October 2010 p. 2. Kobayashi and Maskawa were awarded the Nobel Prize ...
Dark forces and ... *Well established: 2 experiments with at least 5σ observation.
EXOTIC HADRONS, LIGHT HIGGS AND DARK FORCES AT BABAR Bertrand Echenard California Institute of Technology DPNC Seminar - October 2010
Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
p. 1
B-factories factories legacy
BEFORE B-FACTORIES
Confirm CKM mechanism as dominant source of CP-violation CP in meson decays Still not enough to explain matter-antimatter matter asymmetry → New Physics AND AFTER Kobayashi and Maskawa were awarded the Nobel Prize 2008 "for the discovery of the origin of the broken symmetry which predicts the existence of at least three families of quarks in nature."
Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
p. 2
Physics at BABAR
B → τν decays
Bottomonium ground state ηb
D0 – D0 mixing
Upper limit on τ LFV decays
AND MUCH MORE... More than 440 papers published by BABAR on many topics!
Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
p. 3
In this talk
Spectroscopy and exotic hadrons
Bertrand Echenard – Caltech
Search for Light Higgs
DPNC Seminar
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October 2010
Dark forces and dark matter
p. 4
PEP-II II and BABAR
PEP-II delivered ~553 fb-1 BABAR collected about 470 millions Υ(4S) 122 millions Υ(3S) 99 millions Υ(2S)
Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
p. 5
The BABAR detector
Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
p. 6
Spectroscopy and exotic hadrons
Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
p. 7
QCD and exotic hadrons
Besides mesons and baryons, other “exotic” combinations of quarks and gluons could exist (i.e. are not forbidden by QCD). This include for example
Hybrid
Glueball
State with excited gluonic degree of freedom Lattice predictions for lowest mass ccg ~ 4.2 GeV
Bound state of gluons
Tetraquark
Pentaquark
Four-quark bound states Large number of states expected
Five-quark bound states
DD(*) molecule
Hadrocharmonium
Loosely bound state of pair of mesons Small number of states
Charmonium state embedded in a 'shell' of light quark
c
c
And many more... Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
p. 8
Many new hadrons...
Since the last decade, many new states have been discovered at high-luminosity high B-factories (BABAR, Belle), charm-factories factories (BES, CLEO) and hadronic colliders (CDF, D0). Among these new states, some were expected, expected but some were not charmonium spectrum
bottomonium spectrum
Do we finally have observed exotic hadrons? T. Barnes, S. Godfrey, and E.S. Swanson, Phys. Rev. D72, 054026 (2005). Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
p. 9
The XYZ zoo The XYZ zoo Since the observation of the X(3872), many new similar states have been reported
Well established*
Need confirmation
X(3872)
X(3915)
G(3900)
X(3940)
Y(4008)
Z1+ (4050)
Y(4140)
JPC = 1++/2-+
JPC = 0/2?+
JPC = 1--
JPC = ??+
JPC = 1--
JPC = ???
JPC = ??+
Y(4260)
Y(4360)
JPC = 1--
JPC = 1--
X(4160)
Z2± (4250)
X(4350)
Z±(4430)
JPC = ??+
JPC = ???
JPC = 0,2++
JPC = ???
? X(4630) JPC
=
1--
*Well established: 2 experiments with at least 5σ observation Bertrand Echenard – Caltech
DPNC Seminar
Y(4660) JPC = 1--
References in appendix -
October 2010
p. 10
The X(3872)
B+
K+
Belle B+ → K+ π+π- J/ψ
π+π-
Discovered by Belle in exclusive → J/ψ decay, existence now firmly established. Most possibilities for conventional charmonium (ψ2,ψ3,hc',χc1') assignment ruled out by measurement of angular distribution or decay widths.
BABAR
Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
B+ →
K+
π+π-
J/ψ
CDF π+π- J/ψ
p. 11
The X(3872)
BABAR
Mass very close to DD* threshold, molecular state?
