e hadrons in isr and two-photon reactions with belle and...
TRANSCRIPT
INFN Sezione di Roma on behalf of the BABAR Collaboration
Rencontres de Moriond QCD and High Energy Interactions 13 – 20 March, 2010 La Thuile
e+e- → hadrons in ISR and Two-photon reactions with BELLE and BABAR
Fabio Anulli
Outline • selected ISR results
– exclusive light hadron final states • e+e− → π+π−
– e+e− → open charm
• selected γγ results – no-tag mode
• γγ → π0π0, ηπ0
• γγ → DDbar
– single-tag mode • γγ* → π0,ηc ==> Transition Form Factors
3/16/10 F. Anulli 2
hadronic contribution to (g-2)µ
• more results shown yesterday by Pasha Pakhlov on discovery of “exotic charmonium-like” state
3/16/10 F. Anulli 3
selected ISR results
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mf
2 = ′ s = s(1− x)
ISR @ 10.6 GeV ==> access the same observables as low energy e+e- experiments! • Quantum numbers at production vertex JPC=1--
• Continuous ISR spectrum: whole energy range covered with same detector condition and analysis
good efficiency down to threshold and up to √s ~5 GeV • αem suppression compensated by the huge luminosity
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dσe +e − → fγ
(s,mf )dmdcosθγ
∗ =2msW (s,x,θγ
∗) ⋅σe +e − → f
m f( )Radiator function
3/16/10 F. Anulli 4
The Anomalous Magnetic Moment of the muon
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a µSM =
g − 22
µ
= a µQED + aµ
had + aweak
aµ precisely measured at BNL E821 Phys.Rev.D73,072003(2006) aµ
exp - aµSM = ( 30.1± 8.6 ) × 10-10 (arXiv:0908.4300)
• Dominant uncertainty from hadronic vacuum polarization. • Cannot be calculated by QCD “first principles”
R(s) = σ(ee→hadrons)/σ(ee→µµ)
determine it via dispersion relations, by measuring the total hadronic cross section
73% from ππ
Value before BABAR result aµ
had = (690.9 ± 5.3)10-10
62% of uncertainty from ππ
Need to measure R(s) with better than 1% precision!
]2 [GeV/cµµm
0.5 1 1.5 2 2.5 3
data
/QE
D
0.9
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[GeV]s’
0 0.5 1 1.5 2 2.5 3
Cro
ss s
ectio
n [
nb
]
-310
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-110
1
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310
410
(b)
0.6 0.7 0.8 0.9 10
500
1000(c)
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BABAR measurement of Rππ
ISR γ detected ==> powerful background rejection
Kinematic fit including 1 additional γ : NLO! All efficiencies (trigger, filter, tracking, PID, fit)
from the same data Measure ratio of ππ to µµ to cancel : ee Luminosity, additional ISR, vacuum polarization, ISR γ efficiency
Phys. Rev. Lett. 103, 231801(2009)
]2 [GeV/cµµm
0.5 1 1.5 2 2.5 3
data
/QE
D
0.9
1
1.1
(a)
[GeV]s’
0 0.5 1 1.5 2 2.5 3
Cro
ss s
ectio
n [
nb
]
-310
-210
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1
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310
410
(b)
0.6 0.7 0.8 0.9 10
500
1000(c)
3/16/10 F. Anulli 6
BABAR measurement of Rππ
ISR γ detected ==> powerful background rejection
Kinematic fit including 1 additional γ : NLO! All efficiencies (trigger, filter, tracking, PID, fit)
from the same data Measure ratio of ππ to µµ to cancel : ee Luminosity, additional ISR, vacuum polarization, ISR γ efficiency
Phys. Rev. Lett. 103, 231801(2009)
BABAR aµ
ππ[2mπ,1.8GeV] = (514 ± 2.2 ± 3.1) × 10-10
aµhad (10-10) 695.5 ± 4.0exp ± 0.7QCD
aµexp - aµ
SM (10-10) 25.5 ± 8.0
Deviation 3.2 σ
Note: averages taken from M.Davier et al. arXiv:0908.4300
the discrepancy with the esxperimental value is still above 3σ!
