Measurement of luminosity at 2.23GeV

Transcription

1 Measurement of luminosity at 2.23GeV

2 Outline Introduction Data Sets Luminosity measurement by Bhabha process Events selection Data analysis Systematic error Checked by Digamma process Events selection and Data analysis Checked by Dimu process Events selection and Data analysis Results and Summary 2

3 Introduction(1) In e + e - collider experiment, the integrated luminosity is a basic parameter, which relates to the production cross section for e + e - >X. In principle, any process can be used to determine the integrated luminosity of the data set. The integrated luminosity could be measured by: N obs L = σ ε ε trig where N obs is the observed number of the events for the final state in question, σ is the production cross section for the same final states in question, which could be determined by theoretical calculation, ε is the detection efficiency and ε trig is the trigger efficiency for collecting the e+e- events in on-line data acquisition. 3

4 Introduction(2) The QED processes of e + e γ e + e, e + e γ γγ and e + e γ μ + μ are most commonly used for determination of the luminosity because of their large production cross sections, the large detection efficiencies and the simplest final states topology. In this study,we use Bhabha process to calculate the luminosity and use Digamma process and Dimu process to check it 4

5 Data set Boss BESⅢ experiment data Data for rscan at 2.23GeV (664 reconstruction) MC sample Babayaga :1 million for bhabha process 1 million for digamma process 1 million for dimu process 0.5 million for pipi process Lundlw: 1milliom for hadronic process KKMC: 0.5 million for K + K - process 5

6 The setup of babayaga generator ApplicationMgr.DLLs += {"Babayaga"}; ApplicationMgr.TopAlg += {"Babayaga"}; Babayaga.Channel=1; // 1: e+e-->e+e-;2:e+e_->mu+mu-;3:e+e-->gamma gamma;4:e+e--->pi+pi- Babayaga.Ebeam=1.1162; // Ebeam = ECM/2 [GeV] Babayaga.MinThetaAngle=20.00; // minimum angle(deg.) Babayaga.MaxThetaAngle=160.00; //maximum angle(deg.) Babayaga.MinimumEnergy=0.01; //minimum energy (GeV) Babayaga.MaximumAcollinearity=180; //maximum acollinearity (deg.) Babayaga.RunningAlpha=1; //running alpha (0 = off, 1 = on) Babayaga.HadronicResonance=1; //hadronic resonances for ICH = 1 or 2 Babayaga.FSR_swich=1; //FSR switch for ICH = 2 (0 = off, 1 = on) Babayaga.MinEnerCutG=0.01; //minimum energy for CUTG = Y (GeV) Babayaga.MinAngCutG=5; //minimum angle for CUTG = Y (deg.) Babayaga.MaxAngCutG=21; //maximum angle for CUTG = Y (deg.) Babayaga.HBOOK = 0; // close babayaga.ntuple hbook output Babayaga.PHCUT = 0; Babayaga.CUTG = 0; 6

7 Events Selection(bhabha) MDC Track Vr < 1.0 cm Vz < 10.0 cm N + = N - = 1 Δθ < 10 Δϕ < 5 EMC Shower cosθ < 0.8 E shower > 0.65*E beam 7

8 Deposited energy in EMC Scale to the same luminosity of bhabha! Deposited energy of cluster + Deposited energy of cluster -

9 Back to back information After the energy cut,there are few background events left!to remove the bhabha events with FSR gamma which carry big energies, we need the two good candidate tracks are back-to back. 9

10 Cosθ distribution cosθ of e+ in EMC cosθ of e- in EMC 10

11 Compare data and MC(1) E(e+) after selection E(e-) after selection 11

12 Compare data and MC(2) Momentum of e+ in MDC Momentum of e- in MDC Black plots with error bars are data, red histograms are MC. All of them are in the laboratory frame. 12

13 Check the MC Momenta of e+ and e- in laboratory frame Momenta of e+ and e- in center-of-mass frame They are different! 13

14 Systematic error Uncertainty in the event selection criteria Uncertainty in the detection efficiency Uncertainty in the background estimation Uncertainty in the electron tracking Uncertainty from the generator 14

15 Uncertainty in the event selection criteria The difference of the ratios between the data and the Monte Carlo was defined by: sys = R data R MC 1,in which R = N cut N total Cut on cosθ: change cut range of cosθ Cut on Δθ : change cut range of Δθ Cut on Δφ: change cut range of Δφ Cut on deposited energy : change ratio factor (e+ and e- are separated) 15

16 Uncertainty in the detection efficiency The statistical uncertainty in the Monte Carlo efficiency is estimated by: 1 N (1 ε) ε where N is the number of Monte Carlo events for e + e (γ)e + e which are used in the determination of detection efficiency and ε is the detection efficiency. 16

