Uppsala University. October 16, Dark Forces at Accelerators, Frascati, Oct π 0 decays with WASA-at-COSY. Carl-Oscar Gullström

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1 decays with decays with October 16, 2012 Dark Forces at Accelerators, Frascati, Oct. 2011

2 Outline decays with 1 2 COSY 3 4 5

3 decays with Mass: MeV /c 2 uū d d quark content: 2 Life time: s J PC = 0 + decay BR 2γ ± (%) e + e γ ± (%) e + e e + e (3.34 ± 0.16) 10 5 ν νγ < ν ν < e + e (7.48 ± 0.29) 10 8

4 COler SYncrotron Located in Jülich, Germany decays with COSY Ongoing experiment: ANKE PAX TOF completed experiments: COSY-11 EDDA Euroball GEM HIRES JESSICA MOMO NESSI PISA

5 decays with Explore the nature of light mesons and hadronic resonances collisions modes: pp pd dd WASA designed for leptonic decay CD FD COSY setup with pp pp ( )

6 CD FD decays with COSY setup with pp pp ( ) FD Range hodoscope: Plastic scintillators: tracking detectors: CD EM calorimeter: Plastic scintillators: tracking detectors: E dep Time, E φ, θ E dep Time E Momentum, charge, φ, θ

7 PID decays with pp pp 25 (mb) pp pp 1.3 (mb) pp dπ (mb) pp pnπ (mb) p-d separation in FD Cross sections at T lab p = 550 MeV. e + π + separation in CD COSY E E in FD E vs p q in CD ( E E possible)

8 Missing mass 2 proton decays with 2 FD protons 1 FD proton & 1 CD proton COSY : Data : MC pp pp : MC Coincidence from two elastic pp pp events : Total MC sample

9 Invariant Mass of 2γ and e + e γ decays with Missing Mass of 2 protons in FD vs Invariant Mass of 2γ Missing Mass of 2 protons in FD vs Invariant Mass of e + e γ COSY 2010 (reconstructed) 2012 (expected) produced γ

10 Single Dalitz decay decays with Transition Formfactor: q 2 = (P e + + P e ) 2 = Mγ 2 dγ dq = F ( q 2) ( 2 dγ dq ) point : Data : MC External conversion : MC : Total MC sample

11 Conversion reduction decays with Pellet target and Be-beam pipe to minimize external conversion σ() = σ( 2γ(γ e + e )) Conversion mainly in Be-beam pipe : Data : MC : MC External conversion : Total MC sample

12 decays with of high resolution data available Invariant Mass e + e : Data : MC : MC plus false e + from π + : MC External conversion : Total MC sample

13 decays with of high resolution data available Invariant Mass e + e : Data : MC : MC plus false e + from π + : MC External conversion : Total MC sample

14 New Physics in γe + e? New Boson that couples to γ [1] : γu γγ γe + e decays with : γe + e : Simulated U boson with Br=0.001 : SINDRUM γe + e [2] : 2010 : 2012 (expected) 1 M. Reece and L.-T. Wang JHEP (2009) 2 R. Meijer Drees et al. (SINDRUM 1 ), Phys.Rev.Lett. 68(1992) 3845h

15 New Physics in γe + e? decays with ( ) 3 Γ( γu) Γ( γγ) = ɛ2 F (mu 2 ) 2 1 m2 U m 2 : SINDRUM γe + e : 2010 : KLOE : a µ : 2012 (expected)

16 decay decays with in SM: One-loop at lowest order Suppressed w.r.t 2γ by α 2 and 2(m e /m π ) 2 Btheory SM (π0 e + e 8 [3] ) = (6.23 ± 0.09) 10 Fermilab 2007 (794 events in K L 3 ): Bno-rad KTeV (π0 e + e 8 [4] ) = (7.48 ± 0.29 stat ± 0.25 syst ) 10 Fig: Feynman diagram of in SM 3 A. Dorokhov, M. A. Ivanov, Phys. Rev. D 75 (2007) E. Abouzaid et. al, Phys. Rev. D 75 (2007)

17 decays with decay in SM: One-loop at lowest order Suppressed w.r.t 2γ by α 2 and 2(m e /m π ) 2 Btheory SM (π0 e + e 8 [5] ) = (6.23 ± 0.09) 10 Fermilab 2007 (794 events in K L 3 ): Bno-rad KTeV (π0 e + e 8 [6] ) = (7.48 ± 0.29 stat ± 0.25 syst ) 10 Fig: Feynman diagram of in SM Theory is 3.3 standard deviations lower than the KTeV result. 5 A. Dorokhov, M. A. Ivanov, Phys. Rev. D 75 (2007) E. Abouzaid et. al, Phys. Rev. D 75 (2007)

18 New Physics? MeV (light) Dark Matter [7] decays with Neutral scalar χ, m χ 1 10MeV χχ e + e Could explain the large amount of 511 kev photons from galactic center. [8] Mechanism for χ annihilation: light vector boson U, m U MeV If U couples both to l and q: can enhance B( ) 7 C. Boehm and P.Fayet, Nucl. Phys. B 683 (2004) Y Kahn,M. Schmitt, T.M.P. Tait, Phys. Rev. D 78 (2008)

19 Momentum resolution decays with and simulation at 2 and 4 % e + e mass resolution Lepton momentum resolution in central tracker: 2% (90 o, 50 MeV /c) - 12% (25 o, 150 MeV /c). Average resolution 2010 data (> 45 o ): 4%. Designed value: 2% Vertex point used to track particles with desired momentum resolution MC : : no vertex cuts σ = 4% : vertex cuts in X-Y σ = 3.0% : 3-D vertex cuts σ = 2.5%

20 decays with 15 event candidates in 2010 data Missing Mass of 2 protons in FD vs Invariant Mass of e + e Invariant Mass of e + e pair in CD Blue filled: Data Green: MC e + e γ background Red: MC plus e + e γ and external conversion

21 decays with 2012 run: produced week of test run: produced in current sample Extend upper limit on U-Boson search to lower masses 15 candidates (currently) 250 possible with new data and better calibration