Search for dark forces at Belle and Belle II GIANLUCA INGUGLIA, DESY (HAMBURG) for the Belle and Belle II Collaborations Camogli 24/06/2015
STUDIES OF THE DARK SECTOR AT BELLE (AND PROSPECTS FOR BELLE II) OUTLINE Dark sector motivations Dark photon and/or dark Higgs radiative production and decays to SM final states Dark photon decays to DM Higgsstrahlung @ the Belle experiment: topology, events selection, extracted limits Dark sector at the Belle II experiments: expected sensitivity 2
Where does the dark sector come from? The dark sector models come into play first in the tentative to give an explanation to anomalies in the data observed in various experiments underground, at BNL, and in space. See below lists. [DAMA Collaboration] R. Bernabei et al. Eur. Phys. J. 313 C 56 (2008). First results from DAMA/LIBRA and the combined results with DAMA/NaI [CDMSII Collaboration] Z. Ahmed et al., Feb 11, 2010, 315 Science 327:16191621 arxiv:0912.3592 [astroph.co] 316 (2010). Results from the Final Exposure of the CDMS II Experiment [XENON Collaboration] E. Aprile et al. Phys. Rev. Lett. 318 105 131302 (2010). First Dark Matter Results from the XENON100 Experiment [CoGeNT collaboration] C.E. Aalseth et al. Phys. Rev. 320 Lett. 106 131301 (2011). Results from a Search for LightMass Dark Matter with a Ptype Point Contact Germanium Detector [Muon g2 Collaboration] G.W. Bennett et al. Phys. Rev. 322 D 73 072003 (2006). Final Report of the Muon E821 Anomalous Magnetic Moment Measurement at BNL. [PAMELA Collaboration] O. Adriani et al. Nature 458, 324 607609 (2009). Observation of an anomalous positron abundance in the cosmic radiation. [Fermi LAT. Collaboration] M. Ackermann et al. Phys. 326 Rev. D 82 092004 (2010). Fermi LAT observations of cosmicray electrons from 7 GeV to 1 TeV. [AMS Collaboration] M. Aguilar et al. Phys. Rev. Lett. 328 110 141102 (2013) First Result from the Alpha Magnetic Spectrometer on the International Space Station: Precision Measurement of the Positron Fraction in Primary Cosmic Rays of 0.5 350 GeV 3
The general idea: kinetic mixing γa' Dark photon first proposed in P. Fayet, Phys. Lett. B 95, 285 (1980), P. Fayet Nucl. Phys. B 187, 184 (1981). A' Note: ε is the strength of the kinetic mixing and it is supposed to be small, 105102. The Mass of the new boson should be in the range few*mevfew*gev (Nima ArkaniHamed et al. Phys. Rev. D 79, 015014, 2009). 4
Dask sector: how does it look like? γ A' mixing χ1 A' h' (... ) χ2 (?) 5
Dark photon: current limits BABAR: ArXiv: 1406.2980 [HepEx] Many constraints for different region of the parameter space from different experiments. Shown here: top left: BaBar, bottom left NA48, bottom right CMS (containing ATLAS) A ' e e,μ μ, prompt dark photon explanation of (g2)μ ruled out for A' ee ' NA48 arxiv:1504.00607 π0 decays arxiv:1506.00424 [hepex] Long lived, decays to leptons 6
Dark photon searches @ BELLE and BELLE II e (e ) γ e,μ,π A ' /L e, μ, π e (e ) ~ mm cm A' e,μ, π e,μ, π A'= dark photon, L= long lived light gauge boson. A' decays to SM final states through kinetic mixing (if allowed by kinematics). Low multiplicity final states. 2 charged tracks and 1 photon, prompt or displaced vertex decay. Could require dedicated trigger to increase efficiencies, especially for the displaced vertex case. A' decays depend on MA' : Decays to leptons require MA'>1.02 MeV/c2 Decays to hadrons require MA'>0.36 GeV/c2 h h New search just started for the reaction: e e Y (2 S ); Y ( 2 S) π π Y (1 S); Y (1 S) A 0 γ ; A 0 χ 0 χ 0 7 ArXiv:0903.0363 [hepph] M A ' [GeV /c 2 ]
Long lived dark photon search @ BELLE A ' l l (l=e,μ ) 2 M A ' =0.01 0.3 GeV /c 2 W A ' =1 KeV /c c τ=1 cm A' e e ~ mm cm I. Jaegle University of Hawaii This search is a part of more detailed search for long lived gauge bosons currently performed with Belle data. For this more general analysis we are studying the decays: L l l, h h (l=e,μ ; h=π, K ) And LFV decays: L μ e 8
Long lived dark photon search @ BELLE A ' / L e e 2 M A ' =0.01 0.3 GeV / c 2 M L =0.01 10.0 GeV /c W A ' =1 KeV / c c τ =1 10 cm A' 2 e e ~ 1 10 cm From Simulation General case (cτ=10cm) Dedicated lowmass case (cτ=1cm) 9
Invisible decays searches @ Belle and Belle II See R. Essig et al. JHEP11 (2013) 167. Igal Jaegle, University of Hawaii e (e ) γ χ e ( e) A' χ A'= dark photon, χ= dark matter particle (neutral under SU(3)xSU(2)xU(1)) A' decays to dark matter. Onshell (monoenergetic photon) or offshell (broad spectrum) with different gamma spectrum. * 2 radiative production in ee collisions E γ =( s M A ' )/ 2 s ( on shell ) only one photon in the final state with No existing limits Requires high rate single photon trigger, not available in Belle, however the analysis is ongoing using photon conversion. The BaBar Collaboration implemented a single photon 10 trigger ( arxiv:0808.0017 [hepex]), ongoing discussion for Belle II.
