e + e hadrons in ISR and Two-photon reactions with BELLE and BABAR

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1 e + e hadrons in ISR and Two-photon reactions with BELLE and BABAR Fabio Anulli INFN Sezione di Roma on behalf of the BABAR Collaboration Rencontres de Moriond QCD and High Energy Interactions March, 20 La Thuile

2 Outline selected ISR results exclusive light hadron final states e + e π + π e + e open charm hadronic contribution to (g-2) µ selected γγ results no-tag mode γγ π 0 π 0, ηπ 0 γγ DDbar single-tag mode γγ π 0,η c ==> Transition Form Factors more results shown yesterday by Pasha Pakhlov on discovery of exotic charmonium-like state 3/16/ F. Anulli 2

3 selected ISR results m 2 f = s =s(1 x) dσ e + e fγ (s,m f ) dm dcosθ γ = 2m s W (s,x,θ γ ) σ e + e f ( m f ) Radiator function GeV ==> access the same observables as low energy e + e experiments! Quantum numbers at production vertex J PC =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 α em suppression compensated by the huge luminosity 3/16/ F. Anulli 3

4 The Anomalous Magnetic Moment of the muon a SM µ = g 2 2 a µ precisely measured at BNL E821 Phys.Rev.D73,072003(2006) a exp µ a SM µ = ( 30.1± 8.6 ) - (arxiv: ) µ = a µ QED + a µ had + a weak Dominant uncertainty from hadronic vacuum polarization. Cannot be calculated by QCD first principles determine it via dispersion relations, by measuring the total hadronic cross section R(s) = σ(ee hadrons)/σ(ee µµ) Value before BABAR result a µ had = (690.9 ± 5.3) - 73% from ππ 62% of uncertainty from ππ Need to measure R(s) with better than 1% precision! 3/16/ F. Anulli 4

5 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 BABAR measurement of R ππ Cross section [nb] Phys. Rev. Lett. 3, (2009) (b) 00 (c) s [GeV] 3/16/ F. Anulli 5

6 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 BABAR measurement of R ππ Cross section [nb] Note: averages taken from M.Davier et al. arxiv: Phys. Rev. Lett. 3, (2009) 1-3 (b) 00 (c) s [GeV] BABAR a µ ππ [2m π,1.8gev] = (514 ± 2.2 ± 3.1) - previous e + e - average ± 3.5 tot new e + e - average ± 1.3 ± 2.6 new average from tau ± 2.0 exp ±2.2 BF ±1.9 IB Including all other contributions from e + e cross sections a µ had ( - ) ± 4.0 exp ± 0.7 QCD a µ exp - a µ SM ( - ) 25.5 ± 8.0 Deviation 3.2 σ the discrepancy with the esxperimental value is still above 3σ! 3/16/ F. Anulli 6

7 The ISR program in BABAR Vigourous campaign that is still in progress: Κ S0 Κ π +, Κ + Κ π 0, Κ + Κ η - 2(π + π )π 0, 2(π + π )η, Κ + Κ π + π π 0, Κ + Κ π + π η PRD 76, , 2007 Κ + Κ π + π, Κ + Κ π 0 π 0, Κ + Κ Κ + Κ 3(π + π ), 2(π + π π 0 ), Κ + Κ π + π π + π π + π π + π, Κ + Κ π + π, Κ + Κ Κ + Κ PRD 77, , 2008 PRD 76, , 2007 PRD 73, , 2006 PRD 71, , 2005 π + π π 0 PRD 70, , pp PRD 73, , ΛΛ, Σ 0 Σ 0, ΛΣ 0 PRD 76, , 2007 First observations 232 fb 1, 89 fb GeV all analysis with tagged ISR γ ==> efficient background rejection only charmless mesons and baryons in this slide e + e π + π π + π unprecedented accuracy! a factor 2 3 improvement on determinahon of contribuhons to a µ had ( - ) without BABAR with BABAR π + π π ± ± (π + π ) ± ± (π + π ) 0. ± ± (π + π π 0 ) 1.42 ± ± /16/ F. Anulli 7

