COMPASS 1 8 The COMPASS Experiment at the CERN SPS Experimental - - PowerPoint PPT Presentation

SLIDE 1

Meson Spectroscopy at COMPASS

Boris Grube

Physik-Department E18 Technische Universität München, Garching, Germany

MESON2016

• 07. June 2016, Kraków

E 1 8

COMPASS

SLIDE 2

The COMPASS Experiment at the CERN SPS

Experimental Setup

[NIMA 779 (2015) 69]

2 Boris Grube, TU München Meson Spectroscopy at COMPASS

Fixed-target experiment Two-stage spectrometer Large acceptance over wide kinematic range Electromagnetic and hadronic calorimeters Beam and final-state particle ID (CEDARs, RICH)

SLIDE 3

The COMPASS Experiment at the CERN SPS

Experimental Setup

[NIMA 779 (2015) 69]

2 Boris Grube, TU München Meson Spectroscopy at COMPASS

Fixed-target experiment Two-stage spectrometer Large acceptance over wide kinematic range Electromagnetic and hadronic calorimeters Beam and final-state particle ID (CEDARs, RICH) Hadron spectroscopy

2008-09, 2012

190 GeV/c secondary hadron beams h− beam: 97 % π−, 2 % K−, 1 % p h+ beam: 75 % p, 24 % π+, 1 % K+ Various targets: ℓH2, Ni, Pb, W

SLIDE 4

The COMPASS Experiment at the CERN SPS

Experimental Setup

[NIMA 779 (2015) 69]

2 Boris Grube, TU München Meson Spectroscopy at COMPASS

Fixed-target experiment Two-stage spectrometer Large acceptance over wide kinematic range Electromagnetic and hadronic calorimeters Beam and final-state particle ID (CEDARs, RICH) Hadron spectroscopy

2008-09, 2012

190 GeV/c secondary hadron beams h− beam: 97 % π−, 2 % K−, 1 % p h+ beam: 75 % p, 24 % π+, 1 % K+ Various targets: ℓH2, Ni, Pb, W

SLIDE 5

The COMPASS Experiment at the CERN SPS

Experimental Setup

[NIMA 779 (2015) 69]

2 Boris Grube, TU München Meson Spectroscopy at COMPASS

Hadron spectroscopy

2008-09, 2012

190 GeV/c secondary hadron beams h− beam: 97 % π−, 2 % K−, 1 % p h+ beam: 75 % p, 24 % π+, 1 % K+ Various targets: ℓH2, Ni, Pb, W Spectroscopy program Explore light-meson spectrum for m 2 GeV/c2 Search for states beyond the constituent quark model Precision measurement of known resonances

SLIDE 6

Outline

1

Introduction Meson production in diffractive dissociation Partial-wave analysis method

2

PWA of diffractively produced 3π final states Observation of a new narrow axial-vector meson a1(1420) JPC = 1−+ spin-exotic partial wave

3

Conclusions and outlook

3 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 7

Meson Production in Diffractive Dissociation

P π´

beam

ptarget precoil π´

beam

ptarget precoil π´

beam

ptarget precoil π´

beam

ptarget precoil h1 . . . hn Soft scattering of beam particle off target

Production of n forward-going hadrons Target particle stays intact

At 190 GeV/c, interaction dominated by space-like pomeron exchange

4 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 8

Meson Production in Diffractive Dissociation

P π´

beam

ptarget precoil π´

beam

ptarget precoil π´

beam

ptarget precoil π´

beam

ptarget precoil h1 . . . hn Exclusive measurement

Clean data samples

Reduced four-momentum transfer squared t′ ≡ |t| − |t|min

Analyzed range: 0.1 < t′ < 1.0 (GeV/c)2

Example: π−π+π− final state

]

GeV

[

beam

E 180 190 200 Events / (50 MeV) 0.2 0.4

6

10 ×

5 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 9

Meson Production in Diffractive Dissociation

P Ó t1 π´

beam

ptarget precoil π´

beam

ptarget precoil π´

beam

ptarget precoil π´

beam

ptarget precoil h1 . . . hn Exclusive measurement

Clean data samples

Reduced four-momentum transfer squared t′ ≡ |t| − |t|min

Analyzed range: 0.1 < t′ < 1.0 (GeV/c)2

Example: π−π+π− final state

]

2

) c (GeV/

[

t' 1 2 3 4 5

)

2

) c (GeV/

2 −

10

(

Events / 1 10

2

10

3

10

4

10

5

10

6

10

5 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 10

Meson Production in Diffractive Dissociation

P π´

beam

ptarget precoil π´

beam

ptarget precoil π´

beam

ptarget precoil π´

beam

ptarget precoil h1 . . . hn Excitation of beam particle into intermediate resonances X X dissociate into n-body final state Rich spectrum of intermediate states X Disentanglement of all contributing X by partial-wave analysis (PWA)

6 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 11

Meson Production in Diffractive Dissociation

P π´

beam

ptarget precoil X´ π´

beam

ptarget precoil π´

beam

ptarget precoil π´

beam

ptarget precoil h1 . . . hn Excitation of beam particle into intermediate resonances X X dissociate into n-body final state Rich spectrum of intermediate states X Disentanglement of all contributing X by partial-wave analysis (PWA)

6 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 12

Meson Production in Diffractive Dissociation

P π´

beam

ptarget precoil X´ π´

beam

ptarget precoil π´

beam

ptarget precoil π´

beam

ptarget precoil h1 . . . hn Excitation of beam particle into intermediate resonances X X dissociate into n-body final state Rich spectrum of intermediate states X Disentanglement of all contributing X by partial-wave analysis (PWA)

6 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 13

Partial-Wave Analysis Method

P π´

beam

ptarget precoil X´ π´

beam

ptarget precoil π´

beam

ptarget precoil π´

beam

T ptarget precoil A h1 . . . hn

Ansatz: Factorization of production and decay

I(τ; mX) = ∑ǫ=±1

• ∑

waves i

T ǫ

i (mX) Aǫ i (τ; mX)

• 2

Transition amplitudes T ǫ

i (mX) =

⇒ interesting physics Decay amplitudes Aǫ

i (τ; mX)

Describe kinematic distribution of partial waves Calculated using isobar model (for n > 2) and helicity formalism (Wigner D-functions)

ǫ = ±1: naturalities of exchange particle

190 GeV/c beam momentum = ⇒ pomeron (ǫ = +1) dominates

7 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 14

Partial-Wave Analysis Method

P π´

beam

ptarget precoil X´ π´

beam

ptarget precoil π´

beam

ptarget precoil π´

beam

T ptarget precoil A h1 . . . hn

Ansatz: Factorization of production and decay

I(τ; mX) = ∑ǫ=±1

• ∑

waves i

T ǫ

i (mX) Aǫ i (τ; mX)

