June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 1

Beam Background SimulationBeam Background Simulation with with BBAABBARAR

June 29, 2004BBBTF video meeting

Steven RobertsonSteven Robertson Institute of Particle PhysicsInstitute of Particle Physics

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 2

MotivationMotivation● Beam background conditions result in Beam background conditions result in

detector occupancy, radiation detector occupancy, radiation damage and degradation of data damage and degradation of data qualityquality

● Characterization based on dedicated Characterization based on dedicated beam background experiments beam background experiments

● single and two beam colliding/non-colliding, single and two beam colliding/non-colliding, trickle injection etc.trickle injection etc.

● permit extrapolation (under assumptions permit extrapolation (under assumptions about beam conditions) to future running about beam conditions) to future running conditions conditions

● Simulation is needed in order toSimulation is needed in order to1)1) Validate and aid interpretation of bg dataValidate and aid interpretation of bg data

2)2) Identify sources and underlying causes of Identify sources and underlying causes of bgbg

3)3) Evaluate sensitivities to specific sources Evaluate sensitivities to specific sources (e.g. details of IR geometry) (e.g. details of IR geometry)

4)4) Evaluate effects of future upgrades on bg Evaluate effects of future upgrades on bg ratesrates

DCHDCH

EMCEMC

# of

cry

stal

s w

ith

sig

nif

ican

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ergy

LL = 3.3x10 = 3.3x103434 cm cm--

22 s s-1-1

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 3

Background SourcesBackground Sources● Synchrotron RadiationSynchrotron Radiation

● Well understood and not significant (by design!) in current IRWell understood and not significant (by design!) in current IR● Lost particleLost particle (beam gas bremsstrahlung & coulomb (beam gas bremsstrahlung & coulomb

scattering)scattering)● Well characterized in data, simulated with TurtleWell characterized in data, simulated with Turtle● Also inelastic beam-gas / beam-wall contribution to L1 trigger rateAlso inelastic beam-gas / beam-wall contribution to L1 trigger rate

● Touschek effectTouschek effect● Contribution to rates not particularily well understood (not dominant!)Contribution to rates not particularily well understood (not dominant!)● Not currently simulatedNot currently simulated

● LuminosityLuminosity (Bhabha/radiative Bhabha)(Bhabha/radiative Bhabha)● Well measured, but not well understoodWell measured, but not well understood● Neutrons?Neutrons?

● Beam-beamBeam-beam● mechanism understood, measured in datamechanism understood, measured in data

● Trickle injection relatedTrickle injection related● Well characterized from dataWell characterized from data● not currently problematicnot currently problematic

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 4

Simulation ToolsSimulation Tools● Magbends Magbends

● propagates charged particles through magnetic fieldspropagates charged particles through magnetic fields

● Decay Turtle Decay Turtle ● Transport of Coulomb and bremsstrahlung secondaries to vicinity of Transport of Coulomb and bremsstrahlung secondaries to vicinity of

IRIR● Knowledge of aperturesKnowledge of apertures● Modeling of beam phase space and beam tails Modeling of beam phase space and beam tails

● Geant4Geant4● Full modeling of materials and magnetic fields in vicinity of IR (+/- Full modeling of materials and magnetic fields in vicinity of IR (+/-

8m)8m)● Physics of particle interactions and detector responsePhysics of particle interactions and detector response● Can be used as stand-alone simulation of physics processes (e.g. Can be used as stand-alone simulation of physics processes (e.g.

