Recent Results from CLAS

K. Hicks (Ohio University)Hadron 2013 (Nara, Japan)Thursday, November 7

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General Comments

• There are is so much data from CLAS that it is not possible to cover it all in 25 minutes.

• I must make some choices:– New resonances from KY photoproduction– Meson photoproduction: , , , p h w pp– New cross sections: K*Y and KY* photoproduction– Dark photon search from p0 Dalitz decays

• Apologies to Stan: I have only 50 slides.

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The CLAS Detector

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Polarization observables in pseudoscalar meson production4 Complex amplitudes: 16 real polarization observables.

Complete measurement from 8 carefully chosen observables.

πN has large cross section but in KY recoil is self-analysing

I. S. Barker, A. Donnachie, J. K. Storrow, Nucl. Phys. B95 347 (1975).

πN KY

recoil targ γ

γ targ recoil

☻☻☻

☻

linearly polarized photons

☻☻☻☻☻☻

longitudinally polarized target

☻☻☻☻☻☻

circ polarized photons

☻☻☻☻☻☻

☻☻☻☻☻☻

transversely polarized target

Complete, andover-determined

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Establishing the nucleon spectrum

A.V. Anisovich et al (BnGa), EPJ A48, 15 (2012) M. Mc Cracken et al.(CLAS), Phys.RevC81,025201,2010

Essential new data on hyperon production γp→K+Λ→K+pπ- From elastic πN scattering to γN reactions.

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Strangeness production γp→K+Λ→K+pπ-

M. Mc Cracken et al. (CLAS), Phys. Rev. C 81, 025201, 2010 D. Bradford et al. (CLAS), Phys.Rev. C75, 035205, 2007

Λ Recoil polarization γ->Λ Polarization transfer

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V. Crede & W. Roberts, Rept. Prog. Phys. 76 (2013)

Photoproduction data from JLAB, ELSA, GRAAL, LEPS

N/Δ spectrum in RPP 2012

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N* spectrum in LQCD

mπ=396MeV

N(1860)5/2+

N(1900)3/2+

N(1880)1/2+

N(2060)5/2-

N(2120)3/2-

N(1875)3/2-

N(1895)1/2-

Do new candidate states fit in projected Lattice QCD spectrum?

Ignoring the mass scale, new candidate states fit in current LQCD projections

N(1675)5/2-

N(1700)3/2-

N(1520)3/2-

N(1650)1/2-

N(1535)1/2-

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Σ for γp → nπ+

60 1200 60 1200

DU12CM12MAIDBbGa

M. Dugger et al.

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Σ for γ p → p π0 DU12CM12MAIDBbGa

M. Dugger et al.

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Changes in couplingsSolution A1/2 A3/2

D(1700)3/2- DU12 132 ± 5 108 ± 5

CM12 105 ± 5 92 ± 4

BnGa 170 ± 20 170 ± 25

MD07 226 210

PDG12 104 ± 15 85 ± 22

D(1905)5/2+ DU12 20 ± 2 -49 ± 5

CM12 19 ± 2 -38 ± 4

BnGa 25 ± 5 -49 ± 4

MD07 18 -28

PDG12 26 ± 11 -45 ± 20

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T for γ p → n π+

(new)

(new)

(new)

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F for γ p → n π+

• Agreement with predictions get much worse at higher energies

• SAID13 are predictions based on preliminary fits to CLAS pion Σ measurements

(new) (new)

(new)

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E for γ p → p π0

• Early stage results• Predictions agree better

at lower energies

(new)

Cos(θπc.m.)

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Summary of meson photoproduction σ Σ T P E F G H Tx Tz Lx Lz Ox Oz Cx Cz

Proton target

pπ0 ✔ ✓ ✓ ✓ ✓ ✓ ✓ ✓

nπ+ ✔ ✓ ✓ ✓ ✓ ✓ ✓ ✓

pη ✔ ✓ ✓ ✓ ✓ ✓ ✓ ✓

pη’ ✔ ✓ ✓ ✓ ✓ ✓ ✓ ✓

K+Λ ✔ ✓ ✓ ✔ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✔ ✔

K+Σ0 ✔ ✓ ✓ ✔ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✔ ✔

K0*Σ+ ✔ ✓ ✓ ✓ ✓ ✓ ✓ ✓

“Neutron” target

pπ- ✔ ✓ ✓ ✓ ✓ ✓ ✓

K+Σ- ✓ ✓ ✓ ✓ ✓ ✓ ✓

K0Λ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓

K0Σ0 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓

✔ - published ✔ - acquired

N* states in γp pω pπ➝ ➝ +π-π0 ?

M. Williams, et al. (CLAS), Phys. Rev. C80:065209, 2009

W=1.7 – 2.4 GeV, ΔW=10 MeV bins

• Very precise cross sections in W, cosθω. From ω decays => SDME ρ0

00,

ρ01-1, ρ0

10, shown in blue - blue shades.

