# Presentation: 944094

## Which experiment ?   

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

- Which experiment ?
- Collider Detector at Fermilab

- 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.

- Are there different ED models ?

- Tracey Pratt, Oxford University
- t.pratt1@physics.ox.ac.uk

- Supervisors Dr. Todd Huffman, Oxford University
- 		and Dr. Kaori Maeshima, Fermilab

- ED theories are a possible solution to the hierarchy problem (Why is MEW << MPl ?) and do not rely on either supersymmetry or technicolour
- If new compact dimensions of radius ~R exist, then the fundamental Planck scale MPl(4+n) could be close to the electroweak scale MEW
- Gravity can couple with electroweak strength at energy scales of order 1 TeV
- In SM:                   In 4+n dimensions:
- V(r) ~_ m__1__m__2_  _1 _     V(r) ~_   m__1__m__2__   _   _ 1  _ (r << R)    V(r) ~_    m__1__m__2__        _  _ 1  _ (r >> R)
-             MPl2     r                 MPl(4+n)n+2  r n+1                                          MPl(4+n)n+2 Rn     r
- For r >> R their gravitational flux lines can not penetrate into the ED, so V(r) 1/r
- 		   MPl2   ~  MPl(4+n)n+2 Rn
- Putting MPl(4+n) = MEW ~ 1 TeV gives R ~1030/n -17 cm. So for n  2, R < 1 mm .
- This results in observable modifications to SM processes - testable at colliders

- ED

- What affect do ED s  have on the Drell-Yan cross-section ?

- 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 4+n 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

- 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).

- 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]

- CDF Run II dilepton data

- Plot by Koji Ikado, Waseda

- Plot by Tracey Pratt, Oxford

- Z   

- Z  e e