Observation of. San-Qiang Qu Ming-gang Zhao Hai-long Ma Nankai University Institute of High Energy Physics

Transcription

1 Observation of CJ an-qiang Qu Ming-gang Zhao Hai-long Ma Nankai University Institute of High Energy Physics

2 Outline 1 Motivation 2 Data sample 3 Event selection 4 Branching fraction 5 ummary

3 Motivation Theoretical work indicates that the color octet mechanism could have large contributions to the decays of the P-wave charmonium states. However, Many theoretical calculations and experimental measurements still have large errors. more precise experimental data besides more theoretical efforts are mandatory to further understand Thus, the measurement of as many exclusive hadronic possible is valuable. First observations of CJ CJ decay dynamics. CJ decay as 1

4 Data ample 1. DATA : 447.9M Ψ(3686) (16.8M(29) M(212)) 2. Inclusive MC : 56M Ψ(3686) (16M(29) + 4M (212)) (3686 ) anything 3. Exclusive MC : (P2GC/P2GC1/P2GC2 PHP) 1 for J =,1,2 1 for ThemeGallery is a Design Digital ( 3686) Content & Contents mall CJ developed by Guild Design Inc. * bar ( 3686) f(171) 1 for * bar ' ( 3686) f2 Boss Version:

5 Event selection Charged track selection : 1. cosθ < Momentum cut : P < 2.Gev 3. Charge cut : Q = 1 ; um(q) = 4. ngood = 8 reconstruction : 1. econd vertex fit applied 2. DecayLength/DecayLengthError > <.12GeV M 4. n = 4 3

6 Event selection Good photon : 1. The timing information of the EMC should be within t 14 (in the unit of 5 ns). 2. The deposited energy should be larger than 25 MeV in the endcap cos θ <.8 and larger than 5 MeV in the barrel (.86< cosθ <.92); 3. The angle between the photon and the nearest charged track must be larger than 2 to distinguish the shower from charged particles inematicfit If more than one combination survived in one event, the one with the smallest 2 is retained. 4

7 reconstruction 5

8 CJ candidates after event selection 6

9 Backgrounds No. Decay Chain Final states nevt Total: 2 Total: 2 f f,, ' ' 2 _ * ' 2 _ * ' f f, (171) (171), ' _ * _ * ' Table1: topological analysis for Inclusive MC 7

10 Backgrounds Distribution of invariant mass of backgrounds 8

11 9 Backgrounds

12 1 Backgrounds

13 11 Comparison of M

14 12 Comparison of momentum

15 13 Comparison of cosθ

16 Fitting 1. ignal shape: Breit-Wigner convoluted with double Gaussian, where the widths are fixed to the PDG value. 2. Background shape: polynomial function 14

17 Branching fraction obs N B( CJ 4 ) 4 N B( (3686) ) B ( (3686) CJ ) CJ obs 4 N Efficiency [%] ignificance B. F [1 ] C C C notes: ignificance loge(2 ( FCN1 FCN2))

18 ystematic errors Description ψ(3686) total numbers.8 CPC37 (213) 631 γ detection efficiency 1. PRD C C1 C 2 Reconstruction of 6. PRD inematic fit following slide Fitting range following slide ignal shape following slide Background shape following slide MC statistics binomial ' CJ B( ) PDG216 B( ).3 PDG216 Total Add in quadratic 16

19 ystematic errors 1. Reconstruction of We use the same data-mc different of selection criteria as used in PRD The reconstruction is studied in PRD and shown below. The fit give the fitted data-mc difference to be ( assign 1.5% as systematic uncertainty per )%. o we This figures include that systematic uncertainty of tracking, mass window, 17 vertex fitting and second vertex fitting.

20 2. inematic fit systematic error ystematic errors The uncertainty is assigned by the difference of the branching fractions measured with and without cuts. In the case of no cut, the 2 infit 1 9 is set to be. 2 2 signal eff B.F signal eff B.F signal eff B.F no infit err 2.% 4.4% 3.6% 2 C C1 C 2 18

21 ystematic errors 3. Fitting range The uncertainty is estimated by comparing the branching fractions with the alternative fit ranges of C C 1 C 2 Range signal eff B.F signal eff B.F signal eff B.F [3.3, 3.6] [3.32, 3.6] [3.3, 3.58] [3.28, 3.6] [3.3, 3.62] [3.28, 3.62] range err 1.4% 3.6% 2.5%

22 ystematic errors 4. ignal shape The uncertainty is obtained by comparing the branching fractions measured with the signal shapes of Breit Wigner convolution double Gaussian and PDF generated by the MC histogram. C C 1 C 2 signal shape signal eff B.F eff B.F eff B.F BW MC pdf uncertainty.4%.8% 2.2%

23 ystematic errors 5. Background shape The uncertainty is estimated by varying the order of the polynomial. C C 1 C 2 bkg shape signal eff B.F signal eff B.F signal eff B.F flat st order nd order uncertainty.1% 1.% 1.% 21

24 ummary The decays of CJ fractions are measured for the first time. are observed and their decay branching 4 B. F [1 ] CJ C C C

25 Thank you!!

26 Backup Cosθ of CJ in MCtruth

27 Cosθ of CJ in MCtruth 23

28 Cosθ of CJ in MCtruth 24