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Transcript of Hadron Physics
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Hadron Physics
NNPSS 2009 1E. Beise, U Maryland
Lecture #1: The quark model, QCD, and hadron spectroscopy
Lecture #2: Internal structure of hadrons: momentum and spin
Lecture #3: Internal structure of hadrons: charge, magnetism, polarizability
Lecture #4: Hadrons as laboratories (and other miscellaneous topics)
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Properties of hadrons: momentum and spin
Structure functions and Deep Inelastic Electron Scattering
spin and flavor structure
Other processes:Semi-inclusive scattering, transversityDeeply Virtual Compton Scattering & Generalized
Parton Distributions
04/19/20232
E. Beise, U Maryland
“quark model” vs “partons”
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references for this sectionHalzen & Martin: Quarks and LeptonsF.E. Close: An Introduction to Quarks and PartonsPerkins: Introduction to High Energy PhysicsCahn and Goldhaber: The Experimental Foundations of Particle Physics
Xiangdong Ji: Graduate nuclear physics lecture noteshttp://www.physics.umd.edu/courses/Phys741/xji/lecture_notes.htm
Lectures from the Hampton University Graduate School (HUGS), particularly 2007 (Reno), 2008 (Elouadhriri) and 2009 (Burkardt)
http://www.jlab.org/hugs/archive/
Special thanks toZein-Eddine Meziani, Temple UniversityNaomi Makins, University of Illinois
04/19/2023 3E. Beise, U Maryland
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1930’s:
(Chadwick NP 1935)(Stern NP 1943)
1950’s:
proton charge radius from (e,e’) (Hofstadter NP 1961)
1970’s:
partons in proton via inelastic (e,e’) (Friedman,Taylor,Kendall, NP 1990)asymptotic freedom QCD(Gross, Politzer, Wilcek, NP 2004)
1990’s:
polarized targetsIntense CW electron beamsimprovement in polarized e sources
mp ~ 3 mN
rp ~ 1 fm
2000’s:
lattice QCDGeneralized Parton Distributionstransversity, DVCS, moments, ….
1980’s: exploration of phenomenavarious scaling phenomena“the spin crisis”“the EMC effect”
04/19/2023 4E. Beise, U Maryland
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Deep Inelastic Electron ScatteringM. Briedenbach et al, Phys Rev Lett 23, 935 (1969)
from J. Friedman Nobel lecture, 199004/19/2023 5E. Beise, U Maryland
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Kinematics of electron scattering
p
k’k
p’
qm
A common reference frame to work in is the LAB frame with a stationary target:
'),(
cos'ˆˆ
)','('),(
)',(')0,(
kkqq
kk
kEkkEk
pEpMp R
)0(2222 Qqq
It is common to assume the electron is massless (extreme relativistic limit). In this case, if one conserves 4-momentum:
EMMkMEWs 2)( 2222
and can easily show:
222 sin'4 EEQ
case 1: elastic scattering
'EE 04/19/2023 6E. Beise, U Maryland
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Inelastic electron scattering
Wl
E
E
QdEd
d '4
2
Using Fermi’s Golden rule, we integrate over the recoiling target quantities, average over initial spin states, sum over final spin states. For elastic scattering, we integrate over an energy-conserving delta function. For inelastic scattering we skip the last step.
p
k’k
p’
qminteraction strength and photon propagation
lepton current '
21 )','(),(),()','(
s
skuskuskuskul
'2 43
21 pqpPJXXJPW
X
hadron current
)(]?)['( pupuJ
outgoing may no longer be a proton
04/19/2023 7E. Beise, U Maryland
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the hadronic current)(]?)['( pupuJ
Elastic scattering: the target is left intact and we measure its net response to the EM current as a function of momentum transferred to it by the photon.
qiQFM
QF )(2
)(]?[ 22
21
Inelastic scattering: target might to into an excited state, or break up
2222
21
'
q
qpqp
q
qpqp
M
W
q
qqgW
XJPXJPW
where in principle W1 and W2 depend on both Q2 and energy loss ( ). n These
encode all of the strong interaction dynamics between the partons.
04/19/2023 8E. Beise, U Maryland
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Unpolarized electron scattering, cont’d
after some manipulation, the cross section becomes
222
12
22
42
2
2
2
tan,2,sin
cos
4
QWQWEdEd
d
This is the famous “Rosenbluth” formula. Often this is also expressed in terms of helicity of the photon being exchanged.
