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The Instrumented Flux Return

The Instrumented Flux Return. Outline. An Introduction to the IFR - role, status IFR Physics Background Physics Requirements for the IFR Hardware Description Reconstruction Software Particle Identification. Introduction.

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The Instrumented Flux Return

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  1. The Instrumented Flux Return Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  2. Outline • An Introduction to the IFR - role, status • IFR Physics Background • Physics Requirements for the IFR • Hardware Description • Reconstruction Software • Particle Identification Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  3. Introduction • Instrumented Flux Return (IFR) magnet yoke for external flux path of 1.5 Tesla Super Conducting coil. • Iron Structure, largest sub-detector • Absorbs MIP (minimum ionizing particles -  ) and , neutrals (Kl ) • Provides structural, seismic support • Allow access to interior sub-systems • Novel graded segmented design. • Uses established instrumentation technology RPCs ( Resistive Plate Counters) • Novel Cylindrical RPC (iRPC) Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  4. Physics Background (1) • IFR is primary detector for muon identification and long-lived neutral kaon detection: • Muon identification (~18% of decays) • tagging • use  above 1.4 GeV/c to tag flavour of parent B. • Muons contribute to 75% of dilepton measurements. • leptonic analyses • EG: Inclusive analysis B  Xl , |Vcb|, |Vub| • Kl identification • CP violation in B0 J/ + K0l (also use IFR for- J/  + - ) Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  5. Physics Background (2) • Require discrimination between , Hadrons (): M  105.66 MeV/c2 M  139.57 MeV/c2  ()  2.19 x 10-6 sec (658.6 m)  ()  2.60 x 10-8 sec (7.8 m) but … primary decay mode is: +  +(branching ratio  99.99 %) • ~3.5 % of all pions decay before reaching IFR also approximate multiplicities: :  8 : 1 Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  6. Physics Background (3) • Plots of typical muon and pion spectra from B mesons: • From EvtGen - Official BaBar Event Generator 0.179/ Event 1.51/ Event Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  7. Physics Background (4) • Muons are minimum ionizing particles, minimal energy deposited in Crystal Calorimeter (some loss in coil also) • Lose energy via ionization (dE/dx losses) Critical energy (loss rates by radiation processes equal those of ionization process) depends on material traversed. For muons traversing a solid: For Iron, Z=26  Ecrit = several hundred GeV No loss by radiation processes. Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  8. Physics Background (5) • The (Famous) Bethe-Bloch Eqn • Describes energy loss for heavy charged, moderately relativistic particles • Basically a function of . Max. Ek that can be imparted to a single electron Density effect correction Mean excitation energy Mean rate of energy loss Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  9. Physics Background (6) • Bethe-Bloch Curve: Minimum Ionization Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  10. Physics Background (7) • Possible to integrate Bethe-Bloch to get Range • Important quantity to measure range (comparing ,  ) is the Nuclear Interaction Length (- length scale appropriate for hadronic cascades). It is denoted I and defined: I = , where - depends on Energy and Material... I = The Mean Free Path of a particle before undergoing an interaction that is neither elastic nor quasi-elastic (diffractive) in a given medium. Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  11. Physics Background (8) • Probability density function for distances between successive collisions is thus: • Suitable approximation for a given material: • Eg: For Iron, with A=56, I133.8 g cm-2 Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  12. Physics Background (9) • Fundamental idea then is to exploit difference in behavior between muons and hadrons in Iron: • muons above a certain minimum energy will either lose all their energy in a certain depth of Iron, or they will range out; escaping detector volume. • Pions may interacted strongly with Iron Nuclei, producing hadronic showers. May also punch through, mimicking muon, also decay to muon (directly or via hadronic intermediary)- can identify this sometimes (how?) • Sample charged track or shower development in Iron (how?), discriminate between two cases above. Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  13. Physics Requirements • Physics Goals of IFR subsystem: • Highest practical efficiency for detection of , misidentification probability below 5%. Require high efficiency for as low a momentum limit as possible. However, below 500 MeV/c magnetic bending and energy losses mean some  never reachIFR - can return no measurement). Lower limit on mis-identification comes from pion punch through and pion decay to muon before IFR. Not a “calorimeter” - input to physics analysis is  ID likelihood. • Kl identification - reconstruction of direction is sufficient for many analyses. Spectrum is much softer, 70% of Kl never reach IFR. • Also possible to use IFR to veto events with missing hadronic energy. • Practical Goals • Low-maintenance active detector choice • “Easy” accessibility to remainder of detector Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  14. Hardware Description (1) • IFR Iron consists of three major components • Central Barrel, Forward and Backward Endcaps. • Also iRPC inside coil. • Complex geometry Forward Endcap Coil (iRPC not shown) Backward Endcap Barrel Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  