ralf w. gothe phys 745g 1 motivation: why nucleon transition form factors? consistency: n n...
Post on 20-Dec-2015
216 views
TRANSCRIPT
1Ralf W. Gothe PHYS 745G
Motivation: Why Nucleon Transition Form Factors? Consistency: N N Roper, and other N N* Transitions Outlook: Experiment and Theory
Ralf W. Gothe
SeminarPHYS 745G
Columbia, May 29
Hadron Spectroscopy at CLAS: The Evolution of Strong Degrees of Freedom
2Ralf W. Gothe PHYS 745G
Physics Goals
Models Quarks and Gluons as Quasiparticles
ChPT Nucleon and
Mesons
pQCD q, g, qq
< 0.1fm 0.1 – 1.0 fm > 1.0 fm<
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.
v N
p
p?
!!
?
?
?
!
!
3Ralf W. Gothe PHYS 745G
What do we really know?
4Ralf W. Gothe PHYS 745G
Quark Model Classification of N*
(1232)
D13(1520)S11(1535)
Roper P11(1440)
+ q³g
+ q³qq
+ N-Meson
+ …
5Ralf W. Gothe PHYS 745G
N and Excited States …
Orbital excitations
(two distinct kinds)
Radial excitations(also two kinds)
6Ralf W. Gothe PHYS 745G
“Missing” Resonances?
fewer degrees-of-freedom open question: mechanism for q2 formation?
Problem: symmetric CQM predicts many more states than observed (in N scattering) Possible solutions: 1. di-quark model
2. not all states have been found
possible reason: decouple from N-channel model calculations: missing states couple to N, N, N, KY
3. coupled channel dynamicsall baryonic and mesonic excitations beyond the groundstate octets and decuplet are generated by coupled channel dynamics (not only (1405), (1520), S11(1535) or f0(980))
old but always young
new
7Ralf W. Gothe PHYS 745G
Emax ~ 6 GeV
Imax ~ 200 A
Duty Factor ~ 100%E/E ~ 2.5 10-5
Beam P ~ 85%
E(tagged) ~ 0.8 - 5.5 GeV
CLAS
The 6 GeV CW Electron Accelerator at JLab
8Ralf W. Gothe PHYS 745G
CLAS at JLab
9Ralf W. Gothe PHYS 745G
CLAS for Inclusive ep e’X at 4 GeVCLAS
Resonances cannot be uniquely separated in inclusive scattering
10Ralf W. Gothe PHYS 745G
CLAS for Exclusive ep e’pX at 4 GeV
1.50. 0.5 1.0
1.0
1.5
2.0
mis
sing
sta
tes
CLAS
11Ralf W. Gothe PHYS 745G
SU(6): E1+=S1+=0
N (1232) Transition Form Factors
12Ralf W. Gothe PHYS 745G
Multipole Ratios REM, RSM before 1999
Sign?
Q2 dependence?
Data could not determine sign or Q2 dependence
13Ralf W. Gothe PHYS 745G
Lattice QCD indicates a small oblate deformation of the (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.
Need data at low Q2
N (1232) Transition Form Factors
14Ralf W. Gothe PHYS 745G
C. Alexandrou et al., PRL, 94, 021601 (2005)
REM (%)
RSM (%)
Quenched LQCD describes REM within error bars, but shows discrepancies with RSM at low Q2 . Pion cloud effects?
Low Q2 Mutipole Ratios for REM, RSM
Need data at low Q2
15Ralf W. Gothe PHYS 745G
Low Q2 Mutipole Ratios for REM, RSM
C. Alexandrou et al., PRL, 94, 021601 (2005)
preliminary
Quenched LQCD describes REM within error bars, but shows discrepancies with RSM at low Q2 . Pion cloud effects?
Significant discrepancy between CLAS and Bates/MAMI results for RSM.
C. Smith
16Ralf W. Gothe PHYS 745G
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.