previous e+e- average 503.5 ± 3.5tot
new e+e- average 508.4 ± 1.3 ± 2.6
new average from tau 515.2 ± 2.0exp±2.2BF±1.9IB
Including all other contributions from e+e- cross sections
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The ISR program in BABAR e+e– → π+ π–π+π–
unprecedented accuracy! a factor 2‐3 improvement on determinaHon of contribuHons to aµ
had (×10-10)
Vigourous campaign that is still in progress: - ΚS
0Κ-π+, Κ+Κ-π0, Κ+Κ-η PRD 77, 092002, 2008 - 2(π+π-)π0, 2(π+π-)η, Κ+Κ-π+π-π0, Κ+Κ-π+π-η PRD 76, 092005, 2007 - Κ+Κ-π+π-, Κ+Κ-π0π0, Κ+Κ-Κ+Κ- PRD 76, 012008, 2007 - 3(π+π-), 2(π+π-π0), Κ+Κ-π+π-π+π- PRD 73, 052003, 2006 - π+π-π+π-, Κ+Κ-π+π-, Κ+Κ-Κ+Κ- PRD 71, 052001, 2005 - π+π-π0 PRD 70, 072004, 2004 - pp PRD 73, 012005, 2006 - ΛΛ, Σ0Σ0, ΛΣ0 PRD 76, 092006, 2007 • First observations 232 fb-1, 89 fb-1 @ 10.6 GeV • all analysis with tagged ISR γ ==> efficient background rejection • only charmless mesons and baryons in this slide
without BABAR with BABAR π+π-π0 2.45 ± 0.26 3.25 ± 0.09
2 (π+π-) 14.20 ± 0.90 13.09 ± 0.44
3 (π+π-) 0.10 ± 0.10 0.11 ± 0.02
2 (π+π-π0) 1.42 ± 0.30 0.89 ± 0.09
UL @ 90% CL 1 34 40
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BF(Y (4260)→ X )BF(Y (4260)→ J /ψπ +π− )
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X =DD
€
X =D*D *
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X =DD *
e+e- annihilation to open charm via ISR: e+e-→ D(*)D(*)
DD
DD*
D*D*
384 %‐1
Phys.Rev. D79, 092001(2009)
No evidence found:
3/16/10 8 F. Anulli
• Measure properties of heavy charmonium states • Search for Y(4260) D(*)D(*) decays
• should be the dominant decay for a ccbar meson
for comparison (from PDG):
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BF(ψ(3770)→ DD )BF(ψ(3770)→ J /ψπ +π− )
≈400
ψ(3770)
ψ(4040) ψ(4415)
• Full reconstruction of the hadronic part • Both charged and neutral final states • Fit by sum of ψ states with fixed masses&widths from PDG (due to limited statistics)
UL @ 90% CL 1 34 40
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BF(Y (4260)→ X )BF(Y (4260)→ J /ψπ +π− )
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X =DD
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X =D*D *
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X =DD *
e+e- annihilation to open charm via ISR: e+e-→ D(*)D(*)
DD
DD*
D*D*
384 %‐1
Phys.Rev. D79, 092001(2009)
Sum of two body open charm final
states
No evidence found:
BELLE: Phys. Rev. Lett. 98, 092001 (2007)
3/16/10 9 F. Anulli
• Measure properties of heavy charmonium states • Search for Y(4260) D(*)D(*) decays
• should be the dominant decay for a ccbar meson
for comparison (from PDG):
€
BF(ψ(3770)→ DD )BF(ψ(3770)→ J /ψπ +π− )
≈400
ψ(3770)
ψ(4040) ψ(4415)
• Full reconstruction of the hadronic part • Both charged and neutral final states • Fit by sum of ψ states with fixed masses&widths from PDG (due to limited statistics)
e+e- → γISR D0D* − π+
Phys.Rev.D80,091101(2009) (R) 695 %‐1
3/16/10 10 F. Anulli
• No evident structures: only UL’s ! • Baseline fit:
• RBW for ψ(4415) & not-interfering threshold function for non-resonant contribution
σ(e+e–→ψ(4415))×Br(ψ(4415)→D0D*–π+)< 0.76 nb at 90% CL Br(ψ(4415)→ D0D*–π+) < 10.6 % at 90% CL
ψ(4415) Upper Limit
e+e- → γISR D0D(*) - π+
Phys.Rev.D80,091101(2009) (R) 695 %‐1
3/16/10 11 F. Anulli
• No evident structures: only UL’s ! • Baseline fit:
• RBW for y(4415) & not-interfering threshold function for non-resonant contribution
• Search for exotic states X→D0D*–π+, X=Y(4260), Y(4360), Y(4660), X(4630) • Perform different fits, each with one exotic X state , the ψ(4415) and non-resonant contribution (not-interfering amplitudes) • Fix masses and total widths
σ(e+e–→ψ(4415))×Br(ψ(4415)→D0D*–π+)< 0.76 nb at 90% CL Br(ψ(4415)→ D0D*–π+) < 10.6 % at 90% CL
Y(4260)
ψ(4415)
UL at 90% CL
3/16/10 F. Anulli 12
Selected two-photon results in no-tag mode
€
σ e+e− → e+e−γ *γ * → e+e−X( ) = σγγ→X (W )dLγγdW
dW∫
• C-even final states • JPC = 0±+, 2±+, …. (J=1 forbidden for two real photons)
complementary to e+e- annihilation!
