# Presentation: 146419

## dr. Paolo Lenisa

- Università di Ferrara and INFN - ITALY

- ECT – Workshop: Hadronic structure of the nucleon
- Trento, May 9-13

**http://www.fz-juelich.de/ikp/pax**

- PAX: Polarized Antiproton Experiments

- PAX experiment

## PAX Collaboration

*Department of Subatomic and Radiation Physics, University of Gent, ****Belgium***
*University of Science & Technology of China, Beijing, P.R.**** China***
*Department of Physics, Beijing, P.R. ****China***
***Palaiseau, Ecole Polytechnique Centre de Physique Theorique, ******France***
*High Energy Physics Institute, Tbilisi State University, Tbilisi, ****Georgia***
***Nuclear Physics Department, Tbilisi State University******, Georgia***
*Forschungszentrum Jülich, Institut für Kernphysik Jülich, ****Germany***
*Institut für Theoretische Physik II, Ruhr Universität Bochum**, ****Germany***
*Helmholtz-Institut für Strahlen- und Kernphysik, **Bonn, ****Germany***
*Physikalisches Institut, Universität Erlangen-Nürnberg**, ****Germany***
***Langenbernsodorf, UGS, Gelinde Schulteis and Partner GbR,***** ****Germany**
***Department of Mathematics, University of Dublin,Dublin,****** Ireland***
***Università del Piemonte Orientale and INFN,****** ******Alessandria,*** ***Italy***
***Dipartimento di Fisica dell’Università and INFN, Cagliari,****** Italy***
***Università dell’Insubria and INFN,****** ******Como,*** ***Italy***
*Instituto Nationale di Fisica Nuclelare, **Ferrara, ****Italy***

**PAX Collaboration**

- Spokespersons:
- 	Paolo Lenisa		lenisa@mail.desy.de
- 	Frank Rathmann 		f.rathmann@fz-juelich.de

- PAX: Polarized Antiproton Experiments

- PAX experiment

## PAX Collaboration

*Instituto Nationale di Fisica Nucleare, **Frascati, ****Italy***
***Andrej Sultan Institute for Nuclear Studies, Dep. of Nuclear Reactions, Warsaw,****** Poland***
*Petersburg Nuclear Physics Institute, Gatchina, ****Russia**** *
*Institute for Theoretical and Experimental Physics, Moscow, ****Russia***
*Lebedev Physical Institute, Moscow, ****Russia***
***Physics Department, Moscow Engineering Physics Institute, Moscow,****** Russia***
***Laboratory of Theoretical Physics, Joint Institute for Nueclear Research, Dubna******, Russia***
*Laboratory of Particle Physics, Joint Institute for Nuclear Research, Dubna, ****Russia***
*Laboratory of Nuclear Problems, Joint Institute for Nuclear Research, Dubna, ****Russia***
***Budker Institute of Nuclear Physics, Novosibirsk,****** Russia***
*High Energy Physics Institute, Protvino, ****Russia***
***Institute of Experimental Physics, Slovak Academy of Science, Kosice****** Slovakia***
*Department of Radiation Sciences, Nuclear Physics Division, Uppsala University, Uppsala, ****Sweden***
***Collider Accelerator Department, Brookhaven National Laboratory, Broohhaven****** USA***
***RIKEN BNL Research Center Brookhaven National Laboratory, Brookhaven******, USA***
***University of Wisconsin, Madison,****** USA***
***Department of Physics, University of Virginia,****** USA***

**178 physicists**
**35 institutions (15 EU, 20  NON-EU)**

**PAX Collaboration**

- PAX: Polarized Antiproton Experiments

- PAX experiment

## The PAX proposal

- Jan. 04 	LOI submitted
- 15.06.04	QCD PAC meeting at GSI
- 18-19.08.04	Workshop on polarized antiprotons at GSI
- 15.09.04 	F. Rathmann et al., *A Method to polarize stored antiprotons **	**	**to a high degree* (Phys. Rev. Lett. 94, 014801 (2005))
- 15.01.05 	Technical Report submitted
- 14-16.03.05	QCD-PAC meeting at GSI
- 			**Polarization enters in the core of FAIR**

