1. Measurements of Neutron-Proton Spin Observables at 0° using Highest Energy Polarized d, n Probes
L.N. Strunov
Dubna “Delta-SIgma” Experiment
Joint Institute for Nuclear Research, Dubna, Moscow region, Russia

2. Introduction
To advance studies of the short range spin structure of NN interactions, (np) spin observables
were for the first time measured at 0° up to the highest nucleon internal momenta k in np core.
Both the bounded polarized (np)-couple (in deuteron) and a polarized free np-couple were
probed up to k~5 fm-1 and 6 fm-1 respectively. The highest energy polarized deuteron (up to 9
GeV/c) and polarized monochromatic neutron beams (up to 4.5 GeV/c), provided now only by
the JINR accelerators, were used2,3.
These data are in agreement with the SATURNE II ones over the lower k-momentum
common range of 2.5 fm-1. Several years ago Dubna (in collaboration with groups from 12
laboratories) began the transmission measurements3 with both a polarized neutron beam and a
polarized proton target. We first measured the energy dependence of the ΔσL(np), neutron-
proton total cross section difference for the pure longitudinal (L) spin states for parallel and
antiparallel (np) spins, over a new kinetic energy range of 1.2 – 3.7 GeV for a quasi-
monochromatic polarized neutron beam. The ΔσL(np) energy dependence3 shows an anomalous
fast decrease to zero above 1.1 GeV and a structure around 1.8 GeV, predicted4 as a signal of
excitation of the lowest lying exotic six-quark configurations in the isosinglet and spin-triplet
state 3S1 with mass M=2.63 GeV.

3. Introduction
The obtained high momentum dependences of these (np) spin observables2,3 are surprising
for all traditional nuclear models. Their predictions are wrong for the highest momentum
(asymptotic) behaviour of these observables related with almost fully overlapping nucleons
in fact.
We hope now to obtain a complete L,T data set1 of np spin observables at 0° which is
needed for the first direct reconstruction of all three isosinglet amplitudes of forward NN
elastic scattering over a GeV energy range. With this very ambitious aim the following will
be simultaneously measured for the first time at each chosen Tn: ΔσL and A00kk, a spin
correlation parameter for np→pn charge-exchange (180° in the c.m.s) with the L
polarization of n beam and p target; ΔσT and A00nn with the T-polarized beam and target.
The proper equipment mounted in the last year was successfully tested (in simultaneous
measurements of n beam transmission through H2/D2 targets and n→p charge-exchange on
them).

4. Introduction
The Dubna group fulfilled first measurements under 0° of the ratios Rdp “elastic” np
charge-exchange yields on H/D targets and defining of the ratios rnf/fl np→pn (0) nonflip and
spin-flip contributions to np→pn process. In the region of Tn~1.8 GeV one can expect an
anomaly3 of rnf/fl np→pn – energy dependence (as in the case3 of the measurements of ΔσL) if
one conforms to the QCD-motivated reasoning (Lomon et al., Matsuda et al.)4 about a phase
transition at this energy of the NN system into the exotic six-quark configuration in the
isosinglet and the spin-triplet state 3S1 with the mass M≈2.63 GeV. For the exhaustive
analysis of this structure3 using Argand diagrams for Re and Im parts of each of the three
NN forward scattering amplitudes, it is required to measure in Dubna not only the complete
set1 of np-spin observables at 0°, but also needed to carry out pilot measurements in the
same energy region of the ratio Rdp(0) = dσ/dΩ(nd) / dσ/dΩ(np) for yields of “elastic” n→p
charge-exchange of non-polarized neutrons on D/H targets that independently defines1b the
ratio rnf/fl np→pn at 0° the spin-nonflip contribution in np→pn to the spin-flip contribution in
this process: rnf/fl np→pn = 2/3 Rdp-1 – 1. Our preliminary results at Tn=1.0 and 1.2 GeV are:
rnf/fl np→pn (0)=0.30±0.3, χ2~0.5/f.d. obtained by Rdp measurements at 16 points of t≈(Pnθ)2
interval [1÷30]·10-4 GeV2/c2 at each Tn.

