Search for New Physics via η Rare Decays Search for New Physics via η Rare Decays Liping Gan University of North Carolina Wilmington 1 Outline Outline  Physics Motivation Why η is unique for new physics search?Why η is unique for new physics search? η →  0 η →  0  η →  0  0η →  0  0 η →  0 , η → 3 η →  0 , η → 3   Suggested experiment in Hall D  Summary

Why η 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 Γ η =1.3 KeV is extremely narrow (comparing to Γ ρ = 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/c 2 ) sensitive to QCD symmetry breakings 2

Examples of the η Rare Decay Channels ModeBranching RatioPhysics Highlight π0 π0π0 π0 <3.5 × CP, P π 0 2γ ( 2.7 ± 0.5 ) × 10 − 4 χPTh, Ο(p 6 ) 3γ3γ <1.6 × 10 − 5 C π0 γπ0 γ <9 × 10 − 5 C π0 π0 γπ0 π0 γ <5 × 10 − 4 C π+ π−π+ π− <1.3 × 10 − 5 CP, P π0 π0 π0 γπ0 π0 π0 γ <6 × 10 − 5 C π0 e+ e−π0 e+ e− <4 × 10 − 5 C 4π04π0 <6.9 × 10 − 7 CP, P 3

Study of η →  0  0 Reaction  The Origin of CP violation is still a mystery  CP violation is described in SM by Kobayashi-Maskawa (KM) mechanism in Yukawa couplings (flavor-changing ) → a single phase in the CKM quark mixing matrix. Deviations from the KM predictions would be signatures of new physics.  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 additional sources of CP violation. New source of CP violation is also necessary for baryogenesis.  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 yet. The flavor-conserving region remains much less explored. The later represents a better chance for new physics due to suppressed KM contribution.  The η →  0  0 is one of a few available flavor-conserving reactions listed in PDG to test CP violation. The SM predicts: BR<2x An extended SM calculation including spontaneous CP violation in the Higgs sector and a θ -term in the QCD Lagrangian predicts: BR<2x  Unique test of P and CP symmetry violations, and search for new physics beyond SM 4

η →  0 γ and η →3 γ Decays  Both channels are forbidden by C invariance in the Standard Model  Offer an unprecedented opportunity for searching new C violation in the electromagnetic interaction of hadrons.  Current experimental limits: BR( η→  0 γ )<9x10 -5, BR( η→3 γ )<1.6x

Study of the η →  0  Decay AAAA stringent test of the χPTh prediction at Ο(p6) level TTTTree level amplitudes (both Ο(p2) and Ο(p4)) vanish; ΟΟΟΟ(p4) loop terms involving kaons are suppressed by large mass of kaon  Ο Ο Ο Ο(p4) loop terms involving pions are suppressed by G parity TTTThe first sizable contribution comes at Ο(p6) level AAAA long history that experimental results have large discrepancies with theoretic predictions. CCCCurrent experimental value in PDG is BR(η→0 )=(2.7±0.5)x10-4 6

Theoretical Status on η →  0  Average of χPTh 0.42 By E. Oset et al. 7

History of the η →  0  Measurements 8 After 1980 A long standing “η” puzzle is still un-settled.

High Energy η Production GAMS Experiment at Serpukhov D. Alde et al., Yad. Fiz 40, 1447 (1984)  Experimental result was first published in 1981  The η’s were produced with 30 GeV/c  - beam in the  - p → ηn reaction  Decay  ’s were detected by lead- glass calorimeter Major Background Major Background   - p →  0  0 n  η →  0  0  0 Final result: Final result:  (η →  0   (η →  0  ) = 0.84±0.17 eV η →  0  events 40 η →  0  events

Low energy η production CB experiment at AGS Low energy η production CB experiment at AGS S. Prakhov et al. Phy.Rev.,C78, (2008)  The η’s were produced with 720 MeV/c  - beam through the  - p → ηn reaction  Decay  ’s energy range: MeV Final result: Final result:  (η →  0  ) = 0.285±0.031±0.061 eV η →  0  events 92±23 η →  0  events η →  0  0  0 NaI(T1) 10

