Exclusive Pion Photoproduction on Bound Neutrons

Transcription

1 Exclusive Pion Photoproduction on Bound Neutrons Igor Strakovsky The George Washington University A Bit of History. Pion Photoproduction for Baryon Spectroscopy. Phenomenology for Pion Photoproduction. SAID for Pion Photoproduction. SAID Features & Benefits. FSI for gn pn. SAID for Neutral Baryons. Summary. 7/4/2017 Advances in Hadronic Resonances, Bled, Slovenia, July 2017 Supported by DE-SC Igor Strakovsky 1

2 Igor Strakovsky 2

3 Discovery of Pion p + & p - Igor Strakovsky 3

4 The First Pion Photo Production Measurement p + Igor Strakovsky 4

5 The First p - Photo Production Measurement p - Igor Strakovsky 5

6 The First Baryon Resonance Discovery D(1232)3/2 + Then, since 1952 many states were discovered. Columbia BNL Igor Strakovsky 6

7 Baryon Sector at PDG16 [N,D J P ] GW Contribution C. Patrignani et al, Chin Phys C 40, (2016) N D X SW PDG16 has 109 Baryon Resonances (58 of them are 4* & 3*). L Pole position in complex energy plane for hyperons has been made only recently, first of all for L(1520)3/2 -. In case of SU(6) x O(3), it would be required 434 baryons, if all revealed multiplets were completed (three 70 & four 56). Y. Qung et al, Phys Lett B 694, 123 (2010). Igor Strakovsky 7

8 Igor Strakovsky 8

9 Road Map to Baryon Spectroscopy Facility Experiment Data Amplitudes Resonances 7/4/2017 Advances in Hadronic Resonances, Bled, Slovenia, July 2017 Igor Strakovsky 9

10 World Neutral & Charged PionPR Data W.J. Briscoe et al, Eur Phys J A 51, 129 (2015) W < 2.5 GeV gp p 0 p Full UnPol Pol gp p + n gn p - p gn p 0 n Igor Strakovsky 10

11 gn p - p Experiment Many of gn p - p data are old bremsstrahlung measurements with limited angular (q = ) coverage & large energy binning (E = MeV). In several cases, systematic uncertainties have not been given. Existing gn p - p database contains mainly differential cross sections (15% of which are from polarized measurements). At lower energies (E < 700 MeV), there are data sets for inverse p - photoproduction reaction: p - p gn. This process is free from complications associated with deuteron target. T H A N K S However, disadvantage of using p - p gn is large background because of 5 to 500 times larger cross section for p - p p 0 n ggn & there were no tagging high flux pion beams (Dp/p=6%). igor@gwu.edu eg, CB@BNL: A. Shafi et al, PRC70, (2004) gn p 0 n measurement is very small fraction of gn pn database. 7/4/2017 Advances in Hadronic Resonances, Bled, Slovenia, July 2017 Igor Strakovsky 11

12 Phenomenology of Spirit charts development of consciousness as it rises from lowly common sense to heights of what Hegel calls ``absolute knowing unconditioned form of thinking proper to philosophy itself. Igor Strakovsky 12

13 PWA for Baryons Originally PWA arose as technology to determine amplitude of reaction via fitting scattering data. That is non-trivial mathematical problem looking for solution of ill-posed problem following to Hadamard & Tikhonov. Resonances appeared as by-product [bound states objects with definite quantum numbers, mass, lifetime, & so on]. Standard PWA - Reveals only wide Resonances, but not too wide (G < 500 MeV) & possessing not too small BR (BR > 4%). - Tends (by construction) to miss narrow Res with G < 30 MeV. Most of our current knowledge about bound states of three light quarks has come mainly from pn pn PWAs: Karlsruhe-Helsinki, Carnegie-Mellon-Berkeley, & GW. Main source of EM couplings is GW, BnGa, & JuBo analyses. Igor Strakovsky 13

14 Complete Experiment for Pion PhotoProduction There are 16 non-redundant observables. They are not completely independent from each other. Linear Polarized Beam Circular Polarized Beam g Longitudinally Polarized Nucleon Target Transverse Polarized Nucleon Target N N p Nucleon Recoil Polarization 1 un-pol measurement: ds/dw 3 single pol measurements: S, T, P 12 double pol measurements: E, F, G, H, Cx, Cz, Ox, Oz, Lx, Lz, Tx, Tz 18 triple polarization asymmetries [9 for linear pol beam] [9 for circular pol beam] 13 of them are non-vanishing A. Sandorfi et al. AIP Conf. Proc. 1432, 219 (2012) K. Nakayama, private communication, /4/2017 Advances in Hadronic Resonances, Bled, Slovenia, July 2017 Igor Strakovsky 14

