Search for Dark Particles at Belle and Belle II

Transcription

1 Search for Dark Particles at Belle and Belle II Igal Jaegle University of Florida for the Belle and Belle II Collaborations International Workshop on ee collisions from Phi to Psi June 6 3, 17 Mainz, Germany Igal Jaegle (UF) Dark Particle Searches Psi/Phi 17 1 / 16

2 Table of contents 1 Introduction Setup 3 Search for a dark vector gauge boson 4 Search for the dark photon and the dark Higgs boson 5 Search for the dark photon and light dark matter 6 Conclusion Igal Jaegle (UF) Dark Particle Searches Psi/Phi 17 / 16

3 Search for new hidden forces / Introduction Dark matter represents about 8% of all matters Dark matter naturally explained by Supersymmetry, but Absence of Supersymmetry in LHC gives new light to Dark Sector Models Search for new hidden forces accessible to Belle PRD (7) PRD (14) Coupling of charged matter to new, dark photon, A, q = εe L = 1 µν εf dark Fµν Coupling of all quarks to new, baryonic boson, U, g U = 4πα U L = 1 3 g U qγµ qu µ U',l +,π +,l,π Feynman diagram Feynman diagrams for hadronic U decay A short or long lived or invisible Above π threshold U short lived All models point to new particles with mass of the order of MeV GeV Igal Jaegle (UF) Dark Particle Searches Psi/Phi 17 3 / 16

4 Search for new hidden forces / Introduction Dark matter represents about 8% of all matters Dark matter naturally explained by Supersymmetry, but Absence of Supersymmetry in LHC gives new light to Dark Sector Models Search for new hidden forces accessible to Belle Branching ratio for A decay Branching ratio for U decay PRD (8) PRD (14) 1 BR ( final state) + e e µ + µ π + π τ + τ hadrons U' 1 m [GeV/c ] U' All models point to new particles with mass of the order of MeV GeV Igal Jaegle (UF) Dark Particle Searches Psi/Phi 17 4 / 16

5 KEKB and SuperKEKB KEKB/SuperKEKB collider, located in Japan, Tsukuba, is the world s highestluminosity electronposition collider 1999: Belle collected L int = 5 fb 1 at Υ(1S, S, 3S, 4S, 5S) and continuum 16: Belle II (upgrade version of Belle) expects to collect L int = 5 ab 1 Schematic view of KEKB S. Kurokawa and E. Kikutani, NIM A 499, 1 (3) KEKB beam vs. SuperKEKB nanobeam Belle II L peak = 8 35 cm s 1 Igal Jaegle (UF) Dark Particle Searches Psi/Phi 17 5 / 16

6 Belle and Belle II experiments CP violation measurement in the Bmeson system with Belle and BABAR, established the Kobayashi Maskawa mechanism as a valid description of CP violation in the Standard Model. Main motivations Study of CP violation (i.e. matterantimatter asymmetry) Study of heavy flavor Search for physics beyond the Standard Model Complementary to efforts at energy frontier Add PID in endcaps Add µ ID in endcaps Increase K S efficiency Improve IP and secondary vertex resolution Improve π/k separation Improve π efficiency Belle II is an upgrade of Belle Igal Jaegle (UF) Dark Particle Searches Psi/Phi 17 6 / 16

7 New Belle results, Phys. Rev. D 94, 96 (16) (Eunil Won et al.) Search for U π + π in D K S η, η U γ using 977fb 1 of Belle data Exclusive charm meson decays to reduce background ) Events/(3 MeV/c ) Events/(. MeV/c M(K η) (GeV/c ) S M D* (GeV/c ) K S η invariant mass D D mass difference Cut on D and mass difference and look at π + π γ invariant mass Igal Jaegle (UF) Dark Particle Searches Psi/Phi 17 7 / 16

