Search for New Physics via η Rare Search for New Physics via η Rare DecaysDecays

Liping GanLiping Gan

University of North Carolina WilmingtonUniversity of North Carolina Wilmington

11

OutlineOutline Physics MotivationPhysics Motivation

• Why Why ηη is unique for new physics search? is unique for new physics search?• ηη→→00• ηη→→0000

• ηη→→00, , ηη→→33

Suggested experiment in Hall DSuggested experiment in Hall D SummarySummary

Why Why ηη is unique for new physics search? is unique for new physics search?

Due to the symmetries and conservation of angular momentum in the strong and EM interactions, the η decay width Γη =1.3 KeV is extremely narrow (comparing to Γρ= 149 MeV)

η decays have the lowest orders filtered out in the strong and EM interactions, enhancing the contributions from higher orders by a factor of ~100,000.

η decays provide a unique, flavor-conserving laboratory to search for new sources of C, P, and CP violations in the regime of EM and suppressed strong processes, and test the high order χPTh predictions.

The most massive member in the octet pseudoscalar mesons (547.9 MeV/c2) sensitive to QCD symmetry breakings

22

Examples of the Examples of the ηη Rare Decay Channels Rare Decay Channels

Mode Branching Ratio Physics Highlight

π0 π0 <3.5<3.5 ×× 1010 -4-4 CP, P

π0 2γ (( 2.72.7 ±± 0.50.5 )) ×× 1010 −−

44 χPTh, Ο(p6)

3γ <1.6<1.6 ×× 1010 −−

55 C

π0 γ <9<9 ×× 1010 −−

55 C

π0 π0 γ <5<5 ×× 1010 −−

44 C

π+ π− <1.3<1.3 ×× 1010 −−

55 CP, P

π0 π0 π0 γ <6<6 ×× 1010 −−

55 C

π0 e+ e− <4<4 ×× 1010 −−

55 C

4π0 <6.9<6.9 ×× 1010 −−

77 CP, P

33

Study ofStudy of ηη→→0 0 0 0 ReactionReaction The Origin of CP violation is still a mysteryThe Origin of CP violation is still a mystery

CP violation is described in SM by Kobayashi-Maskawa (KM) mechanism in Yukawa CP violation is described in SM by Kobayashi-Maskawa (KM) mechanism in Yukawa couplings (couplings (flavor-changingflavor-changing ) )→→ a single phase in the CKM quark mixing matrix. a single phase in the CKM quark mixing matrix. Deviations from the KM predictions would be signatures of new physics.Deviations from the KM predictions would be signatures of new physics.

The KM mechanism fails by several orders of magnitude to explain the observed The KM mechanism fails by several orders of magnitude to explain the observed matter-antimatter asymmetry of the Universe. Almost all extensions of SM imply matter-antimatter asymmetry of the Universe. Almost all extensions of SM imply additional sources of CP violation. New source of CP violation is also necessary for additional sources of CP violation. New source of CP violation is also necessary for baryogenesis. baryogenesis.

The flavor-changing processes has been intensively investigated in K, B and D The flavor-changing processes has been intensively investigated in K, B and D meson decays, and no positive new source of CP violation has been discovered meson decays, and no positive new source of CP violation has been discovered yet. The flavor-conserving region remains much less explored. The later yet. The flavor-conserving region remains much less explored. The later represents a better chance for new physics due to suppressed KM contribution.represents a better chance for new physics due to suppressed KM contribution.

The The ηη→→0 0 0 0 is one of a few available flavor-conserving reactions listed in PDG to is one of a few available flavor-conserving reactions listed in PDG to

test CP violation. test CP violation. The The SM predicts: BR<2x10 SM predicts: BR<2x10-27-27. . An extended SM calculation An extended SM calculation including spontaneous CP violation in the Higgs sector and a including spontaneous CP violation in the Higgs sector and a θθ-term in the QCD -term in the QCD Lagrangian predicts: Lagrangian predicts: BR<2x10BR<2x10-15-15

Unique test of P and CP symmetry violations, and search for new physics beyond Unique test of P and CP symmetry violations, and search for new physics beyond

SMSM

44

ηη→→0 0 γγ andand ηη→→33γγ DecaysDecays

Both channels are forbidden by C invariance in the Both channels are forbidden by C invariance in the Standard ModelStandard Model

Offer an unprecedented opportunity for searching new C Offer an unprecedented opportunity for searching new C violation in the electromagnetic interaction of hadrons.violation in the electromagnetic interaction of hadrons.

