New Measurements of ψ(3770) Resonance Parameters & DD-bar Cross Section at BES-II & CLEO-c

Transcription

1 New Measurements of ψ(3770) Resonance Parameters & DD-bar Cross Section at BES-II & CLEO-c The review talk is based on the talks given at ICHEP 04 by Anders Ryd, Ian Shipsey, Gang Rong 1

2 Outline Introduction ψ(3770) resonance parameters DD production at GeV Result from BES-II Result from CLEO-c What indicate the new measurements? Summary 2

3 Introduction Puzzle of ψ(3770) decay Puzzle of ψ(3770) production and decays It has long been a puzzle that the measured DDbar cross section fail to fit the measured cross section for ψ(3770) production at GeV in e+e- experiments. ψ(3770) production cross section at peak prd 12π ( 3770 ) = ( (3770) + e ψ BF ψ e ) = 11.6 ± M ψ (3770 ) Mass and branching fraction (PDG02): M ψ ( 3770) = ± 2.5 MeV BF( ψ (3770) e + e ) =

4 DD-bar cross section + ( e e DD) = 5.0 ± 0.5 production cross section (Added all errors in quadrature) f ISR = 0.70 prd + ( e e DD) = 7.1± 0.7 ψ Non-saturate decay? About 39% of ψ(3770) does not decay to DD-bar? 4

5 Theoretical prediction Are there non-ddbar decay? There are theoretical arguments about ψ(3770) decays Lipkin pointed out that ψ(3770) could decay to non- DD-bar final states with large branching fraction Γ( ψ (3770) J / ψ ππ ) < 200 kev, Y.P. Kuang, PRD41(1990 )155 Γ( ψ (3770 ) γ χ ) cj 620 kev (hep - ph/ , J. L. Rosner) 37 < Γ( ψ (3770) J / ψ ππ) < 170 kev, (Y.P. Kuang, PRD65, (2002) ) Γ 3 ( D1 ggg ) = 160 kev Γ( ψ (3770) non DD) PLB kev (1991)11 BF ( ψ (3770) non DD) 4.0% Added all above numbers up! 5

6 About 35% of ψ(3770) missing? Are there non- DD-bar decay? If all measurements are all right, these mean that 35% of ψ(3770) is missing Lipkin proposed a rescattering model many years ago PL B179,278(1986) Very recently Jonathan L. Rosner proposed a new model ---reannihilation model to deal with that ψ(3770) decays to charmless final states arxiv:hep-ph/ v2 To clarify this situation, it is important to more precisely measure both DD-bar cross section and ψ(3770) resonance parameters at same experiment simultaneously! 6

7 The Beijing Electron Positron Collider (BEPC) L ~ /cm 2 s at ψ(3770) peak E cm ~2-5 GeV One of the two e + e - machines in the world in the τ-charm energy region 7

8 BESII Detector VC: xy = 100 µm TOF: T = 180 ps µ counter: rφ = 3 cm MDC: xy = 220 µm BSC: E/ E= 22 % z = 5.5 cm de/dx = 8.5 % φ = 7.9 mr B field: 0.4 T p/p=1.7% (1+p 2 ) z = 3.1 cm 8

9 Muon identification can be done for the charged track with momentum of great than 0.52 GeV/c 9

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12 BES-II ψ(3770) data sample ~18 pb -1 of data taken at GeV ~7 pb -1 of data taken at 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. CLEO-c ψ(3770) data sample about 57 pb -1 of data taken at (around) GeV 12

13 World ψ(3770) Samples (pb -1 ) Largest sample from CLEO-c by Spring, ψ(3770) Energy [GeV] Lum [pb^-1] Exp. Note ~2 MARK-I parameters ~2 DELCO parameters ~2 MARK-IIparameters MARK-III D decays MARK-I DELCO MARK-II MARK-III BES-II CLEO-c

14 ψ(3770) Resonance Parameters Cross section scan experiment The data were collected at 49 energy points from 3.66 to 3.89 GeV, which begin from off-resonance, cover ψ(2s), ψ(3770) and stop at DD* threshold. Separated beam collision data at 3 energy points were collected to study beam associated background. Some J/ψ, ψ(2s) data were also taken to calibrate BEPC energy and determine ε trg 14

