Ralf W. Gothe PAC 25 Mini-Workshop Nucleon Excited States Ralf W. Gothe University of South Carolina Mini-Workshop on Nucleon Excited States PAC25 January 17, 2004 Introduction N  transition “Missing” Resonances, Strange Resonances and Two Pion Production Pentaquark States Outlook

Ralf W. Gothe PAC 25 Mini-Workshop 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

Ralf W. Gothe PAC 25 Mini-Workshop CLAS Coverage for ep e’X at 4 GeV CLAS

Ralf W. Gothe PAC 25 Mini-Workshop CLAS Coverage for ep e’pX at 4 GeV missing states CLAS

Ralf W. Gothe PAC 25 Mini-Workshop 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 Q 2 allows to change the spatial resolution and enhances different multipoles  sensitive to missing resonance states

Ralf W. Gothe PAC 25 Mini-Workshop SU(6): E 1+ =S 1+ =0 N  (1232) Transition Form Factors

Ralf W. Gothe PAC 25 Mini-Workshop Cross Section Decomposition example: e p e’ p  o

Ralf W. Gothe PAC 25 Mini-Workshop  p p   – Response Functions CLAS

Ralf W. Gothe PAC 25 Mini-Workshop Multipole Analysis for  *p p   Q 2 = 0.9 GeV 2 |M 1+ | 2 Re(E 1+ M 1+ *) Re(S 1+ M 1+ *) |M 1+ | 2 CLAS

Ralf W. Gothe PAC 25 Mini-Workshop Multipole Ratios R EM, R SM before 1999 Sign? Q 2 dependence?  Data could not determine sign or Q 2 dependence

Ralf W. Gothe PAC 25 Mini-Workshop Multipole Ratios R EM, R SM in 2002 Sign? Q 2 dependence ! Slope < 0 < 0 !  No trend towards pQCD behavior is observed for Q 2 up to 4 GeV 2.

Ralf W. Gothe PAC 25 Mini-Workshop  Preliminary results from ELSA and Hall A using different techniques confirm CLAS data. N  (1232) Transition Form Factors

Ralf W. Gothe PAC 25 Mini-Workshop Need data at low Q 2 N  (1232) Transition Form Factors  Lattice QCD indicates that the pion cloud makes E 1+ /M 1+ more negative at small Q 2.  Data at low Q 2 needed to study effects of the pion cloud.

Ralf W. Gothe PAC 25 Mini-Workshop  Dynamical models and full LQCD calculations indicate the importance of the pion cloud at low Q 2 consistent with the trend of data.  Full LQCD results indicate a small oblate deformation of the  (1232).  Data at high Q 2 needed to study the transition to pQCD. Preliminary Multipole Ratios R EM, R SM preliminary

Ralf W. Gothe PAC 25 Mini-Workshop  New trend towards pQCD behavior may or may not show up.  Experiment E in Hall C will reach Q²~8 GeV² and after the energy upgrade R EM and R SM can be measured up to Q²~12 GeV². Very Preliminary Multipole Ratios R EM, R SM preliminary

Ralf W. Gothe PAC 25 Mini-Workshop N  Transition and Background Terms  systematic uncertainties in extraction of E 1+ /M 1+ from ep e’p  o around 0.5%  differences in treatment of background terms (models not constrained)  will become more severe for higher Q 2 (  dropping faster)  more experimental information on hand (polarization and isospin)  single-spin asymmetry   TL’ for e p e’p (  o ) and e p e’  + (n)  polarization transfer in e p e’p (  o )  differential cross sections for e p e’  + n (  less important) CLAS Hall A CLAS

Ralf W. Gothe PAC 25 Mini-Workshop Polarized Beam Observables  LT ’ response e p e p   CLAS function for  LT’ = 0 if only a single diagram contributes (sensitive to the interference between  and background)

Ralf W. Gothe PAC 25 Mini-Workshop Polarization Measurement in e p e’ p (  o ) Hall A Q 2 = 1 GeV 2 W = GeV Results sensitive to non-resonant contributions Parametrisations of available data SAID MAID  b/sr

Ralf W. Gothe PAC 25 Mini-Workshop  + Electroproduction CLAS

Ralf W. Gothe PAC 25 Mini-Workshop 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 Q 2 allows to change the spatial resolution and enhances different multipoles  sensitive to missing resonance states

