1. ROOT in the PHOBOS Online System Peter Steinberg Brookhaven National Laboratory Upton, NY, USA

2. PHOBOS experimental setup Spectrometer Multiplicity/ Vertex

3. Readout Channels PHOBOS is meant (CDR) to be a high-rate detector However, while a “small” detector, it has a “big” channel count. Spectrometer 73,728 channels Octagon Multiplicity + Vertex detectors 28,612 channels Ring Multiplicity Detectors 16,384 channels Over 120,000 channels to read out -> 150kB/central event Main Constraint: average bandwidth 10MB/sec allowed by RHIC computing facility (RCF)

4. PHOBOS online data flow Run Control Slow Control Online Monitoring FASTBUS Si TOF RHIC ORACLE Data Validation Event Builder (PhATDAQ) Mercury RCF Trigger

5. PhATDAQ PhAT is the general PHOBOS analysis toolkit (see Gunther Roland’s talk) Originally used for offline tasks Data analysis, algorithms, etc. But what about DAQ? Original DAQ group started to develop using CODA from CEBAF But one day, Andrei Sukhanov (BNL) mentioned that he would try and perform the event building directly using ROOT objects and I/O (very) soon thereafter, PhATDAQ was born

6. PhATDAQ Architecture EB interface Data taking ROC: Length Seq.number CommandSourceType SubEvent or Command SubEvent … Message: Length Event# from Event Manager Header length 0x12345678 SubEvent: Data Run number Structure of the communication messages Legend: Working Being developed Work not started yet Work started Event Builder phatdaq.exe Run Control (root/phat) UDP socket TCP TSocket Data & Commands Data PhatOnline Silicon TOF Trigger ROC ROCDB Gateway Data Base Slow Monitoring events (Andrei Sukhanov, BNL) Gigabit

7. PhATDAQ data format Large segments of detector are read out by “Front- End Controller” (FEC) Each FEC consists of several “strings” of “chips” The chip data is concatenated in each string. Thus, channels are indexed by FEC/String/Channel FEC String FEC String Chip “channels”

8. ROOT in PhATDAQ ROOT objects are used to store and access raw data Each FEC is its own object, which contains arrays of string data. Trees are used for raw data files one event after the other, no tags as of yet. Heavy use of ROOT containers for flexibility Our TPhEvent class is a hash table which store relevant objects (TPhDataObject, TPhObjectContainer) However, hashtables are “heavy” -- we have a substitute object (TPhSubEventArray) which can be turned into a TPhEvent and vice versa. PhATDAQ has been working perfectly for 6 months Extensive performance benchmarks to come.

9. Run Control So far, CINT is our run control interface.L runcontrol.cxx rc_start_run() rc_end_run(), etc. Works very well flexible robust DAQ team is conspiring to move to a GUI Inspired by NA45 RC GUI

10. Online Monitoring Designed and implemented by a team at University of Illinois, Chicago Judith Katzy, Clive Halliwell, Don McLeod, Mike Reuter RCFPHOBOSPhATDAQ TCP/IP Dual Pentium Machines ORACLE (katzy@nanalpc.phy.uic.edu)

11. Monitoring Implementation Based fully on PhAT and ROOT Class library encompassing various functions Main process - event loop Display classes Histogram filling and managing Histogram selecting Geometry and electronics setup is self-configuring GUI controls are created dynamically Easily extendable to add new histogram controls All available online application options available through user interface: Program control, histogram selection, display functions

12. Online Monitoring GUI

13. ROOT-based event display Module of Online Monitoring package Allows selection of sub- detectors Hits can be displayed either on the pixel, or perpendicular (hedgehog display) 2/3 dimensional display Different display options: Lego Color coded Octagon Spectrometer Planes (Don McLeod, UIC)

14. More event displays

15. Oracle, ROOT & PhAT Oracle was chosen long ago as the only PHOBOS database Oracle is used comprehensively in the whole system Silicon testing Pedestals and Calibrations Data Tracking Experimental Logbook Slow control information (from Labview & PhATDAQ) However, Oracle is not OO For storing certain objects, simple tables will not do. Hough tables, tracking templates,... Want to store and retrieve arbitrary objects (as BLOBs) by means of a “generic” key. Should also work with ROOT TTrees For more info, ask George Heintzelman (gah@bnl.gov)

16. Signal Processing in PhAT PHOBOS requires extensive amounts of low-level signal processing before any hits can be found Requirements: Granular - algorithms should be “plug-and-play”. Geometric -- wanted to be able to easily analyze data by subsection (FEC, String, Chip, Channel) without overhead of traversing object trees. Easy to adapt to DSP code (c code, Mercury platform) Easy to debug -- simple interface between data and histograms Need ROOT compatibility Led to development of TPhModules and several new data structures to satisfy these requirements...

17. TPhTopology FEC Detector FEC String FEC String Chip Any particular geometry has a fixed electronics structure Thus, every channel has a well defined location This lets us store a set of values as a flat array. The detector topology can then be used to find the start of data! We can iterate from there. “TopoData” (George Heintzelman, BNL)

18. TPhTopoData With this “topology” we can create data structures of different “depths” “Channel Depth” - one entry for each channel “Chip Depth” - one entry for each chip (e.g. for CMN studies…) etc. The contents of this structure can in principle be any object ( working w/ templates in CINT) Integer, Float, etc. Any TObject - TPhHistogram, TPhCalibration, TPhFrog, etc. NEW

19. Application to Signal Processing Visualization of arrays Makes histograms merely a visualization tool, rather than a fundamental object to be moved around Pedestals stored in a TPhTopoData “TPhTopoData ” Visualize “by string”

20. Things we’d like to see... A collection from the collaboration: More & Better Template support reduces code duplication, increases type-safety need working examples, esp. w/ STL Simple shared memory interface At least a way to directly share simple structures with an object interface Maybe not as critical if thread support improves Rationalization of the relationship between objects and TDirectories “now, where did my pointer go?…” Instead, had to roll our own (TPhObjectManager)

21. And something we really need Help! PHOBOS group at BNL is also looking for a postdoc (or even two) Available immediately Scope very flexible, but a few ideas: Improving Oracle classes (could be of general use to community) We have a very powerful multiple-DSP system (~8 G4’s) between the silicon readout and the event builder. Not fully exploited yet. Plans for Level 3 triggering : multiplicity, vertex, tracking Physics! RHIC is a very exciting place to be right now. Offline framework is still under intensive development.