Hot Topic from Belle : Recent results on quarkonia

Transcription

1 Hot Topic from Belle : Recent results on quarkonia Jolanta Brodzicka (Kraków) on behalf of Belle BEACH 21 June 21, Perugia Outline Puzzling nature of X(3872) X(3872), χ c2 J/ψγ X(3872) ψ γ Summary

2 Discovery of X(3872) X(3872) J/ψπ + π - observed in B X(3872)K by Belle PRL91, 2621 (23) S=36 7 (1 ) 152M BB M(J/ψπ + π - )-M(J/ψ) M(J/ψπ + π - ) M X (3872) X (3872) MeV 9%CL Confirmed by BaBar in B decays, CDF, DØ in pp X(3872)+anything 117M BB M(J/ψπ + π - ) PRD71, 7113 (25)

3 Try to understand X(3872) PRL13, 1521 (29) 2.4 fb -1 B X(3872)K 657M BB arxiv: X X Mode J J M(J/ψπ + π - ) Belle CDF Mass MeV M(J/ψπ + π - ) B D PRD81, 3113 (21) D * K D * Dγ M D M D * X (3872) X (3872) D D D D * * Belle BaBar D * D π 657M BB Mass suggests D D* bound state interpretation Molecular (below threshold) or virtual (above threshold)? Line-shape crucial to distuinguish Bound state scenario supported by: BR( X BR( X If X(3872) is conventional cc, why so narrow? D D J * ) ) 1 M(D D * )

4 Try to understand X(3872) CDF angular analysis: J PC = 1 ++, 2 -+ favored PRL98, 1322 (27) Difficult to discriminate further Belle evidence of X(3872) J/ψπ + π - π BR X J / BR X J Large isospin violation. Unlikely for usual cc arxiv: fb -1 ω(782)-like M(π + π - π ) Babar confirmation of X(3872) J/ψω arxiv: Decay in P-wave favoured J P =2 - preferred Is X(3872) a missing η c2 (2D) charmonium?

5 Radiative decays of X(3872) Radiative transistions of charmonia: well predicted by quark models Good way to probe charmonium interpretation of X(3872) X(3872) γχ c1 X(3872) γχ c2 arxiv:48116 BR X c 9 CL BR X J % M(γχ c1 ) M(γχ c2 ) BR X c 2 9 CL BR X J % ψ 2 ψ 3 BR(X γχ c1 ) too small BR(X γχ c2 ) too small h c ruled out by angular analysis η c2 BR(X J/ψππ) too large η c X(3872) too light and narrow χ c1 BR(X γj/ψ) too small No good charmonium candidate arxiv:4733

6 Radiative decays - first evidence arxiv:5537 X(3872) γj/ψ X(3872) γj/ψ 3.6σ M(γJ/ ) M(γJ/ ) X(3872) γψ 424fb 3.5σ 1 M(γ ) PRL12, 1321 (29) BR X BR X J J.14.5 BR X BR X J ' BR B X ( 3872 ) K BR X J BR X BR X J ' BR B X ( 3872 ) K BR X J Important implications: Imply even C-parity of X(3872) Shed light on X(3872) nature

7 Radiative decays- problematic interpretation BR X BR X J ' is problematic for molecular interpretation of X(3872) Components of molecule: DD* (+ J/ψρ + J/ψω) Decay: vector-meson dominance and light-quark annihilation PRD8, 744 (29) arxiv:99.38 Such decay pattern implies: BR X ' BR X J Solution: admixture of charmonium component (for example χ c1 (2P)) Decrease X(3872) γj/ψ rate through destructive interference Radiative decays worth studying further

8 Radiative decays of quarkonia in B mesons Studied decay chain with data sample of 772M BB Method: B J K X (3872 ), c1, c2 J e e, K K J Reconstruct B mesons: signal window cut on ΔE-M bc plane Constrain ΔE Scale E γ to improve resolution of M(J/ψγ) Study M(J/ψγ), K s Signal MC region of B signal For signal ΔE = Tail due to radiative losses

9 Study of B J/ψγ K χ c region: χ c1 serves as a reference mode χ c2 suppressed by factorization Background sources: B J/ψK*, B ψ K with ψ χ c1 γ non-j/ψ events, other combinatorial Background suppression: E γ >29MeV for χ c E γ >47MeV for X(3872) π veto, cut on photon helicity angle background reduced by 8%, signal by 3% M(J/ψγ) Background components: B + ψ K + B J/ψK* B + J/ψK* + B J/ψK(127), J/ψK 2 (143) non-j/ψ from data outside of J/ψ signal other combinatorial from MC from MC M(J/ψγ) fit to data: background: 1 st order Chebyshev polynomial, signal: double Gaussian fit mass and resolution of χ c1, fix mass and resolution of X(3872) and χ c2 wrt to them

10 Results for χ c1,c2 J/ψγ with BB χ c χ c2 B + χ c1,c2 K + M(J/ψγ) First evidence Significance includes systematics χ c χ c2 B χ c1,c2 K s M(J/ψγ)

