The p—~e0p~–ˇ0 process in the region of the Roper resonance · The p—~e;e0p~–ˇ0 process...

The p�~e; e0~p��0 process in the region of the Roper resonance

S. Širca, U. of Ljubljana, Slovenia Bled | 7 July 2017

1

Motivation

� Masses, widths, (EM and weak) form-factors of ****, *** baryons

� Understand structure of resonances, related to— confinement— chiral symmetry of QCD a meson cloud

� “Roper” == first excited state of nucleon with same quantum numbersbut poorly understood (compared e.g. to ��1232�)

2

Key issues with P11�1440�

� Hard to see directly (in spectra)

� Large width, with large uncertainty

� Atypical behaviour of ImT�N in T �J�1=2 (P11) partial wave

� Is it a radial excitation (“breathing mode”) of proton �1s�3 -! �1s�2�2s�1 ?=) Sizeable monopole strength (C0 / Sp

1=2 / S1�) � dipole (M1 / Ap1=2 / M1�)

� Or is it a �q3g� hybrid ?

=) Equal radial WF =) C0 suppressed, no “breathing”, M1 dominates

� Level ordering (parity inversion) of P11�1440� wrt. S11�1535� on Lattice

In quark model with harmonic-oscillator V�r�:E� � �!�� 3

2�, where � � 2n� ln � 0, l � 0 =) N�JP � 1

2

��

n � 1, l � 1 =) N��JP � 12

��

n � 2, l � 0 =) N��JP � 12

��

But N��1440��12

�� is lighter than N��1535��1

2

�� !

3

PDG 2014

Citation: K.A. Olive et al. (Particle Data Group), Chin. Phys. C38, 090001 (2014) (URL: http://pdg.lbl.gov)

N(1440) 1/2+ I (JP ) = 12 (1

2+) Status: ∗∗∗∗

Most of the results published before 1975 were last included in our1982 edition, Physics Letters 111B111B111B111B 1 (1982). Some further obsoleteresults published before 1984 were last included in our 2006 edition,Journal of Physics (generic for all A,B,E,G) G33G33G33G33 1 (2006).

N(1440) BREIT-WIGNER MASSN(1440) BREIT-WIGNER MASSN(1440) BREIT-WIGNER MASSN(1440) BREIT-WIGNER MASS

VALUE (MeV) DOCUMENT ID TECN COMMENT

1410 to 1450 (≈ 1430) OUR ESTIMATE1410 to 1450 (≈ 1430) OUR ESTIMATE1410 to 1450 (≈ 1430) OUR ESTIMATE1410 to 1450 (≈ 1430) OUR ESTIMATE