15 Importance of Neutron Data EM interaction do not conserve isospin, so multipole amplitudes contain isoscalar & isovector contributions of EM current. Proton Neutron Proton data alone does not allow separation of isoscalar & isovector components. Need data on both proton & neutron! Q: Can we avoid? A: NO! D. Drechsel and L. Tiator, J. Phys. G 18, 449 (1992) 7/4/2017 Igor Strakovsky 15 Advances in Hadronic Resonances, Bled, Slovenia, July 2017

16 Single Pion PhotoProduction on Neutron Target Accurate evaluation of EM couplings N* gn & D* gn from meson photoproduction data remains paramount task in hadron physics. Only with good data on both proton & neutron targets, one can hope to disentangle isoscalar & isovector EM couplings of various N * & D * resonances, as well as isospin properties of non-resonant background amplitudes. K.M. Watson, Phys Rev 95, 228 (1954); R.L. Walker, Phys Rev 182, 1729 (1969) The lack of γn π p & γn π 0 n data does not allow us to be as confident about determination of neutron couplings relative to those of proton.. Radiative decay width of neutral baryons may be extracted from p - & p 0 photoproduction off neutron, which involves bound neutron target & needs use of model-dependent nuclear (FSI) corrections. A.B. Migdal, JETP 1, 2 (1955); K.M. Watson, Phys Rev 95, 228 (1954) Igor Strakovsky 16

17 Screenshot of SAID Website usage Igor Strakovsky 17

18 SAID Progress in PionPR Overall SAID c 2 has remained stable against growing database, which has increased by factor of 5 since Solution Energy (MeV) c 2 /Data Data History MA ,453 PR ,550 ST ,720 DU ,265 GB ,179 CM ,814 SN ,553 SP ,912 SM ,571 SM ,415 SP ,466 CLAS p - ds/dw A2 p 0 ds/dw 1 st FROST p + E CLAS p + /p 0 S CLAS p - ds/dw GRAAL p - /p 0 S CLAS p + ds/dw SP ,936 1 st SAID results Igor Strakovsky 18

19 SAID for Pion Photoproduction P. Mattione et al, arxiv: Energy dependent MA27 E = MeV [W = MeV] PWs = 60 [EM multipoles] [J < 6] Prms = 210 Constraint: Born [no free parameters to fit] pn-pwa [no theoretical input] Reaction Data (Pol) c 2 gp p 0 p 25,540 (23 %) 55,529 gp p + n 8,959 (38 %) 20,736 gn p - p 11,590 (4 %) 16,453 gn p 0 n 364 (59 %) 1,540 Total 46,453 94,258 34,499 data 11,954 data There is disbalance between p 0 & p + data, 35%. Pion photoproduction on the neutron much less known, 35%. 7/4/2017 Advances in Hadronic Resonances, Bled, Slovenia, July 2017 Igor Strakovsky 19

20 Photo-Decay Amplitudes in BW & Pole is main signature of resonance. Pole Forms Evaluated at Res Energy Evaluated at Pole R.L. Workman et al, Phys Rev C 87, (2013) A. Svarc et al, Phys Rev C 89, (2014) Igor Strakovsky 20

21 Minimization & Normalization Factor. Single-Energy Solutions. Forced Fit. Narrow Resonances in PWA. Quasi-Data. 7/4/2017 Igor Strakovsky 21 Advances in Hadronic Resonances, Bled, Slovenia, July 2017

22 Minimization & Normalization Factor for PionProd [c 2 /Data] Modified c 2 function, to be minimized [systematics plays important role] q i exp measured, e i stat error, q i calculated, N norm const, e X its error. Normalization freedom provides significant improvement for our best fit results, we cannot ignore experimental input. } SAID < 2500 MeV MAID < 2000 MeV Modified c 2 [Norm] Standard c 2 [UnNorm] If systematic uncertainty varies with angle. This procedure may be considered as first approximation. CLAS p + & p 0 & LEPS p 0 data included. c 2 /Data SP09 SM02 MAID07 Reaction Norm UnNorm Norm UnNorm Norm UnNorm gp p 0 p gp p + n gn p - p gn p 0 n MAID is valid below W = 2 GeV. For MAID07, normalization constants were searched to minimize c 2 (no adjustment of artial waves was possible). SAID solutions look more stable vs. MAID. D. Drechsel et al, Eur Phys J A 34, 69 (2007) 7/4/2017 Advances in Hadronic Resonances, Bled, Slovenia, July 2017 Igor Strakovsky 20

