Recent results onquarkonium spectroscopy
from BaBar and Belle
Bryan Fulsom
SLAC National Accelerator Laboratory
XXIIIiemes Rencontres de Blois
Blois, France
June 1, 2011
• Heavy quark (q=c,b) bound system: qq• Existence, masses, widths, quantum numbers• Phenomenological models, effective field theory, lattice QCD
Quarkonium Spectroscopy
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The Experiments
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• Operated over the past decade, accumulating ~1.5 ab-1
• Quarkonium production via B/(nS) decay, , ISR
• Decay of X(3872) J/– X(3872) mass, width and BF measurements
• Radiative decays of the X(3872)– Search for X(3872) J/ and (2S)
• Recoil against in (3S) b(2P)b(1P) transitions, (3S) mass, hb(1P) search
• Recoil against in (2S)
– First evidence for hb(1P)
• Bottomonium transitions with converted photons
– Radiative decays of (nS) and b(nP), b(1S) search
Topics covered today
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Topics not covered today
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X(3872)
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• Discovered by Belle in B± X K±, X J/
– Since measured by BaBar, CDF, DØ, LHC– Also decays to DD*, J/, and – JPC assignment 1++ or 2-+
– DD* molecule, charmonium, or tetraquark?
• Mass, width, decays, rates can test these theories– Mass above or below DD* threshold? – Tetraquark predicts splitting between neutral and charged B decay
• Width– Narrow, best limit <2.3 MeV
• Decay rates– Ratio of neutral to charged (~1 for cc, ~0.1 for molecule)
X(3872)
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• Full Belle dataset• Reconstruct B X(3872) K, X(3872) J/(l+l-)
• Perform 3D fit to mBC, E, m(J/ )
X(3872) J/ Update
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• Most precise measurements of branching fraction and mass
• Mass splitting disfavors tetraquark hypothesis• BF ratio consistent with previous BaBar results
– R = (0.41 ± 0.24 ± 0.05)• Best limit on width• m(X(3872)) world average gives “binding energy” of ~0.12 ± 0.35 MeV
X(3872) J/ Results
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Property Value
BF(B+K+X) x BF(XJ/ ) (8.6±0.8±0.8) x 10-6
BF(B0K0X) x BF(XJ/ ) (4.3±1.2±0.4) x 10-6
Ratio (B+/B0) 0.50±0.14±0.04
M = mX(B+) – mX(B0) -0.7±1.0±0.1 MeV
M(X(3872)) 3871.8±0.3±0.2 MeV
(X(3872)) <1.2 MeV
• BaBar evidence (~3.5) for X(3872) decaying to J/ and (2S)
• Analyze same decay channel with ~2x amount of data• Reconstruction
– J/ l+l-, (2S) l+l-, (2S) J/ final states
– Combine with to produce c1,2(1P) and X(3872) candidates
– Add K± or KS to form B± and B candidates
X(3872) J/, (2S)
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• Verify signal extraction technique on B cJ K, cJ J/
• Good agreement with PDG
• First measurement of suppressed B± c2 K± decays
cJ J/
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• Simultaneous fit of K± and KSo modes
• First “observation” (5.5) of X(3872) J/• Confirms C = + • Most precise measurement of branching fractions; agrees with BaBar
– B(B X(3872) K) B(X(3872) J/) = (1.8 ± 0.5 ± 0.1) 10-6
X(3872) J/
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• Combine (2S)K with any ± or in the event and veto if it is consistent with B (2S)K* decay
• Fit (2S) distribution with three components:– Peaking (MC), non-peaking (sidebands/MC), signal
• No evidence for X(3872) (2S) signal– Ratio [X(3872) (2S)] / [X(3872) J/] < 2.1– Compared to R = 3.4 ± 1.4 from BaBar
X(3872) (2S)
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Bottomonium
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• Analysis goal: search for Y(3S) hb(1P)
• Define recoil mass: mR2 = (m(3S) – E
)2 – |P
|2
2 fit to mR
• Peaking components (3S) hb signal
(3S) (2S) (2S) (1S) b1,2(2P) b1,2(1P)
• Smooth backgrounds
– KS
– Non-peaking background
Dipion Recoil in (3S)
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Dipion Recoil Fit Result
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Dipion Recoil Summary
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• Analysis Strategy
– Search for (3S) hb(1P)
– Reconstruct () +
– Require E consistent with hb(1P) b(1S)
– Assume B(hb(1P) b(1S)) 41%
• Define missing mass: m.m.()2 = (m(3S) – E)2 – P
2
– N from m fit in each m.m.() bin
2 fit of m.m.() distribution
– hb(1P) signal: Double Crystal Ball
– Background: 6th order polynomial
Search for hb(1P)
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Y(3S)hb(1P)( b(1S))
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• Measured mass agrees with expectation
– mhb(1P) = (mb0(1P)+3mb1(1P)+5mb2(1P)) / 9 9900 MeV/c2
• Branching fraction consistent with theory
• First evidence for hb(1P), definitively confirmed by Belle
Evidence for hb(1P)
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Property Value
Yield 9145±2804±1082 evts.
Significance 3.0
M [hb(1P)] 9902±4±1 MeV/c2
BF(Y(3S)hb) x BF(hbb)
(3.7±1.1±0.7) x 10-4
• Radiative bottomonium transitions– Rates generally phenomenologically well-predicted
– Gateway to discovery (e.g.: (nS) b(1S))
• Use converted photons ( ee) improve resolution (e.g.: 25 5 MeV)
– Reconstruct pair of tracks, selected with 2fitter, m,
– Additional cuts: |costhrust|, Ntracks, veto
– Fit E* spectrum in four regions of interest
• Goals: Resolve E* spectrum to make precision measurements
Radiative Transitions
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• Three “signal” transitions (bJ(2P) (2S)) and six (1D)-related lines
• Precision measurements of BF(bJ(2P) (2S))
(3S) : 180<E*<300 MeV
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• Complicated photon spectrum: many overlapping signals
• Observation and precise measurement of (3S) b0,2(1P) transitions
• Transition rate pattern J = 2 > 0 > 1 unusual for quarkonium
(3S) : 300<E*<600 MeV
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• Measure bJ(1P) (1S) and search for b(1S) signal
• Due to high bkgd/low eff., no evidence for (2S) b(1S)
(2S) : 300<E*<800 MeV
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• Measure bJ(2P) (1S) and search for b(1S) signal
• E* for b(1S) is lower than expected, but significance is ~2.7
• Need more data to take full advantage of converted photon technique
(3S) : 600<E*<1100 MeV
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• X(3872) at Belle– Improved measurements of X(3872) properties– Observation of X(3872) J/, disagreement on X(3872)
(2S)– Even after ~10 years, still haven’t solved the X(3872) problem!
• Bottomonium studies at BaBar
– Evidence for hb(1P) in Y(3S) hb(1P) decays
– Precision measurements of masses and dipion and radiative transitions offer important tests for theoretical models
• B-Factories have revitalized field of quarkonium spectroscopy– Many new measurements and discoveries of puzzling new states– Very promising future at Belle-II and SuperB
Summary
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