Kei Moriya Reinhard Schumacher Carnegie Mellon...

First Measurement ofDifferential Photoproduction Cross Sections

and Lineshapesof the Λ(1405)

Using CLAS

Kei MoriyaReinhard Schumacher

Carnegie Mellon University

May 4, 2009

what is the Λ(1405) ?

well-established resonance just below NK threshold

long-standing peculiarity on what its nature is:

assignment of L = 1 SU(3)-singlet within constituent quark modelunstable NK bound statedynamically generated resonance in unitary meson-baryon channelcoupling

as a signal of its “peculiar nature”, past experiments have found thelineshape (= invariant mass distribution) to be distorted from asimple Breit-Wigner form

K. Moriya (CMU) Λ(1405) Using CLAS May 2009 2 / 10

theory prediction from unitary chiral approach!"#$%& '(#)%$*+,-./&+0$/.#1)#-(

!+"#

!0"0!#"$

! 2#(/3"%4/+-5+6%789:;<=4$/.#1)/.+)-+./4/(.+-(+"!./1%*+1"%((/&+

! >?+!?+@%1"/$A+B?+C3/)A+D?+E-F#A+G?+H%I-3A+0"*3?+2/))?+J+!""A+;;+78KKK<?! !"#$%& 2%L$%(L#%(+M+IJ NOP+

M+!"%((/&+!-Q4&#(L

! P7" !<+R+S:A8ATU+V (-)+#(+%(+#3-34#( /#L/(3)%)/

! PRT+1-()$#WQ)#-(3+(/L&#L#W&/

! P()/$5/$/(1/+W/)X//(+PR:+%(.+PR8+%I4&#)Q./3+I-.#5#/3+I%33+.#3)$#WQ)#-(3

& ' & '

& ' & '

& '

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

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

0 02

(0) (2)

( ) 1 1 2Re

2 3 6

( ) 1 1 2Re

2 3 6

( ) 1

3

I

I

I

dT T T T O T

dM

dT T T T O T

dM

dT O T

dM

( "

( "

( "

$ #

# $

!) $ $ $

!) $ # $

!) $

!" Invariant Mass (GeV)

d(/d

MI(*

b/G

ev) 1.7

p K

E GeV+

+ "$, !

-

J. C. Nacher et al.,

Nucl. Phys. B455, 55

prediction:not only is the lineshape distorted from a Breit-Wigner form,it is different for each Σπ decay mode


overview of data

data was taken at Jefferson Lab in Newport News, VA

Hall B, CLAS detector

photoproduction on a proton target with Eγ < 3.84 GeV

large data set with ∼ 20 B triggers

aerial view of Jefferson Labopened CLAS detector


reaction of interest

γ + p Σ+π−

Σ0π0

K++ Λ(1405)

Σ−π+

p(π0)π−

(n)π+π−

pπ−(π0, γ)

33%

33%

33%

52%

48%

100%

64%

2MM0.5 0.6 0.7 0.8 0.9 1 1.1 1.2

cou

nts

0

500

1000

1500

2000

2500

3000

3500

4000

4500 2.050 <W< 2.150-0.270<t<-0.135

detect charged particles,

reconstruct missing particle

(neutron)


reaction of interest

γ + p Σ+π−

Σ0π0

K++ Λ(1405)

Σ−π+

p(π0)π−

(n)π+π−

pπ−(π0, γ)

33%

33%

33%

52%

48%

100%

64%

,n)-π(2M1.2 1.4 1.6 1.8 2

,n)

+ π(2M

1.2

1.4

1.6

1.8

2 -0.270 <W< -0.135-0.270<t<-0.135

+Σ

-Σ

reconstruct and select

intermediate hyperons of interest


example of fit to lineshape

Invariant Mass (GeV)π Σ1.3 1.4 1.5 1.6 1.7 1.8

cou

nts

0

100

200

300

400

500

600

data(1405) MCΛ"nominal"

(1520) MCΛ MC+Σ *0K

(1385) MCΣbackgroundsum of MC

2.050 <W< 2.150 -0.270<t<-0.135

reaction:

γ + p→ K+ + Λ(1405)

→ Σ+ + π−

→ n+ π+

”nominal” Λ(1405)

