Probing Leptoquarks at IceCube. Haim Goldberg

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1 1 Leptoquarks in theory Experimental limits: HERA and Tevatron Phenomenology: cross sections and inelasticity Sensitivity reach at IceCube Work done with L. Anchordoqui, C. A. Garcia Canal, D. G. Dumm, F. Halzen, hep-ph/

2 2 Leptoquarks - Theory Carry SU(3) color, B 0, L 0 decay LQ l q Usually superheavy (e.g., heavy triplet in SU(5) Higgs 5 Can in principle be TeV, then exist bounds from EW precision data Example: a µ K. Cheung, 2001 Lower limit of 1 TeV on leptoquark mass can be lowered if L or R coupling is suppressed e.g., in SUSY R/ QLD c only L coupling

3 3 Experimental Limits HERA: first generation, M > 300 GeV but production depends on 1st gen Yukawa coupling if small, bound can decrease Tevatron: QCD pair production ID made through event topology no dependence on trilinear couplings except through branching fractions For 2nd generation, final state topology j c j c µ µ M > 250 GeV

4 4 2nd Generation - DZero limits [pb] 2 σ β 10-1 β = 1/2 σ(pp LQ 2 LQ 2 µqµq) Observed limit Expected limit β = 1 DØ 294 pb Scalar leptoquark mass m LQ [GeV]

5 5 Tevatron: 3rd Generation For 3rd generation, decay into tτ final state is suppressed for smaller M so final state topology j b j bν τ ν τ 2 b jets + missing energy M > 219 GeV

6 6 3rd Generation - DZero limits, pb 2 σ B 1 D0 Run II Preliminary Signal cross-section, µ = 1M LQ B 2 bν 2 Bbν [ σ ± [ σ - δ µ 2 (σ) + δ 2 δ µ 2 (σ) + δ PDF 2 PDF (σ) ], B=1 (σ) ], B=(1-0.5*F ) sp Observed, MHT, 310pb -1 Observed, MUJET, 367pb 213 GeV M LQ, GeV

7 7 IceCube Halzen, astro-ph/ Effective Area 1 km 2 E th 100 GeV 4800 PMT s on 80 strings µ track angular resolution 1 1 bin Calibration IceTop 1 km 2 air-shower detector with 160 stations

8 8 Tracks and Showers at IceCube Tracks: Cosmic muons and CC interactions ν µ µ Very high energy ν τ τ Showers: ν e or ν τ CC interactions All NC interactions Muon bremsstrahlung near detector Cut E ν > 10 6 GeV, reduce µ brem, atmospheric b g d

9 9 Inelasticity In energy decade < E ν /GeV < expect good energy resolution for µ and τ ( double bang ) tracks hadron showers Allows determination of inelasticity y y-dependence of resonant LQ production SM can do y cuts to increase S/N

10 10 The Model Take simple flavor-diagonal invariant Lagrangian L LQ = i (g L Q c il iτ 2 L il + g R u c ir l ir) S i Gives parton level amplitude M L = g 2 L l L (k ) U c L (p ) D c L (p) ν L(k) ŝ M 2 iγm For decay through R channel, g 2 L g L g R

11 11 Cross sections With usual parton model and pole approximation dσ (i) LQ dy = π 2 g 2 L (g2 L + g2 R )(1 λ U) (g 2 L + g2 R )(1 λ U) 2 + g 2 L D (i) (M 2 /s) s λ U = M 2 U /M2, λ U < y < 1 Flat y distribution in contrast to SM dσ CC SM dy = G2 F s π dx M 2 W Q 2 + M 2 W 2 [xq(x, Q 2 ) + xq(x, Q 2 )(1 y) 2 ] Q2 =sxy

12 12 Reach at IceCube: the Waxman-Bahcall Flux To probe σ LQ, need to know ν (i) fluxes Use Waxman-Bahcall (WB) flux E 2 ν φν WB (E ν) GeV cm 2 s 1 sr 1 (all flavors) assumes (1) neutrinos from transparent CR sources (2) adequate transfer of energy to pions in pp collisions at source More neutrinos if Xgalactic CRs dominate at 10 9 GeV increase power requirement at source V. Berezinsky et al. astro-ph/ ; M. Ahlers et al, astro-ph/

13 13 Reach at IceCube: Background and Signal Use downward events Focus on 10 7 < E ν /GeV < atmospheric flux negligible, extraterrestrial flux significant initial WB flux ν µ : ν e : ν τ = 2 : 1 : 0 1 : 1 : 1 with oscillation With E ν = GeV find SM b g d Gandhi, Quigg, Reno, Sarcevic and signal for each flavor i N B (i) N S (i) 2π n T T σ CC SM ( E ν ) y 0.5 φ ν i WB ( E ν ) E ν = 2 for T = 15 yr 2π n T T σ LQ ( E ν ) y 0.5 φ ν i WB ( E ν ) E ν

14 14 IceCube sensitivity Can determine domain of sensitivity of IceCube to LQ production Suppose 2 ν i events in fact observed with y 0.5 Then at 90% CL, there is an upper bound 3.91 on the signal mean Feldman and Cousins N (i) S This then would rule out regions of the g L g R M parameter space Only with 6 events observed is there a lower bound of 1 on the signal mean

15 15 Second generation sensitivity

16 16 Third generation sensitivity

17 17 Summary and Conclusions Introduced cuts on inelasticity as tool for probing new physics in cosmic neutrino interactions Illustrative example: leptoquark production at IceCube Event rate comparable to atmosphere as detector calorimeter M. C. Espirito Santo et al hep-ph/ IceCube y capability allows SM b g d rejection Have shown that production of leptoquarks with M > 250 GeV and diagonal generational couplings can be tested at Antarctic ice cap