Now Pentaquarks, What Next?? Ken Hicks (Ohio U./NSF) Reimei - - PowerPoint PPT Presentation

Now Pentaquarks, What Next??

Ken Hicks (Ohio U./NSF) Reimei Workshop

• Jan. 19, 2016

How MathemaJcians Count

• 1,2,3,4,5,6,7,8,9,10,11…

Pre-2000: how hadron physicists count

q q q

2, 3. 1

2003: how hadron physicists count

2, 3, 4.

Z(4430) confirmed by LHCb

BàKπ+ψ’

4-dim amplitude analysis Model-ind. Argand plot

J

P =1 +

M = 4475 ± 7−25

+15 MeV

Γ =172 ±13−34

+37 MeV

Bf (B

0 →Z(4430) −K +) × Bf (Z(4430) − →π − &

ψ ) ≈ (3.4−2.3

−1.1) ×10 −5

arXiv:1404.1903 BW-like resonant phase moJon

>13.9σ Good agreement with Belle, (with smaller errors)

2015: how hadron physicists count

2, 3, 4, 5.

Pc

+

u u c d c

(?)

Pentaquarks: some history

The Anti-decuplet in the χSM

• D. Diakonov, V. Petrov, M. Polyakov, Z.Phys.A359, 305 (1997)

S=+1 S=0 S=-1 S=-2

Δm = 108 MeV

updated version

• D. Diakonov, V. Petrov,

arXiv:hep-ph/0310212

Theoretical prediction that spurred several experimental searches.

LEPS/SPring8

γC K+K-(n)

PRL91, 012002 (2003)

CLAS/JLab

γD K-pK+(n)

PRL91, 252001 (2003)

Θ+(1540) published (mistakes?)

Aaempt to reproduce CLAS result

n Restricted photon energy range n Two distributions statistically

consistent with each other:

n 26% c.l. for null hypothesis

from the Kolmogorov test (two histograms are compatible).

n G10 mass distribution can be used

as a background for refitting the published spectrum.

2009: Results of Θ+ analysis at LEPS

Δ(-2lnL) =31.1 for Δndf=2 5.2σ

7

Prob(5.2 ) 2 10 σ

−

= ×

Simple (γ,K-) missing mass: No correction on Fermi motion effect. nK+ invariant mass with MMSA: Fermi motion effect corrected. “The narrow peak appears only after Fermi motion correction.”

2

Peak position: 1.527 0.002 GeV/ Signal yeild: 116 21 events Differential cross-section: 12 2 nb/sr c ± ± ±

PRC 79, 025210 (2009)

Unpublished CLAS result

Using the same analysis cuts and procedures as for LEPS (2009).

fquaenergycmLEP0 Entries 19087 Mean 1.561 RMS 0.06258 / ndf

2

χ 90.99 / 98 p5 6.265 ± 1.993 −

2

Gev/c 1.45 1.5 1.55 1.6 1.65 1.7 Counts 50 100 150 200 250 300

fquaenergycmLEP0 Entries 19087 Mean 1.561 RMS 0.06258 / ndf

2

χ 90.99 / 98 p5 6.265 ± 1.993 −

Energy of photon (2.0-2.4 GeV) Proton detected Proton veto 12 nb

Pentaquarks: the LHCb results

(Some slides borrowed from Sheldon Stone)

Physics 8, 77 (2015)

Viewpoint

Elusive Pentaquark Comes into View

Kenneth Hicks

Department of Physics and Astronomy, Ohio University, Athens, OH 45701, USA

Published August 12, 2015

A new type of particle containing five quarks has been observed by the LHCb experiment.

Subject Areas: Particles and Fields A Viewpoint on: Observation of J/p Resonances Consistent with Pentaquark States in 0

b Ω J/K−p Decays

• R. Aaij et al. (LHCb Collaboration)

Physical Review Letters 115, 072001 2015 – Published August 12, 2015

Λb à J/ψ K- p

! First looked for in LHCb as

a potential background for

B0→J/ψK+K-

! Large signal found, used

for Λb lifetime [arXiv:1402.6242]

! Dalitz plot

showed an unusual feature

[arXiv:1507.03414]

Λb→J/ψK p

BNL August 2015!

4

m2(K-p) m2(J/ψ p)

m(J/ψK-p) [MeV]

26,000 signal + 5.4% bkgrnd within ±2σ

• f peak

…Λ*’s

ProjecJons

Projections

arXiv:1507.03414

Be Careful! Previous History:

Prejudices

! No convincing states 51 years after Gell-mann &

Zweig proposed qqq and qqqqq baryonic states

! Previous “observations” of several pentaquark

states have been refuted

! These included

" Θ+→K0p, K+n, mass=1.54 GeV, Γ~10 MeV " Resonance in D*-p at 3.10 GeV, Γ=12 MeV " Ξ--→Ξ-π-, mass=1.862 GeV, Γ<18 MeV

! Generally they were found/debunked by looking

for “bumps” in mass spectra circa 2004 [see Hicks

• Eur. Phys. J. H37 (2012) 1.]

BNL August 2015!

s t Λb → K−pJ/ψ m2

pJψ

m2

Kp

Λ(1520)

Can the s-channel band originate from a non-s-channel pole

! Consider all Λ* states & all allowed L values BNL August 2015!