Monte Carlo generated with PDG values of mass, width

all Monte Carlo was processed through detector simulation




cou

nts

0

100

200

300

400

500

600


(1520) MCΛ MC+Σ *0K


2.050 <W< 2.150 -0.270<t<-0.135

reaction:

γ + p→ K+ + Λ(1405)

→ Σ+ + π−

→ n+ π+

Σ(1385)strong overlap with Λ(1405) due to close mass and widthΛπ0 decay mode was used to fix yield in Σπ decay modesMonte Carlo generated with PDG values of mass, width




cou

nts

0

100

200

300

400

500

600


(1520) MCΛ MC+Σ *0K


2.050 <W< 2.150 -0.270<t<-0.135

reaction:

γ + p→ K+ + Λ(1405)

→ Σ+ + π−

→ n+ π+

Λ(1520)


well-established Breit-Wigner lineshape




cou

nts

0

100

200

300

400

500

600


(1520) MCΛ MC+Σ *0K


2.050 <W< 2.150 -0.270<t<-0.135

reaction:

γ + p→ K+ + Λ(1405)

→ Σ+ + π−

→ n+ π+

K∗0

strong kinematic overlap with Λ(1405)





cou

nts

0

100

200

300

400

500

600


(1520) MCΛ MC+Σ *0K


2.050 <W< 2.150 -0.270<t<-0.135

reaction:

γ + p→ K+ + Λ(1405)

→ Σ+ + π−

→ n+ π+

⇒ after fitting with the above templates, we subtracted off contributionsfrom the Σ(1385), Λ(1520) , K∗0, and assigned the remainingcontribution to the Λ(1405) .


results of lineshape after acceptance correction

Invariant Mass (GeV)π Σ1.3 1.35 1.4 1.45 1.5

b/G

eV]

µ/d

M [

σd

0

0.5

1

1.5

2

2.5<1.77γ1.56<E

weighted average-π +Σ

0π 0Σ+π -Σ

Preliminary

different lineshapes for each Σπ decay mode

lineshapes do appear different for each Σπ decay mode

Σ+π− decay mode has peak at highest mass, most narrow


theory prediction from chiral unitary approach!"#$%& '(#)%$*+,-./&+0$/.#1)#-(

!+"#

!0"0!#"$

! 2#(/3"%4/+-5+6%789:;<=4$/.#1)/.+)-+./4/(.+-(+"!./1%*+1"%((/&+


M+!"%((/&+!-Q4&#(L

! P7" !<+R+S:A8ATU+V (-)+#(+%(+#3-34#( /#L/(3)%)/

! PRT+1-()$#WQ)#-(3+(/L&#L#W&/

! P()/$5/$/(1/+W/)X//(+PR:+%(.+PR8+%I4&#)Q./3+I-.#5#/3+I%33+.#3)$#WQ)#-(3

& ' & '

& ' & '

& '

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

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

0 02

(0) (2)

( ) 1 1 2Re

2 3 6

( ) 1 1 2Re

2 3 6

( ) 1

3

I

I

I

dT T T T O T

dM

dT T T T O T

dM

dT O T

dM

( "

( "

( "

$ #

# $

!) $ $ $

!) $ # $

!) $


d(/d

MI(*

b/G

ev) 1.7

p K

E GeV+

+ "$, !

-

!"#$%& '(#)%$*+,-./&+0$/.#1)#-(

!+"#

!0"0!#"$

! 2#(/3"%4/+-5+6%789:;<=4$/.#1)/.+)-+./4/(.+-(+"!./1%*+1"%((/&+


M+!"%((/&+!-Q4&#(L

! P7" !<+R+S:A8ATU+V (-)+#(+%(+#3-34#( /#L/(3)%)/

! PRT+1-()$#WQ)#-(3+(/L&#L#W&/

! P()/$5/$/(1/+W/)X//(+PR:+%(.+PR8+%I4&#)Q./3+I-.#5#/3+I%33+.#3)$#WQ)#-(3

& ' & '

& ' & '

& '

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

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

0 02

(0) (2)

( ) 1 1 2Re

2 3 6

( ) 1 1 2Re

2 3 6

( ) 1

3

I

I

I

dT T T T O T

dM

dT T T T O T

dM

dT O T

dM

( "

( "

( "

$ #

# $

!) $ $ $

!) $ # $

!) $


d(/d

MI(*

b/G

ev) 1.7

p K

E GeV+

+ "$, !

