recent babar studies of bottomonium states veronique ziegler
DESCRIPTION
1. RECENT BaBaR STUDIES OF BOTTOMONIUM STATES Veronique Ziegler SLAC National Accelerator Laboratory On behalf of the BaBar Collaboration 2011 Meeting of the Division of Particles and Fields of the American Physical Society Providence, Rhode Island, USA August 9 ─13, 2011. 2. - PowerPoint PPT PresentationTRANSCRIPT
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RECENT BaBaR STUDIES OF BOTTOMONIUM STATES
Veronique Ziegler
SLAC National Accelerator LaboratoryOn behalf of the BaBar Collaboration
2011 Meeting of the Division of Particles and Fields of the American Physical Society
Providence, Rhode Island, USAAugust 9 ─13, 2011
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• 2
PEP-II e+e- Asymmetric Collider Running at the U(2S,3S)
BaBar RUN 7 (Dec. 2007 – Apr. 2008)
BABAR DATASETS:
~ 120 x 106 Y(3S) events~ 100 x 106 Y(2S) events~ 8.54 fb-1 above Y(4S)
R-scan
2
k
k
k
Effective
c.m. Energy (GeV)
CUSB
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OUTLINE
1. Spectroscopy circa 2008
2. Radiative transitions from U(2S,3S) events
using g → e+e- conversions
3. Search for the hb(1P) in U(3S) → p+p- hb(1P)
4. Evidence for the hb(1P) in U(3S) → p0 hb(1P)
5. Present status of bottomonium spectroscopy
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2008 Picture of the Bottomonium Spectrum• bb states below Y(3S) not yet discovered:
3 S-wave (hb), 2 P-wave (hb), 4 D-wave &
possibly 4 F-wave.• Among the undiscovered states was the
ground state, the hb(1S), expected to be < 100 MeV/c2 below the Y(1S)
)11020(
)10860(
2 1 Pb 2 2 Pb 2 0 Pb?
?
S-wave P-wave
1 2 Pb 1 1 Pb 1 0 Pb
2 h Pb
1 h Pb
S2 b
3 Sb
1 Sb
)3( S
)4( S
)1( S
)2( S
1 1 1 0 2 0 C P J
BB threshold
hadrons
hadrons
[Orbital Ang. Momentum between quarks]
(nL) where n is the principal quantum number and L indicates the bb angular momentum in spectroscopic notation (L=S, P, D,…)
? )6( S
? )5( S
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Radiative transition studies from inclusive spectra for converted
photons
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Radiative bottomonium transitions from U(3S) events using g→e+e- conversions
Energy in C.M. frame
Significantly improves energy resolution [see later]Efficiency ~(0.1 – 1)%
6
arXiv:1104.5254 (submitted to PRD)
Reconstructed Vertices
Support tube(carbon fiber)
Drift Chamberinner wall (Be)
SVT(5 layers)
SVTsupports
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MeV ]243,207[2
22)(
i
fii
m
mmE
• Resolution dominated• Small Doppler broadening
Inclusive photon energy regions for U(3S) events
0b )2( )2( SPbJ
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MeV ]484,430[2
22)(
i
fii
m
mmE
MeV ]442,391[2
22)(
i
fii
m
mmE
Inclusive photon energy regions for U(3S) events
from U(3S)
to U(1S)
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MeV ]777,743[2
22)(
i
fii
m
mmE
g
Search for the Bottomonium Ground State hb(1S)
Inclusive photon energy regions for U(3S) events
U(3S)→ g hb(1S)
photons from calorimeter
hb significance < 3s
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Inclusive photon energy regions for U(3S) events
MeV ]777,743[2
22)(
i
fii
m
mmE
g
Search for the Bottomonium Ground State hb(1S)
hb significance < 3s
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g
MeV ]442,391[2
22)(
i
fii
m
mmE
ISR hb (1S)
Inclusive photon energy regions for U(2S) events
hb significance < 3s
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g
MeV ]612,391[2
22)(
i
fii
m
mmE
Inclusive photon energy regions for U(2S) events
hb significance < 3s
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Summary of BF measurements from U(2S,3S) radiative decays using converted
photons• Precise measurements of cbJ(nP) n=1,2 → g U(mS)m=1,2
BFs
• Good agreement with theory Kwong & Rosner, PRD38, 279 (1988)
• Measurements of BFs for U(3S)→ g cbJ(1P) transitions transition to cb1(1P) not
seen in general inconsistent with theoretical
predictions
?