8 e + e - annihilation to open charm via ISR: e + e - D(*) D (*) Phys.Rev. D79, (2009) ψ(3770) ψ(4040) ψ(4415) 384 % 1 DD DD * D * D * Measure properties of heavy charmonium states Search for Y(4260) D (*) D (*) decays should be the dominant decay for a ccbar meson No evidence found: 90% CL BF(Y(4260) X ) BF(Y(4260) J /ψπ + π ) for comparison (from PDG): X =DD X =DD * X =D * D * BF(ψ(3770) DD ) BF(ψ(3770) J /ψπ + π ) 400 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) 3/16/ F. Anulli 8

9 e + e - annihilation to open charm via ISR: e + e - D(*) D (*) Phys.Rev. D79, (2009) ψ(3770) ψ(4040) ψ(4415) 384 % 1 DD DD * D * D * Measure properties of heavy charmonium states Search for Y(4260) D (*) D (*) decays should be the dominant decay for a ccbar meson No evidence found: 90% CL BF(Y(4260) X ) BF(Y(4260) J /ψπ + π ) for comparison (from PDG): X =DD X =DD * X =D * D * BF(ψ(3770) DD ) BF(ψ(3770) J /ψπ + π ) 400 BELLE: Phys. Rev. Lett. 98, (2007) 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) Sum of two body open charm final states 3/16/ F. Anulli 9

10 Phys.Rev.D80,0911(2009) (R) 695 % 1 e + e - γ ISR D 0 D * π + Upper Limit ψ(4415) 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) D 0 D * π + )< 0.76 nb at 90% CL Br(ψ(4415) D 0 D * π + ) <.6 % at 90% CL 3/16/ F. Anulli

11 Phys.Rev.D80,0911(2009) (R) 695 % 1 Y(4260) ψ(4415) e + e - γ ISR D 0 D (*) - π + σ(e + e ψ(4415)) Br(ψ(4415) D 0 D * π + )< 0.76 nb at 90% CL Br(ψ(4415) D 0 D * π + ) <.6 % at 90% CL UL at 90% CL 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 D 0 D * 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 3/16/ F. Anulli 11

12 Selected two-photon results in no-tag mode ( ) = σ γγ X (W ) dl γγ σ e + e e + e γ * γ * e + e X dw dw C-even final states J PC = 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/c 2 Beam particles escape with small scattering angle q 2 0 : quasi-real photons can measure Γ γγ two-photon events selected with tight p T cut 3/16/ F. Anulli 12

13 ExtracHon of γγ X cross section: ( ) = σ γγ X (W ) dl γγ σ e + e e + e X dw dw γγ π 0 π 0, ηπ 0 dσ γγ X d cosθ = ΔN ΔB * ΔW Δ cosθ * ε dl γγ dw L ee dσ σ γγ X (W ) = Δ cosθ * d cosθ * γγ π 0 π 0 γγ ηπ 0 Resonance study PRD80,032001(2009) PRD79,052009(2009) PRD78,052004(2008) Clear f 0 (980), f 2 (1270) peaks Structures visible around 1.6 and 2.0 GeV ( f 4 (2050) ) Smooth behaviour above ~2.4 GeV Fit the asymptohc behavior a 0 (980), a 2 (1320), a 2 (1700) seen Smooth behaviour above ~2.4 GeV 3/16/ F. Anulli 13

14 γγ ηπ 0 : resonance region Partial Wave Analysis for 0.9 < W < 1.5 GeV dσ dω γγ π 0 π 0 ( ) = SY D 0 Y D 2 Y = S 2 Y D 0 2 Y D 2 2 Y fit with a 0 (980), a 2 (1320) and a 0 (Y) in the region W < 1.5 GeV S= A a0 (980)e iφ S 0 + A a 0 (Y )e iφ S1 + B S D 0 =B D0 D 2 = A a2 (1320)e iφ D 2 + B D2 a 0 (980) a 0 (980) PDG a 0 (Y) a 0 (1450) PDG Phys.Rev.D80,032001(2009) Mass (MeV/c 2 ) Γ tot Γ γγ B(π 0 π 0 ) (MeV) (ev) ± ± ± ± unknown Nominal fit M(a 0 (Y) = M(a 0 (1450)) No a 0 (Y) χ 2 /ndf 597.6/ / /433 inclusion of a 0 (Y) gives a better χ 2 mass and width of a 0 (Y) significantly smaller than PDG values of a 0 (1450) 3/16/. Anulli 14

