resonances E. Golovach SINP Moscow State University EMIN 2018 - PowerPoint PPT Presentation

First information from photo- and electroproduction of high lying nucleon resonances E. Golovach SINP Moscow State University EMIN 2018

Introduction Excitation spectrum of nucleon and the resonance photocouplings → exploration of the strong interaction in the non-perturbative regime of QCD In the past decay the data on exclusive photo- and electroproduction have been obtained at CLAS, ELSA, MAMI, GRAAL and LEPS. πN, η N, η’N, KΛ , K Σ 0 , ππN → differential x-sec and polarization observables. Multichannel analysis by BoGa → several new baryon states N(1710)1/2+, N(1895)1/2-, N(1900)3/2+ πN .vs. ππN channels. High lying resonances (M > 1.6 GeV) decay preferably in two pion channels. Photo- and electroproduction: resonance must be described with the hadronic decay with. Photoproduction of π 0 π 0 N and π + π - N Search for new states

Missing excited nucleon states and hybrid states Excitation spectrum of nucleon and the resonance photocouplings → exploration of the strong interaction in the non-perturbative regime of QCD

Missing excited nucleon states and hybrid statestates LQCD predicts starting from QCD Lagrangian the same amount of new baryon states as the CQM model based on the SU(6) symmetry. It is a strong motivations for the “missing” baryon state search. Most of the resonances with mass more that 1.6 GeV decay preferably in two pions. regular states hybrid states

Search for new states 1. Missing nucleon states 2. Hybryd baryons with dominant gluonic contributions are predicted by QCD models.  MIT bag model T. Barnes and F. Close, Phys. Lett. 123B, 89  QCD Sum Rule L. Kisslinger and Z. Li, Phys. Rev. D 51, R5986 (1995).  Flux Tube model S. Capstick and P. R. Page, Phys. Rev. C 66, 065204 (2002).  LQCD J.J. Dudek and R.G. Edwards, PRD85 (2012) 054016. Hibryd baryons |qqqg> have the same quantum numbers as regular states |qqq> A 1/2 (Q 2 ), A 3/2 (Q 2 ), S 1/2 (Q 2 ) show different Q 2 evolution. The lowest mass (~2.3 GeV) hybrids are predicted to have J p =1/2 + and J p =3/2 +

CEBAF accelerator and the CLAS (1997-2012) detector Continuous Electron beam: Emax = 6 GeV Maximal current = 200 μ A CLAS ~4 π spectrometer for Photon beam 0.8-5.5 GeV detecting multi-particle final states (DC, TOF, CC, EC)

Cross sections for the two pion photo- and electroproduction  p     2  i = (p   ), (     ), (p   ) d d d d d , , , , ... j = p,   ,   p     dM d d d dM d i j j j i j     The kinematic variables are in the CM frame Unpolarized photoproduction cross sections does not depend on φ j angle 1-fold differential cross sections were obtained for the two pion electroproduction 2-fold and two-fold differential cross sections were obtained for the two pion photoproduction  Two charged particles were required to be in the trigger during g11 run

Cross sections for the two pion electroproduction Q 2 =2.0-2.4 GeV 2 W=1.8 GeV 10 b) m ( s 1 2 2 2.0<Q <2.4 GeV 2 2 2.4<Q <3.0 GeV 2 2 3.0<Q <3.5 GeV 2 2 3.5<Q <4.2 GeV 2 2 4.2<Q <5.0 GeV 1.4 1.5 1.6 1.7 1.8 1.9 2 W (GeV) D33(1700),P13(1720) D13(1520) 3/2 + (1720),F15(1685) S11(1535)

Amplitudes in the JM model

Resonant part of the amplitude γ (v)   (  , r 0 ) * N*, △ Unitarizet Breit-Wigner anzatz D  , (D 0 , p ) p • A 1/2 (Q 2 ), A 3/2 (Q 2 ), S 1/2 (Q 2 ) • G M (Q 2 ), G E( Q 2 ), G C (Q 2 )

The CLAS Data on     p differential cross sections and their fit within the Framework of Meson-Baryon Reaction Model JM G.V.Fedotov et al, PRC 79 (2009), 015204 M.Ripani et al, PRL 91 (2003), 022002 1.30<W<1.56 GeV; 0.2<Q 2 <0.6 GeV 2 1.40<W<2.30 GeV; 0.5<Q 2 <1.5 GeV 2  + F 0  + D 0 r p 15 (1680) full JM calc.  - D ++ 2  direct  + D 0 13 (1520)

