ADD model

1
Tracey Pratt, Oxford University t.pratt1_at_physics.o
x.ac.uk
Supervisors Dr. Todd Huffman, Oxford University
and Dr. Kaori Maeshima, Fermilab
Looking for what? Deviations to the Standard
Model cross-section and forward-backward
asymmetry at high invariant mass caused by new
physics, e.g. Z or Extra Dimensions (ED).
Which experiment ? Collider Detector at
Fermilab
ED

• In some models the SM fields are confined to a
  3-D brane
• This forms the boundary of an n-dimensional bulk
  with compact dimensions of characteristic radius
  R
• Massless gravitons propagate in the full 4n
  dimensional space
• Gravitons appear in our world as a Kaluza-Klein
  tower,
• i.e. a series of very closely spaced massive
  spin-2 states
• Gravitons can be emitted or exchanged along with
  SM gauge bosons
• Gravitons can be detected by
• Graviton Emission - gravitons radiate into the
  bulk appearing as missing energy
• Graviton Exchange - deviations in the
  cross-section from SM prediction

• ED theories are a possible solution to the
  hierarchy problem (Why is MEW ltlt MPl ?) and do
  not rely on either supersymmetry or technicolour
• If new compact dimensions of radius R exist,
  then the fundamental Planck scale MPl(4n) could
  be close to the electroweak scale MEW
• Gravity can couple with electroweak strength at
  energy scales of order 1 TeV
• In SM In 4n dimensions
  
• V(r) m1m2 1 V(r) m1m2 1 (r ltlt
  R) V(r) m1m2 1 (r gtgt R)
• MPl2 r
  MPl(4n)n2 r n1
  MPl(4n)n2 Rn r
• For r gtgt R their gravitational flux lines can not
  penetrate into the ED, so V(r) ?1/r
• MPl2 MPl(4n)n2 Rn
• Putting MPl(4n) MEW 1 TeV gives R 1030/n
  -17 cm. So for n ? 2, R lt 1 mm .
• This results in observable modifications to SM
  processes - testable at colliders

CDF Run II dilepton data
Z ? ? ?
Z ? e e
Plot by Koji Ikado, Waseda
Plot by Tracey Pratt, Oxford
Are there different ED models ?
What affect do ED s have on the Drell-Yan
cross-section ?
RS model Drell-Yan production of a 700 GeV KK
graviton at the Tevatron with k/ Mpl 1.0, 0.7,
0.5, 0.3, 0.2 and 0.1 respectively from top to
bottom 3

• There are several ED models, two of these are ADD
  1 and Randall Sundrum 2
• Both models can be searched for by looking for an
  excess of events in the Drell-Yan cross-section
• In the RS model Mpl is determined by the
  higher-dimensional curvature rather than the size
  of the extra dimension
• The RS model has one additional dimension, as
  opposed to n ? 2
• The experimentally distinctive consequences are
• In RS, there are no light KK modes. The
  excitation scale is of the order a TeV.
  Therefore, current constraints from particle
  physics, astrophysics and cosmology do not apply.
  Because of this the scale at which gravity
  becomes strong can be quite low.
• ADD Graviton tower coupling strength energy/
  Mpl
• RS each excited state coupling is of
  order energy/TeV
• Whereas the graviton tower emission is an
  important probe of the ADD scenario, this is not
  so in the RS model since the graviton states are
  so massive that they can be individually examined
  on resonance.

ADD model Drell-Yan production of a graviton of
varying string scale MS MPl(4n) 4