[PPT] - Exotic meson spectroscopy at LHCb M. Kreps Physics Department PowerPoint Presentation

SLIDE 1

Physics Department

www2.warwick.ac.uk

Exotic meson spectroscopy at LHCb

M. Kreps

SLIDE 2

Introduction

2 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

In the quark model we think of hadrons as qq or qqq
But there is nothing preventing other combinations

→ Where are all those combinations with more than 3 quarks or anti-quarks?

SLIDE 3

Introduction - molecules

3 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

There are lot of objects composed of baryons

SLIDE 4

Introduction - molecules

3 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

There are lot of objects composed of baryons
Where are similar objects from mesons?

SLIDE 5

Scalar mesons

4 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

NOTE ON SCALAR MESONS BELOW 2 GEV Revised September 2013 by C. Amsler (Univ of Bern), S. Ei- delman (Budker Institute of Nuclear Physics, Novosibirsk), T. Gutsche (University of T¨ ubingen), C. Hanhart (Forschungszen- trum J¨ ulich), S. Spanier (University of Tennessee), and N.A. T¨

rnqvist (University of Helsinki).
V. Interpretation of the scalars below 1 GeV: In the

literature, many suggestions are discussed, such as conventional q¯ q mesons, q¯ qq¯ q or meson-meson bound states. In addition one expects a scalar glueball in this mass range. In reality, there can be superpositions of these components, and one often depends

n models to determine the dominant one. Although we have

seen progress in recent years, this question remains open. Here, we mention some of the present conclusions. The f0(980) and a0(980) are often interpreted as multiquark states [140–144] or K ¯ K bound states [145]. The insight into

From RPP by PDG

Candidates beyond qq mesons exist, but real trouble is how to

decide whether they are qq or something else

SLIDE 6

Charmonium

5 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

Back in 2003, many expected

states still missing

Belle started to search for them

and quickly found one

Did not fit into expected spectra
Mass close to m(D0) + m(D∗0)

arXiv:1403.1254

0.40 0.80 1.20 M(π+π-l+l-) - M(l+l-) (GeV) 100 200 300 Events/0.010 GeV

PRL 91, 262001

SLIDE 7

X(3872) properties

6 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

]

2

) [ GeV/c

π

+

π ψ m(J/

3.65 3.7 3.75 3.8 3.85 3.9 3.95 4

2

entries / 2.5 MeV/c

1000 2000 3000 4000 5000 6000 (2S) ψ 228 ± 20285 113 X(3872) ± 2292

CDF Run II

1

780pb ≈ L

) [MeV] ψ ) - M(J/ ψ J/

π

+

π M( 600 800 1000 1200 1400 Number of candidates / (2.5 MeV) 200 400 600 800 1000 1200

LHCb

550 600 200 400 600 800 1000 1200

(2S) ψ

750 800 10 20 30 40 50 60 70

X(3872) /2| π | - π

Φ

∆ || X(3872) yield / unit volume 100 200 300 400 500

0.63 1.15 /2 π 0.63 1.15 /2 π 0.63 1.15 /2 π 0.63 1.15 /2 π

)| < 0.6

ψ J/

θ |cos( )| > 0.6

ψ J/

θ |cos(

)| < 0.5

π π

θ |cos( )| > 0.5

π π

θ |cos( )| < 0.5

π π

θ |cos( )| > 0.5

π π

θ |cos(

CDF Run II Preliminary

1

780pb ≈ L

X(3872) data points

acc. corrected

prediction for ++ p

s

1

++ p

1

+

p

2

) ]

++

(1 L )/

+

(2 L = -2 ln[ t

200
100

100 200 Number of experiments / bin

2

10

3

10

4

10

5

10

6

10

7

10

data

t

+

=2

PC

Simulated J

++

=1

PC

Simulated J

LHCb

PRL 98, 132002 PRL 110, 222001

Quantum numbers JPC = 1++

SLIDE 8

What is X(3872)?

7 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

Lot has been done for X(3872)
Despite all effort during 10 years, our understanding of what

X(3872) is still about same

To find convincing case of non-conventional meson is hard

SLIDE 9

Z(4430)+ history

8 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

3.8 4.05 4.3 4.55 4.8 M(π+ψι) (GeV) 10 20 30 Events/0.01 GeV

200 400

K

θ Flat cos K moments

π

(2S) ψ K moments

π

ψ J/

(b)

)

2

(GeV/c

π

(2S) ψ

m

3.8 4 4.2 4.4 4.6 4.8

200

200

0,+

K

π

(2S) ψ →

,0

B (d)

Candidates Residuals Belle PRL 100, 142001 PRD 79, 112001

Seen by Belle, but not

Babar

Data consistent
Charged state

→ Cannot be cc

Latest Belle result uses 4D

analysis

Is it real and if yes, is it resonance?

