摂動論的 Q C D の発展 - personal view -
DESCRIPTION
摂動論的 Q C D の発展 - Personal View -. QCD old boy’s view of development of pQCD. 植松恒夫 ( 京大理 ). 「核子構造研究の新展開 2011 」. @KEK January 7-8, 2011. 1. Introduction QCD 以前 黎明期 2. 第 1 期 1973 ~ 1970 年代 3. 第 2 期1980年代 4. 第 3 期 1990 年~現在 5. Outlook. Plan of the talk. “温故知新”. - PowerPoint PPT PresentationTRANSCRIPT
摂動論的QCDの発展- Personal View -
植松恒夫 ( 京大理 )
@KEK January 7-8, 2011
「核子構造研究の新展開 2011 」
QCD old boy’s view of development of pQCD
q
xp
p
E
'E
Plan of the talk
1. Introduction QCD 以前 黎明期2. 第 1 期 1973 ~ 1970 年代3. 第 2 期1980年代4. 第 3 期 1990 年~現在5. Outlook
“ 温故知新”
• 核子の構造の研究 (60 年代) deep inelastic scattering
• Current Algebra Bjorken scaling• SLAC-MIT experiment
Introduction QCD 以前 黎明期
Parton Model Feynman , Bjorken-Paschos
( ), ( ) (0 1)q x q x x
Parton 分布関数
1968
核子構造関数
L.W.Mo SLAC-PUB-660
(1969)
• Broken scaling inv. くりこみ群 ε- 展開 • Critical phenomena ( 物理量)• スケーリングの破れ• 場の理論でのくりこみ群的解析 fixed point theory power breaking anomalous dim.
asymptotically free theory logarithmic breaking
Scaling の破れ
)g )g
g g
fixed point theory
g
asymptotically free theory
0 0
UV limit g g
)g
0g
Kogut-SusskindScale-inv. Parton Model
Current Algebra
O P E
Bjorken Scaling
Light-cone
Parton Picture
Renormalization Group
Various Ideas leading to QCD
Perturbative QCD
Asymptotic freedom
K.Wilson
Bjorken
Feynman
Fritzsch-Gell-Mann
Gross-Wilczek, Politzer
Brodsky-Farrar, Matveev et al.
Large PT
Large Angle Scattering
Adler-Dashen
Gell-Mann-Low
Color gauge theory (Color octet gluon) QCD Asymtotic freedom ・ short distance ・・・漸近的自由 ・ long distance ・・・閉じ込め QCD Lagrangian : coupling const.
第1期 1973 - 1970 年代 勃興期
Fritzsch-Gell-Mann-LeutwylerNambu 1966
Weinberg 1973
1973
No free parameterexcept for
Gross-Wilczek, Politzer, ‘t Hooft 1973
S.Bethke
Effective coupling constantFundamental constant of QCD
“dimensional transmutation’’
• OPE+RG analysis of structure function • DGLAP evolution equation for PDFs
• Q2 dep. of fragmentation fn.
• Polalrized structure functions
Leading Order (LO) analysis
Gross-Wilczek, Politzer,…
Dokshitzer-Diakonov-Troyan, Gribov-Lipatov, Altarelli-Parisi,…
Georgi-Politzer, Owens, T.U.,…
Ahmed-Ross, Sasaki
• quark-gluon の系を摂動論で扱うと質量 0 の粒子の 4元運動量が 0 になることから生じる赤外発散( infrared divergence )や質量 0 の gluon が quark とcollinear に放出されることによる質量特異性 (mass singularity )が現れる.
• parton 描像で hadron の cross section
Mass singularity の因子化( Factorization )
mass (collinear) singularity
mass singularity
singular な因子は
hadron 分布関数へ吸収
物理量摂動論非摂動論 convolution
short distancelong distance
Collinear factorization
PDF (Q2dep)Structure fn.
scheme- dep
Q2 dependence DGLAP eq. or OPE+RGE
Factorization (因子化)
OPE
DGLAP equation
クォーク・グルーオン演算子
2 2
1 1 2
0| ( ) | | ( , )q n
n Qp O p x q x Q dx
分布関数と演算子
でくりこまれた演算子
2 2
1 1 2
0| ( ) | | ( , )G n
n Qp O p x G x Q dx
1 2 tracesnqn DO D
11 2 tracesn nGn DO G D G
ツイスト2の演算
子Twist=dim - spin=2
Twist
グルーオン場
クォーク場
Kodaira-TU (1978 )scheme- dependence
Splitting functions
“Plus distribution”
real emission virtual correctioninfrared cancel
Kinoshita-Lee-Nauenberg-Nakanishi Theorem
jet production
Sterman-Weinberg jet
infrared/collinear-safe quantity
Event shapes: Thrust etc.
