The Use of Trigger and DAQ in High Energy Physics Experiments Lecture 3: The (near) future O. Villalobos Baillie School of Physics and Astronomy The University of Birmingham

September 14th The Auger experiment CBM ALICE run 3 Other considerations Summary Contents Lecture ICTDHEP Jammu India - O. Villalobos Baillie

The Auger Experiment This is a very large scale cosmic ray experiment, with a southern station over an extended area in Argentina Detectors are spread over an area of 3100 km 2 (about 1600 in all) Communication with the central trigger is very slow, so the detectors have to be autonomous. September 14th ICTDHEP Jammu India - O. Villalobos Baillie

The Auger Experiment II September 14th ICTDHEP Jammu India - O. Villalobos Baillie

The Auger Experiment III Each unit consists of a water tank with 3 PMTs The PMTs are scanned every 25ns. A local trigger checks for 3 signals above threshold. If found, the values and the timestamp are transmitted to the central trigger via the microwave transmitter Local trigger output is ~20 Hz at each station, so data transmission time is negligible compared to live time. September 14th ICTDHEP Jammu India - O. Villalobos Baillie

Auger IV Final trigger (T3) is made at the central trigger. An event is kept if three stations (non-collinear) simultaneously give a signal (in a 100 ms window). Final (T3) rate ~O(0.01 Hz) If so, readings for all stations giving counts above threshold are read out; if not, event discarded after 5s. Note final trigger decision made long after the data are read out. September 14th ICTDHEP Jammu India - O. Villalobos Baillie

Analysis Auger is a very early example of a “triggerless” system. Detectors (stations) are self-triggering, and the final trigger is made by analysing the data coming from each station, after event readout has taken place. September 14th ICTDHEP Jammu India - O. Villalobos Baillie

The Challenge September 14th 2013 ICTDHEP Jammu India - O. Villalobos Baillie 8  typical CBM event: about 700 charged tracks in the acceptance  strong kinematical focusing in the fixed-target setup: high track densities  up to 10 7 of such events per second  find very rare signals, e.g., by decay topology, in such a background

Trigger Considerations Signatures vary qualitatively: – local and simple: J/ψ->μ + μ - – non-local and simple: J/ψ -> e + e - – non-local and complex: D,Ω->charged hadrons For maximal interaction rate, reconstruction in STS is always required (momentum information), but not necessarily of all tracks in STS. Trigger architecture must enable – variety of trigger patterns (J/ψ: 1% of data, D mesons: 50% of data) – multiple triggers at a time – multiple trigger steps with subsequent data reduction Complex signatures involve secondary decay vertices; difficult to implement in hardware. Extreme event rates set strong limits to trigger latency. September 14th 2013 ICTDHEP Jammu India - O. Villalobos Baillie 9

Running Conditions September 14th 2013 ICTDHEP Jammu India - O. Villalobos Baillie 10 ConditionInteraction ratelimited byApplication No Trigger10 4 /sarchival ratebulk hadrons, low-mass di-electrons Medium Trigger10 5 /s – 10 6 /sMVD (speed, rad. tolerance), trigger signature open charm multi-strange hyperons, low-mass di-muons Max. Trigger /s (even more for p beam) on-line event selection charmonium Detector, FEE and DAQ requirements are given by the most extreme case Design goal: 10 MHz minimum bias interaction rate Requires on-line data reduction by up to 1,000

CBM Readout Concept September 14th 2013 ICTDHEP Jammu India - O. Villalobos Baillie 11 Finite-size FEE buffer: latency limited throughput limited

CBM Although the rates are very different from those of Auger, the concepts are quite similar. –Autonomous detectors that are self-triggering. –Event selection done by analysing readings. September 14th ICTDHEP Jammu India - O. Villalobos Baillie

September 14th ICTDHEP Jammu India - O. Villalobos Baillie

14 luminosity upgrade – 50 kHz target minimum-bias rate for Pb–Pb run ALICE at this high rate, inspecting all events improved vertexing and tracking at low p T preserve particle-identification capability new, smaller radius beam pipe new inner tracker (ITS) (performance and rate upgrade) high-rate upgrade for the readout of the TPC, TRD, TOF, CALs, DAQ-HLT, Muon-Arm and Trigger detectors collect more than 10 nb -1 of integrated luminosity implies running with heavy ions for a few years after LS3 for core physics programme – factor > 100 increase in statistics (maximum readout with present ALICE ~ 500 Hz) for triggered probes increase in statistics by factor > 10 ALICE upgrade after LS2 For CTP after LS2 see M. Krivda talk R. Lietava ICTDHEP Jammu September 2013

15 ALICE

Some detectors (TPC, possibly ITS and Muon system) can read out continuously –Therefore in principle, don’t need trigger. Data instead divided into time frames, separated via a heartbeat trigger (software), which marks the boundaries of each chunk of continuous readout serves to monitor synchronization of local and central clocks Other detectors read out upon a minimum bias like trigger Greatly improved data links allow data to be transferred to an improved High Level Trigger (HLT) for software analysis HLT performs event selection and data compression tasks. –Requires large expansion in online computing for HLT system. Important because ALICE signals require complex data processing of events, not compatible with traditional triggers. ALICE Run 3 Trigger Upgrade September 14th 2013 ICTDHEP Jammu India - O. Villalobos Baillie 16

Summary on Triggerless Operation Original motivation for triggering was that data acquisition cannot keep up with reading out every event for offline analysis. Too much data Too slow Huge improvements in online computing capabilities (speed and massive parallel processing) mean that data can now be filtered in real time. Still don’t write all data to tape, but can analyse events at minimum bias level. September 14th ICTDHEP Jammu India - O. Villalobos Baillie

Other upgrades “Triggerless operation” is not the only option. As we heard in the trigger workshop, ATLAS are keeping the original trigger concept, with strong selections at the first triggering level, but are instead optimising all levels of the system. One general point is the improvement of the granularity of the system. September 14th ICTDHEP Jammu India - O. Villalobos Baillie

Trigger Thresholds September 14th Good Trigger threshold usually quoted as when efficiency reaches 50% There is a tail of completely unwanted below threshold triggers There is a region above the nominal threshold where the efficiency is still poor (and needs corrections, which may be not be precisely known. Not wanted Nominal threshold Low efficiency Sharper decision optimises selection ICTDHEP Jammu India - O. Villalobos Baillie

Summary In these lectures you have seen several aspects of triggering: 1.Why limited data acquisition rates mean triggering is necessary 2.The constraints of dead time 3.Why colliders impose additional constraints on triggers and data throughput, leading to a need for pipelining at high rate 4.Why massive improvements in online processing (HLTs) mean that problem 1 has to some extent gone away, so “triggerless systems” can be considered for some applications. 5.However, close attention to all details of the trigger, and optimisation of all features, remains very important. September 14th ICTDHEP Jammu India - O. Villalobos Baillie