1515 ±15 SHKLYAR 13 DPWA Multichannel

1430 ± 8 ANISOVICH 12A DPWA Multichannel

1485.0± 1.2 ARNDT 06 DPWA πN → πN, ηN

1440 ±30 CUTKOSKY 80 IPWA πN → πN

1410 ±12 HOEHLER 79 IPWA πN → πN

• • • We do not use the following data for averages, fits, limits, etc. • • •

1412 ± 2 SHRESTHA 12A DPWA Multichannel

1440 ±12 ANISOVICH 10 DPWA Multichannel

1439 ±19 BATINIC 10 DPWA πN → N π, N η

1436 ±15 SARANTSEV 08 DPWA Multichannel


1518 ± 5 PENNER 02C DPWA Multichannel

1479 ±80 VRANA 00 DPWA Multichannel

1463 ± 7 ARNDT 96 IPWA γN → πN

1467 ARNDT 95 DPWA πN → N π

1465 LI 93 IPWA γN → πN

1462 ±10 MANLEY 92 IPWA πN → πN & N ππ

1471 CUTKOSKY 90 IPWA πN → πN

1380 1 LONGACRE 77 IPWA πN → N ππ


N(1440) BREIT-WIGNER WIDTHN(1440) BREIT-WIGNER WIDTHN(1440) BREIT-WIGNER WIDTHN(1440) BREIT-WIGNER WIDTH



605± 90 SHKLYAR 13 DPWA Multichannel

365± 35 ANISOVICH 12A DPWA Multichannel

284± 18 ARNDT 06 DPWA πN → πN, ηN

340± 70 CUTKOSKY 80 IPWA πN → πN

135± 10 HOEHLER 79 IPWA πN → πN


248± 5 SHRESTHA 12A DPWA Multichannel

335± 50 ANISOVICH 10 DPWA Multichannel

437±141 BATINIC 10 DPWA πN → N π, N η

335± 40 SARANTSEV 08 DPWA Multichannel


668± 41 PENNER 02C DPWA Multichannel

490±120 VRANA 00 DPWA Multichannel

HTTP://PDG.LBL.GOV Page 1 Created: 8/21/2014 12:54

4

PDG 2014

Citation: K.A. Olive et al. (Particle Data Group), Chin. Phys. C38, 090001 (2014) (URL: http://pdg.lbl.gov)

N(1440) 1/2+ I (JP ) = 12 (1

2+) Status: ∗∗∗∗

Most of the results published before 1975 were last included in our1982 edition, Physics Letters 111B111B111B111B 1 (1982). Some further obsoleteresults published before 1984 were last included in our 2006 edition,Journal of Physics (generic for all A,B,E,G) G33G33G33G33 1 (2006).

N(1440) BREIT-WIGNER MASSN(1440) BREIT-WIGNER MASSN(1440) BREIT-WIGNER MASSN(1440) BREIT-WIGNER MASS



1515 ±15 SHKLYAR 13 DPWA Multichannel

1430 ± 8 ANISOVICH 12A DPWA Multichannel


1440 ±30 CUTKOSKY 80 IPWA πN → πN

1410 ±12 HOEHLER 79 IPWA πN → πN


1412 ± 2 SHRESTHA 12A DPWA Multichannel

1440 ±12 ANISOVICH 10 DPWA Multichannel

1439 ±19 BATINIC 10 DPWA πN → N π, N η

1436 ±15 SARANTSEV 08 DPWA Multichannel


1518 ± 5 PENNER 02C DPWA Multichannel

1479 ±80 VRANA 00 DPWA Multichannel

1463 ± 7 ARNDT 96 IPWA γN → πN

1467 ARNDT 95 DPWA πN → N π

1465 LI 93 IPWA γN → πN

1462 ±10 MANLEY 92 IPWA πN → πN & N ππ

1471 CUTKOSKY 90 IPWA πN → πN



N(1440) BREIT-WIGNER WIDTHN(1440) BREIT-WIGNER WIDTHN(1440) BREIT-WIGNER WIDTHN(1440) BREIT-WIGNER WIDTH



605± 90 SHKLYAR 13 DPWA Multichannel

365± 35 ANISOVICH 12A DPWA Multichannel


340± 70 CUTKOSKY 80 IPWA πN → πN

135± 10 HOEHLER 79 IPWA πN → πN


248± 5 SHRESTHA 12A DPWA Multichannel

335± 50 ANISOVICH 10 DPWA Multichannel

437±141 BATINIC 10 DPWA πN → N π, N η

335± 40 SARANTSEV 08 DPWA Multichannel


668± 41 PENNER 02C DPWA Multichannel

490±120 VRANA 00 DPWA Multichannel

HTTP://PDG.LBL.GOV Page 1 Created: 8/21/2014 12:54ACU, 2004: How can one best improve the determination of the P11 mass(es?),width, pole position and decay properties?

R. Arndt: “I’ve expressed my position on this subject many times. — It justisn’t possible to fit P11 with a ‘simple’ BW form; the amplitude is determinedby nearby singularities consisting of 2 poles and a very prominent cut (�–�).It’s like doing a polynomial fit to a sine wave. [...] I believe that the ‘problem’with P11 is that people keep trying to stuff a square pole in a round hole.”

5

Discovery in �N scattering

� ��1232� (P33) and N��1520� (D13) known at the time

� Roper (+ Moravcsik + Feld + Wright), PRL 12 (1964) 137“I spent [a] much time trying to eliminate the P11 resonance.”

� “The discovery of the P11 resonance was the spark that set offthe baryon resonance explosion of the late 1960s.”

