perspectives for polarized antiprotons (pax: a brief history)

Perspectives for Polarized Antiprotons (PAX: a brief history)

Paolo LenisaUniversità di Ferrara and INFN

44100 – Ferrara - ITALY

P.Lenisa PAX story 1

ANKE-PAX WorkshopGatchina, June 25-27 2012

We have proposed a method to polarize antiprotons by „spin-filtering“

2PAX story

The beginning (2005)

P.Lenisa

High Energy Storage Ring (HESR) for a

beam of antiprotons

3PAX storyP.Lenisa

PAX Proposal to FAIR (2005)178 Collaborators

36 institutions (15 EU, 21 NON-EU)


Polarized antiprotons will pave the way to novel double (and single) spin observables:

* Proton-spin structure:Complete map of transversity Flavour separation

* Electromagnetic Form FactorsIndependent extraction of moduli of GE-GM in Time-Like regionTest of the Rosenbluth separation in TLMeasurement of the phase

* Hard p-pbar scatteringAdditional measurement in one of the most intriguing puzzles of HF

* Hadron spectroscopy

* Low-t pbar-p scatteringSpin and isospin dependence of nucleon-antinucleon interaction at low energy

Physics with Polarized Antiprotons


,...d,d,u,uq

M invariant Massof lepton pair /2 / 2

2121 sQxsMxxxxx LFF

)( )()( )(1

9

42121

2

212

2

2

2

xqxqxqxqexxsMdxdM

d

qq

F

sM 2

llqq *

Inclusive DIS Semi-inclusive DIS Drell-Yan

q q

q qqqqq

TTTT xqxqxqxqe

xhxhxhxheaA

)()()()(

)()()()(ˆ

dd

dd

21212

211121112

h1 from Drell-Yan


Phase I: Fixed target experiments in CSR

direction of

antiprotons

Physics: EMFF pbar-p elastic

Independent from HESR running

pol./unpol. Antiprotons in CSR 0.2 Gev/c<p<2.5 GeV/cpolarized internal proton target

(antiprotons)


Phase II: Asymmetric Proton-Antiproton Collider

direction of

protons

direction of

antiprotons

Physics: Transversity EMFF pbar-p elastic

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

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


Antiproton Polarizer Ring (APR)

Ring Parameter

Beam energy 250 MeV

Number of antip. 1012

Ring acceptance 250 mm

mrad

Betatron ampl. at IP

< 0.3m

Ring circumference

86,5 m

Snake strength 2.4 Tm

Injection/Extraction Target

Electron Cooler Snake

Ion-optics at IPAtomic Beam Source (ABS)

parameter

ABS flow in feeding tube

1,5·1017 /s

Storage cell length 40 cm

Feeding tube diameter length

1 cm 15 cm

Long. holding field 300 mT

Electron polarization 0.9

Cell temperature 100 K

Final configuration after spin-filtering studies


… the PAC would like to stress again the uniqueness of the program with polarized anti-protons and polarized protons that could become available at GSI.

Evaluation by QCD-PAC (March 2005)

The STI requests R&D work to be continued on the proposed asymmetric collider experiment with both polarized anti-protons and protons:

-to demonstrate that the required luminosity for decisive measurements can be reached (->accomplished)

- to demonstrate that a high degree of anti-proton polarisation can be reached

The STI believes that PAX should become part of the FAIR core research program based on its strong scientific merit once the open problems are convincingly solved.

Recommendation of the STI of FAIR (Sept. 2005)


Luminosity Considerations for Collider Mode

Particle species

Momentum / GeV/c

Number of bunches

Total number of particles

Beam lifetime / h

Peak luminosity / cm-2 s-1

CSR HESR

protons antiproton

3.65 15

10 30

1012 3·1011

~ 45 ~ 800

1.6·1030

CSR HESR

antiprotons

proton

3.65 15

- -

0.02 0.006

~ 1500 ~ 300

1.2·1031

“old”

“new”

Antiprotons in HESR -> protons

Bunched beams -> coasting

L>1031s-

1cm-2

2006: I milestone for PAX


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

How to produce polarized antiprotons?Spin-filtering

P.Lenisa

Polarization build-up of a circulating particle beam by interaction with a polarized gas target

12


Experimental SetupExperimental Setup ResultsResults

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

T=23 MeV

Low energy pp scattering

1<0 tot+<tot-

Expectation

Target Beam

1992 Filter Test at TSR with protons


1994 Meyer and Horowitz: three distinct effects1. Selective removal through scattering beyond θacc=4.4 mrad (σR=83

mb)2. Small angle scattering of target prot. into ring acceptance (σS=52

mb)3. Spin-transfer from pol. el. of target atoms to stored prot. (σE=-70 mb)

σ1= σR+ σS + σE = 65 mb

2005 Milstein & Strakhovenko + Nikolaev & Pavlov: only one effectOnly pp elastic scattering contributesNo contribution from other two effects σ1 = 85.6 mb

Observed polarization build-up: dP/dt = ± (1.24 ± 0.06) x 10-2 h-1

P(t)=tanh(t/τ1), 1/τ1=σ1Qdtf

σ1 = 72.5 ± 5.8 mb

Two interpretations of FILTEX result (2006)


Spin Filtering works, but:

1. Controversial interpretations of FILTEX experiment• Further experimental tests necessary

• Which role do electrons play?• How does spin filtering work?