– Measure exclusive final states with invariant mass up to ~4.5 GeV/c2 – Beam particles escape with small scattering angle – q2≈0 : “quasi-real” photons can measure Γγγ – two-photon events selected with tight pT cut
• Clear f0(980), f2(1270) peaks • Structures visible around 1.6 and 2.0
GeV ( f4(2050) ) • Smooth behaviour above ~2.4 GeV
γγ → π0π0, ηπ0
γγ → π0π0 γγ → ηπ0
• a0(980), a2(1320), a2(1700) seen • Smooth behaviour above ~2.4 GeV
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σ e+e− → e+e−X( ) = σγγ→X (W )dLγγdW
dW∫
€
dσγγ→X
d cosθ*=
ΔN −ΔB
ΔW Δ cosθ* εdLγγdW
Lee
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σγγ→X (W ) =dσ
d cosθ*∑ Δ cosθ*
ExtracHon of γγ → X cross section:
Resonance study
Fit the “asymptoHc” behavior
PRD79,052009(2009)
PRD78,052004(2008)
PRD80,032001(2009)
3/16/10 13 F. Anulli
γγ → ηπ0 : resonance region
Phys.Rev.D80,032001(2009)
€
dσdΩ
γγ →π 0π 0( ) = SY00 + D0Y2
0 2+ D2Y2
2 2= S 2Y0
0 2 + D 0
2Y20 2
+ D 2
2Y22 2
fit with a0(980), a2(1320) and a0(Y) in the region W < 1.5 GeV
• inclusion of a0(Y) gives a better χ2
• mass and width of a0(Y) significantly smaller than PDG values of a0(1450)
3/16/10 14 . Anulli
Partial Wave Analysis for 0.9 < W < 1.5 GeV
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S=Aa0 (980)eiφS 0 + Aa0 (Y )
eiφS1 +BS
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D0 =BD0 D2 = Aa2 (1320)eiφD 2 +BD2
Mass (MeV/c2)
Γtot (MeV)
Γγγ B(π0π0) (eV)
a0(980)
a0(980) PDG
a0(Y)
a0(1450) PDG unknown
€
982.3−0.7−4.7+0.6+3.1
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75.6 ±1.6−10.0+17.4
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128−2−43+3+502
€
1316.8−1.0−4.6+0.7+24.7
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65.0−5.4−32.6+2.1+99.1
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432 + 6−256+1073
€
984.7 ±1.2
€
50 −100
€
240−70+80
€
1474 ±19
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265 ±13
Nominal fit M(a0(Y) = M(a0(1450))
No a0(Y)
χ2/ndf 597.6/429 704.5/430 753.6/433
γγ → π0π0 : study of the higher mass region
3/16/10 15 F. Anulli
γγ → π0π0
fitted slopes σ ∼ W-n ( pQCD: n = 6 )
n
π0π0 6.9 ± 0.6 ± 0.7 PRD79,052009 (2009)
π+π- 7.9 ± 0.4 ± 1.5 PLB615 ,39 (2005)
Κ+Κ- 7.3 ± 0.3 ± 1.5 PLB615, 39 (2005)
ηπ0 10.5 ± 1.2 ± 0.5 PLB651, 15 (2007)
KSKS 10.5 ± 0.6 ± 0.5 PRD80,032001 (2009)
Isospin symmetry
leading-order pQCD
• fitted region: 3.1 < W < 4.1 GeV; |cosθ*| < 0.6 • slope compatible with π+π- and pQCD predictions • cross-section ratio incompatible with LO pQCD
Phys.Rev.D 79, 052009 (2009)
Slope: n = 6.9±0.6±0.7
σ(π0π0)/σ(π+π-) = 0.32±0.03±0.05
cross secMon (nb)
γγ → π0π0 : study of the higher mass region
Slope: n = 6.9±0.6±0.7
σ(π0π0)/σ(π+π-) = 0.32±0.03±0.05
cross secMon (nb)
3/16/10 16 F. Anulli
γγ → π0π0
fitted slopes σ ∼ W-n ( pQCD: n = 6 )
n
π0π0 6.9 ± 0.6 ± 0.7 PRD79,052009 (2009)
π+π- 7.9 ± 0.4 ± 1.5 PLB615 ,39 (2005)
Κ+Κ- 7.3 ± 0.3 ± 1.5 PLB615, 39 (2005)
