Measurements of. Jiangchuan Chen. (for BES Collaboration) Institute of High Energy Physics, Beijing , P.R. China

Transcription

1 Measurements of BF ψ 377, & BF ψ 377 non and search for ψ377 exclusive non decays Jiangchuan Chen for BES Collaboration Institute of High Energy Physics, Beijing 149, P.R. China XLI Rencontres de Moriond on QC and High Energy Hadronic Interactions Mar. 18 Mar.5, 6 1

2 Outline Introduction BF ψ 377 non with R & BF ψ 377,, by fitting had E i and E i with scan data. Search for exclusive ψ 377 non Summary

3 Introduction 3

4 The Beijing Electron Positron Collider BEPC L ~ ~ /cm s at ψ377 peak E cm ~-5 GeV One of the two e e - machines in the world in the τ-charm energy region 4

5 BESII etector VC: xy 1 µm TOF: T 18 ps µ counter: rφ 3 cm MC: xy µm BSC: E/ E % z 5.5 cm de/dx 8.5 % φ 7.9 mr B field:.4 T p/p1.7% 1p z 3.1 cm 5

6 ψ377 data sample ~18 pb -1 of data taken at GeV ~7 pb -1 of data taken in the region from GeV to GeV ~8 pb -1 of data taken in the energy region from to GeV about 33 pb -1 of data collected around GeV in total. 6

7 World ψ377 Samples pb ψ MARK-I ELCO MARK-II MARK-III BES-II CLEO-c 7

8 ψ377 resonance S cc It is believed to be a mixture of and states of 1 system, and it is thought to decay almost entirely to pure -bar. BUT Long-standing puzzle of ψ377 production and decays: before BES-II & CLEO-c Cross section at peak PG4 parameters prd 1π e ψ BF ψ e 11.6 ± 1.8 nb M prd ψ 377 e e 5. ±.5 nb e e 7.1±.7 Mark-III nb Previously published data indicate that more than 3% of ψ377 does not decay to -bar? This conflicts with theoretical prediction. 8

9 How to solve the problem? 1 irectly measure the branching fractions for the decays ψ 377,, and ψ 377 non Simultaneously measuring both and 377 could solve the problem or may uncover the puzzle, since there is no systematic uncertainty in normalization luminosity or eff.. ψ 3 Search for some exclusive non--bar decays of ψ

10 BFψ377 non- determined with R & 1

11 e e L 17.3 pb 1 of GeV Single tag method Using Kinematic fit method to improve momentum resolution and select the singly tagged meson tag K - π π Single tag analysis e e - - N tag From Monte L Br ε Carlo PG4 Br X Requiring M fit M X 11

12 K π Observed cross sections for -bar production at GeV K π π π 3.58±.9±.31nb π K π.56 ±.8 ± 6.14 ±.1 ±.6 nb.5 nb PLB

13 R value pqc calculates the R ratio Experimentally, one measures R - e e e - e q - q µ - µ hadrons lowest order ΣQ f flavor color had Born had N L ε had had had 1 δ µ µ N had : # of hadronic events : Luminosity L ε had : Eff. 1 δ : radiative correction factor Born had nb R e e µ µ Ecm GeV 13

14 Including the contribution from high order processes Rtot and R uds E CM [GeV] B e hadrons had R e ± ±.18.4 ± ± ±..18 ± ± ± ±.4 preliminary! see below R uds. ±. ±.9 R 3.75 ± Ruds ψ 3686 & ψ 377 GeV fit to.1±.13 BES contribution paper to Lepton-photon 5 stat. & p-to-p systematic error Ruds GeV. to 3..6±.14 Obtaining by fitting to the R values measured by BES in the range from. to 3. GeV 14

15 R ψ 377 & Born ψ 377 Taking the R for light hadron production to be a constant, then R E cm R cm ψ 377 R E GeV uds We obtain R ψ Including ψ ±.5 ±.13 Born 9.35 ±.9 ± 8 nb Preliminary! ψ 377. My calculation It is consistent with Born 1π e ψ BF ψ e 11.8 ± 1.74 nb 1 δ M VP ψ δ VP 1.47 ±.4 PLB obtained based on PG4 ψ377 resonance parameters 15

16 etermination of branching fractions with and Born ψ 377 Obtained from analysis of R BF ψ 377 N N prd prd ψ 377 Born Born ψ 377 g BES II Born ψ 377 Radiative correction Assuming that ψ377 decay exclusively into Some systematic uncertainties can be canceled out 1 14M / s B s dx f x, s s1 x 1 Π s1 x Π s1 B x 1 δ 1 πγee Γ f s s s M M Γ vp 1.47 ±.4 s PR tot Radiative correction factor g B g.764. BES II ± Radiative correction factor obtained based on new ψ377 resonance parameters measured by BES-II. 16