Tests with protons at COSY

2. No data to predict polarization from filtering with antiprotons Measurements with antiprotons at AD/CERN

Spin Filtering: Status in 2006


Eur. Phys. J. A 34, 447 (2007)

A new idea (2007)

ep spin flip studies at COSY (2008)

• Use proton beam and co-moving electrons

• Turn experiment around: p e → p e into p e → p e

i.e. observe depolarization of a polarized proton beam

COSY electron cooler

(detuned)

Velocity mismatch

17PAX storyP.Lenisa


Principle of the Depolarization Measurementusing co-moving electrons of the e-cooler (COSY-2008)

Nominal CoolerVoltage

Tnominal = 100 s

Detuned CoolerVoltage

Tdetuned= 50 s

D2 Target onEcool on

D2 Target offEcool on/detuned

2T

T

uneddet

alminno

Eh = 0.001 MeVΔV = 235 V

ep spin flip cross section at COSY

No effect observed: measured cross sections at least 6 orders-of-magnitude smaller than predicted 1013 b

19PAX story

0

4107

|Relative velocity of electrons in proton rest frame| (c)

dep

ol (

barn

)

Nominal proton energy in electron rest frame (keV)0 1 2 3

0 110-3 210-3 310-3

2107

-2107

-4107

D.Oellers et al., Physics Letters B 674 (2009) 269

Meanwhile, Mainz group discovered numerical problems in the calculation → two errata.

P.Lenisa

2008: II milestone for PAX

PAX at the AD (2009)

PAX story 20

PAX target section

Electron cooler

Siberian snake

Status in 2009:•No contribution from EM interaction to polarization buildup.

• Spin-filtering only viable option• Spin-dependence of pbar-p interaction unknown

•“Warm” solution for AD lattice

P.Lenisa

Spin-dependence of the pbar-p interaction

21

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 PAX story

PAX story 22

Additional calculations…

PLB 690 (2010)

P.Lenisa

Cross sections

Projected polarizations

PAX story

Stages of installation at AD

P.Lenisa 23

2010 20112012

Phase 1

Phase 2

Phase 3

Installation of six magnets for the low-β insertion

Spin-filtering measurements up to 70

MeV with transverse beam polarization

Installation of the target chamber: Machine

acceptance studies. Stacking studies


The CERN Saga: PAX requests• Oct. 2009 PAX request to start phase I of installation not interfering with other experiments.

• Jan. 2010 PAX informs SPSC of acknowledgement of ERC grant.

• Jan.. 2011Meeting with Heuer• Apr. 2011: PAX sends a draft to SPSC Committee with the successful result of commissioning of single elements of experimental apparatus and request to start installation of phase I in Winter 2011 shutdown, to initiate machine studies in 2012 and to avoid conflicts with ELENA installation during 2013 shutdown.

• Mar. 2012PAX sends to SPSC Committee a draft with the results of spin-filtering studies.


The CERN Saga: SPSC answer• Oct. 2009 unofficial response from the SPS Committee:… Taking into account the timeline and constraints of the various projects concerned, the SPSC encourages the PAX Collaboration to first perform their spin filtering measurements at COSY, and to report these to the Committee, following which the SPSC will further review the proposal.

• Jan. 2010 Valle’s comment to ERC grant communicationCongratulation for getting approval of an ERC advanced grant… The comments by many of the referees on the risk and schedule issues of your project confort me in the prudent attitude of the SPSC in respect with the necessary related AD modification … Looking forward to the PAX filtering measurements at COSY to proceed further with your review!

• Jan.. 2011Meeting with Heuer• Apr. 2011: SPSC 101 recommendation:The SPSC received a report by the PAX collaboration describing the progress of their program at COSY The SPSC remains concerned by the impact of PAX on the AD antihydrogen programme, the risk factors and manpower requirements for implementing the PAX apparatus at the AD. The Committee considers any installation before the long shutdown to be premature.The Committee is looking forward to the results of the spin filtering measurements.

