Transcript Nucleon Excited States Ralf W. Gothe University of South Carolina Mini-Workshop on Nucleon Excited States PAC25 January 17, 2004 Introduction N D transition “Missing” Resonances, Strange Resonances and.

Nucleon Excited States
Ralf W. Gothe
University of South Carolina
Mini-Workshop on Nucleon Excited States
PAC25
January 17, 2004
Introduction
N D transition
“Missing” Resonances, Strange Resonances and Two Pion Production
Pentaquark States
Outlook
Ralf W. Gothe
PAC 25 Mini-Workshop 2004
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Physics Goals
 Understand QCD in the full strong coupling regime
 transition form factors
 mass spectrum, quantum numbers of nucleon excited states
 relevant degrees-of-freedom
 wave function and interaction of the constituents
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CLAS Coverage for ep
e’X at 4 GeV
5.0
4.0
3.0
2.0
1.0
CLAS
0
1.0
1.5
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2.0
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CLAS Coverage for ep e’pX at 4 GeV
2.0
1.5
1.0
CLAS
0.
0.5
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1.0
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1.5
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Electromagnetic Probe
 helicity amplitudes are
sensitive to the difference
in wave functions of N
and N*
 can separate electric and
magnetic parts of the
transition amplitude
 is linearly polarized
 varying Q2 allows to change the spatial resolution and
enhances different multipoles
 sensitive to missing resonance states
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N
D(1232) Transition Form Factors
SU(6): E1+=S1+=0
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Cross Section Decomposition
example:
e p e’ p po
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g*p
ppo – Response Functions
CLAS
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Multipole Analysis for g*p
ppo
CLAS
Q2 = 0.9 GeV2
|M1+|2
Re(E1+M1+*)
|M1+|2
Re(S1+M1+*)
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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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Multipole Ratios REM, RSM in 2002
Sign?
<0!
Q2 dependence !
Slope < 0
 No
trend towards
pQCD behavior is
observed for Q2 up
to 4 GeV2.
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N
D(1232) Transition Form Factors
Preliminary results
from ELSA and
Hall A using
different techniques
confirm CLAS data.
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N
D(1232) Transition Form Factors
Need data at
low Q2
Lattice QCD indicates
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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Preliminary Multipole Ratios REM, RSM
 Dynamical models and
full LQCD calculations
indicate the importance of
the pion cloud at low Q2
consistent with the trend of
data.
 Full LQCD results
indicate a small oblate
deformation of the D(1232).
 Data at high Q2 needed to
study the transition to
pQCD.
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Very Preliminary Multipole Ratios REM , RSM
New trend towards pQCD behavior may or may not show up.
Experiment E-01-002 in Hall C will reach Q²~8 GeV² and after the energy upgrade REM
and RSM can be measured up to Q²~12 GeV².
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N D Transition and Background Terms
 systematic uncertainties in extraction of E1+/M1+ from
ep e’p po around 0.5%
 differences in treatment of background terms (models not
constrained)
 will become more severe for higher Q2 (D dropping faster)
 more experimental information on hand (polarization and
isospin)
 single-spin asymmetry sTL’ for e p e’p (po) and e p e’p+ (n)
 polarization transfer in e p
e’p (po)
 differential cross sections for e p
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CLAS
Hall A
e’p+ n (D less important)
PAC 25 Mini-Workshop 2004
CLAS
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Polarized Beam Observables
CLAS
sLT’
response
function for
ep
e p po
sLT’ = 0 if only a
single diagram
contributes
(sensitive to the
interference between
D and background)
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Hall A
e’ p (po)
mb/sr
Polarization Measurement in e p
Q2 = 1 GeV2
W = 1.232 GeV
Results sensitive
to non-resonant
contributions
Parametrisations of available data
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SAID
MAID
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p+ Electroproduction
CLAS
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Electromagnetic Probe
 helicity amplitudes are
sensitive to the difference
in wave functions of N
and N*
 can separate electric and
magnetic parts of the
transition amplitude
 is linearly polarized
 varying Q2 allows to change the spatial resolution and
enhances different multipoles
 sensitive to missing resonance states
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Quark Model Classification of N*
“Missing”
P13(1870)
Capstick and Roberts
D13(1520)
S11(1535)
D13(1895)
Mart and Bennhold
?
+ q³g
+ q³qq
D(1232)
+ N-Meson
Roper P11(1440)
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+…
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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. chiral symmetry approach
