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

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

3

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

4

Radiative transition studies from inclusive spectra for converted

photons

5

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

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

7

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)

8

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

9

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

10

g

MeV ]442,391[2

22)(

i

fii

m

mmE

ISR hb (1S)

Inclusive photon energy regions for U(2S) events

hb significance < 3s

11

g

MeV ]612,391[2

22)(

i

fii

m

mmE

Inclusive photon energy regions for U(2S) events

hb significance < 3s

12

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))

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)

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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

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

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

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[420 < Eg < 540 MeV]

─ data─ fit

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

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• 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)

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

19

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

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)]

BaBar integrated luminosity since startup

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.

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

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)

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)

• 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

• 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