Search for the missing excited hyperon states

Lei Guo Florida International University

Overview •  Compared with the N* sector, the spectrum of hyperons

receives less attention –  For S=-1 sector, only 14 Λ, and 10 Σ states have been

established –  For S=-2 sector, only 6 Ξ states have been established –  For S=-3 sector, only 2 Ω states have been established

•  Most hyperon data came from kaon-beam experiments •  Photoproduction is a great alternative for strangeness

production –  Photon beam has intrinsic component –  CLAS, CLAS12 and GlueX offers great opportunities in all

hyperon sectors

ss

QM predictions for S=-1 Hyeprons (>2.0GeV)

S. Capstick et al., PRD34, 2809 (1986)

What have been established?

State Rating Λ(2100) 7/2- **** Λ(2110) 5/2+ **** Λ(2350) 9/2+ *** Σ(2030) 7/2+ **** Σ(2250) ?? ***

J. Beringer et al, (PDG), PRD86 , 010001, (2012)

Plenty are missing; Can we discover at least one new state?

Various Unseen/Rare Decay Modes of Hyperons

•  Y*ΞK –  Believed to be the leading contributor to Ξ photoproduction

(Oh, Nakayama et al) –  Never been established; –  Upper Limit was set for Λ(2100) and Σ(2030)

•  Y*Λ/Σ+η Λ(1670)Λη, Σ(1750) Ση

•  Radiative Decay of exited hyperons –  Only two have been measured

•  Σ(1385), and Λ(1520) •  Y*Λ/Σ+η’ –  Never been seen

LQCD prediction for the S=-1 Hyperon Spectra

H.-W. Lin, “Review of Baryon Spectroscopy in Lattice QCD”, Chin.J.Phys 49, 827(2011)

Number of states compatible with QM predictions More expected from the Jlab LQCD group?

Production Mechanisms of Hyperons

•  Λ(1520) photoproduction dominated by K* exchange •  Λ(1520) elctroproduction: more K exchange •  Exchange particle information can be extracted via angular distribution/PWA •  Other exited hyperons? unknown! •  Ξ: photoproudced via intermediate hyperons? •  Ω: photoprodcution mechniasm Totally unknown

Guo et al., PRC76, 025208 (2007)

Barrow et al., PRC 64, 044601 (2001)

Barber et al., Z. Phys. C7,17(1980) SLAC

CLAS

CLAS

CLAS g12 experiment

g12: Photoproduction on a proton target Integrated luminosity: 68pb-1 Eg: up to 5.5GeV Circular polarization: ~70% Target: Unpolarized Channels for hyperon spectroscopy: ! p! pK

+K

"

! p! K+#!,#! p" "

! p! K+#" 0

! p! K+## /$ /# '

! p! K+K

+$",$

"! " "

#

R. Badui C. Yero/D. Puentes J. Bono

Two Pseudoscalar Meson Photproduction: ππ VS KK (non-resonance region)

π-

π+ p π+

π- p

π-

π+ p

Lack of pK+ resonances reduction of one major diagram Different interference pattern?

Beam Helicity Asymmetry:ππ VS KK

φ: Angle between the two-meson plane/production plane Eg: 2.8-5.5 GeV

Strautch et al., PRL 95, 162003 (2005)

! p! p" +" "

! p! pK+K

"R. Badui, FIU

Key difference: sin2φ vs sinφ

  Different strengths   (not necessarily fair comparisons)

)>-

K+

),(K-

K+

(K× γ z,×<y +K

φ0 50 100 150 200 250 300 350

I

-0.3

-0.2

-0.1

0

0.1

0.2

0.3 / ndf 2χ 8.581 / 5

p0 0.00165± 0.008239 p1 0.002656± 0.01918 p2 0.002408± 0.03782 p3 0.002257± -0.02716 p4 0.00196± -0.1587

/ ndf 2χ 8.581 / 5p0 0.00165± 0.008239 p1 0.002656± 0.01918 p2 0.002408± 0.03782 p3 0.002257± -0.02716 p4 0.00196± -0.1587

- K

+ p K→ p γ

Beam Helicity Asymmetry: as a function of the two-meson-plane/produciton-plane angle

