Scalar mesons in VES experiment

Yu.Khokhlov (IHEP Protvino) for VES PhiPsi11 Novosibirsk, 19.09.2011

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SCALAR MESONS IN VES EXPERIMENT


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Outlook Introductory remarks VES Experiment Scalars at VES – various topics

Conclusions


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Why to study scalars NOTE ON SCALAR MESONS by C. Amsler, T. Gutsche, S. Spanier and

N.A.T¨ornqvist (in RPP 2011): quantum numbers of the vacuum (JPC = 0++) can condense into the vacuum and break a

symmetry such as a global chiral U(Nf )L × U(Nf )R

How they break ?


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Experimental approaches and evidences

Numerous and various OPE scattering π/K N N π/K π, N K/π K Diffractive π N N PPP p p̅ PPP (at rest & in flight) γ γ PP D(*)/ B PPP Dalitz plot

J/ψ K* K π τ K π ν φ [a0(980) + f0(980)] γ …..

• In general: mostly PP – S wave


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VES setup

1 - target; 2 - veto counters; 3 - multiplicity discriminator; 4 -magnet ; 5 - Čh detector; 6 –Sci –hodoscope; 7 - Ecal

• secondary (mostly π-) beam of U-70, p ~ 25 – 45 ГэВ/с • magnetic spectrometer pt = 0.5 - 0.7 GeV/с• EM – calorimetry • K/π – identification (4-18 GeV/с)• Fast DAQ (104/spill)• Minimum bias trigger


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Experimental studies of scalars with VES

Form-factor of the decay ηʹ → η π π The (ωφ) in Charge Exchange Reaction ISB decay f1(1285) 3 π Search for ISB decay π(1800) η π π


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Form-factors in the decays ηʹ → η π π The width and spectral shape of the ηʹ → η π π

are of interest for various aspects General tool: ChPT (expansion in p2, mu,d,s, 1/Nc in Nc

approach) + FSI (heavy ηʹ) intermediate Resonances in play

encoded in LEC (@low s) introduced “by hands” or dynamically

Mainly with JPC = 0++ (coupling to 1- suppressed in I=0 P PPP due to G-parity)


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ηʹ → η π+ π- DP with VES Measured in

diffractive associative production ηʹ π-

Charge exchange reaction largest sample at the moment (~23 k ev) more general DP parameterization: |M|2 1 + a Y + b Y 2 + c X + d X2 + … (1)

Compared w. “linear” one ( complex)|M|2 |1 + Y| 2 + c X + d X2 (2)

(1) & (2) equivalent ONLY for b > a2/4 0


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VES Dalitz plot

Y – dependence of Dalitz plot distribution for 8 slices on X.Data (points) and fitting function (line)


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ηʹ → η π+ π- DP with VES (cont’d)

The parameter с compatible with zero as expected from C – symmetry

The b NEGATIVE the “linear” parameterization not

adequate The large and NEGATIVE d impacts

models


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ηʹ → η π π DP: Experiment vs. Theory PL B651 22 (2007) (VES) [26] B.Borasoy and R.Nissler, EPJ A26, 383 (2005) PAN 72 231 (2009) (GAMS) (neutral mode; may differ) PR D 83, 012003 (2011) (BESIII) - New (~44 k ev)

JHEP 1105:094,2011 Rafel Escribano, Pere Masjuan, Juan Jose Sanz-Cillero Large-Nc ChPT vs. RChT


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Scalars in ηʹ → η π π DP• a0(980) contribution dominant• is essential • But … heavier tensor states are not negligible

• Accounting for other states required to study scalers


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Scalar in (ωφ) system in charge-exchange (OPE compatible) reaction


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X(1812): Earlier observation in J/ψ(γ ω φ)

By BESII Collab. ( Ablikim et al.), Phys. Rev.Lett.96:162002,2006


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PWA of (ωφ) system(Hadron-2009, Proceedings of XIII International Conference)


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PWA of (ωω) system


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N(ωφ)/N(ωω) ratio for JP=0+


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OZI rule in 0+ & 2+

The violation of the OZI rule in decays of scalar resonances is expected in many models

“On the origin of the OZI rule in QCD”, Nathan Isgur , H.B. Thacker Phys.Rev. D64 094507, 2001

…….

(1.82 GeV < M < 2.0 GeV)

N2+() /N2+ () = 0.045 0.010

N0+() /N0+ () = 0.65 0.10

Compare with 2+


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ISB Decay f1(1285)π+π-

π0

IGJPC = 0+1++ M = 1282 MeV, = 24 MeV Dominant channels : KKπ, ηππ (incl. a0(980) π), 4π Decay to 3π violates Isospin Symmetry Possible mechanisms - f1(1285) a1(1260) mixing (a la ω ρ, η π, Δ N, Σ

Λ)- «contact» f1 3π- Intermediate scalars mixing: f1 π a0 π f0 3π (possibly) enhanced through KK- loops (Achasov,

Devyanin, Shestakov PL B88, 1979)1/2

2K

2K

2KKKfKKa

fafa0

000

0000 mmm

π16

gg|Ms||Π|


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Experimental findings • 1-st report @Meson-2008 (Cracow)• Final publication EPJ A (2011) 47: 68• Associative f1 π- production π- A A f1 π-

