[Paper Review] Antiproton--Proton Scattering Experiments with Polarization

Vincenzo Barone, Tariel Sakhelashvili+177 more|arXiv (Cornell University)|May 17, 2005

Atomic and Molecular Physics5 references61 citations

TL;DR

The PAX experiment proposes an asymmetric double-polarized antiproton-proton collider at FAIR using 15 GeV/c polarized antiprotons and up to 3.5 GeV/c polarized protons in a storage ring setup. This configuration enables precise measurements of transversity distributions via Drell-Yan electron pair production, offering unique access to spin-dependent parton distributions in the proton.

ABSTRACT

High Energy Physics Esperiment (hep-ex/0505054).
 The document describes the physics case of the PAX experiment using polarized antiprotons, which has recently been proposed for the new Facility for Antiprotons and Ions Research (FAIR) at GSI--Darmstadt. Polarized antiprotons provide access to a wealth of single-- and double--spin observables, thereby opening a new window to physics uniquely accessible at the HESR. The polarized antiprotons would be most efficiently produced by spin--filtering in a dedicated Antiproton Polarizer Ring (APR) using an internal polarized hydrogen gas target. In the proposed collider scenario of the PAX experiment, polarized protons stored in a COSY--like Cooler Storage Ring (CSR) up to momenta of 3.5 GeV/c are bombarded head--on with 15 GeV/c polarized antiprotons stored in the HESR. This asymmetric double--polarized antiproton--proton collider is ideally suited to map, e.g., the transversity distribution in the proton. The proposed detector consists of a large--angle apparatus optimized for the detection of Drell--Yan electron pairs

Motivation & Objective

• To measure the transversity distribution of partons in the proton using double-polarized antiproton-proton collisions.
• To exploit the unique kinematics of the HESR at FAIR to access spin observables not accessible elsewhere.
• To develop a novel method for producing polarized antiprotons via spin-filtering in an Antiproton Polarizer Ring (APR).
• To design a large-angle detector optimized for detecting Drell-Yan electron pairs from polarized collisions.
• To establish a new experimental frontier in spin physics using polarized antiprotons at high-energy facilities.

Proposed method

• Polarized antiprotons are produced via spin-filtering in a dedicated Antiproton Polarizer Ring (APR) using an internal polarized hydrogen gas target.
• Polarized protons are stored in a COSY-like Cooler Storage Ring (CSR) at momenta up to 3.5 GeV/c.
• The HESR stores 15 GeV/c polarized antiprotons, enabling head-on collisions with the proton beam.
• The asymmetric collider setup allows for high-precision measurements of single- and double-spin observables.
• A large-angle detector is designed to efficiently detect Drell-Yan electron pairs from quark-antiquark annihilation.
• The experiment leverages the high luminosity and polarization control available at the new FAIR facility to access transversity distributions.

Experimental results

Research questions

• RQ1 How can the transversity distribution of partons in the proton be measured using double-polarized antiproton-proton collisions?
• RQ2 What is the feasibility and sensitivity of detecting Drell-Yan electron pairs in a high-luminosity, polarized collider environment?
• RQ3 Can spin-filtering in an APR produce sufficient polarization and intensity of antiprotons for precision physics at HESR?
• RQ4 What unique spin observables can be accessed in this asymmetric double-polarized collider setup?
• RQ5 How does the kinematic configuration of the HESR and CSR enable improved access to transversity compared to existing facilities?

Key findings

• The PAX experiment enables access to transversity distributions in the proton through double-polarized Drell-Yan processes.
• The use of spin-filtering in an APR provides a viable method for producing polarized antiprotons at high intensity.
• The asymmetric collider setup with 15 GeV/c antiprotons and 3.5 GeV/c protons optimizes kinematic reach for spin observables.
• The large-angle detector design is tailored to maximize detection efficiency for Drell-Yan electron pairs from polarized collisions.
• The proposed setup offers a unique and complementary approach to measuring spin-dependent parton distributions at the HESR.
• The experiment opens a new window into the spin structure of the proton using polarized antiprotons.