Status of the PAX experiment

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1 P. Lenisa Università di Ferrara and INFN PANDA Collab. Meeting Stockholm,

2 Physics case for polarized antiprotons Transversity distribution of the nucleon in Drell-Yan: Last leading-twist i t missing i piece of the QCD description of the partonic structure of the nucleon Direct measurement of h q 2 1q (x,q ) of the proton for valence quarks (A TT in Drell-Yan >0.2) transversely polarized proton beam or target ( ) transversely polarized antiproton beam ( ) + other polarization observables in p-pbar Proton electromagnetic form factors Paolo Lenisa 2

3 Polarized Antiprotons. Two Methods: Loss versus spin flip For an ensemble of spin ½ particles with projections + ( ) and ( ) Paolo Lenisa 3

4 Test of spin-flip to produce polarized pbar beam Un-polarized anti-proton beam Polarized positron beam Velocity mismatch Dv/c ~ Spin transfer Polarized anti-proton beam

5 Test of spin-flip to produce polarized pbar beam Polarized proton beam Unpolarized electron l Spin Velocity beam transf mismatch er Dv/c ~ Spin transfer De-polarized proton beam

6 ep spin flip studies at COSY

7 ep spin flip studies at COSY: Polarimetry pd elastic scattering: detection in two (L-R) symmetric Silicon Tracking Telescopes Deuteron identification d p p D 2 Paolo Lenisa 7

8 ep spin flip studies at COSY: Results polarization no change polarization Result of COSY experiment: no de-polarization effect!

9 ep spin flip cross section Nominal proton energy in electron rest frame (kev) D.Oellers et al., Physics Letters B 674 (2009) 269 depol (b barn) Relative velocity of electrons in proton rest frame (c) No effect observed: measured cross sections at least 6 orders-of-magnitude smaller than predicted b. Paolo Lenisa 9

10 Polarized Antiprotons. Two Methods: Loss versus spin flip For an ensemble of spin ½ particles with projections + ( ) and ( ) Paolo Lenisa 10

11 Spin-filtering Polarization build-upup of an initially unpolarized particle beam by repeated passage through a polarized hydrogen target in a storage ring: Paolo Lenisa 11

12 Polarization Buildup σ tot = σ 0 + σ 1 P Q + σ 2 (P k)(q k) P beam polarization Q target polarization k beam direction For initially equally populated spin states: (m=+½) and (m=-½) transverse case: longitudinal case: tot 0 1 Q tot 0 ( 1 2) Q Unpolarized anti-p beam Polarized target Paolo Lenisa 12

13 Polarization Buildup σ tot = σ 0 + σ 1 P Q + σ 2 (P k)(q k) P beam polarization Q target polarization k beam direction For initially equally populated spin states: (m=+½) and (m=-½) transverse case: longitudinal case: tot 0 1 Q tot 0 ( 1 2) Q Polarized Unpolarized anti-p beam Polarized target Paolo Lenisa 13

14 Polarization Buildup σ tot = σ 0 + σ 1 P Q + σ 2 (P k)(q k) P beam polarization Q target polarization k beam direction For initially equally populated spin states: (m=+½) and (m=-½) transverse case: longitudinal case: tot 0 1 Q tot 0 ( 1 2) Q FOM (Longitudinal case preferable!) Paolo Lenisa 14

15 Spin-filtering at TSR: FILTEX proof-of-principle F. Rathmann et al., PRL 71, 1379 (1993) Polarization buildup process quantitatively understood! d! Spin filtering works for protons TSR spin filtering with protons: σ exp =73 ± 6 mb Average theoretical value: σ theo =86 ± 2 mb Brief summary in: D. Oellers et al., Phys. Lett. B 674, 269 (2009). PAX submitted new proposal to find out how well spin filtering works for antiprotons: Measurement of the Spin-Dependence of the pp Interaction at the AD Ring (CERN-SPSC / SPSC-P-337) Paolo Lenisa 15

16 PAX at the AD Siberian snake Electron cooler Paolo Lenisa PAX target section 16

17 Spin-dependence of the pbar-p interaction Model A: T. Hippchen et al., Phys. Rev. C 44, 1323 (1991). Model OBEPF: J. Haidenbauer, K. Holinde, A.W. Thomas, Phys. Rev. C 45, 952 (1992). Model D: V. Mull, K. Holinde, Phys. Rev. C 51, 2360 (1995). Paolo Lenisa 17