B0 → K+ π0π- J/ψ
B- → K0s π0π- J/ψ
Isosinglet, no X± (3872) found Branching fraction BABAR: B(X→γ ψ(2S))/B(X→γ J/ψ) = 3.4±1.4 Too large for molecule! Belle:
B(X→γ ψ(2S))/B(X→γ J/ψ)) < 2.1 @ 90% CL Compatible for molecule BABAR X(3872)→ J/ψ ω
Quantum numbers Belle : 1++ favored (no ρ−ω interference) CDF: 1++ or 2-+ BABAR: 2-+ favored → ηc2(1D) ?
CDF
Other possibilities tetraquark, charmonium-molecule mix, hybrid
No conclusive answer about its nature Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
p. 12
The Y(4008),Y(4260), Y(4360), Y(4660) family
BABAR Y(4260) → J/ψ π+π-
Several Y states produced in Initial State Radiation (ISR) Quantum number 1-- but only Y(4660) is close to a predicted 1-- cc state. No dominant open charm decay, as expected for charmonium, DD* molecule Non-trivial dipion distribution, f0(980) contribution?
Bertrand Echenard – Caltech
Belle Y(4008) and Y(4260)
DPNC Seminar
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October 2010
Belle Y(4360) and Y(4660)
p. 13
The Z±(4430)
BABAR
Belle B+ → Z- K, Z-→ψ(2S)πK*(892)
B+,0 → J/ψ π- K0,- and B+,0 → ψ(2S) π- K0,-π-
K*(1430)
M=4433± 4 ± 3 MeV Γ= 45+18-13 +30-13 MeV χ2/dof = 80.2/94 (6.5σ)
Clearly exotic state: tetraquark (ccdu) Observation from Belle (K* veto analysis) Non confirmation from BABAR
Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
p. 14
The Z±(4430)
Belle B+ → Z- K, Z-→ψ(2S)π- Dalitz analysis Belle DP analysis result
K* veto
M = 4443+15-12 +19-13 MeV Γ = 107+86-43 +74-56 MeV Significance 6.4σ BF(B+ → Z- K, Z→ψ ψ(2S)π π-) x 10-5 3.2 +1.8-0.9 +5.3-1.6 Belle 1.9 ± 0.8 (< 3.1) BABAR
No more contradiction, but confirmation of Z±(4430) needed
Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
p. 15
Other states
Z1+(4050) and Z2+(4250)
X(4160)
Y(4140)
Belle B+ → Kπ- χc1
Belle X(4160) → D*D*
CDF B → J/ψ φ K
X(4350) Belle X(4350) → J/ψ φ
All these states need confirmation
Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
p. 16
Summary
ηc2(1D) DD* molecule tetraquark, charmonium charmonium-molecule mix, hybrid
Coupled channel effect (E. ( Eichten et al., PRD 21 (1980) 203)
Hybrid J/ψ f0(980) bound state DD* molecule Tetraquark (ccss)
DD* molecule Tetraquark (ccud) ψ(2S) f0(980) bound state Tetraquark (ccss)
Still no clear idea about their nature Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
p. 17
Bottomonium ground state ηb Non-observation observation of the bottomonium ground state was an annoying thorn in the side of quarkonium spectroscopy. Finally, after 30 years of work BABAR Υ(3S)→ γ ηb First measurement of ηb by BABAR in radiative Υ(3S) and Υ(2S) decays, followed by CLEO.
Measured parameters BF (Υ(3,2S)→γ ηb) (10-4) 5.1 ± 0.7 / 3.9 ± 1.5 Υ(1S) – ηb(1S) mass splitting: 69.3 ± 2.8 MeV
Hyperfine mass splitting predictions (MeV): Potential models: pNRQCD: Lattice QCD:
36-100 (36-87 recent models) 60.3 ± 5.5 ± 3.8 ± 2.1 40-71
BABAR Υ(2S)→ γ ηb
CLEO Υ(3S)→ γ ηb
Confirmation from independent experiment or other decay channel desirable, as well as observation of ηb(2S)
Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
p. 18
Search for glueball Mark III J/ψ ψ→γ K+K- (KsKs)
Glueball: isoscalar meson made of gluons, expected to be produced in gluon-rich environment such as radiative J/ψ decays.
