paolo lenisa università di ferrara and infn - italy

P.Lenisa 1

Paolo LenisaUniversità di Ferrara and INFN - ITALY

5th Georgian-German School and Workshop in Basic ScienceTbilisi, 07.08.12

Polarized Antiprotons:why and how?

Polarized antiprotons: why and how?

P.Lenisa 2

What is spin?

Medical physics: MRI technique based on spin-flip of the

proton

Astrophysics: spin of galaxies possible indication of dark matter

Spin is everywhere:

Solid state physics: superconductivity consequence of electron pairs with Spair=0

Intrinsic rotation of a body around its axis


P.Lenisa 3

W. Pauli

N. Bohr

Even they were puzzled by spin


P.Lenisa 4

half integer SPIN

obey Pauli principle antisymmetric under exchange of identical particles Fermi-Dirac statistics: Fermions

MATTER

integer SPIN don’t care for Pauli principle symmetric Bose-Einstein statistics: Bosons

FORCES

Pauli principle …

Knowledge of the universe


P.Lenisa 5

Spin and particles

Proton and electron both have S=1/2 (h/2p)

… but the proton is a composite object

Naive model. The proton has a structure:• Sproton = ∑Squarks = ½+½-½

But there is more than that…

S = 1/2

S = 1/2


6

< 1960

? 1972-1973

- QCD lagrangian- colors, sea quarks, gluons- discovery of gluons

> 1988

- Quark hypothesis (Gell-Mann - Zweig)- Scaling at SLAC (‘69)- Parton Model

1964-1969

- Elementary particle?

How to study the nucleon structure?… deep-inelastic scattering (DIS)

Internal structure

e e’

P

)cos(12EE'qQlab

22 -q=1/l (ph. wavel.) resolution

P.Lenisa 7

EMC (‘88) DS=0.123 ± ...Spin Puzzle

gluons are important !

GΣ21

21

DD

don’t forget the orbital angular momentum!

gq LGLΔ Σ 21

21

DSLAC, CERN, DESY: 0.2-0.4

Where is the proton spin?“… the proton is an object we thought we knew so well, but which reveals another face when it spins.” J. Ellis

QPM: )

1 Σsvv ΔqΔdΔu

21

21

D


P.Lenisa 8

polarised beam

and/or

polarised target

inclusive dis

gq LGLΔΣ 21

21 D

Polarized deep inelastic scattering


Polarisation Experiments in Storage Rings 9Paolo Lenisa

Polarized electron beam vs polarized proton target:

Virtual photon asymmetries Because of helicity conservation, the virtual photon can couple only to a quark of opposite helicity

23

211SS Nγ

)(2/3 xq by changing the orientation of target nucleon spin or the helicity of

incident lepton beam we can select q+(x) or q-(x) Dq

21

211SS Nγ

)(2/1 xq

P.Lenisa 10

polarised beam

and/or

polarised target

inclusive dis

gq LGLΔΣ 21

21 D


semi-inclusive DIS flavour separation


P.Lenisa 11

p- udK- us

flavour tagging

p+ ud

Df

fff zDdxqz )()()(d hqh , z=Eh/n

distributionfunction

fragmentationfunction

Polarized semi-inclusive DIS


P.Lenisa 12

Quark/anti-quark helicity distributions

u quarks large positive polarisation

d quarks negative polarisation

sea quarks (u, d, s) compatible with 0

(in measured x-range: 0.02-0.6)


P.Lenisa 13

polarised beam

and/or

polarised target

inclusive dis

inclusivehadronsexclusive dis

gq JJ gq LGLΔΣ 21

21 D


semi-inclusive DIS flavour separation


P.Lenisa 14

The puzzle of the proton spin… the (spin) structure of the nucleon …

H1, ZEUS,++

HERMES, ++

HERMES COMPASSCERNRHICSLAC


P.Lenisa 15

the (spin) structure of the nucleon …

H1, ZEUS,++

HERMES, ++

HERMES COMPASSCERNRHICSLAC

HERMESJLabTransversity (h1)

