Cascade Physics and Meson Decays in GlueX

Cascade Physics and Meson Decaysin GlueX

Aleksandr StarostinBernard NefkensUCLA

January 29, 2009 A.Starostin, New GlueX Proposals

Outline

Cascades in GlueX– Motivation– Cascade Photoproduction– Detector Requirements

Physics of Meson Decays Summary


Review of Cascade physics:

Workshop “Cascade Physics: A New Window on Baryon Spectroscopy”, December 1-3, 2005, JLab

Presentations available at http://conferences.jlab.org/cascade/

Cascades: Physics Motivation


Summary of Physics with Cascades

Spectroscopy of cascade exited states

including search for parity doubles

(requires JP)

d-u quark mass difference (m(Ξ-)-m(Ξ0) ~

6.5 MeV, requires good energy resolution)

Search for exotic states: Ξ+ and Ξ--


What is known about cascades?

Only 11 Ξ*; 6 “well-established”

Those we know aren't known well: only have JP for three states and a guess of a fourth

SU(3) symmetry requires one Ξ I=1/2 per octet and per decuplet:

n(Ξ*)=n(N*) +n(Δ*)

Ξ0 = uss, Ξ-= dss

Adamovich et al., EPJ C5, 621 Hemingway et al., PLB 68, 197


Cascades in the Constituent Quark ModelS.Capstick and N.Isgur

Most of the exited Ξ* states

are narrow (10-100 MeV): the

decay mode Ξ*->Ξπ is

suppressed (relative to N*-

>Nπ and Δ*->Δπ)

• Phase-space factor

• Flavor overlap factor


Width of the Cascades

N* and Δ* resonances overlap, because of that spectroscopy N* and Δ* requires complicated and ambiguous phase-sift analysis

Cascades are expected to be narrow, parameters of the cascades can be extracted directly from the mass spectra


Search for parity doublets

1/2 3/2 5/2 7/2 9/2

- + - + - + - + - +

N* 1650(1645-1670)

1710(1680-1740)

1700(1650-1750)

1720(1700-1750)

1675(1670-1680)

1680(1680-1690)

2250(2200-2350)

2220(2200-

2300)


Search for parity doublets

The high-mass light baryon spectrum exhibits occurrence of

parity doublets. Glozman suggested to explain the mass

degeneracy by assuming that chiral symmetry is restored in

highly excited hadronic states.

L.Y. Glozman, PL B 475, 329 (2000)T.D. Cohen and L.Y. Glozman PR D 65, 016006 (2001)R.L. Jaffe et al. Phys. Rep. 435, 157 (2006)M. Shifman and A. Vainshtein PR D 77, 034002 (2008)

“Evidence for a Parity Doublet Δ(1920)P33 and Δ(1940)D33 from γp->pπ0η”I.Horn et al., PRL 101, 202002 (2008)


Quark mass difference

• Quark masses are parameters of the Standard Model

• Cascades may provide d-u mass difference

• The difference can be determined for all for exited of Ξ- and Ξ0

states


Search for exotic Ξ+ and Ξ--

Finding Ξ+ and/or Ξ-- would

be a unique signature for a

five-quark state, member of

the antidecupled

Evidences for existance of

Ξ–- were found by CERN

NA49 (PRL, 92, 042003

(2004))

Search was also conducted

by CLAS


Photoproduction of cascades

Cascades in CLAS g11 run

• Number of events for the ground

state – 7678, for the first exited state

– 658

• for most of the run the maximum

energy of tagged photons 3.8 GeV,

some data with 4.8 GeV (the

threshold is about 2.85 GeV)

• Estimates for the γp -> 2K+Ξ- total

cross section by Denis Weygand –

between 3.5 GeV and 4.8 GeV cross

section is flat, order of 10 nb.L. Guo et al. PRC 76, 025208 (2008)


Detector requirements

Very good K/π separation

There are two detached vertices – high resolution tracking device is essential

For neutral cascades – high acceptance EM calorimeter

Hall-D: tagged photons with energies close to 12 GeV GlueX: coverage close to 4π in particular for EM

Decays of Light Mesons


Physics of Meson Decays

Tests of Chiral perturbation theory and other theories of strong interactions

Measurements of electromagnetic form factors

Search for violation of discrete symmetries: C, P, CP, and T

Search for leptoquark and violation of lepton family number,

Most of the decays do not require a dedicated experiment

JP = 0- : π0, η, η’(958)

Jp = 1- : ρ(770), ω(782), ψ(1020)


Tests of ChPT

η->π0π0π0

η->π+π-π0

η’->ηπ0π0

η’->ηπ+π-

Dalitz plot allows to study ππ and ηπ interactions, slop parameters of the Dalitz plot,