• 2

Transition amplitudes T ǫ

i (mX) =

⇒ interesting physics Decay amplitudes Aǫ

i (τ; mX)

Describe kinematic distribution of partial waves Calculated using isobar model (for n > 2) and helicity formalism (Wigner D-functions)

ǫ = ±1: naturalities of exchange particle

190 GeV/c beam momentum = ⇒ pomeron (ǫ = +1) dominates

7 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 15

Partial-Wave Analysis Method

P π´

beam

ptarget precoil X´ π´

beam

ptarget precoil π´

beam

ptarget precoil π´

beam

T ptarget precoil A h1 . . . hn

Ansatz: Factorization of production and decay

I(τ; mX) = ∑ǫ=±1

• ∑

waves i

T ǫ

i (mX) Aǫ i (τ; mX)

• 2

Transition amplitudes T ǫ

i (mX) =

⇒ interesting physics Decay amplitudes Aǫ

i (τ; mX)

Describe kinematic distribution of partial waves Calculated using isobar model (for n > 2) and helicity formalism (Wigner D-functions)

ǫ = ±1: naturalities of exchange particle

190 GeV/c beam momentum = ⇒ pomeron (ǫ = +1) dominates

7 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 16

Partial-Wave Analysis Method

P π´

beam

ptarget precoil X´ π´

beam

ptarget precoil π´

beam

ptarget precoil π´

beam

T ptarget precoil A h1 . . . hn

Two-step analysis

I(τ; mX) = ∑ǫ=±1

• ∑

waves i

T ǫ

i (mX) Aǫ i (τ; mX)

• 2

1

Determination of mX dependence of spin-density matrix ̺ǫ

ij(mX) = T ǫ i (mX) T ǫ∗ j

(mX)

Independent maximum likelihood fits to measured τ distributions in narrow bins of mX Fits take into account detection efficiency No assumptions about resonance content of X

2

Extraction of resonances

χ2 fit of resonance model to spin-density (sub)matrix

8 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 17

Partial-Wave Analysis Method

P π´

beam

ptarget precoil X´ π´

beam

ptarget precoil π´

beam

ptarget precoil π´

beam

T ptarget precoil A h1 . . . hn

Two-step analysis

I(τ; mX) = ∑ǫ=±1

• ∑

waves i

T ǫ

i (mX) Aǫ i (τ; mX)

• 2

1

Determination of mX dependence of spin-density matrix ̺ǫ

ij(mX) = T ǫ i (mX) T ǫ∗ j

(mX)

Independent maximum likelihood fits to measured τ distributions in narrow bins of mX Fits take into account detection efficiency No assumptions about resonance content of X

2

Extraction of resonances

χ2 fit of resonance model to spin-density (sub)matrix

8 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 18

Partial-Wave Analysis: π−π+π− Final State

[arXiv:1509.00992]

P π´

beam

ptarget precoil X´ π´

beam

ptarget precoil π´

beam

ptarget precoil π´

beam

ptarget precoil π´ π+ π´ X− decay via π+π− resonances = “isobars”

9 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 19

Partial-Wave Analysis: π−π+π− Final State

[arXiv:1509.00992]

P π´

beam

ptarget precoil X´ π´

beam

ptarget precoil π´

beam

ptarget precoil π´

beam

ptarget precoil π´ π+ π´

100 200 300 400 500 600 700 800

]

2

)

2

c (GeV/

[

2

+

π

−

π

m 0.5 1 1.5

]

2

)

2

c (GeV/

[

2

+

π

−

π

m 0.5 1 1.5

2

c < 100 MeV/ 

2

c 1318 MeV/ −

π 3

m  (770) ρ

X− decay via π+π− resonances = “isobars”

9 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 20

Partial-Wave Analysis: π−π+π− Final State

[arXiv:1509.00992]

P π´

beam

ptarget precoil X´ π´

beam

ptarget precoil π´

beam

ptarget precoil π´

beam

ptarget precoil π´ π+ π´

50 100 150 200 250 300 350

]

2

)

2

c (GeV/

[

2

+

π

−

π

m 1 2

]

2

)

2

c (GeV/

[

2

+

π

−

π

m 1 2

2

c < 100 MeV/ 

2

c 1672 MeV/ −

π 3

m  (770) ρ (980) f (1270)

2

f

X− decay via π+π− resonances = “isobars”

9 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 21

Partial-Wave Analysis: π−π+π− Final State

[arXiv:1509.00992]

P π´

beam

ptarget precoil X´ π´

beam

ptarget precoil π´

beam

ptarget precoil π´

beam

ptarget precoil π´ π+ π´

50 100 150 200 250 300 350

]

2

)

2

c (GeV/

[

2

+

π

−

π

m 1 2

]

2

)

2

c (GeV/

[

2

+

π

−

π

m 1 2

2

c < 100 MeV/ 

2

c 1672 MeV/ −

π 3

m  (770) ρ (980) f (1270)

2

f

X− decay via π+π− resonances = “isobars”

9 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 22

Partial-Wave Analysis: π−π+π− Final State

[arXiv:1509.00992]

P π´

beam

ptarget precoil X´ [JPCMǫ] Isobar π´

beam

ptarget precoil π´

beam

ptarget precoil π´

beam

ptarget precoil [L] Bachelor π´ π+ π´ π´

beam

ptarget precoil [L] Bachelor π´ π+ π´

50 100 150 200 250 300 350

]

2

)

2

c (GeV/

[

2

+

π

−

π

m 1 2

]

2

)

2

c (GeV/

[

2

+

π

−

π

m 1 2

2

c < 100 MeV/ 

2

c 1672 MeV/ −

π 3

m  (770) ρ (980) f (1270)

2

f

X− decay via π+π− resonances = “isobars”

9 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 23

Partial-Wave Analysis: π−π+π− Final State

[arXiv:1509.00992]

P π´

beam

ptarget precoil X´ [JPCMǫ] Isobar π´

beam

ptarget precoil π´

beam

ptarget precoil π´

beam

ptarget precoil [L] Bachelor π´ π+ π´ π´

beam

ptarget precoil [L] Bachelor π´ π+ π´ Isobar model

Isobars included into PWA model [ππ]S JPC = 0++ ρ(770) 1−− f0(980) 0++ f2(1270) 2++ f0(1500) 0++ ρ3(1690) 3−− PWA requires precise knowledge of isobar → π+π− amplitude

]

2

c GeV/

[

+

π

−

π

m 0.5 1 1.5 2 )

2

c Entries / (5 MeV/ 0.5 1

6

10 × (770) ρ (980) f (1270)

2

f (1690)

3

ρ

10 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 24

PWA of π− p → (3π)− precoil

Two Data Sets

1

π−π+π− (50 M events)

2

Crosscheck with π−π0π0 (3.5 M events)