23 Single-Energy Solutions (SES) SAID has employed both single-energy (SES) & energy-dependent (Global) solutions over variety of energy ranges in order to estimate uncertainties. SES: based on bin of data spanning narrow E range [5 75 MeV] searches 2 to 29 prms. 110 SES have been generated with central E = 147 to 2650 MeV. # of data in bin varies from 80 to Systematic deviation between SES & global fits is indication of Missing structure in global fit. Possible problems with particular dataset. R.L. Workman, M.W. Paris, W.J. Briscoe, IIS, Phys Rev C 86, (2012) Diagonal Error Matrix generated in SES fits. It can be used to estimate the overall uncertainties for Global solution. Igor Strakovsky 23

24 Forced Fit for Double-Polarization Measurements [R. Arndt, IS, R. Workman, Phys Rev C 67, (2003)] gp p 0 p at 1900 MeV SAID Forced Fit has weighted data by factor of 4-5. By weighting data, we magnify changes in multipole amplitudes, & more clearly see where data conflicts occur. Forced Fit results indicate that what more measurements require for constraint solution. DNPL: T measurements P.J. Bussey et al, Nucl Phys B 159, 383 (1979) JLab Hall A: There are 22 C x & 21 C z below 2 GeV K. Wijesooriya et al, Phys Rev C 66, (2002) That is not artifact as was possible to think a while ago! Hall A data do allow to reproduce previous T measurements well. Igor Strakovsky 24

25 Narrow Resonances in PWA R. Arndt, Ya. Azimov, M. Polyakov, IS, R. Workman, Phys Rev C 69, (2004) Conventional PWA (by construction) tends to miss narrow Res with G < 30 MeV. We assume existence of narrower Res, add it to amplitude, then re-fit over the whole database. Refitting If worse description: Resonance with corresponding M & G is not supported. If better description: Resonance may exist. Effect can be due to various corrections (eg, thresholds). Both possibilities can contribute. Some additional checks are necessary. True Resonance should provide the effect only in single particular PW. While non-resonance source may show similar effects in various PWs. 7/4/2017 Advances in Hadronic Resonances, Bled, Slovenia, July 2017 Igor Strakovsky 25

26 Quasi-Data: What to Expect When you re Expecting Prove motivation of JLab Proposal JLab E Pion Photoproduction from Polarized Target for FROST Project. Transverse Polarization [H, P, T, F] Longitudinal Polarization [G, E] R = u(a MC ) / u(a world ) Average ratio of uncertainties of amplitudes w/o expected FROST data. without The data generated by this work will fill number of gaps in existing database of single & double meson photoproduction. with Greatest effect naturally requires measurement of all possible quantities as accomplished by FROST. hp E: I. Senderovich et al, Phys Lett B 755, 64 (2016) p + n E: S. Strauch et al, Phys Lett B 750, 53 (2015) More results are coming.... Igor Strakovsky 26

27 Previous neutron measurements used modified Glauber approach & procedure of unfolding Fermi motion of neutron target. Igor Strakovsky 27

28 FSI for gd ppn gn pn V. Tarasov, A. Kudryavtsev, W. Briscoe, H. Gao, IS, Phys Rev C 84, (2011) V. Tarasov, A. Kudryavtsev, W. Briscoe, B. Krusche, IS, M. Ostrick, Phys At Nucl 79, 216 (2016) FSI plays critical role in state-of-the-art analysis of gn pn data. For gn pn, effect is 5% 60%. It depends on (E,q). IA pn-fsi vertex Fermi motion of nucleons included Input: SAID: gn pn, pn pn, NN NN amplitudes for 3 leading terms. DWF: full Bonn NN Potential (there is no sensitivity to DWF). NN-fsi vertex 7/4/2017 Advances in Hadronic Resonances, Bled, Slovenia, July 2017 Igor Strakovsky 28

29 FSI for gd p - pp gn p - p V. Tarasov, A. Kudryavtsev, W. Briscoe, H. Gao, IS, Phys Rev C 84, (2011) Cuts: p s > 200 MeV/c p f > 200 MeV/c CLAS data: E > 1 GeV q > 30 deg. For CLAS data FSI correction factor R < 1. Behavior is smooth vs. q. Effect: Ds/s 10%. There is no large sensitivity to cuts. There is sizeable FSI effect from S-wave part of pp-fsi at small angles.. Region narrows as E g increases. Our estimation of Glauber FSI corrections gives value of 5%. Previous estimations gave order of 15-30%. 7/4/2017 q(pp-cm) Advances in Hadronic Resonances, Bled, Slovenia, July [IA + NN fsi ] / IA [IA + (NN+pN) fsi ] / IA Igor Strakovsky 29