SLIDE 10

Z(4430)+ history

8 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

3.8 4.05 4.3 4.55 4.8 M(π+ψι) (GeV) 10 20 30 Events/0.01 GeV

10 20 30

(a) Belle

10 20 30

(b) BABAR (*1.18) )

2

(GeV/c

π

(2S) ψ

m

3.8 4 4.2 4.4 4.6 4.8

2

Diff./10 MeV/c

20
10

10 (c) /NDF = 54.7/58

2

χ

2

Events/10 MeV/c

Belle PRL 100, 142001 PRD 79, 112001

Seen by Belle, but not

Babar

Data consistent
Charged state

→ Cannot be cc

Latest Belle result uses 4D

analysis

Is it real and if yes, is it resonance?

SLIDE 11

Issue of reflections

9 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

]

4

/c

2

[GeV

2

π

+

π

M 0.5 1 1.5 2 2.5 3

4

/c

2

Candidates per 0.01 GeV 1000 2000 3000 4000 5000 6000 7000

Data Fit Function Background

1

CDF Run II preliminary, L = 6.0 fb

PRD 86, 032007 (2012)

Look to bit simpler system of D0 → KSπ+π− (only 2D rather

than 4D system)

Inspecting π+π− invariant mass, is there state around 1.8 GeV?

SLIDE 12

Issue of reflections

10 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

]

4

/c

2

[GeV

2 (RS)

±

π

s

K

M 0.5 1 1.5 2 2.5 3 ]

4

/c

2

[GeV

2

π

+

π

M 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

1

CDF Run II preliminary, L = 6.0 fb

]

4

/c

2

[GeV

2

π

+

π

M 0.5 1 1.5 2 2.5 3

4

/c

2

Candidates per 0.01 GeV 1000 2000 3000 4000 5000 6000 7000

Data Fit Function Background

1

CDF Run II preliminary, L = 6.0 fb

]

4

/c

2

[GeV

2 (RS)

±

π

s

K

M 0.5 1 1.5 2 2.5 3

4

/c

2

Candidates per 0.01 GeV 2000 4000 6000 8000 10000 12000 14000 16000 18000

1

CDF Run II preliminary, L = 6.0 fb Data Fit Function Background

PRD 86, 032007 (2012)

No new π+π− resonance
What is seen in π+π− is result
f reflection from KSπ and its

angular structure

Need

to be careful when making claims in this type of systems

SLIDE 13

LHCb detector

11 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

Good mass resolution
Good time resolution
High trigger rate on c

and b

Uniform running

conditions

SLIDE 14

LHCb detector

11 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

Good mass resolution
Good time resolution
High trigger rate on c

and b

Uniform running

conditions

SLIDE 15

Data sample

12 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

[MeV]

π

+

'K ψ

m 5250 5300 Candidates / 1 MeV 200 400 600 800 1000 1200 1400 1600 1800

LHCb

sideband sideband signal range

]

2

[GeV

2

π

+

K

m

0.5 1 1.5 2 2.5

]

2

[GeV

2

π

' ψ

m

15 16 17 18 19 20 21 22 1 10

2

10

LHCb

Use B0 → ψ(2S)Kπ decays
Large statistics (> 25k), about 10 times what B-factories had
Very clean signal, background 4 % of events (about 8% at

B-factories)

Perform both model-independent analysis (BABAR) and amplitude

fit (Belle)

K∗(892) K∗

J(1430)

Only 2 out of 4 dimensions PRL 112 (2014) 222002

SLIDE 16

Amplitude analysis

13 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

Full 4D amplitude analysis
Amplitude

|M|2 =

∆λµ
λψ
k

Ak,λψ(Ω|m0k, Γ0k) +

λZ

ψ

AZ,λZ

ψ(ΩZ|m0Z, Γ0Z)ei∆µα

2
Mass described by relativistic Breit-Wigner
Angular part using helicity formalism
Imposes model how invariant mass distribution should look like

Rotation between helicity frames

SLIDE 17

Amplitude analysis

14 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

|M|2 =

∆λµ
λψ
k

Ak,λψ(Ω|m0k, Γ0k) +

λZ

ψ

AZ,λZ

ψ(ΩZ|m0Z, Γ0Z)ei∆µα

2

Ak,λψ(Ω|mR, ΓR) = F LB

B

pB mB LB R(m|mR, ΓR)F LR

R

pR mR LR Z(Ω) Blatt-Weisskopf form factor Orbital momentum part Angular distribution (Helicity) R(m|mR, ΓR) = 1 m2

