June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 1 Beam Background Simulation with B A B AR with B A B AR June 29, 2004 BBBTF video meeting Steven Robertson Steven Robertson Institute of Particle Physics Institute of Particle Physics

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 2 Motivation ● Beam background conditions result in detector occupancy, radiation damage and degradation of data quality ● Characterization based on dedicated beam background experiments ● single and two beam colliding/non- colliding, trickle injection etc. ● permit extrapolation (under assumptions about beam conditions) to future running conditions ● Simulation is needed in order to 1)Validate and aid interpretation of bg data 2)Identify sources and underlying causes of bg 3)Evaluate sensitivities to specific sources (e.g. details of IR geometry) 4)Evaluate effects of future upgrades on bg rates DCH EMC # of crystals with significant energy L = 3.3x10 34 cm -2 s -1

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 3 Background Sources ● Synchrotron Radiation ● Well understood and not significant (by design!) in current IR ● Lost particle (beam gas bremsstrahlung & coulomb scattering) ● Well characterized in data, simulated with Turtle ● Also inelastic beam-gas / beam-wall contribution to L1 trigger rate ● Touschek effect ● Contribution to rates not particularily well understood (not dominant!) ● Not currently simulated ● Luminosity (Bhabha/radiative Bhabha) ● Well measured, but not well understood ● Neutrons? ● Beam-beam ● mechanism understood, measured in data ● Trickle injection related ● Well characterized from data ● not currently problematic

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 4 Simulation Tools ● Magbends ● propagates charged particles through magnetic fields ● Decay Turtle ● Transport of Coulomb and bremsstrahlung secondaries to vicinity of IR ● Knowledge of apertures ● Modeling of beam phase space and beam tails ● Geant4 ● Full modeling of materials and magnetic fields in vicinity of IR (+/- 8m) ● Physics of particle interactions and detector response ● Can be used as stand-alone simulation of physics processes (e.g. Bhabha) or using Turtle rays as input ● Data ● Impact of bg occupancy in data “modeled” in BABAR physics Monte Carlo from cyclic triggers in data

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 5 ● Synchrotron radiation simulated using Magbends as intrinsic part of IR design ● No primary synchrotron radiation background seen in BABAR detector ● Relevent for heating etc. of machine elements in the vicinity of IR ● Ongoing simuation studies as part of PEP-II upgrade program Synchrotron radiation

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 6 Turtle ray simulation IP Normalized to: - uniform pressure profile of 1 nT - 1 A beam current IP Coulomb scattering in Arcs (y- plane) e - Brems- strahlung in last 26 m (x-plane) Vacuum pipe / mask apertures

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 7 Pressure zones X (mm) Zone 1 X (mm) Zone 2 Zone 3 X (mm) Bremmsstrahlung in field-free region Bremmsstrahlung ● “zones” are empirically defined based on observation that lost particles from different regions have differing characteristics: LER Zone Range (m) 0 -4, 4 1 4, , , , , 2196 HER Zone Range (m) 0 -4, , , , , -2196

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 8 Comparison with data

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 9 Older simulation studies ● Lots of work performed for BABAR TDR, commissioning and early data taking phases of experiment

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 10 Turtle level studies (~2000) ● bremsstrahlung and Coulomb scatter events generated uniformly around ring assuming a flat 1nTorr pressure profile ● Reweight to “known” profile to get absolute predictions ● Record location, energy etc of primary particles hitting in vicinity of IR ● Useful information about impact regions and background sensitivities to regions of the rings:

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 11 Geant3 simulation (<2001) ● Used during commissioning phase and first few years of running ● Modeled BABAR detector and beam line out to Q5 (+/- 8m from IR) ● Turtle ray input to allow lost particle background studies ● Some known issues with beamline geometry, fields and material model ● occasionally primary particles would vanish ● occasional discrepancies between Turtle z-hit position and Geant hit position ● “Replaced” by Geant4 detector simulation in ~2002 ● Beamline simulation only out to ~Q2 !

