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Measurement of e + e − →p p Cross Section

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1 Measurement of e + e − →p p Cross Section
Lei Xia, Xiaorong Zhou, Guangshun Huang, Zhengguo Zhao University of Science and Technology of China The BESIII Collaboration Winter Meeting 2015 Dec 14th 2015 Institute of High Energy Physics, Chinese Academy of Sciences

2 Measurement of e+e-→ppbar Cross Section
Outline Introduction Data sets and event selection of e + e − →p p Boss version & Data sets Preliminary Selection Criteria Momentum window Cross section of e + e − →p p and effective Form Factor Cross section measurement Effective Form Factor Detection efficiency : Model dependence Extraction of electromagnetic Form Factor ratio Fit on the polar angular distribution of proton Preliminary results Summary December 14th 2015 Measurement of e+e-→ppbar Cross Section

3 Measurement of e+e-→ppbar Cross Section
Introduction December 14th 2015 Measurement of e+e-→ppbar Cross Section

4 Motivation FIGURE I. The Feynman diagram of e + e − →p p .
Improve the uncertainty of G E G M ratio. Research for electromagnetic Form Factor ratio of proton. FIGURE I. The Feynman diagram of e + e − →p p . December 14th 2015 Measurement of e+e-→ppbar Cross Section

5 Measurement of e+e-→ppbar Cross Section
Motivation Reveal the structure around 2.25 GeV and 3.0 GeV observed by Babar. Especially at 2.0 GeV, where large disagreement is observed bet- ween BaBar results. FIGURE II. Cross Section around 2.25 GeV and 3.0 GeV observed by Babar. December 14th 2015 Measurement of e+e-→ppbar Cross Section

6 Data sets and event selection e + e − →p p
Boss version & Data sets Preliminary Selection Criteria Momentum window December 14th 2015 Measurement of e+e-→ppbar Cross Section

7 Boss version & Data sets
Boss version: Boss6.6.5.p01 Data sets: TABLE I. Data set December 14th 2015 Measurement of e+e-→ppbar Cross Section

8 Boss version & Data sets
FIGURE III. Data set 500k p p , p p π 0 MC sample at each c.m. energy, generated with Conexc. 500k p p MC sample at each c.m. energy, generated with Phokhara. 500k bhabha MC sample at each c.m. energy, generated with Babayaga. 500k dimu MC sample at each c.m. energy, generated with Babayaga. December 14th 2015 Measurement of e+e-→ppbar Cross Section

9 Measurement of e+e-→ppbar Cross Section
Preliminary Selection Criteria Good charged tracks V r <1.0cm, V z <10cm, cos θ <0.93 , p<2GeV Particle identification Prob(p)>Prob(K/ For proton track, require 𝐸 𝑝 <0.5, cos θ <0.8 Charged tracks in a good event N charged =2 and N p =N p =1 December 14th 2015 Measurement of e+e-→ppbar Cross Section

10 Preliminary Selection Criteria
FIGURE IV. For proton track, require 𝐸 𝑝 <0.5, cos θ <0.8 @3.08GeV December 14th 2015 Measurement of e+e-→ppbar Cross Section

11 Preliminary Selection Criteria
Selection criteria in TOF tof p − tof p <4ns veto cosmic ray Tracks angle Angle p p >179° @ ~3.08 GeV >175° @ 2.05~2.5 GeV >170° @ 2.0 GeV FIGURE V. TOF cut and Angle cut December 14th 2015 Measurement of e+e-→ppbar Cross Section

12 Measurement of e+e-→ppbar Cross Section
Momentum window Momentum window cut for proton and anti-proton Signal region: p− p exp <5σ FIGURE VII. Momentum window cut for proton and anti-proton at GeV 2.6444GeV December 14th 2015 Measurement of e+e-→ppbar Cross Section