“cusp” at the opening of π0π0->π+π- (carries information on the a0-a2 ππ scattering length)


η->l+l-γη->l+l-l+l- ω->l+l-π0 η’->l+l-γ η’->l+l-l+l-

Spectrum of the l+l- mass in the Dalitz carries information on the EM form-factor of the decay vertex

Dalitz and double Dalitz decays


Tests of C


More decays

Tests of P invariance: η->2π, η’->2π, η-

>4π, η’->4π

Search for leptoquaks: η->μ+μ-, η->e+e-

Search for violation of Lepton Family

number: η->μe, η’->μe, etc

Tests of T invariance: absence of the

transverse polarization of μ in η->γμ+μ-


Branching Ratio of η->e+e- and existence of the leptoquark

Leptoquark – a hypothetical particle suggested by A. Salam, carries interaction between quarks and leptons, encountered in various extensions of the Standard Model, such as technicolor theories or GUTs

The single-photon exchange mechanism is forbidden because of conservation of angular momentum

The decay is dominated by a two-photon intermediate state which is suppressed

Provides lower limits of the masses of leptoquarks and axions.

η->e+e-

)(

10370

4

2/1 eeBRGeV

gg

MRue

Lue

LQ

D.Wyler, in proc. inter. workshop. “Rare decays of light mesons”, Gif-sur-Yvatte, France March 29-30, 1990.


Summary

Universality and resolution of the GlueX detector combined with 12GeV tagged photon beam makes cascade program in Hall-D feasible. Both, charged and neutral cascades will be detected using missing mass and invariant mass

The objectives of the cascade program will be to establish spectrum of the exited states and their spin-parity. These data can be used to establish the existence of the cascade parity doublets, calculate d-u quark mass difference and search for the exotic cascade states

Both neutral and charged decays of light mesons can be detected in GlueX. This data sample will be used to test Chiral Perturbation Theory and other theories of strong interactions, search for violation discrete symmetries, and more.



Predictions of the Cascade spectrum

Many quark models, 1/Nc expansions of QCD, etc.

predict spectrum of exited baryon states

Predicted is a rich spectrum of exited states (the constituent quark model by S.Capstick and N.Isgur predicts 45 states below 2.3 GeV, the algebraic model by F.Iachello predicts 32 states)

The constituent quark model and the algebraic model predict the most of the cascade states to be narrow

Lattice QCD calculations?


Tests P


What is known about cascades?

SU(3) symmetry requires one Ξ I=1/2 per octet and per decuplet

Gell-Mann-Okubo mass relation in octet:

Equal spacing mass relation in decuplet:

Ξ0 = uss, Ξ+= dss


Dalitz and double Dalitz decays

Invariant mass of l+l- in the Dalitz and double Dalitz decays: η->l+l-

γ, η->l+l-l+l-, ω->l+l-π0, η’->l+l-γ, η’->l+l-l+l- carries information on

the EM form-factor of the decay vertex

222

|)(|||1

qFQEDPdq

llPdP


Cascades in 1/Nc expansion

70-plet:• 7 masses in range 1750-2000 MeV• Two pairs of same J states nearly degenerate

L=2 56-plet:• 6 masses in range 2000-2250 MeV• Same J states separated by >140 MeV• Larger errors in predictions than in 70-plet• Parameter free mass relations rather well tested.

Presented by J L Goity


Search for “Cascaderium”

NN scattering length a =-17.3 fm. If ΞΞ 1S0 potential is same as for NN: predicted a BOUND STATE: dibaryon S=-4 decays weakly to ΞΛπ->NN4π ΞΞ binding predicted by many potential

models

γd -> 2K+ 2K0 [Ξ0 Ξ-] γα -> 2K+ 2K0 [Ξ0 Ξ-] n p

Neutral cascades are preferred to avoid repulsion

(J.Miller, Cascade workshop)Figure by R.Jones


Test of Time reversal invariance


Search for exotic Ξ+ and Ξ--

Ξ+ and Ξ–- are unique signatures for a five-

quark state, member of the antidecupled

Evidences for existance of Ξ–- were found

by CERN NA49 (PRL, 92, 042003 (2004))

Search was also conducted by CLAS (run

g12?)


Cascades in quark models

S.Capstick and N. Isgur PRD 34 2809 (1986)

45 cascades states with

masses below 2.3 GeV


Cascades in agebraic model

A.R. Bijker, F.Iachello, and A. LeviatanAnn. Phys. 284 89 (2000)

Documents

Cascade Physics and Meson Decays in GlueX