BES J/ψ ψ→γ K+K- (KsKs) K+K-
K+KPeak?
Glueball lattice QCD spectrum1)
KsKs
KsKs
Peak?
Crystal Barrel pp → π0π0,π π0η
Tensor ground state expected close to 2.2 – 2.5 GeV
Search for glueball in radiative J/ψ ψ decays
1) C. Morningstar and M. Peardon, PRD 60 (1999) 034509 Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
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Search for glueball - Initial state radiation
Select J/ψ ψ in ISR events
Initial State Radiation: Radiation of photon(s) by incoming electron(s) → Reduce center of mass energy
BABAR
√s' < √s
Production of many resonances, even with nominal √s fixed J/ψ ψ→γγ K+KBABAR
Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
J/ψ ψ→γγ KsKs BABAR
p. 20
Search for glueball - Results
No sign of glueball BABAR
KsKs
K+K-
Upper limit BF(J/ψ ψ → γξ) x BF(ξ ξ→KK) KK) @ 90% CL K+K- : 0.2 GeV ➡ Particle Id,, one or two tracks must be identified as muon(s) ➡ Energy and beam spot constraints for Υ(2,3S) (2,3S) candidate ➡ Muon pair and photon must be back-to-back in the CM frame
Major backgrounds ➡ QED: e+e- → γ µ+µ➡ ρ0 production in ISR: e+e- → γ ρ0 → γ π+π- Suppress by requiring both tracks identified as µ in the range 0.5 < mA0 < 1.05 GeV
➡ Υ(1S) production in ISR: e+e- → γ Υ(1S)
Distribution of µµ mass Υ(3S) ρ0
➡ Υ(1S) in Υ(2,3S) decays: Υ(2,3S) → γ2 χb(1,2P), χb(1,2P) → γ1 Υ(1S)
J/ψ
- Reject events with a secondary photon Eγ* > 0.1 (0.08) GeV for 2S (1S)
Signal efficiency: ~ 25% - 55% (as fcn of mR)
Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
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Υ(3S)→γγA0, A0→ττ+τ-
-
Analysis overview
Event selection ➡ Leptonic decays for both τ: ee, eµ and µµ modes ➡ Partially reconstructed,, 2 tracks of opposite charge and a photon with Eγ > 0.1 GeV ➡ Eight discriminating variables: Etot, PT, missing mass/angle, angle photon-lepton lepton plane, angle track-track track or track-photon, angle tracks
➡ Optimization in 5 overlaping regions (reduce discontinuities in efficiency)
Major backgrounds ➡ QED: e+e- → γ τ+τ➡ Higher order QED, such as e+e- → e+e- e+e-, e+e- → e+e-µ+µ➡ Υ(1S) in Υ(2,3S) decays: Υ(2,3S) → γ2 χb(1,2P), χb(1,2P) → γ1 Υ(1S)
Signal efficiency: ~ 10%-14% (ee), 22%-26% (eµ µ), 12%-20% (µµ) (as fcn of Eγ)
Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
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Υ(3S)→γγA0, A0→invisible
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Analysis overview
Event selection ➡ Invisible A0 decay,, only one single photon with E*γ > 2.2 GeV ➡ No charged tracks ➡ Additional discriminating variables: cos(θ*γ), extra neutral energy, photon quality
Single photon event
➡ Optimization in 2 regions (trigger performances) low E*γ : 2.2 < E*γ < 3.7 GeV high E*γ : 3.2 < E*γ < 5.5 GeV Major backgrounds ➡ QED: e+e- → γγ and e+e- → γγγ ➡ Radiative Bhabha: e+e- → e+e-γ ➡ Two-photon: e+e- → e+e- γ + X Signal efficiency: ~ 10% (E*γ > 3 GeV), ~20% (E*γ < 3 GeV) Trigger: special single photon trigger designed for this kind of analysis
Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
p. 29
Υ(3S,2S)→γγA0, A0→µ µ+µ-
-
Signal extraction