15 γγ π 0 π 0 : study of the higher mass region γγ π 0 π 0 Phys.Rev.D 79, (2009) cross secmon (nb) Slope: n = 6.9±0.6±0.7 σ(π 0 π 0 )/σ(π + π ) = 0.32±0.03±0.05 Isospin symmetry fitted slopes σ W -n ( pqcd: n = 6 ) 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 3/16/ F. Anulli 15 n π 0 π ± 0.6 ± 0.7 PRD79, (2009) π + π 7.9 ± 0.4 ± 1.5 PLB615,39 (2005) Κ + Κ 7.3 ± 0.3 ± 1.5 PLB615, 39 (2005) ηπ 0.5 ± 1.2 ± 0.5 PLB651, 15 (2007) K S K S.5 ± 0.6 ± 0.5 PRD80, (2009)

16 γγ π 0 π 0 : study of the higher mass region cosθ < 0.4 γγ π 0 π 0 Phys.Rev.D 79, (2009) cross secmon (nb) Slope: n = 6.9±0.6±0.7 σ(π 0 π 0 )/σ(π + π ) = 0.32±0.03±0.05 Isospin symmetry leading-order pqcd χ c0 observed with 7σ (1.3σ for χ c2 ) fitted slopes σ W -n ( pqcd: n = 6 ) n π 0 π ± 0.6 ± 0.7 PRD79, (2009) 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 π + π 7.9 ± 0.4 ± 1.5 PLB615,39 (2005) Κ + Κ 7.3 ± 0.3 ± 1.5 PLB615, 39 (2005) ηπ 0.5 ± 1.2 ± 0.5 PLB651, 15 (2007) K S K S.5 ± 0.6 ± 0.5 PRD80, (2009) 3/16/ F. Anulli 16

17 Entries / MeV/c 2 35 Discovery (and confirmation) of the χ c2 (2P) in γγ DD Radial excitahon states established for 2S+1 L J = 3 S 1 (ψ) and 1 S 0 (η c ) Lowest 3 P J (χ cj ) well established, but nothing known about radial excitahons In 2006, Belle reported the discovery of the Z(3930) idenhfied as the χ c2 (2P) This state and its interpretahon is now confirmed by BABAR, with consistent parameters Efficiency corrected mass spectrum 395 fb fb 1 PRL 96, (2006) arxiv: (2009) 30 submieed to PRD in the spin=2 hypothesis BABAR BABAR plot: 5 preliminary -5 Efficiency-corrected cos! & bckgd-subtracted 2 m(dd) [GeV/c ] 3/16/ F. Anulli 17 Entries / 0.1 Angular distribuhon in the Z(3930) region J=2 helicity=2 J = 0 results for the Z(3930) <==> χ c2 (2P) BELLE BABAR Events (stat. signif.) 64 ± 18 (5.3) 76 ± 18 (5.8) Mass (MeV/c 2 ) 3929 ± 5 ± ± 3 ± 1 Width (MeV) 29 ± ± 2 21 ± 7 ± 4 Γ γγ BF(Z DD) (kev) 0.18±0.05± ±0.05±0.04

18 Two-photon interactions in single-tag mode: γγ* π 0, η c Transition Form Factors tagged electron inside the detector ==> Off-shell photon Q 2 = q 1 2 = (p p ) 2 > 3 GeV 2 electron along beam axis ==> quasi-real photon q 2 = q 2 2 ~0 GeV 2 3/16/ F. Anulli 18

