Denig, A.

Götzen, K.

Kang, D.

Kliemt, R.

Nerling, F.

Peters, K.

GSI Repository

Studies for the PANDA software triggerF. Nerling∗1,2, A. Denig3, K. Go¨tzen1, D. Kang2, R. Kliemt1, K. Peters1,4, and the PANDA Collab.11GSI, Darmstadt, Germany; 2HIM, Mainz, Germany; 3Univ. Mainz, Germany; 4Univ. Frankfurt, GermanyThe PANDA experiment is one of the key experiments atthe future FAIR facility that provides an anti-proton beamof momenta 1.5–15 GeV/c with excellent energy resolu-tion. Using an hydrogen (proton) and various nuclear tar-gets, PANDA will carry out a broad physics programmecomprising topics of hadron spectroscopy, nucleon struc-ture, hadron in nuclei as well as hypernuclear physics.Given the production cross-sections for the reactions ofinterest either not being known precisely or being predictedby theory to be rather small (pico- to nanobarn range), theaverage design luminosity (for the high luminosity mode)is projected to be L = 2 · 1032cm−2s−1. The high total p¯pcross-section of about 60-100 mb results in an average re-action rate of N˙ = 20MHz, reaching peak values of up toN˙ ≈ 40MHz. With an average event size of 10–20 kB, weexpect a total raw data rate of roughly 200 GB/s. Assum-ing a duty cycle of 50 %, the data stream would produce3000 PB per year to be stored, and thus the data rate hasto be reduced by about a factor of 1000 in order to reducethe required storage capacity down to affordable few PBper year. Due to the similarity of the detector signatures ofinteresting signal and background events, a sophisticatedfiltering strategy has to be developed that goes far beyondconventional hardware based trigger schemes and that isbased on the concept of a trigger-less read-out. This ap-proach of continous sampling and buffering of the data, i.e.without any classical gated trigger signal, allows to pre-analyse the data in order to decide to either reject or keepevents and write them to disc. Technically, the challengeis to perform a high-level reconstruction procedure onlineand provide the information to effectively separate signalfrom background events already during data taking.∗F.Nerling@gsi.deTable 1: List of physics channels presently under study.Physics topic Reaction channel TriggerElectromagn. pp¯→ e+e− pp¯→ e+e−Exotics pp¯→ φφ φ→ K+K−Charmonium pp¯→ ηc pi+pi− ηc → KSK−pi+pp¯→ J/ψ pi+pi− J/ψ→ e+e−pp¯→ J/ψ pi+pi− J/ψ→ µ+µ−Open charm pp¯→ D0D0 D0 →K−pi+pp¯→ D+D− D+ →K−pi+pi+pp¯→ D+s D−s D+s →K+K−pi+Baryons pp¯→ ΛΛ Λ→ ppi−pp¯→ ΛcΛc Λc → pK−pi+Background pp¯ generic (DPM) –The present studies are restricted to a subset of 10physics reaction channels (Tab. 1), still covering the mainphysics topics addressed by PANDA, at 4 different centre-of-mass energies, covering the whole range of about 2–5.5 GeV/c accessible by PANDA. In total a set of ∼1502 2.5 3 3.5 4 4.5 5 5.5 600.20.40.60.81 e+e- φcη (2e)ψJ/)µ(2ψJ/ 0D±D sDΛ cΛ [GeV]s2 2.5 3 3.5 4 4.5 5 5.5 6-310-210-1101mass cut onlyhigh supressionFigure 1: Compilation of present results: Achieved signaldetection efficiencies (top) when optimising for a 103 back-ground reduction factor (bottom).observables has been explored and those, which allow foran efficient signal to background separation, are appliedin addition to the initial cuts on the corresponding invari-ant masses. The studies were carried out using eventsgenerated by a simple toy Monte Carlo and compared tothe results obtained from the full detector simulation us-ing PandaRoot. As optimisation approach, two strategieshave been realised, optimisation for high signal detectionefficiencies and for strong background suppression.The present results based on the full detector simulationare summarised for the ansatz of optimisation for back-ground suppression in Fig. 1. The achieved signal efficien-cies vary from about 6–50 %, strongly depending on thegiven physics channel, while the intended background sup-pression factor is met over the full range of centre-of-massenergies. More realistic results will come soon, and eventhough more work is needed also on the hardware side,these first preliminary results serve as a proof of principle.MU-HADRONS-08 GSI SCIENTIFIC REPORT 2014116 DOI:10.15120/GR-2015-1-MU-HADRONS-08

Studies for the PANDA software trigger

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Studies for the PANDA software trigger

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