偏極ドレル・ヤン実験
偏極標的開発キックオフミーティング
＠山形大学
2010年6月30日（水）
後藤雄二（理研）
内容
• イントロダクション
– 陽子スピンの謎
• 横方向スピン構造
– TMD分布関数
• 偏極ドレル・ヤン実験
– FNAL-E906実験将来計画
– その他の実験計画
• 偏極標的開発
June 30, 2010
2
イントロダクション
1 1
• 陽子スピンの謎
   g  L
– 陽子スピン1/2の起源は何か？ 2
2
– Fundamentalな対象であるにもかかわらず理解されてい
ない。
– QCDを基盤とする研究方法が発展している
• 縦偏極実験と横偏極実験
– 縦偏極
– 横偏極
, g
L
• 深非弾性散乱(DIS)実験とハドロン衝突実験
– DIS実験 
– Semi-inclusive DIS実験
– ハドロン衝突実験
June 30, 2010
g , L,...
3
核子スピン１/２の起源
• 偏極レプトン深非弾性散乱実験
lepton beam
 or 
– パートン模型

g*
 or 

q( x)  q ( x)  q ( x)
nucleon target
quark
Sg  S N  1/ 2
Sg  S N  3 / 2
g*
 1T/ 2 ~  ei2 q  ( x)
i


 
  
A1  

    
 3T/ 2 ~  ei2 q  ( x)
2


e
(
q
(
x
)

q
i i
i ( x ))
i
2
偏極構造関数
e

i qi ( x )
g1 ( x)
i
i
~


2


2
 ei (qi ( x)  qi ( x))  ei qi ( x) F1 ( x)
i
June 30, 2010
g*
i
非偏極構造関数
4
核子スピン１/２の起源
• EMC実験＠CERN
J. Ashman et al., NPB 328, 1 (1989).
1 4
1
1 
0 dxg ( x)  2  9 u  9 d  9 s 
 0.123  0.013(stat )  0.019(syst )
1
p
1
– 中性子およびハイペロン崩壊データを用いて
  u  d  s  12  9(stat )  14(syst )%
「陽子スピンの危機」
• クォークスピンは核子スピンの小さな割り合いにしか寄与しない
– x = 0 ~ 1 の積分による不確定性
• より広いx領域を覆う、よりよい精度のデータが必要
 SLAC/CERN/DESY/JLAB 実験
June 30, 2010
5
核子スピン１/２の起源
• なぜわかっていないのか？
– 偏極実験の難しさ
• 偏極レプトンビーム
– SLAC/CERN/DESY/JLab
• 偏極標的
– SLAC/CERN/DESY/Jlab/FNAL
– (and other low-energy facilities)
• 偏極陽子ビーム
– RHIC
– (and other low-energy facilities)
June 30, 2010
6
偏極レプトン深非弾性散乱実験
• 固定ターゲット実験
– Q2の範囲が限られている
unpolarized DIS
1 < Q2 < 100 (GeV/c)2
June 30, 2010
polarized DIS
1 < Q2 < 100 (GeV/c)2
7
偏極レプトン深非弾性散乱実験
• クォークスピンの寄与
 ~ 0.2
• 核子スピン１/２の起源は何
か？
1 1
   g  L
2 2
– グルーオンスピンの寄与？
– 軌道角運動量？
June 30, 2010
8
Transverse-spin - introduction
• Multi-dimensional structure of the nucleon
– Orbital angular momentum inside the nucleon
– Shape of the nucleon
Lq  Lg
quark distribution quark distribution
with parallel spin with anti-parallel spin
to the nucleon
to the nucleon
direction of
nucleon spin
G. A. Miller, PRC68, 022201(R) (2003)
NSAC Long Range Plan arXiv:0809.3137
• Extension of distribution functions
– GPD (Generalized Parton Distribution)
– TMD (Transverse-Momentum Dependent) distribution
June 30, 2010
9
横偏極非対称度測定
• SSA (Single Spin Asymmetry)、左右非対称度
AN 
d Left  d Right
d Left  d Right
• 前方 xF > 0.2
– Fermilab-E704
•
•
•
•
June 30, 2010
固定標的実験
s = 19.4 GeV
非対称度 ~20%
多くのQCDに基づく理論の開発
10
Transverse-spin – results
Forward rapidity 0 at STAR
at s = 200 GeV
Forward identified particles
at BRAHMS
+