6

PWA of �N scattering in P11 channel SAID FA02

ImT

( ImT�jT j2� 14�1��2�

ReT

PDG 2014: MBW � �1430� 20�MeV, �=2 � �175� 50�MeV

Mpole � 1365� i 95 MeV

7

Dynamical origin of P11 resonances

� Multi-channel reactions may generate multiple resonance polesfrom a single bare state (Eden, Taylor PR 133 (1964) B1575)

� n channels =) 2n Riemann sheets

� Three P11 poles below 2 GeV =) two associated with P11(1440)=) one with P11(1710)

� coupled channels needed

Dynamical origin of P11 nucleon resonances

Suzuki, Julia-Diaz, Kamano, Lee, Matsuyama, Sato arXiv:0909.1356

1. Two almost degenerate poles in the Roper resonance region.

2. All three poles below 2 GeV evolve from a same, single bare state.

ImE (MeV)

Re E (MeV)

100

Findings:

0

-100

-200

-3001400 1600 1800

P11 N* resonances

in the EBAC-DCC model

P11 N* resonances

in the EBAC-DCC model

Jülich (2013) fit A (1353, �106) (1357, �114)

Suzuki++ (EBAC-DCC) PRL 104 (2010) 042302

Rönchen++ (Jülich) EPJA 49 (2013) 44

8

P11�1440� and S11�1535� on the Lattice

� level ordering should change with mq

Heavy q: 1st radial above 1st orbital excCL: reversed levels

Bern-Graz-Regensburg / PRD 70 (2004) 054502PRD 74 (2006) 014504

“... do not attempt a chiral extrapolation of our data ... numbersseem to approach the experimental data reasonably well”

“... the Roper’s leading Fock component is a 3-quark state”

0.00 0.40 0.80 1.20

(mπ)2 [GeV]

2

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

MN

[G

eV]

λ(1), a = 0.148fm

λ(2), a = 0.148fm

λ(3), a = 0.148fm

λ(1), a = 0.119fm

λ(2), a = 0.119fm

λ(3), a = 0.119fm

positive parity

N(938)

N(1440)

N(1710)

Kentucky / PLB 605 (2005) 137

“... � and � parity excited states of the nucleon tendto cross over as the quark masses are taken to the chiral limit.Both results at the physical pion mass agree with the expvalues ... seen for the first time in a lattice QCD calculation”

“... a successful description of the Roper resonance dependsnot so much on the use of the dynamical quarks ... mostof the essential physics is captured by using light quarks” 0

0.5

1

1.5

2

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Mas

ses

(GeV

)

mπ2(GeV2)

Nucleon

S11(1535)

Roper

1.3

1.5

1.7

0 0.1 0.2

MR/MN1.3

1.5

1.7

0 0.1 0.2

MR/MN

9

P11�1440� and S11�1535� on the Lattice

0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40m2 [GeV]

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

m [G

eV]

JP = 12+

Twisted Mass (this work)Clover (this work)CSSM

JLABBGRExperiment

0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40m2 [GeV]

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

m [G

eV]

JP = 12Twisted Mass (this work)Clover (this work)CSSM

BGRExperiment: N (1535)S wave: +N

“this work” = Alexandrou++ PRD 89 (2014) 034502

CSSM = Mahbub++ PRD 87 (2013) 094506

BGR = Engel++ PRD 87 (2013) 074504

JLab = HSC = Edwards++ PRD 84 (2011) 074508

=) talk by S. Prelovšek

10

Wave-function of P11�1440� d-quark in g.s.

� Assign spatial dependence to each quark field in the annihilation operator

�1�x;y;z;w� � "abc�uTa�x �y�C 5db�x � z��uc�x �w�

� Fix position of u quarks

�1�x;0;z;0; t� � "abc�uTa�x; t�C 5db�x � z; t��uc�x; t�

� Construct d-quark wave-function

�d�p; t; z� �X

x

e�i p�xtr� 0 � 1�hjT��1�x;0;z;0; t��j�0;0��jiu�j

� Compute probability distribution Roberts++ PLB 725 (2013) 164

11

S-states in hydrogen atom

Fig: UC Davis ChemWiki

12

Wave-function of P11�1440� d-quark in 2S

Comparison to NRCQM(Coulomb + linear + spin-dependent)

string tension 400 MeV, mq � 360 MeV

=) node at correct place

=) asymptotics bad

Roberts++ PLB 725 (2013) 164

13

Wave-function of P11�1440� d-quark in 3S

Comparison to NRCQM(Coulomb + linear + spin-dependent)

string tension 400 MeV, mq � 360 MeV

=) nodes at wrong places

=) asymptotics bad

Roberts++ PLB 725 (2013) 164

14

Additional qq?