5. THE COMING RESEARCH PROGRAM “Delta-Sigma”
The coming research program under the project on 2004–2006 is following:
1) Using suitable T-polarized neutron beam and T-polarized proton target to perform at Tn=1.2 – 3.7 GeV.
a) the measurements of the ΔσT (np) at the same energy points as for ΔσL (np) with energy steps of 100–200 MeV and expected statistical errors ~ 1 mb;
b) the measurements of the energy dependencies of spin-correlation parameters A00nn(np) at the same energy points as for ΔσT (np) with expected statistical errors 0.02–0.05. These measurements can be performed simultaneously and independently with the ΔσT (np) ones.
2) Using suitable L-polarized neutron beam and L-polarized proton target to perform
a) the more precise and detailed measurements of the ΔσL (np) near Tn=1.8 GeV at 2–3 energy points with energy steps of 100 MeV and expected statistical errors less than 1 mb;
b) the measurements of the energy dependencies of spin-correlation parameters A00kk(np) at the same energy points as for ΔσL(np) with expected statistical errors 0.02–0.05. These measurements can be performed independently with the ΔσL(np) ones.
3) Using a high intensity unpolarized deuteron beam for preparing free neutron beam and liquid hydrogen and deuterium targets, the measurements of ratio Rdp=dσ/dΩ(nd) / dσ/dΩ(np) for elastic charge exchange process nppn at 0 angle with 5% statistical errors at the same energies as for the spin dependent observables.

6. ACCELERATOR RUN TIME REQUEST
Accelerated Beam,
Target
Tn Range,
GeV
Intensity, x109
particles/cycle
Duration, days
Planned Years of the Measurements
Polarized deuterons,
T-polarized proton target
(see item 1)
1.2 – 3.7 2 30
polarized deuterons,
L-polarized proton target (see item 2)
Near 1.8
1.4 – 2.5
10 – 15
2004 – 2006
Unpolarized deuterons,
H2, D2-cryogenic targets
(see item 3) 20

7. Accelerators and Tools
1. THE SYNCHROPHASOTRON AND NUCLOTRON OF THE JINR VBLHE
2. RELATIVISTIC (1–5) GEV:
POLARIZED NEUTRON BEAMS WITH L OR T ORIENTATION OF POLARIZATION, REVERSION OF POLARIZATION DIRECTION CYCLE BY CYCLE AND AVERAGE POLARIZATION VALUE OF ≈ 0.53
HIGH INTENSITY (2-3)*1010 d/CYCLE UNPOLARIZED DEUTERON BEAM
3. LARGE POLARIZED PROTON TARGET (PPT) WITH VOLUME OF 140 cm3
AND POLARIZATION VALUE OF 0.7–0.8
4. CRYOGENIC LIQUID HYDROGEN-H2 AND DEUTERIUM-D2 TARGETS L=30 cm LONG.
5. EXPERIMENTAL SET-UP “DELTA-SIGMA” WITH :
TRANSMISSION NEUTRON DETECTORS
MAGNETIC SPECTROMETER WITH PROPORTIONAL CHAMBERS
DETECTORS FOR H2/D2TARGET SURROUNDING (DTS)
TIME-OF-LINE (TOF) SYSTEM
MODERN DATA ACQUISITION SYSTEM
In the following section a determination of the NN spin-dependent observables and some results of investigation under the “Delta-Sigma” program will be done. The last accurate data on the neutron-proton spin-dependent total cross-section difference ΔσL(np) at the neutron beam kinetic energies 1.4, 1.7, 1.9 and 2.0 GeV will be presented. A number of physical and methodical results on investigation of the elastic np→pn charge-exchange process over the energy region under discussion will be also presented.

