Hadronic Cross Section Measurements at BES-III Sven Schumann Johannes Gutenberg Universität Mainz

Transcription

1 Hadronic Cross Section Measurements at BES-III Johannes Gutenberg Universität Mainz Introduction Hadronic cross sections & R ratio Impact on aμ and Δαhad Physics with Initial State Radiation ISR technique Hadronic final states at s < 2.0 GeV ISR physics with BES-III Energy Scan measurements BES-III Energy Scan for s = GeV

2 The R ratio Hadronic cross section ratio R: BES-III contributions to R data R Both ISR and Energy Scan measurements Energy range 0 < s < 4.5 GeV s [GeV]

3 The R ratio Hadronic cross section ratio R: BES-III contributions to R data R Both ISR and Energy Scan measurements Energy range 0 < s < 4.5 GeV BES-III ISR BES-III Scan s [GeV]

4 Contributions to aμ and Δαhad Contributions to aμ Contributions to Δaμ Dominated by energies s < 1 GeV ρ/ω resonances Dominated by energies s < 2 GeV Contributions to Δαhad Contributions to δδαhad

5 ISR physics with BES-III

6 Initial State Radiation Hadronic cross sections for aμ and Δα required over wide energy range e+e- colliders at fixed (design) energy BEPC-II / BES-III: PEP-II / BABAR: DAΦNE / KLOE: s = mψ(3770) = 3.77 GeV s = mϒ(4s) = GeV s = mφ(1020) = 1.02 GeV Use Initial State Radiation (ISR) from e+ or e to decrease effective s Initial State Radiation Measure cross sections for radiative process, e.g. e+e π+π γ with Radiator function H(s)

7 Tagged and untagged ISR Different analysis types: Tagged analyis: ISR photon detected in EMC Tagged ISR

8 Tagged and untagged ISR Different analysis types: Tagged analyis: ISR photon detected in EMC Untagged analysis: ISR photon leaves detector Most probable case Photon emitted close to e+/e beam direction Tagged ISR Untagged ISR

9 BES-III and BEPC-II Beijing Electron-Positron Collider (BEPC-II) Institute for High-Energy Physics (IHEP)

10 BES-III and BEPC-II Beijing Electron-Positron Collider (BEPC-II) Institute for High-Energy Physics (IHEP) Symmetric e+e collider Beam energy: CMS energy: Ee = GeV s = GeV Energy spread: Design luminosity: Ψ(3770) Achieved luminosity: /cm2/s BES-III data taking since 2009

11 BES-III detector systems Cylindrical drift chamber σp/p = 1 GeV Super-conducting magnet B = 1.0 T Time of Flight σt = 190 ps (Barrel) σt = 110 ps (Endcap) EM calorimeter (CsI) σe/ E = 1 GeV Muon chamber 8-9 layers RPC

12 BES-III data taking July 19, 2008 First e+e collision event in BES-III 11/ Ψ(2S) events 2009 for detector calibration Ψ(2S) events J/Ψ events fb Ψ(3770) fb Ψ(3770) 0.5 fb 4.10 GeV Ψ(2S) events J/Ψ events fb 4.23 GeV 0.8 fb 4.26 GeV 0.5 fb 4.36 GeV 0.3 fb GeV 0.5 fb 4.01 GeV

13 BES-III data taking July 19, 2008 First e+e collision event in BES-III 11/ Ψ(2S) events 2009 for detector calibration Ψ(2S) events J/Ψ events fb Ψ(3770) World s largest set on J/Ψ, Ψ(2S), Ψ(3770) fb Ψ(3770) 2.9 fb Ψ(3770) 0.5 fb 4.10 GeV 2012 used for ISR physics Ψ(2S) events J/Ψ events fb 4.23 GeV 0.8 fb 4.26 GeV 0.5 fb 4.36 GeV 0.3 fb GeV 0.5 fb 4.01 GeV

