Reconstruction of the spectrum of cascades generated by VHE muons in IceCube

1. Reconstruction of the spectrum of cascades generated by VHE muons in IceCube Semyon Khokhlov for the IceCube collaboration National Research Nuclear University MEPhI IV ICPPA, Moscow, Russia, Oct 22-26, 2018

2. Very high energy (VHE) muons Decrease – by the decreasing CR energy spectrum above the knee. Increase – due to inclusion of any additional rapid processes of muon generation: decays of charmed and other short-lived massive particles or appearance of a new state of matter. Muons with energies above 100 TeV are of a special interest, since changes of their energy spectrum can be caused by different physical reasons: One of the best ways for investigations of VHE muon spectrum is measuring the spectrum of stochastic energy losses (cascades).

3. IceCube Neutrino Observatory IceTop air shower detector 81 pairs of water Cherenkov tanks IceCube 86 strings including 8 Deep Core strings 60 PMT per string DeepCore 8 closely spaced strings 1450m Rate of events with total response above 1000 ph.e. is 4 s-1. These are mainly muon bundles. 2450m 2820m

4. Optical properties of ice

5. Selection of cascades generated by VHE muons The idea of cascade searching is based on the analysis of the longitudinal energy deposit profile reconstructed by means of Millipede (the algorithm uses the maximum likelihood method). For the search of the high-energy cascades we use the ratio of the highest local energy deposit to median energy deposit. εreco = max(εi-1 + εi + εi+1), Ratio = εreco/3*median{εi}.

6. Distributions of events in the peak/median-ratio Sim Dataset was used: 5-component simulation with CORSIKA above the ice surface (p, 4He, 14N, 27Al and 56Fe) in the energy range of 1014-1020 eV with the differential spectrum E-2. Sim Reco For small Ratio, the cascades with low energies can be erroneously reconstructed as cascades with high energies. Events with Ratio < 12 should be excluded.

7. Reconstruction of the cascade energy in the events with muon bundles (Sim Dataset, Ratio > 12) Cascades in the dust layer excluded All events Clear ice (zcascade < -150 m) Possibly, muon bundles of large multiplicity imitate cascades in reconstructed longitudinal energy deposit profile in the upper part of detector. Such contamination is less in the lower part.

8. Distribution of log10(εreco/εsim) εreco > 32 TeV: σ[log10(εreco/εsim)] = 0.15 (40 % accuracy). εreco>100 TeV: σ[log10(εreco/εsim)] = 0.10 (25 % accuracy).

9. Reconstruction of cascade spectrum (for the lower detector) Spectra of primary particles (sim Dataset) γ = -3 γ = -2 Spectra of muon-induced cascades

10. Ratio of reconstructed and simulatedenergy spectra of cascades γ = -2 γ = -3 At cascade energies above 10-30 TeV the slope of cascade spectrum is reproduced correctly.

11. VHE-muon candidateEvent 119090/12514768 <dEμ/dx> = a + b∙Eμ; b = 3.7∙10-6 cm2/g; b* = 2.7∙10-6 cm2/g EμSurf > εcascexp(depth∙ρ∙b*) =0.45∙exp(2.4∙105∙2.7∙10-6)=0.86 PeV

12. Conclusions • The technique of reconstruction of the spectrum of cascades generated by muons in the lower part of the IceCube has been developed: effective energy of cascades > 10-30 TeV; accuracy of the energy reconstruction σ[log10(εreco/εsim)] = = 0.10 for cascades with εreco > 100 TeV; the spatial accuracy 5-6 meters. • IceCube is the detector capable of measuring the cascade spectrum in the energy region of tens TeV – one PeV where manifestation of prompt muons is predicted.

13. Thank you for attention!