Search for UHE photons and neutrinos using Telescope Array surface detector

Search for UHE photons and neutrinos using Telescope Array surface detector G.I. Rubtsov, M. Fukushima, D. Ivanov, B. Stokes, G. Thomson, S.V. Troitsky for the Telescope Array Collaboration 32 th ICRC Beijing, August, 2011 Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 1

Telescope Array surface detector 507 SD s, 3 m 2 each 680 km 2 area 3 years of operation Largest UHECR statistics in northern hemisphere Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 2

Photon search strategy proton-induced EAS gamma-induced EAS Deep shower maximum and shortage of muons curved front Linsley s shower front curvature parameter a is used for photon/hadron separation Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 3

Front curvature for typical event, θ = 53.6 0.8 1σ region Fit Photon MC data 0.7 0.6 front delay [1200m]; 0.5 0.4 0.3 0.2 0.1 0-0.1 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 core distance [1200m] Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 4

Dataset Data collected by TA surface detector for three years: 2008-05-11 2011-05-01 Cuts: 7 or more detectors triggered core distance to array boundary is larger than 1200m (one separation unit) χ 2 /d.o.f. < 5 45 < θ < 60 E γ > 10 19 ev (E γ is estimated for every event using photon Monte-Carlo) 877 events after cuts Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 5

Photon Monte-Carlo set CORSIKA with QGSJET-II, FLUKA and EGS4. PRESHOWER for geomagnetic field cascading Thinning with weight optimisation (ε = 10 6 ) Dethinning technique is used Kobal, Astropart.Phys.15:259-273,2001 Stokes et al, arxiv:1104.3182 Detector response is calculated with GEANT sampler E [10 18.4, 10 20.5 ] ev, θ [0, 65 ] Exactly same cuts applied to data and Monte-Carlo sets Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 6

Linsley curvature a : E > 10 19 ev 300 250 200 0 30 h_gm h_dt Entries 1394 7867 Mean 0.7585 0.5867 RMS 0.2024 0.3131 Underflow 0.3548 0 Overflow 1.242 0 300 250 30 45 h_gm h_dt Entries 14348 1031 Mean 0.4829 0.7493 RMS 0.1651 0.3046 Underflow 0.2158 0 Overflow 1.007 0 150 200 100 150 50 100 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 a 50 350 45 60 h_gm h_dt Entries 15420 877 Mean 0.3934 0.6757 RMS 0.1139 0.2813 Underflow 0.3419 0 Overflow 1.368 0 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 a 300 250 200 150 100 50 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 a E γ > 10 19 ev data photon MC, E 2 spectrum Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 7

Event-by-event method For each event with curvature a obs we select photon MC events compatible by arrival direction and S 800. We calculate curvature distribution function f γ (a) for MC photons Let s define C = C is defined event-by-event a obs f γ (a)da For gamma events, C is uniformly distributed between 0 and 1 (independently of the photon primary spectrum). Gorbunov, GR, Troitsky, Astropart.Phys. 28:28-40 GR et al., AIP Conf.Proc. 1367 Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 8

C: E > 10 19 ev 400 350 45 < θ < 60 h_gm h_dt Entries 15420 877 Mean 0.1079 0.4857 RMS 0.1048 0.2821 Underflow 0 Overflow 0 300 250 200 150 100 50 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 C data photon MC, E 2 spectrum Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 9

Results Statistical test gives maximum expected number of photons in the set N γ Exposure A is calculated using photon MC conservatively assuming E 3 spectrum; E γ > 10 19.0 ev, Nγ < 14.1, A = 643 km 2 sr yr E γ > 10 19.5 ev, Nγ < 8.7, A = 887 km 2 sr yr E γ > 10 20.0 ev, Nγ < 8.7, A = 1196 km 2 sr yr F γ = N γ /A E γ > 10 19.0 ev, E γ > 10 19.5 ev, E γ > 10 20.0 ev, F γ < 2.20 10 2 km 2 sr 1 yr 1 F γ < 0.98 10 2 km 2 sr 1 yr 1 F γ < 0.73 10 2 km 2 sr 1 yr 1 (95% CL) /PRELIMINARY/ Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 10