(ω data not yet included in coupled-channel amplitude analyses, in preparation by several groups.)

The data are used as input to a single channel event-based, energy independent partial wave analysis (the first ever for baryons).

ω photoproduction is dominated by the well known F15(1680) and G17(2190), and the “missing” ** F15(2000).

N* states in γp pω pπ➝ ➝ +π-π0

M. Williams, et al. (CLAS) , Phys.Rev. C80 (2009) 065208

F15(2000)/G17(2190)

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Differential cross sections γp pφFirst precision measurement in 80 energy bins at W=10 MeV, and nearly full angle range (CLAS).

φ K+K- φ K0sK0

l

• SDME from φ decay angular distributions.

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The L=1 QM assignmentsFrom Klempt and Richard, Rev. Mod. Phys. 82 (2010).

Note: x = “missing” state (not seen in experiments)

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The L=2 QM assignmentsFrom Klempt and Richard, Rev. Mod. Phys. 82 (2010).

Note: x = “missing” state (not seen in experiments)

Some of these are 2-star PDG

Unknown!

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The L=3 QM assignmentsFrom Klempt and Richard, Rev. Mod. Phys. 82 (2010).

Note: x = “missing” state (not seen in experiments).Half of these are 2-star = evidence is only “fair”.

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K*Y Photoproduction

• The following work is done primarily by the Ohio group at CLAS:– Wei Tang and KH.

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Moorhouse Selection Rule• The transition

amplitudes for gp to all [70,48] are zero.

• For gn, these transitions are allowed, e.g. the N5/2-(1675).

N3/2-

N5/2-

Data from N. Bianchi et al., PRC 54 (1996).

N1/2+

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Lambda Selection Rule

• The [70,48] resonances decouple from the KL and K*L channels.– This assumes the spectator approximation, where

the [ud] quarks are coupled to s=0 in the L.– In the [70,48] N*’s, the [ud] are coupled to s=1.– The selection rule applies to both p and n targets.– This doesn’t apply to KS and K*S final states.

• A study of KL, K*L, KS and K*S final states will test this spectator (diquark) hypothesis.

Reference: Q. Zhao and F.E. Close, Phys. Rev. D 74 (2006) 094014.

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Theoretical models for the K* photoproduction 1. Isobar models:evaluate tree-level Feynman diagrams that include resonant and non-resonant exchanges of baryons and mesons.

Advantage: Identify the dominant contributions to the final statesDisadvantage:Too many parameters, tuning and fixing of those parameters sometimes are tricky.

To describe the physics process completely, all possible Feynman diagrams that could lead to the final state are required to be taken into account in the calculation.

Mandelstam variables:

From: Wei Tang, Ph.D. Dissertation Defense, August, 2012

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2. Regge-ized models:

Rather than focus on selecting of all possible s, t and u channel reaction processes, the reggeized models emphasis the t-channel.The standard propagators in the Lagrangian are replaced by Regge propagators.

Sho Ozaki, http://ific.uv.es/nucth/chirall10/talks/ozaki.pdf

Originally applied to high energy hadron reactions

Might not be able to produce the results in detail, but at least it can tell us about how t-channel mesons exchanges affects the reaction

From: Wei Tang, Ph.D. Dissertation Defense, August, 2012

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K*+L Differential Cross Sections

Curves are simple fits using 4th order Legendra polynomials.

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K*+S0 Differential Cross Sections

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Total Cross Sections

Both data peak at about W=2.25 GeV. There are 3 well-known N*’s there: the N7/2-(2190), N9/2-(2250) and N9/2+(2250).Note: the N9/2- is part of the L-forbidden [70,48] multiplet.

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Comparison with theoryCyan: Oh and Kim (O-K) Isobar ModelBlue: Kim, Nam, Oh, Kim (KNOK) Regge ModelDotted curves include additional s-channel N* with M<2.2 GeV and L<3.

Clearly, the currently available theoretical models cannot reproduce the data. This suggests that higher-mass and higher-L resonances are needed.

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Ratio of K*0S/K*+L and k-meson

Solid: mostly t-channel k-mesonDotted: very little k-meson

There is scarce evidence for the strange scalar called the kappa (k), which is the octet partner of the a0(980) and f0(980) mesons. The CLAS data support an earlier claim by LEPS that also measured K*0S+ photoproduction.

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KY* Photoproduction

• The following work is done primarily by the Carnegie-Mellon University group at CLAS:– Kei Moriya and Reinhard Schumacher.