30 FSI for gd p 0 np gn p 0 n & gp p 0 p V. Tarasov, A. Kudryavtsev, W. Briscoe, B. Krusche, IS, M. Ostrick, Phys At Nucl 79, 216 (2016) gn p 0 n case is much more complicated vs. gn p - p because p 0 can come from both gn & gp initial interactions.. D(1232)3/2+ The corrections for both target nucleons are practically identical for p 0 production in energy range of D(1232)3/2 + due to isospin structure of gn pn amplitude. In general case, N(1440)1/2+ N(1535)1/2 Igor Strakovsky 30

31 7/4/2017 Igor Strakovsky 31 Advances in Hadronic Resonances, Bled, Slovenia, July 2017

32 CLAS g10 for gn p p above 1 GeV W. Chen et al, Phys Rev C 86, (2012); Phys Rev Lett 103, (2009) E = MeV p - p: 626 ds/dw The CLAS g10 cross sections have quadrupled world database for gn p - p above E g = 1 GeV. Systematics: Exp: 6-9% FSI: 2-3% c 2 /dp = 45636/626 = 72.9 [SN11 no fit] c 2 /dp = 1580/626 = 2.5 [GB12 fit ] CLAS data appear to have fewer angular structures than the earlier fits. 7/4/2017 FSI included Advances in Hadronic Resonances, Bled, Slovenia, July 2017 SAID-GB12 SAID-SN11 MAID07 Igor Strakovsky 32

33 S. Capstick, Phys Rev D 46, 2864 (1992). BnGa13 & SAID GB12 used same (almost) data to fit them while BnGa13 has several new Ad Hoc resonances. CLAS Data Impact for Neutron S = 0 & I = ½ Couplings W. Chen et al, Phys Rev C 86, (2012) S S D D GB12 SN11 BnGa13 Kent12 P 11 F New GB12 na 1/2 & na 3/2 couplings shown sometimes significant deviation from our previous SAID determination (SN11) & PDG12 average values, eg, for N(1650)1/2 -, N(1675)5/2 -, & N(1680)5/2 +. Fresh BnGa13 has some difference vs. GB12, PDG12, & relativized quark model, eg, for N(1650)1/2 -,N(1650)1/2 -,& N(1680)5/2 +. Forum for MAX-IV Ring, Lund, Nov 2011 Igor Strakovsky 33

34 MAMI-B for gn p - p around the D W.J. Briscoe et al, Phys Rev C 86, (2012) MAMI-B data for gn p - p (including FSI corrections) & previous hadronic data for p - p ng appear to agree well. SAID-PE12 SAID-SN11 MAID07 T-invariance is good as 2 x 10-3 { 7/4/2017 J. Data: - MAMI-B for gn p - p D - CB@BNL for p - p ng Forum for MAX-IV Ring, Lund, Nov 2011 Advances in Hadronic Resonances, Bled, Slovenia, July 2017 FSI included Ahrens et al, Eur Phys J A 44, 189 (2010) A. Shafi et al, Phys Rev C 70, (2004) o - TRIUMF, CERN, LBL, LAMPF for p - p ng Igor Strakovsky 34

35 CLAS g13 for gn p p above 0.5 GeV P. Mattione et al, arxiv: E = MeV p - p: 8428 ds/dw These data a factor of nearly three increase in world statistics for this channel in this kinematic range. FSI included 7/4/2017 Igor Strakovsky 35 Advances in Hadronic Resonances, Bled, Slovenia, July 2017

36 Comparison of Previous & New SAID Fits P. Mattione et al, arxiv: Recent SAID PR15 applied to g13 data without & with FSI corrections. New SAID MA27 fit obtained after adding new g13 data with FSI corrections. 7/4/2017 Igor Strakovsky 36 Advances in Hadronic Resonances, Bled, Slovenia, July 2017

37 CLAS Data Impact for Neutron S = 0 & I = ½ Couplings Selected photon decay amplitudes N γn at resonance poles are determined for the first time. P. Mattione et al, arxiv: Moduli & phases BW neutron photo-decay amplitudes [g10] [g10] M A I D 7/4/2017 Igor Strakovsky 37 Advances in Hadronic Resonances, Bled, Slovenia, July 2017