Bhabha) or using Turtle rays as inputBhabha) or using Turtle rays as input

● DataData● Impact of bg occupancy in data “modeled” in BABAR physics Monte Impact of bg occupancy in data “modeled” in BABAR physics Monte

Carlo from cyclic triggers in dataCarlo 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 Synchrotron radiation simulated using Magbends as intrinsic part of IR designintrinsic part of IR design

● No primary synchrotron radiation background seen in BABAR No primary synchrotron radiation background seen in BABAR detectordetector

● Relevent for heating etc. of machine elements in the vicinity of IRRelevent for heating etc. of machine elements in the vicinity of IR

● Ongoing simuation studies as part of PEP-II upgrade Ongoing simuation studies as part of PEP-II upgrade program program

Synchrotron radiationSynchrotron radiation

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 6

Turtle ray simulationTurtle 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 zonesPressure zonesX

(m

m) Zone 1

X (

mm

)

Zone 2

Zone 3

X (

mm

)

Bremmsstrahlung in field-free region

Bremmsstrahlung

Bremmsstrahlung

● ““zones” are empirically defined based on observation zones” are empirically defined based on observation that lost particles from different regions have differing that lost particles from different regions have differing characteristics:characteristics:

LER Zone Range (m) 0 -4, 4 1 4, 10 2 10, 21 3 21, 36 4 36, 62 5 62, 2196

HER Zone Range (m) 0 -4, 4 1 -4, -26 2 -26, -42 3 -42, -66 4 -66, -2196

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

Comparison with dataComparison with data

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 9

Older simulation studiesOlder simulation studies

● Lots of work performed for BABAR TDR, Lots of work performed for BABAR TDR, commissioning and early data taking phases of commissioning and early data taking phases of experiment experiment

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 10

Turtle level studies (~2000)Turtle level studies (~2000)

● bremsstrahlung and bremsstrahlung and Coulomb scatter events Coulomb scatter events generated uniformly generated uniformly around ring assuming a around ring assuming a flat 1nTorr pressure flat 1nTorr pressure profileprofile

● Reweight to “known” profile Reweight to “known” profile to get absolute predictionsto get absolute predictions

● Record location, energy Record location, energy etc of primary particles etc of primary particles hitting in vicinity of IRhitting in vicinity of IR

● Useful information about Useful information about impact regions and impact regions and background sensitivities to background sensitivities to regions of the rings:regions of the rings:

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 11

Geant3 simulation (<2001)Geant3 simulation (<2001)● Used during commissioning phase and first few years of Used during commissioning phase and first few years of

running running ● Modeled BABAR detector and beam line out to Q5 (+/- 8m from IR)Modeled BABAR detector and beam line out to Q5 (+/- 8m from IR)

● Turtle ray input to allow lost particle background studiesTurtle ray input to allow lost particle background studies

● Some known issues with beamline geometry, fields and material Some known issues with beamline geometry, fields and material modelmodel

● occasionally primary particles would vanishoccasionally primary particles would vanish● occasional discrepancies between Turtle z-hit position and Geant occasional discrepancies between Turtle z-hit position and Geant

hit positionhit position

● ““Replaced” by Geant4 detector simulation in ~2002Replaced” by Geant4 detector simulation in ~2002● Beamline simulation only out to ~Q2 !Beamline simulation only out to ~Q2 !

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 12

Turtle-Geant3 studiesTurtle-Geant3 studies

Chih-Hsiang Cheng

SVT pin-diode simulation SVT pin-diode simulation studiesstudies

● G-hit based study using G-hit based study using Turtle rays as input to Geant-Turtle rays as input to Geant-3 pin-diode detector model3 pin-diode detector model

● Used during initial PEP-II Used during initial PEP-II commissioning and early data commissioning and early data taking phases of BABARtaking phases of BABAR

● Predictions for SVT background Predictions for SVT background sensitivities to HER and LER sensitivities to HER and LER zoneszones

● Some diodes appeared to be Some diodes appeared to be better modeled than others, but better modeled than others, but overall agreement with data to overall agreement with data to within a factor ~2.5 within a factor ~2.5

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 13

More Turtle-Geant studiesMore Turtle-Geant studies● 4-vectors of Turtle rays which strike apertures near IP are 4-vectors of Turtle rays which strike apertures near IP are

recorded at a point ~8m upstream, then passed to Geantrecorded at a point ~8m upstream, then passed to Geant● Geant propagates particle into IR and simulates interactions in Geant propagates particle into IR and simulates interactions in

beampipe/detector materialbeampipe/detector material● permits identification of turtle rays which produce activity (e.g. permits identification of turtle rays which produce activity (e.g.