9. The method of scattered particle detection is used to measure the yield of charge-exchange
protons and differential cross section for np→pn process at 0°. A magnetic spectrometer for
detection of protons from np→pn elastic charge-exchange at 0°(Lab.), was installed and
tested at the polarized neutron beam line. The spectrometer consist of analyzing dipole
SP94, two sets of multiwire proportional chambers before and after SP94 for momentum
analyzis of detected secondaries, time-of-flight system for particle identification, liquid H2
or D2 targets, surrounded by a device STS for detecting of recoils and gammas, and trigger
counters A, S1, ST.

13. The ΔσL,T(np) Observables

15. Energy dependence of the –ΔσL(np)
Red circles – JINR (Delta-Sigma) Red rhombuses – JINR (Delta-Sigma) Green triangles – PSI Violet triangles – LAMPF Green circles – Saturne Solid curves – ED GW/VPI PSA 1) –-- FA95 solution 2) –-- FA99 solution 3) –-- SP03 solution Dotted curve – contribution from nonperturbative QCD interaction includet by instantons.

16. Energy Dependence of the –ΔσL (I=0) calculated from the obtained –ΔσL(np) results and the known pp values.

17. Measurements of the A00kk(np) and A00nn(np) from nppn process.

19. Rdp ratio for charge-exchange at t=0 and ratio rnf/flnp->pn

20. The momentum spectra of charged secondaries, detected by spectrometer using H2 and D2 liquid targets, at the neutron beam energy of 1.0 GeV.

21. The momentum spectra of charged secondaries, detected by spectrometer using H2 and D2 liquid targets, at the neutron beam energy of 1.2 GeV.

22. An information from the detectors for target surrounding DTS allows to suppress the contributions from
other (inelastic) np-reaction channels. The upper histograms in next figs.
Present spectra of angle of deflection of charged secondaries in analyzing magnet obtained without using the
information from the DTS. The bottom histograms in the figs. show the same as upper ones but when the
signal from the DTS is in anticoincidence with the spectrometer trigger.

23. The detected particle identification, using both the magnetic analyzis and time-of-flight spectra

24. Angular dependences of differential cross sections of the np→pn process at 0°, obtained with H2 and D2 targets at Tn=1.0 GeV.

25. An estimation of the ratio Rdp(0) at neutron beam energy of 1.0 GeV.

26. An estimation of the ratio Rdp(0) at neutron beam energy of 1.2 GeV.

27. PRELIMINARY RESULTS OF C.EX. NP→PN AND ND → P(NN) AT 0°
MEASUREMENTS OF THE RATIO Rdp OF THE YIELDS OF THESE REACTIONS
WERE OBTAINED AT THE FIRST TIME AT Tn > 1 GeV.

28. AS A RESULT, THE VALUES OF THE RATIOS OF NON SPIN-FLIP TO SPIN-FLIP CONTRIBUTION IN
NP → PN C.EX. AT AT 0°, rnp->pn nf/fl = Rdp (0) -1, WERE OBTAINED AT THE FIRST TIME AT Tn > 1 GeV:
ARE OUR PRELIMINARY DATA OBTAINED WITH THE DELTA-SIGMA PECTROMETERWITH LIQUID H2/D2
TARGETS AT THE QUASIMONOCHROMATIC n BEAM (VBLHE,JINR). ALSO, THE RED SQUARE POINT AT
Tn = 380 MeV WAS OBTAINED AT JINR [9].
ARE THE POINTS AT Tn = VeV CALCULATED BY R.DINZ [5a] ON THE BASE OF THE RESULTS OF
THEIR MEASUREMENTS OF THE COMPLETE DATA SET ON NP SCATTERING [5a], THE BLUE CURVE
AND THE EMPTY CIRCLES ARE THE PHASE SHIFT ANALYSIS [8a] RESULTS.

30. Conclusion