1 / 36

R Measurement from BES

R Measurement from BES. Z.G. Zhao (Representing BES Collaboration) University of Michigan, Ann Arbor, MI, USA IHEP of CAS, Beijing, China. Motivation R Scan in 2-5 GeV QCD Test Topics with R scan Data Summary. The B eijing E lectron P ositron C ollider ( BEPC ).

kareem
Download Presentation

R Measurement from BES

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. R Measurement from BES Z.G. Zhao (Representing BES Collaboration) University of Michigan, Ann Arbor, MI, USA IHEP of CAS, Beijing, China • Motivation • R Scan in 2-5 GeV • QCD Test Topics with R scan Data • Summary Zhengguo Zhao

  2. The Beijing Electron Positron Collider (BEPC) A unique e+e- machine operating in Ecm~2-5 GeV since 1989. L~51030 /cm2s at J/ peak Zhengguo Zhao

  3. BESII Detector(General Purpose Collider Detector) VC: xy = 100 m TOF: T = 180 ps  counter: r= 3 cm MDC: xy = 200 m BSC: E/E= 22 % z = 5.5 cm dE/dx= 8.4 %  = 7.9 mr B field: 0.4 T p/p=1.8%(1+p2) z = 2.3 cm Zhengguo Zhao

  4. Experimentally Nhad: observed hadronic events Nbg: background events L: integrated luminosity had: detection efficiency for Nhad : radiative correction Definition of R R: one of the most fundamental quantities in particle physics, counts directly the number of quarks, their flavor and colors Zhengguo Zhao

  5. R/R ~ 15% below 5 GeV Unclear & complex structure in 3.7-5 GeV R Values Below 10 GeV 15% Zhengguo Zhao

  6. Reducing the uncertainty of (MZ2) essential for precision tests of the SM • calculated measured • At MZ2 0.03142 0.02800.0009 • Hunting for new physics from a(g-2)/2  Interpretation of E821 at BNL New physics Motivations Zhengguo Zhao

  7. The indirectly determination of mH depends critically on the precision of (MZ2) Relative uncertainties of three input parameters in the SM fit Zhengguo Zhao

  8. BEPC energy region Relative Contributions to the Uncertainties of a and (MZ2) Zhengguo Zhao

  9. BES R Scan March-May, 1998: • 6 energy points at 2.6, 3.2, 3.4, 3.55, 4.6, 5.0 GeV + separated beam operation at each Feb.- June, 1999: • 85 energy points at 2.0-4.8 GeV + 24 energy points separated beam operation Zhengguo Zhao

  10. Events collected at BESII N N Events Recorded by BESII Event rate Zhengguo Zhao

  11. Hadronic Events Selection Select Nhad(e+e-hadrons) from all other possible contaminations. e- Zhengguo Zhao

  12. Data MC Typical Cuts Used for Selecting Nhad Zhengguo Zhao

  13. Trigger Efficiency (trg) • trg measured by comparing the responses to different trigger requirements in - special runs taken at J/ - R at 2.6, 3.0, 3.5 GeV with larger data sample • trg = 99.96%, 99.33%, 99.76% for Bhabha, dimuon and hadrons with errors of 0.5% Zhengguo Zhao

  14. Background Subtraction Background sources: 1. Cosmic ray 2. Lepton pair production subtracted by event 3. Two-photon processes selection and MC 4. Beam associated  most serious • fit the event vertex distribution with Gaussian for hadronic events, polynomial(degree 2) for BG b) separated beam and single beam operation data Nbg = f  Nsep Both a) and b) are consistent Zhengguo Zhao

  15. Subtraction of the Beam Associated Background Gaussican for Nhad P2 for BG Zhengguo Zhao

  16. Rely on large-angle Bhabha e+e- e+ e- () e+e- cross check Bhabha events Bhabha events Luminosity Measurement Zhengguo Zhao

  17. Detection Efficiency for the Hadronic Events • Rely on hadronic events generatormodel dependent • LUARLW is developed to improve JETSET for low energy region, particularly for Ecm< 3 GeV - final states are simulated exclusively - less parameters in the fragmentation function - remove high energy assumption • D, D*, Ds, Ds* productions are simulated according to Eichiten Model • A generator is built into LUARLW to handle decays of resonances in the radiative return processes e+e- J/ or (2S) Zhengguo Zhao