- PAX: Polarized Antiproton Experiments

- PAX experiment

## Outline

- WHY? 			Physics Case
- HOW? 			Polarized Antiprotons
- WHAT?			Staging
- 					Detector and signal estimate
- WHERE AND WHEN? 	The FAIR project at GSI

**PAX:****P****olarized ****A****ntiproton E****x****periments**

- PAX experiment

## Physic Topics

- Transversity
- Electromagnetic Form Factors
- Hard Scattering Effects
- SSA in DY, origin of Sivers function
- Soft Scattering
- Low-t Physics
- Total Cross Section
- pbar-p interaction

**Physics **** Polarization **** ****Staging   Signals  FAIR**

- PAX experiment

## Physics Case: Central Physics Issue

- Transversity distribution of the nucleon:
- last leading-twist missing piece of the QCD description of the partonic structure of the nucleon
- directly accessible uniquely via the double transverse spin asymmetry ATT in the Drell-Yan production of lepton pairs
- theoretical expectations for ATT in DY > 0.2
- transversely polarized antiprotons
- transversely polarized proton target
- definitive observation of h1q (x,Q2) of the proton for the valence quarks

**Physics **** Polarization **** ****Staging   Signals  FAIR**

- PAX experiment

## Transversity

**Physics **** Polarization **** ****Staging   Signals  FAIR**

- PAX experiment

## Transversity in Drell-Yan processes

- p

- p

- QL

- Q

- l+

- l-

- Q2=M2

- QT

- Polarized Antiproton Beam → Polarized Proton Target
- (both transversely polarized)

**Physics  Polarization **** ****Staging   ****Signals **** FAIR**

- PAX experiment

## ATT for PAX kinematic conditions

**→** **Exploration of** **valence quarks**** ****(h****1****q****(x,Q****2****) large)**

**A****TT**** for PAX kinematic conditions**

**Physics  Polarization **** ****Staging   ****Signals **** FAIR**

- A. Efremov et al. Eur. Phys. J. C 35 (2004) 207

- PAX experiment

## Energy for Drell-Yan processes

**Energy for Drell-Yan processes**

- “safe  region”: M≥MJ/
-   ≥ M2J//s
- QCD corrections at smaller M?

- H. Schimizu, G. Sterman, W. Vogelsang and H. Yokoya, hep-ph/0503270
- V. Barone et al., in preparation

**Physics **** Polarization **** ****Staging   Signals  FAIR**

- PAX experiment

## NLO corrections: cross section

**NLO corrections: cross section**

**Physics **** Polarization **** ****Staging   Signals  FAIR**

- PAX experiment

## NLO corrections: ATT

**NLO corrections: A****TT**

**Physics **** Polarization **** ****Staging   Signals  FAIR**

- PAX experiment

## Resonance region

- Measure ATT also in J/ resonance region

- M. Anselmino, V. Barone, A. Drago, N. Nikolaev

**Physics **** Polarization **** ****Staging   Signals  FAIR**

**Resonance region**

- PAX experiment

## Proton Electromagnetic Formfactors 

- Measurement of relative phases of magnetic and electric FF in the time-like region
- Possible only via SSA in the annihilation pp → e+e-
- Double-spin asymmetry
- independent GE-Gm separation
- test of Rosenbluth separation in the time-like region

- S. Brodsky et al.,
- Phys. Rev. D69 (2004)

**Physics **** Polarization **** ****Staging   Signals  FAIR**

- PAX experiment

## Study onset of Perturbative QCD

- p (GeV/c)

**Study onset of Perturbative QCD**

- Pure Meson Land
-  Meson exchange
-  ∆ excitation
-  NN potential models

- Transition Region
- Uncharted Territory
- Huge Spin-Effects in pp elastic scattering
**large ****t****: non-and perturbative QCD**

- High Energy
-  small t: Reggeon Exchange
-  large t: perturbative QCD

**Physics **** Polarization **** ****Staging   Signals  FAIR**

- PAX experiment

## pp Elastic Scattering from ZGS

- Spin-dependence at large-P (90°cm):
**Hard scattering takes place only with spins ********.**

- D.G. Crabb et al.,
- PRL 41, 1257 (1978)