)-

K+M(K1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9

I

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

° 18± °= 270 )>

- K+),(K

- K+ (K× γ z,×<y

+Kφ ° 18± °= 270

)>-

K+),(K-

K+ (K× γ z,×<y +K

φ

)-

M(p K1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4

I

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

° 18± °= 270 )>

- K+),(K

- K+ (K× γ z,×<y

+Kφ ° 18± °= 270

)>-

K+),(K-

K+ (K× γ z,×<y +K

φ

•  Fit with Fourier series •  Sinφ dominates •  Strength at fixed angles changes as a function of pK-/KK mass •  Need model comparison

Fourier Coefficient as a function of invariant masses

No model/prediction on the market Collaborating with W. Roberts (FSU)

Beam Helicity Asymmetry: as a function of the hyperon plane-produciton plane angle

)>-

),(p K-

(p K× γ z,×<y p

φ0 50 100 150 200 250 300 350

I

-0.3

-0.2

-0.1

0

0.1

0.2

0.3 / ndf 2χ 9.181 / 7

p0 0.002362± -0.02527 p1 0.002487± -0.0254 p2 0.002245± 0.1668

/ ndf 2χ 9.181 / 7p0 0.002362± -0.02527 p1 0.002487± -0.0254 p2 0.002245± 0.1668

- K

+ p K→ p γ

)-

K+M(K1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9

I

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

° 18± ° = 90)>

-),(p K

- (p K× γ z,×<y

pφ ° 18± ° = 90

)>-

),(p K-

(p K× γ z,×<y p

φ

)-

M(p K1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4

I

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

° 18± ° = 90)>

-),(p K

- (p K× γ z,×<y

pφ ° 18± ° = 90

)>-

),(p K-

(p K× γ z,×<y p

φ

Sinφ term dominates

•  The asymmetry strength is mostly flat as a function of w •  Strong dependence on pK- invariant mass -- higher mass hyperons? •  Need theoretical predictions for comparison

 Collaborating with W. Roberts

Fourier Coefficient as a function of invariant masses

JPAC input?

PWA for Y*pK-

PWA software test run Only 3/2 spin allowed Working with JPAC:

Background: X K+K-

PyPWA: C. Salgado Nov 18th talk Can import meson background amplitudes

Waves for different M values: Offer decay/exchange information

Λ(1520) region

Radiative Decay of Excited Hyperons

CLAS Results in PDG

Σ(1385)Λγ

!("! ) /!("" )

Λ(1520)Λγ

!("! ) /!total

The radiative decay is related to the meson Cloud effect on the magnetic moment, and the quark wavefunctions of hyperons Others? None observed

PRC 71, 054609 (2005)

π0 γ

MM(pπ- )>0.55

g12 prospect

Radiative Decay of Excited Hyperons

) 2) (GeV / cΛ γM(1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1

) 2

Cou

nts

/ 8 (M

eV /

c

100

200

300

400

500

600

) 2) (GeV / cΛ γM(1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9

Co

un

ts /

8 M

eV

10

210

310

410

•  Preliminary studies: Puentes et al, FIU •  π0 contamination needs to be estimated •  Kinematic fitting to be used •  25% statistics shown •  Data promising

•  Multiple background processes ! p! K

+"(! )

Λ polarization in K+Λ/K*+Λ photoproduction

R ! P2+C

x

2+C

z

2

•  100% polarization in K+Λ photoproduc,on •  Various models suggest similar behavior in •  K*+Λ photoproduc,on

! p! K+"(" 0

)

) 0π +M(K0.5 0.6 0.7 0.8 0.9 1 1.1 1.2

) 2

Co

un

ts /

7 (

Me

V /

c

0

200

400

600

800

1000

1200

1400

CLAS g12 data Yero et al, FIU

Prior CLAS results (Tang et al, PRC 87, 065204 (2013) ) did not publish polarization results

Feasibility ! p! K

+"(" /# /" ')

Y*Λ/Σ+η Two states reported 

Y*Λ/Σ+ω Some limits established 

Y*Λ/Σ+η’ Never been seen  

  Beam helicity asymmetry could be studied Statistics limited for (PWA) Future experiments (CLAS12/GlueX) Could also be due to strange meson’s decay to K+η/ω/η’