15 Integrated luminosities Luminosities were measured by using large angle Bhabha scattering About 5.4 pb -1 of data were collected for the experiment Monte Carlo Developed a inclusive hadronic event generator with high order ISR corrections to simulate the hadronic event productions (including Lorentz boost due to initial state photon emission) in the full energy region 15

16 Monte Carlo e + e hadrons production Nominal c.m. energy s = 3.78 ρ ω ϕ GeV J /ψ ψ (3770 ' ψ ) 16

17 Events Recorded by BESII n +N had b e- q- n = Nhad(1+δ) had Nhad q e+ e- e- e- + - l l qq e+ e+ e+ e- N b e- µ- τ- e+ µ+ τ+ e- e+ e+ e- γ e+ γ N N Pri maarry ccosprim osm miicc ray rayy 0 + π π0 π π+ ee-- e eee e+ e ννµµ Cosmic-ray and beam associated background µ++ µ Distributions of the vertex of events physics background N could be estimated b based on cross sections, luminosities and 17 acceptances

18 Observed cross section Hadron efficiency vs C.M. energy had ( E ) = cm L( E cm ) n ε had had ( E cm ) ε trg ε had expect B had ( s) dx f ( x, s) ( s(1 x)) B = πΓee Γ f ( s) ( s) = ( s M ) + M Γ (Kuraev and Fadin) tot ( s) f ( x, s) is sampling function E cm [GeV] 18

19 ψ(3770) production had ' ψ To get right resonance parameters, the two resonance productions and decays should be considered simultaneously. In this way the correct QED background ( R uds ) can be determined correctly! had ψ (3770 ) ψ (3770 ) QED (from u, d and s quarks) ' ψ R uds = 2.24 ± 0.14 J /ψ E cm [GeV] BES-II Preliminary! E cm [GeV] 19

20 Comparison of ψ(3770) Resonance Parameters Experiment MARK-I DELCO MARK-II PDG02 BES-II (preliminary!) M ψ (3770) (MeV) 3772 ± ± ± ± ±1.3 Γ tot (MeV) Γ ee 28± 5 370± 90 24± 5 180± 60 24± 5 276± ± ± 40 (ev) M (MeV) 88± 3 86± 2 80± ± ± ± ± 1.3 prd ψ = 9.11 ± ( 3770 ) s = MeV

21 Comparison of ψ(2s) Resonance Parameters experiment M ' ψ (MeV) tot Γ ' ψ (kev) ee Γ ψ ' (kev) This measurement (preliminary!) ± 0.1 ± ± 60± ± 0.12± 0.02 BES-II published (PLB550(2002)24) PDG2002 N.A. 264± ± ± ± ± Using a constant for vacuum polarization correction 21

22 DD-bar Cross Section at GeV 1 BES-II: of GeV L = 17.3 pb Using Kinematical fit method to improve momentum resolution and select the singly tagged D meson Dtag K Single tag analysis e + e - D + D D- N = D tag D D From Monte 2 L Br ε Carlo PDG02 Br X Requiring M fit = M X 22

23 D 0 K π + Observed cross sections for DD-bar production at GeV D K π π π = 3.58± 0.09± 0 0 D D 0.31 D + + π + K π D + D D D = = 2.56 ± 0.08 ± 6.14 ± 0.12 ± Preliminary! 23

24 Radiative correction Assuming that ψ(3770) decay exclusively into DD DD ( s) 1 4M 0 2 / s = D B dx f ( x, s) ( s(1 x)) 1 Π( s(1 x)) 2 1 Π( s(1 x)) 2 = (1 + δ vp ) = 1.047± PR D62 (2000) πΓ eeγ ( s) B f ( s) = ( s M ) + M Γ tot ( s) Initial State Radiation correction factor g = B 24

25 Obtained based on PDG02 ψ(3770) resonance parameters: M = ± 2.5 MeV Γ tot ψ Γ ee ψ " = 23.6 ± 2.7 " = 260 ± 40 MeV ev At s = 3.773GeV Radiative correction factor g = Tree = 0.779± tree + D D tree DD = 4.60 ± 0.12 ± 0 0 tree D D = = 3.29 ± 0.10 ± 7.88 ± 0.15 ± Due to the uncertainties in resonance parameters and vaccum polarization 1+δ s = GeV preliminary ( vp 25

