The COMPASS polarized Target The COMPASS polarized target

The COMPASS polarized Target The COMPASS polarized target F. Gautheron On behalf of the COMPASS collaboration F. Gautheron / Univ. Bielefeld Spin 2004 10 -16 October 2004 Trieste - 1

The COMPASS polarized Target The goal : To measure the gluon polarization ∆G/G by • the open charm lepto-production channel • high p. T hadron pair events D 0 Accessible from the double spin asymmetry: A exp = N ← ← - N + N ← ← = PB PT f A m. N g qq. X PB Beam polarization PT Target polarization Beam polarization orientation f Dilution factor Target polarization orientation N Number of events F. Gautheron / Univ. Bielefeld Spin 2004 10 -16 October 2004 Trieste - 2

The COMPASS polarized Target The challenge: to run the largest solid polarized target for a higher statistic to achieve the highest possible polarization to measure the polarization of the nuclei without harming the experiment to reduce the multiple scattering for efficient reconstruction of D 0 to allow the frequent change of the sign of the polarization to fight against false asymmetries from acceptance changes F. Gautheron / Univ. Bielefeld Spin 2004 10 -16 October 2004 Trieste - 3

The COMPASS polarized Target Choice of the material t-1 - The beam time t to reach a certain statistical accuracy DA shows the dependency r (f P)2 We define the Figure of Merit (Fo. M) Fo. M = k r (f PT)2 SMC COMPASS Material NH 3 D-butanol 6 Li. D Density 0. 85 1. 10 0. 84 Polarization H: ~0. 90 D: ~0. 50 Packing factor k 0. 60 0. 55 Dilution factor f 0. 176 0. 238 ~0. 50 Fo. M 10. 3 6. 7 16. 0 F. Gautheron / Univ. Bielefeld Spin 2004 10 -16 October 2004 Trieste - 4

The COMPASS polarized Target Magnet PSU + instrument. Dilution refrigerator m 3 He pump line Magnet NMR system F. Gautheron / Univ. Bielefeld Spin 2004 10 -16 October 2004 Trieste - 5

The COMPASS polarized Target Still pumping line 3 He precooling line Magnet : 2. 5 T solenoid DB/B < 3. 5 x 10 -5 0. 5 T dipole 3 He/4 He Microwave cavity distiller µ beam Twin target cell 60 cm f=3 cm Total target material : 350 g F. Gautheron / Univ. Bielefeld Mixing chamber : 6 L Temperature: ~60 m. K Spin 2004 10 -16 October 2004 Trieste - 6

The COMPASS polarized Target Material Funnel Granules 6 Li. D Target loading Liquid N 2 Bath Target cell F. Gautheron / Univ. Bielefeld Spin 2004 10 -16 October 2004 Trieste - 7

The COMPASS polarized Target Microwaves system to polarize (DNP) 0. 2 W for both cells Microwave cavity Microwave stopper Mixing Chamber Freq. counter 2 W due to ~20 m waveguide Power attenuators 2 independent microwave generators 10 W output F. Gautheron / Univ. Bielefeld Frequencies concerned for 6 Li. D at 2. 5 T P>0 [~70. 180 –> 70. 238] GHz P<0 [~70. 285 –> 70. 245] GHz Frequencies continuously adjusted Depends on the degree of polarization + Frequency modulation ± 5 MHz at a rate ~500 Hz to improve speed and degree of polarization Spin 2004 10 -16 October 2004 Trieste - 8

The COMPASS polarized Target NMR system for polarization measurement l/2 coax. 8 NMR coils measuring simultaneously 6 Li. D Liverpool Q-meter RF generator Yale card material VME bus Splitter Sweep width: 100 k. Hz, 1000 channels Windows 2000 + Labview Control room Subtracting Q curve + Signal F. Gautheron / Univ. Bielefeld Q curve signal Spin 2004 10 -16 October 2004 Trieste - 9

The COMPASS polarized Target Polarization [%] Typical polarization Build up t 40% (D-but)=5 -6 h Day F. Gautheron / Univ. Bielefeld Spin 2004 10 -16 October 2004 Trieste - 10

The COMPASS polarized Target Magnetic field rotation process Only in frozen spin mode Rotation every 8 hours to cancel systematic error: • time dependant variation • spectrometer acceptance 1 rotation takes 33 minutes B never below 0. 5 T The spin behavior during rotation B up up down up F. Gautheron / Univ. Bielefeld down Spin 2004 10 -16 October 2004 Trieste - 11

The COMPASS polarized Target History of target polarization + pol. (%) - pol. (%) 54. 18 - - -47. 40 2002 upstream 55. 49 -52. 72 2002 downstream 56. 89 -47. 47 2003 upstream 56. 81 -50. 67 2003 downstream 54. 07 -48. 95 2004 upstream - preliminary 56. 94 -51. 21 2004 downstream -preliminary 53. 90 -49. 52 2001 upstream 2001 downstream F. Gautheron / Univ. Bielefeld Spin 2004 10 -16 October 2004 Trieste - 12

The COMPASS polarized Target Summary … • Mainly reusing SMC target system • good figure of merit from 6 Li. D • unique system for magnetic field rotation to reverse polarization • stable operation since 2001 (run ~ 6 month/year) … and outlook • new magnet with a larger acceptance + new microwave cavity • D- butanol with new dopant ? new setup to prepare and study F. Gautheron / Univ. Bielefeld Spin 2004 10 -16 October 2004 Trieste - 13

The COMPASS polarized Target Thank You !!! F. Gautheron / Univ. Bielefeld Spin 2004 10 -16 October 2004 Trieste - 14