Fit procedure ➡ Extended unbinned maximum likelihood fit in 1951 intervals of reduced mass mr = (m2µµ- 42mµ)1/2 from 0.212 – 9.3 GeV
Υ(3S) data
➡ Signal - Sum of two Crystal-Ball Ball functions (Gauss + power-law power tail) ➡ Peaking background, φ,J/ψ,ψ(2S),Υ(1S) - Sum of two Crystal-Ball functions - J/ψ and ψ(2S) veto ➡ Continuum background - tanh for mA0 < 0.23 GeV, Chebychev polynomial above
Distribution of results No significant outliers, agrees with a standard normal distribution for null hypothesis
Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
p. 30
Υ(3S)→γγA0, A0→ττ+τ-
-
Signal extraction Bkg distribution for Eγ 3 GeV) - Resolution σ(m2X) 0.7 – 1.5 GeV2
mA0 = 5.2 GeV (low E*γ )
e+e- →γγ signal
➡ Signal - Crystal-Ball function ➡ QED: e+e- → γγ - Shape and yield fixed using data
mA0 = 7.275 GeV (high E*γ )
➡ Radiative Bhabha and two-photon - Exponential function (continuum) e+e- →γγ
No statistically significant signal
Bertrand Echenard – Caltech
continuum
DPNC Seminar
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October 2010
signal
p. 32
Υ(3S,2S)→γγA0, A0→µ →µ+µ-
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Results PRL 103, (2009) 081803
J/ψ ψ(2S)
Υ(2S)
UL (0.26-8.3)x10-6 @ 90%CL
Υ(3S)
UL (0.27-5.5)x10-6 @ 90%CL
tanβ=10, µ=150 GeV, M1,2,3 = 100,200,300 GeV
0 < mA0 < 2mτ 2mτ < mA0 < 7.5 GeV 7.5 < mA0 < 8.8 GeV 8.8 < mA0 < 9.2 GeV
Combined
A0 = cosθA AMSSM + sinθA AS
Light CP-odd odd Higgs clearly disfavored Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
p. 33
Υ(3S,2S)→γγA0, A0→µ →µ+µ-
-
Results PRL 103, (2009) 081803
J/ψ ψ(2S)
Υ(2S)
UL (0.26-8.3)x10-6 @ 90%CL
Υ(3S)
UL (0.27-5.5)x10-6 @ 90%CL
Combined
“Favored region” for axion-like particle
Severe constraints on axion-like axion particle Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
p. 34
Υ(3S)→γγA0, A0→ττ+τ-
-
Results PRL 103, (2009) 181801
tanβ=10, µ=150 GeV, M1,2,3 = 100,200,300 GeV
BF(Υ(3S)→ γA0) x BF(A0→τ+τ-) x 10-3 2mτ < mA0 < 7.5 GeV
7.5 < mA0 < 8.8 GeV
χb region excluded
90% CL UL
UL (1.5 - 16)x10-5 @ 90%CL
Upper limits (90%CL) BF(Υ(3S)→ γ A0) x BF(A0→τ+τ-) < (1.5 - 16) x 10-5 BF(ηb→τ+τ- ) < 8%
0 < mA0 < 2mτ 2mτ < mA0 < 7.5 GeV 7.5 < mA0 < 8.8 GeV 8.8 < mA0 < 9.2 GeV
No evidence of light CP-odd CP Higgs Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
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Υ(3S)→γγA0, A0→invisible invisible
-
Result Preliminary, arXiv:0808.0017
tanβ=10, µ=150 GeV, M1,2,3 = 100,200,300 GeV
7.5 < mA0 < 8.8 GeV 2mτ < mA0 < 7.5 GeV
mA0 < 2mτ
Upper limits (90%CL)
BF(Υ(3S)→ γ A0) x BF(A0→invisible) < (0.7 - 31) x 10-6
Very light Higgs also disfavored Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
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Υ(1S)→ττ+τ− / Υ(1S)→µ µ+µ−
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Analysis overview
Analysis strategy ➡ Measure ratio Rτµ(Y(1S)) = Γ(Υ(1S)→τ+τ−) / Γ( Γ(Υ(1S)→µ+µ− ) ➡ Tag Υ(1S) mesons using the transition Υ(3S)→ →π+π- Υ(1S) ➡ Fully reconstruct the Υ(1S)→µ+µ- final state, cut on track quality and particle identification for muons ➡ Select all one-track τ decays (no lepton id) ➡ Multivariate classifier (BDT) to improve τ+τ- purity variables: event shape, π+π- mass/angle, π/τ-daughter daughter angle,... ➡ Reconstruct signal using the µ+µ- and π+π- recoil masses Mrecoilππ = (s + M2ππ -2sE*ππ)1/2 Mµµ = Mass µ+µ- pair
