Supernovae: BeyondDC-Phase 1 Some remarks on supernovae Detection principle – Absorption lengths – Effective volumes – Noise Supernova dynamics & fundamental physics with IceCube What‘s good and what‘s bad? how to improve on IceCube – correlated noise from atmospheric neutrinos – first noise rate estimates in coincidence mode Phase 1 simulation: Lukas Schulte Lutz Köpke Johannes Gutenberg University Mainz BeyondDC Workshop, , Amsterdam

Lets start with the bad news … Milky Way: 2  1 core collapse supernovae per century with 3 supernovae/century, probability of observation: 25 % within 10 years 45% within 20 years e.g. arXiv: v2 (Lick survey): 2.84  0.60 total number SN/100 years 2.30  0.48 core collapse SN/100 years … in Milky Way volumetric rate of SN Type II at small z: (4.5  1.4) x /Mpc 3 /yr … but there are closeby clusters type II + type Ib  Marek

Supernova collapse is complex … multi-dimensional simulations necessary: standing accretion shocks? forward and reverse shocks? acoustic vibrations? collapse dynamics depends on details … neutrino physics plays important role: neutrino heating/cooling and emission neutrino MSW effect coherent neutrino oscillations? Lack of sufficiently fast computers explains “… agonizingly slow march since the 1960s towards demonstrating a robust mechanism of explosion“ (Burrows et al.) … let‘s consider only the simple things ….

Energy release  E dominant reaction: e + p  e + + n interaction cross section: ~ E 2 Cherenkov light yield ~ E 3 … R=10 10 m star collapses via a R core =10 6 m core to a R NS =10 4 m neutron star  E   E  E kin   E  E em   E individual neutrino energy ~  E /N 8.8 M  progenitor O-Me-Mg core (1s after bounce) … rates strongly dependent on neutrino energies … in ice: track length ~ 0.57 cm x E e+ (MeV) N  nm ~ 180 x E e+ (MeV)

effective volumes back on the envelope calculation (no scattering) for effective DOM volume per  : effective  volume = effective DOM area * absorption length * DOM threshold # detected photons = effective volume * # Cherenkov  ‘s * neutrino density BeyondDC depends on Cherenkov yield, photon propagation (absorption) and detector sensitivity 1/ 2 and DOM acceptance weighted absorption length: IceCube: ~ 100 m BeyondDC: ~ 150? m … needs to be done precisely with Photonics or GEANT effective DOM area ~ 0.071*0.32* m 2 DOM threshold ~ 0.85

Interaction vertices in IceCube define effective positron volume: N  detected = V e+ eff  neutrino density simulation: V e+ eff =29.5 x E e+ /MeV for E e+ = 20 MeV: „full efficient r=5.2 m sphere“ view from above Geant-3 result, Fazely et al.

Noise standard DOM noise rate: ~ 540 Hz (of which ~ 225 Hz „Poissonian“) HQE DOM noise rate: ~ 680 Hz observe bursts of pulses (presumed origin scintillation in glass …) pulse time differences reduction of correlated noise by artificial deadtime (285 Hz after non-paralyzable 250 μ s cut)

… noise correlated pulses increase background and distort Poissonian character:  /  n ~1.3 Additional background due to atmospheric muons add correlations:  /  n ~1.7 total noise in detector correlated with muon hits 3.6% decrease in noise rate, but ~30% reduction in standard deviation! total noise in IceCube

Rates are very model dependent! 15 solar masses 8.8 solar masses no iron core … two available models that make long term predictions … background level Hüdepohl et al., Phys. Rev. Lett. 104, (2010) IceCube preliminary

Expected rate distribution Lawrence Livermore model, 10 kpc distance (~ distance to center) normal neutrino hierarchy inverted neutrino hierarchy clear differences in model shapes for normal and inverted hierarchy! Totani et al. Astrop. Phys. 496, 216 (1998) preliminary background level IceCube preliminary

Onset of neutrino production „deleptonization peak“ very much dependent on neutrino properties and oscillations  difficult to observe … decreasing noise will probably not be sufficient … no background, only  e with backgrounds, all  ‘s normal hierarchy inverted hierarchy Kachelriess et al., Phys. Rev. D 71, (2005) IceCube preliminary

More exotic signals quark star formation (quark-gluon plasma transition) however, nuclear equation of state excluded by recent measurements of high mass neutron stars? anti-  peak! hierarchy dependence! normal hierarchy inverted hierarchy Dasgupta et al., Phys. Rev. Lett. D 81, (2010) normal hierarchy no oscillations inverted hierarchy black hole formation (>40 m  progenitor)  no explosion! unfortunately unlikely in Milky way  delayed black hole production ? Sumiyoshi et al., ApJ 667, 382 (2007) IceCube preliminary

… if model shapes are known sensitivity on neutrino hierarchy … optimal situation!! IceCube preliminary it would be good to improve on this in order to become less model dependent …

Supernova Progenitors candidates probability distribution for SN progenitors PR D80:123017,2009 Ahlers, Mertsch Sarkar unclear how supernova progenitors follow star distribution … 25 kpc 10 kpc … until now only looked at fixed distance of 10 kpc

Expected significance in IceCube depends on detection technique as well as model and neutrino properties …  > 25 in Galaxy  ~ 3-10 in Magellanic clouds  preliminary (only 5% of all stars!)