13 Measurement of e+e-→ppbar Cross Section
Momentum window Signal region: p− p exp <5σ Sideband region: 6σ< p− p exp <11σ FIGURE VII. Momentum window cut for proton and anti-proton at GeV 2.396GeV December 14th 2015 Measurement of e+e-→ppbar Cross Section

14 Cross section of e + e − →p p and effective Form Factor
Cross section measurement Effective Form Factor (widely adopted by previous experiments) Detection efficiency : Model dependence December 14th 2015 Measurement of e+e-→ppbar Cross Section

15 Cross section measurement
σ Born = N obs − N bkg L∙ε∙ 1+δ σ obs = N obs L N obs : The observed number of signal in data. N bkg : The number of background evaluated from sideband. L: The integrated luminosity ε: Detection efficiency by MC sample generated by Conexc. 1+δ : Radiative correction factor Effective Form Factor (widely adopted by previous experiments): σ p p s = 4π α 2 βC 3s G M s m p 2 s G E s 2 Assuming G E = G M (which holds at pp mass threshold only) 𝐺 = σ Born ∙ 𝛽 𝑠 m p 2 s December 14th 2015 Measurement of e+e-→ppbar Cross Section

16 Cross section of e + e − →p p and effective Form Factor
TABLE II. Cross section of e + e − →p p and effective Form Factor December 14th 2015 Measurement of e+e-→ppbar Cross Section

17 Detection efficiency : Model dependence
d σ p p s dΩ = α 2 βC 4s G M s cos 2 θ p m p 2 s G E s sin 2 θ p G E =0: angular distribution of proton: 1+ cos 2 θ p . G M =0: angular distribution of proton: 1− cos 2 θ p . Two methods to get the nominal detection efficiency: 1. Two sets of MC samples are generated, with G E =0 and G M =0 hypothesis. – The mean detection efficiency is the average of them. 2. Another set of MC samples is generated, with G E = G M hypothesis. December 14th 2015 Measurement of e+e-→ppbar Cross Section

18 Detection efficiency : Model dependence
TABLE III. Detection efficiency : Model dependence December 14th 2015 Measurement of e+e-→ppbar Cross Section

19 Cross section of e + e − →p p and effective Form Factor
TABLE IV. Cross section of e + e − →p p and effective Form Factor Detection efficiency : Average of G E =0, G M =0 December 14th 2015 Measurement of e+e-→ppbar Cross Section

20 Cross section of e + e − →p p and effective Form Factor
FIGURE VIII. Cross section of e + e − →p p and effective Form Factor Detection efficiency : Average of G E =0, G M =0 December 14th 2015 Measurement of e+e-→ppbar Cross Section

21 Cross section of e + e − →p p and effective Form Factor
TABLE V. Cross section of e + e − →p p and effective Form Factor Detection efficiency : | G E |=| G M | December 14th 2015 Measurement of e+e-→ppbar Cross Section

22 Cross section of e + e − →p p and effective Form Factor
FIGURE IX. Cross section of e + e − →p p and effective Form Factor Detection efficiency : | G E |=| G M | December 14th 2015 Measurement of e+e-→ppbar Cross Section

23 Cross section of e + e − →p p and effective Form Factor
TABLE VI. Cross section of e + e − →p p and effective Form Factor Generator : Phokhara December 14th 2015 Measurement of e+e-→ppbar Cross Section

24 Cross section of e + e − →p p and effective Form Factor
FIGURE X. Cross section of e + e − →p p and effective Form Factor Generator : Phokhara December 14th 2015 Measurement of e+e-→ppbar Cross Section

25 Cross section of e + e − →p p and effective Form Factor
FIGURE XI. Cross section of e + e − →p p and effective Form Factor Compare December 14th 2015 Measurement of e+e-→ppbar Cross Section

26 Extraction of electromagnetic Form Factor ratio
Fit on the polar angular distribution of proton Preliminary results December 14th 2015 Measurement of e+e-→ppbar Cross Section

