B A B AR Beam Background Beam Background Simulation Simulation - - PowerPoint PPT Presentation

B BA

AB

BAR

AR

Beam Background

Beam Background Simulation Simulation

Steven Robertson

2nd Hawaii Super B Factory Workshop April 21, 2005

Apr 21, 2005 2 BABAR Beam Background Simulation Steven H. Robertson

Motivation Motivation

• Beam background conditions result in

Beam background conditions result in detector occupancy, radiation damage and detector occupancy, radiation damage and degradation of data quality degradation of data quality

• Background characterization is based on

Background characterization is based on dedicated beam background experiments dedicated 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 to future running conditions permit extrapolation to future running conditions (under assumptions about beam conditions) (under assumptions about beam conditions)

• Simulation is needed in order to:

Simulation is needed in order to:

1) 1) Validate and aid interpretation of background data Validate and aid interpretation of background data 2) 2) Identify sources and underlying causes of Identify sources and underlying causes of background background 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 rates Evaluate effects of future upgrades on bg rates

–

Extrapolate to Super-B ? Extrapolate to Super-B ?

DCH DCH EMC EMC

#

• f

c r y s t a l s w i t h s i g n i f i c a n t e n e r g y

L L = 3.3x10

= 3.3x1034

34 cm

cm-2

• 2 s

s-1

• 1

Apr 21, 2005 3 BABAR Beam Background Simulation Steven H. Robertson

Background simulation Background simulation

• Recent effort to simulate two of the dominant contributions to observed

Recent effort to simulate two of the dominant contributions to observed subdetector background rates subdetector background rates

–

“ “Lost-particle Lost-particle” single beam backgrounds produced by bremmstrahlung or Coulumb ” single beam backgrounds produced by bremmstrahlung or Coulumb scattering of primary beam particles from beam gas scattering of primary beam particles from beam gas

–

“ “Luminosity Luminosity” backgrounds associated with small-angle radiative bhabha events in ” backgrounds associated with small-angle radiative bhabha events in which electron/positron strikes machine elements outside of nominal BABAR fiducial which electron/positron strikes machine elements outside of nominal BABAR fiducial acceptance acceptance

• observed neutron background attributed to this source
• Ingredients:

– machine lattice & apertures (TURTLE) - T. Feiguth, R. Barlow – Geant 4 IR geometry, materials model - M. Bonioli, G.Calderini – Geant 4 IR magnetic field model - G. Bower – small angle bhabha generators - B. Lockman, D. Strom, N. Blount – e/gamma – nuclear physics modeling - D. Wright – study and interpretation of results - subdetector groups

Apr 21, 2005 4 BABAR Beam Background Simulation Steven H. Robertson

Interaction region Interaction region

Apr 21, 2005 5 BABAR Beam Background Simulation Steven H. Robertson

Simulation Tools Simulation Tools

• Magbends

Magbends

–

propagates charged particles through magnetic fields propagates charged particles through magnetic fields

• Decay Turtle

Decay Turtle

–

Transport of Coulomb and bremsstrahlung final state particles to vicinity of IR Transport of Coulomb and bremsstrahlung final state particles to vicinity of IR

–

Modeling of beam phase space and beam tails Modeling of beam phase space and beam tails

–

Knowledge of apertures and assumptions regarding vaccuum pressure profile Knowledge of apertures and assumptions regarding vaccuum pressure profile

• Geant4

Geant4

–

Full modeling of materials and magnetic fields in vicinity of IR (+/- 8m) Full modeling of materials and magnetic fields in vicinity of IR (+/- 8m)

–

Contains physics of particle interactions, detector materials and response Contains physics of particle interactions, detector materials and response

–

Can be used as stand-alone simulation of physics processes (e.g. Bhabha) or Can be used as stand-alone simulation of physics processes (e.g. Bhabha) or using Turtle rays as input using Turtle rays as input

• Data

Data

–

Impact of background occupancy in data “modeled” in BABAR physics Monte Impact of background occupancy in data “modeled” in BABAR physics Monte Carlo from cyclic triggers in data Carlo from cyclic triggers in data

Apr 21, 2005 6 BABAR Beam Background Simulation Steven H. Robertson

Lumi backgrounds at KEK? Lumi backgrounds at KEK?

• Why is Belle apparently not as sensitive to luminosity backgrounds?

– Magbends model suggests that most radiative Bhabha daughters hit machine

elements further from the IP

– however, radiative Bhabha daughters still hit in the vicinity of Belle detector so still

surprising that NO lumi term is observed, particularily if neutrons contribute...