Signal efficiency:
Bertrand Echenard – Caltech
Boosted decision trees
MC
εµµ~ 45% and εττ~ 17%
DPNC Seminar
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October 2010
p. 37
Υ(1S)→ττ+τ− / Υ(1S)→ →µ µ+µ−
-
Results PRL 104 (2010) 191801
Fit procedure
muon
➡ Extended unbinned maximum likelihood fit - muon sample: 2-dim likelihood on Mrecoilππ and Mµ+µµ+µ - tau sample: 1-dim likelihood on Mrecoilππ
➡ Simultaneous fit on both datasets to extract Ntot and Rτµ - Signal PDF fixed from MC - Bkg PDF floating (a few fixed from validation sample)
muon
Systematic studies / checks - Extensive studies on trigger, efficiencies, particle id, selection, PDF, final state radiation, ... - Repeat analysis using only tau leptonic decays → consistent results tau
Result Rτµ(Υ(1S)) = 1.005 ± 0.013 (stat) ± 0.022 (syst) SM: Rτµ(Υ(1S)) = 0.992
CLEO1): Rτµ(Υ(1S))) = 1.02 ± 0.02 ±0.05
No significant deviation from SM predictions 1) PRL 98 (2002) 052002. Bertrand Echenard – Caltech
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October 2010
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Dark matter and dark forces
Bertrand Echenard – Caltech
DPNC Seminar
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October 2010
p. 39
Dark matter
Dark matter (gravitational lensing)
Luminous matter (x-ray emission)
Existence of dark matter is well established, it constitutes about 23% of the mass-energy energy density of the observable universe.
Bertrand Echenard – Caltech
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October 2010
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A few anomalies FERMI1) FERMI HAZE2)
INTEGRAL3)
PAMELA4)
Excess of electrons / positrons Few / no antiprotons Large annihilation cross section
Dark matter with a new GeV-scale force ? 1) FERMI Collab., PRL 102, 181101 (2009) 2) D. Finkbeiner, Astrophys.J.614 (2004)186 3) G. Weidenspointner et al., Astron. Astrophys. 450, 1013 (2006); G. Weidenspointner et al. (2007), astro-ph/0702621. 4) PAMELA Collab., PRL 102 (2009) 051101
Bertrand Echenard – Caltech
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October 2010
p. 41
Dark matter and Dark force
Dark matter and Dark Force: TeV-scale Dark matter particle and a new force with a force-carrier φ having a mass around the GeV. Dark matter annihilate into a pair of φ bosons, and each boson into an e+e- pair. This naturally explain the previous anomalies:
e+ φ e-
- Hard lepton spectrum from boosted φ - No antiprotons, kinematically suppressed - Sommerfeld enhancement boosts the thermal cross-section to levels needed to explain the observations
“Sommerfeld enhancement”
See for example N. Arkani-Ahmed et al., PRD D79 (2009) 015014, M. Pospelov et al., PPLB 662 (2008) 53, PLB 671 (2009) 391. Bertrand Echenard – Caltech
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October 2010
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Inelastic dark matter
DAMA
Inelastic dark matter TeV-scale dark matter has an state a few MeV above the state. Enhance sensitivity of and decreases sensitivity of XENON.
