PDD - Data Model

By Section | Whole Paper | PDF (233 pages, ~6.62mb)

• 8.1 System Elements
  • 8.1.1 Software Management
  • 8.1.2 System Engineering
  • 8.1.3 Development Environment
  • 8.1.4 Analysis Framework
  • 8.1.5 Database
  • 8.1.6 Visualization
  • 8.1.7 Development Interfaces
  • 8.1.8 Integration at Pole
  • 8.1.9 Hardware
  • 8.1.10 Data Distribution
• 8.2 Offline Data Flow
• 8.3 Data Model
  • 8.3.1 High Multiplicity
  • 8.3.2 Upgoing Tracks
  • 8.3.3 Cascades/Taus
  • 8.3.4 GRB Downgoing Muons
  • 8.3.5 Icetop
  • 8.3.6 Supernova
  • 8.3.7 Prescaled Raw Data
  • 8.3.8 Monitor
  • 8.3.9 Calibration
  • 8.3.10 Full-Sky Summary Histograms
  • 8.3.11 Unfiltered Raw
• 8.4 Data Sample Organization
• 8.5 Latency
• 8.6 Schedule
• 8.7 Summary

8.3 Data Model

The signal data will be separated with good efficiency from the downgoing muons using just a few selection criteria. These criteria are desiged to include overlaps between the filtered data sets to ensure that no valid data is lost. Table 12 lists a set of tagged data samples that are to be extracted at high efficiency from the downgoing muon background and the approximate satellite bandwidth required for each one. A short description of these samples follows in order to give correspondence between the data samples and the analysis topics. The purpose of describing the samples is not to solidify their description, but rather to indicate the level of background reduction we believe is necessary for this data model to work. Final available satellite bandwidth will not be known precisely for some time, and event size and event rate can only be estimated at this stage, but table 12 is sufficiently accurate to guide design work.

8.3.1 High Multiplicity

The IceCube trigger system will probably include some sort of majority trigger in which some number N of time-coincident hits fire the trigger. For some M > N, the trigger rate is sufficiently low to fit within the satellite budget. This sample is otherwise unfiltered. It supports the search for new physics at the highest energies accessible to IceCube. The other physics samples are devoted to the lower-energy analyses.

Table 12: Summary of IceCube Data Samples designed to support the science goals. The two right columns indicate tape and satellite bandwidths budgeted to each sample at this very preliminary stage.

8.3.2 Upgoing Tracks

Upgoing tracks are typically muons originating from neutrino interactions in or below the instrumented volume. Upgoing tracks can be selected by zenith angle after a quick reconstruction. Tracks may be triggered via either a global multiplicity trigger or a string multiplicity trigger.

Candidate upgoing muon tracks need further requirements imposed, such as a minimum path length that is greater than the string spacing, and a zenith angle > 80°. The "line fit" angular resolution for short tracks is not good enough to reduce the misreconstructed background sufficiently. However, recent improvements in the speed of the likelihood reconstruction make it possible to include it in the Pole Filter. With a resolution online of roughly 2 degrees, misreconstructed background is eliminated much more efficiently. A similar cut on AMANDA data reduces the data by a factor of 100: (130GB/day)/100 results in < 1.5 GB/day.

Events triggered by a string multiplicity trigger select nearly vertical tracks at lower energy than the previous selection. Additional selection criteria are a veto on activity elsewhere in the detector and timing profiles near the speed of light.

8.3.3 Cascades/Taus

Cascades are the result of electron-neutrino interactions and neutrino neutral-current interactions. IceCube triggers on them using some type of multiplicity trigger. Evidence that the events contain a core of light due to the large number of charged particles in the shower is required to separate them from the downgoing muons. Cascade energies need to be sufficient to light up several strings for analysis purposes.

Cuts on the spatial extent of the charged core may be used provided tau detection efficiency remains high. The high energy cascades, one of which is displayed in fig. 24, are of sufficient energy to be included in the high multiplicity sample. This sample is dedicated to the lower-energy cascade analysis.