半角 δ の cone に全エネルギーの
(1-ε) 倍が放出される
e+e-hadrons
3-jet event @DESY 1979
b
C
A
B
ac
aAf
bBf
ˆd
CcD
,
( , ) ( , )
ˆ ( , , , , ) ( , )
a ba b c A a F B b F
Ca b c R F D c c D
d dx dx dz f x f x
d x x z D z
摂動計算可能
22 2 2 2, , 4
4 R F DQ Q
high-energy QCD process: A B C X
DIS, e+ e -→ hX, Drell-Yan, hadron-hadron semi-inclusive ・・
Factorization in hadron collisions
• Twist-4 4-quark 2-quark&1gluon operators• Anomalous dimensions of 4-quark operators
Gottlieb(78) ,Okawa(80)
• Polarized structure fn. twist-3 contributes to g2
• twist-4 effects to g1
Higher-twist effects
twist=dim-spintwist-6twist-4twist-2
+
Twist-3 or 4
Kodaira-Tanaka-TU-Yasui (96)
Kawamura et al (97)
QCD higher-order (NLO) effects
LO NLO NNLO
1-loop anomalous dim.
RG eq.
1-loop Scheme independent
1-loop 2-loop
Moment of structure fn.
LO
NLO
NNLO
anomalous dim. coefficient fn.1-loop
2-loop
3-loop
1-loop
2-loop
tree
coefficient fn.
Bardeen et al (78)
Floratos et al (78)
Moch et al (04)
第2期 1980 年代 中間期
• QCD の摂動論および非摂動論での様々な 理論的整備 / 実験の進歩• Unpolarized & polarized DIS data SLAC DESY• EMC effects Spin Crisis CERN• Polarized structure functions • Twist-2, twists-3 effects renormalization of higher-twist ops.•Small-x behavior BFKLeq. BK eq.
1 2,g gmixing complicated
Polarized DIS & Structure Functions
q
nucleon
xp
p
spin
incident lepton
scattered quark
scattered lepton
spin2( , )q x Q
2( , )q x Qor
E
'E
Unpolarized structure fns.
polarized structure fns.
Structure tensor
1988 EMC at CERN “Spin Crisis”
Altarelli-Ross
Gluon polarization contributes due to anomaly
Parton distribution functions are scheme-dependent
J. Kodaira and T. U. Nucl. Phys. B141 (1978) 497
Phys. Lett B212 (1988) 391
But this is relativistic quantities !
“quarks carries only a small fraction of nucleon spin”in contradiction with naïve quark model
1st moment sum rule
Kodaira et al. 1979Kyoto Group
Phys.Rev.D20 (1979) 627; Nucl.Phys. B159 (1979) 99
flavor non-singlet
Now Larin-Vermaseren (1991)
Kodaira
Axial anomalyflavor singlet
QCD correction
Nucl.Phys. B165 (1980)129
• Coefficient functions:
• Transversity
• Higher-twist twist-3 contributes in leading order to • Many structure functions
van Neerven-Zijlstra (1994)
Chiral-odd structure fn.
twist-2 op. 2-loop anomalous dim.Hayashigaki, Kanazawa, Koike;Kumano,Miyama
: Collins function: Sivers function
Transversity & Collins and Sivers asymmetries
Asymmetry in Semi-inclusive DIS
• Large logs の足し上げ BFKL 方程式
• Non-linear evolution equation BK 方程式 gluon 分布の saturation color glass condensation (CGC)
Small-x region physics
s1( )ln nx
2F
x
x
22 ( , )F x Q x
20
2 '2'2 2 '2
'2
( , ) ( ; ) ( , )1ln k
f x k dk K k k f x kkx
recombination
2Q
nx P
1x P
Tnk
1Tk2Tk
• 2 mass scales: e.g. Q2&m2 or Q2&QT2
large logs appear at kinematical boundaries spoil perturbative expansions e.g. (real and virtual contributions highly unbalanced) Sudakov resummation=resumming the double-
logarithmic perturbative contributions
Soft-gluon resummation
s ln (1 )mnnmC x ( 2 )m n 1x
2 1 2 11 1 2S S S0
ln (1 ) ln (1 ) ln(1 ) (1 )
n nN nn n nz zdz z N
z z
2 ˆThreshold / 1Hz M s
Threshold Resummation
Sterman(’87),Catani&Trendadue(’89, ’91)
と書くと,以下が示される
(Trentadue and Kodaira Catani, D’Emilio and Trentadue)
LLNLL
NNLL
第3期 1990 年代-現在
Precision of QCD: LO→NLO→NNLO検証から精密化へ
• QCD の量子補正を NNLO の精度に高める
Splitting functions
1-loop 2-loop 3-loop
Coefficient functions
LONLO
NNLO
18
350
9607
# of diagrams
Moch-Vermaseren-Vogt (2004)
Gross-Wilczek, Politzer(1974)Floratos-Ross-Sachrajda(1978)
Color Glass CondensationString-inspired
QCD