-

J. C. Nacher et al., Nucl. Phys. B455, 55

Σ−π+ decay mode peaks at highest mass, most narrow

difference in lineshapes is due to interference of isospin terms incalculation (T (I) represents amplitude of isospin I term)


differential cross sections

summing over the lineshape gives differential cross section

Λ(1520) serves as a check of systematics

at lower energies where lineshape is different, difference in dσdt

isobserved

1.56 < Eγ < 1.77 (GeV)

Λ(1405)

|min

|t-t0 0.2 0.4 0.6 0.8 1 1.2

]2b

/GeV

µ [

dtσd

0

0.05

0.1

0.15

0.2

0.25

average-π +Σ

0π 0Σ+π -Σ

Preliminary

Λ(1520)

|min

|t-t0 0.2 0.4 0.6 0.8 1 1.2

)2b

/GeV

µ(d

tσd

0

0.02

0.04

0.06

0.08

0.1

0.12

average-π +Σ0π 0Σ+π -Σ

Preliminary


differential cross sections

summing over the lineshape gives differential cross section

Λ(1520) serves as a check of systematics

at lower energies where lineshape is different, difference in dσdt

isobserved

3.27 < Eγ < 3.56 (GeV)

Λ(1405)

|min

|t-t0 0.5 1 1.5 2 2.5 3 3.5 4

]2b

/GeV

µ [

dtσd

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

average-π +Σ

0π 0Σ+π -Σ

Preliminary

Λ(1520)

|min

|t-t0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

)2b

/GeV

µ(d

tσd

0

0.05

0.1

0.15

0.2

0.25

average-π +Σ0π 0Σ+π -Σ

Preliminary


conclusion

high statistics measurement of Λ(1405) photoproduction

difference in lineshape for different decay modes has beenobserved

difference in cross section for different decay modes has beenobserved

working to test dynamical resonances generated in chiral unitarymodels

⇒ first clues of a possible deviation from a simple qqq-structure.


final states chosen

Getting the three final states:

γ+p K++ Λ(1405)

γ+p K++ Σ0 (1385)

Σ+ π− p(π0) π- 52% Case 2

π+(n) π- 48% Case 3

Σ− π+ π-(n) π+ 100% Case 3

Σ0 π0 Λ(γ π0) 100% Case 2

Λ π0 pπ-( π0) 64% Case 288%

6%

33%

33%

33%

6%


fit to intermediate states

example: K+, π+ π−, (n) channel

2MM0.5 0.6 0.7 0.8 0.9 1 1.1 1.2

cou

nts

0

500

1000

1500

2000

2500

3000

3500

4000

4500 2.050 <W< 2.150-0.270<t<-0.135

fit to neutron




,n)-π(2M1.2 1.4 1.6 1.8 2

,n)

+ π(2M

1.2

1.4

1.6

1.8

2 -0.270 <W< -0.135-0.270<t<-0.135

+Σ

-Σ

fit to Σ+and Σ−




)-π,+π(2M0.2 0.4 0.60

1000

2000

|<0.27min

2.05<W<2.15, 0.14<|t-t

fit to K0




)+,KγMM(1.4 1.6 1.80

200

400

|<0.27min

2.05<W<2.15, 0.14<|t-t

lineshape for Σ+channel

)+,KγMM(1.4 1.6 1.80

200

400

|<0.27min

2.05<W<2.15, 0.14<|t-t

lineshape for Σ−channel⇒ end up with MM(γ,K+) spectrum for each decay mode


backgrounds

K∗

cannot separate due to strongoverlap (kinematically separated athigher energy bins)

)-π,+M(K0.65 0.7 0.75 0.8 0.85 0.9 0.95 1

)+,Kγ

MM

(

1.3

1.35

1.4

1.45

1.5

1.55

1.6

1.65

1.7|<0.27

min2.05<W<2.15, 0.13<|t-t

(1405)Λ

(1520)Λ

*0K

) for 2.05<W<2.15,-0.3<t<-0.1-π,+) vs M(K+,KγMM(

Σ(1385)cannot distinguish with close massand width

Λ(1405) Σ(1385)mass ∼ 1405 ∼ 1385width ∼ 50 ∼ 35

⇒ use MC to model both backgrounds. scale of Σ(1385) fixed by Λπ0

decay mode.


Kei Moriya Reinhard Schumacher Carnegie Mellon...

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