� � 30% admixture of qqqqq components in the Roper) ��theory��exp�

Li, Riska PRC 74 (2006) 015202

� qqqss as lowest 5q configuration in S11�1535�

) correct P11�1440� wrt. S11�1535� mass ordering) correct S11�1535�! �N, �K couplings) also implies that P11�1440� is qqqqqAn, Zou EPJA 39 (2009) 195, Liu, Zou PRL 96 (2006) 042002

� Can also do it on lattice: create qq from glue =) 5-quark operators) take �1, �2 and couple a � to get JP � 1

2

�

) no coupling of 5-quark operators to Roper CSSM preliminary (2014)

15

Or, perhaps, no qqq at all? =) see also talk by B. Golli

� coupled-channels (�N , ��, �N , �N)meson-exchange model

� �N source of dynamical pole

N N

N Nσ σ

σ σ

Nσ

π

σ

N

N

N

π

σ

N

N

π

ρ

N N ππ

π π∆ ∆

∆

∆

N π

π

N

π

π∆

N*

N

π π

π π∆∆

∆ ρ

∆ ∆π

π ∆

N

∆ π

π∆

N

∆

*

(1520)

(1520)

(a) (b) (c) (d)

(e) (f) (g) (h)

(i) (j) (k) (l)1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9

E (GeV)

−0.4

−0.2

0.0

0.2

0.4

−0.4

−0.2

0.0

0.2

0.4

−0.4

−0.2

0.0

0.2

0.4

−0.4

−0.2

0.0

0.2

0.4

Re(τ)

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9

E (GeV)

0.0

0.2

0.4

0.6

0.8

0.0

0.2

0.4

0.6

0.8

0.0

0.2

0.4

0.6

0.8

0.0

0.2

0.4

0.6

0.8

1.0Im(τ)

KA84

SM95

SE−SM95

S11

P11

P13

D13

Krehl++ PRC 62 (2000) 025207

16

Roper from �p and �N scattering Saturne

TWO structures: �I � �S � 0 in �p, little �I/�S selectivity in �N

� M � �1:39� 0:02�GeV � M � �1:48� 0:03�GeV� � �0:19� 0:03�GeV � � �0:38� 0:05�GeVseen in seen only in�N elastic, �N! N��S , and �p �N elastic, �N! ��

Morsch, Zupranski PRC 61 (1999) 024002PRC 71 (2005) 065203

17

Roper in �� production close to threshold Crystal Ball

� Strong interference of N��1440�! N��T�0S�wave

and N��1440�! �� close to threshold

� Both T � 0 (� ) and T � 1 (�–� correlated pairs)needed to describe angular distributions

200 300 400 500 6000

2

4

6

8

10

Tπ(MeV)

σ (

mb)

(d) π− p −> π

+ π

− n

Kamano, Arima Phys. Rev. C 73 (2006) 055203

18

Roper in pp ! pp�� Wasa/Promice @ Celsius

� Tp � 650, 725, 750, 775 MeV

� N��1440�! N��T�0S�wave

dominant for Tp Ü 1 GeV

� NN ! ��! NN�� alone can explainneither angular nor energy distributions,relevant at Tp Ý 1 GeV

� Important interference ofN��1440�! N� withN��1440�! �� ! N�� Similar situation in channels:pp ! pp��pp ! pp�0�0

pp ! pn��0

]2

[MeV/c -π+πpM

1240 12800

50

100-π+πpM

]2

[MeV/c -π+π

M

280 300 320 3400

20

40

60−π+π

M

-π+πδcos

-1 -0.5 0 0.5 10

2000

4000

-π+πδ

]2

[MeV/c -π+π

M

280 300 320 340

)]2

[nb/(

MeV

/c

-

π+

π/d

Mσ

d

0

10

20

30

40−π+π

M

-π+πδcos

-1 -0.5 0 0.5 1

[nb]

δ/d

cos

σd

0

1000

2000

3000-π+π

δ

]2

[MeV/c -π+πpM

1220 1260

)]2

[nb/(

MeV

/c

-

π+

πp

/dM

σd

0

20

40

60

80

-π+πpM

T = 750 MeVp T = 775 MeVp

Pätzold++ Phys. Rev. C 67 (2003) 052202

19

Roper (and other N?) from e�e� -! J= BES (BEPC ’03, ’04)

e�e� -! J= -! pN? -! pp�0; pp��; np�� ...

