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BOTTOMONIUM RESULTS FROM BABAR Veronique Ziegler (SLAC) Representing the BaBar Collaboration CharmEx 2009, Bad Honnef, Germany, Aug. 10-12 2009 OVERVIEW Observation of the Bottomonium Ground State, h b (1S), in U (3S) → g h b (1S) Decay

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bottomonium results from babar


Veronique Ziegler (SLAC)

Representing the BaBar Collaboration

CharmEx 2009, Bad Honnef, Germany, Aug. 10-12 2009

  • Observation of the Bottomonium Ground State, hb(1S), in U(3S) → g hb(1S) Decay
  • Confirmation of the Observation of the hb(1S) in U(2S) → g hb(1S) Decay
  • Rb Scan above the U(4S)



Charged particle ID by means of velocity measurement


Angles and positions of charged tracks just outside the beam pipe

Charged tracks momentum

dE/dx for PID

(1.5 T)

3.1 GeV

9.03 GeV [Y(4S)]

8.65 GeV [Y(3S)]

8.10 GeV [Y(2S)]

babar run 7 dec 2007 apr 2008 pep ii e e asymmetric collider running at the u 2s 3s




BaBar RUN 7 (Dec. 2007 – Apr. 2008)PEP-II e+e- Asymmetric Collider Running at the U(2S,3S)…



~ 120 x 106Y(3S) events

≈ 20 X previous dataset (CLEO)

~ 100 x 106Y(2S) events

≈ 11 X previous dataset (CLEO)

~ 8.54 fb-1 above Y(4S)

≈ 30 X previous datasets (CLEO,




current picture of the bottomonium spectrum

(nL) where n is the principal quantum number and L indicates the bb angular momentum in spectroscopic notation (L=S, P, D,…)

Current Picture of the Bottomonium Spectrum




[Orbital Ang. Momentum between quarks]




Expected hb Production Mechanism

The U(nS) states are produced in hadronic interactions or from a virtual photon in e+e− annihilation

One of the expected production mechanisms of the hb(n’S) is by M1 (i.e. SS) transition from the U(nS) states [n’≤n]

the search for the h b at babar
The Search for thehbat BaBar
  • Decays of hb not known  Search for hb signal in inclusive photon spectrum

i.e. Search for the radiative transition Y(3S)→ghb(1S)

  • In c.m. frame:
    • For hb mass m = 9.4 GeV/c2 monochromatic line in Eg spectrum at 915 MeV, i.e. look for a bump near 900 MeV in inclusive photon energy spectrum from data taken at the U(3S)

√s = c.m. energy = m(Y(3S))

m = m(hb)



  • Look for a bump near 900 MeV in the inclusive photon spectrum
    • Large background
      • Non-peaking components
      • Peaking components
  • Reduce the background
    • Selection Criteria
    • Optimization of Criteria
    • Optimization Check
  • Fitting Procedure
    • One-dimensional fit to the Eg distribution
      • Obtain lineshapes of the various components
      • Binned Maximum Likelihood Fit
data sets
  • Y(3S) On-peak data
    • Full data sample: L = 28.6 fb-1
  • 122 x 106 Y(3S) events
    • Analysis sample: L = 25.6 fb-1
  • 109 x 106 Y(3S) events
  • expect ~ 20 x 103 Y(3S) g hb events
    • Test sample: L = 2.6 fb-1
  • 11 x 106 Y(3S) events
  • expect ~ 2 x 103 Y(3S) g hb events
    • Use since no reliable event generator for Y(3S) background photon simulation
  • Y(3S) & Y(4S) Off-peak data: L = 2.4 & 43.9 fb-1

L = Integrated Luminosity

(used for optimization

of selection criteria)

much smaller than expected background

(used for background studies)

the inclusive photon spectrum
The Inclusive Photon Spectrum
  • Use ~9% of the Full U(3S) Data Sample

Look for a bump near 900 MeV in the inclusive photon spectrum

Non-Peaking background components:

~1/10 Y(3S) Analysis Sample

Large background

from cbJ(2P) decay

(next slide)

the inclusive photon spectrum12
The Inclusive Photon Spectrum

cbJ(2P) → g U(1S) (Peaking) background parametrization:

PDF: 3 Crystal Ball functions

relative peak positions and yield ratios are taken from PDF

Peaking background components (1):

U(3S)  cb0(2P)g softE(g soft) = 122 MeV

 U(1S) g hard E(g hard) = 743 MeV

U(3S)  cb1(2P)g softE(g soft) = 99 MeV

 U(1S) g hard E(g hard) = 764 MeV

U(3S)  cb2(2P)g softE(g soft) = 86 MeV

 U(1S) g hard E(g hard) = 777 MeV

U(3S)  cbJ(2P)g soft

(J=0,1,2)  U(1S) g hard

~1/10 Analysis Sample

the inclusive photon spectrum13
The Inclusive Photon Spectrum

Expected Signal

  • Very important to determine both lineshape and yield

Depending on hb mass, the peaks may overlap!