27 Fit on the polar angular distribution of proton
We need fit on the polar angular distribution of proton, dσ dΩ q 2 ,θ = α 2 βC 4s G M s cos 2 θ p + R em τ sin 2 θ p τ= 4 m 2 q 2 R em = G E q 2 G M q 2 FIGURE XII. Fit on the polar angular distribution of proton 3.08GeV 2.9GeV 2.6464GeV December 14th 2015 Measurement of e+e-→ppbar Cross Section

28 Fit on the polar angular distribution of proton
FIGURE XII. Fit on the polar angular distribution of proton 2.6444GeV 2.396GeV 2.3864GeV 2.3094GeV 2.2324GeV 2.2GeV December 14th 2015 Measurement of e+e-→ppbar Cross Section

29 Fit on the polar angular distribution of proton
FIGURE XII. Fit on the polar angular distribution of proton 2.175GeV 2.15GeV 2.1GeV 2.05GeV 2.0GeV The distributions of cos θ have been corrected with detection efficiencies by MC simulation samples. December 14th 2015 Measurement of e+e-→ppbar Cross Section

30 Preliminary results Preliminary results of fit on cos θ
TABLE VII. Preliminary results of fit on cos θ The range of relative statistical error of G E G M ratio is between 7.2% and 69.3%. December 14th 2015 Measurement of e+e-→ppbar Cross Section

31 Preliminary results FIGURE XIII. G E G M of proton, Comparation with BaBar, PS170 December 14th 2015 Measurement of e+e-→ppbar Cross Section

32 Measurement of e+e-→ppbar Cross Section
Summary December 14th 2015 Measurement of e+e-→ppbar Cross Section

33 Measurement of e+e-→ppbar Cross Section
Summary Using 21 data sets from 2.0 to 3.08 GeV, the p p cross section is measured. No indication for structure around 2.25 and 3.0 GeV. The cross section at 2.0 GeV is smaller than Babar result. December 14th 2015 Measurement of e+e-→ppbar Cross Section

34 Thanks for Your Attention!
December 14th 2015 Measurement of e+e-→ppbar Cross Section

35 Measurement of e+e-→ppbar Cross Section
Backups December 14th 2015 Measurement of e+e-→ppbar Cross Section

36 Preliminary Selection Criteria
FIGURE IV. For proton track, require 𝐸 𝑝 <0.5 3.08GeV 2.9GeV 2.6444GeV 2.396GeV 2.05GeV 2.0GeV December 14th 2015 Measurement of e+e-→ppbar Cross Section

37 Preliminary Selection Criteria
FIGURE IV. For proton track, require cos θ <0.8 3.08GeV 2.9GeV 2.6444GeV 2.396GeV 2.05GeV 2.0GeV December 14th 2015 Measurement of e+e-→ppbar Cross Section

38 Measurement of e+e-→ppbar Cross Section
Preliminary Selection Criteria FIGURE V. Selection criteria in TOF tof p − tof p <4ns 3.08GeV 2.9GeV 2.6444GeV 3.08GeV 2.396GeV 2.2324GeV 2.0GeV December 14th 2015 Measurement of e+e-→ppbar Cross Section

39 Preliminary Selection Criteria
FIGURE VI. Tracks angle cut at different energy point 3.08GeV 2.9GeV 2.6444GeV 2.396GeV 2.05GeV 2.0GeV December 14th 2015 Measurement of e+e-→ppbar Cross Section

40 Measurement of e+e-→ppbar Cross Section
Momentum window FIGURE VII. Momentum window cut for proton and anti-proton at energy points 2.9GeV 2.6464GeV 2.3094GeV 2.2GeV 2.05GeV 2.0GeV December 15th 2015 Measurement of e+e-→ppbar Cross Section

41 Comparation with HIM Group @2.0 GeV
Particle GeV Preliminary results December 14th 2015 Measurement of e+e-→ppbar Cross Section

