Probing high-momentum neutrons and protons in asymmetric nuclei

Transcription

1 Probing high-momentum neutrons and protons in asymmetric nuclei A data-mining project using JLAB CLAS data Meytal Duer Tel-Aviv University March 8, 017 Workshop on high-density nuclear matter, Weizmann Institute 1

2 SRC Pair Fraction [%] np-dominance in N-SRC N-SRC O. Hen et al., Science 346, 614 (014) n-p n-n p-p Missing Momentum [GeV/c] R. Subedi et al., Science 30, 1476 (008).

3 np-dominance in asymmetric nuclei M. Sargsian Phys. Rev. C89(014)3, O. Hen et al., Science 346, 614 (014) N>Z Pauli principle SRC k T p ( n) = n p( n ) d 3 k m T n > T p? T p > T n Possible inversion of the momentum sharing 3

4 Theoretical predictions for <Tn>/<Tp> N>Z Heavy nuclei (A>1) T n / T p T n / T p Light nuclei (A<1) Neutron Excess [(N-Z)/Z], R. B. Wiringa, R. Sehiavilla. S.C. Pieper, J. Carlson.Phys. Rev. C89, (014) J. Ryckebusch, M. Vanhalst and W. Cosyn, 4 arxiv: v3 [nucl-th] (015).

5 Analysis I Simple np-dominance model n p (k) = η nmp. F.( k) k< k 0 A a ( A / d ) nd ( k) Z k> k 0 (for neutrons: Z N) M.F. T n / T p n (k): * Wood-Saxon * Serot- Walecka * Ciofi & Simula k0 : * 300 MeV/c * kf Neutron Excess [(N-Z)/Z] M. Sargsian O. Hen et al., Science 346, 614 (014) 5

6 Calculation Measurement Simple estimate based on np-dominance 08 Pb : protons k> k Z =8 0 R P= =0.3 protons k< k 8 0 F Rn = neutronsk> k F neutronsk< k F 0 = SRC fractions F N =16 Neutron Excess [(N-Z)/Z] 6

7 The goal: Extracting A( e,e ' n)high / A( e,e ' n)low 1 1 C ( e,e ' n)high / C (e,e' n)low ratios (and same for protons) The steps: * Identify (e,e'n) mean-field events (low missing momentum) * Identify (e,e'n) N-SRC events (high missing momentum) * Extract ratios and their uncertainties 7

8 Analysis I Analysis II Simple prediction based on the np-dominance model 1 A (e,e' n) / C (e,e' n) k> k 1 0 A (e,e' p)/ C(e,e ' p)k> k 0 0 A (e,e' p)/ 1 C(e,e ' p)k< k 0 1 SRC fractions A (e,e' n) / C (e,e' n) k< k Future plans n (k)k dk SRC n (k)k dk M.F. # A(e,e' N ) Neutron Excess [(N-Z)/Z] k< k 0 k> k 0 8

9 Data Mining JLAB CLAS EG data set Run at 004 in Hall-B GeV electron beam Deuterium + Solid target simultaneously C / Al / Fe / Pb 9

10 Particle Identification Drift Chambers: Region 1 Region Region 3 Time-Of-Flight Counters Cherenkov Counters Electro-Magnetic Calorimeter (EC) CLAS analysis note, L. El Fassi, 011 O. Hen et al., Phys. Lett. B 77, 63 (013) O. Hen et al., Science 346, 614 (014) Detecting neutrons in CLAS EC (M. Braverman TAU thesis, 014) 10

11 Detecting neutrons in CLAS EC * No signals from Drift-Chambers & Time-Of-Flight Counters * Hit inside the EC fiducial cut * n/γ separation: β<0.95 β= R T c 11

12 Using an exclusive reaction d (e, e ' p π+π -n) Empirical momentum correction P n [ GeV / c] Momentum resolution σ P measured [ GeV / c] P measured [ GeV / c] Detection efficiency +- ϵ= d ( e, e ' p π π) n d ( e, e ' p π+π-n) ϵ P n [ GeV / c] 1

13 Motivation Analysis I Future plans Analysis of QE events: I. Identifying A(e,e'n) and A(e,e'p) mean-field events II. Identifying A(e,e'n) and A(e,e'p) high-momentum events 13