Radiative return

to theU(1S)


e+e-→ gISR U(1S) (Peaking) background parametrization:

  • Estimate the expected yield using Y(4S) Off-Peak data [high statistics,

no other peaking background near ISR signal], and

extrapolating the yield to Y(3S) On-Peak data

~1/10 Analysis Sample

Peaking background component:

Radiative return from Y(3S)

to Y(1S): e+e-→ gISR Y(1S)

[ Eg = 856 MeV ]


u 3s g h b signal parametrization

Crystal Ball lineshape

obtained from

simulated events


U(3S)g hbSignal Parametrization
  • Fix signal Crystal Ball parameters from zero-width MC
  • Fix the S-wave Breit-Wigner width to 10 MeV
    • Fit the data with 5, 15, 20 MeV widths to study systematic errors

Fit Result

Full data sample

L = 25.6 fb-1

 (109 ± 1) x 106 Y(3S) events


~70000 events/ 5 MeV



All backgrounds


19152 ± 2010 events

The Observation of thehb

  • cbJ Peak Yield : 821841 ± 2223
  • gISR Y(1S) Yield : 25153 (fixed)
  • hb Yield : 19152 ± 2010
  • R(ISR/cbJ) ~ 1/33
  • R(hb/cbJ) ~ 1/43


Background subtracted



study of systematic uncertainties

No significant

change !

  • Vary ISR yield by ± 1s (stat  5% syst) dN = 180, dEg =0.7 MeV
  • Vary ISR PDF parameters by ± 1sdN = 50, dEg =0.3 MeV
  • Vary Signal PDF parameters by ± 1s dN = 98, dEg =0.1 MeV
  • Vary cbJ peak PDF parameters by ± 1s dN = 642, dEg =0.3 MeV
  • Fit with BW width fixed to 5, 15, 20 MeV dN = 2010, dEg=0.8 MeV
  • Systematic uncertainty in the hb mass

associated with the g energy calibration

shift obtained from the fit to the cb peak dEg=2.0 MeV

* Study of Significance

  • Vary BW width
  • Vary all parameters independently
  • Vary all parameters in the direction resulting

in lowest significance

main source of systematic uncertainty in the hb yield


summary of results
Summary of Results
  • Signal Yield :
    • Estimate of Branching Fraction (expected transition rate):
  • Mass of the hb(1S):
    • Peak in g energy spectrum at
    • Corresponds to hb mass
    • The hyperfine (U(1S)-hb(1S)) mass splitting is

The Search for thehb in

U(2S) → g hb(1S) Decay


The Search for the hb in U(2S) → g hb(1S) Decay

Eg ~ 600 MeV

Eg ~ 400 ± 80MeV

Data Sample ~ 100 x 106U(2S) events

Similar analysis strategy in U(2S)→g hbas for U(3S)→g hb

comparison of e g spectra
Comparison of Eg Spectra


Background subtracted

U(3S) spectrum

Comparison with Y(3S) g hb Analysis:

☛ Better photon energy resolution at lower energy

 better separation between peaks

☛ More random photon background at

lower energy

 less significance at similar BF

U(2S) spectrum


summary of h b results
Summary of hb Results
  • hb mass:
  • Hyperfine splitting:
  • Combined mass is m(hb(1S)) = 9390.4± 3.1 MeV/c2
  • resulting in a hyperfine splitting of 69.9 ± 3.1 MeV/c2
comparison of h b results with predictions

Comparison of hb Results with Predictions

Compatible with predictions for hindered M1 transitions taking into account relativistic corrections

S. Godfrey, J.L. Rosner

PRD64, 074011 (2001)

Branching Fraction Values

comparison of h b results with predictions24


□unquenched supercoarse

■unquenched coarse

□ unquenched fine

▲unquenched coarse

∆ unquenched fine

Comparison of hb Results with Predictions

  • Bottomonium spectrum has been computed in effective field theory of (potential) nonrelativistic QCD;

in the next-to-leading logarithmic (NLL) approximation the Hyperfine splitting for charmonium,

M(J/y)-M(hc)=104 MeV [B.A. Kniehl,, Phys. Rev.Lett. 92, 242001 (2004)] is consistent with the experimental value, M(J/y)-M(hc)=117.7±1.3 MeV [CLEO]

