properties of the (1405) via photo- and...

Properties of the (1405) via Photo- and Electroproduction

Reinhard Schumacher

October 2, 2012, Barcelona, Spain

XI International Conference on Hypernuclear and Strange Particle Physics

R. A. Schumacher, Carnegie Mellon University

Outline /Overview

2HYP11 10-2012

Models of the (1405) Hyperon The “Mass Distributions” from CLAS Isospin decomposition: I=0 vs. I=1

(NEW!) Electroproduction of (1405) (no time…)

Y*

K+

p

K

Nature of the (1405)? Dynamically generated resonance, via

unitary meson-baryon channel coupling R. Dalitz & S.F.Tuan, Phys. Rev. Lett. 2, 425 (1959), Ann. Phys. 10, 307 (1960). E. Oset and A. Ramos, Nucl. Phys. A 635, 99 (1998). Very many others…

Quark model genuine three quark state C. G. Wohl, Phys. Lett. B 667 1182 (2008) RPP.... But statement is deleted in (2012) RPP. S. Capstick & N. Isgur, Phys. Rev. D34 2809 (1986).

sub-threshold bound state Y. Akaishi & T. Yamazaki, Phys Rev 65, 044005 (2002).

HYP11 10-2012 R. A. Schumacher, Carnegie Mellon University 3

Nature of the (1405)? (2) Two-pole, I=0, S=-1, solution to the chiral

unitary scattering problem J.A. Oller, U.-G. Meissner Phys. Lett B 500, 263 (2001). D. Jido, J.A. Oller, E. Oset, A. Ramos, U-G Meissner Nucl. Phys. A 725, 181 (2003).

5-quark cluster model: B. Zou, Nucl. Phys. A 835, 199 (2010). Predicts extra ½- baryon nonet with a * at 1380

Hybrids: udsg, udcg with “active” glue O. Kittel & G. Farrar, hep-ph/0010186(2000); /0580815(2005)


1 2B c qqq c qq qq q

R. A. Schumacher, Carnegie Mellon University 5

Chiral Unitary Approach Chiral perturbation

theory fails in the presence of strong threshold effects

Kij kernel from chiral SU(3) effective meson-baryon Lagrangian

(1405)

K+

p

K-

Leading s-wave I=0 interaction: “Weinberg-Tomozawa” driving term

Off-shell kaon

R. A. Schumacher, Carnegie Mellon University 5HYP11 10-2012 N. Kaiser, P. B. Siegel, W. Weise, Nucl. Phys. A 594, 325 (1995)


Chiral Unitary Models (example 1)

SU(3) baryons irreps 1+8s+8a combine with 0-

Goldstone bosons to generate:

Two octets and a singlet of ½- baryons generated dynamically in SU(3) limit

SU(3) breaking leads to two S=-1 I=0 poles near 1405 MeV ~1420 mostly KN ~1390 mostly

Possible weak I=1 pole also predicted

6HYP11 10-2012 R. A. Schumacher, Carnegie Mellon University

D. Jido, J.A. Oller, E. Oset, A. Ramos, U-G Meissner Nucl. Phys. A 725, 181 (2003)J.A. Oller, U.-G. Meissner Phys. Lett B 500, 263 (2001).


Chiral Unitary Models (example 2)

+

00

Mass distribution of the “(1405)” predicted to depend on decay channel

Model with I = 0 and I = 1 amplitudes Chiral Lagrangian +

Channel Coupling I() = {0,1} – not in an

isospin eigenstate Neglect I=2

Interference between I=0 and I=1 amplitudes modifies mass distributions

WT-type interaction: no energy or angle dependence

Inspired CLAS experiment

Invariant Mass (GeV)

d/d

MI(

b/G

ev) 1.7

p KE GeV

2 2(1) (0) (0) (1)* (2)

2 2(1) (0) (0) (1)* (2)

0 02(0) (2)

( ) 1 1 2 Re2 3 6

( ) 1 1 2 Re2 3 6

( ) 1 3

I

I

I

d T T T T O TdM

d T T T T O TdM

d T O TdM

J.C. Nacher, E. Oset, H. Toki, & A. Ramos, Phys. Lett. B 455, 55 (1999). 7HYP11 10-2012 R. A. Schumacher, Carnegie Mellon University

Hadronic Beam Experiments Berkeley bubble chamber

Discovery: M. Alston et al., Phys. Rev. Lett. 6, 698 (1961).

Brookhaven bubble chamber Line shape hints: D. W. Thomas et al., Nucl. Phys. B56, 15 (1973).