Forward rapidity 0 at PHENIX
at s = 62.4 GeV
K
p
p
June 30, 2010
11
Introduction
• Transverse structure of the proton
– Transversity distribution function
– Correlation between nucleon transverse spin and parton
transverse spin
– TMD distribution functions
• Sivers function
– Correlation between nucleon transverse spin and parton
transverse momentum (kT)
• Boer-Mulders function
– Correlation between parton transverse spin and parton
transverse momentum (kT)
Leading-twist transverse momentum dependent (TMD) distribution functions
June 30, 2010
12
Transverse-spin - results
• Results at forward rapidity
– Explained as a mixture of Sivers effect, Collins effect, and
higher-twist effect
– Why similar asymmetry on K+ (valence+sea) and K- (sea+sea)?
– Why large asymmetry on anti-proton?
• How to distinguish Sivers effect?
– Back-to-back jet
• How to separate initial-state and final-state interaction
with remnant partons?
– Forward photon + jet
– Drell-Yan process
June 30, 2010
13
Sivers function
• Single-spin asymmetry (SSA)
measurement
M. Anselmino, et al.
EPJA 39, 89 (2009)
Sivers function
u-quark
– < 1% level multi-points
measurements have been done for
SSA of DIS process
• Valence quark region: x = 0.005 – 0.3
• (more sensitive in lower-x region)
June 30, 2010
d-quark
14
Drell-Yan process
• The simplest process in hadronhadron reactions
DIS
Drell-Yan
– No QCD final state effect
• FNAL-E866
– Unpolarized Drell-Yan experiment with
Ebeam = 800 GeV
– Flavor asymmetry of sea-quark
distribution
 pd 1  d ( x ) 
2 pp
~
2
1 