ηπ0 10.5 ± 1.2 ± 0.5 PLB651, 15 (2007)
KSKS 10.5 ± 0.6 ± 0.5 PRD80,032001 (2009)
Isospin symmetry
leading-order pQCD
|cosθ*| < 0.4
• χc0 observed with 7σ • (1.3σ for χc2 )
• fitted region: 3.1 < W < 4.1 GeV; |cosθ*| < 0.6 • slope compatible with π+π- and pQCD predictions • cross-section ratio incompatible with LO pQCD
Phys.Rev.D 79, 052009 (2009)
]2) [GeV/cDm(D
3.8 4 4.2
2E
ntr
ies
/ 10 M
eV
/c
0
5
10
15
20
25
30
35
]2) [GeV/cDm(D
3.8 4 4.2
2E
ntr
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/ 10 M
eV
/c
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10
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25
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35
Efficiency‐corrected mass spectrum
Discovery (and confirmation) of the χc2(2P) in γγ → DD • Radial excitaHon states established for 2S+1LJ = 3S1 (ψ) and 1S0 (ηc) • Lowest 3PJ (χcJ) well established, but nothing known about radial excitaHons • In 2006, Belle reported the discovery of the Z(3930) idenHfied as the χc2(2P) • This state and its interpretaHon is now confirmed by BABAR, with consistent parameters
|!|cos
0 0.2 0.4 0.6 0.8 1
Entr
ies /
0.1
-5
0
5
10
15
20
Angular distribuHon in the Z(3930) region
J=2 helicity=2
J = 0
BELLE BABAR Events (stat. signif.) 64 ± 18 (5.3) 76 ± 18 (5.8)
Mass (MeV/c2) 3929 ± 5 ± 2 3927 ± 3 ± 1
Width (MeV) 29 ± 10 ± 2 21 ± 7 ± 4
Γγγ × BF(ZDD) (keV) 0.18±0.05±0.03 0.24±0.05±0.04
PRL 96, 082003 (2006)
arXiv:1002.0281 (2009) submieed to PRD
3/16/10 17 F. Anulli
395 fb-1
384 fb-1
BABAR plot: Efficiency-corrected & bckgd-subtracted
results for the Z(3930) <==> χc2(2P)
in the spin=2 hypothesis
BABAR preliminary
3/16/10 F. Anulli 18
Two-photon interactions in single-tag mode:
γγ* → π 0, ηc Transition Form Factors
tagged electron inside the detector ==> Off-shell photon Q2 = -q1
2 = -(p-p′)2 > 3 GeV2
electron along beam axis ==> “quasi-real photon” q2 = -q2
2 ~0 GeV2
γγ*→π0 Transition Form Factor
F(Q2,q2~0) ≡ F(Q2), describing the effect of strong interacHons in γγ*→ π0
for Q2 >> Mγγ the process can be factorized:
3/16/10 19 F. Anulli
single-tag mode:
T(x,Q2) calculable γγ*→ qqbar φπ(x,Q2) non‐perturbaHve, pion distribu5on amplitude (DA) x is the frac5on of pion momentum carried by one of the quarks
T(x,Q2) φπ(x,Q2)
γγ*→π0 Transition Form Factor
F(Q2,q2~0) ≡ F(Q2), describing the effect of strong interacHons in γγ*→ π0
for Q2 >> Mγγ the process can be factorized:
3/16/10 20 F. Anulli
single-tag mode:
T(x,Q2) calculable γγ*→ qqbar φπ(x,Q2) non‐perturbaHve, pion distribu5on amplitude (DA) x is the frac5on of pion momentum carried by one of the quarks
≈14000 events Syst. errors 2.3% (Q2-independent)
precise measurement in the 4 < Q2 < 9 GeV2 region
Q2 >10GeV2 : data exceed the asymptotic limit ( Q2F → √2fπ = 0.185 GeV2)
most models for the pion distribution approach the asymptotic limit from below
new calculations based on flat pion DA give a better agreement
T(x,Q2) φπ(x,Q2)
PRD 80, 052002 (2009)
