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Measurement of phi3 with B

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Measurement of the Spin-dependent part of
inelastic nucleon-antinucleon cross section
(first proposal)
A.Bondar, V.Dmitriev, I.Koop, A.Milstein,
V.Strakhovenko, D.Toporkov
Sept. 26-27, 2008
Novosibirsk
1/15
Polarized antiproton beams
(PAX Collaboration arXiv:hep-ex/0505054)
1. Complete mapping of the nucleon spin structure
2. Measurement of moduli and phases of the nucleon
electromagnetic form-factors GE and GM
3. Investigation of the hard antiprotons scattering
4. Hadron spectroscopy
Spin-filtering method is the most promising way to get polarized
antiprotons beams
Sept. 26-27, 2008
Novosibirsk
2/15
To estimate the beam life-time and degree of polarization the
cross section which describes a loss of antiprotons is necessary
пЃі пЂЅ пЃі ann пЂ« пЃі cex пЂ« пЃі el
Where
пЃі ann
пЃі cex
пЃі el
- total cross section of annihilation
- total charge-exchange cross section
- elastic scattering cross section
пЃІ
пЃІ
пЃІ
пЃІ
пЃІ
пЃІ
пЃі пЂЅ пЃі 0 пЂ« (пЃ– 1 пѓ— пЃ– 2 )пЃі 1 пЂ« (пЃ– 1 пѓ—пЃ® )( пЃ– 2 пѓ—пЃ® )( пЃі 2 пЂ­ пЃі 1 )
пЃІ
пЃІ
пЃ® пЂЅ p/ p
пЃІ пЃІ
пЃ– 1,пЃ– 2
Sept. 26-27, 2008
- vector of the nucleon momentum
- vectors of the polarization
Novosibirsk
3/15
The calculation of the cross sections based on Paris nucleonantinucleon optical potential
The main theoretical uncertainty in the calculation is due to
absence of spin-dependent measurements for annihilation cross
sections
They can be obtained using reaction
with longitudinally polarized electrons as a source of highly
polarized antinucleons
Though direct measurement of the spin-dependent part of
inelastic cross section for slow antiprotons is practically
impossible, both isospin amplitudes can be obtained from
polarized antineutrons interaction with different polarized targets
(H,D)
Sept. 26-27, 2008
Novosibirsk
4/15
пЃі 0 ( mb )
nbar p annihilation cross section
calculation based on Paris optical
potential
T ( MeV )
пЃі 1 ( mb )
пЃі 2 ( mb )
Paris 2008
Paris 1999
T ( MeV )
Sept. 26-27, 2008
Novosibirsk
T ( MeV )
5/15
Sept. 26-27, 2008
Novosibirsk
6/15
(пЃі пЂ« пЂ­ пЃі пЂ­ ) / 2пЃі 0
Spin asymmetry for nbar p
annihilation cross section
T пЂЅ 20 MeV
T пЂЅ 50 MeV
cos пЃ±
(пЃі пЂ« пЂ­ пЃі пЂ­ ) / 2пЃі 0
cos пЃ± пЂЅ 1 .
cos пЃ± пЂЅ 0 . 5
T ( MeV )
Sept. 26-27, 2008
Novosibirsk
7/15
Polarization scheme with 3 snakes (arc=1200
+2 damping wigglers in the arc’s middle )
IP
snake2
snake3
damping
wiggler2
damping
wiggler1
snake1
Sept. 26-27, 2008
Novosibirsk
8/15
Polarization degree overview
1
5 snakes
P olarization D eg ree
0.8
0.6
3 snakes
0.4
1 snake
0.2
0
1
1.2
1.4
1.6
1.8
2
2.2
2.4
2.6
Beam Energy, GeV
Sept. 26-27, 2008
Novosibirsk
9/15
The value of the spin dependent asymmetry for nbar p
annihilation measurement and necessary statistics
Aexp= A0zbeamztargetD = 0.15*0.8*0.8*0.34=3.2%
D = 3/(3+AN2/3)=0.34
dN/dt = пЃіnn*L*h*e*(cosпЃ±max-cosпЃ±min)/(l*sinпЃ±)пЂЅ0.1sec-1
пЃіnn=1nb
L = 5.1033 cm-2sec-1
l = 35cm (T=20MeV)
h=8cm
e=0.3
cosпЃ±max=0.9
cosпЃ±min=0.7
10 days statistic will be enough for пЃі(Aexp) = 0.1%
Sept. 26-27, 2008
Novosibirsk
10/15
Polarization filling pattern
IP
snake
Sept. 26-27, 2008
Novosibirsk
11/15
Summary
1. Super ct factory is unique source of polarized
nucleons
2. It can be used for measurement of spindependent part of inelastic nucleon-antinucleon
annihilation
3. These data may constrain the parameters of the
phenomenological potential of the NNbar
interaction
Sept. 26-27, 2008
Novosibirsk
12/15
Polarization degree of the antineutrons in the e+e- -> n nbar
e GM
пЃІ
пЃ–n пЂЅ 2
2
пЃІ
2
пЃІ пЃІ пЃІ
пЃІ пЃІ пЃІ пЃІ
пЃІ пЃІ пЃІ
*
*
(пЃ– пѓ—пЃ® )пЃ® пЂ« e пѓ— m пѓ— пѓЃ m ( G M G E )( пЃ– пѓ—пЃ® )пЃ® п‚ґ пЃ– пЂ­ e пѓ— m пѓ— пѓ‚ e ( G M G E )пЃ® п‚ґ [пЃ® п‚ґ пЃ– ]
пЃІ пЃІ 2
пЃІ пЃІ 2
2
2
2
2
e G M (1 пЂ« (пЃ– пѓ—пЃ® ) ) пЂ« e G E (1 пЂ­ (пЃ– пѓ—пЃ® ) )
пЃІ
(пЃ– n пѓ— пЃ– )
GE / GM пЂЅ 1
G E / G M пЂЅ 0 .7
GE / GM пЂЅ 2
cos пЃ±
Sept. 26-27, 2008
Novosibirsk
13/15
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