R − m2 − imRΓ(m, ΓR)

Γ(m, ΓR) =ΓR pR pR0 2LR+1 mR m F 2

R

SLIDE 18

Model independent method

15 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

]

2

[GeV

2

π

+

K

m

0.5 1 1.5 2 2.5

]

2

[GeV

2

π

' ψ

m

15 16 17 18 19 20 21 22 1 10

2

10

LHCb

PRL 112 (2014) 222002

Try to build up model

which has proper behaviour for Kπ resonances

But

avoid imposing assumptions

n

the shape

f

m(Kπ) for resonances

Construct Dalitz plot for

pure Kπ activity and project on ψ(2S)π axis

See whether model and

data agree

Test whether contributions in Kπ

system can describe data

Do not impose specific model for

resonances → Model independent test

SLIDE 19

Model independent method

16 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

Look to cos(θK) in bins
f Kπ mass
Allows to find out which

spins contribute

i

1 ǫi Pl(cos θKi)

Take
nly

moments corresponding to J ≤ 2

Construct

Dalitz plot and project on ψ(2S)π axis

2

>/10 MeV/c

U 1

<P

1000
500

500

0,+

K

π

ψ J/ →

,0

B >

U 1

(a) <P

400
200

200

0,+

K

π

(2S) ψ →

,0

B >

U 1

(c) <P )

2

(GeV/c

π

K

m

1 1.5 2

2

>/10 MeV/c

U 2

<P

1000 2000

>

U 2

(b) <P )

2

(GeV/c

π

K

m

0.8 1 1.2 1.4 1.6 500

>

U 2

(d) <P

PRD 79, 112001

SLIDE 20

Why Legendre moments?

17 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

P U

1

= S0P0 cos(δS0 − δP0) + 2

2

5P0D0 cos(δP0 − δD0) +

6

5[P+1D+1 cos(δP+1 − δD+1) + P−1D−1 cos(δP−1 − δD−1)] P U

2

=

2

5P 2

0 +

√ 10 7 D2

0 +

√ 2S0D0 cos(δS0 − δD0) −

1

√ 10

P 2

+1 + P 2 −1

+ 5

√ 10 28

D2

+1 + D2 −1

P U

3

= 3

6

35P0D0 cos(δP0 − δD0) − 3

2

35(P+1D+1 cos(δP+1 − δD+1) + P−1D−1 cos(δP−1 − δD−1))

SLIDE 21

Why Legendre moments?

17 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

P U

1

= S0P0 cos(δS0 − δP0) + 2

2

5P0D0 cos(δP0 − δD0) +

6

5[P+1D+1 cos(δP+1 − δD+1) + P−1D−1 cos(δP−1 − δD−1)] P U

2

=

2

5P 2

0 +

√ 10 7 D2

0 +

√ 2S0D0 cos(δS0 − δD0) −

1

√ 10

P 2

+1 + P 2 −1

+ 5

√ 10 28

D2

+1 + D2 −1

Allows to cut expansion in physically meaningful way
If we cut expansion, we select maximal spin which can contribute
You might wonder why this is important

SLIDE 22

ψ′π reflection

18 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

) [GeV] π ψ M(J/

4 4.5

Events

10 20 30 40 50 60

) [GeV] π M(K

1 1.5

Events

2 4 6 8 10 12 14 16 18 20 22 24

)

K

θ cos(

1
0.5

0.5 1

Events

5 10 15 20 25 30

Example of B0 → Z+(→ ψ′π+)K−
Such contribution reflect to whole

Kπ mass range

Helicity angle distribution peaking

→ Moments will receive contributions from reflection

SLIDE 23

ψπ reflection

19 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

) [GeV] π M(K

1 1.5

>

1

<P

10
8
6
4
2

2 4 6 8 10

) [GeV] π M(K

1 1.5

>

2

<P

10
8
6
4
2

2 4 6 8 10

) [GeV] π M(K

1 1.5

>

3

<P

10
8
6
4
2

2 4 6 8 10

) [GeV] π M(K

1 1.5

>

8

<P

10
8
6
4
2

2 4 6 8 10

Reflections make model independent method hard for measurement

SLIDE 24

Model independent result

20 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

[GeV]

−

π ’ ψ

m 3.8 4 4.2 4.4 4.6 4.8 Efficiency corrected yield / ( 25 MeV ) 0.01 0.02 0.03 0.04

