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
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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
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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
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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
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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