Very different acceptance Isobars separated by isospin

I = 1 isobars in π−π0 I = 0 isobars in π0π0

Complicated correlation of m3π and t′ 2D PWA in bins of t′ and m3π π−π+π−: 11 t′ bins π−π0π0: 8 t′ bins Better disentanglement of resonant and nonresonant contributions

11 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 25

PWA of π− p → (3π)− precoil

Two Data Sets

1

π−π+π− (50 M events)

2

Crosscheck with π−π0π0 (3.5 M events)

Very different acceptance Isobars separated by isospin

I = 1 isobars in π−π0 I = 0 isobars in π0π0

Complicated correlation of m3π and t′ 2D PWA in bins of t′ and m3π π−π+π−: 11 t′ bins π−π0π0: 8 t′ bins Better disentanglement of resonant and nonresonant contributions 800 < m3π < 850 MeV/c2

]

2

) c (GeV/

[

t' 0.2 0.4 0.6 0.8 1

)

2

) c (GeV/

3 −

10 ⋅ 5

(

Events /

2

10

3

10

4

10

2

c < 0.85 GeV/

π 3

m 0.80 <

1600 < m3π < 1650 MeV/c2

]

2

) c (GeV/

[

t' 0.2 0.4 0.6 0.8 1

)

2

) c (GeV/

3 −

10 ⋅ 5

(

Events /

3

10

4

10

5

10

2

c < 1.65 GeV/

π 3

m 1.60 <

11 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 26

PWA of π− p → (3π)− precoil

Two Data Sets

1

π−π+π− (50 M events)

2

Crosscheck with π−π0π0 (3.5 M events)

Very different acceptance Isobars separated by isospin

I = 1 isobars in π−π0 I = 0 isobars in π0π0

Complicated correlation of m3π and t′ 2D PWA in bins of t′ and m3π π−π+π−: 11 t′ bins π−π0π0: 8 t′ bins Better disentanglement of resonant and nonresonant contributions 0.10 < t′ < 0.12 (GeV/c)2

]

2

c GeV/

[

π 3

m 0.5 1 1.5 2 2.5 )

2

c Events / (5 MeV/ 20 40 60

3

10 ×

2

) c < 0.12 (GeV/ t' 0.10 <

0.44 < t′ < 1.00 (GeV/c)2

]

2

c GeV/

[

π 3

m 0.5 1 1.5 2 2.5 )

2

c Events / (5 MeV/ 10 20 30 40

3

10 ×

2

) c < 1.00 (GeV/ t' 0.44 <

11 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 27

PWA of π− p → (3π)− precoil

Two Data Sets

1

π−π+π− (50 M events)

2

Crosscheck with π−π0π0 (3.5 M events)

Very different acceptance Isobars separated by isospin

I = 1 isobars in π−π0 I = 0 isobars in π0π0

Complicated correlation of m3π and t′ 2D PWA in bins of t′ and m3π π−π+π−: 11 t′ bins π−π0π0: 8 t′ bins Better disentanglement of resonant and nonresonant contributions 0.10 < t′ < 0.12 (GeV/c)2

]

2

c GeV/

[

π 3

m 0.5 1 1.5 2 2.5 )

2

c Events / (5 MeV/ 20 40 60

3

10 ×

2

) c < 0.12 (GeV/ t' 0.10 <

0.44 < t′ < 1.00 (GeV/c)2

]

2

c GeV/

[

π 3

m 0.5 1 1.5 2 2.5 )

2

c Events / (5 MeV/ 10 20 30 40

3

10 ×

2

) c < 1.00 (GeV/ t' 0.44 <

11 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 28

PWA of π− p → π−π+π− precoil: Major Waves

[arXiv:1509.00992]

π−π+π− invariant mass spectrum 1++ 0+ ρ(770)π S 2++ 1+ ρ(770)π D 2−+ 0+ f2(1270)π S

12 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 29

PWA of π− p → π−π+π− precoil: Major Waves

[arXiv:1509.00992]

π−π+π− invariant mass spectrum 1++ 0+ ρ(770)π S 2++ 1+ ρ(770)π D 2−+ 0+ f2(1270)π S

12 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 30

PWA of π− p → π−π+π− precoil: Major Waves

[arXiv:1509.00992]

π−π+π− invariant mass spectrum 1++ 0+ ρ(770)π S 2++ 1+ ρ(770)π D 2−+ 0+ f2(1270)π S

12 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 31

PWA of π− p → π−π+π− precoil: Major Waves

[arXiv:1509.00992]

π−π+π− invariant mass spectrum 1++ 0+ ρ(770)π S 2++ 1+ ρ(770)π D 2−+ 0+ f2(1270)π S

12 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 32

PWA of π− p → π−π+π− precoil: Major Waves

[arXiv:1509.00992]

π−π+π− invariant mass spectrum 1++ 0+ ρ(770)π S 2++ 1+ ρ(770)π D 2−+ 0+ f2(1270)π S

12 Boris Grube, TU München Meson Spectroscopy at COMPASS

In total 88 partial waves Largest wave set used so far for π−π+π− Spin J up to 6 Orbital angular momentum L up to 6

SLIDE 33

PWA of π− p → π−π+π− precoil: Selected Small Waves

[arXiv:1509.00992]

2++ 2+ ρ(770)π D 4++ 1+ ρ(770)π G 0−+ 0+ f0(980)π S

13 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 34

PWA of π− p → π−π+π− precoil: Selected Small Waves

[arXiv:1509.00992]

2++ 2+ ρ(770)π D 4++ 1+ ρ(770)π G 0−+ 0+ f0(980)π S

13 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 35

PWA of π− p → π−π+π− precoil: Selected Small Waves

[arXiv:1509.00992]

2++ 2+ ρ(770)π D 4++ 1+ ρ(770)π G 0−+ 0+ f0(980)π S

13 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 36

PWA of π− p → π−π+π− precoil: Selected Small Waves

A New a1(1420) Meson?

[arXiv:1509.00992]

1++ 0+ f0(980)π P

Unexpected peak around 1.4 GeV/c2 Small intensity: ≈ 0.3%

]

2

c GeV/

[

π 3

m 0.5 1 1.5 2 2.5 )

2

c Intensity / (20 MeV/ 5 10 15

3

10 × P π (980) f

+ + +

1

2

) c < 1.000 (GeV/ t' 0.100 < 0.3%

13 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 37

PWA of π− p → π−π+π− precoil: Selected Small Waves

A New a1(1420) Meson?