Ralf W. Gothe PAC 25 Mini-Workshop Quark Model Classification of N*  (1232) “Missing” P 13 (1870) Capstick and Roberts D 13 (1520) S 11 (1535) Roper P 11 (1440) D 13 (1895) Mart and Bennhold ? + q³g + q³qq + N-Meson + …

Ralf W. Gothe PAC 25 Mini-Workshop “Missing” Resonances? fewer degrees-of-freedom open question: mechanism for q 2 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  coupling not suppressed electromagnetic excitation is ideal 3. chiral symmetry approach all baryonic and mesonic excitations beyond the groundstate octets and decuplet are generated by coupled channel dynamics (not only  (1405),  (1520), S 11 (1535) or f 0 (980)) old but always young new

Ralf W. Gothe PAC 25 Mini-Workshop preliminary Resonances in Hyperon Production?  *p K + Y backward hemisphereforward hemisphere N* ? CLAS

Ralf W. Gothe PAC 25 Mini-Workshop  Photoproduction off the Proton Dominant resonances S 11 (1650) P 11 (1710) P 13 (1720) Bump at 1.9 GeV D 13 (1895) ? Carnegie Mellon CLAS

Ralf W. Gothe PAC 25 Mini-Workshop Resonances in  *p p  +  - extra strength CLAS Analysis performed by Genova-Moscow collaboration Step #1: use the best information presently available  N  : PDG  N  : expt. Data or SQTM Q² 0.65 GeV² 1.30 GeV² 0.95 GeV²

Ralf W. Gothe PAC 25 Mini-Workshop Attempts to fit observed extra strength CLAS Step #2:  vary parameters of the photocouplings  vary parameters of known P 13, P 11, D 13  introduce new P 13 New P 13 (1720) consistent with predictied missing P 13, but at lower mass.

Ralf W. Gothe PAC 25 Mini-Workshop Attempts to fit observed extra strength CLAS Step #2:  vary parameters of the photocouplings  vary parameters of known P 13, P 11, D 13  introduce new P 13 W(GeV)

Ralf W. Gothe PAC 25 Mini-Workshop PWA in  p p  +  - CLAS W=2240 MeV

Ralf W. Gothe PAC 25 Mini-Workshop Resonances in  p p  +  - CLAS

Ralf W. Gothe PAC 25 Mini-Workshop Resonances in  p p  +  - CLAS F 15 (1680)P 13 (1720) preliminary

Ralf W. Gothe PAC 25 Mini-Workshop JLab:  + - Exclusive Process I ++ Mass 1.542±0.005 GeV/c²  < 21 MeV/c² Significance 5.2±0.6  CLAS  d K - K + p(n)

Ralf W. Gothe PAC 25 Mini-Workshop JLab:  + - Exclusive Process II K*K*  K-K- p  K0K0 ++ K+K+ n CLAS  p  + K - K + (n) Events K* M(K -  + ) 

Ralf W. Gothe PAC 25 Mini-Workshop JLab:  + - Exclusive Process III CLAS  p  + K - K + (n)   p  ++ N* K+K+ n K-K- Mass 1.555±0.010 GeV/c²  < 26 MeV/c² Significance 7.8±1.0   combined analysis II & III cut

Ralf W. Gothe PAC 25 Mini-Workshop JLab:  + - Exclusive Process III CLAS  p  + K - K + (n)   p  ++ N* K+K+ n K-K- Mass ~ GeV/c² N*?N*?

Ralf W. Gothe PAC 25 Mini-Workshop Outlook: Observation of Exotic  −−  (1530) CERN SPS hep-ex/ M=1.862± GeV/c²  < 18 MeV/c² 00 combined analyis NA49

Ralf W. Gothe PAC 25 Mini-Workshop Outlook: Observation of Exotic  −−  (1530) CERN SPS hep-ex/ M=1.862± GeV/c² 00 Diakonov et al. Hep-ph/ Diakonov, Petrov hep-ph/ Jaffee, Wilczek hep-ph/ Jaffee, Wilczek hep-ph/ R.A. Arndt et al. nucl-th/ PAC 25 at JLab

Ralf W. Gothe PAC 25 Mini-Workshop Hadron multiplets Baryons qqq Mesons qq ── ++ N   K  K Baryons built from meson-baryon, or qqqqq …

