A Short History of Nearly Everything

1. A Short History of Nearly Everything Michele Viti

2. Outline • Myself • About my work in Zeuthen • ILC overview • Beam energy measurement • An brief overview of my work and results • Magnetic measurements • Relative beam energy resolution • Laser Compton energy spectrometer Michele Viti

3. Myself • I was born 31 years ago somewhere in Italy • I studied physics at the Perugia university Michele Viti

4. Myself • Master degree in 2004. • Title of the thesis : “Evaluation of a Tracking Algorithm for the Trigger of KOPIO Experiment on the Decay ”. • I continued working on this topic until the project was canceled by the DOE. Michele Viti

5. Myself • I moved then to Germany and started in February 2006 my PhD. • I joined the Linear Collider working under the supervision of H.J. Schreiber. • Title of the thesis “Precise and Fast Beam Energy Measurements at ILC”. Michele Viti

6. ILC • 30 Km electrons/positrons linear accellerator • Total energy in the cms 500 Gev (upgradeable 1 Tev) • High luminosity (2*10^34 /cm^2*s) • A machine for precise measurements Michele Viti

7. ILC: Precise Top Mass Measurements • Many Standard Model depends strongly on the value of the Top Mass. • Well understood background, clean experimental environment • Best direct measurement of the top mass will be at ttbar threshold • Vary the beam energy (Precise Beam Energy Measurements) • Count number top-antitop events. Michele Viti

8. Basic Requirements for Beam Energy Measurements • In order to make a precise measurement of the top quark mass we need to know some “input” parameters very well such as the mean energy of the bunch • We need to have a fast (bunch-by-bunch), precise and non-destructive monitor for beam energy • Direct measurement of energy at the IP is very difficult. We want to measure the beam energy upstream, downstream the IP plus a slow monitoring at the IP • Relative Energy precision required for upstream measurements Michele Viti

9. BPM L offset d BPM BPM magnets Magnetic Chicane Energy Spectrometer • Electrons are deflected in this chicane and the offset in the mid-chicane is anti-proportional to the energy. • Measuring this position with some special devices (Beam Position Monitor, BPM) together with B-field integral we have access to the beam energy • Method well tested used at LEP with a precision of Michele Viti

10. Experiment T474/491 • At the End Station A (ESA) a 4-magnet chicane energy spectrometer was commissioned in 2006/2007 (experiment T474/491). • The goal is to demonstrate the feasibility of the system. Michele Viti

11. End Station A • Characteristic: • Parasitic with PEP II operation • 10 Hz and 28.5 GeV • Bunch charge, bunch length energy spread similar to ILC • Prototype components of the Beam delivery System and interaction Region. Michele Viti

12. End Station A Beam Parameters at SLAC ESA and ILC Michele Viti

13. Experiment T474/491 • Institutes involved: SLAC, U.C. Berkeley, Notre Dame, Dubna, DESY, RHUL, UCL, Cambridge • 2006: • January (4 days): commissioning steering BPMs • April(2 weeks): commissioning cavity BPMS, optimization digitization and processing • July(2 weeks): commissioning interferometer and stabilty data taken with frequent calibrations • 2007: • March(3 weeks):Commissioning and installation magnets: first chicane data!!! • July(2 weeks):Additional new BPM in the centre of the chicane. Michele Viti

14. Magnetic measurements

15. Magnetic measurements • B-field Integral, essential parameter for beam energy measurement. • Need to be measured with an accuracy of 50 ppm. Michele Viti

16. Magnetic measurements • Between November 2006 – February 2007 measurements on these magnets were performed in the SLAC laboratories (DESY, Dubna, SLAC). • Purpose of the measurements: • General understanding and characterization of the magnets • Stability of the B-field and B-field integral with fixed current and switching the polarity. • Monitoring of the residual B-field. • B-field map. • Measurement of the temperature coefficient for B-field and B-field integral . • Development and test a procedure to monitor the B-field integral. Michele Viti

17. Magnetic measurements • Monitor of the B-field integral: in ESA no device was available to measure directly this quantity. • Solution: measure the B-field in one point and from that determine the integral. • Basic assumption When the field is changing in one point, changes everywhere by the same amount. The field shape stay constant Michele Viti

18. Magnetic measurements • To measure the B-field in one point an NMR probe was used. • Flip coil technique to measure for B-field integral. • Calibration of the NMR: determination of the slope and intercept for the relation. • Comparison of the prediction with the measurement. Michele Viti

19. Magnetic measurements • The total error on the estimation of the B-field integral using the one-point B-field measurement was • Main contributions are alignment errors of the devices. • Several suggestions were given to improve the results. Michele Viti