Preliminary Multipole Ratios REM, RSM
preliminaryNeed data at
low Q2
17Ralf W. Gothe PHYS 745G
quar
k m
ass
(GeV
)
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
high
q
e.m. probe
LQCD (Bowman et al.)
Hadron Structure with Electromagnetic Probes
N,N*,*…
3q-core+MB-cloud
3q-core
pQCD
LQCD, DSE and …
19Ralf W. Gothe PHYS 745G
S11 Q3A1/2
F15 Q5A3/2
P11 Q3A1/2
D13 Q5A3/2
F15 Q3A1/2
D13 Q3A1/2
Constituent Counting Rule
A1/2 1/Q3
A3/2 1/Q5
GM 1/Q4*
Quark mass extrapolated to the chiral limit, where q is the momentum variable of the tree-level quark propagator using the Asqtad action.
quar
k m
ass
(GeV
)
Bowman et al. (LQCD)
20Ralf W. Gothe PHYS 745G
N → Multipole Ratios REM , RSM
New trend towards pQCD behavior does not show up.
CLAS12 can measure REM and RSM up to Q²~12 GeV².
REM +1
M. Ungaro
GM 1/Q4*
GD = 1
(1+Q2/0.71)2
21Ralf W. Gothe PHYS 745G
N → Multipole Ratios REM , RSM
A. Villano
very preliminarye p e'p0
… 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.
22Ralf W. Gothe PHYS 745G
Integrated Target and Beam-Target AsymmetriesA. Biselli
The asymmetries are integrated over * and * in the Q2 range from 0.187 to 0.770 GeV2
and will further reduce the model dependence of the extracted resonance parameters.
e p e'p0
23Ralf W. Gothe PHYS 745G
Progress in Experiment and Phenomenology
Dressed quarks (I. Aznauryan, M. Giannini and E. Santopinto, B. Julia-Diaz et al.)Meson-baryon cloud (EBAC)
N
N
N
N
p0
(1232)P33 N(1440)P11 N(1520)D13
Recent experimental and phenomenological efforts show that meson-baryon contributions to resonance formations drop faster with Q2 than contributions from dressed quarks.
A1/2A1/2
24Ralf W. Gothe PHYS 745G
Resonance Electrocouplings in Lattice QCD
LQCD calculations of the (1232)P33 and N(1440)P11 transitions have been carried out with large -masses. By the time of the upgrade LQCD calculations of N* electrocouplings will be extended to Q2 = 10 GeV2 near the physical -mass as part of the commitment of the JLab LQCD and EBAC groups in support of this proposal.
(1232)P33 N(1440)P11
see White Paper Sec. II and VIII
Huey-Wen Lin
25Ralf W. Gothe PHYS 745G
LQCD & Light Cone Sum Rule (LCSR) Approach
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
N(1535)S11
CLASHall C
26Ralf W. Gothe PHYS 745G
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.
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.
per dressed quark
Q2 = 12 GeV2 = (p times number of quarks)2 = 12 GeV2 p = 1.15 GeV
DSE: lines and LQCD: triangles
28Ralf W. Gothe PHYS 745G
Constituent Quark Models (CQM)
Pion Cloud (EBAC)
|q3+qq(Li, Riska)
3q
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
LC CQM
PDG value N N, N combined analysisN(1440)P11:
29Ralf W. Gothe PHYS 745G
Phenomenological Analyses
Unitary Isobar Model (UIM) approach in single pseudoscalar meson production
Fixed-t Dispersion Relations (DR) Isobar Model for Nππ final state (JM)
Coupled-Channel Approach (EBAC)
see White Paper Sec. VIII
see White Paper Sec. VII
30Ralf W. Gothe PHYS 745G
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. N 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.
Phenomenological Analyses in Single Meson Production
see White Paper Sec. VII
31Ralf W. Gothe PHYS 745G
Legendre Moments of Unpolarized Structure Functions
Q2=2.05GeV2
Two conceptually different approaches DR and UIM are consistent. CLAS data provide rigid constraints for checking validity of the approaches.