� �N from J= ! NN� is pure I � 1=2� no I � 1=2 / 3=2 mixing

as in �N -! �N, N -! �N

� glue-rich =) (?)

� 4 peaks in W��N�I�1=2, Breit-Wigner masses

jAj2 � jC0 � C00M2p�j �

Xi

jCij�M2

p� �M2i �

2 �M2i � 2i

TABLE I: The fitted masses and widths for the four N∗ peaks shown in Fig. 6.

Mass(MeV/c2) Width(MeV/c2)

1358 ± 6 ± 16 179 ± 26 ± 50

1495 ± 2 ± 3 87 ± 7 ± 10

1674 ± 3 ± 4 100 ± 9 ± 15

2068 ± 3+15−40

165 ± 14 ± 40

Because we use a constant width for the Breit-Wigner (BW) formulae, the BW mass and

width are very close to their corresponding pole positions. For the two well-known peaks

at 1500 MeV/c2 and 1670 MeV/c2, the former contains two well-established N∗ resonances,

the N∗(1520) and N∗(1535), while the latter contains more than two N∗ resonances. Here

we only use one BW function to fit each of them.

For the new N∗(2065) peak, orbital angular momentum L = 0 is preferred due to the

suppression of the centrifugal barrier factor for L ≥ 1. If we fit the N∗(2065) peak in Fig. 6

with L = 1 centrifugal barrier factor instead of Eq.(1), then the χ2 increases from 133 to

163 for 102 data points. The much worse fit with L = 1 compared with L = 0 means that

there is substantial L = 0 component for the new N∗(2065) peak.

For L = 0, the spin-parity of N∗(2065) is limited to be 1/2+ and 3/2+. This may be

the reason that the N∗(2065) shows up as a peak in J/ψ decays while no peak shows up in

the πN invariant mass spectra in πN and γN production processes which allow all 1/2±,

3/2±, 5/2±, and 7/2± N∗ resonances and their isospin 3/2 ∆∗ partners around this energy to

interfere with each other. In order to determine its spin-parity, a partial wave analysis using

an effective Lagrangian approach [9] is tried for the pπ−n̄ data by including a new N∗(2065)

with spin-parity either 1/2+ or 3/2+ in addition to all well-established N∗ resonances below

2 GeV/c2 with masses and widths fixed to their PDG values [1]. Comparing with the fit

without including any new N∗(2065) resonance, including a N∗(2065) with spin-parity of

either 1/2+ or 3/2+ improves log likelihood value by more than 400. The new N∗(2065)

peak cannot be reproduced by reflections of well-established N∗ resonances. However, the

spin-parity of the new resonance(s) cannot be well determined. The difference of the fits

with different spin-parity quantum numbers is small and depends on many fitting details,

such as how to treat the background contribution and how large an isospin breaking effect is

10

Ablikim++ PRL 97 (2006) 062001

20

Roper in single-pion electroproduction p�~e; e0p��

When only beam is polarized:

d�d� �T � "�L �

q2"�" � 1��LT cos�� "�TT cos 2�� h

q2"�1� "��LT0 sin�

Separate strong and EM vertex:

With sufficient angular coverage: extract Legendre moments

��W; cos�� XlDl�W�Pl�cos��

! still “easy”

! typical for CLAS (Hall B @ JLab)

21

Example result: Q2-dependence of D0 CLAS

UIMDR D0��T � "�L� � �tot=4�

� For Q2 large, P11�1440�, S11�1535�, D13�1520�become more dominant with respect to P33�1232�

� Similar: slow Q2 decrease of D0;1;2��T � "�L�( due to slow fall-off of A1=2 of the P11, S11, D13