Ξ- induced olarization in photoproduction

γ  K+

π0 p Y*

K+ 

Ξ-  s s d

s s d

First time measurement! (Bono Ph.D Thesis, 2014)

Ξ- Polarization in photoproduction

Theoretical curves from Nakayama et al Model variants: Pseudoscalar/Pseudovector coupling/High-mass hyperons

Man et al., PRC83, 055201, (2011) Nakayama et al., PRC74, 035205 (2006)

•  Results VS prediction: Limited by statistics •  R~0.3

VS R~1 for Λ results •  Unable to distinguish models •  Future data expects multiple orders of magnitude more statistics

GlueX CLAS12: Very Strange Experiment 

CLAS12 Very Strange Experiment: Expected Particle Rate

Detected particles

Measured Decays

Overall Efficiency

Rate/hr Total Detected

Ω- K+K+K0 ~3.9% ~3.6 ~7k Ω- K+K+K0K- Ω- ~0.5% ~0.5 ~1k Ξ- K+K+π-

Ξ-

~9.3% ~440 ~0.9M

Ξ-(1530) K+K+π- Ξ-(1530) ~7.4% ~140 ~270K

Ξ-(1820) K+K+K-p

Ξ-(1820)Λ ~0.63% ~6 ~12K

•  Assuming half field and 80 beam days •  Vertex Efficiency/Branching Ratio included

21

Spin-Parity Determination of Ξ* •  Spin can be measured by angular distributions (PWA) •  Parity measurement challenge: Minami ambiguity Ξ*Y (1/2+) + M1 (0-): two solutions JP •  Double Moment Analysis (DMA) Y (1/2+) B (1/2+) + M2 (0-) Double moments: H(lmLM)= Σ DL

Mm(θ1, φ1) Dlm0(θ2, φ2)

DMA: )10(

)1(2

12)1()11( 2

1

LMHLL

JPLMH

J

+

+!=

+

•  Linear dependence gives simple, multiple tests for J, P for any odd L≤2J and M≤L

22

CLAS12: Parity Measurement of Ξ(1820)

Ξ(1820) counts: ~50 Need to detect whole decay chain  

ImH

(11L

M)

ImH(10LM)

Biagi et al., Z.Phys.C34, 175 (1987)

CERN-SPS Ξ-Be reaction 

!

3

2

"

!

3

2

+

Ξ(1820) Needs corroboration

!

3

2

"

CLAS12 estimate: ~12k Ξ(1820) with complete decay chain At CLAS12 (80 beam days)  23

M (!K0)(GeV / c

2)

)2) (GeV/c+K+MM(K1.5 1.6 1.7 1.8 1.9 2 2.1

2Ev

ents/

10Me

V/c

0

20

40

60

80

100

120

140

160

180

200

220

Im(H(103M))-0.015 -0.01 -0.005 0 0.005 0.01 0.015

Im(H(113

M))

-0.015

-0.01

-0.005

0

0.005

0.01

0.015-

25

-

21

-

23

+

21

-Ξ

*θcos

-0.8 -0.6 -0.4 -0.2 0 0.2 0.4

- ΞP

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

=0.1-ΞP=0.3-ΞP

=8.25 GeVγE

CLAS12: Ξ- Polarization and Ξ-(1820) Spin-Parity

•  Ξ- polarization measurement: (should be Eγ dependent) •  Ξ-(1820) double moments

! p! K+K

+"#! K

+K

+" #($)

! p! K+K

+"#(1820)

"#(1820)! K

#($! " #

p)

Expected M(ΛK-) spectrum

Expected double moments (L=3)

Expected PΞ- vs Eγ

(statistical uncertainty only) 24

Ξ – (1820)

Pythia background

Summary •  Hyperon Spectroscopy offers multiple opportunites for

S=-1/-2/-3 sectors •  CLAS data already has multiple promises

–  First measurement of pK+K- beam helicity asymmetry measurements

–  First measurement of Ξ- polarization in photoproduction –  Radiative decays of excited hyperons could be extended –  K*Λ polarization can be investigated and compare the Λ

polarization mechanism (VS KΛ photoproduction) •  CLAS12/GlueX would be gold mines for hyperons

–  Y*Λη/ω/η’ –  Ξ polarization: Much higher statistics; PWA of Y->KΞ –  Excited cascades and Ω- photoproduction