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 12 Turtle-Geant3 studies Chih-Hsiang Cheng SVT pin-diode simulation studies ● G-hit based study using Turtle rays as input to Geant-3 pin- diode detector model ● Used during initial PEP-II commissioning and early data taking phases of BABAR ● Predictions for SVT background sensitivities to HER and LER zones ● Some diodes appeared to be better modeled than others, but overall agreement with data to within a factor ~2.5

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 13 More Turtle-Geant studies ● 4-vectors of Turtle rays which strike apertures near IP are recorded at a point ~8m upstream, then passed to Geant ● Geant propagates particle into IR and simulates interactions in beampipe/detector material ● permits identification of turtle rays which produce activity (e.g. from secondary particles in specific detector elements

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 14 EMC Occupancy predictions ● Extrapolate simulated lost- particle induced detector occupancies according to measured (or assumed) vacuum profile ● Once appropriate backgrounds data was available, this was done using data instead ● Full detector response to backgrounds can be simulated to obtain “reconstructed” information e.g. clusters, tracks and even triggers

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 15 Radiation dose ● RadFET calorimeter radiation monitoring gives integrated dose in various regions of the EMC ● Not necessarily representative of dose in individual crystals ● Total radiation dose estimated by integrating estimated flux rate from simulation ● Assume pressure profile ● Reasonable agreement with RadFET data (~30%) ● Interesting features! ● simulation predicted region of reduced dose in forward barrel (naively expected to be high dose) RadFET Data

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 16 Recent simulation work

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 17 Geant4 simulation ● Recently, a substantial effort has been made to expand Geant4 simulation to include beamline geometry out to Q4: ● Include also various background sensors (pin diodes, diamond, quartz and CsI) ● Modeling of magnetic fields (incl. Solenoid) and validation against Magbends & Turtle ● Significant improvements in geometry and materials modeling compared to old Geant3 version ● Proceeding concurrently with updating of HER & LER Turtle decks 1)study current IR 2)evaluate proposed IR upgrade

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 18 Current simulation studies ● Synchrotron radiation ● Magbends studies for IR upgrades ● Beam-beam collimation ● affects orbit of outgoing beam particles; collimate downstream? ● topic for future BBBTF meeting? ● Beam gas Coulomb scattering and bremsstrahlung ● Turtle and Turtle/Geant4 ● similar to ~2000 era studies but with upgraded simulation tools ● Radiative Bhabha (“luminosity”) background ● Separate Magbends, Turtle and Geant4 studies in progress ● use fields & apertures in Turtle to study trajectories of charged particles ● or “physics” event can be generated by directly by G4 sim (but need extended beamline geomerty!) ● Where do primary particles go? ● Secondaries, neutrons and shielding? ● Effect of 2005 IR upgrade (and Super-B IR)

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 19 Recent turtle results... ● Updated HER deck to 2004 configuration ● Aperture and orbit checks performed ● LER deck update still in progress ● Coulomb scattering in HER (2004 configuration): Scattered e- impact point Scattered e- production zone

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 20 ● Believed to be responsible for the sizable “luminosity” background observed in data ● Studies for BABAR TDR and predicted to be a possible background source ● Observed in data in ~2000; currently a dominant background source ● Recently, significant interest in simulation ● “proof of principle” using MagBends with off-energy electrons/positrons: Radiative Bhabha background Mike Sullivan

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 21 Lumi background at KEK? ● This also seems to explain why KEK might not be as sensitive to this background ● however, radiative Bhabha daughters still hit in the vicinity of Belle detector so surprising that NO lumi term is observed...

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 22 Neutron backgrounds BF 3 counter installed on forward Q4 magnet - high rate (>10 kHz) during colliding beams, but not single beam running ● Recently discovered neutron background source believed to be due to radiative Bhabhas striking in vicinity of Q2 septum ● Do neutrons interact in detector? ● rates, radiation damage ● Can in principle be simulated using full Geant4 with e/ g -nuclear processes

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 23 Radiative Bhabha studies ● Turtle machinery used to identify initial hit points of particles ● Propagate single particles with Bhabha kinematics outwards from the IP ● Information needed for remediation and upgrades ● Full understanding of lumi background requires simulation of EM (and hadronic?) showers ● How does a multi-GeV electron hitting Q4 result in ~MeV photons in the EMC and DCH charge deposition? ● Effect of neutrons? ● Studies in progress, but most useful initially as a validation of Turtle/Geant simulation ● Anticipate results over next few months

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 24 Summary ● Very active PEP-II/B A B AR background simulation program at the moment ● Development of Geant4 beamline model ● Updating and validation of Turtle decks ● Simulation based studies of (most of) dominant background sources are underway... ● Beam-beam collimation ● Luminosity backgrounds (rad Bhabha) ● Beam-gas Coulomb scattering a bremsstrahlung...but are mostly still in the early stages...but are mostly still in the early stages ● Simulation proved to be extremely useful tool for understanding beam background issues during the initial period of BABAR commissioning and data taking ● anticipate that it will again prove useful for studies of high luminosity running and future upgrades