Current experimental limits:Current experimental limits: BR(η→0 γ )<9x10-5, BR(η→3 γ )<1.6x10-5

55

Study of theStudy of the ηη→→00 DecayDecay

A stringent test of the A stringent test of the χχPTh prediction at PTh prediction at ΟΟ(p(p66) level) level Tree level amplitudes (both Tree level amplitudes (both ΟΟ(p(p22) and ) and ΟΟ(p(p44)) vanish;)) vanish; ΟΟ(p(p44) loop terms involving kaons are suppressed by large ) loop terms involving kaons are suppressed by large

mass of kaonmass of kaon ΟΟ(p(p44) loop terms involving pions are suppressed by G parity) loop terms involving pions are suppressed by G parity The first sizable contribution comes at The first sizable contribution comes at ΟΟ(p(p66) level) level

A long history that experimental results have large A long history that experimental results have large discrepancies with theoretic predictions.discrepancies with theoretic predictions.

Current experimental value in PDG is Current experimental value in PDG is BR(BR(ηη→→00 )=(2.7±0.5)x10 )=(2.7±0.5)x10-4-4

66

Theoretical Status on Theoretical Status on ηη→→00

Average of Average of χχPTh 0.42 PTh 0.42

By E. Oset et al.By E. Oset et al.

77

History of the History of the ηη→→00 Measurements Measurements

88

After 1980

A long standing “η” puzzle is still un-settled.

High Energy High Energy η η Production ProductionGAMS Experiment GAMS Experiment at Serpukhovat Serpukhov D. Alde et al., Yad. Fiz 40, 1447 (1984)D. Alde et al., Yad. Fiz 40, 1447 (1984)

Experimental result was first Experimental result was first published in 1981published in 1981

The The ηη’s were produced with ’s were produced with 30 30 GeV/cGeV/c -- beam in the beam in the --pp→η→ηn n reactionreaction

Decay Decay ’s were detected by lead-’s were detected by lead-glass calorimeterglass calorimeter

Major BackgroundMajor Background --pp→ → 0000n n η →η →000000

Final result: Final result:

((η→η→00 ) = 0.84±0.17 eV

40 η→η→00 events events

99

1981

1984

Low energy Low energy η η production production CB experiment CB experiment at AGSat AGS

S. Prakhov et al. Phy.Rev.,C78,015206 (2008)

The The ηη’s were produced ’s were produced with with 720720 MeV/c MeV/c -- beam beam through the through the --pp→η→ηn n reactionreaction

Decay Decay ’s energy range: ’s energy range: 50-500 MeV50-500 MeV

Final result:Final result:(η→0 ) = 0.285±0.031±0.061 eV92±23 η→η→00 events events

η η →→00 00 00

NaI(T1)

1010

Advantages of Jlab Advantages of Jlab High energy tagged photon beam High energy tagged photon beam to reduce the background from to reduce the background from η→ η→ 3300

Lower relative threshold for Lower relative threshold for -ray detection-ray detection Improve calorimeter resolution Improve calorimeter resolution

Detecting recoil p’sDetecting recoil p’s to have an independent way to reduce non- to have an independent way to reduce non-resonant resonant pp→→0000p and other combinatory p and other combinatory backgroundsbackgrounds

High resolution, high granularity PbWOHigh resolution, high granularity PbWO44 Calorimeter Calorimeter Higher energy resolution → improve Higher energy resolution → improve invariant mass and elasticity spectruminvariant mass and elasticity spectrum Higher granularity→ better position resolution and less overlap clusters to Higher granularity→ better position resolution and less overlap clusters to

reduce reduce background from background from η→ η→ 3300

Fast decay time (~30ns)→ less pile-up clustersFast decay time (~30ns)→ less pile-up clusters High statistics High statistics to provide a precision measurement of Dalitz plot to provide a precision measurement of Dalitz plot

