Transcript Baryon Resonances - University of South Carolina

Hadron Spectroscopy at CLAS:
The Evolution of Strong Degrees of Freedom
Ralf W. Gothe
Seminar
PHYS 745G
Columbia, May 29
 Motivation: Why Nucleon Transition Form Factors?
 Consistency: N D, N Roper, and other N N* Transitions
 Outlook: Experiment and Theory
Ralf W. Gothe
PHYS 745G
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Physics Goals
0.1 – 1.0 fm
<< 0.1fm
?
pQCD
q, g, qq
!
? !
> 1.0 fm
? !
lgp=1/2
Models
N
Quarks and Gluons
lgp=3/2
as Quasiparticles
gv
! ?
ChPT
Nucleon and
Mesons
 Determine the electrocouplings of prominent excited nucleon states (N*, Δ*)
in the unexplored Q2 range of 0-5-12 GeV2 that will allow us to:
 Study the structure of the nucleon spectrum in the domain where dressed
quarks are the major active degree of freedom.
 Explore the formation of excited nucleon states in interactions of dressed
quarks and their emergence from QCD.
Ralf W. Gothe
PHYS 745G
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What do we really know?
Ralf W. Gothe
PHYS 745G
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Quark Model Classification of N*
+ q³g
D13(1520)
S11(1535)
+ q³qq
+ N-Meson
+…
D(1232)
Roper P11(1440)
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PHYS 745G
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N and D Excited States …
 Orbital excitations
(two distinct kinds)
 Radial excitations
(also two kinds)
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PHYS 745G
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“Missing” Resonances?
Problem: symmetric CQM predicts many more states than observed (in pN scattering)
Possible solutions:
1. di-quark model
old but always young
fewer degrees-of-freedom
open question: mechanism for q2 formation?
2. not all states have been found
possible reason: decouple from pN-channel
model calculations: missing states couple to
Npp (Dp, Nr), Nw, KY
3. coupled channel dynamics
new
all baryonic and mesonic excitations beyond the groundstate
octets and decuplet are generated by coupled channel
dynamics (not only L(1405), L(1520), S11(1535) or f0(980))
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The 6 GeV CW Electron Accelerator at JLab
Emax
Imax
Duty Factor
sE/E
Beam P
Eg (tagged)
~ 6 GeV
~ 200 mA
~ 100%
~ 2.5 10-5
~ 85%
~ 0.8 - 5.5 GeV
CLAS
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CLAS at JLab
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CLAS for Inclusive ep
e’X at 4 GeV
CLAS
 Resonances cannot be uniquely separated in inclusive scattering
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PHYS 745G
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CLAS for Exclusive ep e’pX at 4 GeV
2.0
1.5
1.0
CLAS
0.
1.0
0.5
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PHYS 745G
1.5
10
N
D(1232) Transition Form Factors
SU(6): E1+=S1+=0
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Multipole Ratios REM, RSM before 1999
Sign?
Q2 dependence?
 Data could not
determine sign or Q2
dependence
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PHYS 745G
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N
D(1232) Transition Form Factors
Need data at
low Q2
Lattice QCD indicates a
small oblate deformation
of the D(1232) and that the
pion cloud makes E1+ /M1+
more negative at small Q2.
Data at low Q2 needed to
study effects of the pion
cloud.
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PHYS 745G
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Low Q2 Mutipole Ratios for REM, RSM
C. Alexandrou et al., PRL, 94, 021601 (2005)
REM (%)
Need data at
low Q2
RSM (%)
 Quenched LQCD describes REM within
error bars, but shows discrepancies with
RSM at low Q2 . Pion cloud effects?
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Low Q2 Mutipole Ratios for REM, RSM
C. Smith
C. Alexandrou et al., PRL, 94, 021601 (2005)
 Significant discrepancy between CLAS
and Bates/MAMI results for RSM.