Results Statistical test gives maximum expected number of photons in the set N γ Exposure A is calculated using photon MC conservatively assuming E 3 spectrum; E γ > 10 19.0 ev, Nγ < 14.1, A = 643 km 2 sr yr E γ > 10 19.5 ev, Nγ < 8.7, A = 887 km 2 sr yr E γ > 10 20.0 ev, Nγ < 8.7, A = 1196 km 2 sr yr F γ = N γ /A E γ > 10 19.0 ev, E γ > 10 19.5 ev, E γ > 10 20.0 ev, F γ < 2.20 10 2 km 2 sr 1 yr 1 F γ < 0.98 10 2 km 2 sr 1 yr 1 F γ < 0.73 10 2 km 2 sr 1 yr 1 (95% CL) /PRELIMINARY/ Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 11

Results Statistical test gives maximum expected number of photons in the set N γ Exposure A is calculated using photon MC conservatively assuming E 3 spectrum; E γ > 10 19.0 ev, Nγ < 14.1, A = 643 km 2 sr yr E γ > 10 19.5 ev, Nγ < 8.7, A = 887 km 2 sr yr E γ > 10 20.0 ev, Nγ < 8.7, A = 1196 km 2 sr yr F γ = N γ /A E γ > 10 19.0 ev, E γ > 10 19.5 ev, E γ > 10 20.0 ev, F γ < 2.20 10 2 km 2 sr 1 yr 1 F γ < 0.98 10 2 km 2 sr 1 yr 1 F γ < 0.73 10 2 km 2 sr 1 yr 1 (95% CL) /PRELIMINARY/ Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 12

Photon flux limits Log E 2 F Γ ev 2 km 2 yr 1 sr 1 38 37.5 37 36.5 36 35.5 PRELIMINARY A Y TA PA Y PA Y A TA PA TA 18 18.5 19 19.5 20 Log E min ev Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 13

Photon fraction limits Ε Γ,% 100 A HP HP A A TA PA Y PF Y 10 TA PF YN PA PF PF PA AH AY 10 1 0.1 YN YN PRELIMINARY 18 18.5 19 19.5 20 Log E min ev 1 0.1 Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 14

Neutrino search strategy Neutrino produces very inclined young shower young shower, θ = 19.5 old shower, 78.3 long, indented wafeforms one peak Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 15

Neutrino search We count waveform peaks per detector layer. peak FADC count higher than 3 right, 3 left neighbours and 0.2 VEM (separate on upper and lower layers) Dataset: TA surface detector, 2008-05-11 2011-05-01 7 or more detectors triggered core distance to array boundary is larger than 1200m χ 2 /d.o.f. < 5 θ > 70 No energy (S 800 ) cut 785 events after cuts Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 16

Number of peaks vs Zenith angle 7 data 6 5 peaks / layer 4 3 ν 2 1 0 0 10 20 30 40 50 60 70 80 90 Zenith angle No young inclined showers in the dataset no neutrino candidates. Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 17

Conclusions Photon flux limits are obtained above 10 19 ev. Log E 2 F Γ ev 2 km 2 yr 1 sr 1 38 37.5 37 36.5 36 35.5 PRELIMINARY Y Y Y 18 18.5 19 19.5 20 Log E min ev A TA PA PA A TA PA TA Ε Γ,% 100 10 1 0.1 YN A HP HP A A TA PA Y PF Y TA PF YN PF PA PF PA YN 18 18.5 19 19.5 20 Log E min ev AH AY PRELIMINARY 10 1 0.1 No down-going neutrino candidates, E 10 18 ev. Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 18

Backup slides Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 19

Method details 1/2 For each event i we calculate curvature aobs i and curvature distribution fγ(a) i for MC photons. Then determine C i = a i obs f i γ(a)da For gamma events, C is uniformly distributed by definition. Let F γ be an integral flux of primary photons over a given energy range. Then we expect photons (A - exposure). N(F γ ) = F γ A Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 20