K. Park et al. (CLAS), Phys. Rev. C77, 015208 (2008)
I. Aznauryan DR fit w/o P11
I. Aznauryan DR fit
I. Aznauryan UIM fit
32Ralf W. Gothe PHYS 745G
Energy-Dependence of+ Multipoles for P11, S11
imaginary partreal part
Q2 = 0 GeV2
The study of some baryon resonances becomes easier at higher Q2.
Q2 = 2.05 GeV2
preliminary
33Ralf W. Gothe PHYS 745G
BES/BEPC, Phys. Rev. Lett. 97 (2006)
/J p n /J p n Bing-Song Zou
and
±±
- ±
invariant mass / MC phase space
34Ralf W. Gothe PHYS 745G
Nucleon Resonances in Nand N Electroproduction
p(e,e')X
p(e,e'p)
p(e,e'+)n
p(e,e'p+)-
channel is sensitive to N*s heavier than 1.4 GeV
Provides information that is complementary to the N channel
Many higher-lying N*s decay preferentially into N final states
Q2 < 4.0 GeV2
W in GeV
35Ralf W. Gothe PHYS 745G
(1232)P33, N(1520)D13, (1600)P33, N(1680)F15
JM Model Analysis of the p+- Electroproduction
see White Paper Sec. VII
36Ralf W. Gothe PHYS 745G
JM Mechanisms as Determined by the CLAS 2 Data
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.
Full JMcalculation
-
+ +N(1520) D13 +N(1685) F15
p2 direct
37Ralf W. Gothe PHYS 745G
Separation of Resonant/Nonresonant Contributions in 2 Cross Sections
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.
resonant part nonresonant part
38Ralf W. Gothe PHYS 745G
Electrocouplings of N(1440)P11 from CLAS Data
N (UIM, DR)PDG estimation N, N combined analysis N (JM)
The good agreement on extracting the N* electrocouplings between the two exclusive channels (1/2) – having fundamentally different mechanisms for the nonresonant background – provides evidence for the reliable extraction of N* electrocouplings.
39Ralf W. Gothe PHYS 745G
Comparison of MAID 08 and JLab analysis
A1/2
S1/2
Roper Electro-Coupling Amplitudes A1/2, S1/2
L. Tiator
MAID 07 and new Maid analysis with Park data MAID 08
40Ralf W. Gothe PHYS 745G
N(1520)D13 Electrocoupling Amplitudes A3/2, S1/2
I. Starkovski
41Ralf W. Gothe PHYS 745G
Electrocouplings of N(1520)D13 from the CLAS 1/2 data
world data
10-3 G
eV-1
/2
N (UIM, DR)PDG estimation N, N combined analysis N (JM)
Ahel = A1/2
2 – A3/22
A1/22 + A3/2
2
A1/2
A3/2
L. Tiator
43Ralf W. Gothe PHYS 745G
CLAS
NworldNworld Q2=0
(1700)D33
N(1720)P13
Higher Lying Resonances form the 2 JM Analysis of CLAS Data
preliminary
The A1/2 electrocoupling of P13(1720) decreases rapidly with Q2. At Q2>0.9 GeV2 |A3/2|>|A1/2|. Will we able to access the Q2 region where the A1/2 amplitude of P13(1720) dominates?
