Search for efficient antiproton polarimeters in the

energy range 40 MeV-15 GeV

SPIN-05

A.A. Bogdanov, S.B. Nurushev, V.A. Okorokov, M.F. Runzo, M.N. Strikhanov

INTRODUCTION

The polarized antiproton-proton interactions at the HESR at the future FAIR will provide unique access to a number of new fundamental physics observables, which can be studied neither at other facilities nor at HESR without transverse polarization of protons and antiprotons.Main physics aspects that will be explored:1. The transversity distribution;2. Magnetic and electric form factors;3. Hard scattering.

An APR built inside the HESR area with the crucial goal of polarizing antiprotons at momentum around 300 MeV/c. A second ring (CSR) in which antiprotons can be stored with momentum up to 3.5 GeV/c. Polarized antiprotons with momentum up to 15 GeV/c will circulate in the HESR, which has already been approved and will serve the PANDA experiment. Thus it is need to measure antiproton polarization at each stage of PAX.

The proposed accelerator set-up at the HESR, with equipment used by

the PAX collaboration.

1) Elastic antiproton-proton scattering in CNI region.

2) Elastic antiproton-proton scattering.

3) Elastic antiproton-electron scattering.

It is discussed polarimeters based on three reactions.

p p p p

p e p e

p p p p

1. Elastic antiproton-proton scattering in CNI region

We made analysis in terms of Factor of Merit M = AN2.

For first type of polarimeter we obtain M using result of following work N.H. Buttimore et al., Phys. Rev. D 59, 114010-1 (1999)

2 2

0 2 2 21 2

(1 ) | |( )

1 ( ) | | (1 )

bt

T T

e tM t C

C t C t

Where at t<<1, 0, other parameters

presented in table 1.

2

0 2 2

( 1)

16 ( )p

p

Cm c

p, GeV/c Sqrt(s) b (GeV/c)2

15 8 11,65 -0,05

10 6,6 11,97 -0,06

2,5 3,74 11,12 -0,09

1 2,8 10,96 -0,12

0,195 2,18 60 -0,1

Table 1

Using equation (1) and parameters we receive t dependence of Factor of Merit

t t

15 GeV/c10 GeV/c

M M

t t

t

2,5 GeV/c1 GeV/c

0.195 GeV/c

M M

MAs it can be seen, position of factor of merit almost don’t depend from t. Angular position of maximum of M as function of antiproton momentum presented in table 2.

P, GeV/c , rad

15 0,003

10 0,004

2,5 0,018

1 0,045

0,195 0,229

Table 2

Possible experimental set up of polarimeter based on elastic antipp scattering in CNI region.

A. Bravar et al., Spin dependence in Elastic Scattering in the CNI region. Spin -2004.Trieste.

Resume: As it can be seen, position of maximum of factor of merit almost don’t depend from t, but change from 0.003 up to 0.229 rad.

For second type of polarimeters we used experimental data presented in article NN and ND interactions – a compilation Particle Data Group LBL-58. May 1972. Using this data we receive following dependence factor of merit from t

0

50

100

150

200

250

0 0,2 0,4 0,6 0,8 1

0

20

40

60

80

100

120

140

160

180

200

0 0,1 0,2 0,3 0,4 0,5

-500

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

0 0,5 1 1,5 2 2,5 3 3,5 -500

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7

t t

t t

10 GeV/c 14 GeV/c

2,5 GeV/c 0,9 GeV/c

2. Elastic antiproton-proton scattering

Possible experimental set up of polarimeter based on elastic antipp scattering.

C. Bruneton et. al., Measurement of polarization parameter in -p elastic scattering at 40 GeV/c. Phys. Lett., 44B. (1973) 471-473

P, GeV/c , rad

14 0,028

10 0,071

2,5 0,280

0,9 0,622

Table 3

Best range of t (maximum of M) for all momentums of antiproton is 0,15 – 0,3 GeV/c. This correspond range of angles presented in table 3

For polarimeters baised on elastic antiproton electron scattering we are going to use results of following works 1) P. Scofield, Phys. Rev. 113 (1959) 1599.2) M.N. Rosenbluth, Phys. Rev 79 (1950) 6153) I.A. Glavanakov, Yu.F Krechetov, A.P. Polytitsin, G.M. Radutsky, A.N. Tabachenko, S.B. Nurushev .A proton polarimeter based on the elastic pe-scattering. NIM A381 (1996) 275-279. Using this works we can receive a spin correlation asymmetry as

11 2 1 22

( )( )1 ( )( )2 ( ( ) ( )) ( ) ( 2 ) ( )

4LL

P KK K tA mM F t F t t F t F t

X t tM

With the definition 2 2 2 2 2 211 2 1 222 (2 ) ( ( ) /(4 ) ( )) ( 2 )( ( ) ( ))X a a t tM F t t M F t t t m F t F t

And also we can receive cross section2

22 2 2 2 1/ 2

2 1 1 2 1 1

| |1

| | ( ) | | cos( )e e

kdX

d k e E e k pt a m M

In work I.A. Glavanakov, Yu.F Krechetov, A.P. Polytitsin, G.M. Radutsky, A.N. Tabachenko, S.B. Nurushev .A proton polarimeter based on the elastic

pe-scattering. NIM A381 (1996) 275-279 was made calculations of ALL and cross section as function of proton kinetic energy.

3. Elastic antiproton-electron scattering

CNI,

ppElastic,

pp

pe

Type of polarimeter

Factor of Merit at 15 GeV/c, mb

Experimental setup range, rad

Momentum range, GeV/c

absolute 1,1 Si detectors

Jet target

0,003-0,229

0,195-15

relative 0.018 Cherenkov counters,

Scintillation hodoscopes,

Scintillation counters,

Jet target

0,028-0,62

0,9-14

absolute 0.04 Electron bending magnet,

Wire chambers,

Calorimeter,Polarized target

0,005-0,02

0,0 - 15

Summary

1. We considered three versions of polarimeters 2 absolute (CNI and ) and 1 relative (elastic )

2. Best polarimeters in terms of factor of merit is the polarimeter based on reaction of scattering in CNI region

3. In future we’ll made detale description of experimental set up of polarimeters considering real PAX experimental set up

4. It is planned to make theoretical calculation of factor of merit for polarimeter based on elastic scattering.

pp

pppe

pe