Method details 2/2 Let P(N) be a conservative probability to have N photons in a dataset which is defined as a maximum over all subsets of N real events: P(N) = max P({i 1,..., i N }), i 1 <i 2 < <i N where P({i 1,..., i N }) is a statistical probability of the subset {i 1,..., i N } to be compatible with uniform distribution (100% photon events). We use Smirnov-Cramer-von Mises omega-square test. The constraint on the flux F γ at the confidence level of ξ follows from: P(N)W (N, N(F γ )) < 1 ξ. N Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 21

Smirnov-Cramer-von Mises omega-square test Let F(x) be theoretical distribution and F n (x) observed distribution. We define the distance between distributions by: ω 2 = (F n (x) F(x)) 2 df(x). If x 1, x 2,..., x n is a set of observed values in increasing order, we have: nω 2 = 1 n ( ) 2i 1 2 12n + 2n F(x i). i=1 For this study any non-parametric statistical test may be used (e.g. KS test), but ω 2 test allows simple procedure for maximizing over all subsets of the dataset. Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 22

Exposure calculation: E γ > 10 19 ev We take MC photon set with E mc > 10 19 ev conservatively assuming E 3 spectrum. We calculate the fraction of photons entering the search region. Geomertical exposure 45 < θ < 60 : A geom = 1286 km 2 sr yr 100% n det 7 67% χ 2 /d.o.f < 5 63% E γ > 10 19.0 50% A 19 total = 0.5 A geom = 643 km 2 sr yr Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 23

Exposure calculation: E γ > 10 19.5 ev We take MC photon set with E mc > 10 19.5 ev conservatively assuming E 3 spectrum. We calculate the fraction of photons entering the search region. Geomertical exposure 45 < θ < 60 : A geom = 1286 km 2 sr yr 100% n det 7 95% χ 2 /d.o.f < 5 90% E γ > 10 19.5 69% A 19.5 total = 0.69 A geom = 887 km 2 sr yr Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 24

Exposure calculation: E γ > 10 20 ev We take MC photon set with E mc > 10 20 ev conservatively assuming E 3 spectrum. We calculate the fraction of photons entering the search region. Geomertical exposure 45 < θ < 60 : A geom = 1286 km 2 sr yr 100% n det 7 99% χ 2 /d.o.f < 5 96% E γ > 10 19.5 93% A 20 total = 0.93 A geom = 1196 km 2 sr yr Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 25

Comparison to median method Statistical method: E γ 10 19 ev 10 19.5 ev 10 20 ev Events 45 < θ < 60 877 166 18 N γ < 14.1 8.7 8.7 A stat 643 887 1196 F γ < 0.022 0.0098 0.0073 km 2 sr 1 yr 1 (95% CL) /PRELIMINARY/ Median method: E γ 10 19 ev 10 19.5 ev 10 20 ev Events 45 < θ < 60 877 166 18 Events C > 0.5 3 0 0 Poisson 95% upper limit: 8.25 3.06 3.06 A median = A stat /2 322 443 598 F γ < 0.026 0.0069 0.005 km 2 sr 1 yr 1 (95% CL) /PRELIMINARY/ Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 26

Event reconstruction: fit functions Joint 7-parametric fit: x core, y core, θ, φ, S 800, t 0, a ( r f (r) = R m LDF (r) = f (r)/f (800 m) ) 1.2 ( 1 + r ) (η 1.2) (1 + r 2 ) 0.6 R m R1 2 S(r) = S 800 LDF (r) t 0 (r) = t 0 + t plane + a 0.67 (1 + r/r L ) 1.5 LDF (r) 0.5 R m = 90.0 m, R 1 = 1000 m, R L = 30 m η = 3.97 1.79(sec(θ) 1) Grigory I. Rubtsov for the Telescope Array collaboration Photon and neutrino search 27