11 Results for X(3872) J/ψγ with BB B + X(3872)K Significance includes systematic error BR B 1.78 X ( 3872) K BR X J B X(3872)K s BR X J.22.5 BR X J Using Belle X J/ψππ result from arxiv: Ratio consistent with previous Belle measurement BR B X (3872) K BR X J %CL

12 Study of B ψ γ K Studied decay: using 772M BB data Background sources: B ' K K X (3872) ' ' e e, K, K, J B ψ K*, B ψ K, B ψ Kππ non-ψ component and non-j/ψ for ψ J/ψππ Low energy photons: cuts used in B J/ψγK inefficient ψ K*-veto to reduce background from B ψ K* B ψ γk candidate + additional π, form ψ K* and calculate: s E ' K* E ' E K E - E cms beam M K M ( K ) M ' K* bc E cms 2 beam p ' p K p 2 Reject good B ψ K* candidates with: E ' K* 2MeV M K (892 75)MeV M ' K* bc 5.27GeV background reduced by 4% signal reduced by 15%

13 Background in M(ψ γ) Background after selection cuts: ψ e + e -,μ + μ - blinded ψ J/ψπ + π - blinded Background components: B ψ K* B + ψ K* + from MC B + ψ K + B ψ K s non-ψ, non-j/ψ from data other combinatorial from MC M(ψ γ) M(ψ γ) data with X(3872) region blinded Background matches data outside of X(3872) region MC agree with data Parameterization of background components: B ψ K*, ψ K: using B ψ K*,ψ K MC non-ψ: using data outside of ψ signal region other combinatorial: using inclusive B ψ +all MC shapes fixed in fit to data

14 Fit to M(ψ γ): parameterization and validation Pseudo-experiment test: fully simulated MC with embedded X(3872) ψ γ signal Example of B+ XK+, X ψ γ test: (assuming BaBar s BR) ψ e + e -,μ + μ - MC Signal PDF ψ K*+ψ K background PDF combinatorial (with non-ψ) Simultaneous fit to both ψ decay modes Signal: double Gaussian X(3872) mass fixed wrt fitted χ c1 J/ψγ mass σx(3872) fixed wrt fitted σχ c1 Background: shapes fixed from MC/data ψ J/ψπ + π - MC M(ψ γ) Signal PDF ψ K*+ψ K background PDF combinatorial (with non-ψ) Fit successfully tested with 5 pseudoexperiments and Toy MC samples Expected X(3872) ψ γ signals assuming BaBar s BR: ~58 events in B + X(3872)K + ~18 events in B X(3872)K s M(ψ γ)

15 Results for X(3872) ψ γ with BB B + ψ γk ψ e + e -,μ + μ - ψ J/ψπ + π - Fit components: Signal ψ K*+ψ K background combinatorial (with non-ψ) No signal observed BR B X (3872) K BR X ' %CL M(ψ γ) B ψ γk s M(ψ γ) BR X BR X J ' 9%CL ψ e + e -,μ + μ - ψ J/ψπ + π - BR B X (3872) K BR X ' %CL M(ψ γ) M(ψ γ)

16 Summary Mode Signal Product BR Belle B χ c2 K χ c2 J/ψγ [1-5 ] BaBar B <1.8 B <2.8 B X(3872)K X(3872) J/ψγ [1-6 ] B B <4.9 B X(3872)K X(3872) ψ γ [1-6 ] B B <19. X(3872) J/ψγ clearly observed Most precise measurement, agrees with previous evidence No X(3872) ψ γ signal observed Disagree with Babar s evidence Pure molecular interpretation of X(3872) is back? Big effort to understand nature of X(3872). Getting there?

17 Backup

18 Systematic errors in M(J/ψγ)

19 Systematic errors in M(ψ γ)

20 Belle/BaBar comparison

21 Comparison

22 Background in M(J/ψγ) Background in M(J/ψγ) from scaled MC compared with background in data M(J/ψγ) M(J/ψγ) M(J/ψγ) data sideband: red non-j/ψ from M(l + l - ) data sidebands: sky blue J/ψ inclusive + non-j/ψ from MC: dark blue

23 Fits to M(J/ψγ)

24 Backup X(3872) J/ψγ ΔE scaling for χ c1 background subtraction

25 Fit to M(J/ψγ): parametrization χ c region Signal: double Gaussian Background: 2 nd order Chebyshev polynomial Fit accounts for possible data/mc difference in resolution, mass scale X(3872) region Signal: double Gaussian Background: 1 st order Chebyshev polynomial Mean X(3872) fixed wrt fitted Mean χ c1 using PDG mass difference of χ c1 and X(3872) σx(3872) fixed using fitted σχ c1 after taking difference in resolutions from MC Fits checked with Toy MC: no bias found

26 X(3872) J/ψππ

27 x(3872) D D*