38 Meson Production off Deuteron at Differential cross sections for gn p 0 n. E = MeV p 0 n: 589 ds/dw New ds/dws by A2 contribution is 160% to previous world p 0 n data. FSI included Courtesy of Slava Kulikov, /4/2017 Advances in Hadronic Resonances, Bled, Slovenia, July 2017 Igor Strakovsky 38

39 MAX-lab for gn p p at Threshold It is difficult task to measurep p final state close to threshold. We measured p 0 decay in to 2g from gn p p p 0 n. FSI Courtesy of Kevin Fissum Igor Strakovsky 39

40 7/4/2017 Igor Strakovsky 40 Advances in Hadronic Resonances, Bled, Slovenia, July 2017

41 CLAS Data Impact for Neutron S = 0 & I = ½ Couplings D. Ho et al, Phys Rev Lett 118, (2017) E = MeV p - p: 266 E No FSI included Igor Strakovsky 41

42 CLAS Data Impact for Neutron S = 0 & I = ½ Couplings D. Ho et al, Phys Rev Lett 118, (2017) BW I = 3/2 waves ~ unchanged determined by proton data. Inclusion of these g14 data in new PWA calculations has resulted in revised gnn * couplings &, in case of N(2190)7/2 -, convergence among different PWA groups. Such couplings are sensitive to dynamical process of N * excitation & provide important guides to nucleon structure models. Courtesy of Andy Sandorfi, 2017 Igor Strakovsky 42

43 Recent GRAAL S for gn p 0 n R. Di Salvo et al, Eur Phys J A 42, 151 (2009) Difference between previous Pion Prod & new GRAAL measurements result in significant changes in neutron couplings GRAAL Ss are 60% of World p 0 n data c 2 /dp MAID SP MA No FSI included GRAAL data are in Igor Strakovsky 43

44 Recent GRAAL S for gn p - p G. Mandaglio et al, Phys Rev C 82, (2010) Previous gn p - p measurements provided better constraint vs. gn p 0 n case.. c 2 /dp MAID07 27 SP09 89 MA No FSI included GRAAL data are in Igor Strakovsky 44

45 S CLAS cosq = SAID can fit CLAS Ss with c 2 /dp = 2.6 cosq = GRAAL cosq = SAID CM cosq = 0.34 cosq = 0.50 cosq = 0.62 cosq = 0.70 cosq = 0.78 cosq = 0.90 W (MeV) No FSI included Courtesy of Daria Sokhan, 2013 Igor Strakovsky 45

46 Summary for Pion Photoproduction Study Since 1989 pion photoproduction database below W = 2.5 GeV was increased by factor of 5 (most of new data came for gp p 0 p) & is compatible with pn pn database now. Pion photoproduction on proton with p + n final state much less known than with p 0 p one (35%). Pion photoproduction on "neutron" much less known than on proton (35%) & "neutron" database grows. FSI tool is available for diff. cross sections for both p - p & p 0 n final states. Now we are able to extract pole positions on complex energy plane for both N gp & N γn photo-decay amplitudes. Thanks! Forum for MAX-IV Ring, Lund, Nov 2011 Igor Strakovsky 46

47 The End This is just the beginning of the story... We don't know yet which way it will go Would you tell me, please, which way I ought to go from here? That depends a good deal on where you want to get to, said the Cat. I don't much care where --- said Alice. Then it doesn't matter which way you go, said the Cat. --- so long as I get somewhere, Alice added as an explanation. Oh, you're sure to do that, said the Cat if you only go long enough. 7/4/2017 Advances in Hadronic Resonances, Bled, Slovenia, July 2017 Igor Strakovsky 47

48 We update SAID databases, develop & study PWAs, & keep current versions of phenomenological & theoretical models, both those of CNS/DAC & other research groups, on continual basis for relevant two- & three-body reactions of interest. SAID Database below 4 GeV SAID: In the full database, one will occasionally find experiments which give conflicting results. Some data with very large c 2 contributions have been excluded from our fits. Redundant data are also excluded [these include s tot based on ds/dw already contained in database] Measurements of pol observables (P, for instance) with uncertainties more than 0.2 are not included as they have little influence in our fits. However, all available data have been retained in database (excluded data labeled as flagged ) so that comparisons can be made through our on-line facility 50,650 5,576 47,353 12, ,398 [W = 1320 to 1930 MeV ] 241,214 evts+ 38, ,502 2,736 For p 2p, we use log-likelihood while for rest - least-squares technologies. Igor Strakovsky 48