30 GeV/cE 720 MeV/cE

production 1020 MeV

s

High energy η-production

Low energy η-production

GAMS

CB KLOE

1111

12

Suggested Experiment in Hall D Suggested Experiment in Hall D

75 m

Counting House

GlueX FCAL

Simultaneously measure the η→0, η →00, η→3, and

ηη produced on LH produced on LH22 target with target with 11 11 GeV tagged photon beam GeV tagged photon beam γγ+p+p → → ηη+p+p

Further reduce pp→ → 0000p and other p and other combinatory combinatory backgroundbackground by by detecting recoil p’sdetecting recoil p’s with GlueX with GlueX detector detector

Forward calorimeter (upgraded with Forward calorimeter (upgraded with high resolution , high granularity high resolution , high granularity PbWOPbWO44) to detect multi-photons from ) to detect multi-photons from the the ηη decays decays

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η→0FCAL

Kinematics of recoil protons:Kinematics of recoil protons:• Polar angle ~55Polar angle ~55oo-80-80oo

• Momentum ~200-1200 MeV/cMomentum ~200-1200 MeV/c

Probability of two-cluster separation vs. distance between Probability of two-cluster separation vs. distance between hitshits

by I. Larin by I. Larin

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Study done by using PrimEx-II snake scan data

First cluster: “permanent” with energy 5 GeVSecond cluster: “moving” with energy 1-5 GeVArtificially split events are counted as missing

Reco

nst

ruct

ion e

ffici

en

cy (

100

%)

Reco

nst

ruct

ion e

ffici

en

cy (

100

%)

Separation distance (cm)

Separation distance (cm)

Pb glassPWO

S/N Ratio vs. Calorimeter TypesS/N Ratio vs. Calorimeter Typessignal: , background: signal: , background: , , 100 days beam time 100 days beam time

1414

03

Invariant Mass of 4γ (GeV)

0

dmin=2.5cm

S/N=7.74dmin=5.5cm

S/N=8.83x10-2

PWO Pb Glass

Invariant Mass of 4γ (GeV)

Ela

stic

ity

Ela

stic

ity

Invariant Mass of 4γ (GeV)

Invariant Mass of 4γ (GeV)

Event selection cuts:1.Elasticity2.Invariant mass.

PWO Pb Glass

Major improvement:1.Granularity2.Resolutions.

Invariant Mass and Elasticity ResolutionsInvariant Mass and Elasticity Resolutions

PWO

Pb glassσ=15 MeV

σ=6.9 MeVσ=3.2 MeV

σ=6.6 MeV

M M00

M00

M

1515

σ=0.0121

σ=0.0257

Elasticity

Elasticity

Jlab vs. Low Energy Facilities (CB)Jlab vs. Low Energy Facilities (CB)

1616

03

np

0

3

p p

Jlab Low Energy Facility

AcceptanceAcceptance

1717

150x150 cm2 FCAL

118x118 cm2 FCAL

Rate EstimationRate Estimation

23 24 20.0708 306.022 10 1.28 10 p/cm

1p A

LN N

A

The The +p+p→→ηη+p cross section ~70 nb (+p cross section ~70 nb (θθηη=1-6=1-6oo))

Photon beam intensity Photon beam intensity NNγγ~2x10~2x1077 Hz (for EHz (for Eγγ~9-11.7 GeV)~9-11.7 GeV)

• The The ηη→→00 detection rate: detection rate:(a) BR((a) BR(ηη→→00 )~2.7x10 )~2.7x10-4 -4

(b) average detection efficiency is :~26% (118x118 cm(b) average detection efficiency is :~26% (118x118 cm22 FCAL) and FCAL) and

~47% (150x150 cm~47% (150x150 cm22 FCAL) FCAL)

1818FCAL) 150(150 events/day 6.1846.0107.2150000

FCAL) 118(118 events/day 10.526.0107.2150000

4

4

0

0

N

N

factory!s/day)'( 150

Hz 79.1

10701028.1102 33247

k

NNN p

Statistical Error on dΓ/dMγγ for ηπ02γ

112 days

12 days

This figure gives a very rough idea how statistics limits our ability to probe

the dynamics of the ηπ02γ decay.