... LTdEd
d
sMott
,0,0,1
0
0,,1,02
11
2
2
i
photon polarization, wrt q
virtual photon “flux” photoabsorptioncross sections
04/19/2023 9E. Beise, U Maryland
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Deep Inelastic Electron Scattering
222
12
2 tan,2, QWQW
d
d
Edd
d
Mott
2
22
hhtgtbeam EEEEWs
energy available to produce particles in final state
Experimentally, W2 and W1 seem to depend on only one variable
“scaling” (anticipated by Bjorken, 1967)
from Nobel lectures, 1990
)(2)(
)(,
)(,
12
22
2
12
1
xxFxF
xFQWM
xFQW
1,10,
2
2
partonstgt
xxM
Qx
scaling good when (Q2,n) →, and if the partons have no transverse momentum .
04/19/2023 10E. Beise, U Maryland
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DIS and quark momentum distributionsx = fraction of proton’s momentum carried by individual quark(in reference frame where proton moving ~ speed of light…)
)()()()(9
1)()(
9
4)(
)()()()(2)(
2
212
xsxsxdxdxuxuxxF
xfexPxxPxxFxF
p
quarksii
parton distribution functions
proton:
The scaling behavior is good when (Q2,n) →, and holds in the limit that the quark transverse momentum is 0.
)()()()(
9
1)()(
9
4)(2 xsxsxuxuxdxdxxF n
If isospin symmetry is good, which says that u in the neutron is just like d in the proton:
04/19/2023 11E. Beise, U Maryland
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interpretation of parton distributionsx = fraction of the proton’s momentum carried by the struck quark, in the “infinite momentum”frame
i
i xxfdx 1)(
p
xp
(1-x)p
q
limits:1
02
2 xp
n
F
F
4
11
2
2 xp
n
F
F
at very low x, the sea quarksshould dominate
here the valence quarks should dominate and uv >> dv .
04/19/2023 12E. Beise, U Maryland
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parton distribution functions
The parton distribution functions are a property of the target, not of the process.
partons pointlike quarks
Phys. Rev. Lett. 23, 1415 - 1417 (1969)
04/19/2023 13E. Beise, U Maryland
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quark distribution functionsF2(x) “scaling” is violatedwhen the strong interaction is “strong” (low x or small Q2)
1
0
5.0)( dxxPquarks
04/19/2023 14E. Beise, U Maryland
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parton flavors
from http://pdg.lbl.gov
04/19/2023 15E. Beise, U Maryland
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Deep Inelastic nucleon scattering
xxFy
yxxFy
xFyEMG
dxdy
d NF
31
2
2
22
2
12
21
beamtgt E
vy
M
Qx ,
2
2
F1,2,3 are weak interaction equivalents of those measured in electron
scattering. Experimentally, they seem again to only depend on x (to lowest order) and are combinations of quark momentum distributions.
/
hadronsnucleon
quarks
ixPxPxxPxF )()()()(2
Experimentally, for target w/equal numbers of neutrons and protons:
)(5
18)( 22
xFxF e(if ignore s-quarks...)