14 BES-III data taking July 19, 2008 First e+e collision event in BES-III 11/ Ψ(2S) events 2009 for detector calibration Ψ(2S) events J/Ψ events fb Ψ(3770) World s largest set on J/Ψ, Ψ(2S), Ψ(3770) fb Ψ(3770) 2.9 fb Ψ(3770) 0.5 fb 4.10 GeV 2012 used for ISR physics Ψ(2S) events J/Ψ events fb 4.23 GeV 0.8 fb 4.26 GeV 0.5 fb 4.36 GeV 3.1 fb XYZ region usable for ISR physics 0.3 fb GeV 0.5 fb 4.01 GeV

15 ISR at BES-III, KLOE, B-factories BES-III compared to KLOE: Higher energy range covered KLOE BES-III up to s ~ 3.5 GeV with BES max. s ~ 1.0 GeV with KLOE Less Final State Radiation (FSR) Worse statistics for π+π final state Worse mass resolution Larger drift chamber of KLOE BES-III compared to B-factories: Similar effective luminosities Smaller integrated luminosity More advantageous Radiator function Untagged ISR measurements possible already at ~ 1 GeV Similar mass resolution

16 BES-III programme on ISR ISR measurements for 3 main channels contributing to aμ : π+π cross section for s < 1 GeV: Precise measurements of π form factor in ρ/ω region from BABAR & KLOE BABAR: PRL 103, (2009) KLOE: PLB 670, 285 (2009), PLB 700, 102 (2011) Both experiments claiming ~1% precision Discrepancy between both experiments Additional measurement for π+π cross section needed

17 BES-III programme on ISR π+π π0 cross section: VEPP-2000 precision data up to s = 1.4 GeV High-statistics data from BABAR for s > 1.4 GeV Large deviation of BABAR & DM2 results Cross-check with BES-III ISR π+π π0π0 cross section : High statistics BABAR ISR results Huge improvement for s > 1.4 GeV First measurement for s > 2.5 GeV Competitive statistics at BES-III BABAR: 454 fb GeV BES-III: 10 fb 3.77 GeV Advantageous BES-III radiator function

18 e+e π+π γ analysis Goal: Measurement of Rππ: with Main issue: π/μ separation Using Artificial Neural Network (ANN) ANN trained with μ+μ γ and π+π γ MC samples Correct for efficiency differences between data and MC Other analyis steps: μ, π tracking efficiency Photon efficiency Dedicated results for π+π γ analysis Kinematic fit Unfolding of mass resolution FSR corrrection

19 e+e μ+μ γ mass distribution (preliminary) μ+μ mass distribution tagged ISR: BES-III data 2.9 fb GeV, tagged ISR Pr eli mi na ry Simulation PHOKHARA 7.0, e+e μ+μ γ Very good agreement Data & MC difference of (0.5 ± 0.3)%

20 e+e π+π cross section (preliminary) π+π cross section extracted from ISR π+π γ data BES-III data 2.9 fb GeV, tagged ISR Wide energy range up to ~3 GeV Pr eli mi na ry No FSR correction yet

21 e+e π+π cross section (preliminary) π+π cross section extracted from ISR π+π γ data BES-III data 2.9 fb GeV, tagged ISR Wide energy range up to ~3 GeV Pr eli Pr mi e l naim ry ina ry No FSR correction yet

22 e+e π+π cross section (preliminary) π+π cross section extracted from ISR π+π γ data BES-III data 2.9 fb GeV, tagged ISR Wide energy range up to ~3 GeV Pr eli mi na ry No FSR correction yet High statistics with untagged ISR

23 Energy scan measurements with BES-III

24 Previous R measurements with BES Energy scan experiments at BEPC: Pre-studies with BES-I τ mass data 12 continuum data points s ~ 3.55 GeV HEP&NP 24, 609 (2000) Test run 6 data points s = GeV PRL 84, 594 (2000) Full scan 85 data points s = GeV PRL 88, (2002) R around Ψ(3770) 2 data points off-resonance 1 data point on-resonance PLB 641, 145 (2006) Improvements at 3 continuum points PLB 677, 239 (2009) Statistical accuracy: 3 5% Systematic uncertainty: 5 8% Major improvement on R

