Searching for in High Mass Dilepton Spectrum at CDF, Fermilab ADD model Drell-Yan production of a graviton of varying string scale M S = M Pl(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 M pl 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 a)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. b)ADD: Graviton tower coupling strength ~ energy/ M pl 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 SM prediction Quantum Gravity Model for M s values CDF Run 1results for dimuon samples Supervisors Dr. Todd Huffman, Oxford University and Dr. Kaori Maeshima, Fermilab ED theories are a possible solution to the hierarchy problem (Why is M EW << M Pl ?) and do not rely on either supersymmetry or technicolour If new compact dimensions of radius ~R exist, then the fundamental Planck scale M Pl(4+n) could be close to the electroweak scale M EW 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) M Pl 2 r M Pl(4+n) n+2 r n+1 M Pl(4+n) n+2 R n r For r >> R their gravitational flux lines can not penetrate into the ED, so V(r)  1/r M Pl 2 ~ M Pl(4+n) n+2 R n Putting M Pl(4+n) = M EW ~ 1 TeV gives R ~10 30/n -17 cm. So for n  2, R < 1 mm. This results in observable modifications to SM processes - testable at colliders G g g l-l- l+l+  /Z 0 l-l- l+l+ q q G q q l-l- l+l+ + + The SM exchange of a  or Z boson interferes with the exchange of a graviton There is also a gluon-gluon initiated graviton exchange process which has no SM analogue. 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 G Z mass limit, with SM coupling, from CDF Run I (110 pb -1 ) is 690 GeV/c2 [5] M s lower limit ( 95 % C.L.) from Tevatron Run I data TeV for number of extra dimensions n=7-2. [6] Compactification Scales (R -1 ) (95 % C.L.) from Tevatron Run I data  0.9 (TeV) [7] What limits have been set? 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/ M pl = 1.0, 0.7, 0.5, 0.3, 0.2 and 0.1 respectively from top to bottom [3] References: [1] N. Arkani-Hamed, S. Dimopoulos and G.Dvali, Phys. Lett. B429, 263 (1998), hep-ph/ [2] L. Randall and R. Sundrum, hep-ph/ (1999) [3] H. Davoudiasl, J. Hewett and T. Rizzo, hep-ph/ (2000) [4] A. Gupta, N. Mondal, S. Raychaudhuri, hep-ph/ (1999) [5] F. Abe et al., (CDF Collaboration), Phys. Rev. Lett. 79, 2192 (1997) [6] K. Cheung and G. Landsberg, Phys. Rev. D 62, (2000), hep-ph/ [7] I. Antoniadis, K. Benakli and M. Quiros, Phys. Lett. B460, 176 (1999), hep-ph/ When higher gauge theories break down, if they break down to U(1) then Z ´ s are produced: E 6 SO(10) x U(1) SU(5) x U(1) x U (1) Z Z If the breaking down scale is low enough then the Z ´ should produce observable effects. Z´ l+l+ l-l- q q DY+Z’ generated using Pythia v6.158 Dimuon Mass GeV/c entries 1000 entries M z’ =400 GeV /c 2 Invariant mass > 30 GeV M z’ =200 GeV/c 2 CDF Run II dilepton data Plot by Koji Ikado, WasedaPlot by Tracey Pratt, Oxford Z    Z  e e