Ralf W. Gothe
 Quenched LQCD describes REM within
error bars, but shows discrepancies with
RSM at low Q2 . Pion cloud effects?
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Preliminary Multipole Ratios REM, RSM
Need data at
low Q2
 Data at even lower Q2 are
needed to investigate the pion
cloud further.
 Data at high Q2 are needed to
study the transition to pQCD.
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PHYS 745G
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Hadron Structure with Electromagnetic Probes
p,r,w…
Quark mass extrapolated to the chiral limit, where q
is the momentum variable of the tree-level quark
propagator using the Asqtad action.
resolution
low
N,N*,D,D*…
q
LQCD
LQCD,(Bowman
DSE andet …
al.)
quark mass (GeV)
3q-core+MB-cloud
3q-core
e.m. probe
pQCD
high
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Constituent Counting Rule
S11 Q3A1/2
quark mass (GeV )
A1/2 a 1/Q3
Bowman et al.
F15 Q5A3/2
(LQCD) P11 Q35A1/2
D13 Q A3/2
A3/2 a 1/Q5
F15 Q3A1/2
* a 1/Q4
GM
D13 Q3A1/2
Quark mass extrapolated to the chiral limit, where q is the momentum variable of
the tree-level quark propagator using the Asqtad action.
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PHYS 745G
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N → D Multipole Ratios REM , RSM
M. Ungaro
GD =
1
(1+Q2/0.71)2
 New trend towards pQCD behavior
does not show up.
 REM +1
 G*M
1/Q4
 CLAS12 can measure REM and RSM
up to Q²~12 GeV².
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PHYS 745G
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N → D Multipole Ratios REM , RSM
ep
e'pp0
A. Villano
… but the trend that RSM becomes constant in the limit of Q2 → ∞ seems to show
up in the latest MAID 2007 analysis of the high Q2 data.
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PHYS 745G
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Integrated Target and Beam-Target Asymmetries
ep
e'pp0
A. Biselli
The asymmetries are integrated over q* and j* in the Q2 range from 0.187 to 0.770 GeV2
and will further reduce the model dependence of the extracted resonance parameters.
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Progress in Experiment and Phenomenology
Recent experimental and phenomenological efforts show that mesonbaryon contributions to resonance formations drop faster with Q2 than
contributions from dressed quarks.
D(1232)P33
N(1440)P11
N(1520)D13
Np
A1/2
pp0
A1/2
Np
Npp
Npp
Dressed quarks (I. Aznauryan, M. Giannini and E. Santopinto, B. Julia-Diaz et al.)
Meson-baryon cloud (EBAC)
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Resonance Electrocouplings in Lattice QCD
D(1232)P33
N(1440)P11
Huey-Wen Lin
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 Q 2 = 10 GeV2
near the physical p-mass as part of the commitment of the JLab LQCD and EBAC groups in support of
this proposal.
see White Paper Sec. II and VIII
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PHYS 745G
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LQCD & Light Cone Sum Rule (LCSR) Approach
N(1535)S11
CLAS
Hall C
LQCD is used to determine the
moments of N* distribution
amplitudes (DA) and the N*
electrocouplings are determined
from the respective DAs within
the LCSR framework.
Calculations of N(1535)S11 electrocouplings at Q2 up to 12 GeV2 are already available and
shown by shadowed bands on the plot.
By the time of the upgrade electrocouplings of others N*s will be evaluated. These studies
are part of the commitment of the Univ. of Regensburg group in support of this proposal.
see White Paper Sec. V
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PHYS 745G
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Dynamical Mass of Light Dressed Quarks
DSE and LQCD predict the
dynamical generation of the
momentum dependent dressed
quark mass that comes from the
gluon dressing of the current
quark propagator.
These dynamical contributions
account for more than 98% of
the dressed light quark mass.