22

Legendre moments of ep! en�� structure functions CLAS

Q2 � 2:05 GeV2

solid: DRdashed: UIMdotted: DR, Roper off

23

Much harder: p�~e; e0~p��

d�dE0e de d?p

� �0

2

�1� P � bsr � h�Ae � P0 � bsr�

�

xy

z

e

e’

q

scattering plane (lab)

reaction plane (cm)

p

0

t = n x l

ln = q x p p

d�dE0e de d?p

� �vjp?p jWK Mp

��RT � Rn

TSn�� 2"?L �RL � RnLSn�

�q"?L �1� "��RLT � Rn

LTSn� cos�� RlLTSl � Rt

LTSt� sin��" ��RTT � Rn

TTSn� cos 2�� RlTTSl � Rt

TTSt� sin 2��

�hq"?L �1� "��R0LT � R0nLTSn� sin�� R0lLTSl � R0tLTSt� cos��

�hp

1� "2�R0lTTSl � R0tTTSt ��

24

N! ��1232� at Q2 ’ 1 JLab/Hall A (E91-011)

Kelly++ PRL 95 (2005) 102001, PRC 75 (2007) 025201

25

Amplification through interference

L.C. Smith JLAB Users Group Meeting 2005

Amplification Through Interference

• Real LT Response

• Imaginary LT Response

1+

3

+

3

1Im(M ) P (1Im(S )

232)

σ= +

*Re( )Re( ) IRe( ) ( I ( )) mm

LT LTLT TL

Large

Small

σ= −

/ *

Re( )Im( ) IIm

m((

)Re( ))LT

L LLT

T T

0

11

+1- PIm(S )

(

1Re(E )440)

Resonance

Amplify small resonant multipole by interference with large resonant multipole

Amplify small resonant multipole by interference with large real background.

Resonance tails + Born terms

W

W

26

Sample sensitivities

� Many multipole combinations involved:

�Pn�RnT � �ImE�0� �3E1� �M1� � 2M1��

(leading M1� interfering with non-resonant E0�)

�Pl�RlTT0 / ReE�0� �3E1� �M1� � 2M1��

(real part of the same interference)

�Pn�RnTL contains Im L�1�M1� ;

�Pl�RlTL0 contains Re L�1�M1�

((Re and Im) interferences of both resonant multipoles but very small)

�Pn�RnL / �2 ImL�0� �2L1� � L1�� ;

�Pt�RtTL0 / Re

�L�0� �2M1� �M1�� E0�

�2L�1� � L�1�

��

� In typical A1 @ MAMI setup: not a targeted multipole “chase”

— no angular distributions!

27

MAID07 vs. DMT01 (Roper “on”/“off”) p�~e; e0~p��0

� Different treatment of resonances in isobar models (e.g. MAID)vs. dynamical models (e.g. DMT) ... “dressed” vs. “bare” vertices

� nice distinctions in all components of ~P

28

MAID07 vs. DMT01 (full calculations) p�~e; e0~p��0

� Tremendous sensitivity to Roper

� CLAS results on P11, S11, D13 great,but lagging behind the ��1232� sophistication

� (Too) few measurements of double-polarization observables

29

p�~e; e0~p��0 experiment @ MAMI/A1 2011, 2014

1400 1420 1440 1460 1480

W[MeV]

0.4

0.2

0.0

0.2

0.4P ′x

1400 1420 1440 1460 1480

W[MeV]

0.4

0.2

0.0

0.2

0.4Py

1400 1420 1440 1460 1480

W[MeV]

0.0

0.2

0.4

0.6

0.8

1.0P ′z

×(− 1)×(− 1)×(− 1)×(− 1)

MAID

DMT

SAID

Exp.

Štajner++ accepted in PRLSame thing on ��1232�: Pospischil++ 86 (2001) 2959

Same thing on S11�1535�: Merkel++ PRL 99 (2007) 132301

A model-dependent attempt to extract S1=2

=) Assume that the MAID value of A1=2�Q2� is OK

=) Fit S1=2 to P 0x, Py and P 0z (unequal sensitivities)

30

P11�1440� helicity amplitudes: 3q state or q3g hybrid?