20. Relative beam energy resolution

21. Relative Beam Energy Resolution • At the End Station A several problems occurred for 4-magnet chicane prototype • A complementary method to cross-check the absolute energy measurement was not implemented • Only relative energy measurement possible at ESA Michele Viti

22. Relative Beam Energy Resolution Beam direction • The offset d in the mid-chicane point is determined by two points, namely Xb and X0 • Xb is measured by the BPMs the mid-chicane and X0 is extrapolated using BPMs upstream and downstream of the chicane. Michele Viti

23. Relative Beam Energy Resolution • BPMs, Beam Position Monitors. They measure the transverse position (X and Y) and angle (tilt) in the X-Z and Y-Z plane (X’ and Y’). • Accuracy on position measurement < 500 nm. Michele Viti

24. Relative Beam Energy Resolution • X0 can be written as • For zero current magnet Xb=X0, the BPM measures directly X0. • The coefficients in Eq. above can be determined with a minimization. Michele Viti

25. Relative Beam Energy Resolution Beam direction • One fundamental condition: the magnetic chicane must work symmetrically • The upstream path must be restored downstream Michele Viti

26. Relative Beam Energy Resolution • Unfortunately this was not the case of the 4-magnet chicane in ESA • For a given current the magnet fields were different up to ~3% • BPMs downstream could not be used to determine X0. This resulted in a worse resolution for d. Michele Viti

27. Relative Beam Energy Resolution • A resolution of 24 MeV was found (Resolution -- the smallest amount of energy change that the instrument can detect reliably) • For a beam energy of 28.5 GeV this corresponds to a relative resolution of ~ • The largest contribution to this number comes from the resolution on d (>2 microns). Michele Viti

28. Laser Compton Energy Spectrometer

29. Laser Compton Energy Spectrometer • At LEP it was possible to have redundant beam energy measurement devices  cross check!!! • At ILC so far, complementary methods for upstream beam energy measurements not implemented. • Studying the feasibility of an upstream energy spectrometer based on Compton backscattering (CBS) events. Michele Viti

30. Laser Compton Energy Spectrometer • Compton process with initial electron not at rest. • Energy spectrum for electrons (photons) present a sharp cut-off (Compton edge). • Scattered particles collimated in forward region. Michele Viti

31. Laser Compton Energy Spectrometer Michele Viti

32. Energy measurement • , is the center of gravity of the scattered photons, or, equivalently, the end point of the SR fan. • , position of beam, possible to measure with BPMs • , position of the electrons with minimum energy. Michele Viti

33. Laser Compton Energy Spectrometer • Beam parameters • Beam energies 50-500 GeV • Beam size in x (y) 20-50 (2-5) microns • Geometrical parameters • Drift distance 25-50 m • B field 0.28 T, magnet length 3 m • Laser parameters • Smaller wavelength preferable (e.g. green laser) • Pulsed laser with 3 MHz frequency • Laser spot size 50-100 microns • Laser pulse energy must ensure 10^6 scatters (e.g. 30 mJ per pulse) • Crossing angle ~8 mrad • Accuracy required to achieved • < 1-2 microns • < 1-2 microns • < 20 microns Michele Viti

34. Laser Compton Energy Spectrometer • Beam position can measured with a normal BPM (very well know and precise technique). • Edge position: Diamond strip detector or quartz fiber detector. Basic simulation shows that this feasible. • Photon detection: Basically 2 possibilities, using the backscattered photons or the synchrotron radiation photons. Michele Viti

35. Laser Compton Energy Spectrometer • Number of backscattered photons (BP) 4 order of magnitude less than SR photons • <Energy> BP ~100 GeV, <energy> SR photons ~3 MeV. • 2 possibilities • Place a thick absorber in front of detector and measure the profile of shower (signal from BP dominant), quartz fiber detector suitable. • No absorber, detector in front of the photon beam (signal from SR photons dominant). Novel detector under development in DUBNA (Xenon gas detector). • Main problem for both configurations: very high radiation dose (10-100 GGy per year). Michele Viti

36. Conclusions • A prototype of 4-magnet chicane was built in ESA. • The absolute value of the B-field integral can be monitored with an accuracy 184 ppm (ESASLAC note and PAC poster) • The resolution of the chicane was found to be ~24 MeV, where the main contribution is the resolution on the beam offset in the mid-chicane (to be published…) • A novel method based on Laser Compton events was studied(NIM publication). An experiment is under study to proof the feasibility (proposal in preparation). Michele Viti