Kate Husband Cambridge University, UK Development of an Online Filter for Selection of Cascade-like Events in IceCube Supervisor: Eike Middell

Signals IceCube looks for high-energy astrophysical E.g. from supernova remnants Also detects atmospheric ’s Primary cosmic rays produce muons which is the main background to IceCube.

IceCube 1km 3 high energy, telescope at S Pole Contains DOMs with PMT which record amp. & time of photons Ice contains dust particles and air bubbles so photons scatter

Events: Cascade-like interact through weak force only Quarks produce cascade of Cherenkov photons Photon intensity decays rapidly Muons can also knock out e - resulting in em cascade

Events: Track-like Muons move close to c Don’t lose much energy in producing Cherenkov light Only arrive from above detector as decay quickly Hence long straight downwards tracks

Multi- Vs. Single-Peak If triggered, DOM records continuous waveform 1.Try and fit pulses of different times and amp. into waveform = MULTI-PEAK (mp) OR 2. Find no. of photons from total amplitude and give all photons the same time = SINGLE- PEAK (sp)

AIMs Online filter must separate multiple background events from signal within constraints. Constraints: limited bandwidth & CPU power Aim to improve efficiency by looking at possible new single- peak cut variables

A. ToI Each DOM is given a mass proportional to amount of charge it records Centre of gravity of distribution is used as approx. to interaction vertex Good cut variable as spherical ~0.3, tracks ~0.

B. LineFit Velocity Fits a straight line through triggered DOMs Var(time) is not a good cut variable

Charge weighting doesn’t increase separation

C: Cumulative Charge Cumulative sum of charge of each DOM over time Take time at x% of total charge to get t x Single-peak

~t 75 found to give largest separation

D: Charge Propagation Decay of charge- energy ratio different Total charge ≈energy and centre of gravity ≈ interaction vertex Single-peak

Mean on new axis for each event weighted with distance is new variable: M CD

Optimization New filter: M CD +ToI (sp): 73% e Previous filter: vel+ToI (mp): 71.7% e (smaller detector)

Energy Efficiency New filter is slightly better at low energies Blue: vel +ToI (mp), Red: M CD +ToI (sp)

Summary LineFit velocity cannot be replaced by variance of time New single-peak cut variables: t 75 and M CD New filter suggested with M CD >61.4, ToI>0.14 passing 73.0% sig. for 1% bkd. New filter has slightly better low energy efficiency.