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))
g coupling not suppressed
electromagnetic excitation is ideal
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Resonances in Hyperon Production?
CLAS
g*p
forward hemisphere
K+Y
backward hemisphere
N* ?
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L Photoproduction off the Proton
CLAS
Dominant resonances
S11(1650)
P11(1710)
P13(1720)
Bump at 1.9 GeV
D13(1895) ?
Carnegie Mellon
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Resonances in g*p
pp+p-
CLAS
Analysis performed
by Genova-Moscow
collaboration
0.65 GeV²
Step #1:
0.95 GeV²
Q²
use the best
information
presently available
GNpp : PDG
GNg : expt. Data or
1.30 GeV²
extra strength
SQTM
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Attempts to fit observed extra strength
CLAS
Step #2:
 vary parameters of
the photocouplings
 vary parameters of
known P13, P11, D13
 introduce new P13
New P13(1720)
consistent with
predictied missing P13 ,
but at lower mass.
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Attempts to fit observed extra strength
CLAS
Step #2:
 vary parameters of
the photocouplings
 vary parameters of
known P13, P11, D13
 introduce new P13
W(GeV)
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PWA in gp
CLAS
pp+p-
W=2240 MeV
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Resonances in gp
pp+p-
CLAS
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Resonances in gp
CLAS
pp+p-
F15(1680)
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P13(1720)
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JLab: Q+- Exclusive Process I
gd
CLAS
K-K+p(n)
Q+
Mass 1.542±0.005 GeV/c²
G< 21 MeV/c²
Significance 5.2±0.6 s
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JLab: Q+- Exclusive Process II
gp
Events
CLAS
Q+
K*
p+K-K+(n)
p+
g
K*
K0
M(K-p+)
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p
Q+
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KK+
n
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JLab: Q+- Exclusive Process III
gp
CLAS
p+K-K+(n)
g
Q+
p+
p-
p
N*
KK+
Q+
n
combined analysis II & III
Mass 1.555±0.010 GeV/c²
G< 26 MeV/c²
Significance 7.8±1.0 s
cut
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JLab: Q+- Exclusive Process III
gp
CLAS
N*
?
p+K-K+(n)
g
p+
p-
p
N*
K-
K+
Q+
n
Mass ~ 2.440 GeV/c²
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Outlook: Observation of Exotic X−−
ssd du
X0
X(1530)
combined analyis NA49
ssd ud
ssd ud
ssd du
M=1.862± 0.002 GeV/c²
G< 18 MeV/c²
CERN SPS hep-ex/0310014
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Outlook: Observation of Exotic X−−
ssd du
X0
X(1530)
Diakonov et al. Hep-ph/9703373
Diakonov, Petrov hep-ph/0310212
Jaffee, Wilczek hep-ph/0307341
Jaffee, Wilczek hep-ph/0312369
R.A. Arndt et al. nucl-th/0312126
ssd ud
ssd ud
ssd du
PAC 25 at JLab
M=1.862± 0.002 GeV/c²
CERN SPS hep-ex/0310014
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Hadron multiplets
Mesons qq
3  3  8 1
Baryons qqq
N
3  3  3  10  8  8  1
S
X
W─
Baryons built from meson-baryon, or qqqqq
+
Q
8  8  27 10 10  8  8 1
…
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New Tools: Exploit Weak Decays in Direct Reconstruction
X −− → p− X−
L → p− p
X − → p− L
Electron
beam
gn→K+K+X5−−
X− ct = 4.9 cm
L ct = 7.9 cm
Negatives bend outwards
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PAC 25 Mini-Workshop 2004
<gb> ~ 1.5
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New Tools: Frozen Spin Target for CLAS
Technical problem:
build polarized target for tagged photon beam
- minimum obstruction of CLAS solid angle
- low distortion of particle trajectories in
magnetic field
Solution:
Bonn target at Mainz GDH experiment
- frozen spin target
- temperature 50mK
5 Tesla polarizing magnet
Status:
- design in progress at JLab
CLAS
- magnetic field 5kG
- procurement started for
polarizing magnet
JLab design
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PAC 25 Mini-Workshop 2004
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New Tools: Bound Nucleon Structure (BoNuS)
Physics issue:
CLAS coils
tag process off a neutron bound in deuterium by
detecting the spectator proton in coincidence with
the scattered e’
Technical problem:
spectator protons have
 - low momentum and low range
 - isotropic angular distribution (no correlation)
 - high rate
Solution:
 - high pressure gas target
 - surrounded by radial drift
chamber
 - GasElectronMultiplier gap
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New Tools: BoNuS Detector
 Radial Time Projection Chamber (RTPC)
Goal: detect spectator protons with momenta as low as 70 MeV/c
 Cylindrical prototype with
GEM readout being developed by
Howard Fenker
 Flat GEM prototype has been
built and is being tested
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New Tools: Gas Cherenkov Counter
 Needed for E-03-106 (GDH Integral at very low Q2), M. Ripani, et al.
Mirrors
PMTs +
Winston
cones
multilayer m-metal
+ iron shield
New Cherenkov
detector optimized
for low Q2 kinematics
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PAC 25 Mini-Workshop 2004
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New Tools: DVCS in N* Physics
ep
e’
e
g*
x+x
e’gN*
g (p, h, w, …)
CLAS (preliminary)
x-x
GPDs
p