**T=10.85 GeV**

- Similar studies in pp elastic scattering

**Physics **** Polarization **** ****Staging   Signals  FAIR**

- PAX experiment

**Notes:**
t=-2Pcm2(1-cos(cm))

## Outline

- WHY? 			Physics Case
- HOW? 			Polarized Antiprotons
- WHAT?			Staging
- 					Detector and signal estimate
- WHERE AND WHEN? 	The FAIR project at GSI (D)

**PAX:****Polarized Antiproton Experiments**

- PAX experiment

## Polarized internal target

**Polarized internal target**

| point-like | 5-10 mm | free jet | low density | 1012 cm-2 |
| --- | --- | --- | --- | --- |
| extended | 200-500 mm | storage cell | high density | 1014 cm-2 |

**Physics **** Polarization**** **** ****Staging   Signals  FAIR**

- PAX experiment

## The HERMES target

**The HERMES target**

**Physics **** Polarization**** **** ****Staging   Signals  FAIR**

- PAX experiment

## The HERMES target

**P****z+**** = |1> + |4>**
**P****z-**** = |2> + |3>**

**Physics **** Polarization**** **** ****Staging   Signals  FAIR**

- PAX experiment

## The HERMES target

**Physics **** Polarization**** **** ****Staging   Signals  FAIR**

- PAX experiment

## The HERMES target

**Physics **** Polarization**** **** ****Staging   Signals  FAIR**

- PAX experiment

## Performance of Polarized Internal Targets

- Transverse Field (B=297 mT)

- HERMES: Stored Positrons

- PINTEX: Stored Protons

**Targets work very reliably (months of stable operation)**

**Physics  ****Polarization  ****Staging   Signals  FAIR**

- PAX experiment

## Principle of spin filter method

**Physics  ****Polarization  ****Staging   Signals  FAIR**

- PAX experiment

## Principle of spin filter method

**Principle of spin filter method**

**Polarized H target**

**Physics  ****Polarization  ****Staging   Signals  FAIR**

- PAX experiment

## Principle of spin filter method

| Expectation |  |
| --- | --- |
| Target | Beam |
|  |  |
|  |  |

- For low energy pp scattering:
- 1<0  tot+<tot-

**Physics  ****Polarization  ****Staging   Signals  FAIR**

- PAX experiment

## Experimental Setup at TSR (1992)

**Physics  ****Polarization  ****Staging   Signals  FAIR**

- PAX experiment

## 1992 Filter Test at TSR with protons

**1992 Filter Test at TSR with protons**

- Experimental Setup

- Results

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

**T=23 MeV**

**Physics  ****Polarization  ****Staging   Signals  FAIR**

- PAX experiment

## Puzzle from FILTEX Test

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

**Expected** build-up: P(t)=tanh(t/τpol),
-  1/τpol=σ1Qdtf**=2.4x10****-2 ****h****-1**
****** ****about factor 2 larger!**

- σ1 = 122 mb (pp phase shifts)
- Q = 0.83 ± 0.03
- dt = (5.6 ± 0.3) x 1013cm-2
- f = 1.177 MHz

**Three distinct effects:**
**Selective removal through scattering beyond ****Ψ****acc****=4.4 mrad**** ****	**		**σ****R********=83 mb**
**Small angle scattering of target protons into ring acceptance** 			**σ****S********=52 mb**
**Spin transfer from polarized electrons of the target atoms to the stored protons**** **
**	****	****σ****EM********=70 mb (-)**

- Horowitz & Meyer, PRL 72, 3981 (1994)
- H.O. Meyer, PRE 50, 1485 (1994)

- PAX: Polarized Antiproton Experiments

- PAX experiment

## Spin transfer from electrons to protons

**Polarization   ****Staging   Signals  Timeline**

- PAX: Polarized Antiproton Experiments

- PAX experiment

## Spin Transfer Cross Section

**Physics  ****Polarization  ****Staging   Signals  FAIR**

- PAX experiment

## Beam lifetimes in the APR

**Physics  ****Polarization  ****Staging   Signals  FAIR**

- PAX experiment

## Polarization Buildup: optimal polarization time

**Physics  ****Polarization  ****Staging   Signals  FAIR**

- PAX experiment

## Optimum Beam Energies for Buildup in APR

| Maximum FOM |  |  |  |
| --- | --- | --- | --- |
| Ψacc (mrad) | Τbeam 
(h) | P(2·τbeam) | T
(MeV) |
| 10 | 1.2 | 0.19 | 163 |
| 20 | 2.2 | 0.29 | 88 |
| 30 | 4.6 | 0.35 | 61 |
| 40 | 9.2 | 0.39 | 47 |
| 50 | 16.7 | 0.42 | 38 |