8.3.4 GRB Downgoing Muons

To study Southern Hemisphere GRBs, one needs to keep all downgoing muons for a 10 min period around the GRB time. At the South Pole it takes a day or two to receive the GRB trigger times from other experiments, so the raw data needs to be cached for a minimum of 2 days. One external GRB trigger per day and saving 10 min of raw IceCube centered around the external trigger time corresponds to 1 GB/day required bandwidth out of the Pole.

It will be some time before another satellite is launched to provide these data as frequently as once per day. The next generation experiment may have a higher GRB notification rate. For the first few years, therefore, we expect the IceCube GRB bandwidth requirements to be much less than 1 GB/day.

A recent paper by Waxmann suggests that once every 40 years a supernova is close enough to produce about 100 muons in IceCube shortly after the event. Presumably this event would be very bright and we could search for it in the same way that we search for GRB.

8.3.5 Icetop

The IceTop array detects high energy cosmic ray shower events. These events typically have high multiplicity and are expected to include waveforms. Their estimated raw data rate is 1–2 GB/day, reduced to 0.1 GB/day after filtering.

8.3.6 Supernova

Supernova are expected to produce a large number of low energy neutrinos. The experimental signal is an increase in all the PMTs of about 100 photons over a 10 s period. This analysis requires us to record the PMT noise rates in 10 s bins for the duration of the experiment. This adds up to about 0.1 GB/day.

8.3.7 Prescaled Raw Data

A minimum bias sample of prescaled downgoing muons can be used for geometry and timing calibrations, to monitor detector stability, and as a test of background rejection algorithms used in other analyses. Taking this data at 4 Hz yields a data sample of 0.5 GB/day.

8.3.8 Monitor

Monitor data is used to measure the quality of the data and verify the stability of the detector over the lifetime of the experiment. Types of monitor data that we considered are: trigger, filter, and reconstruction rates, temperature sensors, DOM RAP jitter, PMT gain, risetime, peak-to-valley, occupancies and noise rates, network activities, system deadtime, building power, UPS status, local weather conditions, and station parameters such as satellite status, drilling, and airplane landings. Measuring the DAQ related quantities once every 10 min seemed sufficient and contributes about 1.5 MB/day for each item monitored on 4800 PMTs. The 1 GB/day bandwidth allows us to measure 600 such quantities. Many quantities are recorded much less often, and some have fewer than 4800 channels.

There is no reason to limit the monitor data to activities at the Pole. The software is also designed to include monitor data from any post-processing filters as well. We will build on the AMANDA experience to implement a web-based monitoring interface and electronic logbook for IceCube.

8.3.9 Calibration

This sample consists of data from in situ light sources. This kind of data is triggered event data, although several different triggers may contribute. Triggering either from the light pulse or with coincident hits is possible. Our other calibration source is downgoing muons which will be available in the prescaled raw data.

Other calibrations, such as PMT gain and efficiency, may be generated in real time in the DOM firmware, and as such will already exist in the data stream. These calibrations need to be extracted and analyzed offline.

From various sources, calibration constants are compiled and stored for use by the reconstruction. Since constants may be modified as the analysis improves, a database implementation is the obvious preferred choice with version numbers to keep track of what has been done.

8.3.10 Full-Sky Summary Histograms

High energy photons are predicted to send showers deep into the ice, triggering the IceCube detector. Since this analysis requires sifting through every downgoing muon that triggers the detector, it would be too cumbersome to achieve without a predefined histogramming of the data. Full-sky summary histograms are therefore created every few minutes, resulting in 0.5 GB/day. From these histograms energetic point sources in the Southern Hemisphere may be discovered.

8.3.11 Unfiltered Raw

After the first year, all unfiltered raw data is written to tape at the Pole, hand-carried out of the Pole at station re-opening each November, copied and stored in at least two locations in the northern hemisphere. The limitations on the use of the raw data are described in sec. 8.4.

Table of Contents