Transcript 齊藤 直人,京大
ニュートリノ核子弾性散乱実験
齊藤 直人
(京都大学)
NeuSpin Working Group
• 東工大
– 柴田さん、宮地さん、武居くん、坂下くん
• 阪大RCNP
– 酒見さん
• 京大
– 齊藤、今井さん
• 理研
– 後藤さん
• KEK
– 澤田さん
• NMSU
– S. Pate
• その他にも興味を示してくれている方多数
Physics Goal
• ストレンジネスの偏極Dsの直接測定
– DISとバリオン8重項のβ崩壊定数から予測されるDs<0
は本当か?
• ニュートリノ核子の反応断面積の精密測定
• ニュートリノ原子核反応におけるコヒーレントパイオ
ン生成断面積の測定
– K2K CCの結果を更にimproveできるか?
– NC?
From g1(x,Q2) to DS
• Integrate over x (0,1)!
1 44
11
11
p
Proton
1
11
1
1
1
4
Proton
p
n
D
U
D
D
D
S
0.119
n
pe
1
1 2 9 DU 9 DD 9 DS 0.119 1 DU DD DS e 0.053
2 9
9
9
29
9
9
11
4
1
1n DUp DD DS 0.053
n
29
9
9
pe
e
Deuteron
=
Proton
Neutron
Deuteron
1 Octet Baryon b-Decay
1= Proton + +Neutron
Utilize
Constants!
p
•
n
DU DD 1.2692 0.0112 DU DD 2DS 0.1952 0.0083
( g A / gV ) np DU DD F D 1.2695 0.0029
– SU(2) OK!
3 e e
3
( g A / gV(Bjorken
) p (2DSR)
U DD DS ) / 3 F DHe=Neutron
/He=Neutron
3 0.718 0.015
((D
g AU/ ,gDV D
) , DS()DU DD 2DS ) / 3 F D / 3 0.25 0.05
S ne e
(
0
.
802
,
0
.
465
,
0
.
124
)
( g A / gV ) Sn DD DS F D | 0.340 0.017 |
DS 0.213 0.138
Constant in front of D/3
DS from SDIS and Global Analysis
• Global Analyses suffer from a lack of DS data:
SU(3) symmetric sea assumed
• In SDIS, with Final State Hadron Detection, DS can
be extracted
ストレンジクォークは本当に偏極して
るのか?
• Flavor Singlet ⇒Axial Anomaly
– If Dg ~ 0.3 axial anomaly contribution alone ~
0.15/2p ~ - 0.025
– So far DS = - 0.14 ± 0.05 (DIS + Baryon b)
• Violation of Eliis-Jaffe Sum Rule ⇒DS≠0
• Independent DS measurement would be
sufficient to obtain DS (together with
Baryon b-decay)
Why Should the Nucleon be Strange?
• The vacuum is strange:
chiral symmetry for π, K mesons →
0 |s s | 0 (0.8 0.1) 0 | qq | 0
• Cannot be expected to disappear when one inserts
•
•
qqq ‘test charge’ into vacuum
Expected to be generated in perturbative QCD:
s sbar gluon quark
Also, generated by non-perturbative effects:
instantons, chiral soliton models
How Strange is the Nucleon?
• Momentum fraction at
Q2=20
GeV2:
Not very?
Ps= 4%
(CCFR)
• Electric and magnetic form factors
at Q2=0.48 (GeV)2
(HAPPEX)
GsE + 0.39 GsM= 0.025 0.020 0.014
at Q2=0.23 (GeV)2
(A4)
GsE + 0.225 GsM= 0.039 0.034
• Contribution to the nucleon magnetic moment
-0.1 5.1%
(SAMPLE)
Pion-Nucleon σ Term
• Related to strange scalar
density
y
2 p | ss | p
p | uu | p p | dd | p
• Two recent
determinations:
• Maybe y ~ ½ ?
Important later for chiral soliton models of exotic baryons
Trial Fit!
•
p0
LL
A
22
c
model
0
Utilized NLO p (0.73±0.39)x 10.8
calculation (thanks
(-1.03±0.43)x 11.3
to Vogelsang and
(5.74±3.10)x 2 10.8
Stratmann) (-9.64±2.99)x 2 10.5
– to find “relevant-x”
for each pT bin
2
Dg
Dg
ALL b
g
g
• Trial Fit to
– A*x (GRSV ~ 1*x)
– A*x*x
Lepton Scatt.
ndfprob.c22 ndfprob.
7 0.15 6.2 5 0.29
7 0.13 14.6 5 0.01
7 0.15 5.3 5 0.38
7 0.16 18.3 5 0.00
Dg
0.30
-0.42
0.35
-0.60
pT (GeV/c)
Is this Dg Large or Small?