Ralf W. Gothe PAC 25 Mini-Workshop New Tools: Exploit Weak Decays in Direct Reconstruction Electron beam Negatives bend outwards  − c  = 4.9 cm  c  = 7.9 cm  −− →  −  −  − →  −   →  − p  n → K + K +   −−  ~ 1.5

Ralf W. Gothe PAC 25 Mini-Workshop New Tools: Frozen Spin Target for CLAS Solution: - frozen spin target - temperature 50mK - magnetic field 5kG Status: - design in progress at JLab - procurement started for polarizing magnet Technical problem: build polarized target for tagged photon beam - minimum obstruction of CLAS solid angle - low distortion of particle trajectories in magnetic field 5 Tesla polarizing magnet CLAS Bonn target at Mainz GDH experiment JLab design

Ralf W. Gothe PAC 25 Mini-Workshop New Tools: Bound Nucleon Structure (BoNuS) pair spectrometer Solution:  - high pressure gas target  - surrounded by radial drift chamber  - GasElectronMultiplier gap Technical problem: spectator protons have  - low momentum and low range  - isotropic angular distribution (no correlation)  - high rate CLAS coils Physics issue: tag process off a neutron bound in deuterium by detecting the spectator proton in coincidence with the scattered e’

Ralf W. Gothe PAC 25 Mini-Workshop 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

Ralf W. Gothe PAC 25 Mini-Workshop New Cherenkov detector optimized for low Q 2 kinematics Mirrors PMTs + Winston cones New Tools: Gas Cherenkov Counter  Needed for E (GDH Integral at very low Q 2 ), M. Ripani, et al. multilayer  -metal + iron shield

Ralf W. Gothe PAC 25 Mini-Workshop New Tools: DVCS in N* Physics ep e’  N*  t,  dependence of N* transition  map out transition-GPDs GPDs p N*N* e e’   …  hard process Bjorken regime 2-particle correlations function x+  x-   decouple  virtuality from momentum transfer to the nucleon  study nucleon dynamics at the parton level  N*’s M n  (GeV) CLAS (preliminary)

Ralf W. Gothe PAC 25 Mini-Workshop New Tools: Setup for DVCS Physics Goal measure , t, Q 2 - dependence of ep e’p   in a wide kinematics range to constrain GPD models. Technical Problem  need to detect all final state particles to identify process  double luminosity to 2x10 34 cm -2 s -1 Technical solution  add forward calorimeter (436 lead PbWO 4 crystals)  readout via avalanche photodiodes (APD)  super conducting 5 Tesla solenoid Moller shield PbWO 4 Electromagnetic calorimeter s.c. solenoid CLAS

Ralf W. Gothe PAC 25 Mini-Workshop

Ralf W. Gothe PAC 25 Mini-Workshop 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

Ralf W. Gothe PAC 25 Mini-Workshop DVCS Experiment Superconducting solenoid: needed for shielding Moller electrons PbWO 4 e.m. calorimeter needed for photon detection calorimeter coil windings cryostat Solenoid under construction at SACLAY

Ralf W. Gothe PAC 25 Mini-Workshop Fixing plate on the CLAS support Optical fiber system mounted on the front frame Connectors Alignement system + / - 5 mm Back frame Mother board + preamplifier Connexion board APD / Preamplifier Support frame DVCS Crystal Prototype for Test Run Ph. Rosier, Orsay

Ralf W. Gothe PAC 25 Mini-Workshop  PbWO 4 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 DVCS Experiment

Ralf W. Gothe PAC 25 Mini-Workshop PrimEx Experiment Electron beam test resultsPbWO 4 crystal channel

Ralf W. Gothe PAC 25 Mini-Workshop ep e’X at 4 GeV CLAS events

Ralf W. Gothe PAC 25 Mini-Workshop A di-quark model for pentaquarks JW hep-ph/ JM hep-ph/ SZ hep-ph/ Decay Width:   MeV  Mass Prediction for  −− is 1.75 instead of 2.07 GeV q q q

Ralf W. Gothe PAC 25 Mini-Workshop  Needed for Search for missing N* in pion and kaon photoproduction, Experiment E , F. Klein et al., E , S. Strauch et al.  Polarizing magnet ordered, estimated delivery: Feb  Longitudinal holding magnet; prototype constructed – being tested  Transverse holding magnet: prototype for “racetrack” design completed  Design for dilution refrigerator 50% completed, construction underway. Work by Target group (Chris Keith, et al.) Frozen Spin Target