CERN bubble chamber One charge combo: R. J. Hemingway, Nucl. Phys. B253, 742 (1985).

COSY/ANKE Only I. Zychor et al., Phys. Lett. B660 167 (2008).


K p

0p K

K p

0 0 0( )pp pK pK p

Photon Beam Experiments LEPS/SPring-8

Differing line shapes J. K. Ahn et al., Nucl Phys A721, 715 (2003).

LEPS/SPring-8 Differing line shapes M Niiyama et al., Phys Rev C78, 035202 (2008).

CLAS / Jefferson Lab – this talk


p K


CLAS

10HYP11 10-2012


CLAS Experiment

Jefferson Lab, Newport News, VA, USA PhD work of KEI MORIYA, currently at

Indiana University g11a data set, 2004

LH2 target unpolarized tagged photon beam well studied: ~5 papers so far 20x109 trigger 1.41x106 Y* events



Getting the three final states:

p(0) - 52% 440k

+(n) - 48% 316k

+ -(n) + 338k

0 0 ( 0) 76k 33%

33%

33%

+p K++ (1405)

+p K*+,0+ 0,+ Subtracted incoherently bin by bin using Monte Carlo model

12

Quark model expectation: equally-strong decays to each of three states, with Breit-Wigner mass distributions

HYP11 10-2012

CLAS

Events

Selecting in n


Using 1-C kinematic fit

Events in Final State


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

Removing the K* Incoherently

line shape data for worst case overlap at W=2.2 GeV

No significant change in result, despite very “wide” K* removal: no coherence seen


Scaling away the (1385)


(1405)

(1385)

(1385) has small branching ratiointo the final state that we want

17

CLAS Result for Line Shape

Decay-channel asymmetry of (1405) line shape confirmed Line shapes are not Breit-Wigner and depend on charge Subtracted backgrounds: (1385), (1520), K*(892) Status: Final results

00

+

R. A. Schumacher, Carnegie Mellon UniversityHYP11 10-2012 17

All W & All Line Shapes

Full and final CLAS data setHYP11 10-2012 R. A. Schumacher, Carnegie Mellon University 18

Isospin Interference


K+

Y*p

3 =,

Final state

Three charge combinations:

Cross Sections


K+

Y*p

pp,q

Fully differential d

Factorized 3-body phase space(m)

Angle & mass differential

Angle integrated

pK+

Line Shapes


Single amplitude, I

Breit-Wigner line shape

For a single decay mode “1” = “” in isospin state Iand c.m. momentum q1, use

Width (with L0)

Flatté Channel-Coupling


For a second decay mode “2” = “ ” in isospin state I and c.m. momentum q2, use

Below mode “2” threshold, analytically continue the amplitude to preserve unitarity

Below

Above


Isospin Decomposition

23HYP11 10-2012

t0 to only – pretty good fit t0A , t0B to only – two amplitudes; very good t0A , t0B to all – very poor, as expected t0A , t0B , t1 to all – good! t0 , t1A

, t1B to all – best! showing this one

Separate {, , } into I=0 and I=1 amplitude contributions

Roster of fits to all data in nine W bins

Example at W=2.40 GeV


I=1 contributions

I=0 contribution withthreshold break

0 0

Details…

Use MINUIT with 34 parameter, 1130 data points across all W’s

Best fit has 2 = 2.12

All isospin amplitude shapes are the SAME in ALL bins of W; only C(W) varies with W


Line Shapes for


W dependence of CI(W)


Smooth variations I=0 dominant but

falls off I=1 total is ~half

as big as I=0 and stays about constant

“Best Fit” Isospin Decomposition


I=0 centroid fitted to threshold Flatte effect big; pulls high-point to ~1405MeV Two I=1 amplitudes give best fit Parameter uncertainties hard to compute accurately

Theory Connections I=0 is dominant

Centroid is well below 1405, close to threshold Some models expect I=0, JP= ½- near this low mass

Ramos

Oller

Flatté line shape is evident - channel-coupling is large Support for “two-pole” picture

Hyodo

I=1 is not small Possible support of I=1, JP= ½- low-mass states

Oller and Meissner again (see above)

Possible connection with 5-quark model of baryon excitations Zou


Summary/Conclusion

CLAS has provided highest statistics look at all three mass distributions in photoproduction on the proton,

Clear need for I=0 and I=1 separation at all W, especially nearer threshold,

Amplitude fits show: I=0 ‘(1405)’ centroid near threshold I=1 strength centered near 1391 and 1411 MeV Channel-coupling effects evident in all decays


properties of the (1405) via photo- and...

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