442 fb-1
Q2 (GeV
2)
|F(Q
2)/
F(0
)|
0
0.2
0.4
0.6
0.8
1
0 10 20 30 40 50
γγ*→ηc Transition Form Factor
3/16/10 F. Anulli 21
• reconstruct ηc → ΚSΚ+-π-+ • no-tag mode:
• measure ηc parameters • determine F(0)
systematic uncertainties independent of Q2 sum up to ~4.3%
LO pQCD
monopole fit
469 fb-1
• fit to the FF distribution with
€
F(Q2) =F(0)
1+Q2 /Λconsistent with both - VMD: Λ = mJ/ψ
2 = 9.6 GeV2
- Lattice QCD: Λ = 8.4 ± 0.4 GeV2
• BABAR data lie systematically below a leading-order pQCD calculation (but within the large errors)
Dudek, Edwards PRL97, 172001 (2006) Feldmann, Kroll PLB413, 410 (1997)
Λ = 8.5 ± 0.6 ± 0.7 GeV2
mass 2982.2 ± 0.4 ± 1.6 MeV/c2
Width 31.7 ± 1.2 ± 0.8 MeV
Γγγ × BF(ηc→KSKπ) 0.374 ± 0.009 ± 0.031 keV
BABAR preliminary
arXiv:1002.3000 (2010) accepted by Phys.Rev.D
• single-tag mode: • dσ/dQ2 F(Q2) normalized to F(0)
Conclusions • Thanks to the very high luminosity of the B-factories BELLE and BABAR
have exploited the full potential of the ISR and two-photon processes for studying low energy hadron physics
☞ A totally new era in charmonium sector opened after the discovery of the X(3872) (in B decays) and Y(4260) via ISR ☞ searches for new “exotic” states routinely performed via ISR, two-photon
fusion and B-decays at B-factories ☞ Two-photon fusion has proven to be a very clean way to study the structure
of low energy scalars ☞ Measurements of exclusive e+e- annihilation processes via ISR, performed
by BABAR, provide the most precise and most complete determination of the hadronic contribution to (g-2)µ and αQED
☹ Unfortunately, only a tiny fraction of the results obtained from the two experiments could been shown here
3/16/10 F. Anulli 22
Thank you!
BACKUP
3/16/10 23 F. Anulli
3/16/10 F. Anulli
24
aµhad
aµππ in the range 0.630-0.958 GeV
BABAR consistency test: comparison of σµµ with EW prediction: agreement within 0.4±1.1%, dominated by absolute luminosity (±1%)
Fπ fit to BABAR data
KLOE (ISR untagged, 2008)
SND (energy scan)
CMD-2 (energy scan)
γγ*→π0 cross section and TFF extract number of signal events from fit to the
γγ mass spectrum in each Q2 bin, corrected for data/MC differences and resolution effects
3/16/10 25 F. Anulli
≈14000 events Syst. errors ~3%
F. Anulli 26 Bari, April 2, 2009
γγ → π0π0 : resonance region Phys.Rev.D79,052009(2009) Phys.Rev.D78,052004(2008)
Wγγ < 1.7 GeV Wγγ > 1.7 GeV
f4(2050)
M (MeV/c2) Γγγ (eV)
π0π0 982.2 ± 1.0 +8.1-8.0 286 ± 17 +211
-70
π+π- 985.6 +1.2-1.5
+1.1-1.6 205 +95
-83 +147
-117
PDG 980 ± 10 310 +80-110
(uu+dd)/√2 1300 - 1800
ssbar 300 - 500
k molecule 200 - 600
tetra-quark 270
€
dσdΩ
γγ →π 0π 0( ) = SY00 +D0Y2
0 +G0Y40 2
+ D2Y22 +G2Y4
2 2
f4(2050) f2(1950)
M (MeV/c2) 1885 +14-13 2038 +13
-11
Γ (MeV) 453 ± 20 441 +27-25
Γγγ B(π0π0) (eV) 7.7 +1.2-1.1 54 +23
-14
parameters of f0(980) consistent between π0π0 and π+π- (PRD 75,051101) channel
inclusion of both f2(1950) and f4(2050) looks necessary
3/16/10 27 F. Anulli