DSE: lines and LQCD: triangles
per dressed quark
Q2 = 12 GeV2 = (p times number of quarks)2 = 12 GeV2
p = 1.15 GeV
The data on N* electrocouplings at 5<Q2<12 GeV2 will allow us to chart the
momentum evolution of dressed quark mass, and in particular, to explore the
transition from dressed to almost bare current quarks as shown above.
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PHYS 745G
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Constituent Quark Models (CQM)
3q
LC CQM
|q3+qq> (Li, Riska)
Pion Cloud (EBAC)
N(1440)P11:
PDG value
Np, Npp combined analysis
Np
Relativistic CQM are currently the only available tool to study the electrocouplings for the
majority of excited proton states.
This activity represent part of the commitment of the Yerevan Physics Institute, the University
of Genova, INFN-Genova, and the Beijing IHEP groups to refine the model further, e.g., by
including qq components.
see White Paper Sec. VI
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PHYS 745G
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Phenomenological Analyses
 Unitary Isobar Model (UIM) approach in single
pseudoscalar meson production
 Fixed-t Dispersion Relations (DR)
 Isobar Model for Nππ final state (JM)
see White Paper Sec. VII
 Coupled-Channel Approach (EBAC)
see White Paper Sec. VIII
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PHYS 745G
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Phenomenological Analyses in Single Meson Production
Unitary Isobar Model (UIM)
Nonresonant amplitudes: gauge invariant Born terms consisting of t-channel
exchanges and s- / u-channel nucleon terms, reggeized at high W.
pN rescattering processes in the final state are taken into account in a
K-matrix approximation.
Fixed-t Dispersion Relations (DR)
Relates the real and the imaginary parts of the six invariant amplitudes in a
model-independent way. The imaginary parts are dominated by resonance
contributions.
see White Paper Sec. VII
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PHYS 745G
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Legendre Moments of Unpolarized Structure Functions
K. Park et al. (CLAS), Phys. Rev. C77, 015208 (2008)
Q2=2.05GeV2
I. Aznauryan
I. Aznauryan
I. Aznauryan
DR fit
DR fit w/o P11
UIM fit
Ralf W. Gothe
Two conceptually different approaches
DR and UIM are consistent. CLAS data
provide rigid constraints for checking
validity of the approaches.
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Energy-Dependence of p+ Multipoles for P11, S11
Q2 = 0 GeV2
Q2 = 2.05 GeV2
The study of some
baryon resonances
becomes easier at
higher Q2.
real part
Ralf W. Gothe
PHYS 745G
imaginary part
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J /  pp  n
and
J /  pp  n
Bing-Song Zou
BES/BEPC, Phys. Rev. Lett. 97 (2006)
N*(1440): M = 1358 ± 17
G = 179 ± 56
N*(2050): M = 2068  15- 40
G = 165 ± 42
pN invariant mass / MC phase space
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PHYS 745G
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Nucleon Resonances in Np and Npp Electroproduction
Q2 < 4.0GeV2
p(e,e')X
Npp channel is sensitive
to N*s heavier than
1.4 GeV
p(e,e'p)p0
Provides information
that is complementary
to the Np channel
p(e,e'p+)n
Many higher-lying N*s
decay preferentially into
Npp final states
p(e,e'pp+)pW in GeV
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PHYS 745G
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JM Model Analysis of the pp+p- Electroproduction
p
D(1232)P33, N(1520)D13,
D(1600)P33, N(1680)F15
p
see White Paper Sec. VII
Ralf W. Gothe
PHYS 745G
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JM Mechanisms as Determined by the CLAS 2p Data
Full JM
calculation
p-D
p+D0
2p direct
p+N(1520) D13
rp
p+N(1685) F15
Each production mechanism contributes to all nine single differential cross sections in a unique
way. Hence a successful description of all nine observables allows us to check and to establish the
dynamics of all essential contributing mechanisms.
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PHYS 745G
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Separation of Resonant/Nonresonant Contributions in 2p Cross Sections
nonresonant part
resonant part
Due to the marked differences in the contributions of the resonant and nonresonant parts
to the cross sections, the nine observables allow us to neatly disentangle these competing
processes.