• Expectation (Phenomenological)
– Dg ~ 2 to save DS thru axial anomaly (if
DS=0.58 ⇔Ds=0⇔EJ SR)
– Dg ~ 0.3-0.4 to save “proton spin”
• Model predictions
– Dg ~ 2±1 (…)
– Dg ~ -0.4 (Bag model)
– No lattice prediction
• Gauge Invariance
– See Jaffe’s talk
– (http://wwwctp.mit.edu/gluonspinbasics080203.pdf)
• Scale Dependence of Dg
– Product S Dg ~ constant
– Dg(1 GeV)=0.3
⇒Dg (MZ)=1.5
– “Fine tuning” by Lg
~ N f S
DS DS
Dg
2p
1 1
DS Dg LZ
2 2
Extend x Range
• ALL(p0) from Run
6/7 (65 pb-1) will
extend x range to
larger x
• STAR jet
measurement also
provides precision
data
• 500 GeV run will
cover smaller xrange
Direct photon in Run-2006/7
P1
k2
P2
k1
RHIC Spin and HERMES SIDIS
• Complementary!
– RHIC W
• No fragmentation
ambiguity
• x-range limited
• Useless for
transversity studies
• Otherwise WR!
– HERMES SemiInclusive DIS
• Wide x-range
• Could be used for
transversity studies
Ds 測定がもたらす物理的インパクト
• 核子のスピンフレーバー構造に対する理解が深
まる
– Flavor SU(3) 仮定を超えて
• 中性子のEDM
J.Ellis and R.A.Flores PLB377(96)83
– n-EDM の予言は、 d
n
q-EDM and Dqに基づく
(Dud Ddd Dsd )
mu Du md Dd ms Ds
E
E
u
E
d
• ダークマター探索
J.Ellis and M. Karliner Lecture at Erice School 95 hep-ph/9601280
– ダークマターと核子の相互作用
4
1
( cp cp) Du (Dd Ds) (photino) or
9
9
17
5
Du (Dd Ds ) (pure U (1) gaugino)
36
36
E
s
荷電カレントコヒーレントパイオン生成
• K2K results on CC coherent pion production
– Phys. Rev. Lett. 95 252301 (2005)
N 弾性散乱
• N 弾性散乱断面積
d GF2 Q 2
2
A
BW
CW
dQ 2 2p E2
for ; for
k
W 4( E / M p ); Q 2 / 4M p2
– Where
(Q2
dropped for brevity)
k’
q
P
P’
1 2
A G1 (1 ) F12 F22 (1 ) 4F1F2
4
s
2
1
0
.
631
G
(
Q
)
2
1
B G1 F1 F2
G1 (Q )
2
2 2
4
(1 Q / M A )
2
2
M
1 p 2
2
2
s
C
G
F
F
1
1
2
2
G1 (0) Ds
16 Q
BNL E734 (PRD 35 (87) 785)
• Measurement of p and p elastic
scattering
•170 metric-ton segmented detector
@ E~1.2 GeV
( m p m p)
R
0.153 0.007 0.017
( m n m p)
•951 mp events
•776 mp events R ( m p m p) 0.218 0.012 0.023
( m p m n)
( m p m p)
R
0.302 0.019 0.037
( m n m p)
2.5+0.55 1019 pot
Extraction of Strange FF
• Fit cross section with dipole approximation
BNL-Experiment 734
(L.A.Ahrens et.al PRD35(87)785; Reanalysis G.T. Garvey et. al PRC48(93)761)
• Measured elastic
scattering cross section
p p and p p
– Liquid scintillator + Drift
2 Cut-off
Too
High
Q
Tube 170 t
Go to lower Q2
– 0.5E19 POT for neutrino
and 2.5E19POT for antineutrino
79% from Carbon
– Q2>0.40 GeV2
Extract Pure Proton
N-Elastic Scattering Exp at J-PARC
• On-axis at near detector hall for T2K
Experiment
• Utilize both two types of LiqScintillator with
different H/C mixture for pure proton signal
– e.g Bicron BC510A (H/C=1.212) and BC-533
(H/C=1.96)
– Pure Carbon can be extracted for A Xsection
– e.g. 5x5x5m3 ~ 125 t
• 1E21 POT possible in one year (130 days)
– 30 times BNL-E734
– Better with polarity change for
v and
Sensitivity for Ds
• Assumptions
– Similar Detection Efficiency to
E734:
• 7.6% for neutrino-N elastic
• 5.4% for anti-neutrino-N elastic
– However with lower Q2 cut-off :
0.1 GeV2
• Achievable with more uniform
detector ?