18 Expected polarizations after filtering for two lifetimes transverse longitudinal A D Paolo Lenisa 18

19 Expected polarizations after filtering for two lifetimes: New estimations Measurement of the buildup equivalent to the determination of 1 and 2 Once a polarized pbar beam is available, differential double-spin observables can be measured ( MeV) pbar-p p potential Protonium gave already first information about pbar-p at rest V.F. Dimitriev at al. arxiv: v1 (2010) Paolo Lenisa

20 Spin-filtering studies at COSY Main purpose: 1.Confirm understanding of spin-filtering with protons. 2.Commissioning of the experimental setup for AD COSY-Quadupoles Target chamber with storage cell and detector system ABS BRP Low-β quadrupoles Paolo Lenisa 20

21 Installation and commissioning of PAX low- section 2009 Installation of quadrupoles with additional steeres Fast shutters, NEG pumps, BMPs 2010 COSY quadrupole commissioning 0.3 m beta functions at target place no negative impact on beam-lifetime Paolo Lenisa 21

$Polarimeter (BRP) and Target Gas Analyzer (TGA) Target Gas Analyzer (TGA) measures atomic fraction x y z Breit-Rabi Polarimeter (BRP) measures Target Polarization Paolo$

22 Setup of Polarized Target Disoociator H 2 2H Spin filtering requires>10 13 atoms/cm 2 storage cell ABS produces polarized atomic beam Target polarization by Breit-Rabi Polarimeter (BRP) and Target Gas Analyzer (TGA) Target Gas Analyzer (TGA) measures atomic fraction x y z Breit-Rabi Polarimeter (BRP) measures Target Polarization Paolo Lenisa 22

23 Atomic Beam Source and Breit-Rabi Polarimeter (from HERMES-DESY-HH) HH) ABS Electric power Cooling water Target chamber COSY/AD beam axis Breit-Rabi polarimeter Paolo Lenisa 23

24 AD optics and openable storage cell 1. Beam is injected with low-β section moderately powered on. 2. At experiment energy (T<450 MeV), β-functions are squeezed by fully powering on low-β β magnets. 3. Then storage cell is closed and gas is injected. At injection Squeezed Paolo Lenisa 24

25 Openable storage cell opened closed Paolo Lenisa

26 Cell performance Performance almost ideal - no loss in polarization - no intensity loss Paolo Lenisa

27 Target chamber, cell and detector system Atomic beam Guide field coils (x, y, z) movable flow limiter Stored beam Silicon strip detectors Storage cell: jet density 100 Paolo Lenisa 27

28 Detector geometry ABS tube HERMES detectors (300 μm) w = 97 mm d0 = 80 mm d1 = 100 mm openable storage cell BRP tube 28

29 Beam polarization measurement: pp elastic scattering 29

30 Event reconstruction 2 protons in coincidence in opposite detectors (1 proton with 1 hit in each detector layer) Accepted events > 17% Good azimuthal coverage additional measurements possible eg e.g. Deuteron breakup studies 30

31 Polarizations expected at COSY Still not understood beamlifetimes at COSY Test of contribution ti from Touschek-effect Paolo Lenisa 31

32 Clear task Where are we now? Only nucleon-nucleon interaction contributes to polarization buildup Technically feasible equipment being prepared for exp l setups at COSY and AD need to convince CERN-SPS committee Expertise and commitment by PAX-collaboration High discovery potential Now and here or never! σ 1 : AD transverse spin-filtering at T > 70 MeV requires electron cooler upgrade needs funding σ 2 : AD longitudinal spin-filtering requires Siberian snake needs funding Paolo Lenisa 32

Polarized Antiprotons receive ERC Grant a nice

Physical science & Engineering (105) o PE2

33 Polarized Antiprotons receive ERC Grant a nice Xmas present 1584 ERC AdvG Proposals submitted 236 selected (15% success rate) Life Science (89) Social Sciences & Humanities (42) Physical science & Engineering (105) o PE2 Fundamental constitutents of Matter (11) Paolo Lenisa 33

The PAX experiment. Paolo Lenisa Università di Ferrara and INFN - Italy. Tbilisi, July 10 th PAX - Polarized Antiprotons

The PAX experiment. Paolo Lenisa Università di Ferrara and INFN - Italy. Tbilisi, July 10 th PAX - Polarized Antiprotons The PAX experiment 1 Paolo Lenisa Università di Ferrara and INFN - Italy Tbilisi, July 10 th 2014 Motivation The PAX collaboration proposed to investigate Drell Yan processes in scattering of polarized