• Mar. 2012Draft sent to SPSC with final results of August-October 2011 beamtime• Apr. 2012 mail from Vallee.We were pleased to see that you finally succeeded to perform a spin filtering measurement at COSY, showing good control of your apparatus as well as theoretical understanding of spin filtering for protons. However inbetween many positive developments have occured at the AD, leading to an updated program for the coming years which is very constrained on both the scientific and logistic points of view. We consider that PAX is now incompatible with this program.


PAX gets acknowledgment in the community:EU – grants

• 2008-2011 – I3HP2 WP25 (PolAntiP)• Depolarization studies• Transverse spin-filtering at COSY

• 2012-2014 – I3HP3 WP25 (PolAntiP)• Longitudinal spin-filtering at COSY

• 2010-2015 – Advanced Resarch Grant POLPBAR


The CERN Saga• Oct. 2009 unofficial response from the SPS Committee:… Taking into account the timeline and constraints of the various projects concerned, the SPSC encourages the PAX Collaboration to first perform their spin filtering measurements at COSY, and to report these to the Committee, following which the SPSC will further review the proposal.




WASA

e-cooler

ANKE

PAX

Spin-filtering at COSY (2008-2011)

Main purpose:1. Commissioning of the experimental setup for CERN/AD2. Quantitative understanding of the machine parameters

P.Lenisa 29PAX story

ABS

ABS

Breit-Rabi

polarimeter

Breit-Rabi

polarimeter


Commissioning (2008-2011):

• 2008-11: Installation and commissioning of the HERMES pol. target

p D2

• 2008-11: Installation and commissioning of the ANKE beam polarimeter

Commissioning (2008-2011):


• 2009-10: Installation and commissioning of the low-β section

• 2010-11: Studies of beam-lifetime limitations (: 300 s 8000 s)

PAX story

p

cluster targ. + STT (beam

polarimetry)

polarized target

COSY ring

Spin-flipper

Spin-filtering at COSY (2011)

P.Lenisa 34

2011: III milestone for PAX

(more about in Dieter’s talk)


Spin-filtering: status in 2012

• No contribution from EM interaction to polarization buildup.

• Only viable solution for “in-situ” polarization is spin-filtering

• Complete understanding of the physics spin-filtering mechanism

• Spin-dependence of proton antiproton interaction still unkown

• New prediction existing

What about the physics case for polarized antiprotons?

38L.L. Pappalardo - QNP2012 – Palaiseau – April 16-20 2012

P

Pxp

Status in 2005: The nucleon collinear structure



P

Pxp

+ -+ - DF

FF

Status in 2005: Transversity totally unkown!



Anselmino et al. Phys. Rev. D 75 (2007)

Soffer bound

xh1(x

)d

xh1(x

)u

xh1(x

, k )T

uxh

1(x, k

)T

d

DF

FF

FF

FF+

Tensor charge

1

0 11 )()( xhxhdxq qq

1: Quark-diquark model2: Chiral quark soliton model3: Lattice QCD 4: QCD sum rules

M. Anselmino et al hep-ph:0812.4366

2007 milestone in hadron physics: Transversity first extraction



DF

FF

2h Semi-Inclusive DIS2011: II independent extraction!

FF

FF+- Survives integration over transverse momentum- Collinear factorization (simple product)- DGLAP evolution



Phys.Rev.Lett.107:072004,2011

Bacchetta et al., PRL 107 (11) Bacchetta et al., PRL 107 (11)

COMPASS 2010HERMES

2011: II independent extraction!



Sivers worm-gears

Boer-Mulders

pretzelosity

helicity

transversity

momentum

P

q

Tp


2005-2012: A new field has born: The non-collinear structure of the nucleon


Physics case for pol.-pbar: status in 2012

• ATT in DY production remains the unique direct way to access h1

• Pbar-p, pbar-d, p-p, p-d collider remains a unique machine to perform the flavour decomposition of transversity

• Interest in Transverse Momentum dependent effect has increased

• PAX physics case should be updated with the novel TMDs

• Interest in proton EMFF has developed:• Different SL experiment addressing two-photon

contribution• Still no individual determination yet of FF in the TL region• Necessity of a complete space-time description


PAX between past and future…

• Pol.-pbar remain a missing and unique tool for hadron physics• Antiproton polarization:

• Spin-filtering only viable mechanism • Complete understanding of spin-filtering• Data on spin-dependence of pbar-p interaction needed

• Keep the option open… • … but additional horizon in perspective:

• besides polarization technology for hadron physics… also polarization technology for fundamental physics

• The bridge to the new hera is the new PAX detector:• Longitudinal spin-filtering• Deuteron-breakup• Time Reversal Invariance • … (EDM)

(More about in the talks of Alex, Christian and Yuri…)

perspectives for polarized antiprotons (pax: a brief history)

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