2-particle correlations
function
hard process
Bjorken regime
N*
t, x dependence of N* transition
map out transition-GPDs
 decouple g virtuality from momentum
transfer to the nucleon


D
N*’s
study nucleon dynamics at the parton level
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Mnp+ (GeV)
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New Tools: Setup for DVCS
CLAS
Physics Goal
measure x, t,
- dependence of
ep e’p g in a wide kinematics
range to constrain GPD models.
Q2
s.c.
solenoid
Technical Problem
need to detect all final state particles to
identify process
double luminosity to 2x1034 cm-2 s-1
PbWO4
Electromagnetic
calorimeter
Technical solution
add forward calorimeter (436 lead PbWO4 crystals)
readout via avalanche photodiodes (APD)
super conducting 5 Tesla solenoid Moller shield
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Deeply Virtual Meson Production
Final state selects the quark flavors u, d, s
=> probes the GPD structure complementary
to DVCS
 Filter for spin-(in)dependent GPDs

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DVCS Experiment
Superconducting solenoid: needed for shielding Moller electrons
PbWO4 e.m. calorimeter needed for photon detection
Solenoid under
construction at
SACLAY
cryostat
coil windings
calorimeter
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PAC 25 Mini-Workshop 2004
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DVCS - 100 Crystal Prototype for Test Run
Connexion board
APD / Preamplifier
Back frame
Support frame
Mother board
+ preamplifier
Optical fiber system
mounted on the front frame
Alignement system
+ / - 5 mm
Connectors
Fixing plate on the CLAS support
Ph. Rosier, Orsay
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DVCS Experiment
 PbWO4 crystal calorimeter
–
–
–
–
440 tapered crystals, APDs, on site (ITEP, JLab)
Mechanical structure in final design stage (Orsay)
Preamps - designs being evaluated (ITEP, Orsay)
5 x 5 crystal prototype built and being tested
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PrimEx Experiment
PbWO4 crystal channel
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Electron beam test results
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ep e’X at 4 GeV
events
CLAS
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A di-quark model for pentaquarks
JW hep-ph/0307341
JM hep-ph/0308286
q
SZ hep-ph/0310270
q
q
Decay Width: ud ud  s uud us 

1 G  200 MeV 
8 MeV
2
2 6
2 6
( )
Mass Prediction for X−− is 1.75 instead of 2.07 GeV
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Frozen Spin Target
 Needed for Search for missing N* in
pion and kaon photoproduction,
Experiment E-02-112, F. Klein et al.,
E-03-105, S. Strauch et al.
Work by Target group (Chris Keith, et al.)
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Polarizing magnet ordered,
estimated delivery: Feb. 2004
 Longitudinal holding magnet;
prototype constructed – being
tested
 Transverse holding magnet:
prototype for “racetrack” design
completed
 Design for dilution refrigerator
50% completed, construction
underway.

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