IceTop and Cosmic Ray Filters¶
WG Tech Lead: Katherine Rawlins (krawlins@alaska.edu)
Executive Summary¶
Filter: |
5-Tank |
2-Station |
1-Station Southwest |
IceAct |
|---|---|---|---|---|
Split: |
IceTopSplit |
IceTopSplit |
IceTopSplit |
IceTopSplit(?) |
Triggers: |
any trigger |
IceTop 2-Station (21002) |
any trigger |
IceAct (30002) |
Inputs needed: |
an IceTop HLC pulseseries |
an IceTop HLC pulseseries + the I3TriggerHierarchy |
an IceTop HLC pulseseries |
just the I3TriggerHierarchy |
Requirements: |
None |
None |
None |
None |
New frame objects: |
IceTopHLCCount |
None |
IceTopHLCCount_SW |
None |
Filter rate: |
~ 4.5-5.0 Hz |
~ 1.6 Hz |
~ 3 Hz |
~ 2 Hz |
I3Bool result: |
IceTopNHLCTank5_24 |
IceTopTwoStation_24 |
IceTopSouthwestNHLCTank1_24 |
IceActTriggerPresent_24 |
Note that all the IceTop filter rates are expected to vary (a lot more than IceCube filter rates do) with atmospheric conditions. Also, many of these filters overlap with each other (ADD A VENN DIAGRAM?)
The “5-Tank” filter¶
This filter simply counts the number of IceTop tanks with an HLC hit, and the filter passes if this “Ntanks” count is >=5. It provides the “bread and butter” of most IceTop analyses, cosmic ray primaries of roughly ~1 PeV and above.
In IceTop, HLC hits normally come in pairs (one from TankA and one from TankB within a station), and so the number of HLC tanks is usually an even number. However, every once in a while one of the HLC hits is invalidated for some reason and the number of HLC hits comes out odd: for instance, 5 in stead of 6 when three stations participated. So choosing >=5 as the criterion is intended to be roughly equivalent – inclusive, in any case – to what we used to call the “3-station filter” back in the old days.
Historical note: there used to be two different 3-station filters in the old days: one that excluded InFill tanks, and one that included them. In this version, all tanks in the array are treated the same, and any 5 tanks from anywhere in the array will cause this filter to pass. It is designed to “keep it simple” and be inclusive of any 3-station-style event. Analyzers who are interested in InFill events, or non-InFill events, can make use of the legacy tags (computed for users, but not used to perform any filtering) in order to restrict their samples further.
The “2-Station” filter¶
To extend the sensitivity of IceTop to low-energy events (below 1 PeV), the “2-station IceTop trigger” was introduced in 2016. It takes advantage of the densely-populated “InFill” region of the IceTop detector: it is actually a “volume” (a.k.a. “cylinder”) trigger, which requires a minimum number of pairs of tanks from the InFill region. For details about the trigger and its physics application, see this paper: [1].
Its associated filter is designed to simply select these triggers and pass them through. If the trigger is present in the Q-frame, the filter re-evaluates the trigger conditions on the IceTop pulses in each IceTopSplit P-frame. Most of the time there is only one IceTop P-frame – especially for these small events. But if there is more than one, re-evaluating the trigger conditions ensures that the filter passes the P-frame associated with the firing of the trigger.
The “Southwest 1-station” filter¶
Coincident events between IceTop and IceCube have always been of interest. IceCube is read out for interesting IceTop triggers, and IceTop is read out for interesting IceCube triggers. But there is a class of potentially sub-threshold events which would be missed by other filters: small events that hit just one station at IceTop, but have muons that survive to IceCube. Potential uses for these events include: calibration of IceCube with single downgoing muons, and use by surface array R&D efforts (such as scintillators, radio, and IceAct). Saving all of them would be too resource-intensive, but we’d like to save a few of them for targeted studies.
The surface array R&D efforts are envisioned to be the primary users of these events, and those prototype detectors are clustered in the east-southeast region of the detector, near stations 33, 34, and 43. So this filter selects events with at least 1 HLC hit in any one of these three particular stations.
This filter was introduced as an online filter in IC86.2022, and is discussed in a little more detail in this “TFT-style” proposal document from 2022: [2].
The IceAct filter¶
Like the 2-Station filter, this filter is designed to simply select events for which an IceAct trigger is present, and passes them. The IceAct telescopes are Imaging-Air-Cherenkov-Telescopes which measure cosmic ray air showers in the atmosphere above IceCube/IceTop. The “roof” telescope on top of the IceCube Laboratory(ICL) at South Pole is connected to a dom-mainboard “Reliant_Robin” in the ICL. The event trigger of the telescope gets passed on to the dom-mainboard which triggers a full detector readout of the IceCube/IceTop, with the goal to measure low energy coincidences between all three detector types. The energy range for the cosmic ray particles detectable with an IceAct starts at around 10 TeV upto above 10 PeV. The telescopes just operate during the night so events are expected from the end of April until the beginning of September.
The nominal trigger rate should be around 2Hz but rate changes are expected on short and long time scales. The trigger rate drops due to increased night sky background light during full moon phases. Auroras can lead to short term rate spikes up to 10Hz. Bad atmospheric conditions can lead to changes in the trigger rate as well.