Assumptions are 18.6 accepted events per live

day, negligible background, and 7 bins spanning 0.025-0.375.

Prakhov et al., PRC 78, 015206 (2008).

19

2020

SummarySummary• 12 GeV tagged photon beam with GlueX setup will provide a great 12 GeV tagged photon beam with GlueX setup will provide a great

opportunity for precise measurements of various opportunity for precise measurements of various ηη rare decays to rare decays to test higher order test higher order χχPTh, C, P and CP symmetry violations, and PTh, C, P and CP symmetry violations, and search for new physics beyond the Standard Modelsearch for new physics beyond the Standard Model

• Propose simultaneous measurements on BR(Propose simultaneous measurements on BR(ηη→→00), ), BR(BR(ηη → →0000), ), BR(BR(ηη → →33), and ), and BR(BR(ηη→→00).).

• Three experimental techniques will be combined:Three experimental techniques will be combined:

– 12 GeV high intensity 12 GeV high intensity tagged photon beam to produce tagged photon beam to produce ηη’s.’s.

– Further reduce the Further reduce the pp→ → 0000p and other combinatory p and other combinatory backgrounds backgrounds by by detecting recoil p detecting recoil p with GlueX detector with GlueX detector

– Upgrade FCAL Upgrade FCAL with PbWOwith PbWO44 crystals crystals1.1. High high granularity calorimeter to reduce the High high granularity calorimeter to reduce the η →η →000000

background due to over-lap showersbackground due to over-lap showers..2.2. Fast decay time to reduce low energy pile-up clustersFast decay time to reduce low energy pile-up clusters3.3. High energy and position resolutions to have precise invariant High energy and position resolutions to have precise invariant

mass and elasticity spectrum for event selectionmass and elasticity spectrum for event selection

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The EndThe End

Thanks you!Thanks you!

2222

Examples of the Examples of the ηη’ Rare Decay Channels ’ Rare Decay Channels

Mode Branching Ratio Physics Highlight

π0 π0 <1.0<1.0 ×× 1010 -3-3 CP, P

π0 e+ e− <1.4×<1.4× 1010 −3−3 C

3γ <1.0×10<1.0×10 −−

44 C

ηe- e+ <2.4×<2.4× 1010 −3−3 C

2323

Budget vs. Acceptance Budget vs. Acceptance

Size of Cal.(cm2)

#crystals

Crystal Cost

PMTs ADC HV Total

118x118 3481 $0.87 M $1.04 M $0.98 M $1.04 M $3.93 M

150x150 5625 $1.41 M $1.69 M $1.58 M $1.69 M $6.37 M

FCAL(r=120cm)

11304 $2.83 $3.39M $3.18 M $3.39 M $12.79 M

$250 per crystal , $300 per PMT, $281 per ADC channel, $300 per HV channel

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Possible cutting

price

PrimEx (1200 channels of crystal and PMT)

$0.66 M

FCAL (2800 channels of ADC )

$0.84 M

total $1.50 M

Detection of recoil p by GlueXDetection of recoil p by GlueX

2525

Reconstructed missing mass and efficiency Reconstructed missing mass and efficiency

2626

p p

Kinematics of Recoil ProtonKinematics of Recoil Proton

• Polar angle ~55Polar angle ~55oo-80-80oo

• Momentum ~200-1200 Momentum ~200-1200 MeV/cMeV/c

Angle θη (Deg)

Recoil θp vs θη (Deg)

Recoil Pp (GeV) vs θp (Deg) 2727

Recoil θp (Deg) Recoil Pp (GeV)

Comparison of different crystalsComparison of different crystals(From R. Y. Zhu)(From R. Y. Zhu)

2828

How Many How Many ηη’s Can We Make?’s Can We Make?A year of Jlab operations is about 32 weeks. Assuming 50% efficiency for the accelerator and end-station, that is 112 live days.

With a 30 cm LH2 target, 70 nb cross section, and 2.0E7 gammas/second, we can produce 1.7E7 η’s per year.

