Nucleon tomography through exclusive and semi-inclusive processes
Theory Introduction to Semi-Inclusive Physics
description
Transcript of Theory Introduction to Semi-Inclusive Physics
Theory Introductionto
Semi-Inclusive Physics
Jianwei QiuBrookhaven National Laboratory
Jefferson Lab (Jlab) 2014 Joint Hall A/C Summer Meeting JLab, Newport News, VA, June 4-5, 2014
DIS vs. SIDIS Inclusive DIS – one scattering plane:
EE’
Localized probe:
Two independent variables:
Semi-inclusive DIS (SIDIS) – two scattering planes: Leptonic plane:
Hadronic plane:
Angle between two planes:
Path of the color flow
Semi-inclusive DIS Naturally, two scales:
high Q – localized probeTo “see” quarks and gluons
Low pT – sensitive to confining scaleTo “see” their confined motion
Confinedmotion
Theory – QCD TMD factorization
Spin-motion correlation:
4 spin combinations
4 spin combinations
Various TMDs: vector, axial vector, tensor
Needs
TMDs – role of spin and motion Rich quantum correlations:
8 leading power (twist) quark TMDs:
Similar for gluons
Quantum correlation between hadron and parton
Sivers effect – between hadron spin and parton motion:
Hadron spin influences parton’s transverse motion
Sivers functionoObservedparticle
Parton’s transverse spininfluence its hadronization
Collins functionTransversity
Collins effect – between parton spin and hadronization:
Observedparticle
JLab12, COMPASS, and low energy EIC for valence, EIC@US covers the sea and gluon!
SIDIS – the best for probing TMDs Naturally, two planes:
1( , )
sin( ) sin( )
sin(3 )
l lUT h S
h SSiverCollins
Pretzelosi
UT
tyU
sUT h S
h ST
N NAP N
A
ANA
1
1 1
1
1 1
sin( )
sin(3 )
sin( )Co
PretzelosityU
SiversUT
llins
T h S T
h S
UT
UT h S
TU
UT
TA
H
f
A
D
A h H
h
Collins frag. Func. from e+e- collisions
Separation of TMDs:
Very hard, if not impossible, to separate TMDs in hadronic collisions
Using a combination of different observables (not the same observable): jet, identified hadron, photon, …
QCD corrections Sources of parton kT at the hard collision:
Gluon shower
Confined motion
Emerge of a hadronhadronization
Parton kT generated by the shower caused by the collision:
Input distribution for the Q2 evolution - nonperturbative
“True” parton structure:
Has very little to do with the kT in hadron wave function – hadron structure At large Q2 and collision energy (large phase space), the shower generated kT could be perturbative Q2 – evolution of the cross section
Factorization for SIDIS Leading power contribution:
Low PhT – TMD factorization:
High PhT – Collinear factorization:
PhT Integrated - Collinear factorization:
TMD fragmentation
Soft factors
TMD parton distribution
Modified Universality of TMDs TMD distributions with non-local gauge links:
Parity + Time-reversal invariance:
The sign change is a critical test of TMD factorization approach
Evolution of TMDs Evolution in the b-space – Fourier transform of
kT:
RG equations:
Evolution equations for Sivers function:
CS:RGs:
Boer, 2001, 2009, Idilbi, et al, 2004Aybat, Rogers, 2010Kang, Xiao, Yuan, 2011Aybat, Collins, Qiu, Rogers, 2011Sun, Yuan, 2013…
Numerical “prediction” for evolution Aybat, Prokudin, Rogers, 2012:
Sun, Yuan, 2013:
Huge Q dependence
Smaller Q dependence
No disagreement on evolution equations!Issue: extrapolation to non-perturbative large b-region
choice of the Q-dependent “form factor” – more work needed!!!
World effort on TMDs
Partonic scattering amplitudeFragmentation amplitudeDistribution amplitude
proton
lepton lepton
pion
Drell-Yan
BNLJPARCFNAL
proton
proton lepton
antilepton
EIC
SIDIS
electron
positron
pion
pion
e–e+ to pions1 1(SIDIS) (DY)h h
BESIII
1 1(SIDIS) (DY)q qT Tf f
Test of the sign change!
Transition from low pT to high pT
TMD factorization to collinear factorization:
TMD Collinear Factorization
Two factorization areconsistent in the overlap
region where
Quantum interference – high pT region (integrate over all kT):
Non-probabilistic quark-gluon quantum correlation
Single quark state quark-gluon composite state
(Spin flip)interfere with
Kang, Yuan, Zhou, 2010
Twist-3 correlation functions Twist-2 parton distributions:
Unpolarized PDFs:
Polarized PDFs:
Two-sets Twist-3 correlation functions:
Kang, Qiu, PRD, 2009
Role of color magnetic force!
