Collider Signals of Large Extra Dimension Nobuchika Okada (KEK) The 7th Acfa Workshop November 9-12, Taipei, Taiwan

1. Introduction Large extra-dimension (ADD) scenario (Arkani-Hamed-Dimopoulos-Dvali, ’98) Basic picture: dimensional model We are confined on “3-brane” graviton lives in the bulk SM fields graviton compact extra-dimensions ( with common radii r ) “3-brane”

Alternative solution to the gauge hierarchy problem without SUSY, TC, etc. Low scale gravity model Gauss law  We can take with  We can expect collider signal!

2. Theoretical Framework 4D description : graviton in dimensions  Kaluza-Klein (KK) mode decomposition in 4 dimensions + periodic boundary conditions  Infinite tower of KK modes Ex) if 6 dim. 

KK graviton: KK gravi-scalar: KK vectors KK scalars do not couple to SM fields Reduced Planck mass : negligible at high energies Characteristic features: infinite tower of KK gravitons universal couplings

Feynman rules ex) QED + KK graviton

3. Collider signal of large extra dimension Phenomenology of extra-dimension scenario = Phenomenology of graviton Kaluza-Klein modes Detection of Extra-dimension @ future colliders  detection of KK graviton direct  KK graviton emission processes indirect KK graviton mediated processes First detection of spin 2 particle !

KK graviton emission process 3-1. direct detection KK graviton emission process Ex) Each process is suppressed by Emitted KK graviton  non-interacting & stable particle  missing energy event is very small  can be sizable 

KK graviton emission process @ linear colliders Giudice, Rattazzi & Wells, NPB 544 (1999) 3 Example: SM background:

KK graviton emission process @ LHC Giudice, Rattazzi & Wells, NPB 544 (1999) 3 Example: SM background: a: integrating the cross section over b: all

KK graviton mediated process 3-2. indirect detection KK graviton mediated process Need regularization Naïve: Cut Off by

II: angular dependence of cross section Important points: I: total cross section 　　　 new physics evidence deviation from the SM collider energy LC < LHC II: angular dependence of cross section 　  effects due to spin 2 particle exchange precise measurements of angular dependence LC > LHC

process Example: KK graviton exchange is dominant N. Delerue, K. Fujii & N. Okada hep-ex/0403029, to appear in PRD process KK graviton exchange is dominant SM background free  very interesting if this cross section is large enough Comparable to

Angular dependence of cross section

Qualitative understanding of angular dependence Initial state helicity:  or Final state helicity: 0 Orbital angular momentum is needed to make up spin 2 of intermediate KK gravitons Angular distribution reflects the spin 2 nature of KK gravitons

Monte Carlo Simulation process two pair of b-jets SM background: processes producing two pair of jets

Invariant mass distributions

Invariant mass distributions

Event selection Criteria: More than 25 tracks with an energy > 100 MeV A visible energy larger than 600GeV Transverse momentum larger than 50 GeV More than 4 jets Invariant mass less than 16 GeV away from Higgs mass One of the jets of each Higgs candidate to be b-taged

15/17 Number of remaining evens per 700 Higgs Pair events @ 1TeV LC integrated luminosity 500 Essentially No SM backgrounds!

Reconstruction of Angular Distribution (after selection) integrated luminosity 500

4. Summary Large extra dimension Scenario is an interesting candidate for new physics beyond the standard model The existence of extra dimensions may be revealed through processes involving the KK gravitons, KK graviton emission processes KK graviton mediated processes LC has an advantage to measure the angular dependence of the cross section of the KK graviton mediated process, which reflects the spin 2 nature of the intermediate KK gravitons