04/19/2023 16E. Beise, U Maryland
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NuTeV: deep inelastic scattering
http://home.fnal.gov/~bugel/tour.html
SSQT: series of magnets selects charge state of p,K
p
ee 2
04/19/2023 17E. Beise, U Maryland
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neutrino scattering: F3(x)
M. Tzanov, et al., Phys. Rev. D 74 (2006) 012008
)()(2
)()(2
)()(2
)()(2
3
2
3
2
xdxuF
xdxuxF
xuxdF
xuxdxF
04/19/2023 19E. Beise, U Maryland
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NuTeV s-quark momentum distributions
RR WCCCC
NCNC
2sin
2
1
)s(
9
4s
3
71 2
212
Ws
W
vvvv
vv
dxdux
dxssx
dxdux
dxduxNR
see also http:// home.fnal.gov/~gzeller/nutev.html
0013.00013.0
dxssxS
NuTeV fit (NLO)
0 0.1 0.2 0.3 0.4 0.5
x
0.01
0
-0.01
-0.02
-0.03
-0.04
x[s(
x)-s
(x)]
CTEQ6M, NLONuTeV D. Mason et al, hep-ex/0405037
from this they extract sin2qW
04/19/2023 20E. Beise, U Maryland
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The Drell-Yan process: antiquarks
1 2 1 2
1 2 1 2
4 1( ) ( ) ( ) ( )
9 94 1
( ) ( ) ( ) ( )9 9
pp
pn
u x u x d x d x
u x d x d x u x
FNAL E866: E. Hawker, etal, PRL 80 (1998) 3715
FNAL E906: scheduled for 2010
future program at J-PARC
04/19/2023 21E. Beise, U Maryland
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sum rules
counts the net excess of quarks over anti-quarks of each type
Gross-Llewellyn-Smith sum rule: counts the excess quarks over anti-quarks, as seen by neutrinos
2)()( 22
1
0
xFxFx
dx pn Adler sum rule (neutrinos)
3
1)()( 22
1
0
xFxFx
dx enep Gottfried sum rule (electrons)
V
Aenenepep
g
gxFxAxFxA
x
dx
3
1)()()()( 22
1
0
Bjorken sum rule (axial charge)
04/19/2023 22E. Beise, U Maryland
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The hadronic tensor with spin-dependencehttp://pdg.lbl.gov
04/19/2023 23E. Beise, U Maryland
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Spin Structure Functions
Unpolarized structure functions F1(x,Q2)
and F2(x,Q2)
Polarized structure functions
g1(x,Q2) and g2(x,Q2)
Q2 :Four-momentum transferx : Bjorken variable : Energy transferM : Nucleon massW : Final state hadrons mass
L
T
U
(slide from Z. Meziani)
iiiii
ii xqexqxqexg )()()()( 2
212
21
1
04/19/2023 24E. Beise, U Maryland
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Polarized Deep Inelastic Scattering
Semi-inclusive asymmetry
q(x) = q(x)+ – q(x)–
q(x) = q(x)+ + q(x)–
+ quark nucleon
– quark nucleon
q~
q~
)Q,x(F
)Q,x(g
)Q,x(q e
)Q,x(q e)Q,x(A
21
21
2
q
2q
2
q
2q2
1
)Q,z(D)Q,x(q e
)Q,z(D)Q,x(q e)Q,z,x(A
2hq
2
q
2q
2hq
2
q
2q
hh
hh2h
1
Inclusive asymmetry
04/19/2023
fragmentation function
25E. Beise, U Maryland
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Many experiments…..
SLAC:E80, E130,E142, E154,and others…
CERN:EMC,SMC, COMPASS
Brookhaven:RHIC-Spin program gluon spin
DESY:HERMES
JLAB:Hall A, Hall B
04/19/2023 27E. Beise, U Maryland
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A relatively simple magnetic spectrometer
drift chambers
plastic scintillator arrays
aerogel Cerenkov
electromagneticshower detector
High MomentumSpectrometer,Hall C,Jefferson Lab
04/19/2023 28E. Beise, U Maryland
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Example of a standard setup (in Hall A at JLab)
Polarized beamEnergy: 0.86-5.1 GeVPolarization: > 70%Average Current: 5 to 15 µA
Hall A polarized 3He targetPressure ~ 10 atmPolarization average: 35%Length: 40 cm with 100 µm thickness
Measurement of helicity dependent 3He cross sections Extract g1 and g2 spin structure functions of 3He Extract moments of spin structure functions of 3He and Neutron
Highest polarized luminosity: ~1036cm-2s-1
L
Spectrometersset at 15.5º
Electron beam
R
Hall A polarized 3He target
(slide from Z. Meziani)
04/19/2023 29E. Beise, U Maryland
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COMPASS NIM A 577(2007) 455
160 GeV m
SciFiveto
6LiD target
Si Micromegas
Drift Chambers
GEMs
Straws
SM1
RICH
ECALs & HCALs
m Filters/ Walls
Trigger Hodoscopes
MWPCs
50 mSM2
O. Kouznetsov, CIPANP 2009
04/19/2023 30E. Beise, U Maryland
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HERMES detector at DESY (Hamburg)
04/19/2023 31E. Beise, U Maryland
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Polarized Electrons
Reverse pol’n of beam at rate of 30 Hz
Feedback on laser intensity and position at high rate
Electron retains circular polarization of laser beam: Pe ~ 85%
See also Physics Today, Dec 2007
D.T. Pierce et al., Phys. Lett. 51A (1975) 465.