from secondary particles in specific detector elementsfrom secondary particles in specific detector elements

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 14

EMC Occupancy predictionsEMC Occupancy predictions

● Extrapolate simulated Extrapolate simulated lost-particle induced lost-particle induced detector occupancies detector occupancies according to measured according to measured (or assumed) vacuum (or assumed) vacuum profileprofile

● Once appropriate Once appropriate backgrounds data was backgrounds data was available, this was done available, this was done using data insteadusing data instead

● Full detector response Full detector response to backgrounds can be to backgrounds can be simulated to obtain simulated to obtain “reconstructed” “reconstructed” information e.g. information e.g. clusters, tracks and clusters, tracks and even triggers even triggers

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 15

Radiation doseRadiation dose

● RadFET calorimeter radiation RadFET calorimeter radiation monitoring gives integrated monitoring gives integrated dose in various regions of the dose in various regions of the EMCEMC

● Not necessarily representative of Not necessarily representative of dose in individual crystals dose in individual crystals

● Total radiation dose Total radiation dose estimated by integrating estimated by integrating estimated flux rate from estimated flux rate from simulationsimulation

● Assume pressure profileAssume pressure profile● Reasonable agreement with Reasonable agreement with

RadFET data (~30%)RadFET data (~30%)● Interesting features!Interesting features!

● simulation predicted region of simulation predicted region of reduced dose in forward barrel reduced dose in forward barrel (naively expected to be high (naively expected to be high dose)dose)

RadFET Data

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

Recent simulation workRecent simulation work

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 17

Geant4 simulationGeant4 simulation

● Recently, a substantial effort Recently, a substantial effort has been made to expand Geant4 has been made to expand Geant4 simulation to include beamline simulation to include beamline geometry out to Q4:geometry out to Q4:

● Include also various background sensors Include also various background sensors (pin diodes, diamond, quartz and CsI) (pin diodes, diamond, quartz and CsI)

● Modeling of magnetic fields (incl. Solenoid) and Modeling of magnetic fields (incl. Solenoid) and validation against Magbends & Turtlevalidation against Magbends & Turtle

● Significant improvements in geometry and Significant improvements in geometry and materials modeling compared to old Geant3 materials modeling compared to old Geant3 versionversion

● Proceeding concurrently Proceeding concurrently with updating of HER & with updating of HER & LER LER Turtle decksTurtle decks

1)1)study current IRstudy current IR2)2)evaluate proposed IR evaluate proposed IR

upgradeupgrade

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 18

Current simulation studiesCurrent simulation studies● Synchrotron radiationSynchrotron radiation

● Magbends studies for IR upgradesMagbends studies for IR upgrades● Beam-beam collimationBeam-beam collimation

● affects orbit of outgoing beam particles; collimate downstream?affects orbit of outgoing beam particles; collimate downstream?● topic for future BBBTF meeting?topic for future BBBTF meeting?

● Beam gas Coulomb scattering and bremsstrahlungBeam gas Coulomb scattering and bremsstrahlung● Turtle and Turtle/Geant4Turtle and Turtle/Geant4● similar to ~2000 era studies but with upgraded simulation toolssimilar to ~2000 era studies but with upgraded simulation tools

● Radiative Bhabha (“luminosity”) backgroundRadiative Bhabha (“luminosity”) background● Separate Magbends, Turtle and Geant4 studies in progressSeparate Magbends, Turtle and Geant4 studies in progress

● use fields & apertures in Turtle to study trajectories of use fields & apertures in Turtle to study trajectories of charged particles charged particles

● or “physics” event can be generated by directly by G4 sim or “physics” event can be generated by directly by G4 sim (but need extended beamline geomerty!) (but need extended beamline geomerty!)

