each sign,
• from calorimeter beam spot

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Forward Electron Tracking Algorithm

• Form 2 seed tracks,
• one of each sign,
• from calorimeter beam spot
• Project into silicon
• and attach hits using
• standard silicon pattern recognition

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Forward Electron Tracking Algorithm

• Form 2 seed tracks,
• one of each sign,
• from calorimeter beam spot
• Project into silicon
• and attach hits using
• standard silicon pattern recognition
• Select best c2 match

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Plug Alignment
Align plug to COT using the subset of COT tracks
which match plug electrons just above h1. Then
align silicon to the COT.
COT
Plug
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Plug Calorimeter Alignment
Global
Internal
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Obtain 1mm resolution
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Results from central electrons
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Results from central muons
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Limits
hep-ex/0507104
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More recent results
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Angular Distribution sensitive to interference
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Limits of about 845 GeV/c2 for Z with SM
couplings

• Next, we could
• look for other modes
• Z ? tt-
• Z ? t t
• exclude other models

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Strong Gravity

• Geometrical factor generates TeV masses
• m m0 e-kRp
• where k is a scale of order the Planck scale.
• kR12 generates the observed hierarchy.
• Similarly, the graviton mass becomes
• MPl e-kRp 1 TeV

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Strong Gravity
Coupling ? k/MPl
Also mm, gg, tt, WW, HH, ZZ
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High Mass Diphoton Search
Background is 2/3 dijets, 1/3 gg.
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Other di-boson modes in progress
Several modes (eeee, eenn, eejj) with potentially
very low backgrounds Z mass constraint rejects
background, and SM Z bosons are low pT.
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What else could lead to high pT Z bosons?
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What else could lead to high pT Z bosons?
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What else could lead to high pT Z bosons?
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Z bosons from GMSB
Weak coupling could lead to long life.
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Z bosons from a 4th generation quark
Weak coupling, Vtbltlt1, could lead to long life.
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Search for displaced Zs

• Search strategy
• Select dimuons
• from a Z
• Require a good vertex
• measurement (verify
• efficiency with J/Ys)
• Opening angle cut
• Require pTgt30 for Z
• Aim for simple selection to limit
• model dependence. (aka, X?YZ)

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Search for displaced Zs

• Search strategy
• Select dimuons
• from a Z
• Require a good vertex
• measurement (verify
• efficiency with J/Ys)
• Opening angle cut
• Require pTgt30 for Z
• Aim for simple selection to limit
• model dependence. (aka, X?YZ)

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Search for displaced Zs

• Search strategy
• Select dimuons
• from a Z
• Require a good vertex
• measurement (verify
• efficiency with J/Ys)
• Opening angle cut
• Require pTgt30 for Z
• Aim for simple selection to limit
• model dependence. (I.e., X?YZ)

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Search for displaced Zs
Expect 1.1?0.8, observe 3 A posteriori inspection
consistent with background hypothesis.
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And now for something completely different
While the prospect of a discovery that can lead
us to the theory beyond the SM is exciting, the
most probable answer in each such measurement is
Data - Background 0. It is appealing to
better measure the SM properties along the
way.... So, let me tell you about a measurement
where we dont already know the answer.
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Parton distribution functions
u 2d, plus much going on in the sea that is
incalculable. But, we can measure it.
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u/d ratio causes an asymmetry in W production
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Asymmetry in W production complicated by unknown
n pz
Use lepton asymmetry
Which convolves production asymmetry with V-A
decay.
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Production asymmetry largest in forward
direction, but so is decay asymmetry
We use our forward tracking algorithm to probe
the hgt1 region.
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W Event Selection

• Electron with ET gt 25 GeV
• Missing ET gt 25 GeV
• 50 lt MT lt 100 GeV/c2
• No other EMO with ET gt 25 GeV to suppress DY and
  QCD
• Calorimeter seeded silicon track
• We are less worried about acceptance/purity here
• and more worried about charge identification
• hits gt 4
• c2 lt 8
• Dc2 gt 0.5

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Observed asymmetry (before any corrections)
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Charge mis-identification
Measured with same vs opposite sign electrons
from Z?ee Large uncertainty in the forward
direction, due to poisson fluctuations, Is the
dominant systematic uncertainty
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Backgrounds

• Correct for
• Z ? ee (lost leg)
• W ? tn ? ennn
• QCD fakes

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Fully corrected asymmetry
A(-h) -A(h), with c2 9.5/11 dof
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We can enhance the sensitivity to the production
asymmetry
Ideally, wed reconstruct the Ws direction
to avoid the decay smearing Since we cant,
we instead use the electrons kinematics For
he1.8, e.g., look at yW and x of u
quark. Different ET electrons probe different x
regions.
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We can enhance the sensitivity to the production
asymmetry
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Compare to existing pdf fits
PRD 71, 051104
MRST02
CTEQ6.1m
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The End
but more to come.
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Auxiliary slides
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What else could lead to high pT Z bosons?
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