The puzzle of the proton spin…


P.Lenisa 16

transversely polarisedquarks and nucleons

1h longitudinally polarisedquarks and nucleons

Dq unpolarised quarks

and nucleons

q

D nxhxqxqx T1

55LTw2Corr Sγγ)(γ)(S)(

21)( 1

Quark structure of the nucleon


P.Lenisa 17

Transversity

- Probes relativistic nature of quarks- No gluon analog for spin-1/2 nucleon- Different evolution than - Sensitive to valence quark polarizationtransversely polarised

quarks and nucleons

q1h

2Q qD

Inclusive DIS Semi-inclusive DIS Drell-YanHERMES,COMPASS,JLab

h1 is chirally odd -> it needs a chirally odd partner


P.Lenisa 18

)(A 1)s in (

U T 1S zHh q

e-

e+

Xπe 'pe Xhe 'de Xee j e t 21j e t pp

2007 milestone in hadron physics: Transversity first extraction


P.Lenisa 19

Transversity

- Probes relativistic nature of quarks- No gluon analog for spin-1/2 nucleon- Different evolution than - Sensitive to valence quark polarizationtransversely polarised

quarks and nucleons

q1h

2Q qD

Inclusive DIS Semi-inclusive DIS Drell-YanHERMES,COMPASS,JLab

h1 is chirally odd -> it needs a chirally odd partner


Accesso to transversity through Drell-Yan

20

llqq *

q q

q qqqqqTTTT xqxqxqxqe

xhxhxhxheaA

)()()()(

)()()()(ˆ

dddd

21212

211121112

Polarized AntiprotonsP.Lenisa

P.Lenisa 21

h1u from p-p Drell-Yan at PAX

PAX : M2/s=x1x2~0.02-0.3 valence quarks (ATT large ~ 0.2-0.3 )

)()()()(ˆ

21

2111

xuxuxhxhaA uu

TTTT

q q

q qqqqqTTTT xqxqxqxqe

xhxhxhxheaA

)()()()(

)()()()(ˆ

dddd

21212

211121112

• u-dominance• |h1u|>|h1d|

P.Lenisa 22

EXPERIMENT:Asymmetric collider:

polarized protons in HESR (p=15 GeV/c)polarized antiprotons in CSR (p=3.5 GeV/c)

s=200 GeV2

Antiproton-proton collider for FAIR


P.Lenisa 23

Intense beam of polarized antiprotons was never produced:• Conventional methods (ABS) not appliable• Polarized antiprotons from antilambda decay

• I < 1.5∙105 s-1 (P ≈ 0.35)• Antiproton scattering off liquid H2 target

• I < 2∙103 s-1 (P ≈ 0.2)Little polarization from pbarC scattering exp’ts at LEAR• Stern-Gerlach spin separation in a beam (never tested)

Spin filtering is the only succesfully tested technique

Polarized Antiprotons


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

24P.LenisaPolarized antiprotons: why and

how?

P beam polarizationQ target polarizationk || beam direction

σtot = σ0 + σ1·P·Q + σ2·(P·k)(Q·k)

transverse case:

Qtot 10 longitudinal case:

Qtot )( 210

For initially equally populated spin states: (m=+½) and (m=-½)

Unpolarized anti-p beam

Polarized target

Polarization Buildup

P.Lenisa 25Polarized antiprotons: why and

how?