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( In CLAS detector in Hall B at JLab,slide from K. Griffeon, DIS2007)
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Polarized 3He
p p
n
Spin –dependent scattering
eHe 3
ne
looks like
photo from G. Cates, CIPANP 2009used in Hall A at JLab
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spin structure of the neutron and proton
04/19/2023
from http://pdg.lbl.gov
35E. Beise, U Maryland
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spin structure of the proton
04/19/2023
example: HERMES
A. Airapetian, et al. PRD 71 (2005) 012003
Uses semi-inclusive scattering aswell to disentangle u,d,s and valence/sea
009.0033.0028.0
011.0033.0054.0
050.0039.0226.0
029.0036.0002.0
049.0039.0601.0
s
d
d
u
u
36E. Beise, U Maryland
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a twist-2 term (Wandzura & Wilczek, 1977):
a twist-3 term with a suppressed twist-2 piece (Cortes, Pire & Ralston, 1992):
Twist -2 Twist -3
Transversityq-g correlations
g2 and Quark-Gluon Correlationsg2 and Quark-Gluon Correlations
(QCD & Hadron Physics Town meeting, Rutgers)
coming in the future….
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Measurement of the gluon polarization DG at RHIC
Courtesy of G. Bunce, S. Vigdor
Dominates at high pT
Dominates at low pT
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Structure of the nucleon – valence region
Courtesy of Z.-E. Meziani, K. Griffioen, S. Kuhn, G. Petratos
Helicity conservationd/u = 1/5
Scalar diquarkdominanced/u=0
SU(6)d/u=1/2
proposed to be done at JLAB with 11 GeV beam
coming in the future….
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quark angular momentum
04/19/2023
lattice QCD (LHPC, QCDSF)Lu + Ld small, but individual parts large
gq JL 2
1
quark spins 30%
gluon polarizationsmall but still uncertain
??
40E. Beise, U Maryland
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GPDs: Non-local, off-diagonal matrix elements
(x + ξ) and (x - ξ) : longitudinal momentum fractions of quarks
The structure of the nucleon can be described by 4 Generalized Parton Distributions :
Vector : H (x, ξ ,t)
Tensor : E (x, ξ ,t)
Axial-Vector : H (x, ξ ,t)
Pseudoscalar : E (x, ξ ,t)
~
~
x + ξ x - ξ
P - Δ/2 P + Δ/2GPD (x, ξ ,t)
Mueller
(1995)
slide from F. Sabatie, CIPANP 2009
, ,
g r pK,…
.
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Properties, applications of GPDs
first moments : nucleon electroweak form factors
ξ-independence :
Lorentz invariance
P - Δ/2 P + Δ/2
Δ
Pauli
Dirac
axial
pseudo-scalar
forward limit : ordinary parton distributions
unpolarized quark distributions
polarized quark distributions
: do NOT appear in DIS … new information
They contain what we know already through sum rules and kinematical limits: Form Factors, parton distributions
slide from F. Sabatie, CIPANP 2009
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Generalized Parton Distributions
Elastic Scatteringtransverse quark distribution in coordinate space
DISlongitudinal
quark distributionin momentum space
DES (GPDs)fully-correlated
quark distribution in both coordinate and
momentum space
GPDs yield 3-dim quark structure of the nucleon
Burkardt (2000, 2003)
Belitsky, Ji, Yuan (2003)
slide from F. Sabatie, CIPANP 2009
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CHL-2
Upgrade magnets and
power supplies
Enhance equipment in existing halls
JLab at 12 GeV new Hall
plan:construction 2009-2013begin physics 2014
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Overview of 12 GeV Physics Program
Hall C – precision determination of valence quark properties in nucleons and nuclei
Hall A – short range correlations, form factors, hyper-nuclear physics, future new experiments
Hall D – exploring origin of confinement by studying exotic mesons
Hall B – understanding nucleon structure via generalized parton distributions
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04/19/2023 51E. Beise, U Maryland
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Summary of this section
04/19/2023 E. Beise, U Maryland 52
Lepton scattering and parton distributions explicitly reveal the intracacies of hadron structure, and the inadequacy of the simple quark model
Decades of precision data now give a clear picture of flavor and spin, particularly in the regime where QCD is a perturbative theory.
Still to be understood are the “motional” dynamics (orbital motion), the full role of gluons, and how to numerically make the transition from a perturbative to a non-pertubative theory.