Luminosity measurement for the data taken at s=4.18 GeV

Transcription

1 Luminosity measurement for the data taken at s=4.18 GeV 1 Liu Ke 1 Liu Feng 2 Ma Hailong 1 CCNU& 2 IHEP

2 Outline Motivation Data and MC Luminosity determination Systematic uncertainty Checks Summary 2

3 Motivation In e + e - collider experiment, the integrated luminosity is a basic parameter. In e + e - collisions, the most useful final states for measurement of luminosity are e + e -, + - and gg final states. At present, we are preparing for the measurement of the integrated luminosity of the data taken at s=4.18 GeV by analyzing the large angle Bhabha scattering events. 3

4 Data and MC BOSS version BOSS Data /besfs/offline/data/700-1/4180/dst January 9 th --June 14 th (runno: ) Online L= pb -1 MC Event generator: Babayaga (BOSS664p02)/besfs/groups/psipp/psippgroup/service/ DsHi/v2/4180/ 4

5 V xy <1 cm, V z <10 cm for the charged tracks; 0.05<P trk <E beam +0.3 GeV/c; P e+ +P e- >0.9*E ecm ; 1.0< E EMC < 2.5 GeV; 5 < <40, cosq EMC <0.80 ( = , and q are the azimuthal angle and the polar angle of charged tracks in EMC); NGood=2 and Q 1 +Q 2 =0. Event selection 5

6 Typical distributions of e + and e - Error bar: DATA Histogram: MC (MC events are generated at BOSS700) 6

7 Luminosity determination The integrated luminosity could be measured by : L N obs N obs : is the observed number of the events for the final state. : is the production cross section for the same final state. : is the detection efficiency. 7

8 In the signal region (-40, -5 ) and (5, 40 ), we obtain the number of Bhabha events observed in all the data to be N obs,data BB=238,600,132 8

9 Input parameters for generator Detection efficiency N net N prod bhabha % (nb) 9

10 Measured L BB is ~4.7% higher than online L measured /L online (BB) L total measured=( )pb -1. Good run Uncertain run runno: ( :25:42) runno: ( :21:36 ) 10

11 Typical distributions of e + and e - cosq <0.80 for the charged tracks Black Histogram: DATA(45049abnormal) Error bar: DATA(44655normal) 11

12 Typical distributions of e + and e - cosq <0.93 for the charged tracks Black Histogram: DATA(45049abnormal) Error bar: MC [RealizationSvc.RunIdList = {45049}] 12

13 Systematic uncertainty [Chin. Phys. 34, 1779(2010)] [Nucl. Phys. B758, 227(2006)] 13

14 cosq requirement For cosq, we change the requirements from cosq <0.80 to cosq <0.75, cosq <0.70, cosq <0.65 and cosq <0.60. The maximum changes of the luminosity which is 0.2%, we assign 0.2% as the uncertainties for selection criteria. 14

15 Tracking efficiency We re-measure the luminosity with the same selection criteria excluding the MDC tracking information. Efficiency (%) Cross section (nb) The measurement results Bhabha events Luminosity (pb -1 ) Error (%) ,661, We assign 0.1% as the associated systematic uncertainty. 15

16 EMC requirement We examine the EMC distributions of e + (e - ) applying all other selection criteria and further requiring q MDC <10 0 and MDC <5 0 The measurement results Track MC Efficiency(%) DATA Efficiency(%) Difference between DATA and MC e % e % To be conservative, we take 0.1% as the systematic uncertainty of the EMC requirement. 16

17 Background estimation MC events are produced with BOSS664p02 N sur : is the number of events which survive after the event selection. f scale : is the scaled factor. N scale : the scaled number of background events. The background rate is only 0.01%. In the measurement, we do not subtract these backgrounds and take 0.1% as the systematic uncertainty. 17

18 Check 1: L measured by diphotons The total charged track reconstructed in the MDC should be zero; cosq <0.80 for the shower; E EMC1 >0.7*E beam ; E EMC2 >0.7*E beam ; N g 2. 18

19 Typical distributions of photons Black Histogram: MC(MC events are generated at BOSS700) Error bar: DATA 19

20 Measured L GG is ~4.4% higher than online L measured /L online (diphotons) L total measured=( )pb -1. Good run Uncertain run 20

21 Check 2: L under BOSS700/701 Data taken from Jan. 9 to Mar. 25 We can see the difference of the measured luminosities with the two BOSS versions is not more than 0.5%. 21

22 Check 3:Scaled inclusive hadron yields charged tracks: V xy <1 cm, V z <10 cm, cosq <0.93; 0.05 <P trk < E beam +0.15GeV/c; If EMC information is valid: E EMC <1.0 GeV; q cc >5 ; 2ns<t<t p +2ns; If MUC information is valid: depth<30 cm; q cg >10 ; Scaled hadron yields NGood 3. As a test, had is taken to be 70% here. And we used the measured L that obtained by using Bhabha process. 22

23 Typical distributions of hadrons Black Histogram: DATA(43810normal) Error bar: DATA(43807abnormal) BESIII Physics & Software Workshop in Autumn of

24 Summary The luminosity of the data taken at 4.18 GeV in 2016 L BB measured = ( ) pb -1 L measured BB/L online -1.0 = 4.7% L measured BB/L measured GG -1.0 = 0.5% L measured (Jan.9 to Mar.25) is in-sensitive to BOSS version The scaled hadron yields are stable Analysis note is ready Thanks! 24