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PHYS 745G
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Electrocouplings of N(1440)P11 from CLAS Data
PDG estimation
Np (UIM, DR)
Np, Npp combined analysis
Npp (JM)
The good agreement on extracting the N* electrocouplings between the two exclusive
channels (1p/2p) – having fundamentally different mechanisms for the nonresonant
background – provides evidence for the reliable extraction of N* electrocouplings.
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PHYS 745G
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Roper Electro-Coupling Amplitudes A1/2, S1/2
L. Tiator
A1/2
Comparison of MAID 08
and JLab analysis
S1/2
MAID 07
and new Maid analysis
with Park data
MAID 08
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PHYS 745G
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N(1520)D13 Electrocoupling Amplitudes A3/2, S1/2
I. Starkovski
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PHYS 745G
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10-3 GeV-1/2
Electrocouplings of N(1520)D13 from the CLAS 1p/2p data
Ahel =
A1/22 – A3/22
A1/22 + A3/22
A1/2
L. Tiator
A3/2
world data
PDG estimation
Np (UIM, DR)
Ralf W. Gothe
Np, Npp combined analysis
PHYS 745G
Npp (JM)
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Higher Lying Resonances form the 2p JM Analysis of CLAS Data
D(1700)D33
N(1720)P13
The A1/2 electrocoupling of P13(1720) decreases rapidly with Q2. At Q2>0.9 GeV2 |A3/2|>|A1/2|.
2=0
Npp CLAS
Np world
WillNp
we world
able toQaccess
the Q2 region
where the A1/2 amplitude
of P13(1720) dominates?
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PHYS 745G
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Combined 1p-2p Analysis of CLAS Data
PDG at Q2=0
2p analysis
1p-2p combined at
Q2=0.65 GeV2
Previous world data
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PHYS 745G
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CLAS12 Detector Base Equipment
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Inclusive Structure Function in the Resonance Region
P. Stoler, PRPLCM 226, 3 (1993) 103-171
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PHYS 745G
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CLAS 12 Kinematic Coverage and Counting Rates
Genova-EG
(e',p+) detected
Genova-EG
(e',p) detected
(E,Q2)
(5.75 GeV, 3 GeV2)
p+
NSI-DIS
Npp0
Nph
(11 GeV, 3 GeV2)
(11 GeV, 12 GeV2)
1.41*105
6.26*106
5.18*104
-
4.65*105
1.45*104
-
1.72*104
1.77*104
+) detected
(e’,p
60 days
L=1035 cm-2 sec-1, W=1535 GeV, DW= 0.100 GeV, DQ2 = 0.5 GeV2
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PHYS 745G
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Angular Acceptance of CLAS12
p+ Acceptance for cos(q) = 0.01
Full kinematical coverage in W, Q2, Q, and F
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PHYS 745G
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W and Missing Mass Resolutions with CLAS12
Final state selection
W calculated from
electron scattering
1.5 < W < 2 GeV
60 MeV
exclusive pp+p final state
1.5 < W < 2 GeV
FWHM
10 MeV
by Missing Mass
W < 2 GeV
FWHM
2p
3p
MX2 (GeV2)
W = (qg  Pp ) 2
W = ( Pp  Pp  Pp ) 2
Ralf W. Gothe
PHYS 745G
ep  e'p'p +X
50
Kinematic Coverage of CLAS12
60 days
L= 1035 cm-2 sec-1, DW = 0.025 GeV, DQ2 = 0.5 GeV2
(e’,ppp) detected
Q2 GeV2
Genova-EG
2p limit > 1p limit >
2p limit > 1p limit >
1h limit >
W GeV
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PHYS 745G
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Summary
 We will measure and determine the electrocouplings A1/2, A 3/2, S1/2 as a function of
Q2 for prominent nucleon and Δ states,
 see our Proposal http://www.physics.sc.edu/~gothe/research/pub/nstar12-12-08.pdf.
