study of the decays at wasa-at-cosy · elisabetta prencipe mesonnet, 17.06.2013 summary and...

Study of the decays at Wasa-at-COSY

Elisabetta Prencipeon behalf of the Wasa CollaborationMesonNet Workshop, 17th -19th June 2013, Praha

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Outline

Introduction

The Wasa-at-COSY detector

decays in the pd reaction ▸ e+e

▸ e+ee+e

▸ ▸ e+e

decays in the pp reaction

Introduction

The WASa detector

decays in pd reaction p+p-e+e- e+e-e+e- p+p-g e+e-g

H decays in pp reaction

Introduction

The WASa detector

decays in pd reaction p+p-e+e- e+e-e+e- p+p-g e+e-g

H decays in pp reaction

Elisabetta Prencipe MesonNet, 17.06.2013

▸ e+e

e+e e+e

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Introduction

The study of light mesons provides an ideal laboratory for:

➢ high precision measurements➢ rare process search➢ test symmetry and symmetry breaking

High statistics of light mesons in many experiments


CLEO, Cornell

CLAS, JLab

WASA-at-COSY, JülichCrystal Ball, Mainz

KLOE, Frascati

BES III. Beijing

CMD/SND, Novosibirsk

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The COSY facility

WASA-at-COSY


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The detector Wasa-at-COSY


Target: fixed hydrogen/deuterium pellet target Forward detector: measurement of recoil particles Central detector: measurement of charged and neutral decay products PID from deposit of energy in different detector layers Tracking: drift chamber

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decays @ Wasa-at-COSY

The reactions under study here are:

pd 3Hek = 1.0 GeV

pp ppk = 1.4 GeV

➢3 x 107 mesons tagged➢10 /s produced

➢5 x 108 mesons produced ➢100 /s produced


The missing mass is used to identify mesons

inclusivepd

exclusivepp

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Which decays and why


PDG

See the poster session: D. LerschD. Lersch,

this evening

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and e+e


The decays and e+e are closely related 2 anomalous contributions to the decay amplitudes:

Triangle anomaly Box anomaly

Strong contribution from the triangle diagram via -coupling vector meson dominance

Information extracted from: inv. Mass (E angular distribution.

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PLB 707 (2012) 242-249

With a model independent parameterization


PLB 718 (2013) 910-914

: results (I)

p-wave

s

= inv. mass of Stollenwerk et all., PLB 707 (2012), 184

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The measurement from CLEO is ~3 lower than the PDG average global fit [PRL 99 (2007) 122001]

The CLEO measurement was confirmed by KLOE[ PLB 718 (2013), 910-914 ]

The WASA-at-COSY measurement:

(98002±382) reconstructed events in pd

BR extracted: work in progress... (need to finalize systematic effects)

Analysis in pp data in progress: x10 higher statistics available


: results (II)

D. Coderre

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e+e

Possible interference between the M1 transition (CP conserving) and E1 transition (CP violating)

in the decay e+e

: polarization of a real photon is possible, but not yet measured

e+e : we can measure the asymmetry in the decay plane e

Theoretical upper limit: ~1%Experimental value: (-0.6± 2.5 ±1.8)%

[PLB 675 (2009), 283-288]


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e+e: results


(263±24) reconstructed events BR in agreement with other experiments A

limited by statistical error in pd data:

analysis in progress with pp data

10-2

D. Coderre

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e+e and e+ee+e

The interest in the decay e+e is to extract the form factor: it is useful to describe the couplingof the virtual photon to the vector meson

We can compare the e+e invariant mass spectrumwith the QED prediction:

The interest in the double Dalitz decay e+ee+e is: - precise determination of BF - double form factor


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e+e: Branching Ratio

(16637±117) reconstructed eventsin pd data PID to reduce bkg from pions Eliminated background from conversion e+ein the beam pipe BR evaluated, not yet released Analysis in pp in progress....


D. Coderre

Fullrange

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e+eForm Factor


Preliminary results from pd data sample

M. HodanaM. Hodana

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e+ee+e: Branching Ratio

Very limited from the statistics in pd data:

(54 ±13) reconstructed events In the new analysis the kinematic fit is

used lower background Consistent with previous result Improvement expected with pp data to extract the double form factor


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e+e: Branching Ratio

Very rare decay: theoretically BF ~ 10-8

Sensitive to non-standard model process Discrepancy found between theory and experimental

result for the channel e+e[PRD 75 (2007) 012004]

What about the meson?


Analysis on 2 weeks data from pp pp Consistent with HADES [Eur J.P. A 48 (2012) 64] Additional 15 weeks of data collected at WASA

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Summary and conclusions

Wasa-at-COSY has high statistics in pd and pp datasets to analyze decays

The study of the decays is useful for: precise measurement of the BR

form factor box anomaly C and CP violation eventually new physics beyond the Standard Model

Preliminary results of several decay modes today were presented,using the pd dataset: the Wasa Collaboration will soon provide BR measurements.

Improvements are expected when the pp dataset is used for these analyses work in progress: a statistics x10 is available with the pp dataset

Stay tuned!Stay tuned!

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THANK YOU!

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Back up slides

Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20

study of the decays at wasa-at-cosy · elisabetta prencipe mesonnet, 17.06.2013 summary and...

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