Eur.Phys.J.C67 (2010) 39
excited ground DAMA CDMS/ CDMS
Science 327 (5973)
Can explain the positive observation from DAMA and null observations from CDMS/XENON
D.Tucker-Smith, Smith, Neil Weiner, PRD 64 (2001) 043502;PRD 72 (2005) 063509 Bertrand Echenard – Caltech
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October 2010
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Dark sector
The idea of a hidden sector interacting weakly with the standard model has a rich history (e.g axions). Recent astrophysical anomalies can be naturally by introducing a new ‘dark’ force(s) mediated by a new dark gauge boson(s) with a mass around a GeV (regardless of the detailed structure at the TeV-scale). The dark gauge boson(s) couples to the SM gauge bosons via kinetic mixing (other portals are possible, like higgs mixing). mixing)
Standard Model
UY(1)
x
Dark Sector GD
UD(1)
GD group can be Abelian: One dark photon AD Non-abelian: Many dark bosons WD
Mixing strength
Lint = ε Fµν Bµν
Thanks to their large integrated luminosity, B factories offer an ideal environment to probe this new sector. Bertrand Echenard – Caltech
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October 2010
p. 44
Dark bosons
The idea of a hidden sector interacting weakly with the standard model has a rich history (e.g axions). Recent astrophysical anomalies can be naturally by introducing a new ‘dark’ force(s) mediated by a new dark gauge boson(s) with a mass around a GeV (regardless of the detailed structure at the TeV-scale). The dark gauge boson(s) couples to the SM gauge bosons via kinetic mixing (other portals are possible, like higgs mixing). mixing) Dark photon AD (abelian)
Dark gauge bosons (non-abelian)
σ ~ ε2 AD
(‘)
4 leptons (+gamma) final state
2 leptons (+gamma) final state See for example M. Pospelov et al., PPLB 662 (2008) 53, PLB 671 (2009) 391. B. Batellet al., PRD79 (2009) 115008 R. Essig et al., PRD 80 (2009) 015003 Bertrand Echenard – Caltech
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Dark photon AD (2 leptons) arXiv:0906.0580
Re-interpret interpret the upper limit on light Higgs search in Y(ns) →γ A0 decays*
Limit on ε between 10-3 – 10-2
* As limit on ε scales with luminosity1/4, little improvement by analyzing all data Bertrand Echenard – Caltech
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p. 46
Dark bosons WD (4 leptons) arXiv:0908.2821
Search for e+e- → WD WD, WD → e+e- with l=e,µ l=e,µ Very clean mode, especially for 4 muons Require 2 dilepton resonances with similar masses 4e
Cut and count analysis with background estimated from sidebands
Expected Signal
Use full BABAR dataset (540 fb-1) Extract upper limit on production cross-section and mixing ε mA < Ecm
4µ Expected Signal
mA > Ecm
Bertrand Echenard – Caltech
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October 2010
p. 47
Dark bosons arXiv:0908.2821
No signal, limit on ε between 10-4 – 10-3
Note: on-going going analysis with initial state radiation will improve these limits Bertrand Echenard – Caltech
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October 2010
p. 48
Dark Higgs and Dark QCD
Since the dark sector is spontaneously broken at about a GeV, it is reasonable to expect that there is a dark Higgs boson at this scale too1). Therefore, we can have dark Higgs'-strahlung, analogous to Higgs-strahlung in the Standard Model, as an interesting channel of production. In non-abelian scenarios, a confined dark sector with dark quarks is also possible, resulting in dark mesons and dark baryons (dark “QCD”).