17 Results of branching fractions BF ψ ± 1.3 ± 3.9% BF ψ ± 1.1 ± 3.5% BF ψ ± 1.7 ± 6.% BF ψ 377 non 14. ± 1.7 ± 6.% These results are preliminary! 17

18 BF ψ377,, by fitting had E i & E i line-shape with scan data. Cross section scan experiment determined We use energy dependent inclusive hadronic cross sections and -bar cross sections to determine the branching fraction. BF ψ 377 non Monte Carlo eveloped a inclusive hadronic event generator with high order ISR corrections to simulate the hadronic event production in the full energy region. 18

19 MC generator & simulation Full energy range ISR e e hadrons Generator s 3.78 GeV ψ 377 Nch KNO φ ensity [nb/gev] ω ϕ ρ ρ17 J ψ 3686 /ψ Thrust Oblateness Aplanarity Sphericity cosθ Jet axis cosθ x η Y P t <P Tin > <P Tout > Effective energy [GeV] 19

20 Observed cross section Hadron efficiency vs C.M. energy had E cm L E cm n ε had had E cm ε trg expect B had s dx f x, s s1 x B 1 1πΓee Γ f s s s M M Γ Kuraev and Fadin tot s f x, s is sampling function

21 ψ377 Resonance parameters had ' ψ To get right resonance parameters, the two resonance production and decays should be considered simultaneously. In this way the correct QE background R uds can be determined correctly! had ψ 377 ψ 377 QE from u, d and s quarks ' ψ R uds.1 ±.13 J /ψ E cm [GeV] BES-II Preliminary! E cm [GeV] 1

22 Energy dependent cross sections -bar production K π istributions of invariant masses of combinations at different c.m. energies K π π π mknπ Ecm Lε N single tag singletag E cm B mode K π π

23 Observed cross sections Inclusive hadrons Inclusive hadrons 3 Observed cross section for hadron production [nb]

24 4 Fit to the erved cross sections 1 s M M s s tot ee B Γ Γ Γ π Fitting the erved inclusive hadron and -bar production cross sections to the theoretical cross sections, one obtains the branching fractions s M M s s tot tot ee B Γ Γ Γ π ψ s s s s non tot Γ Γ Γ Γ B p p rp rp M E s cm Γ Γ ψ θ Γ Γ B p p rp rp M E s cm ψ θ momentum of at peak momentum of threshold function ψ377 total width Γ Γ B B s non ψ ψ exp exp exp j j j j j j i i i had had had χ

25 Line shape of the cross sections for hadron and -bar production Inclusive hadrons had Inclusive hadrons had Ecm [ GeV ] [GeV ] E cm 5

26 Red: inclusive had. After subtracting the backgrounds from J/ψ and ψs radiative tails and QE continuum. Black: -bar Blue: - E cm [GeV ] 6

27 Branching fractions Obtained from fitting to the inclusive hadron and the -bar production cross sections simultaneously. BF ψ ± 5. ± BF ψ ± 4.1 ± BF ψ ± 6.8 ± BF ψ 377 non 16. ± 6.8 ± 3. % 3.5 % 6.4 % 6.4% BF ψ 377 non < at 9% C.L. Considered the correlation between the two branching fractions for the two modes where the first error is statistical and second systematic, which arises from the un-canceled systematic uncertainties in hadron cross sections ~3.4 %, neutral -bar cross sections ~6. % and charged -bar cross sections ~8.6 %. These results are preliminary! 7

28 Search for exclusive decay ψ377 non- 8

29 Evidence for ψ '' J /ψπ analysis of the fitted dilepton masses of Open histogram is for ee- channel, histogram in yellow is for mumu- channel ' ψ production due to π l ISR l π π The histogram is psi3686, while error bars are the psi3686 psi377 times large than the data data ψ '' J /ψπ π mainly MC ψ 3686 J /ψπ π 17.8± 4.8 /ψπ π signal events obtained J 6. ±. 8 N ψ 377 J / ψπ π 11.8 ± ± 4.8 ψ 3686 J /ψπ π J /ψπ π out of signal events 9

30 Previous ervations of non--bar decays BES erved 1 signal events for the decay ψ 377 non measured the branching fraction to be BF ψ 377 J / ψπ π.34 ±.14 ±.9 % CLEO confirmed BES ervation of the decay, and PLB measured the branching fractions to be π BF ψ 377 J / ψπ.189 ±. ±. % PRL 96,846 BES searched for ψ 377 ρπ, and determined the limits region 6 3 BF ψ 377 ρπ 6. 1,.4 1 PR 7, 77 5 CLEO also searched for some other non--bar exclusive decay modes 3