LHCb

PRL 112 (2014) 222002

Clearly, pure kaon resonances cannot explain M(ψ(2S)π) spectrum
Understanding details difficult
Resonances in ψ(2S)π will contribute to Kπ and its moments
Any fit to ψ(2S)π on top of reflections neglects interference

between two axes

SLIDE 25

Only K∗ resonances

21 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

]

2

[GeV

2

−

π ' ψ

m 16 18 20 22 )

2

Candidates / ( 0.2 GeV 500 1000

LHCb

]

2

[GeV

2

−

π ' ψ

m 16 18 20 22 )

2

Candidates / ( 0.2 GeV 100 200

LHCb

2

< 1.8 GeV

2

−

π

+

K

1.0 < m

PRL 112 (2014) 222002

SLIDE 26

Only K∗ resonances

21 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

]

2

[GeV

2

−

π ' ψ

m 16 18 20 22 )

2

Candidates / ( 0.2 GeV 500 1000

LHCb

]

2

[GeV

2

−

π ' ψ

m 16 18 20 22 )

2

Candidates / ( 0.2 GeV 100 200

LHCb

2

< 1.8 GeV

2

−

π

+

K

1.0 < m

PRL 112 (2014) 222002

D a t a c a n n

t

b e d e s c r i b e d b y K

∗

n

l y

SLIDE 27

Adding Z+

22 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

]

2

[GeV

2

−

π ’ ψ

m 16 18 20 22 )

2

Candidates / ( 0.2 GeV 500 1000

LHCb

]

2

[GeV

2

−

π

+

K

m 0.5 1 1.5 2 2.5 )

2

Candidates / ( 0.02 GeV 1 10

2

10

3

10

LHCb

data total fit excluded

Z(4430)

(892)

*

K S-wave

*

K

(1430)

2 *

K

Z(4430)

background (1680)

*

K (1410)

*

K

total fit with no Z(4430)

’ ψ

θ cos

1
0.5

0.5 1 Candidates / 0.05 200 400 600

LHCb

[degrees] φ

100

100

Candidates / 20

500 1000

LHCb

PRL 112 (2014) 222002

SLIDE 28

Dalitz plot slices

23 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

]

2

[GeV

2

π

+

K

m

0.5 1 1.5 2 2.5

]

2

[GeV

2

π

' ψ

m

15 16 17 18 19 20 21 22 1 10

2

10

LHCb

]

2

[GeV

2

−

π ' ψ

m 16 18 20 22 )

2

Candidates / ( 0.2 GeV 20 40 60 80

LHCb

2

< 0.7 GeV

2

−

π

+

K

m

data total fit excluded

Z(4430)

(892)

*

K S-wave

*

K

Z(4430)

background (1410)

*

K (1680)

*

K (1430)

2 *

K

]

2

[GeV

2

−

π ' ψ

m 16 18 20 22 )

2

Candidates / ( 0.2 GeV 200 400

LHCb

2

< 1.0 GeV

2

−

π

+

K

0.7 < m

]

2

[GeV

2

−

π ' ψ

m 16 18 20 22 )

2

Candidates / ( 0.2 GeV 100 200

LHCb

2

< 1.8 GeV

2

−

π

+

K

1.0 < m

]

2

[GeV

2

−

π ' ψ

m 16 18 20 22 )

2

Candidates / ( 0.2 GeV 50 100 150 200

LHCb

2

> 1.8 GeV

2

−

π

+

K

m

PRL 112 (2014) 222002

SLIDE 29

Results

24 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

]

2

[GeV

2

−

π ’ ψ

m 16 18 20 22 )

2

Candidates / ( 0.2 GeV 500 1000

LHCb

PRL 112 (2014) 222002

M(Z) 4475 ± 7+15

−25 MeV

Γ(Z) 172 ± 13+37

−34 MeV

fZ 5.9 ± 0.9+1.5

−3.3 %

f I

Z

16.7 ± 1.6+2.6

−5.2 %

Significance > 13.9σ

Data are described well with 1+ Z(4430)+ contribution

(χ2 p-value 12%)

Parameters extracted consistent with Belle
Large interference effects seen
Adding additional K∗ resonances to model does not alter

conclusion

fZ =

AZ(Ω)dΩ
A(Ω)dΩ

f I

Z = 1 −

AnoZ(Ω)dΩ
A(Ω)dΩ

SLIDE 30

Z(4430)+ spin

25 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

) L ln 2 (- ∆

200

200 400 Pseudo-experiments / 10.0 50 100 150 200 250 300

Data

Simulated experiments

−

= 0

Z P

J Simulated experiments

+

= 1

Z P

J

LHCb

PRL 112 (2014) 222002

As we use full kinematic information, we have sensitivity to quantum

numbers

Test spins 0,1 and 2 with both parities
Based on likelihood ratio
Quote exclusion based on asymptotic formula (lower bound)
Verified by simulation
All rejections relative to 1+
Z(4430)+ is 1+ state without any doubts

Hypothesis Rejection 0− 9.7 σ 1− 15.8 σ 2+ 16.1 σ 2− 14.6 σ

SLIDE 31

Is Z(4430)+ resonance?