  18. Some Hadronic Event Shapes at Ecm=2.2 GeV (LUARLW) Tune the parameters to reproduce 14 distributions of the observed kinematic variables and hadronic event shape. Hatched region: MC Histogram: Data Zhengguo Zhao

  19. Some Hadronic Event Shapes at Ecm=3.55 GeV Zhengguo Zhao

  20. ISR: remove high order effects from Leading order [O(2), diagram (a)] All the high order contributions Born term vertex Vacuum polarization Bremsstrahlung Initial States Radiative Correction Zhengguo Zhao

  21. Initial States Radiative Correction • Four schemes are compared to calculate ISR. (1) G. Bonneau and F. Martin, NP B 27(1971)387 (2) F.A. Berends and R. Kleiss, NP B 178(1981)14 (3) E. A. Kuraev and V.S. Fadin, Sov. J. NP 41(1985)3 (4) A. Osterheld et al., SLAC-PUB-4160, 1986. (T/E) • (2) + multi-soft photon = (4) • (1) – (4) are consistent within1% in the continuum region, 1-3% above charm threshold Zhengguo Zhao

  22. Syst. error Variation of Detection Efficiency and ISR in 2-5 GeV Zhengguo Zhao

  23. Some Values at a Few Typical Energy Points to Determine R Systematic Errors (in %) at a Few Typical Energy Points Zhengguo Zhao largest

  24. R Values in 2-5 GeV PRL 88:101802,2002 (3770) Preliminary results reported at ICHEP2000 are the same as the final published ones in 2002 Zhengguo Zhao

  25. R Below 10 GeV Before BES R Scan After BES R Scan Zhengguo Zhao

  26. CLEO CMD,SND KROE BESIII CLEOC had(MZ2) and Its Relative Contribution in Magnitude and Uncertainty Zhengguo Zhao

  27. With BES data Without BES data (95% C.L.) (95% C.L.) The Impact of BES R-value on SM Fit to mH Zhengguo Zhao

  28. R(pQCD) and R(BES) pQCD calculation agree well withBESdata (D. Michel et.al.) under current uncertainty Zhengguo Zhao

  29. Evaluation of s and s(MZ) from R(BES) Exhibits QCD correction known to O(s3(s)) so far. Precision measurement of R can determine s and thus evaluate s(MZ). Using R at 3.0 and 4.8 GeV, one has: Which gives: PDG2000: J.H. Kuhn, M.Rreinhauser Nucl. Phys. B619(2001)588 consistent Zhengguo Zhao

  30. A wonderful laboratory to study E.W. and strong interaction. Unique place to investigate pQCD, hadron production mechanism With BES R scan data  distribution (MLLA/LPHD) Multiplicity: second binomial moment R2 (NLO) e+e-(K) + X processes (polarized parton density) Hadron Production from e+e- Annihilation MLLA: Modified Leading Log Approximation LPHD: Local Parton Hadron Duality Zhengguo Zhao

  31.  Distribution: =-ln(2p/s) MLLA/LPHD calculations BES data can be reasonably well described by MLLA/LPHD Zhengguo Zhao

  32. *: Peak Position of  Distribution MLLA/LPHD predict: eff: free parameter C=0.2915/0.3190/0.3513 For nf = 3/4/5 BES data support MLLA/LPHD prediction Zhengguo Zhao

  33. BES KLPHD and eff Zhengguo Zhao

  34. Average multiplicity NLO Multiplicity Zhengguo Zhao

  35. Second Binomial Moment NLO calculation c=0.5603/0.3196/0.3513 for nf=3,4,5 BES data systematically lower than what NLO predicted, and consistent with the tendency of that from high energy e+e- data Zhengguo Zhao

  36. Summary • BES measured R in 2-5 GeV with average uncertainties of 6.6% (a factor of 2-3 improvement) • R scan data at continuum is used to test QCD. However precision test of QCD need more accuracy data (~1-3% level) • BES is planning to collect hadronic event sample with high statistics at a few energy points between 2-3 GeV • Further meaningful improvement on R measurement, and understand the broad structure between 4-4.5 GeV need BESIII at BEPCII. Zhengguo Zhao

More Related