3 2.5 2 1.5 1 0.5

LER Radiative Bhabhas

• 7.5
• 5
• 2.5

2.5 5 7.5 10 20 30

• 10
• 20
• 30

m cm

• M. Sullivan
• Feb. 8, 2004

3.1 GeV 3.1 GeV 9 GeV 9 GeV

Apr 21, 2005 7 BABAR Beam Background Simulation Steven H. Robertson

Turtle ray simulation 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

Apr 21, 2005 8 BABAR Beam Background Simulation Steven H. Robertson

GEANT4 IR Simulation GEANT4 IR Simulation

• Most subdetector background occupancies are due to flux of low

Most subdetector background occupancies are due to flux of low energy secondary particles rather than primary electrons/positrons energy secondary particles rather than primary electrons/positrons from bhabhas or beam particles from bhabhas or beam particles

–

EM shower fragments or neutrons from primary particle hits in various EM shower fragments or neutrons from primary particle hits in various machine elements machine elements

• Need full geometry+magnetic fields+materials+interactions for IR

Need full geometry+magnetic fields+materials+interactions for IR

• utside of nominal detector acceptance
• utside of nominal detector acceptance

–

previously only B1 & Q1 geometry were modeled, but no magnetic fields previously only B1 & Q1 geometry were modeled, but no magnetic fields

Apr 21, 2005 9 BABAR Beam Background Simulation Steven H. Robertson

• Believed to be responsible for sizable “luminosity” background observed

– 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 Radiative Bhabha background

Mike Sullivan

Apr 21, 2005 10 BABAR Beam Background Simulation Steven H. Robertson

Radiative Bhabha simulation Radiative Bhabha simulation

• In absence the of complete magnetic field model in GEANT4, TURTLE

In absence the of complete magnetic field model in GEANT4, TURTLE model has been used to simulate radiative bhabha backgrounds model has been used to simulate radiative bhabha backgrounds

• Use magnetic field and machine aperture definitions from TURTLE decks

Use magnetic field and machine aperture definitions from TURTLE decks

• Yields information on primary particle impact point but no information on

Yields information on primary particle impact point but no information on secondaries (i.e neutrons, EM showers) secondaries (i.e neutrons, EM showers)

photons electrons

HER radiative bhabhas

Achille Stochi & Patrick Roudeau

• Use small-angle bhabha generator

(bbbrem) to obtain particle trajectories and energy flux through beamline elements

– Results recently updated using new

HER/LER Turtle decks including BABAR solenoid

“Golden orbit”

Apr 21, 2005 11 BABAR Beam Background Simulation Steven H. Robertson

Turtle-based bhabha simulation Turtle-based bhabha simulation

• Simulation reproduces main features predicted

from “Magbends” accelerator magnetic field model

• Obtain quantitative estimates of effective cross

section and total energy flux through beamline elements:

3 2.5 2 1.5 1 0.5

LER Radiative Bhabhas

• 7.5
• 5
• 2.5

2.5 5 7.5 10 20 30

• 10
• 20
• 30

m cm

• M. Sullivan
• Feb. 8, 2004

3 . 1 G e V 3 . 1 G e V 9 GeV 9 GeV

13.5 50 117 27.7 2.5 E x σ (mb GeV) 5.2 2.8<Z 20. 2.2<Z<2.8 56.7 1.4<Z<2.2 26.4 .8<Z<1.4 9.2 <.8 σ (mb) Z range (m)

Q1 Q2

Apr 21, 2005 12 BABAR Beam Background Simulation Steven H. Robertson

Off energy electrons Off energy positrons

GEANT4 Bhabha Simulation GEANT4 Bhabha Simulation

• Bbbrem generator adapted and tested in BABAR framework

(“BrmBbbrem”)

– Working on including BHLUMI generator as well

• Initial ghit-level studies performed with single-particle generator (i.e. no

crossection info) yield results consistent with magbends/turtle:

Ben Campbell, McGill

Apr 21, 2005 13 BABAR Beam Background Simulation Steven H. Robertson

A complication: neutrons A complication: neutrons

BF3 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/ - nuclear processes

– Neutron detectors added to Geant4

detector model

• J. Va'vra

Apr 21, 2005 14 BABAR Beam Background Simulation Steven H. Robertson

Low-Energy Nuclear processes Low-Energy Nuclear processes

• Electro-nuclear and gamma-nuclear

physics processes included for the first time in BABAR simulation

– Results in production of additional

low-energy (0-20 MeV) particles

– Important for EMC (?)

• High precision neutron processes included

in test releases for study of thermalized neutrons produced by beam backgrounds

– Will be included in future production

releases with enable/disable switch (off by default!)