Advantages of Jlab  High energy tagged photon beam to reduce the background from η → 3  0  Lower relative threshold for  -ray detection  Improve calorimeter resolution  Detecting recoil p’s to have an independent way to reduce non-resonant  p →  0  0 p and other combinatory backgrounds  High resolution, high granularity PbWO 4 Calorimeter  Higher energy resolution → improve invariant mass and elasticity spectrum  Higher granularity → better position resolution and less overlap clusters to reduce background from η → 3  0  Fast decay time (~30ns) → less pile-up clusters  High statistics to provide a precision measurement of Dalitz plot High energy η-productionLow energy η-production GAMS CB KLOE 11

12 Suggested Experiment in Hall D 75 m Counting House GlueX FCAL Simultaneously measure the η →  0 , η →  0  0, η → 3 , and  η produced on LH 2 target with 11 GeV tagged photon beam γ+p → η+p  p →  0  0 p and other combinatory background by detecting recoil p’s with GlueX detector  Further reduce  p →  0  0 p and other combinatory background by detecting recoil p’s with GlueX detector  Forward calorimeter (upgraded with high resolution, high granularity PbWO 4 ) to detect multi-photons from the η decays 12 η→0η→0 FCAL Kinematics of recoil protons: Kinematics of recoil protons: Polar angle ~55 o -80 oPolar angle ~55 o -80 o Momentum ~ MeV/cMomentum ~ MeV/c

Probability of two-cluster separation vs. distance between hits by I. Larin 13 Study done by using PrimEx-II snake scan data  First cluster: “permanent” with energy 5 GeV  Second cluster: “moving” with energy 1-5 GeV  Artificially split events are counted as missing Reconstruction efficiency (100%) Separation distance (cm) Pb glassPWO

S/N Ratio vs. Calorimeter Types signal:, background:, 100 days beam time 14 Invariant Mass of 4 γ (GeV) d min =2.5cm S/N=7.74 d min =5.5cm S/N=8.83x10 -2 PWO Pb Glass Invariant Mass of 4 γ (GeV) Elasticity Invariant Mass of 4 γ (GeV) Event selection cuts: 1.Elasticity 2.Invariant mass. PWO Pb Glass Major improvement: 1.Granularity 2.Resolutions.

Invariant Mass and Elasticity Resolutions PWO Pb glass σ=15 MeV σ=6.9 MeV σ=3.2 MeV σ=6.6 MeV  M   0 M  0  M  15 σ= σ= Elasticity

Jlab vs. Low Energy Facilities (CB) 16 Jlab Low Energy Facility

Acceptance Acceptance x150 cm 2 FCAL 118x118 cm 2 FCAL

Rate Estimation The  +p → η+p cross section ~70 nb (θ η =1-6 o ) The  +p → η+p cross section ~70 nb (θ η =1-6 o ) Photon beam intensity N γ ~2x10 7 Hz (for E γ ~ GeV) Photon beam intensity N γ ~2x10 7 Hz (for E γ ~ GeV) The η →  0  detection rate: (a) BR(η →  0  )~2.7x10 -4The η →  0  detection rate: (a) BR(η →  0  )~2.7x10 -4 (b) average detection efficiency is :~26% (118x118 cm 2 FCAL) and (b) average detection efficiency is :~26% (118x118 cm 2 FCAL) and ~47% (150x150 cm 2 FCAL) ~47% (150x150 cm 2 FCAL) 18  factory!

Statistical Error on dΓ/dM γγ for η  π 0 2γ 112 days 12 days This figure gives a very rough idea how statistics limits our ability to probe the dynamics of the η  π 0 2γ decay. Assumptions are 18.6 accepted events per live day, negligible background, and 7 bins spanning Prakhov et al., PRC 78, (2008). 19

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Summary 12 GeV tagged photon beam with GlueX setup will provide a great opportunity for precise measurements of various η rare decays to test higher order χPTh, C, P and CP symmetry violations, and search for new physics beyond the Standard Model12 GeV tagged photon beam with GlueX setup will provide a great opportunity for precise measurements of various η rare decays to test higher order χPTh, C, P and CP symmetry violations, and search for new physics beyond the Standard Model Propose simultaneous measurements on BR(η →  0  ), BR(η →  0  0 ), BR(η → 3  ), and BR(η →  0  ).Propose simultaneous measurements on BR(η →  0  ), BR(η →  0  0 ), BR(η → 3  ), and BR(η →  0  ). Three experimental techniques will be combined:Three experimental techniques will be combined: 1.12 GeV high intensity tagged photon beam to produce η’s. 2.Further reduce the  p →  0  0 p and other combinatory backgrounds by detecting recoil p with GlueX detector 3.Upgrade FCAL with PbWO 4 crystals  High high granularity calorimeter to reduce the η →  0  0  0 background due to over-lap showers.  Fast decay time to reduce low energy pile-up clusters  High energy and position resolutions to have precise invariant mass and elasticity spectrum for event selection 21