25 R measurement with BES-III New energy scan experiments at BEPC-II: Phase 1 Energy range s = GeV about 104 events per scan point about 3% systematic accuracy Improvement on αem(mz) by factor 2 Phase 2 Energy range s = GeV about 105 events per scan point high statistics Time-like p, n, Λ form factors GE, GM Improvement on GE / GM by factor 10 Phase 3 Fine energy binning in charmonium region Determination of Rc Charmonium spectroscopy

26 Phase 1: Mini R Scan (2012) BES-III data taking during June 8-16, 2012: 4 energy points s = 2.23 GeV (ΛΛ threshold) s = 2.40 GeV s = 2.80 GeV s = 3.40 GeV Total integrated luminosity ~12pb 1 Useful information for BEPC-II performance at low energies Preparations for extended Phase 1 scan Data used to establish analysis chain Studies of baryon form factors, fragmentation function,

27 Phase 2: Nucleon Form Factors e+e NN cross section and time-like baryon form factors: Parametrised by electric and magnetic form factors GE, GM Energy region s ~ GeV Previous data on GE / GM inconclusive Investigate cross section drop around ~2.15 GeV BABAR 06

28 Phase 3: Charmonium spectroscopy Understanding the nature of charmonium resonances: All possible two-body decays of Ψ(3770), Ψ(4040), Ψ(4160), Ψ(4415) need to be considered High statistic data at peak positions required Measure the resonance parameters Determine cross section of exclusive decay channels Investigate possible broad resonance structures Mass region where some X, Y, Z particles are found Possible new resonances, which are not yet discovered?

29 Summary & Outlook Hadronic cross section measurements important for aμ and Δαhad Precise data at low energies required ISR and Energy Scan measurements ISR physics programme at BES-III 2.9 fb Ψ(3770), 3.1 fb XYZ region Highly competitive with other facilities Precise measurements of hadronic final states for s < 2 GeV Significant contributions to aμ and Δαhad expected Energy Scan measurements at BES-III Covering energy range from s = GeV Complementary to ISR programme Impact on Δαhad and baryon form factors Phase 1 (Mini R Scan) currently being analysed

30 Summary & Outlook Hadronic cross section measurements important for aμ and Δαhad Precise data at low energies required ISR and Energy Scan measurements ISR physics programme at BES-III 2.9 fb Ψ(3770), 3.1 fb XYZ region Highly competitive with other facilities Precise measurements of hadronic final states for s < 2 GeV Significant contributions to aμ and Δαhad expected Energy Scan measurements at BES-III Covering energy range from s = GeV Complementary to ISR programme Impact on Δαhad and baryon form factors Phase 1 (Mini R Scan) currently being analysed Thank you for your attention

31

32 The muon anomaly: (g 2)μ Experimental value and Standard model predictions of aμ = (g 2)μ BNL-E821

33 The muon anomaly: (g 2)μ Experimental value and Standard model predictions of aμ = (g 2)μ BNL-E821 Standard model contributions to aμ aμ needs experimental input Exp. uncertainty on σ limits SM precision Low-energy contributions important

34 Hadronic cross section data & αem(s) Vacuum polarisation corrections Running of αem(s) Davier, et al. (2010) Leptonic vacuum polarisation calculable within QED Hadronic vacuum polarisation not accessible in pqcd Dispersion integral relates Δαem with σ Experimental R data essential up to ~5 GeV pqcd for higher energies

35 Initial State Radiation

36 Initial State Radiation H(s) Radiator function H(s) PHOKHARA MC generator

37 Initial State Radiation H(s) Radiator function H(s) PHOKHARA MC generator σππ(s) Cross section σππ(s) for non-radiative process e+e π+π

38 Initial State Radiation σππ(s) H(s) Cross section σππ(s) Radiator function H(s) PHOKHARA MC generator for non-radiative process e+e π+π σππγ Cross section σππγ for ISR process e+e π+π γ