15. Hardware Description (2) • Hexagonal configuration - suited to role of structural support and for active detector choices • Layers of Iron Absorber / Flux Return interspersed with active detector. • Overall dimensions: • 635cmlength, 584cm height, width of675cm • Mass: • Barrel: 312tonnes(excluding supports) • Endcaps: 225tonnes(each, approximate value. Excludes supports) • Coil: 4.9tonnes(excluding cryostat and associated systems) Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  16. Hardware Description (3) Photograph of detector, IFR for scale Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  17. Hardware Description (4) • Question: Which type of Active Detector? Require low maintenance, high efficiency, and good reliability • Resistive Plate Counters (Plastic Streamer Tubes were considered - see note 205, RPCs chosen as more durable solution) • Basic idea: Instrument gaps between absorber sheets; charged component of hadronic shower will signal, as will passage of single charged MIP. • Question: Is there a better segmentation option than “uniform”? Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  18. Hardware Description (5) • From the middle outwards - the 2 mm gap is filled with an Argon-Freon-Isobutane based gas mixture (gas mixture - spark quenching, safety requirements) • PVC spacers (0.8 cm2 area) placed in 10 cm-square grid ensure RPC planarity, & gas gap (hence also field) remains constant. • Two Bakelite plates with bulk resistivity in range 8-800 giga ohm cm, (coated on outside with thin layer of graphite, surface resistivity around 10 kohm cm-2) and a 300 micron PVC insulating film, enclose this gap. • A high (8 kV nominal) potential is applied between the graphite layers. (Al grounded) • Resistive Plate Counters: (used at L3, and Belle) • Total RPC areas: • Barrel: 1320 m2 • Endcaps: 1100 m2 Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  19. Hardware Description (6) • Resistive Plate Counters (cont.): • Orthogonal aluminium readout strips affixed above and below PVC insulating film. • Barrel: • Longitudinal strips (measuring z) have a pitch of 38.5 mm (2 mm of which is space between strips) • Transverse strips (measure ) increase in pitch from 19.7 to 33.5 mm, depending on layer. • End Caps: • X strips: oriented horizontally - pitch 28.4 mm giving information on x coordinates. • Y strips: oriented vertically (38 mm) - y coordinates. • PVC spacers cause reduction (few %) of active detector area  lowered efficiency Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  20. Hardware Description (7) • Resistive Plate Counters (cont.): • Charged particle traversing gap produces quenched spark • detected on external pickup electrodes • The discharge (around 100 pC) is very fast • pulse rise time is 2ns and duration typically around 20-30ns •  Can use IFR for triggering • At 300 mV, signal pulse requires only very simple fixed threshold electronics for readout. Digital readout. •  Measurement error (approx 1.1 cm). • Can do better than this due to multiple (>2) strip firing - centroid position determined about ~20% more acurately • 16 strips are attached to one front end card (FEC) which signal TDC (Time to Digital Converter) circuits to deliver timing information for the active strips Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  21. Hardware Description (8) • RPC Efficiencies • From Cosmic Rays test facility at Frascati, • Currently ~80% efficiency in live RPC chambers in barrel (Cosmic run 11.29.99) ~120 RPCs Mean 97% Effect of spacers Courtesy Fabio Anulli Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  22. Hardware Description (9) RPC with a circular cut to match the Endcap geometry Courtesy Francesca Pastore Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  23. Hardware Description (10) • Graded Segmentation - why? note 194 describes optimization procedure: • Simulate different configurations, use Monte Carlo Hadronic shower simulation to estimate achievable efficiency • uniform segmentation: Muon identification and Kaon detection efficiency improve for a given amount of absorber as thickness of plate decreases; but effect is most important in first interaction length (first 17 cm). ~30% improvement in Kaon efficiency. • Graded segmentation can decrease instrumentation in subsequent interaction lengths, allow thicker plates, less instrumentation Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  24. Hardware Description: Barrel • The central (Barrel) section is ~375 cm in length. Constructed from (near identical) sextants, situated ~170 cm radially from beam-line, outside the coil. Each extends ~130 cm outwards. • Innner edge of sextant ~190 cm, outer ~325 cm • Inner volume segmented into 18 iron plates of increasing thickness in radial distance. • 9 innermost plates are 2 cm thick (equivalent to one interaction length), followed by • 4 of 3 cm • 3 of 5 cm • 2 of 10 cm each, total thickness of 65 cm of Iron (approximately 4 interaction lengths at normal incidence). • Layers of RPCs between these plates fill remaining volume: • Gap of 3.2 cm between Iron plates for housing RPCs • Exceptlast RPC layer (layer 19) on exterior of detector (reduced geometry) • And first 10 layers (between thinnest plates), gaps of 3.5 cm • Iron plates and RPCs held together by 5 cm thick plates on outside of each sextant. Marginal impact on performance of detector as function of  , but structural support role of IFR makes these mandatory Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  25. Hardware Description: Barrel Barrel Sextant during installation Courtesy Francesca Pastore Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  26. Hardware Description: Endcap • The Endcaps extend solid angle coverage down to 300 mrad in backward direction, 400 mrad in forward direction. • Constructed flush with Barrel, however, layer and strip geometry orthogonal to that found in Barrel. • In addition, approximately 15 cm of iron (providing needed flux return and extra support) between Barrel and both End Caps. • In order to allow access to rest of the detector, each End Cap divided into two halves vertically. • Each half also divided into three sections which are reinforced by spacers designed to withstand large magnetic forces on End Cap. • End Cap has 18 RPC detector layers, starting behind the innermost iron plate. • Total depth of iron in End Cap is 60 cm, slightly less than in barrel; 5 cm difference due to penultimate iron plate being only 5 cm thick rather than 10 cm as in Barrel. Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  27. Hardware Description: Endcap Courtesy Francesca Pastore Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  28. 30º   z z Hardware Description: iRPC • iRPC important for Kaon identification • Geometry divided into 4 quadrants (contrast remainder of IFR), each ¼ cylinder • Each quadrant has 2 layers (inner & outer) rotated relative to each other by 30º so joins are mismatched. • Each layer consists of 4 modules (32 in all). • 147 cm in radius, 2.5 cm thick • Each layer has different view: u,v; , z • 128 strip readouts per view • Strip pitch for u and v is 2.86 cm.  is 1.623 cm, and z is 2.87cm  u 30º z v Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  29. Hardware Description: iRPC Inner RPC during insertion Courtesy Francesca Pastore Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  30. Hardware Description (17) • IFR Electronics and Readout: • >40000 readouts • 16 channels per FEC  > 2500 FECs (located adjacent to RPCs) • ITB (IFR TDC Board) - identifies bunch crossing time of event using good time resolution of RPCs. Input signal is OR of FECs • IFB (IFR FIFO board) - buffer between front end and DAQ • FEE (Front-End Electronics) crate contains the IFB, ICB (IFR Crate Controller), ITB and the ICC (IFR Crate Controller). (8 - 4 for Barrel, 1 per Endcap door) FEC Readout logical layout Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  31. Reconstruction (1) • 3D imaging, assembles cluster candidates from more primitive candidates • Neutral 3D clusters are formed in 3 stages: Hits 1D clusters 2D clusters (2 views) 3D cluster (Composite Finder) 3D Composite Cluster For charged hypotheses, track - 1D cluster association performed with a Swimmer (also used for PID) Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  32. Reconstruction (2) 2D cluster 1D cluster Strip 3D cluster Luca Lista, with permission Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  33. Reconstruction (3) • The Swimmer • Used for track cluster matching (relatively easy due to low occupancy of IFR), Particle Identification, and alignment • Extrapolates DCH (charged) track through: EMC, iRPC, Coil, IFR, exit • Also used for clustering using alternative reconstruction technique • Operation: • Iterative method (Geant like) using Runge-Kutta to update kinematic quantities • B-Field strength, momentum, direction, position • Interaction lengths, radiation lengths • Swimmer road width increases due to multiple scattering estimations • Need to swim with apriori particle hypothesis • After track swam, calculate 2 for “near-by” 1D - clusters, and associate track to cluster for which this value minimum. Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  34. Muon Identification (1) Geometry Swimmer Cluster SW+CL Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  35. Muon Identification (2) Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  36. Muon Identification (3) • Discriminating variables from hit layers - length and extent of cluster   Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  37. Muon Identification (4) • Discriminating variables from hit layers and strips - measure of width of cluster • Strip multiplicity must be determined from data Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  38. Muon Identification (5) • Discriminating variables from the Swimmer, interaction lengths • In principle, PID with swimmer can accommodate dead or inefficient RPC chambers Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  39. Muon Identification (6) Muon identification using theta and momentum dependent cuts on difference between penetration depth and expected penetration Muon Efficiency ~ 80% Pion Misidentification < 5% Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  40. Muon Identification (7) • J/ reconstruction from Muon Pairs • Dl= expected - measured interaction lengths • Apply a tight cut on the track with the smaller Dl • Apply a loose cut on the other track • Tight cut • Dl < 0.9 for p  1 GeV/c • Dl < for p < 1 GeV/c • Loose cut (parametric) • same as tight but substitute 0.9 with 0.9 × s where 2 < s < 5 Guglielmo De Nardo, with permission Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  41. Muon Identification (8) Signal = 134 Background = 42 M=3.08 GeV s= 17 MeV Signal = 90 Background = 14 M=3.08 GeV s= 14 MeV Two different values of the scale paramenter s s=5 (left) and s=2 (right) Guglielmo De Nardo, with permission Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

  42. Conclusions • IFR working OK, muon identification possible, robust, well characterized on real data early 2000 • Teething troubles addressed, or have already been addressed • Need to fully understand loss in RPC efficiencies and rectify • Work on Neutral Detection started relatively recently Daniel Azzopardi, December 1999 Graduate Student Detector Seminar Series.

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