Evidence for a new N’( 1720)3/2 + state from combined analysis of the two pion photo- and electroproduction off protons p ’ Resonant part of the amplitude N(1720)3/2 + hadronic decays from the CLAS γ (v)   (  , r 0 ) data fit with conventional resonances only * N*, △ BF( D ), % BF( r p), % D  , (D 0 , p ) p electroproduction 64-100 <5 photoproduction 14-60 19-69 A 1/2 (Q 2 ), A 3/2 (Q 2 ), S 1/2 (Q 2 ) N* hadronic decays from the data fit that incorporates the new N’(1720)3/2 + state The contradictory BF values for N(1720)3/2 + decays to the D and r p final states deduced BF( D ), % BF( r p), % Resonance from photo- and electroproduction data make it N’(1720)3/2 + impossible to describe the data with electroproduction 47-64 3-10 conventional states only. photoproduction 46-62 4-13 Successful description of  +  - p photo- and N(1720)3/2 + electroproduction data achieved by electroproduction 39-55 23-49 implementing new N’(1720)3/2 + state with photoproduction 38-53 31-46 Q 2 -independent hadronic decay widths of D (1700)3/2 - all resonances contributing at W~1.7 GeV electroproduction 77-95 3-5 provides strong evidence for the existence of photoproduction 78-93 3-6 new N’(1720)3/2 + state.

1-fold differential cross section for the two pion photoproduction Example of the θ p’ distribution at W = 1.71 GeV. Uncertainties are related substantially to the presence of the inefficient areas in the CLAS detector. Contribution from the inefficient areas to the cross section were determine: 1. The cross section value determined in each 1-D bin was multiplied by the ratio of the total number of the contributing 4-D cells to the number of bins with non zero efficiency. 2. Improved extrapolation of the 4-D cross section into inefficient areas of CLAS was carried out within the framework of the JM model.

1-fold differential cross sections for the two pion photoproduction Systematic uncertainties are related to the extrapolation of the cross section into inefficient area.

2-fold differential cross sections for the two pion photoproduction  - D ++ subchannel,  + D 0 subchannel, W=1.81 GeV t D -exchange t D -exchange crossed cells are the cells with large contributions from the reaction phase space area of zero acceptance were taken out. First results on 9 one-fold differential and 28 r subchannel, two-fold differential  +  - p photoproduction t pp ’ -exchange cross sections have become available from CLAS at W from 1.6 to 2.0 (2.5) GeV.

Two pion photoproduction Fully integrated cross section CLAS data CLAS data SAPHIRE data (C.Wu et al .Eur.Phys.J. A23 317 (2005)) ABBHM data (ABBHHM collab. Phys. Rev. 188, 2060 (1969))

Fit of the cross sections by the JM17 model   r p     + D 0     - D ++     + D 0 13 (1520)  .   + N (1520)3/2- JM17 model is the Improved model of V.I. Mokeev et al., PRC 80, 045212 (2009).

Starting values for the hadronic decay parameters

Resonance electrocouplings determined from the     p photoproduction data

SUMMARY  The first results on nine 1-fold differential cross section of the two pion photoproduction off the proton in the range of W from 1.6 to 2.0 GeV were obtained with the CLAS detector. The data amounts to a factor ~50 increase in the number of events compared to previous measurements.  For the first time, the nucleon resonance photocouplings for the states in the mass range 1.6 to 2.0 GeV were determined from the analysis of the photoproduction data.  The Δ (1620)1/2-, Δ (1700)3/2-, N(1720)3/2+, and Δ (1905)5/2+ resonance photocouplings were extracted with much improved accuracy compared to previous π N analysis.  Combined analysis of the photo- and electroproduction data requires including the new baryon state N’(1720)3/2 + , since the cross sections can be successfully described with Q 2 - independent hadronic decay widths to the D and r p of all contributing resonances only with new state added. This provide an evidence for the existence of N’(1720)3/2 + new baryon state  Analysis of the data for W from 2.0 to 2.5 GeV is in progress.  We have plans to include 2-fold differential cross sections Obtained photoproduction results were accepted for publication in PLB