Transcript Polarization Observables with Circularly

VI
International Conference on
Quarks and Nuclear Physics
Philip L Cole
Idaho State University
April 17, 2012
Motivation
L2I 2J
N*
L
J.J.Dudek and R.G.Edwards, Hybrid Baryons in QCD
arXiv:1201.2349[hep-ph] (January 10, 2012)
Photo & Electroproduction
• Difficulties (New Opportunities)
– Access to N* structure
– Non-perturbative strong interactions
responsible for formation of N*s
– A lot of resonances could be present
in a relatively narrow energy region
– Nonresonance background is almost
equally as complicated
• Experiments
–
–
–
–
Jefferson Lab (USA)
MAMI (Germany)
ELSA (Germany)
ESRF (France)
– SPring-8 (Japan)
–
¶
BES (China) ¶
A unique way of studying the baryon spectrum and
N* hadronic decays is via BES: J/ψ  N*,…
CLAS and JLab
e/
p
/
q
ee
Studying N*s gives insight into structure
Indeed in the words of the theorist, Craig Roberts:
“there is no greater challenge in the Standard Model, and few in physics, than learning to
understand the truly non-perturbative long-range behavior of the strong interaction.”
Electromagnetic Excitation of N*s
The experimental N* Program has two major components:
1) Transition helicity amplitudes of known resonances to study their
internal structure and the interactions among constituents, which
are responsible for resonance formation.
2) Spectroscopy of excited baryon states, search for new states.
•
Both parts of the program are being pursued in various meson photo and
electroproduction channels, e.g. Nπ, pη, pπ+π-, KΛ, KΣ, pω, pρ0 using cross
sections and polarization observables.
•
Global analysis of ALL meson photo- and electroproduction channels – within
the framework of an advanced coupled-channel approach developed by EBAC
(Excited Baryon Analysis Center – JLab).
Physics Goals for CLAS6
Announcement of Firsts from CLAS
• First electroproduction data:
• channels: p+n, p0p, and hp
• Q2 evolution information on the gvNN* electrocouplings
for the states: P33(1232), P11(1440), D13(1520), and
S11(1535) for Q2 < 5.0 GeV.
I.G. Aznauryan et al., (CLAS Collaboration) Phys. Rev. C80, 055203 (2009).
• We recently published the preliminary (first) results on the
electrocouplings of the states P11(1440), D13(1520), S31(1620),
P13(1720), and D33(1780) at Q2 < 0.6 GeV2 in Npp electroproduction from protons
V.I. Mokeev, I.G. Aznauryan, V.D. Burkert, arXiv:1109.1294 [nucl-ex] +
I.G. Aznauryan, V.D. Burkert, V.I. Mokeev, arXiv:1108.1125 [nucl-ex]
Number of data points >116000, W<1.7 GeV, 0.15<Q2<6.0 GeV2 ,
almost complete coverage of the final state phase space.
Observables
Q
2
Number of
data points
Range [GeV2]
dσ/dΩ(π0)
dσ/dΩ(π+)
Ae(π0) , At(π0)
Ae(π+) , At(π+)
Aet(π0)
0.16-1.45
3.0-6.0
39830
9000
0.25-0.60
1.7-4.3
25588
30 849
0.25-0.65
3981
0.40-065
1.7 - 3.5
1730
3 535
0.25-0.61
1521
All datasets can be found in:
I. Aznauryan et al.,
PRC 71, 015201 (2005);
PRC 72, 045201 (2005).
I. Aznauryan et al.,
PRC 78, 045209 (2008).
I.G.Aznauryan, V.I Mokeev,
V.D. Burkert (CLAS Collaboration),
PRC 80. 055203 (2009).
/
Why Np/Npp electroproduction channels are important
• Np/Npp channels are the two major
contributors in N* excitation region;
• these two channels combined are
sensitive to almost all excited proton
states;
• they are strongly coupled by