26 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

1 m2

R − m2 − imRΓ(m, ΓR)

Data are consistent with BW for

Z(4430)+

But will they follow if BW is not

imposed?

Change

BW in Z(4430)+ amplitude to 6 complex numbers in 6 M(ψ(2S)π) bins

Plot

resulting amplitude

n

Argand plot

SLIDE 32

Is Z(4430)+ resonance?

26 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

1 m2

R − m2 − imRΓ(m, ΓR)

Data are consistent with BW for

Z(4430)+

But will they follow if BW is not

imposed?

Change

BW in Z(4430)+ amplitude to 6 complex numbers in 6 M(ψ(2S)π) bins

Plot

resulting amplitude

n

Argand plot ⇒ It shows resonance behaviour without imposing it

−

Z

Re A

0.6
0.4
0.2

0.2

−

Z

Im A

0.6
0.4
0.2

0.2

LHCb PRL 112 (2014) 222002

SLIDE 33

Second Z+ state

27 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

]

2

[GeV

2

−

π ' ψ

m 16 18 20 22 )

2

Candidates / ( 0.2 GeV 100 200

LHCb

2

< 1.8 GeV

2

−

π

+

K

1.0 < m

PRL 112 (2014) 222002

M(Z0) 4239 ± 18+45

−10 MeV

Γ(Z0) 220 ± 47+108

−74 MeV

fZ0 1.6 ± 0.5+1.9

−0.4 %

f I

Z0

2.4 ± 1.1+1.7

−0.2 %

Significance 6σ

Data can be described even better by adding second ψ(2S)π state
On its own, it is significant
Preferred 0− (but 660 ± 150 MeV wide 1+ option cannot be ruled out)
Argand diagram is inconclusive
No evidence in model-independent approach
Will need more data to clarify situation

SLIDE 34

Second Z+ state

27 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

]

2

[GeV

2

−

π ’ ψ

m 16 18 20 22 )

2

Candidates / ( 0.2 GeV 100 200

LHCb

2

< 1.8 GeV

2

−

π

+

K

1.0 < m

PRL 112 (2014) 222002

M(Z0) 4239 ± 18+45

−10 MeV

Γ(Z0) 220 ± 47+108

−74 MeV

fZ0 1.6 ± 0.5+1.9

−0.4 %

f I

Z0

2.4 ± 1.1+1.7

−0.2 %

Significance 6σ

Data can be described even better by adding second ψ(2S)π state
On its own, it is significant
Preferred 0− (but 660 ± 150 MeV wide 1+ option cannot be ruled out)
Argand diagram is inconclusive
No evidence in model-independent approach
Will need more data to clarify situation

SLIDE 35

Excitement?

28 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

Z(4430) is the first confirmed unambiguous four-quark candidate

SLIDE 36

Interpretation

29 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

What Z(4430)+ really is?
Large decay width ⇒ strong decay
cc state in final state ⇒ cc has to be also in initial state
Charged, so cannot be conventional charmonia with cc only
From Argand plot it behaves as resonance
Often there are threshold effects (cusps) when new channels opens
In case of Z(4430)+ we are close to D

∗–D1 threshold

Cusp would be S-wave effect, so would have JP = 0−, 1− or 2−
We find JP = 1+ thus excluding threshold effect
From all this all conventional explanations fail
We have something “exotic” like tetraquark, molecule, ...
If there is one “exotic” state, then there should be whole spectrum of

them, so lot of work ahead of us

First natural choice to look for is neutral partner of Z(4430)+

SLIDE 37

Conclusions

30 28 October 2014 Michal Kreps – Exotic meson spectroscopy at LHCb

At LHCb we collected large samples of B decays
Started to check various claims for new states
Often those analyses are difficult as we want to do careful job
We confirmed existence of Z(4430)+
Belle and Babar had different conclusion due to lower statistics and

lower sensitivity of method at Babar

We improved measurement of Z(4430)+ properties
Our date show proper resonance behaviour of Z(4430)+
We exclude non-exotic interpretation of Z(4430)+
Exotic spectroscopy is now fully open for new states