Misha Nekipelov, Kolya Nikolaev*, Frank Rathmann Institut für Kernphysik, Forschungszentrum Jülich *Landau Institute, Chernogolovka, Russia Spin Filtering in Storage Rings from a Theorists Perspective: Anno 2009 DSPIN-2009, 1-5 September 2009, Dubna

2 W. Pauli N. Bohr  Even they were puzzled by spin… then A. Krish et al stormed the field

3 Why polarized antiprotons? Quest for the transversity: the last missing leading twist SF of the proton Without transversity the spin tomography of the proton will be ever incomplete PAX at FAIR (E.Steffens‘ talk): double spin DY as a direct access to transversity, a unique successor to 4 decades of DIS physics M.Anselmino et al: Encouraging signals from model- dependent extractions of transversity Spin filtering: a unique way to HIGH LUMI double polarized proton-antiproton collider Other ideas on how to polarize antiprotons?

4 Long way to Tippereray: Dreams & Misconceptions & Enlightenment 40 years of dreaming of polarized antiprotons LEAR: missed opportunities FILTEX! Meyer & Horowitz: asking key questions Rathmann et al.: immaculate conception of PAX misdriven by Meyer‘s interpretation of FILTEX Milstein & Strakhovenko & NNN & Pavlov & infidels (Shatunov...): electrons are useless Hoegel‘s dialectic spiral: backdoor e‘s Walcher et al. 1st PAX expt at COSY: back to hadronic spin filtering for antiprotons

5 What Could Happen to a Spin in a Polarized Internal Target? For an ensemble of spin ½ particles with projections + (  ) and - (  )

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12 Spin Filtering Anno 2004: betting on e‘s ~ 5 years ago, PAX proposed a method to polarize antiprotons by „spin-filtering“ Milstein & Strakhovenko & NNN & Pavlov: a no-go theorem

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20 Georg Christoph Lichtenberg ( ) “Man muß etwas Neues machen, um etwas Neues zu sehen.” “You have to make something new, if you want to see something new”

21 New ideas: spin flip in polarized e-cooler

22 No effect expected ! Confirmed by PAX-ANKE at COSY. The corollary: bet on hadronic spin filtering of anti-p‘s /JNIMB

23 Antiproton-nucleon interactions: more in Nurushev‘s talk A wealth of good data from LEAR Nice measurements of single-spin asymmetries No substantial data on double spin observables: only low statistics recoil proton polarization estimates Ask theorists: Could the theory help?

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25 Good and not so good news from models: A good news: All models „predict“ non-vanishing double spin observables percent polarization of filtered antiprotons is feasible Not so good news: Predictions differ by factor 2- 3 in magnitude and wildely regading the energy dependence: hence I omit slides K. Adenauer: „Why should I care about that nonsense I promised yesterday?“ --- go to AD CERN and measure youself!

26 Summary and oulook: We possess a quantitative theory of spin-filtering & spin-flip phenomena in storage rings Still it is prudent to check everything with protons at COSY where the theory is under tight control (SAID & Nijmegen databases) The deuterium PIT must not be forgotten! Antiprotons: neither solid theory no exptl database for double spin observables: do it yourself at AD CERN (PAX) A consolation: still the models do “predict“ a nonvanishing filtering cross section and per sent polarization of filtered antiprotons

27 Georg Christoph Lichtenberg ( ) “Man muß etwas Neues machen, um etwas Neues zu sehen.” “You have to make something new, if you want to see something new”

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