- F. Rathmann et al.,
- Phys. Rev. Lett. 94, 014801 (2005)

**Physics  ****Polarization  ****Staging   Signals  FAIR**

- PAX experiment

## Beam Polarization

- Filter Test: T = 23 MeV
- 	      Ψacc= 4.4 mrad

**Beam Polarization**

**Physics  ****Polarization  ****Staging   Signals  FAIR**

- PAX experiment

## Antiproton Polarizer Ring (APR)

**Physics**** **** ****Polarization**** **** ****Staging   Signals  FAIR**

- PAX experiment

## Spin-filtering with hadronic interaction

- Model A: T. Hippchen et al. Phys. Rev. C 44, 1323 (1991)

- P

- Kinetic energy (MeV)

**Physics**** **** ****Polarization**** **** ****Staging   Signals  FAIR**

- PAX experiment

## Outline

- WHY? 			Physics Case
- HOW? 			Polarized Antiprotons
- WHAT?			Staging
- 					Detector and signal estimate
- WHERE AND WHEN? 	The FAIR project at GSI (D)

**PAX:****Polarized Antiproton Experiments**

- PAX experiment

## Staging: Phase I (PAX@CSR)

**Physics:****	****EMFF**
**	****	****pbar-p elastic**

**Experiment:****	**** pol./unpol. Pbar (3.5 GeV/c) on int. pol. target**

**Independent from HESR running**

**Physics  Polarization **** Staging****   Signals  FAIR**

- PAX experiment

## Staging: Phase II (PAX@HESR)

**EXPERIMENT:**
- 1. Asymmetric collider:
- 	**polarized antiprotons in HESR (p=15 GeV/c)**
- 	**polarized protons in CSR (p=3.5 GeV/c)**
- 2. Internal polarized target with 22 GeV/c polarized antiproton beam.

**Physics: ****Transversity**

**Second IP with minor interference with PANDA**

**Physics  Polarization **** Staging****   Signals  FAIR**

- PAX experiment

## Outline

- WHY? 			Physics Case
- HOW? 			Polarized Antiprotons
- WHAT?			Staging
- 					Detector and signal estimate
- WHERE AND WHEN? 	The FAIR project at GSI (D)

**PAX:****Polarized Antiproton Experiments**

- PAX experiment

## Kinematics and cross section

- M2 = s x1x2
- xF=2QL/√s = x1-x2

- Estimated luminosities:
**Fixed target: ****	****2.7x10****31**** cm****-2****s****-1**
**Collider:****	****1-2 x 10****30**** cm****-2****s****-1**

**Physics  Polarization **** ****Staging   ****Signals **** FAIR**

- PAX experiment

## ATT asymmetry: angular distribution

**Needs a large acceptance detector (LAD)**

**Asymmetry is largest for angles  ********=90****°**
**Asymmetry varies like cos(2********).**

**Physics  Polarization **** ****Staging   ****Signals **** FAIR**

- PAX experiment

## PAX detector concept

**Designed for Collider but compatible with fixed target**

- Cerenkov

**(200 ********m)**

**(20 ********m)**

**GEANT simulation**

**PAX detector concept**

**Physics  Polarization **** ****Staging   ****Signals **** FAIR**

- PAX experiment

## Estimated signal for h1 (phase II)

**Estimated signal for h****1 ****(phase II)**

**1 year of data taking**

**Collider:**
**L=2x10****30**** cm****-2****s****-1**

**Fixed target:**
**L=2.7x10****31**** cm****-2****s****-1**

**Physics  Polarization **** ****Staging   ****Signals **** FAIR**

- PAX experiment

## Estimated signal for EMFF (Phase I)

| Beam
(MeV/c) | 
 (GeV2) | e+e-
(nbarn)* | L
(cm-2s-1) | Days
DS | Days
SS |
| --- | --- | --- | --- | --- | --- |
| 549 | 3.76 | 7.3 | 7.8x1030 | 2.9 | 0.3 |
| 900 | 4.18 | 3.7 | 1.1x1031 | 4.7 | 0.5 |
| 3600 | 8.75 | 0.044 | 1.5x1031 | 132 | 13 |