– 25 times more statistics but pure
proton only 1/6
• Factor 2 reduction in statistical error
– Systematic control improvements
to ~5%
• E734 7.6% dominated by Beam Flux
and Nuclear Effects
• Possible to remove Nuclear Effects
which could be larger in lower Q2
region
Comparison with E734
• If Ds is the only parameter to
– E734: Ds 0.10 0.08
– J-PARC: Ds 0.10 0.03
• But… Ds and MA coupled
= -Ds/gA(=1.256)
be determined
determination of Ds with
– E734: Ds 0.10 0.27
Significantly improved Sytematics
significantly
Better
– J-PARC: Ds 0.10 0.12
– N.B. other analysis of E734
Separation
with
provided
better precision:
MA might be
Problematic
G0 Physics Asymmetry
• “no vector strange” asymmetry ⇒ ANVS
– em form factors: Kelly PRC 70 (2004) 068202
• inside error bars: stat, outside: stat. & pt-pt syst.
GEs and GMs extracted
• Significant non-zero contributions
Asymmetry measured…
• Axial Form Factor contribution is
suppressed by (1-4sZ2)=0.076
p n
p
n
GF Q 2
G
G
G
G
2
p
n
E E
M M
ALR (e p)
(1 4 sin W )(1 RV ) (1 RV )
p 2
p 2
(
G
)
(
G
4p 2
E
M)
p
GF Q 2
G
s
E
(1 RV( 0) )
G
E
p 2
p 2
(
G
)
(
G
)
4p 2
E
M
GF Q 2
GMp
(0)
s
(1 RV )
G
(GEp ) 2 (GMp ) 2 M
4p 2
2
p
(
1
4
sin
)
'
G
GF Q 2
(0)
W
M ~p
(1 RV )
GA
p 2
p 2
(GE ) (GM )
4p 2
~p
T 1 ( 3)
T 0 (8)
( 0) s
GA -1.65
A GA -0.44
A GA +0.45
A GA
陽子からの散乱と原子核からの散乱
• 原子核からが4~5倍
• Q2分布の違い(モデル)
Hi Intensity Proton Accelerators
Completion of J-PARC
• Power will evolve to ~1 MW in 5 years
Summary
• ストレンジクォークの核子中での役割は大き
いと思われる
• 偏極DSの測定は、素粒子・宇宙・原子核に渡
るインパクトがある
• ニュートリノ散乱で得られる情報は大きい
• 一緒に実験・解析について考えましょう!
– http://www.nucl.phys.titech.ac.jp/~neuspin/
http://www.nucl.phys.titech.ac.jp/~neuspin/
LSND (1993-98)
Nearly 49,000 Coulombs of
protons on target
Baseline 30 m
Neutrino Energy
20-55 MeV,
1280 phototubes
167 tons Liquid scintillator
MiniBooNE (Started last year)
MiniBooNE Signals (1021pot)
Approximate number of electron
neutrino-like events expected in
MiniBooNE with two years of
running before cuts
Intrinsic e background:
1,000 events
m mis-ID background:
500 events
p0 mis-ID background:
500 events
LSND-based me:
1,000 events
Direct Measure of Ds(?)
• Nucleon Neutral Weak Current
J m N GA m 5 F1 m F2 m q N
•
g A 3
s
2
GA (q )
G
(
q
)
A
2
2 2
(1 q / M A )
Axial Form Factor:
2
• gA, F1,2pn known, F1,2s measured (PV e)
s
2
G
(
q
• Strange Axial Form Factor: A 0) Ds
(p p) yields Ds
Elastic Scattering p p
• Assuming no second-class current…
Conclusion from E734
• No decisive determination of Ds due to …
– Q2 extrapolation down to 0
– Possible contamination from nuclear effects
• 79% from Carbon
• 1.5 mm resolution should be improved
• Pure Hydrogen desirable … at least BG
subtraction preferred
E734 Target and Detector
• Calorimeter
– Liquid Scintillator (80% of
mass)
– 79% protons are bound in
Carbon 21% are free
• Proportional Drift Tubes
– 1.5 mm position resolution
Beam Flux
• Measured using CC
Processes
– Anti-nu contamination in
nu beam 0.024+\-0.005
– Nu contamination in
anti-nu beam 0.087+\0.013
m
m
• Time Structured Beam
(every 224 nsec) for BG
reduction
0.55e19 POT 5.5E5 nu events
2.5E19 POT 2.5E6 anti-nu events
Event Topology Cuts& PID
• Fully contained single
track (= proton
candidates)
• Three PDT hits required
– Q2 cut > 0.035 GeV2
• Likelihood Functions
basing of energy deposit
– P: Probability Density Fn
A typical event
PID Cuts
• L (SCIN) and L (PDT)