Challenges for Polarimetry at the ILC Spin Tracking Studies Moritz - PowerPoint PPT Presentation

Challenges for Polarimetry at the ILC Spin Tracking Studies Moritz Beckmann, Jenny List DESY - FLC LCWS 2012, Arlington, TX, USA October 25, 2012

Introduction: Polarimetry at the ILC • Two laser Compton polarimeters per beam in the beam delivery system (BDS) upstream downstream polarimeter IP polarimeter 150 m ~1 650 m • Polarimeters measure with 0.25 % systematic uncertainty (goal) • What happens between polarimeter and IP? Moritz Beckmann (DESY) LCWS Oct 25, 2012 2/ 17

Introduction: Polarimetry at the ILC • Two laser Compton polarimeters per beam in the beam delivery system (BDS) upstream downstream polarimeter IP polarimeter 150 m ~1 650 m • Polarimeters measure with 0.25 % systematic uncertainty (goal) • What happens between polarimeter and IP? • In addition: calibration with average polarization from collision data (up to 0.1 %) • Must understand spin diffusion/depolarization to 0.1 % Moritz Beckmann (DESY) LCWS Oct 25, 2012 2/ 17

Introduction: Simulation Framework Particle / spin tracking along the BDS Bmad UP IP DP Polarimeter simulation Beam-beam collision Polarimeter simulation LCPolMC LCPolMC GP++/CAIN Data analysis ROOT UP/DP: up-/downstream polarimeter Framework could be used with different input also for other machines, e. g. CLIC Moritz Beckmann (DESY) LCWS Oct 25, 2012 3/ 17

Introduction: Principles of Spin Propagation • Spin propagation in electromagnetic fields is described by T-BMT equation ( semi- classical ) • Approximation ( � B ⊥ only) for illustration: spin precession B � � g − 2 · E θ spin = m + 1 · θ orbit 2 � �� � ≈ 568 Moritz Beckmann (DESY) LCWS Oct 25, 2012 4/ 17

Introduction: Principles of Spin Propagation • Spin propagation in electromagnetic fields is described by T-BMT equation ( semi- classical ) • Approximation ( � B ⊥ only) for illustration: spin precession B � � g − 2 · E θ spin = m + 1 · θ orbit 2 � �� � ≈ 568   P x � � • Polarization vector �  with polarization � � � � P = P y P  � P z Moritz Beckmann (DESY) LCWS Oct 25, 2012 4/ 17

Introduction: ILC Beam Delivery System Latest available beamline design (SB2009 Nov10 lattice) Moritz Beckmann (DESY) LCWS Oct 25, 2012 5/ 17

Spin Propagation through BDS (Idealized Lattice) polarization 0.8 0.6 0.4 0.2 0 - e -0.2 P -0.4 z | P | -0.6 UP IP DP -0.8 0 500 1000 1500 2000 2500 3000 3500 distance s along BDS [m] UP/DP: up-/downstream polarimeter • 1000 runs with random bunches, 10 000 sim. particles each • Drawn: median ± 1 σ • Perfect magnet alignment, no collision effects Moritz Beckmann (DESY) LCWS Oct 25, 2012 6/ 17

Spin Fan-Out polarization ] -3 0.8 0 relative change [10 0.7998 0.7996 -0.5 - 0.7994 e P z | P | 0.7992 -1 3400 IP 3450 3500 3550 DP distance s along BDS [m] Only minor spin fan-out in quadrupoles Moritz Beckmann (DESY) LCWS Oct 25, 2012 7/ 17

Spin Fan-Out polarization ] -3 0.8 0 relative change [10 0.7998 0.7996 -0.5 - 0.7994 e P z | P | 0.7992 -1 3400 IP 3450 3500 3550 DP distance s along BDS [m] Only minor spin fan-out in quadrupoles P' P P Moritz Beckmann (DESY) LCWS Oct 25, 2012 7/ 17

Collision Effects Simulation of Collision Effects (GP++): • T-BMT precession : deflection from colliding bunch ( ∼ 10 − 4 rad) • Sokolov-Ternov: spin flip by emission of beamstrahlung Moritz Beckmann (DESY) LCWS Oct 25, 2012 8/ 17

Collision Effects: Energy Loss • Energy loss by beamstrahlung: 7 10 # of entries before collision 6 10 5 after collision 10 4 10 3 10 2 10 10 1 -0.6 100 150 -0.4 200 -0.2 250 0 particle energy [GeV] • Spin precession ∝ E ⇒ Spin fan-out due to energy spread Moritz Beckmann (DESY) LCWS Oct 25, 2012 9/ 17

Collision Effects: Energy Loss vs. Laser-Spot • Laser-spot size at Compton IP only ∼ 0 . 1 − 1 mm • chicane ⇒ dispersion (black: reference particle) • Without collision: 0.124 % beam energy spread Entire beam within laser-spot � × -3 10 no collision 0.15 vertical particle position y [mm] 5 10 0.1 0.1 4 10 0.05 3 0 0 10 -0.05 2 10 -0.1 -0.1 10 -0.15 1 -0.005 249 250 0 251 0.005 particle energy [GeV] Moritz Beckmann (DESY) LCWS Oct 25, 2012 10/ 17