14 Motivation Analysis II Selecting M.F. QE events neutrons Emiss [GeV ] Emiss [GeV ] protons Pmiss [GeV /c] QE peak: Pmiss<0.5 GeV/c Emiss<0.08 GeV T.G. ONeill et al., Phys. Lett. B 87, 351 (1995). D. Abbott et al. Phys. Rev. Lett. 80, 507 (1998). K. Garrow et al. Phys. Rev. C. 66, (00) Pmiss [GeV /c] Problem: Poor resolution in the EC - Δ P 0.GeV / c 14

15 Motivation Solutions I. Using electron quantities & scattering angle of the nucleon 0.05< y< 0.5 y [( M A + ω) 0.95< ω<1.7gev λ M W q λ ]/ W A 1 θ pq < 8o W = ( M A + ω ) q λ =( M A 1 M N + ω ) / II. Using smeared protons to: * Define and test the cuts * Study bin migration P p P smeared = Gauss (P p,σ ) P p Psmeared [GeV /c ] 15

16 Analysis II 'impurity' Pmiss cut [GeV /c] The selected cuts for smeared p/n: P miss <0.3GeV /c, Emiss <0.19 GeV False Negative [%] False Positive [%] False Positive & Negative probabilities 'inefficiency' Pmiss cut [GeV /c] The cuts for un-smeared p: P miss <0.5GeV /c, Emiss <0.08 GeV False Positive False Negative 10% 16

17 Selecting high-momentum QE events (e,e'p): Following CLAS analysis note (O. Hen 01) (e,e'n): Same strategy as M.F.: I. Cut on common quantities: x B > P N q 1.1 o θ Nq 5 II. Using smeared protons: To determine cuts on P miss & M miss 17

18 Analysis I False Negative [%] False Positive [%] False Positive & Negative probabilities 'impurity' Pmiss lower cut [GeV /c] The selected cut for smeared p/n: miss miss 0.4<P <1GeV /c, M <1.175GeV /c 'inefficiency' Pmiss lower cut [GeV /c] The cut for un-smeared protons: miss 0.3<P <1GeV /c, M miss <1.1GeV /c False Positive False Negative 15 % 18

19 A(e,e'p)/C(e,e'p) ratios (compare smeared and un-smeared protons) High-momentum σ A/ σ C Pb/ C Fe / C Al/ C σ A/ σ C Mean-Field Pb/ C Fe / C Al/ C Neutron Excess [(N-Z)/Z] 19

20 A(e,e'n)/A(e,e'p) ratios High-momentum σ A (e,e' p)/ σ p σ A( e, e' n)/ σ n Mean-Field Neutron Excess [(N-Z)/Z] 0

21 Protons and neutrons super ratios A( e,e ' N )high / A(e,e' N)low 1 C ( e,e ' N )high / C (e,e' N )low T n / T p SRC fractions 1 Neutron Excess [(N-Z)/Z] Protons move faster than neutrons in N>Z nuclei > 1

22 Backup Slides

23 Analysis II Solution 1: Using cuts common to (e,e'p) and (e,e'n) QE cuts:pmiss<0.5 GeV/c Emiss<0.08 GeV protons After the QE cuts y y Before the QE cuts ω [GeV ] θ pq [deg.] θ pq [deg.] ω [GeV ] Q [GeV /c ] Q [GeV /c ] 3

24 Motivation Analysis II neutrons Emiss [GeV ] Emiss [GeV ] smeared protons Pmiss [GeV /c] Pmiss [GeV /c] Without applying any cuts 4

25 Future plans With the common cuts: 0.05< y< 0.5 θ pq < < ω<1.7gev o 1.3<Q <3.5GeV /c smeared protons neutrons 0.5 Emiss [GeV ] 0.5 Emiss [GeV ] Pmiss [GeV /c ] Pmiss [GeV /c ] 5

26 Motivation Emiss P miss cuts un-smeared protons smeared protons (neutrons) 'good event': P miss unsmeared <0.5GeV /c Emiss unsmeared <0.08 GeV && 'bad event': P miss [GeV /c] P miss unsmeared >0.5GeV /c Emiss unsmeared >0.08 GeV 6

27 Comparing un-smeared protons QE cuts: Emiss <0.08GeV P miss <0.5GeV / c y All un-smeared protons θ p [ deg. ] y EC un-smeared protons 7

28 Comparing un-smeared protons xb y QE events Q [GeV /c ] EC un-smeared protons Q [GeV /c ] All un-smeared protons x b 1 8 ω [GeV ] ω [GeV ]