pN→ppN final state interaction;
• may substantially affect exclusive
channels having smaller cross
sections, such as hp,KL, and KS.
Therefore knowledge on
Np/Npp electroproduction
mechanisms is key for the
entire N* Program
CLAS data on meson electroproduction at Q2 < 4.0 GeV2
How N* electrocouplings can be accessed
• Isolate the resonant part of production amplitudes by fitting the
measured observables within the framework of reaction models,
which are rigorously tested against data.
• These N* electrocouplings can then be determined from resonant
amplitudes under minimal model assumptions.
p, h, pp,..
e’
e
p, h, pp,..
γv
N*,△
N’
N
A3/2, A1/2, S1/2
GM, GE, GC
+
γv
lgp1/2
gv
N
N
N’
lgp3/2
Non-resonant
amplitudes.
Consistent results on N* electrocouplings obtained in analyses of various
meson channels (e.g. πN, ηp, ππN) with entirely different non-resonant
amplitudes will show that they are determined reliably
Advanced coupled-channel analysis methods are being developing at EBAC: B.Julia-Diaz,
T-S.H.Lee et al., PRC76, 065201 (2007);T.Sato and T-S.H.Lee arXiv:0902.353[nucl-th]
G.V.Fedotov et al., PRC 79 (2009), 015204
Full JM calc
p-D++
p+D0
2p direct
M.Ripani et al., PRL 91 (2003), 022002
p+D13(1520)
p+F15(1685)
rp
• Any contributing mechanism has considerably different shapes of cross sections
in various observables defined by the particular behavior of their amplitudes.
• A successful description of all observables allows us to check and to establish the
dynamics of all essential contributing mechanisms.
Hadron Structure with Electromagnetic Probes
Allows to address central question:
What are the relevant degrees-of-freedom
at varying distance scale?
resolution
of probe
N,N*,D,D*
low
q
3-q core+
MB cloud
3-q core
quark mass (GeV)
p,r,w,..
LQCD/DSE
pQCD
high
e.m. probe
Effects of Meson-Baryon Dressing
One third of G*M at low Q2 is
due to contributions from
meson–baryon (MB) dressing:
Data from exclusive π0 production
bare quark core
Within the relativistic Quark Model
framework [B.Julia-Diaz et al., PRC
69, 035212 (2004)], the bare-core
contribution is reasonably
described by the three-quark
component of the wavefunction
GD =
Q2=5GeV2
1
(1+Q2/0.71)2
The P11(1440) electrocouplings from the CLAS
data
Quark models:
I. Aznauryan LC
S1/2
S. Capstick LC
Relativistic
covariant
approach by
G.Ramalho/F.Gross .
A1/2
EBAC-DCC
MB dressing
(absolute values).
p+pp
2010
p+pp
2011
Np
.
A3/2
A1/2
MB dressing abs val. (EBAC)
S1/2
M.Giannini/E.Santopinto
hCQM
The data on A1/2 electrocoupling at Q2>2.0 GeV2 for the first time offer almost direct access
to quark core. They are of particular interest for the models of N* structure based on QCD .
CLAS12 JLab Upgrade to 12 GeV
Luminosity > 1035cm-2s-1
• General Parton Distributions
• Transverse parton distributions
• Longitudinal Spin Structure
• N* Transition Form Factors
• Heavy Baryon Spectroscopy
• Hadron Formation in Nuclei
Solenoid, ToF,
Central Tracker
Forward Tracker,
Calorimeter,
Particle ID
• explore the interactions between
the dressed quarks, which are
responsible for the formation for
both ground and excited
nucleon states.
Q2 = 12 GeV2
• probe the mechanisms of light
current quark dressing, which is
responsible for >97% of nucleon
mass.
Approaches for theoretical analysis of N*