Good and bad IceCube is the world‘s most precise detector for determining the neutrino light curve of close supernovae no detection of individual neutrinos (statistical excess on top of noise) standard deviation of noise larger than Poissonian expectation –sensitivity limited to our galaxy, quickly deteriorating with distance, low during onset (low sensitivity to e (H 2 O target...) and cooling phase –limited time resolution of 2 ms –no determination (and selection) of neutrino energy, type, and direction Could a phase 1 detector do substantially better? …however,

Reducing noise is crucial! some improvement in IceCube possible, however, major step is needed as Significance = Signal /  (Background)  strongly reduce muon induces background  look for coincident  ‘s in several modules from same neutrino interaction [IceCube SN signal: O(1%); Phase 1 O(15%)] limited improvement of reach in IceCube [Southern, Lausanne]  needs dense detector!

Coincident noise rate estimate Atmospheric Muons 20 Hz atmospheric muon noise rate per DOM  needs to be reduced to < 1 Hz !  not trivial, needs effective trigger and veto ! (in IceCube only 50% reduction)  active IceCube veto  discard O(3 μs) time slice around triggered muon (3% kHz trigger rate) muon induced noise rate ( m): ~ 20 Hz / DOM for HQE DOMs standard efficiency DOMs … for BeyondDC phase 1

…coincident noise rate estimate Random Hits f=680 Hz noise rate per DOM, can be reduced to ~ f/2 by artificial deadtime N DOMs used to form coincidences  rate needs to be reduced to < 1 Hz in coincident mode  not trivial! Limit combinatorics, short coincidence time  t Estimate: probability for >0 hit per DOM: probability for 2 or more coincident hits: note that actual rate in DeepCore is higher than simple model … radioactive decays may trigger DOMs in coincidence ….

…coincident noise rate estimate Rate per DOM in coincident mode (for >1 coincidences): For the numbers we assume: N total =6300 DOMs (1 m DOM distance) and p = f  t with f=340 Hz (after deadtime) and  t= 100 ns The first number is given for combinatorics limited to DOMs within 20 m in z-coordinate of event (N=720); the second number uses all N=6300 DOMs combinatorics needs to be reduced!

32 Hz 2.2 Hz 0.12 Hz 0.47 Hz Hz Hz … also analyse events with  3 coincident hits … purple dots: coincidences between all DOMs blue dots: only within  20 m in height needs smart way of reducing combinatorics … very preliminary! …coincident noise rate estimate

neutrino energy tracking … very preliminary! Lawrence Livermore model flux, averaged over 15 s 3 hits vs 2 hits: 2.2, 30 Hz background 2 hit vs 1 hit: 30 Hz background 2 hit vs 1 hit: 0.5 Hz background O(1%)  E/E resolution at 10 kpc! Seems not to be valid, unfortunately Systematics will probably be significant …

...take this with a grain of salt IceCube [kton] Phase 1,  2 hits 0.5 Hz bg. [kton] Phase 1,  3 hits 2.2 Hz bg. [kton] Phase 1,  2 hits 30 Hz bg. [kton] Distance 10 kpc Distance 50 kpc equivalent size of a background free detector for beginning 0.38 s of Lawrence Livermore model, 1 m DOM and 10 m string distance, 18 strings Phase 1,  2 hits, no noise Phase 1,  2 hits, 0.5 Hz noise Phase 1  3 hits, 2.2 Hz noise IceCube Phase 1  2 hits, 30 Hz noise very preliminary! … results depend on signal/background for specific model

Summary 1 Fine grained detector will improve model sensitivity and detector reach Track average neutrino energy ? –improved measurements on supernova dynamics –increase sensitivity on neutrino properties –obtain sensitivity to low flux phenomena (delayed BH production..) –however, no „killer application yet …“... provided that noise rate can be limited to < 1Hz !! Quantitative results in Lukas‘ talk … Analyses to dream about: directional reconstruction with „golden events“, enhance e, Andromeda? … we are only at the beginning …