29 Checking the event selection Energy momentum conservation: ' (Ebeam,(0,0, Ebeam))+(M N, 0)=(E, P e' )+(E N, P N ) neutrons Pn [GeV /c] P p [GeV /c] smeared protons P N = ( E+ M N P e ' ) M N Pe ' [GeV / c] Pe ' [GeV / c] 9

30 Checking the event selection From energy momentum conservation: ϕ N ϕ e ' =180 smeared protons ϕ p ϕe ' [deg.] o neutrons ϕ n ϕe ' [deg.] 30

31 Comparing the smeared protons and neutrons smeared protons Pe [GeV /c] ω[gev ] neutrons θe [deg.] y Q [GeV /c ] xb 31

32 Comparing the smeared protons and neutrons smeared protons neutrons P p/n [GeV /c] θ p/n [deg.] θ pq/nq [deg.] ϕ p/n ϕ e [deg.] 3

33 Applying corrections protons neutrons * Coulomb correction * Detection efficiency * Detection efficiency * Acceptance correction * Acceptance correction 33

34 Protons simulation * 10,000 electrons from the data. * Proton momentum & scattering angle uniformly distributed. * 100xphi angle uniformly distributed. * Running through CLAS MC simulation. * Dividing event by event by the ratio of reconstructed/generated. 34

35 Protons simulation - results Sector #1 Sector # Sector #3 Sector #4 Sector #5 Sector #6 35

36 Analysis II A(e,e'p)/A(e,e'n) M.F. ratios [4] (e,e ' p)/z (e,e' n)/n 1 C σ R ep(n) ϵ = τ GE +G M 7 Al 56 Fe Q τ=, 4 MN 08 Pb θ e 1 ϵ=[1+(1+τ)tan ( )] [4] W. P. Ford, S. Jeschonnek & J. W. Van Orden, arxiv: v1 [nucl-th] (014) 36

37 Uncertainties of the event selection Cut Cuts sensitivity Range C -0.05<y<0.5 ± <ω<1.7 GeV θ pq < 8 Al Fe Pb 0.84% 0.83% 0.58% 0.81% ±0.05 GeV.1%.0% 1.9% 1.8% ±1º.0% 1.8% 1.6% 1.4% ±0.05 GeV/c 0.8% 0.49% 0.56% 0.78% ±0.0 GeV 1.9%.%.1%.1% 30 cm 0.1% 0.11% 0.10% 0.09% o Pmiss < 0.3 GeV / c Emiss <0.19 GeV EC fiducial cut: 10 cm 37

38 Contributions to the uncertainty Nuclei A(e,e'p)/A(e,e'n) Statistics Neutron Effic. Simulation Event selection C.37±0.17 ±0.15 ±0.07 ±0.031 ±0.09 Al.36±0.3 ±0.19 ±0.08 ±0.030 ±0.09 Fe.48±0.0 ±0.15 ±0.07 ±0.03 ±0.08 Pb.1±0. ±0.18 ±0.09 ±0.034 ±

39 Uncertainties of the event selection A(e,e'p)/C(e,e'p) M.F. Cut Cuts sensitivity Range Al/C Fe/C Pb/C -0.05<y<0.5 ± % 1.3% 1.% 0.95<ω<1.7 GeV ±0.05 GeV 1.4% 0.8%.0% ±1º 1.9% 1.9% 1.6% Pmiss < 0.3 GeV / c ±0.05 GeV/c.0%.0% 1.8% Emiss <0.19 GeV ±0.0 GeV 1.8% 1.8% 1.9% θ pq < 8 o Nuclei A(e,e'p)/C(e,e'p) Statistics FP & FN Event selection Al/C 1.71±0.08 ±0.05 ±0.0 ±0.06 Fe/C.4±0.11 ±0.03 ±0.0 ±0.1 Pb/C 5.±0.3 ±0.1 ±0.05 ±0. 39

40 σ A/ σ C A(e,e'n)/C(e,e'n) M.F. ratios A Nuclei A(e,e'p)/A(e,e'n) Statistics FP & FN Event selection Al/C.1±0.14 ±0.1 ±0.0 ±0.06 Fe/C 3.±0.1 ±0.07 ±0.0 ±0.1 Pb/C 9.±0.4 ±0.17 ±0.06 ±