1++ 0+ f0(980)π P

Unexpected peak around 1.4 GeV/c2 Small intensity: ≈ 0.3%

π−π0π0 final state Very different detector acceptance Similar signal

)

2

(GeV/c

−

) π (3

m 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 )

2

intensity (per 40 MeV/c 2 4 6 8 10 12 14 16 18 20 22 24

3

10 × p)

−

) π (3 → p

−

π COMPASS 2008 ( P π (980) f

+ + +

1 (scaled)

+

π

−

π

−

π , π π

−

π

2

/c

2

0.100 < t' < 1.000 GeV (incoherent sum)

Preliminary

13 Boris Grube, TU München Meson Spectroscopy at COMPASS

π−π0π0 π−π+π− scaled

SLIDE 38

Resonance-Model Fit

[PRL 115 (2015) 082001]

Coherent sum of resonant (Breit-Wigner) and nonresonant terms

14 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 39

Resonance-Model Fit

[PRL 115 (2015) 082001]

Coherent sum of resonant (Breit-Wigner) and nonresonant terms

14 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 40

Resonance-Model Fit

[PRL 115 (2015) 082001]

]

2

c GeV/

[

π 3

m 1 1.2 1.4 1.6 1.8 2 2.2 )

2

c Intensity / (20 MeV/ 5 10 15 20 25

3

10 × P π (980) f

+ + +

1

2

) c < 1.0 (GeV/ t' 0.1 < (1) Model curve (1420) resonance

1

a (2) (3) Non-resonant term (3) (2) (1)

1++ peak consistent with Breit-Wigner resonance a1(1420): M0 = 1414+15

−13 MeV/c2

Γ

0 = 153+8 −23 MeV/c2

Work in progress: extension to more partial waves

15 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 41

Resonance-Model Fit

[PRL 115 (2015) 082001]

]

2

c GeV/

[

π 3

m 1 1.2 1.4 1.6 1.8 2 2.2 )

2

c Intensity / (20 MeV/ 5 10 15 20 25

3

10 × G π (770) ρ

+

1

+ +

4

2

) c < 1.0 (GeV/ t' 0.1 < (1) Model curve (2040) resonance

4

a (2) (3) Non-resonant term (3) (2) (1)

]

2

c GeV/

[

π 3

m 1 1.2 1.4 1.6 1.8 2 2.2 )

2

c Intensity / (20 MeV/ 5 10 15 20 25

3

10 × P π (980) f

+ + +

1

2

) c < 1.0 (GeV/ t' 0.1 < (1) Model curve (1420) resonance

1

a (2) (3) Non-resonant term (3) (2) (1)

1++ peak consistent with Breit-Wigner resonance a1(1420): M0 = 1414+15

−13 MeV/c2

Γ

0 = 153+8 −23 MeV/c2

Work in progress: extension to more partial waves

]

2

c GeV/

[

π 3

m 1 1.2 1.4 1.6 1.8 2 2.2 Phase [deg] 200 − 100 − 100 200 G π (770) ρ

+

1

+ +

4 − P π (980) f

+ + +

1

2

) c < 0.113 (GeV/ t' 0.100 <

2

) c < 0.189 (GeV/ t' 0.164 <

2

) c < 0.724 (GeV/ t' 0.449 <

15 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 42

Resonance-Model Fit

[PRL 115 (2015) 082001]

]

2

c GeV/

[

π 3

m 1 1.2 1.4 1.6 1.8 2 2.2 )

2

c Intensity / (20 MeV/ 5 10 15 20 25

3

10 × G π (770) ρ

+

1

+ +

4

2

) c < 1.0 (GeV/ t' 0.1 < (1) Model curve (2040) resonance

4

a (2) (3) Non-resonant term (3) (2) (1)

]

2

c GeV/

[

π 3

m 1 1.2 1.4 1.6 1.8 2 2.2 )

2

c Intensity / (20 MeV/ 5 10 15 20 25

3

10 × P π (980) f

+ + +

1

2

) c < 1.0 (GeV/ t' 0.1 < (1) Model curve (1420) resonance

1

a (2) (3) Non-resonant term (3) (2) (1)

1++ peak consistent with Breit-Wigner resonance a1(1420): M0 = 1414+15

−13 MeV/c2

Γ

0 = 153+8 −23 MeV/c2

Work in progress: extension to more partial waves

]

2

c GeV/

[

π 3

m 1 1.2 1.4 1.6 1.8 2 2.2 Phase [deg] 200 − 100 − 100 200 G π (770) ρ

+

1

+ +

4 − P π (980) f

+ + +

1

2

) c < 0.113 (GeV/ t' 0.100 <

2

) c < 0.189 (GeV/ t' 0.164 <

2

) c < 0.724 (GeV/ t' 0.449 <

15 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 43

Resonance-Model Fit

[PRL 115 (2015) 082001]

]

2

c GeV/

[

π 3

m 1 1.2 1.4 1.6 1.8 2 2.2 )

2

c Intensity / (20 MeV/ 5 10 15 20 25

3

10 × G π (770) ρ

+

1

+ +

4

2

) c < 1.0 (GeV/ t' 0.1 < (1) Model curve (2040) resonance

4

a (2) (3) Non-resonant term (3) (2) (1)

]

2

c GeV/

[

π 3

m 1 1.2 1.4 1.6 1.8 2 2.2 )

2

c Intensity / (20 MeV/ 5 10 15 20 25

3

10 × P π (980) f

+ + +

1

2

) c < 1.0 (GeV/ t' 0.1 < (1) Model curve (1420) resonance

1

a (2) (3) Non-resonant term (3) (2) (1)

1++ peak consistent with Breit-Wigner resonance a1(1420): M0 = 1414+15

−13 MeV/c2

Γ

0 = 153+8 −23 MeV/c2

Work in progress: extension to more partial waves

]

2

c GeV/

[

π 3

m 1 1.2 1.4 1.6 1.8 2 2.2 Phase [deg] 200 − 100 − 100 200 G π (770) ρ

+

1

+ +

4 − P π (980) f

+ + +

1

2

) c < 0.113 (GeV/ t' 0.100 <

2

) c < 0.189 (GeV/ t' 0.164 <

2

) c < 0.724 (GeV/ t' 0.449 <

15 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 44

Is the a1(1420) a Model Artifact?

P π´

beam

ptarget precoil X´ [1++0+] f0(980) π´

beam

ptarget precoil π´

beam

ptarget precoil π´

beam

ptarget precoil [L = 1] Bachelor π´ π+ π´ π´

beam

ptarget precoil [L = 1] Bachelor π´ π+ π´ Calculation of decay amplitudes

Awave(τ) needs precise knowledge of isobar → π+π− amplitude At least 3 isobars with JPC = 0++

[ππ]S-wave f0(980) f0(1500)

Parametrization of mπ+π− dependence difficult

16 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 45

Is the a1(1420) a Model Artifact?

P π´

beam

ptarget precoil X´ [1++0+] f0(980) π´

beam

ptarget precoil π´

beam

ptarget precoil π´

beam

ptarget precoil [L = 1] Bachelor π´ π+ π´ π´

beam

ptarget precoil [L = 1] Bachelor π´ π+ π´ Calculation of decay amplitudes

Awave(τ) needs precise knowledge of isobar → π+π− amplitude At least 3 isobars with JPC = 0++

[ππ]S-wave f0(980) f0(1500)

Parametrization of mπ+π− dependence difficult

16 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 46

Is the a1(1420) a Model Artifact?