Neutron kinetic energy (MeV) 1 ms Dennis Wright

Neutron TOF (0.025 eV cutoff)

Apr 21, 2005 15 BABAR Beam Background Simulation Steven H. Robertson

Status and plans Status and plans

• Still some problems with GEANT4 model and with TURTLE apertures

– Q2 septum geometry incomplete and Q5 magnets still missing – Magnetic fields believed to be correct

• Detailed validation of full simulation chain in progress

– Comparison of TURTLE/GEANT particle trajectories and impact positions – Large scale production of TURTLE lost-particle events

• Implement background (e.g. neutron) detectors in Geant model
• Validation of simulated neutron production and interactions

– Study of sources and rates

• Validation of small-angle bhabha generators (BHWIDE/BHLUMI/BBBREM)

– Study of luminosity backgrounds

• Absolute predictions of background rates in subdetectors and detailed studies
• f sources etc.

Apr 21, 2005 16 BABAR Beam Background Simulation Steven H. Robertson

Background Sources 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

– Contribution to background rates not well understood

• Luminosity (Bhabha/radiative Bhabha)

– Well measured, but not well understood (neutrons?)

• Beam-beam

– mechanism understood, measured in data

• Trickle injection related

– Characterized from data and not currently problematic

Apr 21, 2005 17 BABAR Beam Background Simulation Steven H. Robertson

Background simulation studies Background simulation studies

• Synchrotron radiation

Synchrotron radiation

–

Magbends studies for IR upgrades Magbends studies for IR upgrades

• Beam-beam collimation

Beam-beam collimation

–

affects orbit of outgoing beam particles; collimate downstream? affects orbit of outgoing beam particles; collimate downstream?

• Beam gas Coulomb scattering and bremsstrahlung

Beam gas Coulomb scattering and bremsstrahlung

–

Turtle and Turtle/Geant4 Turtle and Turtle/Geant4

–

similar to ~2000 era studies but with upgraded simulation tools similar to ~2000 era studies but with upgraded simulation tools

• Radiative Bhabha (“luminosity”) background

Radiative Bhabha (“luminosity”) background

–

Separate Magbends, Turtle and Geant4 studies in progress Separate Magbends, Turtle and Geant4 studies in progress

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

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

• or “physics” event can be generated by directly by G4 sim
• r “physics” event can be generated by directly by G4 sim

(but need extended beamline geomerty!) (but need extended beamline geomerty!)

• Questions:

Questions:

–

Where are primary particles produced and where do they go? Where are primary particles produced and where do they go?

–

Secondaries, neutrons and potential for shielding? Secondaries, neutrons and potential for shielding?

–

Effect of “2005 IR upgrade”, Super-B IR etc... Effect of “2005 IR upgrade”, Super-B IR etc...

Apr 21, 2005 18 BABAR Beam Background Simulation Steven H. Robertson

• 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 simulation studies as part of PEP-II upgrade program

Synchrotron radiation Synchrotron radiation

Apr 21, 2005 19 BABAR Beam Background Simulation Steven H. Robertson

GEANT4 Simulation GEANT4 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 geometry simulation to include beamline geometry

• ut beyond Q4:
• ut beyond 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 validation Modeling of magnetic fields (incl. Solenoid) and validation against Magbends & Turtle against Magbends & Turtle

–

Significant improvements in geometry and materials Significant improvements in geometry and materials modeling compared to old Geant3 version modeling compared to old Geant3 version

• Proceeding concurrently with

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

Apr 21, 2005 20 BABAR Beam Background Simulation Steven H. Robertson

GEANT4 beamline model GEANT4 beamline model

• Challenging geometry! – problems with G4 representation

Challenging geometry! – problems with G4 representation (M. Bondioli and G. Calderini)

(M. Bondioli and G. Calderini)

–

(Almost) complete model out to Q5 magnets (Almost) complete model out to Q5 magnets

–

Final checks of geometry in progress (overlapping Geant volumes etc) Final checks of geometry in progress (overlapping Geant volumes etc)

• Magnetic field modeling

Magnetic field modeling (G. Bower)

(G. Bower)

–

Validated against Magbends/Turtle Validated against Magbends/Turtle

–

Technical issues tracking particles through a varying field (“resolved”) Technical issues tracking particles through a varying field (“resolved”)

• Remaining issues:

– extended model runs ~10x

slower than nominal detector model

– Sources outside of +/-10m? Do

we need additional beam elements?