10

# parameters 64 146

Flatte´ BW ↓

Two PWA: Reduced and Extended

PWA using only known Λ* states

c

! Use extended model, so all possible known Λ*

• amplitudes. mKp looks fine, but not mJ/ψp

! Additions of non-resonant, extra Λ*’s doesn’t help

Fit with Λ* and one Pc signal

! Try all JP up to 7/2± ! Best fit has JP =5/2±. Still not a good fit

Reduced PWA with two Pc states

c

! Best fit has JP=(3/2-, 5/2+), also (3/2+, 5/2-) &

(5/2+, 3/2-) are preferred

Argand diagrams: phase moJon

Argand diagrams

Amplitudes for 6 bins between +Γ & -Γ

Breit- Wigner Breit- Wigner

Why two Pc states are needed:

)

P

• cos(
• 1
• 0.8
• 0.6
• 0.4
• 0.2

0.2 0.4 0.6 0.8 1

Corrected events/(0.1)

100 200 300 400 500

LHCb

c

Combined P (4450)

c

P (4380)

c

P

Data demands 2 states

! Interference between opposite parity states

needed to explain Pc decay angle distribution

! Fit projections BNL August 2015! Large m(Kp) region negative interference Small m(Kp) region positive interference

CauJon! Strong interference of Λ*

gular distributions

14

8

Some TheoreJcal Models

Meson-Baryon Molecule 5-quark “bag”

Why Heavy Quarks?

• Karliner and Rosner: arXiv:1506.06386

– Predict a host of Pc and Pb states corresponding to various meson-baryon thresholds. – Based on meson-meson molecule model for XYZ – Note conspicuous absence of DD and BB states.

• Pion exchange is suppressed b/w two pseudoscalars.

– The “repulsive kineJc energy is inversely proporJonal to the reduced mass” (Ericson, Karl).

• Requires heavy quarks to provide sufficient aaracJon.

Dibaryons?

What comes aqer 5?

Dibaryons

(some slides borrowed from Reinhard Schumacher)

6 quarks in a bag The deuteron

• 2.2 MeV bound

The only clear-cut

“dibaryonic molecule”

Recall the nn, pp, and np

strong spin singlet states are unbound…

… by only ~100 keV One of the great “fine-tuning”

mysteries of nature!!

3S1

I(JP)=1(0+) I(JP)=0(1+)

1S0

Bound N, bound ,

(Jaffe’s “H-particle”)

Binding? Width: ‘narrow’ or ‘wide’? Spin, Isospin ?

CLAS study: new

• bservations

Recent WASA@COSY

claim of discovery I (JP) I (JP)=1 (2+) (?) N I (JP)=0 (3+)

“3-body model of N and dibaryons”

• A. Gal, H. Garcilazo, arXiv:1402.3171 (2014)

Three-body model with separable pairwise

interactions

Solve NN and N Faddeev equations found below threshold for I(JP) = 1(2+) & 2(1+) found below threshold for I(JP) = 0(3+) & 3(0+)

• P. Adlarson et al, Phys Rev Lett 106, 242302 (2011)

The WASA@COSY

result for

M ~ 2370 MeV

= 2m – 90 MeV

~ 70 MeV < 1/3 “ABC effect”:

enhancement of low- mass pion pairs

Dibaryon interpretation

is controversial (D. Bugg) m

ΔΔ resonance with I (JP) = 0 (3+)

CLAS collab. 11-14-14

• R. A. Schumacher, Carnegie Mellon University

11

• R. Arndt, I. Strakovsky, R. Workman, Phys Rev C 50, 1796(1994)
• 3P2 wave in d elastic scattering

is most prominent

SAID analysis: “resonance-like”

behavior in several partial waves

190 MeV W=2.18 GeV

• d*

d d

• Off-

shell pion

Resembles d elastic scattering but

with an off-shell pion.

PhotoproducJon at CLAS

• R. Schumacher, P. Masone (CMU):

CLAS Preliminary!!

ProjecJons: CLAS preliminary!!

Background from ρ-meson removed: Preliminary!!

Fit to resonance shape: Preliminary!

Fit to Resonance-like Shapes

• W=2.75 GeV

Next Steps

• Study of coherent ρ-meson photoproducJon

– PhD of T. Chetry, Ohio U. grad student.

• PWA that includes all possible final states:

– First steps being done by CMU (P. Masone)

• In addiJon to d*++ and d*0, look for d*+.

– Also part of T. Chetry’s PhD. – Interferes with ω-meson photoproducJon. – Clearly shows isospin 1 triplet of dibaryon states.

What’s Next??

Summary

• Pre-2000: only mesons and baryons

– N = 2 or 3 (except for nuclei, such as deuterium)

• Post-2000: many new mulJ-quark hadrons:

– Tetraquark (XYZ mesons), Pentaquark (Pc states), Dibaryon (ΔΔ and NΔ). – N = 4, 5 and 6.

• What’s next? Probably hybrid mesons.

– Predicted already by Lasce Gauge theory.

Backup Slides

Some theoreJcal references

• Roca, Nieves, Oset: arXiv:1507.04249

– Pentaquarks as a D*Σc and D*Σc* molecule. – Explains the best-fit spin and parity of Pc states.

• Guo, Meissner, Wang, Yang: arXiv:1507.04950

– Possible rescaaering from χc1 to J/ψ p.

• Maiani, Polosa, Riquer: arXiv: 1507.04980

– Compact 5-q structure using diquarks.

• R. Lebed: arXiv: 1507.05867

– Compact (cu) diquark and color triplet c(ud).