Post on 12-Aug-2020
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
K. Moriya (CMU) Λ(1405) Using CLAS May 2009 3 / 10
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
K. Moriya (CMU) Λ(1405) Using CLAS May 2009 4 / 10
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)
K. Moriya (CMU) Λ(1405) Using CLAS May 2009 5 / 10
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
K. Moriya (CMU) Λ(1405) Using CLAS May 2009 5 / 10
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
K. Moriya (CMU) Λ(1405) Using CLAS May 2009 6 / 10
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+
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
K. Moriya (CMU) Λ(1405) Using CLAS May 2009 6 / 10
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+
Λ(1520)
Monte Carlo generated with PDG values of mass, width
well-established Breit-Wigner lineshape
K. Moriya (CMU) Λ(1405) Using CLAS May 2009 6 / 10
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+
K∗0
strong kinematic overlap with Λ(1405)
Monte Carlo generated with PDG values of mass, width
K. Moriya (CMU) Λ(1405) Using CLAS May 2009 6 / 10
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+
⇒ 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) .
K. Moriya (CMU) Λ(1405) Using CLAS May 2009 6 / 10
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
K. Moriya (CMU) Λ(1405) Using CLAS May 2009 7 / 10
theory prediction from chiral unitary 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+
+ "$, !
-
!"#$%& '(#)%$*+,-./&+0$/.#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
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)
K. Moriya (CMU) Λ(1405) Using CLAS May 2009 8 / 10
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
K. Moriya (CMU) Λ(1405) Using CLAS May 2009 9 / 10
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
K. Moriya (CMU) Λ(1405) Using CLAS May 2009 9 / 10
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.
K. Moriya (CMU) Λ(1405) Using CLAS May 2009 10 / 10
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%
K. Moriya (CMU) Λ(1405) Using CLAS May 2009 1 / 3
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
K. Moriya (CMU) Λ(1405) Using CLAS May 2009 2 / 3
fit to intermediate states
example: K+, π+ π−, (n) channel
,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−
K. Moriya (CMU) Λ(1405) Using CLAS May 2009 2 / 3
fit to intermediate states
example: K+, π+ π−, (n) channel
)-π,+π(2M0.2 0.4 0.60
1000
2000
|<0.27min
2.05<W<2.15, 0.14<|t-t
fit to K0
K. Moriya (CMU) Λ(1405) Using CLAS May 2009 2 / 3
fit to intermediate states
example: K+, π+ π−, (n) 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
)+,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
K. Moriya (CMU) Λ(1405) Using CLAS May 2009 2 / 3
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.
K. Moriya (CMU) Λ(1405) Using CLAS May 2009 3 / 3