31 Search For ψ377 decay to Φπ and Φη Ecm around GeV L33 pb -1 Ecm3.65GeV L6.5 pb -1 π η π η Φ Φ Φ signal Φ sideband Ecm [GeV] NΦ π NΦη around ±

32 Search For ψ377 decay to Φπ π -, ΦK K - and Φpp Ecm around GeV L33 pb -1 Ecm3.65GeV L6.5 pb -1 Φπ π - Φπ π - ΦK K - ΦK K - Φpp Φpp- Ecm NΦ π π - NΦK K - NΦpp Around GeV L33 pb ± ± GeV L6.5 pb ±.6 3

33 Search For ψ377 decay to multi-body decays containing π or η Around 3.773GeV Ecm3.65GeV π π - π Around 3.773GeV L33 pb -1 Ecm3.65GeV L6.5 pb -1 KKπ π - π K K - π ppπ ppπ π - π 3π π - π π π - η bar events have been removed. 33

34 Observed Cross Sections Preliminary! 34

35 SUMMARY preliminary!. BES measured R at GeV and around GeV with average uncertainties of ~ 5% R 3.75 s Ruds R s in the range GeV GeV from 3.67 to 3.89 Born ψ ±.9 ±.8 nb. BES measured the energy dependent -bar cross sections, and the cross section at GeV 6.14 ±.1 ± Obtained from fitting to ψ3686 and ψ377.5 nb GeV Singly tagged analysis 5.93 ±.46 ±.35 nb oubly tagged analysis 35

36 SUMMARY preliminary!. BES measured the branching fractions for inclusive non--bar decays of ψ377 using two different data sample and two different methods BF BF BF BF ψ ψ ± 1.1 ±.1 ± ± 3.9 % 3.5 % ψ ± 1.7 ± 6. % ψ 377 non 14. ± 1.7 ± 6. % etermined from analysis of R values and -bar cross sections BF BF BF BF BF ψ ± 5. ± 3. % ψ ± 4. 1 ± 3. 5 % ψ ± 6. 8 ± 6. 4 % ψ 377 non 16. ± 6. 8 ± 6. 4 % ψ 377 non < 3.1 at 9% C.L. Obtained from fitting to the inclusive hadron and the -bar production cross sections simultaneously.. We searched for some exclusive multi-hadronic final state at Ecm3.773 GeV and Ecm3.65 GeV. We did not erve obvious cross section discrepancy at the two energy points. 36

37 Thank You 37

38 Comparison with those measured by CLEO-c BES-II BF ψ 377 non 16. ± 6.8 ± 6.4% Taking ψ 377 [ ψ 7 nb / 6.95 nb] ψ 377 CLEO-c 6.39 ± hadrons 6.38 ±.8 hep-ex/5138 nb nb ψ 1.1 ± 377 non the error in ψ 377 is ignored Method:.7 nb Based on inclusive hadron and cross section scan data. Fitting the erved inclusive hadron and production cross sections line-shape to the theoretical cross sections to obtain the branching fractions. Both results are not contradiction. ψ ± non nb CLEO-c directly counted the number of hadronic events erved at GeV, and subtracted the backgrounds from the J/ ψ, ψs tails and QE continuum. CLEO-c averaged the efficiencies for the decay.8 and ψs decay.68 to estimate the efficiency for the decay ψ377 non- hadrons. CLECO-c considered the possible effect of Interferences between the final states of resonance decays and non-resonant annihilation, assumed the amplitude for : γ qq hadrons interfere in the same way 38 as one for γ µ µ.

39 Comparison with those measured by CLEO-c BES-II 6.14 ±.1 ±.5 nb BF ψ 377 non 14. ± 1.7 ± 6.% Taking ψ nb ψ 377 CLEO-c 6.39 ± hadrons 6.38 ±.8 nb nb [ ψ / 6.95 nb] ψ 1. ± 377 non.44 nb ψ ± non nb Based on measured R values. Method: BES measured R uds near threshold and R at GeV with traditional method, then calculate the Born order cross section for ψ377 production. By comparing the cross sections for and ψ377 production, BES obtained the branching fraction. BES used an generator which included ISR to simulate the decay ψ377 hadrons. iscussion: If BES considered the interference effect between RES γ* qq hadrons and e e γ* qq hadrons, we obtain: BF ψ 377 non 1. ± 1.7 ± 6.% ψ ±.44 nb non In this case, if we take 6.39 nb, ψ nb non These results are not contradiction. 39

40 Comparison of measurements of the cross sections for -bar production [nb] 4