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

B A B AR B A B AR Beam Background Beam Background Simulation Simulation Steven Robertson 2 nd Hawaii Super B Factory Workshop April 21, 2005

Motivation Motivation EMC EMC y g r Beam background conditions result in Beam background conditions result in e ● n e detector occupancy, radiation damage and detector occupancy, radiation damage and t n a c degradation of data quality degradation of data quality i f i n g Background characterization is based on Background characterization is based on i ● s h t dedicated beam background experiments dedicated beam background experiments = 3.3x10 34 34 cm cm -2 -2 s s -1 -1 L = 3.3x10 i L w s l single and two beam colliding/non-colliding, single and two beam colliding/non-colliding, a – t s y trickle injection etc. trickle injection etc. r c f o permit extrapolation to future running conditions permit extrapolation to future running conditions – # (under assumptions about beam conditions) (under assumptions about beam conditions) DCH DCH Simulation is needed in order to: Simulation is needed in order to: ● 1) Validate and aid interpretation of background data Validate and aid interpretation of background data 1) 2) Identify sources and underlying causes of Identify sources and underlying causes of 2) 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) Evaluate effects of future upgrades on bg rates Evaluate effects of future upgrades on bg rates 4) Extrapolate to Super-B ? – Extrapolate to Super-B ? Steven H. Robertson BABAR Beam Background Simulation Apr 21, 2005 2

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

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

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

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 LER Radiative Bhabhas 30 3.1 GeV 20 10 cm 9 GeV 0 9 GeV -10 0.5 1 2 1.5 3.1 GeV -20 2.5 3 -30 -7.5 -5 -2.5 0 2.5 5 7.5 M. Sullivan m Feb. 8, 2004 API88k3_R5_RADBHA_TOT_7_5M – 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... Steven H. Robertson BABAR Beam Background Simulation Apr 21, 2005 6

Turtle ray simulation Turtle ray simulation Coulomb scattering in Arcs (y- plane) IP e - Brems- Normalized to: strahlung - uniform pressure profile of 1 nT Vacuum pipe / mask apertures in last 26 m - 1 A beam current (x-plane) IP Steven H. Robertson BABAR Beam Background Simulation Apr 21, 2005 7

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 ● outside of nominal detector acceptance outside 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 – Steven H. Robertson BABAR Beam Background Simulation Apr 21, 2005 8

Radiative Bhabha background Radiative Bhabha background 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: Mike Sullivan Steven H. Robertson BABAR Beam Background Simulation Apr 21, 2005 9

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) Achille Stochi & Patrick Roudeau Use small-angle bhabha generator ● electrons (bbbrem) to obtain particle trajectories and energy flux through beamline elements “Golden orbit” – Results recently updated using new HER/LER Turtle decks including photons BABAR solenoid HER radiative bhabhas Steven H. Robertson BABAR Beam Background Simulation Apr 21, 2005 10

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: σ E x σ Z range LER Radiative Bhabhas (m) (mb) (mb GeV) 30 V <.8 9.2 2.5 e G 1 20 . 3 .8<Z<1.4 26.4 27.7 10 Q1 1.4<Z<2.2 56.7 117 cm 9 GeV 0 Q2 9 GeV 2.2<Z<2.8 20. 50 -10 0.5 1 2 1.5 2.8<Z 5.2 13.5 V -20 e G 1 . 3 2.5 3 -30 -7.5 -5 -2.5 0 2.5 5 7.5 M. Sullivan m Feb. 8, 2004 API88k3_R5_RADBHA_TOT_7_5M Steven H. Robertson BABAR Beam Background Simulation Apr 21, 2005 11

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: Off energy electrons Off energy positrons Ben Campbell, McGill Steven H. Robertson BABAR Beam Background Simulation Apr 21, 2005 12