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BOTTOMONIUM RESULTS FROM BABARPowerPoint Presentation

BOTTOMONIUM RESULTS FROM BABAR

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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

BOTTOMONIUM RESULTS FROM BABAR

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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)

6580

DIRC

Charged particle ID by means of velocity measurement

DCH

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)]

k

k

k

Effective

BABAR DATASETS:

~ 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,

CUSB)

R-scan

4

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

threshold

hadrons

hadrons

[Orbital Ang. Momentum between quarks]

P-wave

S-wave

The hb(1S) State

(11S0)

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. SS) transition from the U(nS) states [n’≤n]

- 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)

ANALYSIS STRATEGY

- Look for a bump near 900 MeV in the inclusive photon spectrum
- Large background
- Non-peaking components
- Peaking components

- Large background
- 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

- One-dimensional fit to the Eg distribution

- 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)

- 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)

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

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 ]

ISR

Crystal Ball lineshape

obtained from

simulated events

M.C.

- 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

cbJ(2P)

~70000 events/ 5 MeV

15

All backgrounds

subtracted

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

Non-peaking

Background subtracted

gISR

hb

- No significant
change !

- Vary ISR yield by ± 1s (stat 5% syst) dN = 180, dEg =0.7 MeV
- Vary ISR PDF parameters by ± 1sdN = 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

17

- 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

Non-peaking

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

21

- 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 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

x

□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, et.al., 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, et.al., Phys. Rev. D72, 094507 (2005)]
Agrees well with BaBar measurement, M(U(1S))-M(hb)=80±10 MeV [T-W. Chiu, et.al., Phys. Rev.Lett. B651, 171 (2007)]

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

Hyperfine Splitting *

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

HFS (MeV)

Rb Scan above theU(4S)

cross section for

0th order cross section for

- 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))

- Precision scan in √s from 10.54 to 11.20 GeV
- Measurement
- Inclusive hadronic cross section
- Search for unexpected structures in Rb(s)

s

s

Clear structures corresponding to the bb opening thresholds

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

Consistent with

coupled channel predictions

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

s

28

SUMMARY

- 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)

BACK-UP SLIDES

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

Hyperfine splitting

Fine splitting

S = 1

S = 0

Triplet-Singlet mass splitting of quarkonium states

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

cc,b(n3P1),

cc,b(n3P2)

Non-relativistic

approximation

= 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

6

- 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

CLEO

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)