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Detect K+pp-(p0) or K+p+p-(n)

L(1405)

S(1385)

S(1385) has small branching ratiointo the L(1405) state we want

L(1520)

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Events in K+S+p- Final State

Note K* overlap: must be subtracted in some W bins

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Differential S0(1385) Cross Section

• g + p K+ + S0 (1385)• Experiment: see t-channel-

like forward peaking & u-channel backward rise– Agreement with LEPS

• Theory by Oh et al.1: contact term dominant; included four high-mass N* and D resonances– Prediction was fitted to

preliminary CLAS total cross section

1. Y. Oh, C. M. Ko, K. Nakayama, Phys. Rev. C 77, 045204 (2008). .cos c m

K

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g + p K+ + L(1520) Good agreement among Sp decay modes Corrected with 42% branching fraction to Sp

Differential L(1520) Cross Section

2.05<W<2.15 GeV

Agreement between S+p- decay modes: tests acceptance consistency

Agreement among S+p-, S0p0, S-p+

decay modes: tests acceptance consistency

2.45<W<2.55 GeV

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Differential L(1520) Cross Section g + p K+ + L (1520) Experiment: see t-channel-

like forward peaking & u-channel backward rise Agreement with LEPS1,2

Theories: Nam & Kao3: contact term

dominant; no K* or u-channel exchanges

He & Chen4: K* and N(2080)D13 JP=3/2- added

. .cos c m

K

1. H. Kohri et al. (LEPS) Phys Rev Lett 104, 172001 (2010)2. N. Muramatsu et al. (LEPS) Phys Rev 103, 012001 (2009)3. S.I. Nam & C.W. Kao, Phys. Rev. C 81, 055206 (2010)4. J. He & X.R. Chen, Phys. Rev. C 86, 035204 (2012)

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Differential L(1405) Cross Section g + p K+ + L (1405)

Experiment: each S pchannel yields a different cross section (! Not expected1 !)

Indication of isospin interference in (1405)L mass region Threshold < m Sp < 1.50 GeV

. .cos c m

K

1. K. Moriya, R. A. Schumacher et al., Phys. Rev. C 87, 035206 (2013)

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Differential L(1405) Cross Section g + p K+ + L (1405) Experiment: first-ever

measurements See t-channel-like forward

peaking & u-channel backward rise at high W Same as other hyperons

See very different behavior at low W Charge channels differ

Channels merge together at high W

. .cos c m

K

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Differential L(1405) Cross Section g + p K+ + L (1405) Sum three Sp decay modes

“total” differ-ential cross section Mixed agreement with LEPS

data1

Theories: Nam et al.2: s-channel Born term

dominant ; K* exchange for 3 values of g K*NL*

Williams, Ji, Cotanch3: crossing and duality contraints; no N*, estimated g KNL*

1. M. Niiyama et al. (LEPS) Phys Rev C78, 035202 (2008)2. S.I. Nam et al., J. Kor. Phys. Soc. 59, 2676 (2011)3. R. Williams et al., Phys. Rev. C43, 452 (1991)

Nam

Williams

. .cos c m

K

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Direct Y* Cross Section Comparison

. .cos c m

K

g + p K+ + Y* Sum L(1405) channels Apply branching fractions for

(1520), (1385)L S

All three hyperons have Strong forward peaking Similar t-slopes Back-angle rises Similar-size cross sections

(1115)LS0(1193)S0(1385)(1405)L(1520)L

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(1115)LS0(1193)S0(1385)(1405)L(1520)L

Direct Y* Cross Section Comparison

g + p K+ + Y* (showing spline fits)

All three have Near- threshold peaking Similar size cross sections Sp-fraction (42%) of

(1520)L has same cross section as (1405)L at high W!

L*’s have a hint of second peak/plateau

-0.2 < cos QK c.m. < +0.1

-0.7 < cos QK c.m. < -0.5

+0.6 < cos QK c.m. < +0.9

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Total Cross Section Comparison

(1115)LS0(1193)S0(1385)(1405)L(1520)L

1. R. Bradford et al. (CLAS) Phys. Rev. C 73, 035202 (2006)

g + p K+ + Y(*)

All three Y*s have similar total cross sections Ground states L and S0 are comparable to Y* in size1

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Dark Photon Search

• The following work is done primarily by the ODU group at CLAS:– M. Kunkel and M. Amaryan

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48

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Summary

• Precise data from CLAS has contributed to identification of new baryon resonances.– Complete set of spin observables for PS mesons.

• New data from K*Y and KY* will likely help to identify new high-mass baryon resonances.– PWA for these data are in progress.

• Search for dark photons possible at CLAS using the high statistics data set.– Better limits on parameter space.

51R. A. Schumacher, Carnegie Mellon University 51

The Low-Mass S=-1 Hyperons

(1115)

Energ

y (

Mass

) M

eV

1100

1200

1300

1400

1500

1600

1700

(1670)

…

(1670)

…

NK

(1385)

Mass thresholds:

1525

1432

1390

1331

Isospin = 0 Isospin = 1

(1405)L

(1520)L

(1385)S

(1192)