Download ppt file - Physics - Kent State University

Future Hadronic Spectroscopy
at JLAB and J-PARC
•
•
•
•
•
•
Introduction
 and Λ Resonances
Quark-Model Predictions
 Resonances
Experimental Considerations
Summary
Hawaii 2005
Second Joint Meeting of the Nuclear Physics
Divisions of the APS and JPS
September 18, 2005
Introduction
Historically, hadron spectroscopy experiments
led to several important discoveries, including:
•
•
•
•
Development of concept of SU(3) symmetry;
Discovery of strange quark;
Discovery of charm quark;
Evidence for glueballs and multiquark states.
This talk will focus on hyperon spectroscopy,
at the request of the organizers.
Introduction (continued)
• In comparison with N* and Δ* resonances,
very little is known about hyperon states.
• Due to relative paucity of K‾p and K‾n
data, our knowledge of properties of Λ*
and * comes almost entirely from energydependent PWAs.
• In comparison with strangeness 0 and -1,
very little is known about * and Ω* states.
Open Questions
• Where are the “missing” hyperon states?
• Are there hybrid hadrons (i.e., states involving
gluonics degrees of freedom)?
• Are there “exotic” hadrons, and if so, what are
their spectra?
• Are there new symmetries to be discovered by
improving our knowledge of hadron spectra?
Expected and Observed Baryon States
Assuming baryons to be formed of three quarks (u,d,s), then SU(3)
provides the decomposition into multiplets to which these states will
belong as 3×3×3=10+8+8+1. Thus, the states should be in the ratio
N*:Δ*:Λ*:*:*:Ω*=2:1:3:3:3:1.
There are 14 N* listed in the PDG tables as 3* and 4* resonances, so
the expected number and observed number of 3* and 4* resonances
is:
Resonance
Δ*
Λ*
*
*
Ω*
Expected #
7
21
21
21
7
Observed #
10
14
10
6
2
From V.V. Abaev et al., “Hadron Spectroscopy at J-PARC” LOI.
Status of Λ and  Resonances
Methods for Identifying * and Λ* Events
• Strangeness -1 hyperons may be identified by
formation in KN experiments or by production
in γN experiments.
• Examples of formation reactions are KN → KN,
Λ, , ηΛ, η, KΔ, K*N, Λ(1520), and
(1385), where the last two reactions are
typically identified from the 3-body final states
KN →  and KN → Λ.
Typical Data at 1165 and 1177 MeV/c
Typical Data for KN→ at 1245 and 1233 MeV/c
Crystal Ball Results for K‾p→0Λ at 750 MeV/c
Partial-Wave Analyses of KN Scattering
• Advantage of formation reactions to study Λ* and *
production is that such reactions lend themselves to
partial-wave analyses.
• Prior PWAs were limited not only by the available
data, but also by computers slow by modern
standards.
• Essentially all resonance information is based on
simplistic energy-dependent parametrizations that
violate unitarity of the S-matrix.
• There is a strong need for high-statistics data
(including spin observables) for a variety of formation
reactions with broad energy coverage.
Example of an Argand Diagram Showing the
Λ(1520) and Λ(1690) Resonances
Quark-Model Predictions
6 

2

2

1  

(r1  r2 )
2
 
r1  r2
2


1  

(r1  r2  2r3 )
6
On Missing Λ* and * States
• Presence of heavier strange quark leads to segregation
of states into ρ oscillations, in which the two nonstrange
quarks oscillate, and Λ oscillations, in which the strange
quark oscillates against the nonstrange pair.
• The nonstrange ρ oscillations trivially decouple from KN
and related channels in the single-quark transition
model.
• Better data are needed in order to make comparisons
with predictions.
 Resonances
Not much is known about  resonances. This is because*
(1)They can only be produced as a part of a final state, and
so the analysis is more complicated than if direct formation
is possible,
(2)The production cross sections are small (typically a few
μb), and
(3)The final states are topologically complicated and difficult
to study with electronic techniques.
*Note
taken from Review of Particle Physics, PLB 592, p. 967 (2004).
Status of  Resonances
Methods for Identifying * Resonances
* events must be identified in production
experiments by either
(1) constructing invariant-mass distributions from
the * decay products, or by
(2) making missing-mass distributions.
Examples will be presented of both methods.
Typical Criteria for Selecting ‾
(or Ω‾ ) Events in K‾p→‾ + anything
• Require invariant mass of
‾ and p to be consistent
with Λ mass.
• Require invariant mass of
‾ (or K‾ ) and Λ to be
consistent with ‾ (or Ω‾).
D. Aston et al., PRD 32, 2270 (1985).
• Require reconstructed Λ
and ‾ (or Ω‾ ) tracks to
be at least 2 cm.
Distributions of Λ‾ Invariant Mass
D. Aston et al., PRD 32, 2270 (1985).
* Detection by Missing-Mass Distributions
• Study of K‾ p → K+ X,
where X contains *
• Completely avoids
problem of detecting
decay products
• Analogous to study of
γ p → K+ K+ X, which
can be studied at
JLab
C.M. Jenkins et al., PRL 51, 951(1983)
States Seen in K‾ p → K+ *‾
C.M. Jenkins et al., PRL 51, 951(1983)
Experimental Considerations:
Hyperon Spectroscopy Physics at J-PARC
In Summer 2002, J-PARC Project Director called
for LOIs for the nuclear and particle physics
experiments at J-PARC. A total of 30 LOIs were
received.
Of these, at least three relate directly to hadron
spectroscopy (baryons and mesons), and two of
those involve spectroscopy requiring highmomentum kaon beams.
LOIs for Hadron Spectroscopy with
Kaon Beams
L13 – Hadron spectroscopy at J-PARC
Contact persons: Shin-ya Sawada (KEK, Japan) and Hal
Spinka (ANL, USA).
L28 – Letter of intent for a hadron
spectroscopy experiment with RFseparated high energy K± beam at JHF
Contact persons: V. Obraztsov (IHEP, Russia) and T.
Tsuru (KEK, Japan).
Kaon beams for Hyperon Spectroscopy
at J-PARC
• Proposed K1.8 beam (high-intensity K‾ beam at
~1.8 GeV/c available at the 50-GeV PS) opens
the possibility for a rich program in Λ* and *
spectroscopy for states up to ~2 GeV in mass.
• To carry out a program in * spectroscopy will
require separated K‾ beams up to about 6
GeV/c.
• As already noted, present data are statistically
limited, and polarization data are especially
needed.
Hyperon Spectroscopy at JLAB
• Program to explore * spectroscopy has already begun
at JLAB using missing-mass methods (J. Price et al.).
• Great opportunity exists to open a new frontier in Λ*
and * spectroscopy by photoproduction and
electroproduction.
• Production by real or virtual photons offers possibility to
discover states that decouple from KN and therefore,
which are not likely to be seen, in formation
experiments with kaon beams.
Summary
• Hyperon spectroscopy is a fundamental area of
physics about which we still know very little.
• Presence of one or two “heavy” quarks
represents a departure from the permutation
symmetry characterizing N* and Δ*
spectroscopy. Quark-model predictions for
mass spectrum and decay mechanisms have
not been stringently tested due to almost no
experimental progress in past two decades.
• High-intensity beam lines with modern 4
detectors offer opportunity to open a new frontier
on the study of S=-1 and S=-2 baryons.