The number of accepted η decays per year would be ~1/3 this, or ~4E6 per year.

η production is conservatively similar to KLOE

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Selection Rule Summary Table:Selection Rule Summary Table:ηη Decay to Decay to ππ’s and ’s and γγ’s’s

Gamma Column

implicitly includes γ*e+e-

Key: C and P

allowed, observed

Forbidden by energy

and momentumconservatio

n.

C and Pallowed, upper

limits only

C violating,

CP conserving, etc.

L = 0

L = 1

L = even or odd (no parity

constraint).....

3030

Major background in CB-AGS experimentMajor background in CB-AGS experiment

3131

data

MC

03

np

np 00

MC

MC

Low Energy Low Energy η η Production Continue Production Continue KLOE experiment KLOE experiment

B. Micco et al., Acta Phys. Slov. 56 (2006) 403 B. Micco et al., Acta Phys. Slov. 56 (2006) 403

Produce Produce ΦΦ through e through e+ee- collision at collision at √s~1020 MeV√s~1020 MeV

The decay The decay η→η→00γγγγ proceeds through: proceeds through: Φ→Φ→ηη, , η→η→00γγγγ, , 00→→γγγγ

Final result:Final result:(η→0γγ)=0.109±0.035±0.018

eV η→η→00 events events

1267

3232

Can we use existing FCAL located at 10 m?Can we use existing FCAL located at 10 m?

PWO

Pb

Pbσ=6.7 MeV

σ=16.2 MeV

σ=14.5 MeV

Z=5.5 m

Invariant Mass of 4γ (GeV)

Invariant Mass of 4γ (GeV)

Invariant Mass of 4γ (GeV)

Z=5.5 m

3333

Resolution of ElasticityResolution of Elasticity

Elasticity Elasticity

PWO Pb

σ=0.0121 σ=0.0257

3434

Figure of MeritFigure of Merit

B

S

N

NFOM

•Signal is η→π0γγ•Background is η→3π0

•Signal window is ±3σ118x118 cm2 PWO

Cal.

150x150 cm2 PWO Cal.

3535

Experiment Figure of Merit Experiment Figure of Merit for “Forbidden Branch” Searchesfor “Forbidden Branch” Searches

In C and CP violation searches in η decays to date, it’s been true that Bkg Events >> Signal Events. Since the background fluctuations are sqrt(N), the upper limit for the branching ratio at ~95% CL is then approximately

BR upper limit ≈ 2*sqrt(fbkg*NMε)/NMε = 2*sqrt(fbkg/NMЄ)where

NM= number of mesons decaying into the experimental acceptanceЄ = efficiency for detecting products from the signal branch

fbkg = fraction of NM which remains in the signal box after all cuts

The figure of merit for experiments is therefore NMЄ /fbkg.

This means that to reduce the BR upper limit by one order of magnitude, one must either

•Increase NMЄ by TWO orders of magnitude, or •Decrease fbkg by TWO orders of magnitude.

While maintaining a competitive η production rate, Jlab would reduce BR upper limits by one order of magnitude using background reduction alone.

3636

Collaboration with Chinese InstitutesCollaboration with Chinese Institutes

• One week visit Beijing in Oct 2011: Peking One week visit Beijing in Oct 2011: Peking University, Chinese High Energy Physics Institute, University, Chinese High Energy Physics Institute, Chinese Theoretical Institute.Chinese Theoretical Institute.

• Peking University group showed strong interests Peking University group showed strong interests in making a significant contribution to the FCAL in making a significant contribution to the FCAL upgrade. MOU between Peking University and Jlab upgrade. MOU between Peking University and Jlab is in process. is in process.

3737

IIsland algorithm for the PWO calorimetersland algorithm for the PWO calorimeterby I. Larin by I. Larin

3838

Island algorithm:

1. Find maximum energy deposition cell 2.Declare all simply connected area around as initial “raw” cluster

3.Try to split “raw” cluster into many hits based on the shower profile function

PWO Transverse Shower ProfilePWO Transverse Shower Profile

3939

Experimental electron scan data (Ee~4 GeV)

extracted shower profile function