13
(except Moxhay-Rosner PRD28,1132 (1983))
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Searches for the hb(1P) State of Bottomonium
at BaBar• Essential to measure the hyperfine mass
splitting for P-wave states to understand the spin dependence of q q̅� potentials for heavy quarks.
• Hyperfine splitting between hb(1P) mass & spin-weighted center of gravity of the cbJ(1P) states (9899.87±0.27 MeV/c2) expected to be ~0 [confirmed for hc].
• Hyperfine mass splitting larger than 1 MeV/c2 might be indicative of a vector component in the confinement potential.
• BaBar searched for the hb(1P) meson in the transitions:
U(3S)p+p- hb(1P) U(3S)p0 hb(1P) (requiring a photon
consistent with subsequent hbghb(1S) decay)
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p0
pp
9/)1(5)1(3)1(~)1(
0~)(
/
)()(
23
13
03
11
1
)12( )12(
3
PMPMPMPM
LnMLnMnLM LJ
JMJ
JHF
J JJ
Search for a peak in invariant mass of system
recoiling against p+p- or p0
2*2**)3( )()()( XXSrecoil pEEXm
cbJ(1P)
U(3S)
hb(1S)
hb(1P)
15
Expected Mass of the hb(1P) StateHyperfine splitting for L=1 states M [c.o.g.(13PJ)] – M(11P1)
= 9899.87 ± 0.27 MeV/c2
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background-subtracted result:
Search for the hb(1P) in the decay U(3S)p+p-hb
• No hb observation: -1106 ± 2432(stat.) signal events (mass fixed at 9.9 GeV/c2)
• BF(U(3S)p+p-hb)<1.0x10-4 (@90% C.L.)
--suppressed by a factor >3 compared to p0 mode
• First separate observation of cb1,2(2P)p+p- cb1,2(1P) transitions and BF measurements:– BF(cb1(2P)p+p- cb1,2(1P)) = (9.2±0.6±0.9)×10-3
– BF(cb2(2P)p+p- cb1,2(1P)) = (4.9±0.4±0.6)×10-3
)1()2( 2.12.1 PP bb
0SKXS )3( )1()2( SS
)2()3( SS
hb ?
Phys.Rev. D 84, 011104(R)
hb signal region
16
later
see
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Search for the hb(1P) in U(3S) pohb • Analysis Strategy
– Reconstruct po(g1g2) + g
– Require Eg consistent with hb(1P) ghb(1S) transition
– Selection criteria on Ntracks, R2, po veto (all g candidates), po cosqh
• Define po missing mass: m.m.(po)2 = (m(3S) – E*po)2 – P*
po2 mrecoil(po)
– Constrain mpo to improve resolution on mrecoil(po)
– Npo from mg1g2 fit in each mrecoil(po) interval using modified MC
p o –lineshape and backgroundFull statisticsSample
17
[420 < Eg < 540 MeV]
─ data─ fit
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Evidence for the hb(1P) in the decay U(3S) pohb
• 10814± 2813 signal events• M(hb) = 9902±4 ±2 MeV/c2
(C.G.=9899.87±0.27 MeV/c2 )• Stat. Signif. = 3.8 (s √Dc2); including
systematic errors = 3.3s• B(U(3S)p0hb(1P) = (4.1±1.1±0.9)10-4 < 6.110-4 (@
90% CL)• Existence subsequently confirmed by Belle
in (Υ 5S)→ p+p- hb(1P) (arXiv:1103.3419 (*)) with combinatorial bkg. 2X BaBar U(3S) search also observe hb(2P)
arXiv:1102.4565
18
• 2 fit of mrecoil(po) distribution:
– hb(1P) signal: Double Crystal Ball function
– Background: 5th order polynomial– Parameters determined with
hb signal region excluded (i.e. blind analysis strategy)
uncertainty from background fit
background-subtracted result:hb signal region
((*) La Thuille 2011)
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2011 Picture of the Bottomonium Spectrum• bb states below Y(3S) not yet discovered:
2 S-wave (hb(2S,3S)) , 3 D-wave &
possibly 4 F-wave.• Recently discovered states including the
hb(1P) and hb(2P) states
)11020(
)10860(
2 1 Pb 2 2 Pb 2 0 Pb?