42 Measurement of e+e-→ppbar Cross Section
Particle GeV Good charged tracks V r <1.0cm, V z <10cm, cos θ <0.93 , p<2GeV Vertex fit 𝜒 2 𝑣𝑡𝑥 <100 Tracks angle Angle p p >178° @ ~3.08 GeV >175° @ 2.05~ GeV >170° @ 2.0 GeV Veto cosmic rays tof p − tof p <4ns If p or p does not have hit TOF, event is kept at (2.0~2.3094) GeV, but discarded at (2.3864~3.08)GeV. December 14th 2015 Measurement of e+e-→ppbar Cross Section

43 Measurement of e+e-→ppbar Cross Section
Particle GeV Particle identification Probability of p and p larger than that of electron, pion, kaon and 𝐸 𝑝 ( ~ 3.08) GeV Probability of p and p larger than that of pion, kaon and 𝐸 𝑝 < (2.15 ~ ) GeV (tracks with no EMC info are accepted) normPH>CUT of p and p CUT=(3.0, 2.5, 2.0, 1.7, 1.7, 1.5, 1.5, 1.4, 1.265) for (2.0, 2.05, , 2.175, 2.2, , , , 2.396) GeV Charged tracks in a good event N charged =2 and N p =N p =1 December 14th 2015 Measurement of e+e-→ppbar Cross Section

44 Measurement of e+e-→ppbar Cross Section
Particle GeV Momentum window cut for proton and anti-proton Signal region: p−4σ< p exp <p+3σ December 14th 2015 Measurement of e+e-→ppbar Cross Section

45 Measurement of e+e-→ppbar Cross Section
Preliminary results Preliminary results p and p events comparation: Mine:4857 Vs Yadi:4814 Efficiency comparation Mine:62.1%7 Vs Yadi:59.6% December 14th 2015 Measurement of e+e-→ppbar Cross Section

46 Measurement of e+e-→ppbar Cross Section
Tracking Efficiency Tracking Efficiency with p Tracking Efficiency with p December 14th 2015 Measurement of e+e-→ppbar Cross Section

47 Measurement of e+e-→ppbar Cross Section
Events December 14th 2015 Measurement of e+e-→ppbar Cross Section

48 Tracking Efficiency with p
FIGURE VIII. Tracking Efficiency with GeV December 15th 2015 Measurement of e+e-→ppbar Cross Section

49 Tracking Efficiency with p
FIGURE VIII. Tracking Efficiency with GeV December 15th 2015 Measurement of e+e-→ppbar Cross Section

50 Tracking Efficiency with p
FIGURE VIII. Tracking Efficiency with GeV December 15th 2015 Measurement of e+e-→ppbar Cross Section

51 Tracking Efficiency with p
FIGURE VIII. Tracking Efficiency with GeV December 15th 2015 Measurement of e+e-→ppbar Cross Section

52 Tracking Efficiency with p
FIGURE VIII. Tracking Efficiency with GeV December 15th 2015 Measurement of e+e-→ppbar Cross Section

53 Tracking Efficiency with p
FIGURE IX. Tracking Efficiency with p @3.08 GeV December 15th 2015 Measurement of e+e-→ppbar Cross Section

54 Tracking Efficiency with p
FIGURE IX. Tracking Efficiency with p @2.9 GeV December 15th 2015 Measurement of e+e-→ppbar Cross Section

55 Tracking Efficiency with p
FIGURE IX. Tracking Efficiency with p @ GeV December 15th 2015 Measurement of e+e-→ppbar Cross Section

56 Tracking Efficiency with p
FIGURE IX. Tracking Efficiency with p @ GeV December 15th 2015 Measurement of e+e-→ppbar Cross Section

57 Tracking Efficiency with p
FIGURE IX. Tracking Efficiency with p @2.396 GeV December 15th 2015 Measurement of e+e-→ppbar Cross Section


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