M(π+ π- ) for M(3 π) within f1(1285) mass region

Effect of angular weighting 1+ (0+ 0- ) P on M(π+ π- )

M(ηπ+π-) in η3π

f1(1285)


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Experimental result %.)(20.0)(16.086.0

)())"980("(

1

0001

syststatfBRffBR

%)(16.086.0)()( 70.0

20.01

01

statfBRfBR

%4.06.00.2))980()980( 00 faBR

More: accounting for lower 2-mass tail

Estimates within “Achasov’ model” varying a0/f0 parameters

BR(f1 π+π-π0) / BR(f1 ηπ+π- ) ~ 0.05 – 0.5 %

VES result exceeds maximal (with extreme f0(980)-KK coupling)


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Comparison w. BES-III

%)6.05.05.2()(

))980((0000

01

000

0001

afBrfafBr

af

%)1.02.03.0()'(

))980('(0000

01

000

0001

aBrfaBr

c

caf BES-III

VES

arxiv/1012.1377v1.pdf


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Possible (another) mechanism? FSI (re - scattering) expected -- small @ BES as a0(f0) and well separated -- large @ VES as all products “confined” An example: Triangle Singularity (TS) ISB (1405/1475) f0 arXiv:1108.3772v1 Jia-Jun Wu et

al.

a) TSb) a0 f0 mixingf1(128

5)f1(1285)

• JP = 1+ vs. 0- other TS character • f1(1285) light loop particles off-shell


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Search for ISB π(1800) η π π Assuming a0 (980) f0 (980) mixing major JP=0- π(1800) f0(980) π a0 π η π π Rich source: diffractive π- N → N π-(1800) with

π-(1800) → (ηπ0) π-

3-particles final state compared w. f1 π case but: broad (>120 MeV) π(1800) compared w.

narrow (~25 MeV) f1(1285) Specific feature (PWA needed): 0-(1800)→ 0+(ηπ) π M(0+)~0.98 ГэВ neutral only


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Experimental observations

for π(1800) region 1.72 < M(η π0 π- )< 1.92 GeV M(η π0) - left M(η π-) - right

Signal compatible w. a0(980): N(a0

0 ) 600 60 N(a0- )

130 60

π- N → N η π0 π- with → +-

0


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PWA of (+-0)0-

→ +-0 with final experimental width Very large (combinatorial) background 5–particles PWA (includes ω(782) → +-0 and bckg.) Many isobars ρ(770), a2(1320), a1(1260), b1(1235),

a0(980) 24 waves (JPC=0--, 0-+,1+-,1--,1++,2-+,2++,…) Different production mechanisms (exchanges)

(OPE, ω, diffraction) → t - dependencies Separate waves w. (not symmetric) a0

0 and a0

-

Model dependent a0 (980) f0 (980) “mixing” signal JP = 0- for π(1800) “a0

0” -


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Some (large) waves (preliminary)

2++ ωρ

0-+ a1 ρ

0- →“a00”

-


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Preliminary result %9.1

)()980()1800())()"980(")1800(

0

00

fBRaBR @ 90% CL

N.B.: π(1800) K*K => no TS – like enhancement • Analyses π- N → N π-(1800) → (ηπ0) π- → () () π- desired • much less bckg lower noise; less states; (relatively) larger signal • pilot VES run (2010) with 1-track final state: promising• full run planned for November 2011


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Conclusions Specific shape of Dalitz plot for ηʹ → η π+ π- adopted with

RChT; scalars AND tensors contribute Scalar near threshold in ω(782)

(1020) compatible w. X(1812) by BESII strongly violates OZI rule

ISB–decay f1(1285)π+π-π0 incompatible with “KK-loop mixing” of a0 (980) f0 (980) alone: too intensive and structured

An indication to ISB–decay π(1800) η π π through “a0 (980)” needs more analyses


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Backup slides ηʹ → η π+ π- by VES in BES interpretation


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Backup slidesRChT vs. large-Nc ChPT


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Backup slides waves for PWA of (ωω)

1 - (0++)0- JLS=000 11 - (0-+)0+ JLS=011 2 - (2++)0- JLS=202 12 - (2-+)0+ JLS=211 3 - (2++)0- JLS=220 13 - (1++)0+ JLS=122 4 - (2++)0- JLS=222 14 - (3++)0- JLS=322 5 - (2++)1- JLS=202 15 - (2++)1+ JLS=202 6 - (4++)0- JLS=422 16 - (4++)1+ JLS=422 7 - (4++)0- JLS=440 17 - FLAT 8 - (4++)0- JLS=442 9 - (4++)0- JLS=422 10 - (6++)0- JLS=642


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Backup slides K*K* rescattering vs. () resonance

arXiv:1107.0781v1


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Backup slides X(1812) search @ BELLE

X(1812) search @ BELLE in B+ K+ (ω ) - no signal (arXiv:0902.4757v2)


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Backup slides(1405) f0(980)0 @BESIII


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Backup slidesM(π+ π- ) in (1440) → w. TS

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Scalar mesons in VES experiment