Collision Effects: Energy Loss vs. Laser-Spot • Laser-spot size at Compton IP only ∼ 0 . 1 − 1 mm • chicane ⇒ dispersion (black: reference particle) • After collision: Off-energy particles evade laser-spot • Downstream polarimeter needs detailed investigation (energy and polarization correlated!) after collision vertical particle position y [mm] 0.02 20 6 10 0.015 5 10 0.01 10 4 10 0.005 0 0 3 10 -0.005 2 10 -0.01 -10 10 -0.015 -0.02 -20 1 -0.4 150 -0.3 200 -0.2 -0.1 250 0 particle energy [GeV] Moritz Beckmann (DESY) LCWS Oct 25, 2012 11/ 17

Collision Effects: Spin Propagation • Collisions, but still perfect alignment • Crossing angle 14 mrad, bunches crabbed z ] -3 long. polarization P 0.8 0 relative change [10 -10 0.79 no collision -20 lumi-weighted 0.78 after collision measurable -30 - e 0.77 -40 3400 IP 3450 3500 3550 DP distance s along BDS [m] • Much stronger spin fan-out • Polarization within 0.1 mm laser-spot different: “measureable” Moritz Beckmann (DESY) LCWS Oct 25, 2012 12/ 17

Collision Effects: Spin Propagation no coll. full lumi z ] longitudinal polarization P -3 0.8 0 relative change [10 -10 0.79 UP IP before collision -20 IP lumi-weighted IP after collision 0.78 DP DP measurable -30 (r=0.1, 0.2, 0.5, 1 mm) 0.77 -40 0 10 20 30 Moritz Beckmann (DESY) LCWS Oct 25, 2012 13/ 17

Collision Effects: Spin Propagation no coll. full lumi z ] longitudinal polarization P -3 0.8 0 relative change [10 -10 0.79 UP IP before collision ≈ -20 IP lumi-weighted 2.5% IP after collision 0.78 DP DP measurable -30 ≈ 0.3% (r=0.1, 0.2, 0.5, 1 mm) 0.77 -40 0 10 20 30 • What does the measurement tell us about the polarization at the IP?? ∆P z ∼ 2 . 5 % • Can we trust the simulation to calculate back? More details to come: detector magnets, misalignments • Uncertainty in DP laser-spot size/position ⇒ ∆ P z = O (0 . 1 %) Moritz Beckmann (DESY) LCWS Oct 25, 2012 14/ 17

Collision Effects: Spin Propagation no coll. low lumi full lumi z ] longitudinal polarization P -3 0.8 0 relative change [10 -10 0.79 UP IP before collision -20 IP lumi-weighted IP after collision 0.78 DP DP measurable -30 (r=0.1, 0.2, 0.5, 1 mm) 0.77 -40 0 10 20 30 Low luminosity sample (switched off bunch crabbing): • Collision effects and also their consequences reduced • Downstream measurement less affected by collision effects and less dependent on laser-spot size/position Moritz Beckmann (DESY) LCWS Oct 25, 2012 15/ 17

Conclusion • A spin tracking framework for high energy linear colliders including collision effects has been set up • ILC: understanding of polarization to permille-level required • Precision goals for upstream measurement seem achievable Moritz Beckmann (DESY) LCWS Oct 25, 2012 16/ 17

Conclusion • A spin tracking framework for high energy linear colliders including collision effects has been set up • ILC: understanding of polarization to permille-level required • Precision goals for upstream measurement seem achievable • Downstream polarimeter struggles fiercely with collision effects : • High-precision simulation including all effects required at high luminosities to obtain polarization at IP from data • Measurement highly sensitive to size/position of laser-spot • Idea : determine lumi-weighted polarization rather/also from upstream polarimeter and luminosity measurement? Moritz Beckmann (DESY) LCWS Oct 25, 2012 16/ 17

Conclusion • A spin tracking framework for high energy linear colliders including collision effects has been set up • ILC: understanding of polarization to permille-level required • Precision goals for upstream measurement seem achievable • Downstream polarimeter struggles fiercely with collision effects : • High-precision simulation including all effects required at high luminosities to obtain polarization at IP from data • Measurement highly sensitive to size/position of laser-spot • Idea : determine lumi-weighted polarization rather/also from upstream polarimeter and luminosity measurement? • Downstream polarimeter needed nevertheless : • Measure depolarization without collision effects / calibrate UP • Measure additional depolarization at low luminosities to test simulations Moritz Beckmann (DESY) LCWS Oct 25, 2012 16/ 17

Thanks for your attention! Thanks for support and useful discussions to: • David Sagan (Cornell U.) • Deepa Angal-Kalinin (Daresbury Lab.) • Anthony Hartin, Mathias Vogt, Nick Walker (DESY) • Andrei Seryi (JAI) • Kenneth Moffeit, Yuri Nosochkov, Michael Woods (SLAC) • Jeff Smith (formerly SLAC) • und many others... Moritz Beckmann (DESY) LCWS Oct 25, 2012 17/ 17

Backup slides Moritz Beckmann (DESY) LCWS Oct 25, 2012 18/ 17