electrocouplings: LQCD, DSE, Ads/CFT
relativistic quark models. See details in the
62-page White Paper of EmNN* JLAB
Workshop, October 13-15, 2008:
http://www.jlab.org/~mokeev/white_paper/
Aznauryan et al., arXiv:0907.1901[nucl-th]
Independent QCD Analyses
Line Fit: DSE Points: LQCD
Need to multiply by 3p2
to get the Q2 per quark
CLAS12
Projections for N* Transitions
For the foreseeable future, CLAS12 will be the only facility worldwide, which
will be able to access the N* electrocouplings in the Q2 regime of 5 GeV2 to
10 GeV2, where the quark degrees of freedom are expected to dominate.
Our experimental proposal “Nucleon Resonance Studies with CLAS12” was
approved by PAC34 for the full 60-day beamtime request.
http://www.physics.sc.edu/~gothe/research/pub/nstar12-12-08.pdf.
CLAS published
CLAS published
CLAS PRL subm.
CLAS12 projected
CLAS preliminay
CLAS12 projected
Nucleon Resonance Studies with CLAS12
R. Arndt4, H. Avakian6, I. Aznauryan11, A. Biselli3, W.J. Briscoe4, V. Burkert6,
V.V. Chesnokov7, P.L. Cole5, D.S. Dale5, C. Djalali10, L. Elouadrhiri6, G.V. Fedotov7,
T.A. Forest5, E.N. Golovach7, R.W. Gothe*10, Y. Ilieva10, B.S. Ishkhanov7,
E.L. Isupov7, K. Joo9, T.-S.H. Lee1,2, V. Mokeev*6, M. Paris4, K. Park10,
N.V. Shvedunov7, S. Stepanyan6, P. Stoler8, I. Strakovsky4, S. Strauch10,
D. Tedeschi10, M. Ungaro9, R. Workman4, and the CLAS Collaboration
JLab PAC 34, January 26-30, 2009
Approved for 40 days beamtime
Argonne National Laboratory (IL,USA)1, Excited Baryon Analysis Center (VA,USA)2,
Fairfield University (CT, USA)3, George Washington University (DC, USA)4,
Idaho State University (ID, USA)5, Jefferson Lab (VA, USA)6,
Moscow State University (Russia)7, Rensselaer Polytechnic Institute (NY, USA)8,
University of Connecticut (CT, USA)9, University of South Carolina (SC, USA)10,
and Yerevan Physics Institute (Armenia)11
Spokesperson
Contact Person*
21
V.M. Braun8, I. Cloët9, R. Edwards5, M.M. Giannini4,7, B. Julia-Diaz2, H. Kamano2,
T.-S.H. Lee1,2, A. Lenz8, H.W. Lin5, A. Matsuyama2, M.V. Polyakov6, C.D. Roberts1,
E. Santopinto4,7, T. Sato2, G. Schierholz8, N. Suzuki2, Q. Zhao3, and B.-S. Zou3
JLab PAC 34, January 26-30, 2009
Argonne National Laboratory (IL,USA)1,
Excited Baryon Analysis Center (VA,USA)2,
Institute of High Energy Physics (China)3,
Istituto Nazionale di Fisica Nucleare (Italy)4,
Jefferson Lab (VA, USA)5,
Ruhr University of Bochum (Germany)6,
University of Genova (Italy)7,
University of Regensburg (Germany)8,
and University of Washington (WA, USA)9
Open invitation.
List is open to any and all who wish to participate!
22
The electroproduction cross sections and beam-spin asymmetries
of pπ, nπ, pη for W =1.1 – 2.0 GeV, Q2 < 12 GeV2 with full
coverage in cosθ*π,η and φ* π,η ;
9 single differential cross sections of the pπ+π- channels in the
energy range W =1.3 – 2.0 GeV, Q2 < 8 GeV2 with full angle
coverage
Thus armed, we can extract the electrocouplings for the
helicity amplitudes
, and
as a function of
for prominent nucleon and Δ states.
The results from our experiment will be used
by EBAC and the Theory Support Group for
our proposal to provide
• access to the dynamics of non-perturbative strong
interactions among dressed quarks and their emergence
from QCD and the subsequent formation into baryon
resonances;
