# Presentation: 935978

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-           New facets of the pion-nucleon interaction experimental investigation
-                           in the first and second resonance regions.
-                                                       V.V.Sumachev,
-                                                              Abstract.
-     The theoretical predictions for the non strange baryon resonance spectrum have the visible differences. This disagreement invites further experimental investigation of the pion-nucleon elastic interactions.
-      Recent experiments of the PNPI-ITEP collaborations resolved a part of the twofold ambiguities of the PWA. The PNPI-ITEP results were used in the new partial-wave analysis (PWA) FA02 of the George Washington University groups (2004 year).
-       The proposal for the additional spin-rotation parameters R and A measurements in the resonance region below 2.0 GeV is motivated. Such additional experiments are necessary to       resolve possible remaining twofold ambiguities of the PWAs.
-                    This work is supported by Russian Foundation for Basic Research,
-                                                   grant No 04-02-16335.

- HEPD

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-                                 Contents.
- 1.Introduction.
- 2.New FA02 PWA and a problem of the “missing” resonances.
- 3.Results of PNPI-ITEP collaboration measurements.
- 4.Program of the spin rotation parameters A and R measurements.
- 5.Experimental setup.
- 6. Conclusion.

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-       2. The new PWA and a problem of the “missing” resonances.
-      Numerous attempts to create a model that would exactly reproduce the baryon
- resonance spectrum that was presented in the RPP failed. The existing models usually
- predicted considerably more resonances  (twice or more in number) than were found
- in elastic N scattering. This problem is known as the problem of  “missing”
- resonances.
-      The latest SP06  PWA that was made at George Washington University (2006) and
- included the modern experimental data appearing after 1980 revealed considerably
- fewer ( approximately half) non strange baryon resonances than those presented in
- the RPP tables (2006) .
-       Tables 1 and 2 compare the results of the KA84, SM9and FA02  PWAs with
- RPP 2002,  3P0-model and Skyrme model predictions.
-         You can see from Tables 1 and 2 that the FA02 PWA keeps only resonances that
-  have the highest confidence status (****) in the RPP except for D35(1930) (which has
- the status ***).
-       Comparison of the PWA results and model predictions for the N* - and - resonances
-  numbers is in the table 2a.

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-                                                        Table 2a. Comparison of the PWA results and model predictions
-                                                   for the N* - and - resonances numbers.

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-    At the next picture the prediction of the harmonic oscillator
- SU(6)xO(3) model is shown (R.H.Dalitz, L.J.Reinders - 1977).
-    It can be seen that this model predictions are far from all PWAs
- results.

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-                   3.Results of PNPI-ITEP collaboration measurements.
-      Earlier, the authors of the global PWAs supposed that the appearance
- of new experimental data would allow reliable determination of those
- Baryon resonances which had low status (**) and (*) in the RPP.
-      However, the series of the PNPI-ITEP Collaboration experiments that was aimed at resolving the discrete ambiguities in the PWA procedure and that was supported by the Russian Foundation for Basic Research ( projects
- from no. 99-02-16635 before no. 04-02-16335) unexpectedly  led to the opposite result. Namely , they confirmed the predictions of the PWA of the VPI-GWU group for the spin rotation parameters A and R. This analysis did not reveal the baryon resonances with low confidence status (**) and (*) that were presented in the RPP tables (see Tables 1 and 2 in this submission).
-     At next pictures the results of PNPI-ITEP collaboration measurements are compared with PWAs predictions.

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-                                     5. Experimental setup.
- Main elements of the experimental setup for the spin rotation parameters
- A and R measurements.
- There are:
- Polarized target.
- Carbon polarimeter.
- Track detectors (MSC).
- Scintillation counters (C ).

- Carbon polarimeter.

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**The experiment planning by the zero trajectory consideration.**
***                             ******                                         ******{ Barrelet method employment. }***
- The basic idea of the Barrelet methods is to represent the transverse amplitudes Fat fixed energy by the following ansatz, which exhibits the zeros in the complex                  z = coscm – plane:
-                                 N
-          F(;z)=F(1)x П [(z-zi )/(1-zi )] x R(;z) ; R(;1)=1.
-                                           i=1
- as functions of a variable , which is connected with z by a conformal mapping            eiz  (z2-1)1/2.  When is real, it corresponds to the center-of-mass scattering angle.             This mapping has the property, that a physical value of z (i.e. z real and |z| < 1) is mapped onto two points in the -plane, which lies on the upper and lower halves of the unit circle, respectively. Here and  belong to the same value of z..

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-      Transverse amplitudes have the advantage, that their modulus can be determined from ddand P data alone |F| = ddx (1 P).
- This equation shows that the zeros of the amplitude can be derived from the zeros of ddand P data but, unfortunately, there is a 2 2N  fold ambiguity because for each pair of zeros zi and zi* (or i and 1/i* ) one has the choice whether zi or zi* belongs to the amplitude F.
- The spin rotation parameters A and R measurements can help in such choice.
-      The positions of the zeros of Fdepends of course on the incident pion beam momentum. This allows one to locate problems of the unknown PWA ambiguities  simply by looking at the zero trajectories on the - planes which are near the physical region.

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