41 Uncertainties of the event selection A(e,e'n)/C(e,e'n) M.F. Cut Cuts sensitivity Range Al/C Fe/C Pb/C -0.05<y<0.5 ± % 1.3% 1.% 0.95<ω<1.7 GeV ±0.05 GeV 1.4% 1.% 1.7% ±1º 1.5% 1.6% 1.0% Pmiss < 0.3 GeV / c ±0.05 GeV/c 1.% 1.3% 1.5% Emiss <0.19 GeV ±0.0 GeV 0.8% 0.9% 1.4% θ pq < 8 o 41

42 Protons and neutrons M.F ratios M.F. ratios np-dominance model: protons neutrons Data: protons neutrons A Corrected for transparency and normalized by Z (N). 4

43 Motivation Analysis I 1 st step: Following approved CLAS analysis note (O. Hen 01) to identify high momentum (e,e'p) events * 0.3 P miss 1 GeV / c * x B >1. * 0.6 P lead / q 0.96 * θ pq 5 * M miss 1.1 GeV / c o nd step: Modifying the cuts to select high momentum (e,e'n) events 43

44 Analysis I * Low statistics * Poor resolution Q [GeV /c ] Future plans x B >1.1 smeared protons Q [GeV /c ] 44

45 Motivation Analysis I Future plans Identifying the Leading Nucleon smeared protons neutrons P p / q P n / q θ pq [deg.] un-smeared protons P p / q θ pq o P N q 0.96 θ pq P N q o

46 Analysis I Missing Mass cut M miss=(q+m N P lead ) un-smeared protons neutrons M miss [GeV /c ] M miss mean+mπ =1.1GeV /c smeared protons M miss [GeV /c ] M miss <? 46

47 Missing Momentum & Missing Mass cuts un-smeared protons smeared protons neutrons 'good event': 0.3<P miss unsmeared <1GeV /c && M miss unsmeared <1.1GeV /c Pmiss [GeV /c] 'bad event': P miss unsmeared <0.3 P miss unsmeared >1GeV / c M miss unsmeared >1.1GeV /c 47

48 Future plans The selected events: This analysis Proton analysis (smeared protons & neutrons) (O. Hen et al.) x B >1.1 x B > < p/q< < p/q<0.96 θ pq<5o θ pq<5o M miss <1.GeV /c 0.4<Pmiss <1GeV /c M miss <1.1GeV /c 0.3<P miss <1GeV /c 48

49 Comparing smeared protons & neutrons distributions: Pe [GeV /c] Q [GeV /c ] θe [deg.] ω[gev ] xb 49

50 Comparing smeared protons & neutrons distributions: P p/n [GeV /c] θ p/n [deg.] Pmiss [GeV /c] θ pq/nq [deg.] 50

51 Analysis I Missing energy distribution Emiss [GeV ] Emiss [GeV ] 51 Emiss [GeV ]

52 A(e,e'p)/C(e,e'p) ratios (for smeared protons) Corrections: 1. Normalization: target density & beam charge (FC) C Al Fe Pb Beam charge Thickness [g/cm²] Radiative correction 3. False positive & negative probabilities C Al Fe Pb False positive [%] False negative [%]

53 Contributions for the uncertainty 1. Statistical error. Cut sensitivity Cut Sensitivity range Al/C Fe/C Pb/C x>1.1 ± % 1.5%.0% 0.6<p/q<1.1 ±0.05.0%.5%.4% ±0.05 GeV/c² 1.7% 1.8% 1.% ±0.05 GeV/c.% 1.1%.6% o ±5 θ pq < 5 M miss <1.175GeV /c 0.4<Pmiss <1GeV /c 3. Radiative correction (negligible) 4. False positive and negative probabilities Al/C Fe/C Pb/C 0.3% 0.9% 1.0% 5. Target density and beam charge (negligible) 53

54 Contributions for the uncertainty Al/C Fe/C Pb/C.0±0.1 3.± ±0.8 Event selection ±0.13 (9%) ±0.5 (80%) ±0.75 (93%) False positive & negative ±0.0 (14%) ±0.03 (10%) ±0.08 (10%) Statistics ±0.08 (57%) ±0.06 (0%) ±0.15 (19%) σ A /σ C 54

55 Protons and neutrons high momentum ratios High momentum ratios np-dominance model: protons * * neutrons Data: protons neutrons A Corrected for transparency and normalized by Z (N) 55