8 Search for a light vector gauge boson Background estimated and subtracted using the side bands Events/(1 MeV/c ) 3 ) Events/(3 MeV/c M(π + π γ) (MeV/c ) M(π π ) (MeV/c ) π + π γ invariant mass π + π invariant mass after background substraction π + π line shape fitted by dγ ds P(s)F V (s) (mη s)3 s(1 4mπ /s)3/ [PLB 77, 43 (1) and PLB 77, 184 (1)] P(s) reactionspecific perturbative part F V (s) pion vector form factor No signal found, example of U MC sim. signal of 4 MeV/c mass is shown Igal Jaegle (UF) Dark Particle Searches Psi/Phi 17 7 / 16

9 New Belle limit PRD, Phys. Rev. D 94, 96 (16) (Eunil Won et al.) α U % CL limit on the baryonic fine structure constant Better limit for m U > 45MeV/c and φ e + e γ U mass (MeV/c ) Igal Jaegle (UF) Dark Particle Searches Psi/Phi 17 8 / 16

10 Search for the dark photon and the dark Higgs boson Belle limits, PRL (15). Production in the socalled Higgsstrahlung channels, e + e A h, with h A A. A and h assuming prompt decays m h > m A.1 < m A < 3.5 GeV/c and. < m h <.5 GeV/c + e * γ e α D : dark sector constant ε: kinetic mixing x ε * h' α D + l, hadron l, hadron + l, hadron l, hadron l, hadron + l, hadron exclusive channels: 3(l + l ), (l + l )(π + π ), (π + π )(l + l ), and 3(π + π ), where l + l is an electron or muon pair 3 inclusive channels for m A > 1.1 GeV/c : (l + l )X, where X is a dark photon candidate detected via missing mass If α D = 1, Higgsstrahlung channels most sensitive to A Igal Jaegle (UF) Dark Particle Searches Psi/Phi 17 9 / 16

11 Belle limits / results Belle limits for L = 977 fb 1 on B σ Born and σ Born 9% CL upper limit for each of the 13 final states 9% CL upper limit on the combined Born cross section 3 + 3(e e ) 3( µ + µ ) 3( π + π ) + (e e )(µ + µ ) + (e e )(π + π ) 6 [ab] B σ Born 3 ( µ + µ )(e + e ) ( µ + µ )(π + π ) ( π + π )(e + e ) ( π + π )(µ + µ ) + (e e )(µ + µ )(π + π ) [GeV/c ] 5 4 [ab] σ Born (e e )X (µ + µ ) X [ab]} Born #cal{b x σ (e e )(µ + µ )X 1 3 m [GeV/c ] Belle [GeV/c ] = 1(3) = 3(4) = 5 = 7 = m [GeV/c ] 9 % Credibility Level (CL) upper limit determined by Bayesian inference method with the use of Markov Chain Monte Carlo A. Caldwell et al., CPC 18 (9) 1979 Limits from 3(π + π ) and (e + e )X are the first placed by any experiment Igal Jaegle (UF) Dark Particle Searches Psi/Phi 17 / 16

12 Limits on the product of α D ε / results Belle combined limits compared to BABAR combined limits Belle limits for L = 977 fb 1 based on the Born cross section, ISR effect non negligible BABAR limits for L = 5 fb 1 based on the visible cross section PRL (1) ε α D = 1 GeV/c = 3 GeV/c = 5 GeV/c = 7 GeV/c = 9 GeV/c ε α D =.3 GeV/c m Belle upper limit Belle expected limit BaBar upper limit =.5 GeV/c m m [GeV/c ] m = 1. GeV/c m [GeV/c h' ] 1 3 = 1.5 GeV/c m = 3. GeV/c m % CL upper limit on the product α D ε versus dark photon mass (top row) and dark Higgs boson mass (bottom row) Assuming branching fractions and couplings versus cross section from B. Batell et al. PRD 79 (9) 1158 esults scale nearly linearly with integrated luminosity.this bodes well for future searches with Belle II. Igal Jaegle (UF) Dark Particle Searches Psi/Phi / 16

