SEARCHES FOR LIGHT NEW PHYSICS WITH BABAR

Transcription

1 SEARCHES FOR LIGHT NEW PHYSICS WITH BABAR Bertrand Echenard on behalf of the BABAR Collaboration California Institute of Technology PANIC11, Cambridge p. 1

2 Light exotic particles could be discovered at BABAR or New Physics probed at TeV scale! Discovery potential for light Higgs, dark matter, dark forces, LFV,... A hunt for Light Higgs in ϒ(3S,2S) decays Lepton universality breaking in ϒ(1S) decays Dark Matter in ϒ(1S,2S,3S) decays Dark forces in e+e- interactions See also: M. Bellis thursday afternoon (parallel 5G) Baryon/lepton number violation at BABAR p. 2

3 BABAR experiment ( ) BABAR collected around 513 fb-1 of e+e- collisions around the ϒ(4S) BABAR data sample contains ~470 x 106 ϒ(4S) ~120 x 106 ϒ(3S) ~100 x 106 ϒ(2S) (10x Belle, 25x CLEO) (10x CLEO) ~ 18 x 106 ϒ(1S) from ϒ(2S) p+p- ϒ(1S) p. 3

4 Upsilon resonances e+e- g* ϒ(nS) Beam energy spread ~ 5 MeV CLEO CESR BB threshold G1S,2S,3S~ kev G4S~ 20 MeV BF( ϒ(nS) X ) / BF(ϒ(4S) X) = G4S,total / GnS,total (n=1,2,3) Significantly better sensitivity to direct production of light degrees of freedom at narrow resonances p. 4

5 LIGHT HIGGS p. 5

6 Light Higgs Many SM extensions (NMSSM, Type II 2HDM,...) include the possibility of a light Higgs NMSSM proposed to solve the m problem, adding one CP-odd Higgs, one CP-even Higgs and one neutralino to MSSM content A light CP-odd Higgs A0 with mass lower than 2mb is not excluded by LEP constraints Radiative ϒ(nS) decays (n=1,2,3) offer an ideal environment to search for light Higgs Radiative ϒ(nS) g A0 production tanb=10, m=150 GeV, M1,2,3 =100,200,300 GeV Fully reconstructed in A0 m+m Invisible decay A c1 c1 if ma0 > 2mc 0 Mixing hb A0 could enhancement the rate BF(Υ g A0) Partially reconstructed in A0 t+t-,qq 0 < ma0 < 2mt 2mt < ma0 < 7.5 GeV 7.5 < ma0 < 8.8 GeV 8.8 < ma0 < 9.2 GeV Can have a very large branching fraction Shrok,Suzuki, PLB 110, 250 (1982) Hiller, PRD 70, (2004) Dermisek,Guinon,McElrath., PRD 76, (2007) A0 = cosqa AMSSM + sinqa AS p. 6

7 Light Higgs Many SM extensions (NMSSM, Type II 2HDM,...) include the possibility of a light Higgs NMSSM proposed to solve the m problem, adding one CP-odd Higgs, one CP-even Higgs and one neutralino to MSSM content A light CP-odd Higgs A0 with mass lower than 2mb is not excluded by LEP constraints Radiative ϒ(nS) decays (n=1,2,3) offer an ideal environment to search for light Higgs Lepton universality Light CP-odd Higgs in NMSSM, mixing with hb ϒ(nS) l l independent of lepton in SM (up to small mass effects) 1 R tm ~ Rtl resonant non-resonant Total New physics can induce deviations. Effects often larger if one lepton is a tau E. Fullana and M. Sanchis-Lozano, Int. J. mod. Phys. A19 (2004) 2183; Phys. Lett. B653 (2007) 67. F. Domingo et al., JHEP 0901 (2009) 61 p. 7