?
S-wave P-wave
1 2 Pb 1 1 Pb 1 0 Pb
2 h Pb
1 h Pb
S2 b
3 Sb
1 Sb
)3( S
)4( S
)1( S
)2( S
1 1 1 0 2 0 C P J
BB threshold
hadrons
hadrons
[Orbital Ang. Momentum between quarks]
(nL) where n is the principal quantum number and L indicates the bb angular momentum in spectroscopic notation (L=S, P, D,…)
? )6( S
)5( S
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SUMMARY OF BaBar RESULTS
1. Precision measurements of radiative transitions between known bottomonium states using g → e+e- conversions
2. No evidence for the hb(1P) in the transition U(3S) → p+p- hb(1P)
3. Evidence at 3.3s level for the hb(1P) in U(3S) → p0 hb(1P) decay
– confirmed by Belle using U(5S) data
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Backup Slides
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Angles and positions of charged tracks just
outside the beam pipe
DCH
Charged tracks momentumdE/dx for PID
DIRC
Charged particle ID by means
of velocity measurement
6580
(1.5 T)
3.1 GeV
9.03 GeV [Y(4S)]8.65 GeV [Y(3S)]8.10 GeV [Y(2S)]
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BaBar integrated luminosity since startup
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background subtracted results
Confirmation of the existence of the hb(1P) by Belle in e+e-→p+p- transitions at the U(5S)
Observation of the hb(1P) and hb(2P) states
• Measured hb(1,2P) mass values consistent with predictions
• Observed hb production rate enhancement may be indicative of exotic process violating HQ spin-flip suppression
• Resonant structures in hb(1P, 2P) seen in
(5S) hb(1P, 2P) +- events
(also in (5S) (nS) +-)charged exotic candidates Zb1, Zb2
arXiv:1103.3419
Consistentwith BaBarmeasmt.
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Evidence for the hb(1P) in the decay U(3S) pohb
• 9145 ± 2804 signal events
• M(hb) = 9902±4 ±1 MeV/c2
consistent with predictions • Stat. Signif = 3.2 (s i.e. √Dc2),
including systematic errors = 3.0s (evaluated with the hb mass fixed at expected value of 9.9 GeV/c2)
• B(U(3S)p0hb(1P) = (3.7±1.1±0.4)10-4
• B(U(3S)p0hb(1P)< 5.810-4 (@ 90% CL)
background-subtracted result:arXiv:1102.4565
• 2 fit of m.m.(po) distribution:– hb(1P) signal: Double
Crystal Ball function– Background: Polynomial
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hb Search: Comparison of Eg Spectra for U(3S) and U(2S) Events
Results from Y(2S) and Y(3S) analyses are consistent!
U(3S) U(2S)
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BF measurements: B((3S) ghb(1S)) = (5.1 ± 0.7) 10-4 B((2S) ghb(1S)) = (3.9 ± 1.5) 10-4
Compatible with predictions
Combined values of mass and HF splitting:
mhb(1S) = 9390.9 ± 2.8 MeV/c2 (Ghb(1S) 10 MeV)
(m(1S) – mhb(1S)) = 69.3 ± 2.8 MeV/c2
Unquenched lattice QCD calculations (~50-60 MeV/c2) agree better
than NRQCD predictions (~40 MeV/c2)
hb Search: Summary of Results
S. Godfrey, J.L. Rosner PRD 64 074011 (2001)
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• Radiative transitions– Rates generally phenomenologically well-predicted– Gateway to discovery (e.g.: (nS) g hb(1S))
• Use converted photons (g e+e-) improve resolution (e.g.: 25 5 MeV)– Reconstruct pair of tracks, selected with c2
fitter, mg, rg
– Additional cuts: |cosqthrust|, Ntracks, po veto
– Fit Eg* spectrum in four regions of interest
• Goals: Resolve Eg* spectrum to make precision measurements
Radiative Bottomonium Transitions
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• Precise measurements of bottomonium transition rates in good agreement with predictions
• (3S) g b0,2(1P) rates are an exception
– Further theoretical/experimental work needed
• b(1S) mass measurement inconclusive
– Need more data to take full advantage of converted photon technique
Converted Photon Conclusions