The End Thanks you! 22

Examples of the η’ Rare Decay Channels ModeBranching RatioPhysics Highlight π0 π0π0 π0 <1.0 × CP, P π0 e+ e−π0 e+ e− <1.4× 10 −3 C 3γ3γ <1.0×10 − 4 C ηe- e+ηe- e+ <2.4× 10 −3 C 23

Budget vs. Acceptance Size of Cal.(cm 2 ) #crystalsCrystal Cost PMTsADCHVTotal 118x $0.87 M$1.04 M$0.98 M$1.04 M$3.93 M 150x $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 24 Possible cuttingprice 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 GlueX 25

Reconstructed missing mass and efficiency 26

Kinematics of Recoil Proton Polar angle ~55 o -80 oPolar angle ~55 o -80 o Momentum ~ MeV/cMomentum ~ MeV/c Angle θ η (Deg) Recoil θ p vs θ η (Deg) Recoil Pp (GeV) vs θp (Deg) 27 Recoil θp (Deg) Recoil Pp (GeV)

Comparison of different crystals (From R. Y. Zhu) 28

How Many η’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 29

Selection Rule Summary Table: η Decay to π’s and γ’s ηXηX 0π0π1π1π2π2π3π3π4π4π 0γ0γ P, CP 1γ1γ C, CP 2γ2γ 3γ3γ CCCCC 4γ4γ Gamma Column implicitly includes γ*  e + e - Key: C and P allowed, observed Forbidden by energy and momentum conservation. C and P allowed, upper limits only C violating, CP conserving, etc. L = 0 L = 1 L = even or odd (no parity constraint). C, CP 30

Major background in CB-AGS experiment 31 data MC

Low Energy η Production Continue KLOE experiment B. Micco et al., Acta Phys. Slov. 56 (2006) 403  Produce Φ through ee collision at √s~1020 MeV  Produce Φ through e + e - collision at √s~1020 MeV  The decay η→  0 γγ proceeds through: Φ→  η, η→  0 γγ,  0 →γγ Final result: Final result:  (η →  0 γγ)=0.109±0.035±0.018 eV η →  0  events 32

Can we use existing FCAL located at 10 m? PWO Pb σ=6.7 MeV σ=16.2 MeV σ=14.5 MeV Z=5.5 m Invariant Mass of 4 γ (GeV) Z=5.5 m 33

Resolution of Elasticity Elasticity PWO Pb σ= σ=

Figure of Merit Signal is η →π 0 γγ Background is η →3π 0 Signal window is ±3σ 118x118 cm 2 PWO Cal. 150x150 cm 2 PWO Cal. 35

Experiment Figure of Merit for “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(f bkg *N M ε)/N M ε = 2*sqrt(f bkg /N M Є) where N M = number of mesons decaying into the experimental acceptance Є = efficiency for detecting products from the signal branch f bkg = fraction of N M which remains in the signal box after all cuts The figure of merit for experiments is therefore N M Є /f bkg. This means that to reduce the BR upper limit by one order of magnitude, one must either Increase N M Є by TWO orders of magnitude, or Decrease f bkg 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. 36

Collaboration with Chinese Institutes One week visit Beijing in Oct 2011: Peking University, Chinese High Energy Physics Institute, Chinese Theoretical Institute.One week visit Beijing in Oct 2011: Peking University, Chinese High Energy Physics Institute, Chinese Theoretical Institute. Peking University group showed strong interests in making a significant contribution to the FCAL upgrade. MOU between Peking University and Jlab is in process.Peking University group showed strong interests in making a significant contribution to the FCAL upgrade. MOU between Peking University and Jlab is in process. 37

I sland algorithm for the PWO calorimeter by I. Larin 38 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 Profile 39 Experimental electron scan data (E e ~4 GeV) extracted shower profile function