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RHIC Spin and Collider

RHIC Spin and Collider. Mei Bai. Outline. Introduction: why polarized protons spin “crisis” accelerate polarized protons to high energy RHIC: the first polarized proton collider brief history of RHIC spin program achieved performance of RHIC pp Conclusion plan for RHIC improvements.

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RHIC Spin and Collider

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  1. RHIC Spin and Collider Mei Bai

  2. Outline • Introduction: why polarized protons • spin “crisis” • accelerate polarized protons to high energy • RHIC: the first polarized proton collider • brief history of RHIC spin program • achieved performance of RHIC pp • Conclusion • plan for RHIC improvements

  3. What is Spin? From Google… • revolve quickly and repeatedly around one's own axis, "The dervishes whirl around and around without getting dizzy" • twist and turn so as to give an intended interpretation, "The President's spokesmen had to spin the story to make it less embarrassing" • a distinctive interpretation (especially as used by politicians to sway public opinion), "the campaign put a favorable spin on the story"

  4. What is Spin? • Classical definition • the body rotation around its own axis • Particle spin: • an intrinsic property, like mass and charge • a quantum degree freedom associated with the intrinsic magnetic moment. q: electrical charge of particle m: particle mass • G: anomalous gyromagnetic factor, describes • the particle internal structure. For particles: • point-like: G=0 • electron: G=0.00115965219 • muon: G=0.001165923 • proton: G=1.7928474

  5. I  spin vector and spin-orbit interaction • Spin: single particle • pure spin state align along a quantization axis • Spin vector S: a collection of particles • the average of each particle spin expectation value • along a given direction • Spin orbit interaction S S S N N

  6. Discovery of Spin: 1925 “This is a good idea. Your idea may be wrong, but since both of you are so young without any reputation, you would not lose anything by making a stupid mistake.” --- Prof. Ehrenfest G.E. Uhlenbeck and S. Goudsmit, Naturwissenschaften 47 (1925) 953. A subsequent publication by the same authors, Nature 117 (1926) 264,

  7. Spin Crisis: what makes up the proton spin? Sum of spins of all quarks P u d CERN EMC and SLAC SMC: ~ 20%!

  8. Current model: Proton spin sum-rule Spin contribution from all the gluons? Orbital angular momentum of quarks and gluons?

  9. Quest to unveil the proton spin structure: High energy proton proton collisions: gluon gluon collision and gluon quark collision gluon spin contribution g g q g quark/antiquark spin contribution

  10. STAR RHIC: world’s first polarized proton collider

  11. STAR RHIC spin physics • measure gluon spin contribution g • measure quark and anti quark spin contribution • Excellent calorimeter granularity • and muon detection • electrons, muons, photons and • leading hadrons • Large acceptance with Time • Projection Chamber and calorimeters • Jets and photons and electrons

  12. Design parameters for RHIC pp

  13. Figure of merit of polarized proton collider • Luminosity: • number of particles per unit area per unit time. The higher the luminosity, the higher the collision rates • beam polarization • Statistical average of all the spin vectors. • zero polarization: spin vectors point to all directions. • 100% polarization: beam is fully polarized if all spin vectors point to the same directions. # of particles in one bunch # of bunches Transverse beam size

  14. Basics of circular accelerator • bending dipole • Constant magnetic field • Keeps particles circulating around the ring • quadrupole • Magnetic field proportional to the distance from the center of the magnet. • Keeps particles focused • radio frequency cavities • Electric field for acceleration and keeping beam bunched longitudinally

  15. Closed orbit in a circular accelerator Closed orbit: particle comes back to the same position after one orbital revolution Closed orbit in a perfect machine: center of quadrupoles Closed orbit in a machine with dipole errors Courtesy of Lingyun Yang

  16. Betatron oscillation in a circular accelerator Betatron tune: number of oscillations in one orbital revolution Beta function Courtesy of Lingyun Yang

  17. B beam Spin motion in circular accelerator: Thomas BMT Equation • In a perfect accelerator, spin vector precesses around the bending dipole field direction: vertical • Spin tune Qs: number of precessions in one orbital revolution. In general, Spin vector in particle’s rest frame

  18. polarized proton acceleration challenges: preserve beam polarization • Depolarization(polarization loss) mechanism • Come from the horizontal magnetic field which kicks the spin vector away from its vertical direction • Spin depolarizing resonance : coherent build-up of perturbations on the spin vector when the spin vector gets kicked at the same frequency as its precession frequency y y y beam beam beam z z z x x x 1st full betatron Oscillation period 2nd full betatron Oscillation period Initial

  19. spin depolarizing resonance • Intrinsic resonance • Source: horizontal focusing field from betatron oscillation • Resonance location: • G = kP±Qy, • P is the periodicity of the accelerator, • Qy is the vertical betatron tune • Imperfection resonance • Source: dipole errors, quadrupole mis-alignments • Resonance location: G = k k is an integer

  20. Spin depolarization resonance in RHIC • For protons, imperfection spin resonances are spaced • by 523 MeV • the higher energy, the stronger the depolarizing • resonance Intrinsic spin resonance Qx=28.73, Qy=29.72, emit= 10

  21. Innovative polarized proton acceleration techniques: Siberian snake • First invented by Derbenev and Kondratenko from Novosibirsk in 1970s • A group of dipole magnets with alternating horizontal and vertical dipole fields • rotates spin vector by 180o

  22. Particle trajectory in a snake:

  23. How to preserve polarization using Siberian snake(s) • Use one or a group of snakes to make the spin tune to be at ½ • Break the coherent build-up of the perturbations on the spin vector y y beam beam z z