● Where do primary particles go?Where do primary particles go?● Secondaries, neutrons and shielding?Secondaries, neutrons and shielding?● Effect of 2005 IR upgrade (and Super-B IR) 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...Recent turtle results...● Updated HER deck to 2004 configurationUpdated HER deck to 2004 configuration

● Aperture and orbit checks performedAperture and orbit checks performed● LER deck update still in progressLER deck update still in progress

● Coulomb scattering in HER (2004 configuration):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” Believed to be responsible for the sizable “luminosity” background observed in databackground observed in data

● Studies for BABAR TDR and predicted to be a possible background Studies for BABAR TDR and predicted to be a possible background sourcesource

● Observed in data in ~2000; currently a dominant background Observed in data in ~2000; currently a dominant background sourcesource

● Recently, significant interest in simulationRecently, significant interest in simulation● “ “proof of principle” using MagBends with off-energy proof of principle” using MagBends with off-energy

electrons/positrons:electrons/positrons:

32.5

2 1.51

0.5

LER Radiative Bhabhas

-7.5 -5 -2.5 0 2.5 5 7.5

0

10

20

30

-10

-20

-30

m

cm

M. SullivanFeb. 8, 2004API88k3_R5_RADBHA_TOT_7_5M

9 GeV

9 GeV

Radiative Bhabha backgroundRadiative Bhabha background

Mike Sullivan

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 21

Lumi background at KEK?Lumi background at KEK?● This also seems to explain why KEK might not be as This also seems to explain why KEK might not be as

sensitive to this backgroundsensitive to this background● however, radiative Bhabha daughters still hit in the vicinity of Belle however, radiative Bhabha daughters still hit in the vicinity of Belle

detector so surprising that NO lumi term is observed...detector so surprising that NO lumi term is observed...

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 22

Neutron backgroundsNeutron backgrounds

BF3 counter installed on forward Q4 magnet

- high rate (>10 kHz) during colliding beams, but not single beam running

● Recently discovered neutron Recently discovered neutron background source believed background source believed to be due to radiative to be due to radiative Bhabhas striking in vicinity of Bhabhas striking in vicinity of Q2 septumQ2 septum

● Do neutrons interact in detector? Do neutrons interact in detector? ● rates, radiation damagerates, radiation damage

● Can in principle be simulated Can in principle be simulated using full Geant4 with e/using full Geant4 with e/-nuclear -nuclear processesprocesses

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 23

Radiative Bhabha studiesRadiative Bhabha studies● Turtle machinery used to identify initial hit Turtle machinery used to identify initial hit

points of particlespoints of particles

● Propagate single particles with Bhabha kinematics Propagate single particles with Bhabha kinematics outwards from the IP outwards from the IP

● Information needed for remediation and upgradesInformation needed for remediation and upgrades

● Full understanding of lumi background Full understanding of lumi background requires simulation of EM (and hadronic?) requires simulation of EM (and hadronic?) showersshowers

● How does a multi-GeV electron hitting Q4 result in How does a multi-GeV electron hitting Q4 result in ~MeV photons in the EMC and DCH charge deposition? ~MeV photons in the EMC and DCH charge deposition?

● Effect of neutrons?Effect of neutrons?

● Studies in progress, but most useful initially as Studies in progress, but most useful initially as a validation of Turtle/Geant simulationa validation of Turtle/Geant simulation

● Anticipate results over next few monthsAnticipate results over next few months

June 28, 2004 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 24

SummarySummary● Very active PEP-II/Very active PEP-II/BBAABBARAR background simulation program background simulation program

at the moment at the moment ● Development of Geant4 beamline modelDevelopment of Geant4 beamline model● Updating and validation of Turtle decksUpdating and validation of Turtle decks

● Simulation based studies of (most of) dominant Simulation based studies of (most of) dominant background sources are underway...background sources are underway...

● Beam-beam collimationBeam-beam collimation● Luminosity backgrounds (rad Bhabha)Luminosity backgrounds (rad Bhabha)● Beam-gas Coulomb scattering a bremsstrahlungBeam-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 Simulation proved to be extremely useful tool for

understanding beam background issues during the understanding beam background issues during the initial period of BABAR commissioning and data taking initial period of BABAR commissioning and data taking

● anticipate that it will again prove useful for studies of high anticipate that it will again prove useful for studies of high luminosity running and future upgradesluminosity running and future upgrades