26 R D D R DD = e + e tree DD + µ µ R D D = 1.29± 0.02± 0.12 Assuming that ψ(3770) decays exclusively into DD-bar and The contribution to R in the charm threshold region from the light quarks is estimated to be R uds =2.26± 0.14, which is obtained by fitting to the R values from 2.0 to 3.0 GeV measured by BES-II. The theoretical expectation is that R uds is approximately independent of center of mass energy in this region. R uds R R + = R D R or D uds uds D yielding = R = 3.55 ± 0.02 ± ± 0.14 R = R D + R + + R e e µ µ 86.8 = E (GeV) = 2 2 cm The open square is charm counting method of R measurement (preliminary!) Squares are the BES-II direct R measurements by counting inclusive hadronic events (at 3.773GeV) which is obtained in measurement of ψ(3770) resonance parameters 26

27 DD-bar Cross Section at GeV 1 CLEO-c: of GeV L = 57.2 pb Using double tag method, pioneered by MARK-III K - D + tag D D- D + + Singly tagged D sample e + e - e + e - D D0 D tag D 0 K - + X Doubly tagged D X 0 27

28 N D 0 0 = ( D ) N D = + ( D )

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30 N N i ii = 2 = ε ε ii i B B i 2 i N N DD DD N DD = N 2 ε i ii 4N ε 2 ii i N D 0 = (1.98± 0.04± 0.03) 10 0 D + D N D = ( 1.48± 0.06± 0.04) =. (347. ± 007. ± 015) D D + = ± D D ( 2. 59± ). = ± D D ( 6.06 ± ) 30

31 What indicate the new measurements? What information can we obtain from the new measurements at BES-II and CLEO-c? Based on the measured DD-bar cross sections from BES-II & CLEO-c, we obtain the averaged DD-bar cross section 0 0 =. (349. ± 015) D D + = 258. ± D D = 6.08± D D ( 014). ( 0. 23) averaged cross sections Using the new ψ(3770) resonance parameters measured by BES-II, we obtain the ISR correction factor at GeV g =

32 Tree level cross sections 0 0 =. tree (459. ± 0 20) D D tree + = 339. ± D D tree = 7.99± D D ( 018). ( 030). averaged cross sections from BES-II and CLEO-c From BES-II preliminary result of prd ψ ( 3770) = 9.11± s= MeV 0.99 We can obtain the tree level cross section for ψ(3770) production to be ψ tree = (8.70± 0.95) ( 37770) 32

33 Branching fractions of ψ(3770) decays Using the BES-II & CLEO-c preliminary results on and presented at ICHEP 04, we can obtain ψ (3770) DD Branching fraction [%] 0 0 ψ D 52.8 ± 6.2 (3770) D + ψ (3770) D D 39.0 ± 4.7 ψ (3770) DD ψ (3770) non DD 91.8 ± ±

34 SUMMARY. BES measured ψ(3770) resonance parameters Experiment BES-II (preliminary!) PDG02 M ψ (3770) (MeV) ± ± 2.5 Γ tot (MeV) Γ ee 23.6± ± 40 (ev) M (MeV) 25.5 ± ± ± ± 2.4 prd = (BES-II preliminary!) ψ ( 3770 ) ±. Ruds = 2.24±0.14 From 3.66 to 3.87 GeV BES measured the DD-bar Cross Section at GeV to be = 7.88 ± 0.15 ± 0.74 tree D D ( ISR based on PDG02 ) (BES-II preliminary 34!)

35 SUMMARY Both the BES-II and the CLEO-c results were reported at ICHEP 04 as well. Measured the Observed cross section at GeV 0 D D 0 + D D D D BES-II ( 3.58 ± 0.09 ± ( 2.56 ± 0.08 ± 0.31) 0.26) ( 6.14± 0.12± 0.50) CLEO-c (preliminary!) (preliminary!) ( 347. ± 0. 07± 015). ( 2. 59± 011. ± 011). ( 6.06± 013. ± 022)..What is the non-dd-bar branching fraction of ψ(3770) It is reduced to about ( 8 ± 11 )% from 39 % using the new measurements at BES-II and CLEO-c 35

36 Thank You 36