45Ralf W. Gothe PHYS 745G
Combined 1-2 Analysis of CLAS Data
PDG at Q2=0
2 analysis
1-2 combined at Q2=0.65 GeV2
Previous world data
preliminary
46Ralf W. Gothe PHYS 745G
CLAS12 Detector Base Equipment
47Ralf W. Gothe PHYS 745G
Inclusive Structure Function in the Resonance Region
P. Stoler, PRPLCM 226, 3 (1993) 103-171
48Ralf W. Gothe PHYS 745G
CLAS 12 Kinematic Coverage and Counting Rates
Genova-EG
Genova-EG
SI-DIS
(e',+) detected
(e',p) detected
(e’,+) detected
(E,Q2) (5.75 GeV, 3 GeV2) (11 GeV, 3 GeV2) (11 GeV, 12 GeV2)
N+ 1.41105 6.26106 5.18104
Np - 4.65105 1.45104
Np - 1.72104 1.77104
60 days
L=1035 cm-2 sec-1, W=1535 GeV, W= 0.100 GeV, Q2 = 0.5 GeV2
49Ralf W. Gothe PHYS 745G
Angular Acceptance of CLAS12
+ Acceptance for cos= 0.01
Full kinematical coverage in W, Q2, , and
50Ralf W. Gothe PHYS 745G
1.5 < W < 2 GeV
60 MeV
1.5 < W < 2 GeV
10 MeV
W < 2 GeV
3
2
W and Missing Mass Resolutions with CLAS12
W calculated from
electron scattering exclusive p+ final state
2)( pPqW ep e'p' +X2)(
PPPW p
Final state selectionby Missing Mass
MX2 (GeV2)
FWHM FWHM
51Ralf W. Gothe PHYS 745G
Kinematic Coverage of CLAS12
60 daysL= 1035 cm-2 sec-1, W = 0.025 GeV, Q2 = 0.5 GeV2
Genova-EG (e’,p) detected
W GeV
Q2 G
eV2 2 limit > 1 limit >
2 limit > 1 limit >
1 limit >
52Ralf W. Gothe PHYS 745G
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].
53Ralf W. Gothe PHYS 745G
Conclusion: Do Exclusive Electron Scattering
Q2 = 2.05 GeV2
D13(1520)
D13(1520)
... to
Learn QCD!
54Ralf W. Gothe PHYS 745G
Supplement
55Ralf W. Gothe PHYS 745G 55
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
SpokespersonContact Person*
56Ralf W. Gothe PHYS 745G 56
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
57Ralf W. Gothe PHYS 745G
Physics Goals
Measure differential cross sections and polarization observables in single and double pseudoscalar meson production: +n0p, p and +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.
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.
“ultimate goal”
“address more sharply”
58Ralf W. Gothe PHYS 745G
Projected A1/2 Helicity AmplitudesCLAS published
CLAS preliminary
CLAS12 projected
59Ralf W. Gothe PHYS 745G
Angular Acceptance of CLAS12
+ Acceptance for cos= 0.01
Full kinematical coverage in W, Q2, , and
60Ralf W. Gothe PHYS 745G
preliminary
S11(1535) Electro-Coupling Amplitudes A1/2, S1/2
electro-production (UIM, DR)
PDG estimation
production (SQTM S11, D13 analysis)
K. Park (Data) I. Aznauryan (UIM)
production (UIM, DR)
nr |q3
LF |q3
LF |q3nr |q3
nr |q3LF |q3
LF |q3
nr |q3
61Ralf W. Gothe PHYS 745G
preliminary
D13(1520) Helicity Asymmetry
Ahel = A1/2
2 – A3/22
A1/22 + A3/2
2
A1/2
A3/2
62Ralf W. Gothe PHYS 745G
direct 2production
Full calculationsp -++
p +0
p p
p -++(1600)
p +F015(1685)
p +D13(1520)
The combined fit of nine single differential cross sections allowed to establish all significant mechanisms.
Isobar Model JM05
Contributing Mechanisms to p → p+-
63Ralf W. Gothe PHYS 745G
Separation of Resonant/Nonresonant Contributions in 2 Cross Sections
full cross sections
resonant part
non-resonant part
The reliable resonant / non-resonant cross section separation allows to isolate the N* contribution and demonstrates the degree of model independence.
64Ralf W. Gothe PHYS 745G
Helicity Asymmetry in 2 ProductionCLAS
parity conservation
Calculations: Mokeev (dashed) Fix (solid)
S. Strauch
65Ralf W. Gothe PHYS 745G
Helicity Asymmetry in 2 Production
Sequential Decay of the D13(1520) resonance via … or higher lying resonances
CLAS S. Strauch