John W. Price N* 2005 12-15 October 2005 Cascade Physics A New Window on Baryon Spectroscopy John W....
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Transcript of John W. Price N* 2005 12-15 October 2005 Cascade Physics A New Window on Baryon Spectroscopy John W....
![Page 1: John W. Price N* 2005 12-15 October 2005 Cascade Physics A New Window on Baryon Spectroscopy John W. Price California State University, Dominguez Hills.](https://reader034.fdocuments.us/reader034/viewer/2022051821/56649edb5503460f94bea5f8/html5/thumbnails/1.jpg)
John W. Price N* 2005 12-15 October 2005
Cascade PhysicsA New Window on Baryon Spectroscopy
John W. PriceCalifornia State University, Dominguez Hills
N* 2005 WorkshopOctober 12-15, 2005
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John W. Price N* 2005 12-15 October 2005
Outline
● Motivation for Ξ studies
● Description of Ξ program
● Summary and “call for help”
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John W. Price N* 2005 12-15 October 2005
Why Cascades?
● N* physics getting hard to do
– Need lots of data
– Need complicated computer analysis
– Interpretation difficult
● States broad, overlapping
● We need another type of particle that...
– ...is narrow & easy to isolate
– ...is otherwise similar to N*
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John W. Price N* 2005 12-15 October 2005
Why Cascades?
● Cascade widths are ~9 times narrower than N* widths
● Identifiable in a missing mass plot
– related to (# of light quarks)2 in baryon (“9:4:1” ratio) [Riska, Eur. Phys. J. 17, 297 (2003)]
![Page 5: John W. Price N* 2005 12-15 October 2005 Cascade Physics A New Window on Baryon Spectroscopy John W. Price California State University, Dominguez Hills.](https://reader034.fdocuments.us/reader034/viewer/2022051821/56649edb5503460f94bea5f8/html5/thumbnails/5.jpg)
John W. Price N* 2005 12-15 October 2005
SU(3)F symmetry
● LQCD=L0+Lm
● L0 same for all quarks
● L0 sets the mass scale for a given multiplet
q
mq q
i
qi● Lm=
● Lm sets the mass splitting within a multiplet
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John W. Price N* 2005 12-15 October 2005
SU(3)F MultipletsWith only qqq states, SU(3)F gives four multiplets
one
singlet: N 0 N0
0two octets:
0
0
0one
decuplet:
For every N*, a Ξ with
“similar properties"
For every Δ*,
a Ξ with
“similar properties”
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John W. Price N* 2005 12-15 October 2005
Producing Cascades
● K-p→K+Ξ-
– Get Cascade with missing mass or reconstruction
– No suitable kaon beams available
● γp→K+K+Ξ-
– Detect K+K+, infer cascade in missing mass plot
– Small physics background; none below 1.6 GeV
– Same technique used for all excited states
– Hall B, CLAS suitable
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John W. Price N* 2005 12-15 October 2005
Quality of Cascade Data
● Recent publication indicates σt(γp→K+K+Ξ-)=3.5±0.5
±1.5 nb
3.2<Eγ<3.9 GeV
3.0<Eγ<5.2 GeV
Price et al., PRC 71, 058201
(2005)
● Careful analysis yields very clean signal
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John W. Price N* 2005 12-15 October 2005
Cascades with higher statistics
● 70 pb-1 γp data
● 1.6 < Eγ < 3.8 GeV
● Talk by Lei Guo
– Session P2-C
● Large Ξ production rate
– Sufficient for a Ξ program
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John W. Price N* 2005 12-15 October 2005
Areas of study
● (Study of known/Search for missing) Ξ*'s
● Study of the Ξ0 excited states
● Ξ production mechanism
● Ξ decay modes
● JP determination of the Ξ*'s
● s-d quark mass difference
● Ξp scattering
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John W. Price N* 2005 12-15 October 2005
Known/Missing Ξ* study
● Recall from SU(3)F symmetry
– Octets: each N* has a corresponding Ξ
– Decuplets: each Δ* has a corresponding Ξ
● We're missing 14-33 Ξ's
● Those we know aren't known well
– Only have JP for three states
● Much to learn from a survey of the Ξ spectrum
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John W. Price N* 2005 12-15 October 2005
The Ξ(1950)● 3-star state● JP unknown● “something” seen by
several groups● Large disagreement about
mass● “The accumulated evidence for a Ξ near 1950
MeV seems strong enough to include a Ξ(1950) in the main Baryon Table, but not much can be said about its properties. In fact, there may be more than one Ξ near this mass.”