8 ϒ(3S,2S) A0, A Analysis overview PRL103, (2009) Event selection Two tracks and a photon with Eg* > 0.2 GeV Particle Id, one or two tracks must be identified as muon(s) Energy and beam spot constraints for ϒ(2,3S) candidate Muon pair and photon must be back-to-back in the CM frame Major backgrounds QED: e+e- g m+m r0 production in ISR: e+e- g r0 g p+p ϒ(1S) production in ISR: e+e- g ϒ(1S) ϒ(1S) in ϒ(2,3S) decays: ϒ(2,3S) g cb, cb gϒ(1s) Signal extraction Fit the reduced mass mr = (m2a0-42mm)1/2 Scan A0 mass GeV in steps of 2-5 MeV p. 8

9 ϒ(3S,2S) A0, A Analysis overview PRL103, (2009) Event selection ϒ(3S) + - Two tracks and a photon with Eg* > 0.2 GeV Particle Id, one or two tracks must be identified as muon(s) Energy and beam spot constraints for ϒ(2,3S) candidate Muon pair and photon must be back-to-back in the CM frame r0 J/y Major backgrounds QED: e+e- g m+m r0 production in ISR: e+e- g r0 g p+pϒ(2s) + - ϒ(1S) production in ISR: e+e- g ϒ(1S) ϒ(1S) in ϒ(2,3S) decays: ϒ(2,3S) g cb, cb gϒ(1s) Signal extraction r0 Fit the reduced mass mr = (m2a0-42mm)1/2 J/y Scan A0 mass GeV in steps of 2-5 MeV p. 9

10 ϒ(3S,2S) A0, A Results PRL103, (2009) J/y ϒ(2S) Distribution of fit results, sign(nsig) x (2 log(lmax/l0))1/2 Υ(2S) Υ(2S) UL 90%CL Υ(3S) UL 90%CL Υ(3S) Combined No significant outliers, agrees with a standard normal distribution for null hypothesis No significant signal is observed! fy: effective Yukawa coupling of bound b-quark to A0 p. 10

11 ϒ(3S,2S) A0, A Results PRL103, (2009) tanb=10, m=150 GeV, M1,2,3 =100,200,300 GeV BF(Υ g A0) Upper limits (90% CL) 0 < ma0 < 2mt 2mt < ma0 < 7.5 GeV 7.5 < ma0 < 8.8 GeV 8.8 < ma0 < 9.2 GeV Significant constraints on other theories (axion-like particles, dark photons,...) p. 11

12 ϒ(3S,2S) A0, A0 t+t- - Analysis overview PRL103, (2009) Event selection Leptonic decays for both t: ee, em and mm modes Two oppositely-charged tracks and a photon with E g > 0.1 GeV Cuts on additional discriminating variables to improve purity ϒ(3S,2S) A0, A0 t+t- Υ(3S) g2 cbj(2p), cbj(2p) g1υ(2s) Major backgrounds QED: e+e- g t+t Higher order QED: e+e- e+e- e+e-,... ϒ(1S) in ϒ(2,3S) decays: ϒ(2,3S) g cb, cb gϒ(1s) Υ(3S) g2 cbj(2p), cbj(2p) g1υ(1s) Signal extraction Fit the photon energy spectrum for peak, include continuum and peaking backgrounds Scan A0 mass GeV in steps of 4-23 MeV E (GeV) p. 12

13 ϒ(3S,2S) A0, A0 t+t- - Results cb region excluded 90% CL UL BF(Υ g A0) BF(Υ(3S) ga0) x BF(A0 t+t-) x 10-3 UL 90%CL Upper limits (90%CL) BF(ϒ(3S) g A0) x BF(A0 t+t-) < (1.5-16) x 10-5 Upper limits (90% CL) No evidence of light CP-odd Higgs p. 13

14 ϒ(1S) A0, A0 invisible - Analysis overview PRL107, (2011) Event selection Tag the dipion transition ϒ(2S) p+p- ϒ(1S) using MVA classifier Two tracks of opposite charge and a photon with E g > 0.15 GeV No additional activity Missing energy and momentum Major backgrounds Continuum: e+e- g p+p-, ϒ(1S) g l+l Peaking: ϒ(2S) p+p- ϒ(1S), ϒ(1S) g nn, g KLKL Signal extraction Consider both ϒ(1S) ga0 (two-body) and ϒ(1S) gcc (multi-body) decays 2D fit the the recoil mass squared (M2recoil) and missing mass (M2x) squared Scan A0 mass GeV and c mass GeV p. 14

