Photoproduction of Cascade baryons Yongseok Oh (UGA) H. Haberzettl (GWU) K. Nakayama (UGA) nucl- th/

The University of Georgia What do we know about  ? PDG –If all the particles can be classified as SU(3) flavor octet or decuplet, N(  ) = N(N*) + N(  *) –So far, only a dozen or so of  have been identified. –Only  (1318) and  (1530) have four-star status. –Even the quantum numbers of most of the  resonances are unknown. –So, very little is known about the  resonances. But this may offer a good opportunity to find many interesting physics. possibility of being in part a pentaquark  (1520)S 11 (B.-S. Zou, this meeting).

The University of Georgia Cascade (S=-2) baryons: GS:  (1318)P 11 1st ES:  (1530)P 13

The University of Georgia Theory of  baryons (spectrum and decays):  Quark Models : ● SU(3), NR, EME decay model ( Chao, Isgur, Karl, PRD23, ‘81 ). ● SU(3), NR, OPE model ( Glozman, Riska, PR268, ‘96 ). ● SU(3), semi-rel., OBE model ( Glozman et al., PRD58, ‘98 ). ● SU(3), OBE+OGE model ( Valcarce, Garcilazo, Vijande, PRC72, ‘05 ). ● 1/N c expansion of QCD ( Schat, Goity, Scoccola, PRL88, ‘02 ).  Other works in progress: ● SU(3) quark model, relativistic ( S. Capstick & collaborators ). ● (quenched) lattice QCD ( N. Mathur, D. Richards ).

The University of Georgia  baryon spectrum (predictions and expt): Extracted from S. Capstick, July

The University of Georgia An interesting feature of Cascades:  *   decays are suppressed with respect to  N . For example:   (1232)   p   ~ 120±5 MeV         ~ 9-10 MeV - Other channels involve K, which cuts down the available phase space. - Leads to the possibility of narrow excited states. - Why are they narrow? Some of this is phase space: decay momentum for  (P-wave) is 227 MeV;  *(1530)  (P-wave) is 152 MeV.

The University of Georgia  decay widths: Extracted from S. Capstick, July

The University of Georgia  baryons should be investigated  Cascade baryons should be studied as an integral part of the baryon spectroscopy program: ● being an S=-2 baryons they are produced only indirectly and have relatively low production rates (~ nb). ● it has received attention recently in connection with the search for pentaquark baryons ( NA49 collab., PRL92, ’04 ). ● the CLAS collaboration at JLab has initiated a cascade physics program recently: cascade spectroscopy through  photoproduction off nucleons ( J.Price et al., PRC71, ’05 and refs. therein ). ● only one early inclusive photoproduction of  reported ( TAPS collab., NPB282, ‘87, at T  =105 GeV ).

The University of Georgia  p→K + K +   L. Guo & D. P. Weygand, for CLAS collab., hep-ex/ , Proc. NSTAR05 preliminary CLAS data

The University of Georgia Aim of the present work : (Exploratory) theoretical investigation of the reaction  N→KK  within a relativistic meson-exchange model of hadronic interactions. As a first step toward building a reliable reaction model for analyzing the cascade spectroscopy data, one needs to understand in detail the production mechanism(s) of the well established cascades (  (1318)P 11,  (1530)P 13 ). To date, no cascade photoproduction calculation is available so far, except for the hadronic model calculation by Liu and Ko ( PRC69, ’04 ) in connection with the pentaquark cascade production in  →KK  5 [includes only the hyperon  (1193) in the intermediate state].  (1520)S 11 ? (B.-S. Zou).

The University of Georgia  KK  (model): K-exchangeN/N’ K*-exchange contact current  ’ + ( K 1 (q 1 )↔K 2 (q 2 ) ) Y= Y’ resonance current Y≠Y’ radiative decay

The University of Georgia  N → KK  (model): require an exotic meson (S=+2) exchange; therefore, they are not considered in the present model t-channel Drell-type processes:

The University of Georgia  KK  (baryon resonances included):  (1116),  (1405),  (1520)  (1193),  (1385)  (1530)  (1232) ← negligible all the model parameters fixed from the relevant decay rates(PDG) and/or quark models and SU(3) symmetry considerations. no enough information to fix the parameters of the model.

The University of Georgia  KK  (model parameters):

The University of Georgia  N →KK  (free parameters of the model) : ps-pv mixing parameter: BYK vertex (spin-1/2 baryons B and Y):  = ps-pv mixing parameter) = 0, ps-coupling = 1, pv-coupling g B  K = ± 0.91,  ), B=N,  g  ′  = ± 1.26,  (1116),  ′(1520) g  = ± 2.22,  (1193),  ′(1520) signs of : ← radiative transition vertex ← B  K vertex

The University of Georgia  KK  (hadronic form factors): pp′p′ q F   B & n: free parameters but the same for all B  K = 1.3 GeV  K* = 1.0 GeV [n→∞: f B (p 2 ) → Gaussian with width  B ]