17 Uncertainty in the background estimation Scale to the same luminosity of bhabha(2.638pb -1 ): s=2.23gev : Bkg N total N sur σ (nb) Scale N scale γγ 1,000, μ + μ - 1,000, π + π - 495, K + K - 500, qqbar 1,000, background level is very low! So we regard the uncertainty of background estimation as 0! 17

18 Uncertainty from the generator the uncertainty of babayaga3.5 is 0.5% 18

19 Uncertainty in the electron tracking We use two different methods : 1.use both MDC and EMC information 2.only use EMC information so, sys = R data R MC - 1, in which R = N method2 N method1 19

20 Method2(without MDC) N cluster == 2 E 1,2 > 0.65*E beam cosθ < < Δφ < 40 20

21 Δϕ Distribution ϕ1- ϕ2-180 in MC ϕ1- ϕ2-180 (data and MC) 21

22 Results of systematic error Source Δ sys (%) cosθ < Δθ < Δφ < Deposited energy of e Deposited energy of e MC statistics 0.09 Background estimation 0 Generator 0.50 Tracking efficiency 0.40 total 0.75 Any others are needed? 22

23 Events Selection(digam) MDC Track Vr < 1.0 cm Vz < 10.0 cm N + = N - = 0 EMC Shower N gamma = 2 cosθ < 0.8 E gamma > 0.65*E beam -4 < Δϕ < 2 Δθ < 10 23

24 Events Selection(add gamma conversion) MDC Track Vr < 1.0 cm Vz < 10.0 cm N + = N - = 1 EMC Shower N gamma == 1 cosθ < 0.8 E gamma > 0.65*E beam Combine MDC and EMC: E/P > 0.8 to ensure they are electron angle(e+ e-) < 15 M(e+ e-) < 0.1 GeV

25 Data Analysis(1) ϕ1- ϕ2-180 in EMC θ1+ θ2-180 in EMC Black plots with error bars are data, red histograms are babayaga MC. 25

26 Data Analysis(2) Cosθ distribution in EMC 26

27 Gamma conversion Angle(e+e-) < 15 and M(e+e-) < 0.1GeV 27

28 Events Selection(dimu) MDC Track Vr < 1.0 cm Vz < 10.0 cm N + = N - = 1 Δθ < 10 Δϕ < 5 EMC Shower cosθ < 0.8 E/P < 0.4 Isolated Nγ <= 2 If Nγ =2,M(γγ) < 0.1GeV TOF tof + -tof - < 1ns 28

29 E/P ratio E/P of cluster+ Scale to the same luminosity of bhabha! E/P of cluster- Set E/P < 0.4 to remove almost all the bhabha and digamma events and many hadronic events. 29

30 Back to back information We need the two muon candidates are back-toback, so the angle cut is the same as bhabha 30

31 Tof information We cut the tof + -tof - < 1ns to remove the cosmicray 31

32 Potential background MC As the muon counter is closed at that moment, in order to remove the potential hadronic events, we require the number of isolated photons is not larger than 2 and the M(γ1γ2) is smaller than 0.1 GeV if Nγ ==2. 32

33 M(γ1γ2) cut Data and MC As η is heavier than π 0,so the hadronic tracks with η can not be back-to-back strictly. In Data, we can not find obviously η signal. But the cut for gamma is still needed. 33

34 Momentum distribution Momentum of u+ Momentum of u- 34

35 π + π - and K + K - background Born cross section given by CLEO-C: Babar s result of σ(π + π - ) Babar s result of σ(k + K - ) σ(π + π - ) = 180pb σ(k + K - ) = 127pb 35

36 Background estimation Scale to the same luminosity of bhabha(2.638pb -1 ): s=2.23gev : Bkg N total N sur σ (nb) Scale N scale bhabha 1,000, γγ 1,000, π + π - 495, K + K - 500, qqbar 1,000, But in MC of qqbar, σ(π + π - ) = 1.27nb, σ(k + K - ) = nb (by learning the MC truth information in qqbar MC),so we can not use qqbar MC to estimate the background of dimu! 36

37 Check the MC Momenta of u+u- in MC (Lab ) Momenta of u+u- in MC (cms ) The same as bhabha! 37

38 Results 2*Ebeam Process Bhabha Digamma Dimu MC generator Babayaga Babayaga Babayaga Events Number Cross-Section(nb) ± ± ±0.02 Efficiency(%) Luminosity(pb -1 )

39 Summary By analyzing the Bhabha scattering events, Digamma scattering events and Dimu scattering events, we measure the integrated luminosities of the data taken at 2.23GeV to be 2.638pb -1, pb -1 and 2.645pb -1. But there still are some details need to be checked: 1.the momenta of e+ and e- in MC (in progress) 2.systematic error 39