15 ϒ(1S) A0, A0 invisible - Results Most significant peak at ma = 7.58 GeV with significance 2.0s. Υ(1S) KLKL Recoil mass (GeV) Missing mass squared (GeV2) Probability >30% to observe a peak of this significance anywhere p. 15

16 ϒ(1S) A0, A0 invisible - Results ϒ(1S) ga0, A0 invisible ϒ(1S) g cc Predictions1,2) Upper limits (90% CL) BF(ϒ(1S) g A0, A0 invisible) < (1.9-37) x 10-6 BF(ϒ(1S) g A0, A0 invisible) ~ 10-4 BF(ϒ(1S) gcc) < (0.5-25) x 10-5 BF(ϒ(1S) gcc) Previous limit (CLEO3) ) Significant constraints on these models BF( ϒ(1S) g cc) ~ ) PRD 76, (2007) 2) PRD 80, (2009), arxiv: ) CLEO, PRD 51, 2053 (1995) p. 16

17 Light Higgs ϒ(3S) A0, A0 m+m- - Summary ϒ(3S) A0, A0 t+t- ϒ(1S) A0, A0 invisible BF(Υ g A0) Upper limits (90% CL) 0 < ma0 < 2mt 2mt < ma0 < 7.5 GeV 7.5 < ma0 < 8.8 GeV 8.8 < ma0 < 9.2 GeV Light CP-odd Higgs clearly disfavored p. 17

18 TEST OF LEPTON UNIVERSALITY p. 18

19 Test of lepton universality in ϒ(1S) decays PRL104, (2010) Test of lepton universality in ϒ(1S) decays, measure the ratio R (1S) = G(ϒ(1S) t+t- ) / G(ϒ(1S) m+m- ) tm SM: Rtm (1S) = CLEO1): Rtm (1S) = 1.02 ± 0.02 ±0.05 Analysis overview Tag ϒ(1S) mesons using the transition ϒ(3S) p+p- ϒ(1S) Fully reconstruct the ϒ(1S) m+m- final state Select all one-prong t decays and use multivariate classifier to improve t+t- purity Reconstruct signal using the m+m- and p+p- recoil mass variables Simultaneous fit on both datasets to extract Ntot and Rtm Extensive systematic studies on trigger, efficiencies, particle id, selection, PDF, final state radiation,... 1) PRL 98, (2002). p. 19

20 Test of lepton universality in ϒ(1S) decays PRL104, (2010) Test of lepton universality in ϒ(1S) decays, measure the ratio Muons R (1S) = G(ϒ(1S) t+t- ) / G(ϒ(1S) m+m- ) tm SM: Rtm (1S) = CLEO1): Mmm (GeV) Rtm (1S) = 1.02 ± 0.02 ±0.05 Muons Result Rtm(ϒ(1S)) = ± (stat) ± (syst) Mpp (GeV) No significant deviation from SM predictions Mpp (GeV) 1) PRL 98, (2002). Tau p. 20

21 DARK MATTER AND DARK FORCES p. 21

22 Generic Dark Matter model McElrath, PRD 72, (2005) Generic Dark Matter model Minimal model introducing a dark matter particle c and a new scalar or gauge boson A' to serve as a s-channel annihilation mediator (ma > 2mc) Scalar/boson A' couples to SM via Higgs mixing (scalar) or kinetic mixing with SM hypercharge (vector) Could explain 511 kev gamma rays excess from the galactic center reported by INTEGRAL and electon/positron excess by PAMELA/FERMI Could increase the invisible decay width of the Υ(1S) predicted by SM1) by orders of magnitude. Rate estimates are fairly model independent, based on cosmological observations and assuming time-reversal symmetry Rate predictions BF(ϒ(1S) cc ) ~ 4.2 x 10-4 (s-wave) (PRD 72, (2005)) BF(ϒ(1S) cc ) ~ 1.8 x 10-3 (p-wave) (PRD 72, (2005)) BF(ϒ(1S) nn ) ~ 9.9 x 10-6 (PLB 441, 419 (1998)) Large increase from SM predictions 1) PLB 441, 419 (1998). p. 22