19 single-tag mode: γγ π 0 Transition Form Factor F(Q 2,q 2 ~0) F(Q 2 ), describing the effect of strong interachons in γγ π 0 for Q 2 >> M γγ the process can be factorized: T(x,Q 2 ) φ π (x,q 2 ) T(x,Q 2 ) calculable γγ qqbar φ π (x,q 2 ) non perturbahve, pion distribu5on amplitude (DA) x is the frac5on of pion momentum carried by one of the quarks 3/16/ F. Anulli 19

20 single-tag mode: γγ π 0 Transition Form Factor F(Q 2,q 2 ~0) F(Q 2 ), describing the effect of strong interachons in γγ π 0 for Q 2 >> M γγ the process can be factorized: PRD 80, (2009) T(x,Q 2 ) φ π (x,q 2 ) T(x,Q 2 ) calculable γγ qqbar φ π (x,q 2 ) non perturbahve, pion distribu5on amplitude (DA) x is the frac5on of pion momentum carried by one of the quarks 442 fb events Syst. errors 2.3% (Q 2 -independent) precise measurement in the 4 < Q 2 < 9 GeV 2 region Q 2 >GeV 2 : data exceed the asymptotic limit ( Q 2 F 2fπ = GeV 2 ) most models for the pion distribution approach the asymptotic limit from below new calculations based on flat pion DA give a better agreement 3/16/ F. Anulli 20

21 reconstruct η c Κ S Κ + π + no-tag mode: measure η c parameters determine F(0) γγ η c Transition Form Factor mass ± 0.4 ± 1.6 MeV/c 2 Width Γ γγ BF(η c K S Kπ) 31.7 ± 1.2 ± 0.8 MeV ± ± kev single-tag mode: dσ/dq 2 F(Q 2 ) normalized to F(0) fit to the FF distribution with F(Q 2 ) = F(0) Λ = 8.5 ± 0.6 ± 0.7 GeV 2 1+Q 2 /Λ consistent with both - VMD: Λ = m J/ψ 2 = 9.6 GeV 2 - Lattice QCD: Λ = 8.4 ± 0.4 GeV 2 Dudek, Edwards PRL97, (2006) F(Q 2 )/F(0) fb 1 monopole fit arxiv: (20) accepted by Phys.Rev.D BABAR preliminary LO pqcd Q 2 (GeV 2 ) systematic uncertainties independent of Q 2 sum up to ~4.3% BABAR data lie systematically below a leading-order pqcd calculation (but within the large errors) Feldmann, Kroll PLB413, 4 (1997) 3/16/ F. Anulli 21

22 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 α QED Unfortunately, only a tiny fraction of the results obtained from the two experiments could been shown here Thank you! 3/16/ F. Anulli 22

23 BACKUP 3/16/ F. Anulli 23

24 a µ had F π fit to BABAR data a µ ππ in the range GeV KLOE (ISR untagged, 2008) SND (energy scan) BABAR consistency test: comparison of σ µµ with EW prediction: agreement within 0.4±1.1%, dominated by absolute luminosity (±1%) CMD-2 (energy scan) 3/16/ F. Anulli 24

25 γγ π 0 cross section and TFF extract number of signal events from fit to the γγ mass spectrum in each Q 2 bin, corrected for data/mc differences and resolution effects events Syst. errors ~3% 3/16/ F. Anulli 25

26 F. Anulli 26 Bari, April 2, 2009

27 Phys.Rev.D78,052004(2008) W γγ < 1.7 GeV γγ π 0 π 0 : resonance region dσ dω γγ π 0 π 0 ( ) = SY D 0 Y 2 0 +G 0 Y D 2 Y 2 2 +G 2 Y Phys.Rev.D79,052009(2009) W γγ > 1.7 GeV f 4 (2050) parameters of f 0 (980) consistent between π 0 π 0 and π + π (PRD 75,0511) channel f 4 (2050) f 2 (1950) M (MeV/c 2 ) M (MeV/c 2 ) Γ γγ (ev) Γ (MeV) 453 ± π 0 π ± ± Γ γγ B(π 0 π 0 ) (ev) π + π PDG 980 ± (uu+dd)/ ssbar k molecule inclusion of both f 2 (1950) and f 4 (2050) looks necessary tetra-quark 3/16/ 270 F. Anulli 27