Cesare Bini, Bernhard Ketzer

Workshop on New Partial Wave Analysis Tools for Next Generation Hadron Spectroscopy Experiments

Camogli, Italy

22 June 2012

ATHOS 2012Discussion Session I

Discussion Session - Experiments

                     Conveners: Cesare Bini and Bernhard Ketzer

Recent results on pi-pi amplitudes at BES III (10’+5’)

B. Liu (Institute of High Energy Physics)

Search for exotics in three pion production at COMPASS (10’+5’)

S. Neubert (TU-Munchen)

Search for exotics in three pion production at CLAS (10’+5’)

P. Eugenio (Florida State University)

Discussion (45’)

State of the Art Lattice QCD

[J. Dudek, Phys. Rev. D 84, 074023 (2011)][J. Dudek at al., Hadron Spectrum Collaboration, Phys. Rev. D 82, 034508 (2010)]

negative parity

positive parity

exotic

Structure of states: study

with e.g.

C. Meyer

Comparison with Models

L-QCD Bag Flux tube Constituent gluon

S wave P wave

1−−,(0,1,2)−+

1++,(0,1,2)+−

1++,(0,1,2)+−

1−−,(0,1,2)−+

1+−,(0,1,2)++

JPC & Degeneracy pattern:

(0,1,1,1,2,2,3)+−

(0,1,2)++

(0,1,2)−+,1−−

(0,13,22,3)−−

(0,1,2)−+

1−−,(0,1,2)−+

(0,13,22,3)+−

(0,1,2)++

Model with a quasigluon in a P-wave with respect to the qq pair,

i.e. with successfully reproduces the L-QCD multiplets

Production Mechanisms

• Diffractive production: Regge- or Pomeron exchange

• pN annihilation: formation and production

• Photo-production

VES, E852, COMPASSCrystal Barrel

COMPASSCLAS

JPC=1−+ ‒ Pb vs H Target

[Alekseev et al., Phys. Rev. Lett. 104, 241803 (2010)]

[F. Haas, arXiv:1109.1789 (2011)]

Pb Pb p p 0 0 p p

S. Paul

S. Neubert

Nuclear Effect

Pb, Ni, H2 targets

M=1 enhanced for nuclei

1 1PCJ M 1 1PCJ M

S. Paul

S. Neubert

Photoproduction of JPC=1−+

Pion beam:

• JPC = 0−+ mainly S=0 hybrids: 1−−, 1++

mix with qq states

Photon beam:

• JPC = 1−−, VMD

mainly S=1 hybrids

exotic JPC , strength comparable to a2(1320)?

Flux tube model (Isgur 85, Close 95):

L-QCD (Dudek 09)

• strong photocoupling for cc hybrids

photoproduction more favorable for exotic hybrids?

Photoproduction of JPC=1−+

• no clear resonance signal• high-mass results fluctuate• accounts for 2% of total intensity at most• no evidence for 1−+ phase motion

P. Eugenio

Photoproduction of JPC=1−+

CLAS COMPASS

P. Eugenio

hp- vs h’p- Final States

• hp- waves scaled according to

phase space and BR to final state

• D, G waves very similar

• P wave very different in hp and h’p

Status of Analyses

• Isobar model analysis• isobar parameterizations: r, (pp)S

• rank of fit, full vs partial coherence• leakage, acceptance, resolution• t’ dependence• estimation of systematic error

• Signals for exotic mesons• diffraction, pbarp: rp, hp, h’p, f1p, b1p• photoproduction: none

Future

• Go beyond standard isobar model analysis:• where does the model fail?

study channels like

• include non-resonant production (dynamical effects, e.g. Deck)• analytic amplitudes • final state interactions• unitarity• understand a1

• multi-particle final states

Non-Resonant Production

Resonant production Non-resonant production

• Generate pure Deck-like events

[G. Ascoli et al., Phys. Rev. D 8, 3894 (1973)]

• Pass through Monte Carlo & PWA

• Normalize to 6−+0+ rp H wave

• Examine intensity in other waves

21

Duality and PWA FESR should work separately for Pomeron (background)

and classic Regge components and for fixed t and u.– At fixed u in π- π+ π- π+ one has zero Regge contribution

In π N elastic scattering one was able to use Regge exchange contributions as an approximation to high partial waves– This approach should be applicable to photon or meson

induced “top vertices” including reactions like π- Pomeron π- π- π+ with internal π exchange

This phenomenology suggests a PWA model that is combination of– Regge Born with low partial waves removed and – Parameterized low partial waves– FESR constraints on parameterized waves

G. Fox

Understand the a1

JPC = 1−+

• Higher masses accessible many disputed states: 0-+, 1++, 2-+,...

Multi-Particle (>3) Final States

Motivation:• Clarify the hybrid nature of the p1 branching ratios to different channels

Under investigation:

•

•

, 0,

0, , , ,

01 1, ,f f 1 1, ,f f

•

•

Model b1p f1p rp hp h’p h(1295)p Reference

Flux Tube, 3P0 170 60 5 - 20 0 - 10 0 – 10 [Isgur et al., Close et al.]

Flux Tube, IKP m=1.6 GeV/c2

24 5 9 2 [Isgur et al.]

Flux Tube, PSSm=1.6 GeV/c2

59 14 8 1 [Page et al.]

L-QCD 66 15 [McNeil and Michael]

Future

• Go beyond standard isobar model analysis:• multi-particle final states• coupled-channel analysis• final state interactions, unitarity• understand production mechanism: bins in t, s, polarization, probes• higher statistics, enlarge phase space• study model dependence• specify systematic errors

• Tools, etc.• common PWA framework across different experiments• plugin for amplitudes• validation of software• computing: fitting procedures, GPUs, etc.• access to data• teach young researchers

Conclusions

Hybrid mesons

are allowed in QCD, but are they realized in nature?

provide a test of flux tube formation confinement

can appear in exotic JPC quantum numbers smoking gun

High statistics data with p beam: COMPASS

exotic 1−+ waves in rp, h’p, f1p

non-resonant and resonant contributions

A dependence of M=1 production

Photoproduction: CLAS (also COMPASS)

no evidence for p1(1600) in charge transfer reaction

examine Pomeron production

Have we observed the lowest hybrid supermultiplet?

p1(1600), p(1800), p2(1880), ?

Many more interesting questions: Strangeness, Scalars, Glueballs, …

Partial Wave Analysis

Photoproduction Prim '( ') b tt e

'( ') ' btt t e

0.0015 < t’ < 0.01 GeV2/c2

t’ < 0.5·10-3 GeV2/c2

vanishes for t’→0

a2(1320) (M=1) present in both t’-ranges different production mechanisms?

Diffraction

Two clearly separated regions:

Phase difference a2(1320) - a1(1260): offset for two t’-regions!

Phase Difference a2-a1

Experiment Theory[G. Faeldt et al., Phys. Rev. C 79 014607 (2009)]

Plot by N. Kaiser, TUM

smooth transition between a2 photoproduction

to diffractive production with increasing t‘ possibility to cleanly separate photoproduction from diffraction

PWA in t’ bins for single mass bin 1.26 < m3p < 1.38 GeV/c2 (a2 region)

F(a1)F(a2)

(DF a2-a1)

determination of radiative width of a2(1320), p2(1670)