23 ϒ(1S) invisible - Analysis overview PRL 103, (2009) Analysis strategy Tag ϒ(1S) mesons in ϒ(3S) p+p- ϒ(1S) transition using MVA classifier No extra activity Estimate peaking background from MC, use ϒ(1S,2S) l+l- with one or two reconstructed leptons to check and correct simulations Blind analysis, optimize analysis using sidebands and MC Background Non-peaking background: suppressed by a factor > 1000 Peaking background: ϒ(3S) l+l- decays Signal extraction Fit recoil mass Mrec= (s + M2pp -2sE*pp)1/2, should peak at ϒ(1S) Subtract peaking background p. 23

24 ϒ(1S) invisible - Results PRL 103, (2009) Fit Extended unbinned maximum likelihood fit of recoil mass Mrec Sum of signal + peaking background (Nsum) - Crystal-Ball (Gaussian with power-law tail) Non-peaking background Signal + peaking bkg - 1st order polynomial Results Fit yield (Nsum) Peaking bkg (MC) Signal only 2326 ± ± ± 105 ± 124 Upper limit (90% CL) BF(ϒ(1S) invisible) < 3.0 x 10-4 Previous measurements BF(Υ(1S) invisible) CLEO: BF < 3.9 x 90% CL PRD 75 (2007) Belle: BF < 2.5 x 90% CL PRL 98 (2007) No evidence of dark matter contribution to invisible ϒ(1S) decays p. 24

25 Dark forces Dark forces Models of dark matter introduce a new dark sector with a U(1)D gauge group (and corresponding charge). The corresponding gauge boson has a mass O(GeV) and is usually called a dark photon. Standard Model UY(1) x UD(1) Dark Sector GD e DLmix = e Fmn Bmn Interaction with the SM is via kinetic mixing e Fmn Bmn For a low mass dark photon, the mixing is essentially with the photon with a mixing strength e. Non-Abelian group allows non-elastic scattering that could explain the modulation observed by DAMA and the absence of signal reported by Xenon and CDMS. Parameter space is largely unexplored Essig et al. See for example: N. Arkani-Hamed et al., PRD 79, (2009) M. Pospelov et al., PLB 662 (2008) 53, PLB 671, 391 (2009). B. Batellet al., PRD 79, (2009) R. Essig et al., PRD 80, (2009) p. 25

26 Dark forces - Search for dark bosons arxiv: Search for e+e- A'* WD WD (l+l-) (l+l-) l=e, Two dilepton resonances with full beam energy and momentum Resonances have similar masses 4 Signal extracted using a cut-and-count analysis, background estimated from sidebands Expected Signal Use full BABAR dataset No evidence of dark boson found yet! points: bin UL line: average UL Assume Upper limits (90% CL) BF(W e+e-)=bf(w m+m-) s(e+e- WD WD (l+l-) (l+l-)) < ab gde2 < gd - dark sector coupling constant p. 26

27 Summary of results ϒ(3S) A0, A0 m+m- ϒ(3S) A0, A0 t+t- ϒ(1S) A0, A0 invisible Light Higgs BF(Υ g A0) Upper limits (90% CL) 0 < ma0 < 2mt 2mt < ma0 < 7.5 GeV 7.5 < ma0 < 8.8 GeV 8.8 < ma0 < 9.2 GeV Lepton universality Rtm(ϒ(1S)) = ± (stat) ± (syst) Generic dark matter BF(ϒ(1S) invisible) < 3.0 x 10-4 Dark forces s(e+e- WD WD (l+l-) (l+l-)) < ab p. 27

28 On our way back from the hunt... No significant evidence for light new Physics has been found and upper limits have been set with a sizable improvement over previous measurements Excluded a large fraction of parameters space for some New Physics models. A Super-B factory can significantly improve these searches, exploring regions difficult to access at the LHC, and help elucidate the structure of New Physics. Still many on-going analyses, the quest continues... p. 28