- Npbar = 1x1011
- f=LCSR/c
- dt=1x1014cm-2
- Q=0.8 (p pol)
- P=0.3 (pbar pol)
- =0.5

**Estimated signal for EMFF ****(Phase I)**

**PS170 ****and E835**

**PAX could run down to 200 MeV/c with double polarization**

**Running days to get ********O = 0.05**

**Polarization****   ****Staging   ****Signals****  Timeline**

- PAX: Polarized Antiproton Experiments

- PAX experiment

## Estimated Signal for pbar p elastic (Phase I)

- BNL E838

**Estimated Signal for pbar p elastic ****(Phase I)**

**Cross section estimation for p=3.6 GeV/c, ********=120****°**

**Event rate (********t=0.1 GeV****2****):**

**2 hours to get**

- N10

**Polarization****   ****Staging   ****Signals****  Timeline**

- PAX: Polarized Antiproton Experiments

- PAX experiment

## PAX Integrated Luminosities for Physics Cases

**PAX Integrated Luminosities for Physics Cases**

- pb-1

- fb-1

- Integrated Luminosity

- EMFF, DSA, s=3.76 GeV2

- ppbar elastic, DSA, t=4 GeV2

- Phase-I: L=1.5·1031 cm-2s-1

- Antiproton Beam Polarization Ppbar=0.3,  Proton Polarization Pp=0.8

- Phase-II: L=2·1030 cm-2s-1

- EMFF, DSA, s=9 GeV2

- Absolute Error ΔDSA=0.05

- h1, DSA, M>2 GeV, Δ=10%

- h1, DSA, M>4 GeV, Δ=20%

- (1 y)

- (4 y)

- (1 y)

- PAX: Polarized Antiproton Experiments

- PAX experiment

## Outline

- WHY? 			Physics Case
- HOW? 			Polarized Antiprotons
- WHAT?			Staging
- 					Detector and signal estimate
- WHERE AND WHEN? 	The FAIR project at GSI (D)

**PAX:****Polarized Antiproton Experiments**

- PAX experiment

## Faciltiy for Antiproton and Ion Research

** ****(GSI, Darmstadt, Germany)**

- Proton linac (injector)
- 2 synchrotons (30 GeV p)
- A number of storage rings
-  Parallel beams operation

**Physics  Polarization **** ****Staging   Signals  ****FAIR**

- PAX experiment

##  The FAIR project at GSI

**FLAIR:**
**(Facility for very Low energy Anti-protons and fully stripped Ions)**

**SIS100/300**

**HESR: High Energy Storage Ring:**
**PANDA and PAX**

**NESR**

**CR-Complex**

-  The FAIR project at GSI

- 50 MeV Proton Linac

**Physics  Polarization **** ****Staging   Signals  ****FAIR**

- PAX experiment

##  Timeline

**	****Polarization tests, polarizer design and construction.**

**Phase I: 2013-2017**
**	****APR+CSR @ GSI**
**	****Physics: EMFF with fixed target****	**

**Phase II: 2018 - ...**
**	****HESR+CSR asymmetric collider**
**	****Physics: h****1**** ****	**

-  Timeline

**Physics**** **** Polarization **** ****Staging   Signals  ****FAIR**

- PAX experiment

## Conclusions

**Challenging opportunities accessible with polarized pbar.**
- Unique access to a wealth of new fundamental physics observables
- Central physics issue: h1q (x,Q2) of the proton in DY processes
- Other issues:
- Electromagnetic Formfactors
- Polarization effects in Hard and Soft Scattering processes
- differential cross sections, analyzing powers, spin correlation parameters
**Staging approach**
**Projections for double polarization experiment (tests) :**
- Pbeam > 0.30
- L> 1.6 ·1030 cm-2s-1 (Collider), L 2.7 ·1031 cm-2s-1(fixed target)
**Detector concept:**
- Large acceptance detector with a toroidal magnet

- PAX experiment

## Slide 55

- PAX experiment