Novel analysis method

inspired by E791 analysis [PRD 73 (2006) 032204]

Replace JPC = 0++ isobar parametrizations by piece-wise constant amplitudes in mπ+π− bins Extract m3π dependence of JPC = 0++ isobar amplitude from data

Advantage: drastic reduction of model bias Caveat: significant increase in number of fit parameters

− →

17 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 47

Is the a1(1420) a Model Artifact?

Novel analysis method

inspired by E791 analysis [PRD 73 (2006) 032204]

Replace JPC = 0++ isobar parametrizations by piece-wise constant amplitudes in mπ+π− bins Extract m3π dependence of JPC = 0++ isobar amplitude from data

Advantage: drastic reduction of model bias Caveat: significant increase in number of fit parameters

− →

17 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 48

ππ S-Wave Amplitude in JPC = 1++ 3π Wave

[arXiv:1509.00992]

Correlation of 3π intensity around 1.4 GeV/c2 with f0(980) f0(980) semicircle in Argand diagram Confirms that f0(980)π signal is not an artifact of isobar parametrization

18 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 49

ππ S-Wave Amplitude in JPC = 1++ 3π Wave

[arXiv:1509.00992]

Correlation of 3π intensity around 1.4 GeV/c2 with f0(980) f0(980) semicircle in Argand diagram Confirms that f0(980)π signal is not an artifact of isobar parametrization

18 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 50

ππ S-Wave Amplitude in JPC = 1++ 3π Wave

[arXiv:1509.00992]

]

1/2

)

)

2

c Events/(GeV/

(

[

) T Re( 200 400 600

]

1/2

)

)

2

c Events/(GeV/

(

[

) T Im( 200 − 200 400

0.299 0.925 0.965 0.995 1.075 1.220

P π

+ +

]

π π

[

+ + +

1

2

) c < 0.326 (GeV/ t' 0.194 <

2

c < 1.42 GeV/

π 3

m 1.38 <

Correlation of 3π intensity around 1.4 GeV/c2 with f0(980) f0(980) semicircle in Argand diagram Confirms that f0(980)π signal is not an artifact of isobar parametrization

18 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 51

ππ S-Wave Amplitude in JPC = 1++ 3π Wave

[arXiv:1509.00992]

]

2

c GeV/

[

π 3

m 0.5 1 1.5 2 2.5 )

2

c Intensity / (40 MeV/ 5 10

3

10 × P π

+ +

]

π π

[

+ + +

1

2

) c < 0.326 (GeV/ t' 0.194 < P π

+ +

]

π π

[

+ + +

1

2

c < 1.00 GeV/

+

π

−

π

m 0.96 <

Correlation of 3π intensity around 1.4 GeV/c2 with f0(980) f0(980) semicircle in Argand diagram Confirms that f0(980)π signal is not an artifact of isobar parametrization

18 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 52

ππ S-Wave Amplitude in JPC = 1++ 3π Wave

[arXiv:1509.00992]

]

2

c GeV/

[

π 3

m 0.5 1 1.5 2 2.5 )

2

c Intensity / (20 MeV/ 5 10 15

3

10 × P π (980) f

+ + +

1

2

) c < 1.000 (GeV/ t' 0.100 < 0.3%

]

2

c GeV/

[

π 3

m 0.5 1 1.5 2 2.5 )

2

c Intensity / (40 MeV/ 5 10

3

10 × P π

+ +

]

π π

[

+ + +

1

2

) c < 0.326 (GeV/ t' 0.194 < P π

+ +

]

π π

[

+ + +

1

2

c < 1.00 GeV/

+

π

−

π

m 0.96 <

Correlation of 3π intensity around 1.4 GeV/c2 with f0(980) f0(980) semicircle in Argand diagram Confirms that f0(980)π signal is not an artifact of isobar parametrization

18 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 53

What is the Nature of the a1(1420)?

[PRL 115 (2015) 082001]

Still unclear JPC = 1++ ground state is a1(1260) Mass: 1230 ± 40 MeV/c2 Width: 250 to 400 MeV/c2 No quark-model states expected at 1.4 GeV/c2 First excited 1++ state expected to be heavier and wider Isospin partner of narrow f1(1420)? a1(1420) has peculiar decay mode Only seen in f0(980)π decay f0(980) has large ss content Some models explain f0(980) as tetra-quark state a1(1420) lies suspiciously close to KK∗ threshold

]

2

c GeV/

[

π 3

m 1 1.2 1.4 1.6 1.8 2 2.2 )

2

c Intensity / (20 MeV/ 5 10 15 20 25

3

10 × P π (980) f

+ + +

1

2

) c < 1.0 (GeV/ t' 0.1 < (1) Model curve (1420) resonance

1

a (2) (3) Non-resonant term (3) (2) (1)

19 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 54

What is the Nature of the a1(1420)?

[PRL 115 (2015) 082001]

Still unclear JPC = 1++ ground state is a1(1260) Mass: 1230 ± 40 MeV/c2 Width: 250 to 400 MeV/c2 No quark-model states expected at 1.4 GeV/c2 First excited 1++ state expected to be heavier and wider Isospin partner of narrow f1(1420)? a1(1420) has peculiar decay mode Only seen in f0(980)π decay f0(980) has large ss content Some models explain f0(980) as tetra-quark state a1(1420) lies suspiciously close to KK∗ threshold

]

2

c GeV/

[

π 3

m 1 1.2 1.4 1.6 1.8 2 2.2 )

2

c Intensity / (20 MeV/ 5 10 15 20 25

3

10 × P π (980) f

+ + +

1

2

) c < 1.0 (GeV/ t' 0.1 < (1) Model curve (1420) resonance

1

a (2) (3) Non-resonant term (3) (2) (1)

19 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 55

What is the Nature of the a1(1420)?

Several proposed explanations

Genuine resonance Two-quark-tetraquark mixed state

[Wang, arXiv:1401.1134]

Tetraquark with mixed flavor symmetry

[Chen et al., PRD 91 (2015) 094022]

Effect in a1(1260) production Two-channel unitarized Deck amplitude + direct a1(1260) production

[Basdevant and Berger, PRL 114 (2015) 192001 and arXiv:1501.04643]

Effect in a1(1260) decay Singularity in triangle diagram

[Mikhasenko et al., PRD 91 (2015) 094015]

Similar diagrams proposed to explain some X, Y, Z states and pentaquark candidate Pc in heavy-meson sector

20 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 56

What is the Nature of the a1(1420)?