Weber PRC 41 (1990) 2783

Capstick, Keister PRD 51 (1995) 3598

Cardarelli++ PLB 397 (1997) 13

Aznauryan PRC 76 (2007) 025212

Li, Burkert, Li, PRD 46 (1992) 70

� All LF RQM: sign change of A1=2, magnitude of S1=2, fail at low Q2

� S1=2 suppressed due to form of ?q! qg vertex� In the flux-tube model, Mhyb > �1870� 100�MeV ... Capstick PRD 60 (1999) 111501

� Evidence for P11�1440� as radial excitation of 3q g.s., hybrid q3g ruled out

31

P11�1440� helicity amps from N�/N�� electroproduction

-80

-60

-40

-20

0

20

40

60

80

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5Q

2 GeV

2

A1

/2*1000 G

eV

−1/2

0

10

20

30

40

50

60

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5Q

2 GeV

2

S1/2

*1

00

0 G

eV

−1/2

� good agreement between values obtained from N� , N�� (CLAS)

� electro-couplings at Q2 Ý 2 consistent with 3q radial excitation

� meson cloud effects large below 1 GeV2

1 == LFQM, Capstick PRD 51 (1995) 35982 == LFQM, Aznauryan PRC 76 (2007) 025212

3 == spectator di-quark, Ramalho PRD 81 (2010) 074020

Mokeev++ PRC 86 (2012) 035203

1

3

2

32

P11�1440� helicity amps in “�PT-inspired” theory

(1) (2)

1 1

(3)

1 11

(4)

01 1

1

(5)

11

1

1

01

11

11 011 0 111 0 111

(6) (7) (8) (9)

(10)

1

(11)

1

(12)

11 1

(13)

1 1

1

0

(14)

11

1

1

1

011 1 011

1 1

0 11111

(15) (16) (18)(17)

1

11

æ

æ

àà

à

ìì

ò

ò

ò ò

ò

ò ò

0.0 0.1 0.2 0.3 0.4 0.5 0.6

-50

0

50

Q2 @GeV2D

pA1�2

æ

æà

à àòòò ò

ò

ò

ò

0.0 0.1 0.2 0.3 0.4 0.5 0.6-20

-10

0

10

20

30

40

50

Q2 @GeV2D

pS1�2

ìì

0.0 0.1 0.2 0.3 0.4 0.5 0.6-100

-50

0

50

100

Q2 @GeV2D

nA1�2

0.0 0.1 0.2 0.3 0.4 0.5 0.6-150

-100

-50

0

50

100

Q2 @GeV2D

nS1�2

æ

æ

àà

à

ìì

ò

ò

ò ò

ò

ò ò

0.0 0.1 0.2 0.3 0.4 0.5 0.6

-50

0

50

Q2 @GeV2D

pA1�2

æ

æà

à àòòò ò

ò

ò

ò

0.0 0.1 0.2 0.3 0.4 0.5 0.6-20

-10

0

10

20

30

40

50

Q2 @GeV2D

pS1�2ìì

0.0 0.1 0.2 0.3 0.4 0.5 0.6-100

-50

0

50

100

Q2 @GeV2D

nA1�2

0.0 0.1 0.2 0.3 0.4 0.5 0.6-150

-100

-50

0

50

100

Q2 @GeV2D

nS1�2

� effective L: tree + loops (NNLO), including � , N , R, � as explicit DOFs

� complex mass scheme Bauer, Scherer, Tiator PRC 90 (2014) 015201

33

p�~e; e0~p��0 experiment @ MAMI/A1 2011, 2014

0.5 1.0 1.5

Q 2[GeV2]

0

10

20

30

40

50

60

S1/

2[1

0−

3G

eV−

1/2]

LFQM 1

LFQM 2

MB

CLAS

This work

MAID

JM

Models

Štajner++ accepted in PRL

34

Conclusion

� Roper seen indirectly in many places, but hard to quantify unambiguously

� Lack of neutron data

� Advantage of polarized degrees of freedom

� First determination of P 0x, Py and P 0z in the p�~e; e0~p��0 process

=) Good agreement with MAID, disagreement with DMT and SAID

=) Extracted S1=2 at very low Q2 � 0:1 GeV2

=) Strong interplay of quark-core / meson-cloud effects

35

The p—~e0p~–ˇ0 process in the region of the Roper resonance · The p—~e;e0p~–ˇ0 process...

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