Dark mesons (on-going)
Dark Higgs (on-going) hD A‘* A'
σ ~ ε2 6 leptons final state 6+ leptons final state
1) see for example: B. Batell, M. Pospelov, and A. Ritz, arXiv:0906.5614. (abelian), R. Essig, P. Schuster, and N. Toro, arXiv:0903.3941. ar (non-abelian) Bertrand Echenard – Caltech
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Dark Higgs search
Dark Higgs
Off-shell boson / 2 body loop induced decays
Estimated reach on ε mH > 2mA
mH < 2mA
direct decay h→A’A’
Invisible hD decay 2 leptons final state
Prompt hD decay 6 leptons final state
And searches in meson decays: π0/η→γA’ B decays : B0→4l and B0→K(*)4l Interesting results to come Bertrand Echenard – Caltech
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p. 50
Υ(1S)→invisible invisible decays McElrath, PRD 72 (2005) 103508
“Generic” Dark Matter model and Y(1S) decays ➡ Minimal model introducing a dark matter particle χ and a new scalar or gauge boson U to serve as a s-channel annihilation mediator (mU > 2mχ). ➡ Could increase the invisible decay width of the Υ(1S) predicted by SM1) by orders of magnitude. ➡ Rate estimates are fairly model independent, independent based on cosmological observations and assuming time-reversal symmetry.
Rate predictions BF(Υ(1S)→χχ ) ~ 4.2 x 10-4 (s-wave) BF(Υ(1S)→χχ ) ~ 1.8 x 10-3 (p-wave) BF(Υ(1S)→νν ) ~ 9.9 x 10-6
Large increase from SM predictions 1) PLB 441 (1998) 419.
Bertrand Echenard – Caltech
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Υ(1S)→invisible
-
Analysis overview
Analysis strategy ➡ Tag Υ(1S) mesons in Υ(3S)→π+π- Υ(1S) (1S) transition using the π+π- pair ➡ Dipion recoil mass Mrec should peak at Y(1S) mass, Mrec = (s + M2ππ -2sE*ππ)1/2 +l- with ➡ Estimate peaking background from MC, use Υ(1S,2S)→l Υ one or two reconstructed leptons to check and correct simulations
➡ Blind analysis, optimize analysis using sidebands and MC Event selection ➡ Two low-momentum oppositely-charged charged tracks ➡ Little extra activity ➡ Multivariate classifier (Random Forest) to improve signal purity:
Backgrounds ➡ Non-peaking background: suppressed by a factor > 1000 ➡ peaking background: Υ(3S)→l+l- decays
Bertrand Echenard – Caltech
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Υ(1S)→invisible invisible
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Results PRL 103 (2009) 251801
Fit procedure
➡ Extended unbinned maximum likelihood fit of recoil mass Mrec ➡ Signal and peaking background - Crystal-Ball function
➡ Non-peaking background - 1st order polynomial
Signal efficiency ~ 18% Results
Yield (fit) Background Signal
2326 ± 105 2444 ± 123 -118 ± 105 ± 124 Previous measurements BF(Υ(1S) → invisible) CLEO: BF < 3.9 x 10-3 @ 90% CL PRD 75 (2007) 031104 Belle: BF < 2.5 x 10-3 @ 90% CL PRL 98 (2007) 132001
Upper limit (90% CL)
BF(Υ(1S) → invisible) < 3.0 x 10-4
No evidence of dark matter contribution in invisible Υ(1S) decays Bertrand Echenard – Caltech
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Conclusion
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Conclusion
BABAR has a very rich physics program and has published more than 440 papers. There is still an active analysis program and many more results are expected. Many tests of SM predictions, confirmed CKM mechanism as dominant source of CP-violation in meson decays. No unambiguous sign of New Physics so far, but searches continues. A super-B factory (SuperB / Belle II) would be a perfect complement to LHC for probing physics at the TeV-scale.
The End
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References
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