Several proposed explanations

Genuine resonance Two-quark-tetraquark mixed state

[Wang, arXiv:1401.1134]

Tetraquark with mixed flavor symmetry

[Chen et al., PRD 91 (2015) 094022]

Effect in a1(1260) production Two-channel unitarized Deck amplitude + direct a1(1260) production

[Basdevant and Berger, PRL 114 (2015) 192001 and arXiv:1501.04643]

Effect in a1(1260) decay Singularity in triangle diagram

[Mikhasenko et al., PRD 91 (2015) 094015]

Similar diagrams proposed to explain some X, Y, Z states and pentaquark candidate Pc in heavy-meson sector

20 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 57

What is the Nature of the a1(1420)?

Several proposed explanations

Genuine resonance Two-quark-tetraquark mixed state

[Wang, arXiv:1401.1134]

Tetraquark with mixed flavor symmetry

[Chen et al., PRD 91 (2015) 094022]

Effect in a1(1260) production Two-channel unitarized Deck amplitude + direct a1(1260) production

[Basdevant and Berger, PRL 114 (2015) 192001 and arXiv:1501.04643]

Effect in a1(1260) decay Singularity in triangle diagram

[Mikhasenko et al., PRD 91 (2015) 094015]

a1(1260) K˚(892) K´ K+ f0(980) π´ π+ π´

Similar diagrams proposed to explain some X, Y, Z states and pentaquark candidate Pc in heavy-meson sector

20 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 58

Spin-Exotic JPC = 1−+ Signal in (3π)− PWA

Broad intensity bump Similar in both 3π channels

21 Boris Grube, TU München Meson Spectroscopy at COMPASS

π−π0π0 π−π+π− scaled

SLIDE 59

Spin-Exotic JPC = 1−+ Signal in π−π+π− PWA

Drastic Change of Mass Spectrum with t′

“Low” t′ ≈ 0.1 (GeV/c)2 “High” t′ ≈ 0.8 (GeV/c)2 Dominant nonresonant contribution

Needs to be better understood in order to extract resonance content

22 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 60

Spin-Exotic JPC = 1−+ Signal in π−π+π− PWA

Model for Nonresonant Component

Deck effect

π´

beam

Isobar π´

beam

π´ P π´

beam

ptarget precoil π´

beam

π´ π+ ptarget precoil π´

MC pseudodata generated according to model of Deck amplitude

based on [ACCMOR, NPB 182 (1981) 269] see D. Ryabchikov’s contribution for further details

Analyzed like real data

23 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 61

Spin-Exotic JPC = 1−+ Signal in π−π+π− PWA

Deck-Model for Nonresonant Component

“Low” t′ ≈ 0.1 (GeV/c)2 “High” t′ ≈ 0.8 (GeV/c)2 Deck MC scaled to t′-summed intensity

Similar mass spectrum at low t′ Different shape at high t′

24 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 62

One Last Thing. . .

Leptoproduction of ψ(2S) and X(3872) at COMPASS Muon beam with 160 to 200 GeV/c on 6LiD and NH3 targets ψ(2S) and X(3872) observed in J/ψπ+π− Production = “reversal” of ψ(2S) and X(3872) decays Possible mechanism Full muon-beam data set (2003 to 2010) 87 exclusive (J/ψπ+π−)π± events

25 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 63

One Last Thing. . .

Leptoproduction of ψ(2S) and X(3872) at COMPASS Muon beam with 160 to 200 GeV/c on 6LiD and NH3 targets ψ(2S) and X(3872) observed in J/ψπ+π− Production = “reversal” of ψ(2S) and X(3872) decays Possible mechanism

γ˚ µ µ1 J/ψ µ µ1 ψ(2S) X(3872) π+˚ µ µ1 p n π+ π+ π´ µ µ1 p n π+ π+ π´ J/ψ µ µ1 p n π+ π+ π´ J/ψ µ+ µ´ µ µ1 p n π+ π+ π´ J/ψ µ+ µ´ µ µ1 p n π+ π+ π´ J/ψ µ+ µ´

Full muon-beam data set (2003 to 2010) 87 exclusive (J/ψπ+π−)π± events

25 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 64

One Last Thing. . .

Leptoproduction of ψ(2S) and X(3872) at COMPASS Muon beam with 160 to 200 GeV/c on 6LiD and NH3 targets ψ(2S) and X(3872) observed in J/ψπ+π− Production = “reversal” of ψ(2S) and X(3872) decays Possible mechanism

γ˚ µ µ1 J/ψ µ µ1 ψ(2S) X(3872) π+˚ µ µ1 p n π+ π+ π´ µ µ1 p n π+ π+ π´ J/ψ µ µ1 p n π+ π+ π´ J/ψ µ+ µ´ µ µ1 p n π+ π+ π´ J/ψ µ+ µ´ µ µ1 p n π+ π+ π´ J/ψ µ+ µ´

Full muon-beam data set (2003 to 2010) 87 exclusive (J/ψπ+π−)π± events

25 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 65

Leptoproduction of ψ(2S) and X(3872) at COMPASS

J/ψπ+π− invariant mass spectrum Mψ(2S) = 3680 ± 8 MeV/c2 MX(3872) = 3860 ± 8 MeV/c2

26 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 66

Conclusions

World’s largest π−π+π− data set PWA reliably extracts even very small signals Novel analysis techniques PWA in bins of t′ Better separation of resonant and nonresonant contribution Extraction of ππ S-wave amplitude from π−π+π− system Study dependence on 3π source Study rescattering effects Unexpected new axial-vector signal a1(1420) Independently confirmed in π−π0π0 Nature still unclear; several possible explanations COMPASS data will put models to the test Nonresonant contributions play important role First studies using Deck models Improved models needed =

⇒ collaboration with JPAC

see contributions by A. Szczepaniak, A. Jackura, V. Pauk, and V. Mathieu

27 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 67

Conclusions

World’s largest π−π+π− data set PWA reliably extracts even very small signals Novel analysis techniques PWA in bins of t′ Better separation of resonant and nonresonant contribution Extraction of ππ S-wave amplitude from π−π+π− system Study dependence on 3π source Study rescattering effects Unexpected new axial-vector signal a1(1420) Independently confirmed in π−π0π0 Nature still unclear; several possible explanations COMPASS data will put models to the test Nonresonant contributions play important role First studies using Deck models Improved models needed =

⇒ collaboration with JPAC

see contributions by A. Szczepaniak, A. Jackura, V. Pauk, and V. Mathieu

27 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 68

Conclusions

World’s largest π−π+π− data set PWA reliably extracts even very small signals Novel analysis techniques PWA in bins of t′ Better separation of resonant and nonresonant contribution Extraction of ππ S-wave amplitude from π−π+π− system Study dependence on 3π source Study rescattering effects Unexpected new axial-vector signal a1(1420) Independently confirmed in π−π0π0 Nature still unclear; several possible explanations COMPASS data will put models to the test Nonresonant contributions play important role First studies using Deck models Improved models needed =