Evolution of twist-3 correlation functions
Closed set of evolution equations (spin-dependent):
Plus two more equations for:
and
Kang, Qiu, 2009
Sample scale dependence of twist-3 correlations
Follow DGLAP at large x Large deviation at low x (stronger correlation)
Kang, Xiao, Yuan, 2011Matching between low pT (resum) and high pT (fixed)
Kang, Qiu, 2009
Single-spin asymmetry in hadronic collisions Consistently observed for over 35 years!
ANL – 4.9 GeV BNL – 6.6 GeV FNAL – 20 GeV BNL – 62.4 GeV
BNL – 200 GeV Definition:
Do we understand it? Early attempt:
QCD factorization at twist-3:
2Kane, Pumplin, Repko, PRL, 1978
Cross section:
Asymmetry:
Too small to explain available data!Qiu and Sterman, NPB, 1991
Sivers - type
Collins - type
Kang, Qiu, Vogelsang, Yuan, 2011 Sivers function and twist-3 correlation:
+ UVCT
“direct” and “indirect” twist-3 correlation functions: Calculate Tq,F(x,x) by using the measured Sivers functions
direct
directindirect
indirect
A sign “mismatch” if keeps only Sivers-type
Important role of Collins’ effect to single pion production – twist-3 FFsMetz & Pitonyak, 2013
SIDIS – separate two effects by difference in angular distribution
Flavor structure of the proton sea The proton sea is not SU(3) symmetric!
Violation of Gottfried sum rule Confirmed by Drell-Yan exp’t
Why ? Why does change sign?
Future experiments:
Challenges for d(x) – u(x) All known models predict no sign change!
Meson cloud Chiral-quark soliton model Statistic model
Fermilab E906
What is the ratio asx increases?
Very important non-perturbative physics
Asymmetry between strange and up/down sea?
LO and NLO QCD global fitting to DIS data:for x > 0.1
New LHC data on W/Z data:with
HERMES data:
Does not follow the shape of u(x) + d(x)?Why strange sea behave so different?
PT-integrated SIDIS:Need FFs
Hadronization puzzle
How do hadrons emerge from a created quark or gluon?How is the color of quark or gluon neutralized?
Emergence of hadrons:
Need a femtometer detector or “scope”:Nucleus, a laboratory for QCDEvolution of partonic properties
Strong suppression of heavy flavors in AA collisions:
Nucleus as a “detector”
THE “VERTEX” DETECTORAT A FERMI SCALE
Need a good control of the kinematics of fragmenting parton
Almost impossible for a hadron machine
Nucleus in SIDIS is
an ideal “vertex” detector
Color neutralization – energy loss Unprecedented ν range at EIC:
semi-inclusiveDIS
Heavy quark energy loss:- Mass dependence of fragmentation
pion
D0 Need the collider energy of EICfor heavy flavors
Control of ν and medium length!
π
D0
PT broadening of leading hadron in SIDIS
Definition:
Color fluctuation – azimuthal asymmetry Preliminary low energy data: Hicks, KEK-JPAC2013
Contain terms in cos(φpq) and cos(2φpq) only statistical uncertainties shown Classical expectation:
Any distribution seen in Carbon should be washed out in heavier nuclei Surprise:
Azimuthal asymmetry in transverse momentum broadeningSpin-”orbital” correlation + soft multiple scattering Qiu & Pitonyak
In preparation
SIDIS’ role in probing the gluon saturation
Strong suppression of dihadron correlation in eA@EIC:
Never been measured! Directly probe Weizsacker-Williams (saturated) gluon distribution in a large nucleus A factor of 2 suppression of away-side hadron-correlation! No-sat: Pythia + nPDF (EPS09)
ϕ12
Theory Simulation
Summary
SIDIS in eP offers many more better controlled observables to probe QCD’s confining features and hadron’s partonic structure
A future EIC@US could help continue to keep the US’s leadership position in nuclear physics and …
SIDIS in eA collision is ideal for probing “hadronization”, “color neutralization”, QCD energy loss, …
Thanks!
JLab12 is excellent for the valence region, while a future EIC will cover the sea and gluon
From 3D confined motion to quantum interference of different parton statesBest channel for probing TMDs
Electron-Ion Collider (EIC) A giant “Microscope”
A sharpest “CT”
To “see” quarks and gluons
To “cat-scan” nucleons and nuclei