  • For bottomium, non-perturbative contribution to Hyperfine splitting expected to be smaller than for charmonium
  • Nonrelativistic QCD NLL prediction: M(U(1S))-M(hb)=39±11(th)+9-8(das)MeV (das(MZ)=0.118±0.003)
  • Need proper description of QCD non-perturbative long distance effects...
  • Lattice QCD: unquenched prediction, M(U(1S))-M(hb)=61±14 MeV [A. Gray,, Phys. Rev. D72, 094507 (2005)]

Agrees well with BaBar measurement, M(U(1S))-M(hb)=80±10 MeV [T-W. Chiu,, Phys. Rev.Lett. B651, 171 (2007)]

* A.Penin [arXiv:0905.429v1] and private conversation with M. Karliner

Hyperfine Splitting *

A. Gray,, Phys. Rev. D72, 094507 (2005)


energy scan above the u 4s

cross section for

0th order cross section for

Energy Scan above the U(4S)
  • Motivation
    • Search for bottomonium states that do not behave as two-quark states (in analogy to Y(4260), Y(4350) and Y(4660) exotic states); such states would have a mass above the U(4S) and below 11.2 GeV.
  • Procedure
    • Precision scan in √s from 10.54 to 11.20 GeV
      • 5 MeV steps collecting ~25 pb-1 at each step (3.3 fb-1 total)
      • 600 pb-1 scan in energy range 10.96 to 11.10 GeV in 8 steps with unequal energy spacing (investigation of U(6S))
  • Measurement
    • Inclusive hadronic cross section
    • Search for unexpected structures in Rb(s)
energy scan above the u 4s results



Clear structures corresponding to the bb opening thresholds

Energy Scan above the U(4S): Results

Inclusive hadronic cross section measurement (PRL 102,012001 (2009))

Consistent with

coupled channel predictions

u 5s and u 6s mass and width measurement
U(5S) and U(6S) Mass and Width Measurement

Fit with non-resonant amplitude & flat component added coherently with two interfering relativistic Breit-Wigner functions

Incoherent superposition of Gaussians and bckgr.

  • Compared to CLEO & CUSB,
  • BaBar has:
  • >30 x more data
  • 4 x smaller energy steps
  • Much more precise definition of shape



first observation of the h b 1s bottomonium ground state in the decay u 3s g h b 1s
- First observation of the hb(1S) bottomonium ground state in the decay U(3S) → g hb(1S)


- Confirmation from U(2S) →g hb(1S)

- Combined mass is m(hb(1S)) = 9390.4 ± 3.1 MeV/c2 and hyperfine splitting DMHFS = 69.9 ± 3.1 MeV/c2

- Precision scan of Rb in the energy range 10.54 < √s < 11.20 GeV yields parameters for U(5S) and U(6S), which differ from the PDG averages (also confirmed by Belle \'s exclusive studies)


Bottomonium Transitions

  • U(nS) resonances undergo:
  • Hadronic transitions via p0, h,

w, pp emission

  • Electric dipole transitions
  • Magnetic dipole transitions

-- Allowed transition:

  • Electromagnetic transitions between the levels can be calculated in the quark model  important tool in understanding the bottomonium internal structure
mass splittings in heavy quarkonia

Hyperfine splitting

Fine splitting

S = 1

S = 0

Mass Splittings in Heavy Quarkonia

Triplet-Singlet mass splitting of quarkonium states

Mass splitting of triplet nP quarkonium states: cc,b(n3P0),





= 0 for L≠ 0 (→ 0 for r → 0), if long-range spin forces are negligible

≠ 0 for L=0

U(1S)-hb(1S) mass splitting meast.key test of applicability of perturbative QCD to the bottomonium system



QCD Calculations of the ηb mass and branching fraction

  • Recksiegel and Sumino, Phys. Lett. B 578, 369 (2004) [hep-ph/0305178]
  • Kniehl et al., PRL 92 242001 (2004) [hep-ph/0312086]
  • Godfrey and Isgur, PRD 32, 189 (1985)
  • Fulcher, PRD 44, 2079 (1991)
  • Eichten and Quigg, PRD 49, 5845 (1994) [hep-ph/9402210]
  • Gupta and Johnson, PRD 53, 312 (1996) [hep-ph/9511267]
  • Ebert et al., PRD 67, 014027 (2003) [hep-ph/0210381]
  • Zeng et al., PRD 52, 5229 (1995) [hep-ph/9412269]

e+e-→gISRY(1S) Calculations

summary of h b measurements from y 3s


arXiv: hep-ph/0412158


Segmented array of 6580 Thallium-doped CsI crystals 16 to 17.5 radiation lengths deep (Rad. L. >1.85 cm)

energy & position resolution:

The ElectroMagneticCalorimeter

Designed to detect electromagnetic showers over the energy range from 20 MeV to 4GeV

  • Also used to:
  • detect KL’s
  • identify electrons

e+ (3.1 GeV)

e- (8.65 GeV)