⇒ collaboration with JPAC

see contributions by A. Szczepaniak, A. Jackura, V. Pauk, and V. Mathieu

27 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 69

Conclusions

World’s largest π−π+π− data set PWA reliably extracts even very small signals Novel analysis techniques PWA in bins of t′ Better separation of resonant and nonresonant contribution Extraction of ππ S-wave amplitude from π−π+π− system Study dependence on 3π source Study rescattering effects Unexpected new axial-vector signal a1(1420) Independently confirmed in π−π0π0 Nature still unclear; several possible explanations COMPASS data will put models to the test Nonresonant contributions play important role First studies using Deck models Improved models needed =

⇒ collaboration with JPAC

see contributions by A. Szczepaniak, A. Jackura, V. Pauk, and V. Mathieu

27 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 70

Outlook

Other ongoing analyses Pion diffraction into π−η(′), π−ηη, π−π0ω, KKπ, KKππ, . . . Kaon diffraction into K−π+π− Central-production reactions πγ scattering using Primakoff reactions on heavy targets Leptoproduction of X(3872)

28 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 71

Outline

4

Backup slides PWA of diffractively produced 3π final states PWA of diffractively produced π−η and π−η′ final states

29 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 72

PWA of π− p → (3π)− precoil: Low t′ vs. High t′

2++ 1+ ρπ D Peak does not change with t′ 1++ 0+ ρπ S Peak moves with t′ Strong nonresonant contribution

)

2

(GeV/c

−

) π (3

m 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 )

2

intensity (per 40 MeV/c 0.02 0.04 0.06 0.08 0.1 0.12

6

10 × p)

−

) π (3 → p

−

π COMPASS 2008 ( D π (770) ρ

+

1

+ +

2 (scaled)

+

π

−

π

−

π , π π

−

π

2

/c

2

0.100 < t' < 0.116 GeV

2

/c

2

0.100 < t' < 0.113 GeV

Preliminary

)

2

(GeV/c

−

) π (3

m 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 )

2

intensity (per 40 MeV/c 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

6

10 × p)

−

) π (3 → p

−

π COMPASS 2008 ( D π (770) ρ

+

1

+ +

2 (scaled)

+

π

−

π

−

π , π π

−

π

2

/c

2

0.285 < t' < 0.395 GeV

2

/c

2

0.262 < t' < 0.326 GeV

Preliminary

)

2

(GeV/c

) (3

m 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 )

2

intensity (per 40 MeV/c 0.1 0.2 0.3 0.4 0.5

6

10 p) ) (3 p COMPASS 2008 ( S (770) 1 (scaled) ,

2

/c

2

0.100 < t' < 0.116 GeV

2

/c

2

0.100 < t' < 0.113 GeV

Preliminary

)

2

(GeV/c

) (3

m 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 )

2

intensity (per 40 MeV/c 0.05 0.1 0.15 0.2 0.25 0.3

6

10 p) ) (3 p COMPASS 2008 ( S (770) 1 (scaled) ,

2

/c

2

0.285 < t' < 0.395 GeV

2

/c

2

0.262 < t' < 0.326 GeV

Preliminary

30 Boris Grube, TU München Meson Spectroscopy at COMPASS

π−π0π0 π−π+π− scaled for each plot

SLIDE 73

PWA of π− p → (3π)− precoil: Low t′ vs. High t′

2++ 1+ ρπ D Peak does not change with t′ 1++ 0+ ρπ S Peak moves with t′ Strong nonresonant contribution

)

2

(GeV/c

−

) π (3

m 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 )

2

intensity (per 40 MeV/c 0.02 0.04 0.06 0.08 0.1 0.12

6

10 × p)

−

) π (3 → p

−

π COMPASS 2008 ( D π (770) ρ

+

1

+ +

2 (scaled)

+

π

−

π

−

π , π π

−

π

2

/c

2

0.100 < t' < 0.116 GeV

2

/c

2

0.100 < t' < 0.113 GeV

Preliminary

)

2

(GeV/c

−

) π (3

m 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 )

2

intensity (per 40 MeV/c 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

6

10 × p)

−

) π (3 → p

−

π COMPASS 2008 ( D π (770) ρ

+

1

+ +

2 (scaled)

+

π

−

π

−

π , π π

−

π

2

/c

2

0.285 < t' < 0.395 GeV

2

/c

2

0.262 < t' < 0.326 GeV

Preliminary

)

2

(GeV/c

−

) π (3

m 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 )

2

intensity (per 40 MeV/c 0.1 0.2 0.3 0.4 0.5

6

10 × p)

−

) π (3 → p

−

π COMPASS 2008 ( S π (770) ρ

+ + +

1 (scaled)

+

π

−

π

−

π , π π

−

π

2

/c

2

0.100 < t' < 0.116 GeV

2

/c

2

0.100 < t' < 0.113 GeV

Preliminary

)

2

(GeV/c

−

) π (3

m 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 )

2

intensity (per 40 MeV/c 0.05 0.1 0.15 0.2 0.25 0.3

6

10 × p)

−

) π (3 → p

−

π COMPASS 2008 ( S π (770) ρ

+ + +

1 (scaled)

+

π

−

π

−

π , π π

−

π

2

/c

2

0.285 < t' < 0.395 GeV

2

/c

2

0.262 < t' < 0.326 GeV

Preliminary

30 Boris Grube, TU München Meson Spectroscopy at COMPASS

π−π0π0 π−π+π− scaled for each plot

SLIDE 74

ππ S-Wave Amplitude in JPC = 0−+ 3π Wave

[arXiv:1509.00992]

]

1/2

)

)

2

c Events/(GeV/

(

[

) T Re( 600 − 400 − 200 − 200

]

1/2

)

)

2

c Events/(GeV/

(

[

) T Im( 200 − 200 400 600

0.925 0.965 0.995 1.075 1.420 1.540 1.620

S π

+ +

]

π π

[

+ + − 2

) c < 0.326 (GeV/ t' 0.194 <

2

c < 1.82 GeV/

π 3

m 1.78 <

Coupling of π(1800) to f0(980)π and f0(1500)π decay modes

31 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 75

ππ S-Wave Amplitude in JPC = 2−+ 3π Wave

[arXiv:1509.00992]

]

2

c GeV/

[

π 3

m 0.5 1 1.5 2 2.5

]

2

c GeV/

[

+

π

−

π

m 0.5 1 1.5 2 10 20 30 40 50 60 70

3

10 × D π

+ +

]

π π

[

+ + −

2

2

) c < 0.326 (GeV/ t' 0.194 <

]

1/2

)

)

2

c Events/(GeV/

(

[

) T Re( 300 − 200 − 100 − 100

]

1/2

)

)