13 Belle II prospects for the Higgsstrahlung channels Predicted Belle II upper limits U αd ε in the α Dε vs m A vs m h plane by scaling the Belle limits linearly with the integrated luminosity: U αd ε U α D ε = L L, where the superscript corresponds to Belle values. L is integrated luminosity. The scaling uses both statistical and systematic uncertainties. ε α D ε α D 1 4 = 1 GeV/c..3.4 Belle upper limit BaBar upper limit m =.3 GeV/c = 3 GeV/c Belle II 5 fb Belle II 5 fb m =.5 GeV/c = 5 GeV/c m [GeV/c ] Belle II 5 ab Belle II 5 ab m = 1. GeV/c m [GeV/c h' ] 1 1 = 7 GeV/c 1 3 m = 1.5 GeV/c = 9 GeV/c.5 1 = 3. GeV/c m Igal Jaegle (UF) Dark Particle Searches Psi/Phi 17 1 / 16

14 Belle (II) prospect for the radiative decays Predicted Belle II upper limits extrapolated from BABAR PRL 113, 181 (14) (C. Hearty, BTIP14) ε e + e γa, A l + l, with l = e or µ Belle II will have an improve low multiplicity trigger compared to Belle (g) e WASA Phenix KLOE 13 KLOE (g) ± σ µ favored E774 DarkLight E141 VEPP3 MESA HADES HPS 1 APEX APEX BaBar Belle II 5 fb 5 fb 5 ab 5 ab 1 (GeV) m.4. Belle Belle II 5 [GeV/c ] m Left: Belle II prediction. Right: preliminary Belle and Belle II preliminary fiducial detection efficiency for A µ + µ Belle II will have a better efficiency for low momentum muon compared to Belle Igal Jaegle (UF) Dark Particle Searches Psi/Phi / 16

15 Belle (II) prospect for the radiative decays Predicted Belle II upper limits extrapolated from BABAR PRL 113, 181 (14) (C. Hearty, BTIP14) ε e + e γa, A l + l, with l = e or µ Belle II dimuon invariant mass resolution improved by 35% compared to Belle 3 4 (g) e (g) ± σ µ favored E774 DarkLight VEPP3 E141 WASA Phenix MESA HADES HPS KLOE 13 1 APEX KLOE 14 APEX BaBar Belle II 5 fb 5 fb 5 ab 5 ab 1 (GeV) m count [a.u.].5 1 Belle σ = 19.9 MeV/c Belle II σ = 1.7 MeV/c [GeV/c ] m µ + µ Left: Belle II prediction. Right: simulation for m A = 5.15 GeV/c Complementary to fixed target experiments Igal Jaegle (UF) Dark Particle Searches Psi/Phi / 16

16 Belle (II) prospect for the radiative decays Predicted Belle II upper limits extrapolated from BABAR arxiv:88.17 (C. Hearty, BTIP14) e + e γa, A χχ, χ light dark matter R. Essig et al. arxiv: Require implementation of a single photon trigger in Belle II ε (g) e 3 (g) ± µ σ favored Belle II 5 fb BaBar expected 5 fb 5 ab 5 ab 4 1 (GeV) m Left: Belle II prediction. Right: Simulated monoenergetic photon signature for m A = 6 GeV/c Belle II is expected to have a better single photon trigger with a lower energy sum than BABAR Igal Jaegle (UF) Dark Particle Searches Psi/Phi / 16

17 Conclusion New Belle limit has been presented on the baryonic fine constant, α U, in a exclusive charm decays 8 < m U < 55 MeV/c We found that: No signal found Better limit for m U > 45MeV/c and φ e + e γ Belle limits for prompt decays of the dark photon and the dark Higgs boson:.1 < m A < 3.5 GeV/c. < m h <.5 GeV/c We found that: No significant excess over the background estimation Belle limit improvement scales nearly linearly with integrated luminosity Ongoing Belle analysis on e + e A γ (prompt and displaced vertex), e + e χχγ, e + e µ + µ Z, and e + e τ + τ h Belle II will also search for dark particles With 5 ab 1, Belle II might potentially also crosscheck any signals discovered by fixed target experiments First collisions in 18 with partial vertex detector Thank you for your attention Igal Jaegle (UF) Dark Particle Searches Psi/Phi / 16