P beam polarizationQ target polarizationk || beam direction

σtot = σ0 + σ1·P·Q + σ2·(P·k)(Q·k)

transverse case:

Qtot 10 longitudinal case:

Qtot )( 210

For initially equally populated spin states: (m=+½) and (m=-½)

Unpolarized anti-p beam

Polarized target

Polarized anti-p beam

P.Lenisa 26

Polarization Buildup


Spin-filtering at TSR: „FILTEX“ – proof-of-principle

Spin filtering works for protons

F. Rathmann et al., PRL 71, 1379 (1993)

27

PAX submitted new proposal to find out how well does spin filtering work for antiprotons Measurement of the Spin-Dependence of the pp Interaction at the AD Ring

(CERN-SPSC-2009-012 / SPSC-P-337)

P.Lenisa Polarized antiprotons: why and how?

PAX at the AD

P.Lenisa 28

PAX target sectionElectron cooler

Siberian snake


Spin-dependence of the pbar-p interaction

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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).

• Measurement of the polarization buildup equivalent to the determination of σ1 and σ2

• Once a polarized antiproton beam is available, spin-correlation data can be measured at AD (50-500 MeV)

P.Lenisa Polarized antiprotons: why and how?

WASAe-cooler

ANKE

PAX

Spin-filtering experiment at COSYMain purpose:1. Commissioning of the experimental setup for CERN/AD2. Quantitative understanding of the machine parameters

P.Lenisa 30Polarized antiprotons: why and how?

2009: Installation of low-β section

• Beam has to fit through storage cell target (dt=5x1013 atoms/cm2)

• Increase acceptance angle at target position

P.Lenisa 31

Experimental setup for spin-filtering studiesI – Low-b section


ABS

Breit-Rabipolarimeter

Spin filtering requires >1013 atoms/cm2 → ABS + openable storage cell

Analysis of target polarization by Breit-Rabi polarimeter (BRP) and a target gas analyzer (TGA)

P.Lenisa 32

Experimental setup for spin-filtering studiesII – Polarized Internal Target

2010: Installation of polarized targetPolarized antiprotons: why and how?

p D2

pd elastic scattering: detection in two (L-R) symmetric Silicon Tracking Telescopes

P.Lenisa 33

Experimental setup for spin-filtering studiesIII – Beam polarimeter


p

cluster targ. + STT (beam

polarimetry)

polarized target

COSY ring

Spin-flipper

2011: Spin-filtering measurement


Result

Milestone for the field! Confirms understanding of spin-filtering as a viable method to

polarize a stored beam. Confirms complete control of the systematics of the experiment Does not cover for the lack of knowledge of the pbar-p interaction.



Acknowledgments- 2012P. Benati (PhD – thesis): Development of a new trigger system for spin-filtering studiesS. Bertelli (PhD – thesis): Proton induced deuteron breakup reactions at COSYZ. Bagdasarian (Diploma – thesis): Beam-polarization studies at COSY

- 2011:Ch. Weidemann (PhD – thesis): Preparations for the Spin-Filtering Experiments at COSY/Jülich

- 2010 D. Oellers (PhD – thesis) Polarizing a Stored Proton Beam by Spin-Flip?C. Barschel (Diploma – thesis): Calibration of the Breit-Rabi Polarimeter for the PAX Spin-Filtering Experiment at COSY/Jülich and AD/CERN

- 2009L. Barion (PhD – thesis) Internal polarized gas targets: systematic studies on intensity and correlated effectsG. Guidoboni (Diploma – thesis) Design of the interlock system of a test-bench for silicon detectorsA. Lupato (Diploma – thesis) Sviluppo di sorgenti atomiche di idrogeno gassoso e deuterio ad alta intensita

- 2008P. Benati (Diploma – thesis) Caratterizzazione di una nuova scheda di trigger per esperimenti di liltraggio in spinS. Bertelli (Diploma – thesis) Studio della reazione di deuteron breakup in esperimenti di spin-filtering per la polarizzazione di fasci di antiprotoni

- 2013 - …. – New students are welcome!

P.Lenisa Polarized antiprotons: why and how? 37

38

Additional calculations…

PLB 690 (2010)

P.Lenisa

Cross sections

Projected polarizations


paolo lenisa università di ferrara and infn - italy

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