  24. Accelerate polarized protons in RHIC

  25. BRAHMS(p) Absolute Polarimeter (H jet) RHIC pC Polarimeters Siberian Snakes Spin flipper PHENIX (p) STAR (p) Spin Rotators (longitudinal polarization) Spin Rotators (longitudinal polarization) Solenoid Partial Siberian Snake LINAC BOOSTER Helical Partial Siberian Snake Pol. H- Source AGS 200 MeV Polarimeter AGS Polarimeters Strong AGS Snake

  26. E20 5.9% A20 10~15% Polarized proton in the AGS • AGS (Alternating Gradient Synchrotron) • Energy: 2.3 GeV ~ 23.8 GeV • A total of 41 imperfection resonances and 7 intrinsic resonances from injection to extraction

  27. AGS polarized proton development

  28. Polarized proton acceleration setup in RHIC • Energy: 23.8 GeV ~ 250 GeV (maximum store energy) • A total of 146 imperfection resonances and about 10 strong intrinsic resonances from injection to 100 GeV. • Two full Siberian snakes

  29. Polarized proton acceleration in RHIC

  30. 5/6 Store working pt. Ramp working pt. 3/4 7/8 5/8 snake depolarization resonance • Condition • even order resonance • When m is an even number • Disappears in the two snake case like RHIC if the closed orbit is perfect • odd order resonance • When m is an odd number • Driven by the intrinsic spin resonances

  31. y y y beam beam beam z z z -x -x -x y y y beam beam beam z z z -x -x -x

  32. Snake resonance observed in RHIC 7/10 snake resonance

  33. How to avoid a snake resonance • snake current setting • Keep the spin tune as close to ½ as possible • set the vertical tune to • 0.745 • measure the beam • polarization with • different snake current • expect no depolarization • if the corresponding spin • tune is very close to 0.5

  34. Keep the vertical closed orbit as flat as possible How to avoid a snake resonance rms: 0.45mm

  35. Keep the spin tune as close to ½ as possible snake current setting Keep the vertical closed orbit as flat as possible orbit control Keep the betatron tunes away from snakeresonance locations Precise tune control How to avoid a snake resonance

  36. Betatron tune along the ramp ¾ snake resonance 7/10 snake resonance beta1 *=2m 10 seconds after flattop flattop *=2m

  37. Milestones of RHIC pp development

  38. RHIC pp performance Courtesy of W. Fischer

  39. RHIC pp performance: polarization transmission efficiency

  40. RHIC intrinsic spin resonance strength Design goal Achieved Physics Run Intrinsic spin resonance Qx=28.73, Qy=29.72, emit= 10

  41. First look of beam polarization at 250 GeV 45% !

  42. Resonance around 138 GeV Polarization 250 GeV ramp measurement

  43. Plan for RHIC polarized protons

  44. Increase the average luminosity at 100 GeV from 6.0x1030 cm-2s-1 to 20x1030 cm-2s-1(x3) Luminosity limit beam-beam effect Accelerator developments to mitigate the beam-beam effect increase bunch intensity eliminate emittance grow At 250 GeV: 150x1030 cm-2s-1 Improve luminosity performance

  45. AGS: operating the AGS with both betatron tunes in the spin tune gap to avoid additional polarization loss due to horizontal betatron oscillation as observed in RHIC 2006 Run RHIC: preserve beam polarization to 250 GeV Improve the tune control technique Improve the orbit control system to control the orbit distortion within 0.3mm or less. Reach polarization of 70% or higher

  46. Conclusion • Over the past 5 years, • all the essential hardware and diagnostic apparatus for polarized beam were put in place and successfully commissioned. • successfully accelerated polarized protons to 100 GeV with no polarization loss. • The performance of RHIC pp in Run 2006 was greatly improved due to the great success of the AGS dual snake setup as well as the improvement of RHIC systems. • The 500 GeV development demonstrated a beam polarization of 45% at 250 GeV and also identified the location of depolarizing resonances. • With the success in the AGS and improvements in RHIC, we expect RHIC to achieve the design goal in the near future.

  47. Great physics is ahead of us, stay tuned in …

  48. Acknowledgement L. Ahrens, I.G. Alekseev, J. Alessi, J. Beebe-Wang, M. Blaskiewicz, A. Bravar, J.M. Brennan, D. Bruno, G. Bunce, J. Butler, P. Cameron, R. Connolly, J. Delong, T. D’Ottavio, A. Drees, W. Fischer, G. Ganetis, C. Gardner, J. Glenn, T. Hayes, H-C. Hseuh. H. Huang, P. Ingrassia, U. Iriso-Ariz, O. Jinnouchi, J. Laster, R. Lee, A. Luccio, Y. Luo, W.W. MacKay, Y. Makdisi, G. Marr, A. Marusic, G. McIntyre, R. Michnoff, C. Montag, J. Morris, A. Nicoletti, P. Oddo, B. Oerter, J. Piacentino, F. Pilat, V. Ptitsyn, T. Roser, T. Satogata, K. Smith, D.N. Svirida, S. Tepikian, R. Tomas, D. Trbojevic, N. Tsoupas, J. Tuozzolo, K. Vetter, M. Milinski. A. Zaltsman, A. Zelinski, K. Zeno, S.Y. Zhang.

  49. Acknowledgement

  50. Special Thanks to my mentors Prof. S. Y. Lee, Indiana University Dr. Thomas Roser, C-A Department Dr. Mike Syphers, Fermi Lab.

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