April 21, 2005 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 21

Pressure zones Pressure zones

X (mm)

Zone 1

X (mm)

Zone 2 Zone 3

X (mm)

Bremmsstrahlung in field-free region Bremmsstrahlung Bremmsstrahlung

• “

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

April 21, 2005 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 22

X (mm)

Zone 1 Zone 3

X (mm)

Bremmsstrahlung in field-free region Bremmsstrahlung

TURTLE ray simulation TURTLE ray simulation

• Simulates production and propagation of

Simulates production and propagation of Bremsstrahlung and Coulomb scattered Bremsstrahlung and Coulomb scattered primary beam particles through PEP-II primary beam particles through PEP-II magnet lattice magnet lattice

• gives rates and impact point of particles in

gives rates and impact point of particles in vicinity of IR vicinity of IR

• requires knowledge of vacuum profile in the

requires knowledge of vacuum profile in the rings (particularily incoming HER and LER rings (particularily incoming HER and LER straights near the IR) straights near the IR)

• Effort in progress to update TURTLE

Effort in progress to update TURTLE magnet and aperture descriptions magnet and aperture descriptions

• not updated since 1998 (commissioning run!)

not updated since 1998 (commissioning run!)

• LER optics done but apertures still to come

LER optics done but apertures still to come

• HER optics (essentially) done, aperture

HER optics (essentially) done, aperture description is available but not yet description is available but not yet implemented implemented

T.Feiguth, R.Barlow

April 21, 2005 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 23

Comparison with data Comparison with data

April 21, 2005 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 24

Recent turtle results... Recent turtle results...

• Updated HER deck to 2004 configuration

Updated HER deck to 2004 configuration

• Aperture and orbit checks performed

Aperture and orbit checks performed

• LER deck update still in progress

LER 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

April 21, 2005 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 25

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

• bremsstrahlung and Coulomb

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

• Reweight to “known” profile to get

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

• Record location, energy etc of

Record location, energy etc of primary particles hitting in vicinity primary particles hitting in vicinity

• f IR
• f IR
• Useful information about impact

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

April 21, 2005 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 26

Geant3 simulation (<2001) Geant3 simulation (<2001)

• Used during commissioning phase and first few years of running

Used during commissioning phase and first few years of 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 studies

Turtle ray input to allow lost particle background studies

• Some known issues with beamline geometry, fields and material model

Some known issues with beamline geometry, fields and material model

• ccasionally primary particles would vanish
• ccasionally primary particles would vanish
• ccasional discrepancies between Turtle z-hit position and Geant hit position
• ccasional discrepancies between Turtle z-hit position and Geant hit position
• “

“Replaced” by Geant4 detector simulation in ~2002 Replaced” by Geant4 detector simulation in ~2002

• Beamline simulation only out to ~Q2 !

Beamline simulation only out to ~Q2 !

April 21, 2005 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 27

Chih-Hsiang Cheng

Turtle-Geant3 studies (circa 1998) Turtle-Geant3 studies (circa 1998)

SVT pin-diode simulation studies SVT pin-diode simulation studies

• G-hit based study using Turtle rays as

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

• Used during initial PEP-II commissioning

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

• Predictions for SVT background

Predictions for SVT background sensitivities to HER and LER zones sensitivities to HER and LER zones

• Some diodes appeared to be better

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

April 21, 2005 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 28

More Turtle-Geant studies More Turtle-Geant studies

• 4-vectors of Turtle rays which strike apertures near IP are recorded at a point ~8m

4-vectors of Turtle rays which strike apertures near IP are recorded at a point ~8m upstream, then passed to Geant upstream, then passed to Geant

• Geant propagates particle into IR and simulates interactions in beampipe/detector

Geant propagates particle into IR and simulates interactions in beampipe/detector material material

• permits identification of turtle rays which produce activity (e.g. from secondary

permits identification of turtle rays which produce activity (e.g. from secondary particles in specific detector elements particles in specific detector elements

April 21, 2005 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 29

EMC Occupancy predictions EMC Occupancy predictions

• Extrapolate simulated lost-

Extrapolate simulated lost- particle induced detector particle induced detector

• ccupancies according to
• ccupancies according to

measured (or assumed) vacuum measured (or assumed) vacuum profile profile

• Once appropriate backgrounds

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

• Full detector response to

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

April 21, 2005 BBBTF Steven H. Robertson McGill University, Institute of Particle Physics 30

EMC Radiation dose EMC Radiation dose

• RadFET calorimeter radiation

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

• Not necessarily representative of dose in

Not necessarily representative of dose in individual crystals individual crystals

• Total radiation dose estimated by

Total radiation dose estimated by integrating estimated flux rate from integrating estimated flux rate from simulation simulation

• Assume pressure profile

Assume pressure profile

• Reasonable agreement with RadFET data

Reasonable agreement with RadFET data (~30%) (~30%)

• Interesting features!

Interesting features!

• simulation predicted region of reduced

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

RadFET Data