• information on how the constituent quark mass arises
from a cloud of low-momentum gluons, which constitute
the dressing to the current quarks.
[This process of dynamical chiral symmetry breaking
accounts for over 97% of the nucleon mass]
• enhanced capabilities for exploring the behavior of the
universal QCD b-function in the infrared regime.
Thank you
BACKUP SLIDES
Dyson-Schwinger Equation (DSE) Approach
DSE provides an avenue to relate N* electrocouplings at high Q2 to
QCD and to test the theory’s capability to describe the N* formation
based on QCD.
DSE approaches provide a link between
dressed quark propagators, form
factors, and scattering amplitudes and
QCD.
N* electrocouplings can be determined
by applying Bethe-Salpeter /Fadeev
equations to 3 dressed quarks while the
properties and interactions are derived
from QCD.
By the time of the upgrade DSE electrocouplings of several excited nucleon states
will be available as part of the commitment of the Argonne NL and the University
of Washington.
P11(1440) electrocouplings from the CLAS data
on Np/Npp electroproduction
Npp
Np
Light front models:
I. Aznauryan
S. Capstick
hybrid P11(1440) [Q3g]
• Good agreement between the electrocouplings obtained from the Np and
Npp channels: Reliable measure of the electrocouplings.
• The electrocouplings for Q2 > 2.0 GeV2 are consistent with P11(1440)
structure as a 3-quark radial excitation.
• Zero crossing for the A1/2 amplitude has been observed for the first time,
indicating an importance of light-front dynamics.
• Hypothesis on the hybrid origin of P11(1440) has been ruled out.
Current Status of Lattice QCD
D(1232)P33
N(1440)P11
LQCD calculations of the D(1232)P33 and N(1440)P11 transitions have been carried out with
large p-masses.
By the time of the upgrade LQCD calculations of N* electrocouplings will be extended to Q2 =
10 GeV2 near the physical p-mass as part of the commitment of the JLAB LQCD and EBAC
groups in support of this proposal.
JLAB-MSU meson-baryon model (JM) for N* electrocoupling extraction from the
p+p-p electroproduction data
V. I. Mokeev , V.D. Burkert, T.-S.H. Lee et al., Phys. Rev. C80, 045212 (2009)
Isobar channels included:
3-body processes:
p-D++
• All well established N*s with pD decays
and 3/2+(1720) candidate.
• Reggeized Born terms with effective FSI
and ISI treatment (absorptive
approximation).
• Extra pD contact term.
r0p
•All well established N*s with rp decays and
3/2+(1720) candidate.
•Diffractive ansatz for non-resonant part and
r-line shrinkage in N* region.
Unitarized Breit-Wigner anstaz for resonant amplitudes.
JLAB-MSU meson-baryon model (JM) for N* electrocoupling extraction from the
p+p-p electroproduction data
3-body processes:
(p )
(P++33(1640))
F015(1685)
(p+)
Isobar channels included:
• p+D013(1520), p+F015(1685), p-P++33(1640)
isobar channels observed for the first time
in the CLAS data at W > 1.5 GeV.
Evidence for p+D013(1520) isobar channel in the CLAS p+p-p data
full JM results with
p+D013(1520) implemented
W=1.74 GeV Q2=0.65 GeV2
full JM results without
p+D013(1520) and adjusted
direct 2p production
p+D013(1520) contribution
Mp+p, GeV
N* parameters of the JM model and their relationships to the observables
Regular Breit-Wigner (BW) ansatz as the start point :
l
l
l
l
l
T
T
g