 Comparing our results with LQCD, DSE, LCSR, and rCQM will gain insight into
 the strong interaction of dressed quarks and their confinement in baryons,
 the dependence of the light quark mass on momentum transfer, thereby shedding light on
chiral-symmetry breaking, and
 the emergence of bare quark dressing and dressed quark interactions from QCD.
 This unique opportunity to understand origin of 98% of nucleon mass is also an
experimental and theoretical challenge. A wide international collaboration is needed
for the:
 theoretical interpretation on N* electrocouplings, see our White Paper
http://www.physics.sc.edu/~gothe/research/pub/white-paper-09.pdf, and
 development of reaction models that will account for hard quark/parton contributions at
high Q2.
 Any constructive criticism or direct participation is very welcomed, please contact:
 Viktor Mokeev [email protected] or Ralf Gothe [email protected].
Ralf W. Gothe
PHYS 745G
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Conclusion: Do Exclusive Electron Scattering
D13(1520)
Q2 = 2.05 GeV2
D13(1520)
... to
Learn QCD!
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PHYS 745G
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Supplement
Ralf W. Gothe
PHYS 745G
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Nucleon Resonance Studies with CLAS12
D. 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, G. Stancari5, M. Stancari5, 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
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*
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Theory Support Group
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
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Physics Goals
 Measure differential cross sections and polarization observables in single and
double pseudoscalar meson production: p+n, p0p, hp and p+pp over the full
polar and azimuthal angle range.

 Determine electrocouplings of prominent excited nucleon states (N*, Δ*) in
the fully unexplored Q2 range of 5-12 GeV2 and extend considerably the data
base on fundamental form factors of nucleon states, which is needed to
explore the confinement in the baryon sector.
“ultimate goal”
 These data for the first time will allow us to:
 Study the structure of the nucleon spectrum in the domain where dressed
quarks are the major active degree of freedom.
 Explore the formation of excited nucleon states in interactions of dressed
quarks and their emergence from QCD.
“address more sharply”
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PHYS 745G
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Projected A1/2 Helicity Amplitudes
CLAS published
CLAS preliminary
CLAS12 projected
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PHYS 745G
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Angular Acceptance of CLAS12
p+ Acceptance for cos(q) = 0.01
Full kinematical coverage in W, Q2, Q, and F
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PHYS 745G
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S11(1535) Electro-Coupling Amplitudes A1/2, S1/2
LF
LF
LF |q3>
nr |q3>
|q3>
|q3>
LF |q3>
nr |q3>
nr |q3>
nr |q3>
PDG estimation
h production (UIM, DR)
p electro-production (UIM, DR)
K. Park (Data)
I. Aznauryan (UIM)
h production (SQTM S11, D13 analysis)
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D13(1520) Helicity Asymmetry
Ahel =
A1/22 – A3/22
A1/22 + A3/22
A1/2
A3/2
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Contributing Mechanisms to g p → pp+p(*)
Isobar Model JM05
Full calculations
gp  p-D++
gp  p+D0
gp  p+D13(1520)
gp  rp
gp  p-D++(1600)
gp  p+F015(1685)
direct 2p production
 The combined fit of nine single
differential cross sections allowed to
establish all significant mechanisms.
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PHYS 745G
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Separation of Resonant/Nonresonant Contributions in 2p Cross Sections
full cross sections
resonant part
non-resonant part
The reliable resonant / nonresonant cross section separation
allows to isolate the N*
contribution and demonstrates the
degree of model independence.
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PHYS 745G
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Helicity Asymmetry in 2p Production
CLAS
S. Strauch
Calculations: Mokeev (dashed) Fix (solid)
parity conservation
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PHYS 745G
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Helicity Asymmetry in 2p Production
CLAS
S. Strauch
 Sequential Decay of the D13(1520) resonance via pD
 … or higher lying resonances
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PHYS 745G
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