The University of Georgia  N→KK  (preliminary CLAS data, L. Guo & D. P. Weygand, for CLAS collab., hep-ex/ , Proc. NSTAR05) BYK (ps-coupling) (  B, n)=(1.25GeV, 2) BYK (pv-coupling) (  B, n)=(1.38GeV, ∞) phase space PRELIMINARY CLAS DATA

The University of Georgia  N→KK  (dynamical content : spin-3/2 hyperon contributions) : + Y≠Y′ (rad. decay) Y=Y′ (res)

The University of Georgia  N→KK  (preliminary CLAS data, L. Guo & D.P.Weygand, private communication) : (x 15) Y≠Y′ (rad. decay)  p→K + K +  - PRELIMINARY CLAS DATA

The University of Georgia  N→KK  (higher mass resonances) Consider spin-1/2 and -3/2 resonances: ● |g NYK | can be estimated from the partial decay widths. ● unless g  YK is unrealistically large : J P =1/2 + and 3/2 - are negligibly small ! on-shell:

The University of Georgia  N→KK  ( addition of higher mass resonances) :  (2000)3/2 + (g N  K g  K ~2.5)  (1850)1/2 - (g N  K g  K ~2.0)  (1950)3/2 + (g N  K g  K ~2.0) (  B,n) = (1.23GeV,∞) BYK (pv-coupling) (  B,n) = (1.25GeV,∞) BYK (pv-coupling)

The University of Georgia  N→KK  ( adding  (1850)1/2 - &  (1950)3/2 + ) : PRELIMINARY CLAS DATA

The University of Georgia  N→KK  ( adding  (1850)1/2 - &  (1950)3/2 + ) : PRELIMINAY CLAS DATA (L.Guo & D.Weygand, private communication)

The University of Georgia  N→KK  ( adding  (1800)1/2 -,  (1890)3/2 + &  (2050)3/2 + ) :  (1800)1/2 - (g N  K g  K ~2.0)  (1890)3/2 + (g N  K g  K ~1.2)  2050)3/2 + (g N  K g  K ~1.4)

The University of Georgia  N→KK  ( adding  (1800)1/2 -,  (1890)3/2 + &  (2050)3/2 + ) : PRELIMINARY CLAS DATA (L.Guo & D. Weygand, private communication)

The University of Georgia  N→KK  (higher spin resonances in the GeV region) ● work in progress to include them ! ● unidentified  (2050)3/2 + : simulating these high spin states as far as the invariant mass distribution is concerned.

The University of Georgia Spin asymmetries Photon beam asymmetry & target asymmetry Caution: Spin asymmetries may be sensitive to production mechanisms and need careful and detailed analyses. What do we have in these simple models?

The University of Georgia Beam Asymmetry  B Low-mass hyperons+ higher-mass hyperons pv coupling ps coupling K-exchange    = -1. pv and ps couplings give the similar beam asymmetry. beam asymmetry distinguishes the models with and without higher resonances.

The University of Georgia Target Asymmetry  T pv coupling ps coupling Target symmetry has different sign depending on the coupling scheme. with higher-mass hyperons

The University of Georgia Summary of our findings : The dominant  - production mechanism in  p→K + K +  - is the t-channel K-exchange process which is crucial in describing the observed backward peaked  - and forward peaked K + angular distributions. Also, the beam asymmetry can possibly provide an independent test of the t- channel K-exchange dominance. Higher mass hyperons in the mass region of ~ GeV (in particular,  (1800)1/2 - and  (1890)3/2 + ) are needed to possibly provide the required t-channel K-exchange dominance. Low mass hyperons instead give raise to a dominant radiative hyperon-hyperon transition processes which lead to a forward peaked  - and backward peaked K + angular distributions (just opposite to what is observed in the preliminary CLAS data). The target asymmetry can possibly impose a constraint on the ps-pv mixing parameter.

The University of Georgia Summary of our findings : The K +  - invariant mass distribution data indicate a need for additional resonance(s) in the ~ GeV region. In fact, there are known spin-5/2 and -7/2 hyperons (with 3 and 4 stars status) precisely in this energy region. We are currently working to include these resonances into the model. ( the unknown  (2050)3/2 + was introduced in the present calculation for illustration purposes to make this point )  Measurements of other isospin channels would help disentangle the isoscalar  and isovector  hyperon resonance contributions.

The University of Georgia Conclusion : To our knowledge, this is the first quantitative calculation of the cascade photoproduction off nucleons. The basic features of the  p→K + K +  - (1318) reaction could be understood. In particular, this reaction can be used to help extract information on higher mass hyperon resonances. The findings of the present work should serve as a basis for building more complete models of cascade photoproduction to help analyze the forthcoming cascade data.

The University of Georgia The End

The University of Georgia Resonance widths,,, q iR =q i (W=m R ) R→N  R→N 

The University of Georgia  KK  (phenomenological contact current): q1q1 pp′p′ q2q2 B bare NBK  contact vertex = NBK vertex C=C= 11 e i -e B -e 1 =0