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John W. Price N* 2005 12-15 October 2005
Looking for new Ξ states
● Look for new Ξ states based on existing baryons
● Consider:
– N(1535)½-→N(940)η
– Λ(1670)½-→Λ(1115)η
– Σ(1750)½-→Σ(1190)η
● Is there a Ξ(1870)½- that decays to Ξ(1321)η?
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John W. Price N* 2005 12-15 October 2005
Ξ0 Properties
● Ξ0 detected by requiring an additional π-
● Mass must be near Ξ- mass
● related to m m m 0 mq
md
mu
– ΔmΞ(1321) = +6.48±0.24 MeV
– ΔmΞ(1530) = +3.2±0.6 MeV
● Only other measurements: N(940), Δ(1232)
● Related to medium modification
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John W. Price N* 2005 12-15 October 2005
The Ξ Production Mechanism
● Ξ's must be produced via an intermediate state
● Ξ structure related to relative contributions of these and other mechanisms
● Different energy, angular dependence expected
● Much data, theoretical input needed to resolve
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John W. Price N* 2005 12-15 October 2005
Decays of the Ξ*'s
● Ξ-(1321) and Ξ0(1321) decays well-known: Λπ
● All Ξ*'s decay strongly
● Ξ(1530)→Ξπ; BR[Ξ(1530)→Ξγ]<4%
● Ξππ channel opens up at 1585 MeV; ΛK at 1608 MeV, ΣK at 1682 MeV
● Can use BR's to distinguish nearby states
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John W. Price N* 2005 12-15 October 2005
JP measurements of the Ξ*'s● 8 of 11 Ξ's lack JP determination
● PWA technique not applicable
● Use Ξ* decay to determine JP
– Method of Byers & Fenster (PRL 11, 52)
● Ξ*→Ξπ, Ξ→Λπ; used to find JP for Ξ(1530)
– Method of J. Button-Shafer (PR 139, B607)
● Ξ*→Ξ(1530)π
– Generalized by Minnaert (PL B66, 157)
● Ξ*→Ξπ and Ξ*→ΛK
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John W. Price N* 2005 12-15 October 2005
ms-md
● For octets: 2(mN+mΞ) = 3mΛ+mΣ
● For decuplets: mΔ-mΣ = mΣ-mΞ = mΞ-mΩ
● Can only test with one decuplet and two octets
● Once JP is measured, place Ξ's into multiplets and compare with the above
● Issue: is ms-md the same for excited baryons
as it is for ground-state baryons?
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John W. Price N* 2005 12-15 October 2005
Ξp scattering● Very little work done on Ξp
scattering
– Useful for hypernuclear studies
● CERN data on σt at 101.5
GeV/c and 133.8 GeV/c
● new KEK preprint; upper limit of 24 mb for elastic; 4.3(+6.3,-2.7) mb for Ξ-p→ΛΛ Ahn et al.,
nucl-ex/0502010
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John W. Price N* 2005 12-15 October 2005
Summary and Prognosis
● Cascade photoproduction has opened up a wide range of research areas
● Many things to keep experimentalists occupied
● We have a “new window” on baryon spectroscopy
● Lots of theoretical support needed
– Production models
– Lattice calculations (easier for cascades...)
● JLab Ξ workshop: 1-3 December 2005
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John W. Price N* 2005 12-15 October 2005
Ξ Workshop● December 1-3, 2005
@JLab
● Confirmed speakers:
– A. Thomas
– G. Miller
– S. Capstick
– F. Iachello
● Look forward to seeing you there!