2  u ( x2 ) 
• x = 0.01 – 0.35 (valence region)
• FNAL-E906
– Similar experiment with main-injector
beam Ebeam = 120 GeV
• x = 0.1 – 0.45
June 30, 2010
15
FNAL-E906
• Dimuon spectrometer
Momentum
analysis
Focusing magnet
Hadron absorber
Beam dump
– Main injector beam Ebeam = 120 GeV
– Higher-x region: x = 0.1 – 0.45
– Beam time: 2010 – 2013
June 30, 2010
16
Polarized Drell-Yan experiment
• Many new inputs for remaining proton-spin puzzle
– Single transverse-spin asymmetry
• Sivers function measurement
• Transversity  Boer-Mulders function
– Double transverse-spin asymmetry
• Transversity (quark  antiquark for p+p collisions)
– Double helicity asymmtry
• Flavor asymmetry of quark polarization
– Other physics
• Parity violation asymmetry…
June 30, 2010
17
Polarized Drell-Yan experiment
• “Non-universality” of Sivers function
– Sign of Sivers function determined by SSA measurement of DIS and Drell-Yan
processes should be opposite each other
• final-state interaction with remnant partons in DIS process
• Initial-state interaction with remnant partons in Drell-Yan process
– Fundamental QCD prediction
– Milestone for the field of hadron physics to test the concept of the TMD
factorization
DIS
Drell-Yan
attractive
repulsive
“toy” QED
QCD
June 30, 2010
Explanation by Vogelsang and Yuan
from “Transverse-Spin Drell-Yan
Physics at RHIC,” Les Bland, et al.,
May 1, 2007
18
偏極ドレル・ヤン実験
• FNAL-E906実験将来計画
•  ビーム、偏極標的
• その他の実験計画
– COMPASS
•  ビーム、偏極標的
– RHIC
• 偏極陽子ビーム
– J-PARC
• 偏極陽子ビーム（？）、偏極標的
– FAIR, …
June 30, 2010
19
Comparison with other experiments
experiment
particles
energy
x1 or x2
luminosity
COMPASS
+ p
160 GeV
s = 17.4 GeV
x2 = 0.2 – 0.3
2 × 1033 cm-2s-1
COMPASS
(low mass)
+ p
160 GeV
s = 17.4 GeV
x2 ~ 0.05
2 × 1033 cm-2s-1
PAX
p + pbar
collider
s = 14 GeV
x1 = 0.1 – 0.9
2 × 1030 cm-2s-1
PANDA
(low mass)
pbar + p
15 GeV
s = 5.5 GeV
x2 = 0.2 – 0.4
2 × 1032 cm-2s-1
J-PARC
p + p
50 GeV
s = 10 GeV
x1 = 0.5 – 0.9
1035 cm-2s-1
NICA
p + p
collider
s = 20 GeV
x1 = 0.1 – 0.8
1030 cm-2s-1
RHIC PHENIX
Muon
p + p
collider
s = 500 GeV
x1 = 0.05 – 0.1
2 × 1032 cm-2s-1
RHIC Internal
Target phase-1
p + p
250 GeV
s = 22 GeV
x1 = 0.2 – 0.5
2 × 1033 cm-2s-1
RHIC Internal
Target phase-2
p + p
250 GeV
s = 22 GeV
x1 = 0.2 – 0.5
3 × 1034 cm-2s-1
June 30, 2010
20
COMPASS facility at CERN (SPS) II
June 30, 2010
21
DY@COMPASS - set-up
π- p  μ - μ X
π-
190 GeV
Key elements:
1. COMPASS PT
2. Tracking system (both LAS abs SAS) and beam telescope in front of PT
3. Muon trigger (in LAS is of particular importance - 60% of the DY acceptance)
4. RICH1, Calorimetry – also important to reduce the background (the hadron flux downstream
of the hadron absorber ~ 10 higher then muon flux)
June 30, 2010
22
DY@COMPASS kinematics - Indication
TMD PDFs – ALL are sizable in the valence quark region
Sivers effect in Drell-Yan processes. M.
Anselmino, M. Boglione U. D'Alesio, S.
Melis, F. Murgia, A. Prokudin Published
in Phys.Rev.D79:054010, 2009
June 30, 2010
23
DY@COMPASS – kinematics - valence quark range
π- p  μ- μ X
•
•
•
In our case (π- p  μ- μ X)
contribution from valence
quarks is dominant
In COMPASS kinematics uubar dominance
<PT> ~ 1GeV – TMDs
induced effects expected to
be dominant with respect to
the higher QCD corrections
June 30, 2010
24
DY@COMPASS - feasibility
•
•
•
•
•
•
•
Small cross section - High luminosity experiment
Polarised target is the key instrument of the program
Radioprotection issue – experiment similar to NA3
Detector occupancies
Trigger rates
DY event rate (J/Psi as a monitoring signal)
Physics background study:
– D-Dbar semi-leptonic decays
– Combinatorial background from π and K
• COMPASS spectrometer kinematic range
June 30, 2010
25
2XE F1
RHIC-IP2 (overplotted on BRAHMS)
Internal target position
20 TO N
CR AN E LIM IT
St.4
MuID
X
DX
CR YO GEN IC PI PIN G
IP
St.1
X
C.O.D.P .
F MAG3.9 m
Mom.kick
2.1 GeV/c
St.2
St.3
KMAG 2.4 m
Mom.kick
0.55 GeV/c
20 TO N
CR AN E LIM IT
June 30, 2010
14 m
18 m
26
Requirement for the RHIC accelerator
• Appropriate beam lifetime and low background
– Affected by beam blow-up (small-angle scattering, beam
energy loss at the target, …)
– low background for collider experiments (in phase-1)
• Compensation for dipole magnets in the
experimental apparatus
– both beams need to be restored on axis in two collidingbeam operation
• Higher beam intensity at phase-2
– 1.5-times more number of bunches (assumed at eRHIC)
– Otherwise, 1.5-times longer beam time is required
• Radiation issues
– Beam loss/dump requirement?
• Experimental site issues
– Magnet, civil engineering works, …
June 30, 2010
27
Experimental sensitivities
• PYTHIA simulation
– s = 22 GeV (Elab = 250 GeV)
– luminosity assumption 10,000 pb-1
•  10 times larger luminosity
necessary than that of the collider
experiments
• because of ~10 times smaller cross
section  acceptance (in the same
mass region)
– 4.5 GeV < M < 8 GeV