Global PDFanalysis
AdS/CFT
Precision QCD
Recent topics in QCD
Perturbative QCD
Heavy quark mass effects
Higgs production
Multi-partonamplitudes
• MSTW (MRST) LO NLO NNLO• CTEQ LO NLO Tevatron jet analysis• NNPDF NLO Neural networks• ABKM NNLO heavy quark effects • GRV, AAC NLO polarized PDFs
Global PDF Analysis
Collaborations
QCD and HERA data
QCD @ LHC era
• CMS@7TeV pp collision ~ RHIC heavy ion collision Ridge structure pseud-rapidty (η ) correlation • ALICE heavy ion collision high multiplicities• ATLAS & CMS ジェット抑制( Jet quenching)
Higgs production
g luon fusion Diffractive production of Higgs
RHIC から LHC へ
• heavy quark coefficient functions deep inelastic lepton-hadron scattering for mass factorization: • low では heavy quark は radiative に作られる
high では light quark と同等 matching condition :
Heavy quark mass effects
2 2Q m
heavy quark coeff. fn
massive operator matrix element
Buza et al. (‘96) light quark coeff. fn
heavy quark
2Q
2Q
• Fixed Flavor Number Scheme (FFNS) u,d,s:massless heavy quarks (H):c,b,s are radiatively generated
for large log spoils perturbation• Zero Mass Variable Flavor Number Scheme (ZMVFNS)
ZMVFNS shows discontinuity at transition → • General mass variable flavor number (GMVFN)scheme
Fixed and variable flavor number schemes
To achieve smooth transition
• AdS/CFT 対応 String on AdS5×S5 ~ N=4SCFT • 5 次元 AdS 時空での弦の semi-classical な振る舞いと
boundary の4次元 Yang-Mills 理論の対応関係 Polyakov et al• AdS/CFT 対応(弦/ゲージ双対性)と form factor およ
び大角度散乱と強結合領域での DIS 構造関数 Polchinski et al• String 理論でエネルギーについてベキ的振舞い 5 次元方向の寄与による warp factor
• AdS/QCD (Holographic QCD) spectrum, decay width, Pomeron, BFKL anom.dim.
Maldacena
QCD and String Theory
• MHV 振幅に対する Parke-Taylor 公式の拡張( spinor-helicity)
• Witten Commun.Math.Phys.252(2004)189 N=4 超対称理論で運動量空間から Fourier 変換で得た twistor space における散乱振幅を弦理論のインスタントンの寄与に結びつけた
• Cachazo-Svrcek-Witten (CSW) JHEP09(2004)006 最大にヘリシティーを破る (MHV) 振幅を vertex に拡張し,
一般の MHV でない helicity 振幅を計算するルールを与えた
• 任意の 1-loop multi-leg amplitudes A ~ (Box)+(triangle)+(bubble)+(tadpole)
multi-parton amplitudesMHV
+ +
+ +
-
• QCD は30有余年を経て確立 検証から精密化へ• Hadron 物理にとって必須の理論的枠組み• 標準模型の確立とそれを超えた Physics の探索に
は強い相互作用 QCD の効果の精密な評価が必要• pQCD は LHC での pp および重イオン衝突におけ
る新たな現象の解析に必須• ハドロン物理研究の新たなアイデアの創出• QCD は素粒子論と原子核理論の community を繋ぐ• 理論屋と実験家の collaboration@LHC,J-PARC…
Summary and Outlook
More efforts needed! Even for old boys!
Backup Slides
proton spin sum rule
quark orbital angular mom.
gluon orbital angular mom.
Nucleon’s total angular momentum
atSizable contributions are from gluon pol.Or from orbital angular mom. and
Asymptotic values from evolution eq.
Semi-inclusive Deep Inelastic Scattering (SIDIS)
Transverse-spin asymmetry at leading-twist in SIDIS
fragmentation function : Collins function
Transverse distribution in the initial stateSivers function
Final-state interaction important for Sivers fn. not to vanish Earlier claim was that Sivers asymmetry vanish time reversal inv.
Wilson lines in the op. def required by gauge inv.
Generalized Parton distribution (GPD)
Deeply virtual Compton
scattering (DVCS)
non-forward proton matrix elements can be measured at
skewdness parameter
Bjorken variable
null vector
See Wakamatsu’s talk
: Generalized Parton distribution (GPD)
Experimentally knownLattice calculation Not in accordance with exp.
Spin-dependent fragmentation function
@BELLE at KEK
Chiral-odd fragmentation function e.g. Collins function
e+e- collider KEK-B at Tsukuba
unpolarized Collins function
See Seidl’s talk
Buza-Matiounine-Smith-van Neerven (BMVN) prescription