Achim Denig. InsEtute for Nuclear Physics Johannes Gutenberg University Mainz

Transcription

1 Achim Denig InsEtute for Nuclear Physics Johannes Gutenberg University Mainz July 21-24, 2014 Centerville, Cape Cod, USA 5th Intl. Symposium on Lepton Moments Achim Denig Rhad, γγ form factors and the Muon Anomaly

2 2 The Hadronic Contribution to (g-2) µ (g- 2) µ Standard Model Theory Theory R had ratio, i.e. σ had = σ( e + e - Hadrons) Meson transition form factors F(Q 2,Q 2 ) Perturbative Calculations (Theory) Hadronic Vacuum Polarization Hadronic Light-by- Light Scattering Electroweak Contribution (g- 2) µ Experiment (g- 2) µ Interpreta/on

3 3 Outline Hadronic Vacuum PolarizaHon <- > R had Overview hadronic cross sec=on measurements Ini=al State Radia=on: KLOE vs. BABAR BES III status and expecta=ons Hadronic Light- by- Light <- > F(Q 12,Q 22 ) Overview meson transi=on form factors BES III status and expecta=ons Conlusions & Outlook

4 4 R had Hadronic Cross Section σ had

5 5 Hadronic Cross Section Data (last 20 years) SLAC/Stanford BABAR s=10.58 GeV LNF/Frascati KLOE(-II) s=1.02 GeV R Scan < GeV Novosibirsk/CMD, SND KEK/Tsukuba BELLE-II s=10.58 GeV IHEP/Beijing BESII, R scan >2 GeV BESIII* s = GeV also new R scan > 2 GeV R Scan e+e- Radiative Return e+e-

6 6 Initial State Radiation Rev. Mod. Phys. 83, (2011)! IniHal State RadiaHon (ISR) aka RadiaHve Return ISR spectra measured by e + H rad γ ISR E CM e - E M hadr Hadrons Pioneered by KLOE Needs no systema=c varia=on of beam energy High sta=s=cs thanks to high integrated luminosi=es Precise knowledge of radia=ve correc=ons mandatory (H rad ) PHOKHARA event generator Czyż, Kühn, et al.! pqcd E, GeV EnHre E range <E CM accessible

7 7 Most relevant Channel: e + e - π + π - ρ resonance ρ - ω interference SystemaHc UncertainHes BABAR 0.5% KLOE 0.8% CMD2 0.8%* SND 1.5%* * limited in addi=on by sta=s=cs

8 8 Most relevant Channel: e + e - π + π - Note: KLOE05 superseded by KLOE08 ObservaHons KLOE and BABAR dominate the world average Rela=vely large systema=c differences, esp. above ρ peak Knowledge of a µ had drama=cally limited due to this difference

9 9 Status Hadronic Vacuum Polarization Future improvement of a µ had? 1 st priority: Clarify situa=on regarding π+π- (KLOE vs. BABAR puzzle) 2 nd priority: Measure 3π, 4π channels Ongoing ISR analyses BESIII, BEPC- II collider 3 rd priority: KK and higher mul=plici=es

10 10 BEPC II Project Storage Ring Linac BES- III Detector CM Energy GeV Design Luminosity 1033 cm- 2 s- 1 Achieved Luminosity 70%@ψ(3770) Achim Denig Rhad, γγ form factors and the Muon Anomaly

11 11 Data Samples for ISR Physics Integrated luminosi=es BESIII ψ(3770) XYZ ψ(2s) J/ψ ψ(4040) ) / 20 MeV -1 L ISR dt (pb e + E CM e - H rad E γ ISR Hadrons ISR luminosity = Ldt x H rad BABAR (500 fb ) BESIII E CM >3.77 GeV E cm (GeV)

12 12 BES III Detector Main DriX Chamber (MDC) σ(p)/p = 0.5% σ de/dx = 6.0% Time- of- flight system (TOF) σ(t) = 90ps (barrel) σ(t) = 110ps (endcap) EMC 6240 CsI(Tl) crystals σ(e)/e = 2.5% σ Z,Φ (E) = cm Muon Chambers 8 9 layers of RPC p>400 MeV/c δrφ = 1.4 ~ 1.7 cm SuperconducHng Magnet 1 T magne=c field

13 13 Flagship ISR Analysis: e + e - π + π - γ ISR Event yield aqer acceptance cuts only events / 20 MeV ρ - γ π + π MC - µ + µ γ MC data preliminary Features: J/ψ ψ(3770) data only (2.9 r - 1 ) no dedicated background subtrac=on tagged ISR photon m 2π [GeV] large sta=s=cs of e+e- ππγ events background dominated by e+e- µµγ data MC differences visible ini=al publica=on MeV

14 14 e + e - π + π - γ ISR : π - µ Separation TMVA overtraining check for classifier: CFMlpANN dx (1/N) dn/ Signal (test sample) Signal (training sample) Background (test sample) Background (training sample) Kolmogorov-Smirnov test: signal (background) probability = (0.455) preliminary µ π CFMlpANN response U/O-flow (S,B): (0.0, 0.0)% / (0.0, 0.0)% events / 5 MeV Event yield ππγ aqer π- µ separa=on TMVA method (Neural Network): trained using µµγ and ππππγ MC events informa=on based on track level efficiency matrix (p,θ) for data, MC correct for data - MC differences cross checked for different TMVA methods preliminary m 2π [GeV]