2
T
2
res


i
(
W
)N
N
*M
W

N
*
N
* M
*
f
dec
N
* N
* em p
lTl amplitudes are related to the partial N* decay
Definition of g NN* electrocouplings :
widths to the pD or rp final states of definite helicity l

J(cos(
l

))
l
l
l
l
d

e
T
T
q
l
l
g 2
M



+

A
A
g

,
p
,
)
f(
p
l
l
J
T
M

p
(
2
+
1
)
l
JM
f
decN
*
v
f
0
f
dec
N
*
f
dec
N
*
N
*f
N
*f
2
f
*
N
*,N
dec
nuc
N
*
N
*
0
f
i
N
*
dec
N
*
2
1
/
2
N
*
f
2
3
/
2
N
*
g is N* electromagnetic decay width, qgN* is abs.
photon CM 3-momentum value at W=MN* .
fdec is the kinematical factor, which depends on
resonance spin, mass and abs. CM 3-momenta
values of the stable final hadron averaged over the
line of unstable final hadron at the running W (p)
and at W=MN* (pN*). f and f are the CM final stable
hadron ermission angles.
The A1/2, A3/2, S1/2 gvNN* electrocouplings and lf N* partial decay widths are determined at resonant point W=MN*.
l
l
l
The relationships between N* electroproduction amplitudes Tem and gvNN* electrocouplings A1/2, A3/2, S1/2
g
2
2
(
),
(
)
Q
Q
A
A
1
/
2
3
/
2

(
,
,
)
*
{
2
f
q
q
T
M
em
N
*
N
*
p em
N
*
(
)
Q
2
S
1
/
2
gg
are obtained imposing the requirement: fully integrated resonant cross section should be described by the
relativistic Breit-Wigner formula in a case of single contributing resonance.
Exact expressions for the factors fem and fdec can be found in: M.Ripani et al., Nucl. Phys. A673, 220 (2000).
Electromagnetic Excitation of N*s
e’
γv
e
p, h, pp
lgp1/2
N*,△
N’
N
A3/2, A1/2, S1/2
Ml+/-, El+/-, Sl+/-
gv
N
lgp3/2
DOE Milestone 2012
Measure the electromagnetic excitations of low-lying
baryon states (<2 GeV) and their transition form factors
over the range Q2 = 0.1 – 7 GeV2 and measure the electroand photo-production of final states with one and two
pseudo-scalar mesons.
D13(1520) electrocouplings from the CLAS data
on Np/Npp electroproduction
• electrocouplings as determined
from the Np & Npp channels are
in good agreement overall
• but the apparent discrepancies
for the A3/2 amplitude at Q2 < 0.4
GeV2 will be further investigated
in a combined Np/Npp analysis
• hypercentric Consituent Quark
Model calculations reasonably
describe electrocouplings at
Q2>2.5 GeV2, suggesting that the
3-quark component is the
primary contribution to the
structure of this state at high Q2.
error bars include
systematic uncertainties
M.Giannini/
E.Santopinto
hyper-centric
CQM
Meson-baryon dressing / Quark core contributions in the
A1/2 electrocouplings of the P11(1440) & D13(1520) states.
Estimates from EBAC for
the MB dressing: B.JuliaDiaz et al., PRC 76,
5201 (2007).
Light Front
quark model
by I.Aznauryan
P11(1440)
hypercentric quark model
by M.Giannini
D13(1520)
•MB dressing effects have substantial contribution to low lying N* electrouplings at
Q2<1.0 GeV2 and gradually decrease with Q2;
•Contribution from dressed quarks increases with Q2 and are expected to be
dominant at Q2>5.0 GeV2.
Roper resonance in LQCD
Includes the quark loops in the sea, which are critical
in order to reproduce the CLAS data at Q2<1.0 GeV2
A1/2, S1/2 => F1*, F2*
H.W. Lin and S.D. Cohen, arXiv:1108.2528
Mπ = 390, 450, 875 MeV
L box =3.0, 2.5, 2.5 f
CLAS
data
•