Background study plans : from ATF2@KEK to ILC

1. Background study plans : from ATF2@KEK to ILC Hayg GULER LLR-Ecole Polytechnique, France SOCLE Clermont-Ferrand 19 et 20 novembre 2007

2. Background study plans : from ATF2@KEK to ILC • ATF2 : design & goals • Strategy and tools • Background extraction @ ATF2 : a possible way to test our simulation programs • Background studies for ILC • Conclusion/Outlook

3. existing extraction New diagnostics New FF New Beamline http://lcdev.kek.jp/ILC-AsiaWG/WG4notes/atf2/proposal/public/ ATF2 goals • Prototype final focus system for luminosity challenges of ILC : • Small beam size • Learn to obtain sy ~ 35nm • And maintain for long time • Stabilization of beam center • Learn to keep it stable at IP within < 2nm • Measure with nano-BPM • Control with bunch-to-bunch feedback of ILC-like train

4. ATF2 collaboration, presently >88 people from 21 labs and institutions and growing KEK, Tsukuba IHEP, Beijing BINP, Novosibirsk CCLRC/DL/ASTeC,Daresbury CEA, Gif-sur-Yvette CERN, Geneva Hiroshima University Kyoto ICR, Kyoto LAL, Orsay LAPP, Annecy LLR, Palaiseau LLNL, Livermore NIRS, Chiba-shi North Carolina A&T State University Oxford University Pohang Accelerator Laboratory Queen Mary University of London Royal Holloway, University of London DESY, Hamburg SLAC, Stanford UCL, London University of Oregon University of Tokyo ATF2 proposal was web-released just after BDIR workshop in London, => KEK, SLAC, CERN, … preprints LAL:Work on beam correction algorithms of ATF-2 beam line, commissioning, instrumentation developments. LAPP: Studies to provide a suitably stabilized support for the final doublet, commissioning LLR: Background study (algorithms, GEANT4, « event biasing technique»), commissioning ATF2 collaboration End of September 2007

5. Background studies strategy • Prototype @ATF2 part of the background estimation for ILC • Using common simulation tools • BDSIM • Comparison with DATA • e+, e-, g background • Neutrons (in addition) for the beam dump • Challenges • 105 e- in the simulation beam • How to extrapolate to the 1010 e- in the real beam ?

6. Possible source of background @ ATF2 Photons (Bremsstrahlung ) In opposition to signal (= Compton photons) from LASER scattering on Beam Core electrons Synchrotron radiation : This is major background at FFTB experiment, but at ATF2, critical energy at bending magnet (assuming 1 Tesla) is about 1 keV. As a result, synchrotron photons can be easily stopped by beam pipe. Scattering with residual gas Because ATF2 beam line is relatively short (~50m), number of photons of this background is negligibly small. Beam halo scattering with beam pipe by Bremsstrahlung This is the major background in ATF2. It has large energy up to beam energy (1.3GeV), and large number of photons created without halo-cut components Particles from beam dump This may also be large background, but it can be reduced by geometry, but large uncertainty today on this source. Involve also neutron production

7. BDSIM overview 2mrad Extraction Author: G.Blair --- Developers: I. Agapov, J. Carter • BDSIM is a C++ tool, Geant4 based • All physics processes from Geant4 • Accelerator tracking code Inside beam-pipe • Use analytic solution to the equations of motion (CPU time consuming) • otherwise “normal” G4 tracking inside materials • BDSIM is already used for the ILC simulation • Can be interfaced with : • MAD • Mokka • ROOT output 20mrad IR 2mrad IR More info http://flc.pp.rhul.ac.uk/bdsim.html EUROTeV-Report-2006-014

8. Beam Halo • Source of background by hitting the beam pipe • and creating Bremsstrahlung photons • Generated mainly by Intra Beam Scattering • Non Gaussian tail • Contains 0.1 1% of the beam core electrons • Energy spread  the same width/shape • as the beam core (0.1%)? • Photons scattering in the beampipe well simulated ? •  Consider having to measure this in a separated setup Previous measurements 2005 2007 New measurement end 2007

9. On going studies: Trying to describe the background normalization  Better describe the HALO (Shape, population, energy distribution)  Include (design) collimator to eliminate background Further steps:  Background from the dump  Photons and charged particles  Neutrons  Special techniques  “event biasing methods” What can we learn for ATF2 Background ? BDSIM Simulation Generated 100% flat HALO • DE=0.1% Gaussian • From 0.1%  1% electron in Halo • Signal : 2-4 103 Compton signal photons •  Use Collimator to eliminate the background photons Background Photons inside 1m Background Photons inside 10cm Photons spectrum from the Beam Position measurement device (Shintake monitor)

12. Conclusion & Outlook • ATF2 is a prototype for the ILC final focus • That we wish to use to prototype the background simulation • Coming from the HALO • Coming from the DUMP (backscattered) • Using tools common with ILC • Validation with measurements foreseen

13. C’est FINI

14. From halo to measurement Comparison to data ATF/ATF2 line Beam dump Detector simulation GEANT4 Geometry Physics processes Statistics Input e- Distribution Test the input properties Test the Simulation tool Need flexible simulation code (re-weighting the initial distribution) • Test the physics processes • Better describe the geometry • Improve speed of the code • (Unlikely configurations  • event biasing methods ?)