15 15 Measurement of µ + µ - γ: Data vs. QED Event yield µµγ aqer π- µ separa=on and all efficiency correc=ons χ 2 / ndf 134 / 134 events / 20 MeV data / MC data / MC π + π γ MC - µ + µ γ MC data preliminary p ± m 2µ [GeV] χ 2 / ndf 134 / 134 p ± Features: background from ππγ very small PHOKHARA accuracy <0.5% luminosity measurement based on Bhabha ev., 1.0% accuracy excellent agreement with QED Δ(MC/QED- data) = (0.51 ± 0.28) % accuracy on 1% level as needed to be compe==ve!

16 16 Result (still blind): σ(e + e - π + π - ) 2 normalizahon methods: 1) normaliza=on to L int (obtained from Bhabha events) bare(e + e! + )= N / exp L int H rad vac (1 + FSR ) 2) normaliza=on to µµγ events, i.e. R ra=o (ππγ/µµγ) L int, H rad, δ vac cancel in ra=o! bare(e + e! + + ) - )) [nb] π + π - (γ e σ bare (e luminosity / R ra=o FSR scale s=ll blinded no scale shll blind luminosity / R ratio using the luminosity using the R ratio Efficiency study ε exp Pion tracking Muon tracking Photon detec=on Pion PID (TMVA) Muon PID (TMVA) Electron PID (TMVA) FSR correct. + Unfolding preliminary s [GeV] 1 χ 2 / ndf / 60 p ± luminosity / R raho = (0.35 ± 1.68) % limited by low µµγ sta=s=cs

17 17 Meson Transition Form Factors F(Q 12,Q 22 )

18 18 Meson Transition Form Factors P γ* γ ( * ) Time- like transihon form factors: Dalitz decays 0 < q² < M P ² Annihila=on process q² = s > M P ² Space like transihon form factors: Two- photon produc=on of mesons in e+e-

19 19 Space-Like FFs γ γ * P Single Tag Method Selec=on criteria 1 electron (positron) detected 1 positron (electron) along beam axis Meson fully reconstructed cut on angle of missing momentum Momentum transfer tagged: Q 2 = - q 1 2 = - (p - p ) 2 Highly virtual photon Form Factor F(Q 2 ) π 0, η, ηʹ untagged: q 2 = - q 2 2 ~ 0 GeV 2 Quasi- real photon EKHARA event generator Czyż, Ivashyn!

20 20 Existing Data on SL Transition Form Factors e + e - e + e - π 0 Features: recent high- Q 2 data from BABAR and BELLE Q 2 > 4 GeV 2 above 1.5 GeV 2 data from CLEO below 1.5 GeV 2 data from CELLO, very poor accuracy low Q 2 range not covered most relevant for HLbL contribu=on to (g- 2) µ most relevant channels: π 0, η, η', ππ e + e - e + e - η e + e - e + e - η' ini=al BESIII publica=on < 3.1 GeV 2

21 21 BES III Analysis: e + e - e + e - π 0 L int : 927 pb - 1, Tagged Lepton: e - π 0 2-Octet Model η 2-Octet Model MC only Frac=on of full sta=s=cs π 0 Ψ(3770) Rad. Return (J/Ψ,Ψ') rad. Bhabha MC Sum η Event SelecHon: exactly one lepton candidate at least two, max four photons Helicity angle cos Θ H > 0.8 Kinema=c cuts to reject ISR background cut on angle of missing momentum Count π 0 yield in bins of Q 2 Strategy: dσ/dq 2 Form factor F(Q 2 )

22 22 BES III Analysis: e + e - e + e - π 0 only MC shown red error bars correspond to BESIII sta=s=cs Full Simula=on L int : 2.92 fb - 1 Single Tag with both, e ± Extract TFF for 0.3 Q 2 [GeV 2 ] 3.1 KLOE- II/Frasca= Unprecedented Q 2 < 1.5 GeV 2 Input for (g- 2) μ

23 23 23 Conclusions & Outlook

24 24 Conclusions and Outlook arxiv: arxiv: Exci=ng results to be expected from BESIII Precision R measurements relevant for HVP contribu=on to (g- 2) µ Space- like transi=on form factors of meson(s) Compe=ng experiments ongoing in Frasca=, Novosibirsk, soon BELLE- II (?) What accuracy can be achieved for a µ had? ReducHon of factor 2 of uncertainty in reach

25 25 Anomalous Magnetic Moment of the Muon New (g- 2) µ ring arrived at FNAL, also JPARC measurement Factor 4 improvement! Let's speculate assume new exptl. measurement will be 1 sigma lower than today's value assume we observe New Physics in (g- 2) µ without change in theore=cal uncertainty: Δa μ = a μ exp a μ SM = 4.3 sigma reduc=on of theore=cal uncertainty of factor 2: Δa μ = 7.7 sigma