– acceptance for Drell-Yan dimuon
signal is studied
June 30, 2010
all generated
dumuon from
Drell-Yan
accepted by
all detectors
28
Experimental sensitivities
• About 50K events for 10,000pb-1 luminosity
Mass
(GeV/c2)
Total
Rapidity
45 – 50
50 – 60
60 – 80
45 – 80
-0.4 – 0
3.1 K
3.1 K
1.4 K
7.6 K
0 – 0.4
6.2 K
6.1 K
3.0 K
15.3 K
0.4 – 0.8
7.6 K
6.4 K
2.3 K
16.3 K
0.8 – 1.2
4.4 K
2.5 K
0.4 K
7.3 K
• x-coverage: 0.2 < x < 0.5
June 30, 2010
x1: x of beam proton (polarized)
x2: x of target proton
29
Experimental sensitivities
• Phase-1 (parasitic operation)
– L = 2×1033 cm-2s-1
– 10,000 pb-1 with 5×106 s ~ 8 weeks, or 3 years (10 weeks×3) of
beam time by considering efficiency and live time
• Phase-2 (dedicated operation)
– L = 3×1034 cm-2s-1
– 30,000 pb-1 with 106 s ~ 2 weeks, or 8 weeks of beam time by
considering efficiency and live time
Theory calculation:
U. D’Alesio and S. Melis, private communication;
M. Anselmino, et al., Phys. Rev. D79, 054010 (2009)
Measure not only the sign of
the Sivers function but also
the shape of the funcion
10,000 pb-1 (phase-1)
40,000 pb-1 (phase-1 + phase-2)
June 30, 2010
30
• x1 & x2 coverage
Collider vs fixed-target
– Collider experiment with PHENIX muon arm (simple PYTHIA simulation)
• s = 500 GeV
• Angle & E cut only
– 1.2 < || < 2.2 (0.22 < || < 0.59), E > 2, 5, 10 GeV
– (no magnetic field, no detector acceptance)
• luminosity assumption 1,000 pb-1
• M = 4.5  8 GeV
• Single arm: x1 = 0.05 – 0.1 (x2 = 0.001 – 0.002)
– Very sensitive x-region of SIDIS data
– Fixed-target experiment
• x1 = 0.2 – 0.5 (x2 = 0.1 – 0.2)
– Can explore higher-x region with better sensitivity
PHENIX muon arm (angle & E cut only)
x2
June 30, 2010
Fixed-target experiment
x2
x1
x1
31
Charm/bottom background
• In collider energies, there is non-negligible
background from open beauty production
• In fixed-target energies, background from charm &
bottom production is negligible
PHENIX muon arm
s = 200 GeV
FNAL-E866
Elab = 800 GeV
charm
bottom
Drell-Yan
June 30, 2010
32
Polarized proton acceleration at J-PARC
• How to keep the polarization given by the polarized
proton source
– depolarizing resonance
• imperfection resonance
– magnet errors and misalignments
• intrinsic resonance
– vertical focusing field
– weaken the resonance
• fast tune jump
• harmonic orbit correction
– intensify the resonance and flip the spin
• rf dipole
• snake magnet
• How to monitor the polarization
– polarimeters
June 30, 2010
33
Polarized proton acceleration at AGS/RHIC
• Proposed scheme for the polarized proton acceleration at JPARC is based on the successful experience of accelerating
polarized protons to 25 GeV at BNL AGS
BRAHMS
& PP2PP
PHOBOS
Absolute Polarimeter RHIC pC
(H jet)
Polarimeters
PHENIX
Full Helical
Siberian Snakes
STAR
Spin Rotators
Spin Rotators
Pol. H- Source
LINAC BOOSTER
rf Dipole
AGS
200 MeV
Polarimeter
Partial Solenoidal Snake
Warm Partial
Helical Siberian Snake
AGS Internal
Polarimeter
Cold Partial
Helical Siberian Snake
June 30, 2010
AGS pC Polarimeters
34
Polarized proton acceleration at J-PARC
pC CNI Polarimeter
Pol. H Source
BRAHMS
Extracted
& PP2PPBeam
Polarimeter
PHOBOS
Absolute Polarimeter RHIC pC
(H jet)
Polarimeters
rf Dipole
PHENIX
STAR
180/400 MeV Polarimeter
30% Partial
Helical Siberian Snakes
Pol. H- Source
LINAC BOOSTER
rf Dipole
AGS
200 MeV
Polarimeter
Warm Partial
Helical Siberian Snake
AGS Internal
Polarimeter
Cold Partial
Helical Siberian Snake
June 30, 2010
AGS pC Polarimeters
35
Polarized Drell-Yan experiment at J-PARC
• Single transverse-spin
asymmetry
51cm
127cm
polarized
beam
analyzing
magnet
– Sivers effect measurement
• Experimental condition
– higher beam intensity is possible
for unpolarized liquid H2 target,
or nuclear target
• 51012 ppp = 2.510122sec in
1pulse (5sec) possible?
– PYTHIA simulation
red liquid H2 target
blue nuclear target
4 < M+- < 5 GeV
integrated over qT
• 75% polarization beam
• 120 days, beam on target 51017
(with 50% duty factor)
• ~5% liquid H2 target
– 10000 fb-1 luminosity
• ~20% nuclear target
– 40000 fb-1 luminosity
Theory calculation by Ji, Qiu, Vogelsang and Yuan
• mass 4 – 5 GeV/c2
based on Sivers function fit of HERMES data
June 30, 2010
(Vogelsang and Yuan: PRD 72, 054028 (2005))
36
J-PARC and/or RHIC
• J-PARC
– Advantage
• High intensity = high luminosity
– Disadvantage
• Smaller cross section (at the same invariant mass)
– Uncertainties
• Availability of 50 GeV beam
• Polarized proton beam?
• RHIC
– Advantage
• Polarized proton beam available
• Larger cross section (at the same invariant mass)
– Disadvantage
• Luminosity?
– Collider or fixed-target (internal-target) experiment
June 30, 2010
37
偏極標的開発
• KEK
• 山形
• 偏極ヘリウム３
June 30, 2010
38
Polarized target at KEK
• Michigan polarized target
– target thickness ~3 cm (1%
target)
– maybe operational with 1011 ppp
(luminosity ~1034 cm-2s-1)
June 30, 2010
39
June 30, 2010
40
June 30, 2010
41