2

c Events/(GeV/

(

[

) T Im( 200 − 100 − 100 200

0.299 0.925 0.965 0.995 1.075 1.420 1.740

D π

+ +

]

π π

[

+ + −

2

2

) c < 0.326 (GeV/ t' 0.194 <

2

c < 1.94 GeV/

π 3

m 1.90 <

Correlation of intensity around m3π = 1.9 GeV/c2 with f0(980) f0(980) semicircle in Argand diagram Coupling of π2(1880) to f0(980)π decay mode

32 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 76

ππ S-Wave Amplitude in JPC = 2−+ 3π Wave

[arXiv:1509.00992]

]

2

c GeV/

[

π 3

m 0.5 1 1.5 2 2.5

]

2

c GeV/

[

+

π

−

π

m 0.5 1 1.5 2 10 20 30 40 50 60 70

3

10 × D π

+ +

]

π π

[

+ + −

2

2

) c < 0.326 (GeV/ t' 0.194 <

]

2

c GeV/

[

π 3

m 0.5 1 1.5 2 2.5 )

2

c Intensity / (40 MeV/ 1 2

3

10 × D π

+ +

]

π π

[

+ + −

2

2

) c < 0.326 (GeV/ t' 0.194 < D π

+ +

]

π π

[

+ + −

2

2

c < 1.00 GeV/

+

π

−

π

m 0.96 <

Correlation of intensity around m3π = 1.9 GeV/c2 with f0(980) f0(980) semicircle in Argand diagram Coupling of π2(1880) to f0(980)π decay mode

32 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 77

Spin-Exotic JPC = 1−+ Signal in π−π+π− PWA

Relative Phase w.r.t. 1++ 0+ ρ(770)π S Wave

Slow phase 60° motion in 1.6 GeV/c2 region independent of t′

33 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 78

PWA of π− p → π− η(′) precoil

[PLB 740 (2015) 303]

Odd-spin waves: spin-exotic quantum numbers

Disputed JPC = 1−+ resonance signals

π1(1400) in πη and π1(1600) in πη′

Comparison of πη and πη′: information about flavor structure Reconstruction from exclusive π−π+π−γγ final state η → π+π−π0 with π0 → γγ η′ → π+π−η with η → γγ

34 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 79

PWA of π− p → π− η(′) precoil

[PLB 740 (2015) 303]

Odd-spin waves: spin-exotic quantum numbers

Disputed JPC = 1−+ resonance signals

π1(1400) in πη and π1(1600) in πη′

Comparison of πη and πη′: information about flavor structure Reconstruction from exclusive π−π+π−γγ final state η → π+π−π0 with π0 → γγ η′ → π+π−η with η → γγ

π−η invariant mass

34 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 80

PWA of π− p → π− η(′) precoil

[PLB 740 (2015) 303]

Odd-spin waves: spin-exotic quantum numbers

Disputed JPC = 1−+ resonance signals

π1(1400) in πη and π1(1600) in πη′

Comparison of πη and πη′: information about flavor structure Reconstruction from exclusive π−π+π−γγ final state η → π+π−π0 with π0 → γγ η′ → π+π−η with η → γγ

π−η invariant mass π−η′ invariant mass

34 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 81

Comparison of JPC = 2++ Partial Waves

[PLB 740 (2015) 303]

Quark-line picture for n = (u, d) and pointlike resonances π−η and π−η′ partial-wave intensities for spin J related by Different phase space and barrier factors Branching fraction ratio b of η and η′ into π−π+γγ Nπη′

J

(m) ∝ b

• qπη′(m)

qπη(m) 2J+1 Nπη

J (m)

q = breakup momentum

35 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 82

Comparison of JPC = 2++ Partial Waves

[PLB 740 (2015) 303]

Quark-line picture for n = (u, d) and pointlike resonances π−η and π−η′ partial-wave intensities for spin J related by Different phase space and barrier factors Branching fraction ratio b of η and η′ into π−π+γγ Nπη′

J

(m) ∝ b

• qπη′(m)

qπη(m) 2J+1 Nπη

J (m)

q = breakup momentum

π−η final state π−η′ final state

35 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 83

Comparison of JPC = 2++ Partial Waves

[PLB 740 (2015) 303]

Quark-line picture for n = (u, d) and pointlike resonances π−η and π−η′ partial-wave intensities for spin J related by Different phase space and barrier factors Branching fraction ratio b of η and η′ into π−π+γγ Nπη′

J

(m) ∝ b

• qπη′(m)

qπη(m) 2J+1 Nπη

J (m)

q = breakup momentum

π−η final state π−η′ final state; π−η scaled

35 Boris Grube, TU München Meson Spectroscopy at COMPASS

SLIDE 84

Even-Spin Waves

[PLB 740 (2015) 303]

JPC = 4++ 2++ Phase: 4++ − 2++ Similar even-spin waves Intermediate states couple to same final-state flavour content Similar physical content also in nonresonant high-mass region

36 Boris Grube, TU München Meson Spectroscopy at COMPASS

π−η′ final state; π−η scaled

SLIDE 85

Even-Spin Waves

[PLB 740 (2015) 303]

JPC = 4++ 2++ Phase: 4++ − 2++ Resonance-model fit (Breit-Wigner) N(a2 → πη′) N(a2 → πη) = (5 ± 2) % First-time measurement of N(a4 → πη′) N(a4 → πη) = (23 ± 7) %

36 Boris Grube, TU München Meson Spectroscopy at COMPASS

π−η′ final state; π−η scaled

SLIDE 86

JPC = 1−+ Spin-Exotic Wave

[PLB 740 (2015) 303]

Spin-exotic JPC = 1−+ 2++ Phase: 1−+ − 2++ 1−+ intensities very different Suppression in πη channel predicted for intermediate |qqg state Different phase motion in 1.6 GeV/c2 region

37 Boris Grube, TU München Meson Spectroscopy at COMPASS

π−η′ final state; π−η scaled

SLIDE 87

JPC = 1−+ Spin-Exotic Wave

[PLB 740 (2015) 303]

Spin-exotic JPC = 1−+ 2++ Phase: 1−+ − 2++ 1−+ resonance interpretation requires better understanding

• f

2++ wave Nonresonant contributions

37 Boris Grube, TU München Meson Spectroscopy at COMPASS

π−η′ final state; π−η scaled

SLIDE 88

JPC = 1−+ Spin-Exotic Wave

[PLB 740 (2015) 303]

Spin-exotic JPC = 1−+ 2++ Phase: 1−+ − 2++ 1−+ resonance interpretation requires better understanding

• f

2++ wave Nonresonant contributions

37 Boris Grube, TU München Meson Spectroscopy at COMPASS

π−η′ final state; π−η scaled

Multi-Regge exchange, e.g.

a2 P π´

beam

ptarget precoil π´

beam

η ptarget precoil π´