RANDALL-SUNDRUM GRAVITON IDENTIFICATION IN DILEPTON AND DIPHOTON EVENTS WITH ATLAS V.A. Bednyakov JINR, LNP with A.A. Pankov, A.V. Tsytrinov ICTP Affiliated Technical University of Gomel (Belarus) JINR-Atlas meeting, May 24, 2011, JINR, Dubna

V.A. Bednyakov :: JINR-ATLAS :: :: RS graviton identification...2 Preamble Heavy quantum states (M>>M W,Z ) predicted by New Physics models. Manifestations at colliders: – Indirect [M>E CM ] → deviations from SM predictions – Direct production → peaks in cross sections. Discovery reach: peak observation at some M R over SM background => allowed region on model parameters. Identification reach: identify source of the observed peak (different models can give same M R and same number of events under the peak) ↔ test of peak/resonance quantum numbers.

V.A. Bednyakov :: JINR-ATLAS :: :: RS graviton identification...3 Model examples Models of gravity with extra spatial dimensions (spin-2) [M Pl >> M EW ] Z’ models (spin-1) [extended EW gauge symmetry] SUSY with R P sneutrinos (spin-0) They all can produce (narrow) peaks in cross sections with same number of events under the peak “Confusion regions” of parameters Identify the spin of the observed peak → discriminate models against each other in confusion regions. /

V.A. Bednyakov :: JINR-ATLAS :: :: RS graviton identification...4 Here: focus on Discovery and Identification at LHC of spin-2 resonance (vs. spin1 and spin-0) in: Clean signals: peaks in dilepton, diphoton invariant mass Basic observables: – Discovery: - resonant cross section ↔ number of events – Identification: angular distributions  evenly-integrated asymmetry A CE. Phys.Rev. D78, (2008); Yadernaya Fizika, 2010, V73, N7, p. 1307

Hadron level SM: Graviton exchange signatures in RS scenario: Parton distribution functions – CTEQ6 Partonic cross sections K-factors ~ 1.3 5V.A. Bednyakov :: JINR-ATLAS :: :: RS graviton identification... [Giudice et al., 1999; Han et al., 1999]

Cross section for Cross section for 6V.A. Bednyakov :: JINR-ATLAS :: :: RS graviton identification... I) Production cross section: II) Angular distribution → number of events under the peak Minimal number of signal events over SM background (discovery): Inputs: reconstruction efficiency cuts ATLAS detector resolution:  M = 24 (0.625 M + M ) 1/2 GeV, dilepton mass M measured in TeV units. Experimental inputs & cuts ( y  rapidity of lepton pair, M  dilepton mass, z  cosθ * )

V.A. Bednyakov :: JINR-ATLAS :: :: RS graviton identification...7 RS1 model with one warped extra dimension Fundamental mass scales (G = Newton constant) 4D effective theory gives “Natural” model assumption: Mass spectrum on Planck brane Mass spectrum on TeV brane exponentially warped down: warp factor, (5D curvature) [Randall – Sundrum, 1999]

Junction conditions at y=0,  R => spin-2 graviton excitations h n : Interaction: Zero mode: (ordinary graviton). Higher modes: V.A. Bednyakov :: JINR-ATLAS :: :: RS graviton identification...8

9 RS-model parameters and notations: – M 1  M G mass of first KK graviton (expected M G ≈ TeV) – c = k/M Pl coupling to matter [universal] Unevenly spaced spectrum: M n = (x n /x 1 ) M G distinctive of the model by itself “Theoretical” constraints: M 1 =1.5 TeV and subsequent tower states at LHC (c = 1, 0.5, 0.1, 0.05, 0.2, and 0.01, from top to bottom).  0.01 ≤ c ≤ 0.1  Λ  < 10 TeV Width Γ n = ρ M n x n 2 c 2 : narrow resonances for small c Experimental (TEVATRON): M G > 560 GeV (c = 0.01) M G > 1050 GeV (c = 0.1) [Davoudiasl et al.] [arXiv: v1 [hep-ex], 2010] _

Z’ at parton level 10V.A. Bednyakov :: JINR-ATLAS :: :: RS graviton identification... Popular Z’s with coupling constants fixed by theory: TEVATRON: M Z’ > 800 – 1000 GeV [Aaltonen et al., Phys.Rev.Lett.102:091805, 2009] [but we will be more general] [Review: Langacker, 2008]

Sneutrino at parton level 11V.A. Bednyakov :: JINR-ATLAS :: :: RS graviton identification... Theoretically “reasonable” range: < X < Current limits on sneutrino mass (Tevatron): 400 − 870 GeV (for 10 −4 ≤ X ≤ 10 −2 ), Effective parameters: : R-parity-violating couplings of to and [Kalinowski et al., 1997] [R.Barbier et al., hep-ph/ ] [Aaltonen et al., Phys.Rev.Lett.102:091805, 2009]

Summary of angular distributions 12V.A. Bednyakov :: JINR-ATLAS :: :: RS graviton identification... c = 0.01, M R = 1.6 TeV, equal numbers of DY resonant events ( l = e, m ) z-even

Identification reach on spin Difficulty of angular analysis: boost to CM frame and sign of z Difficulty of angular analysis: boost to CM frame and sign of z Centre-Edge Asymmetry : Centre-Edge Asymmetry : 13V.A. Bednyakov :: JINR-ATLAS :: :: RS graviton identification... A CE is the same for Z’ models and SM. z-symmetric integration!

V.A. Bednyakov :: JINR-ATLAS :: :: RS graviton identification...14 SPIN-2 GRAVITON IDENTIFICATION graviton vs sneutrinograviton vs Z’ CONFUSION REGIONS N S = signal events; M R = M G

Simple χ 2 -like analysis using A CE Constraints for identification reach on spin-2: – Exclusion spin-0: – Exclusion spin-1: Condition: => determine signal N min => domain in (c, M G ) Results for [95% C.L.]: 15V.A. Bednyakov :: JINR-ATLAS :: :: RS graviton identification... & “distance” between models

16V.A. Bednyakov :: JINR-ATLAS :: :: RS graviton identification... RS parameter plane domain allowing for spin-2 identification vs. domain allowed for discovery (95% C.L.) at the 14 TeV LHC

excludes spin-1: – predicted => strong test (work in progress) V.A. Bednyakov :: JINR-ATLAS :: :: RS graviton identification...17 z = cosθ* : dominant, peaked at z = ±1 Can exclude spin-0? A CE –based analysis applicable. Potential background from initial brehmsstrahlung – not for M G ~ TeV

Foreseen experimental cuts: p > 40 GeV; |η| < 2.4; ε = 80% Comparable identification sensitivity, spin-1 automatically excluded. T 18V.A. Bednyakov :: JINR-ATLAS :: :: RS graviton identification...

19 Conclusion