Higgsstrahlung See B. Batell, M. Pospelov, and A. Ritz Phys. Rev. D 79, 356 115008 (2009), arxiv:0903.0363 l,π e l, π A' γ e x ε A' * αd h' l, π A' A' l, π ( *) Higgsstrahlung process l,π h'= dark Higgs, l, π Higgsstrahlung: h' decays depending on Mh' and MA. Measures the coupling constant of the dark photon to the dark Higgs, αd. *)αd can be measured experimentally 11
Higgsstrahlung: topologies of final states Higgsstrahlung: h' decays depending on Mh' and MA. Measures the coupling constant of the dark photon to the dark Higgs, αd. *) Mh'>2MA' : h' A'A', Very low background. Exclusive: 3 charged tracks pairs with same invariant mass and total energy of the event. Inclusive: 2 charged tracks pairs, same invariant mass, third A' from 4mom. of ee system **) MA'<Mh'<2MA' : h' A'A'* ***) Mh'<MA': h' long lived and h' ll,ππ. 12
Higgsstrahlung at the Belle experiment: results 13
The Belle Experiment 1.0 ab1 14 13
Events selection From Igal Jaegle, University of Hawaii, Dark Interaction 2014: prompt production, Mh'>2MA' ' ' ' ' ' ' 15 14
Background From Igal Jaegle, University of Hawaii, Dark Interaction 2014 16
Background (ii) Phys. Rev. Lett. 114, 211801 (2015) 17
Belle limits Phys. Rev. Lett. 114, 211801 (2015) (add 3(ππ), limits on 2(ee)X first time placed) 2 N obs =σ Born (1 δ) 1 Π L B ϵ N bkg (1 δ)=isr correction factor 1 Π 2=vacuum polarization factor 18
Limits on αdε2 Phys. Rev. Lett. 114, 211801 (2015) Belle: 977 fb1 (Born cross section; ISR no negigible) Babar: 520 fb1 based on visible cross section (PRL 108 2118012012) 19
Dark sector at the Belle II experiment: expected sensitivity/limits 20
BELLE II Experiment More than 600 people, 99 institutions, 23 different countries/regions Belle II Detector EM Calorimeter: CsI(Tl), waveform sampling (barrel) Pure CsI waveform sampling (endcaps) electron (7 GeV) electron Beryllium Beryllium beam beam pipe pipe 2cm diameter 2cm(7GeV) diameter Vertex Detector 2 layers DEPFET 4 layers DSSD Central Drift Chamber He(50%):C2H6(50%), Small cells, long lever arm, fast electronics KL and muon detector: Resistive Plate Counter (barrel) Scintillator WLSF MPPC (endcaps) Particle Identification TimeofPropagation counter (barrel) Prox. focusing Aerogel RICH (fwd) positron (4GeV) 21 20
Belle/KEKB recorded ~1000 fb1. Now change units on yaxis to ab1 22
Dark photon, decays to SM particles: expected limits at Belle II compared to other experiments e e γ A ' γ e e, γ μ μ, prompt From Christopher Hearty, University of British Columbia/IPP Belle II Theory Interface Platform meeting 2014 Belle II limits scaled from BABAR 23
Dark photon, decays to DM particles: expected limits at Belle II compared to other experiments e e γ A ' γ χ χ From Christopher Hearty, University of British Columbia/IPP Belle II limits scaled from BABAR*. *The level 1 trigger required a single energy cluster > 800 MeV in the laboratory frame. Rate: 350 Hz (8% of the total) at a typical luminosity of 8 1033 running on the Υ(2S) or Υ(3S) resonances 24
STUDIES OF THE DARK SECTOR AT BELLE Conclusions Studies of the dark sector represents an interesting alternative to standard DM searches and are gaining daily attention from the scientific community. Very general analysis techniques useful to search for new particles Discussed ongoing analysis at Belle for radiative production of dark photon with subsequent decay to ee, μμ, ππ. Discussed possibility to study decays to DM. Shown results of Higgsstrahlung process at Belle Shown expected limits from Belle II THANK YOU FOR YOUR ATTENTION! 25