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, 141980 Dubna, Moscow region, Russia

E-mail: strunov@sunhe.jinr.ru

IntroductionTo 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.

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).

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.

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 performa) 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 nppn at 0 angle with 5% statistical errors at the same energies as for the spin dependent observables.

ACCELERATOR RUN TIME REQUESTACCELERATOR 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 2005 - 2006

polarized deuterons,

L-polarized proton target

(see item 2)

Near 1.8

1.4 – 2.5

2 10 – 15 2004 – 2006

Unpolarized deuterons,

H2, D2-cryogenic targets

(see item 3)

1.2 – 3.7 20 10 – 15 2004 - 2006

Accelerators and ToolsAccelerators and Tools1. THE SYNCHROPHASOTRON AND NUCLOTRON OF THE JINR VBLHE2. 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 BEAM3. LARGE POLARIZED PROTON TARGET (PPT) WITH VOLUME OF 140 cm3

AND POLARIZATION VALUE OF 0.7–0.84. 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.

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.

The ΔσL,T(np) Observables

In this contribution, we use NN formalism and notations for elastic nucleon-nucleon scattering observables.

The general expression for the total cross section of a polarized nucleon beam trasmitted through a polarized proton target, with arbitrary directions of beam and target polarizations is (S.M.Bilenky and R.M.Ryndin, Phys.Lett. 6 (1963) 217, R.J.N. Phillips, Nucl.Phys. 43 (1963) 413):

σtot = σ0tot + σ1tot (PB PT) + σ2tot (PB k)(PT k), (1) where PB and PT are the beam and target polarizations, and k is the unit vector in the incident beam direction.

The term σ0tot is the spin-independent total cross section, and σ1tot and σ2tot are the spin-dependent contributions which connect with the observables ΔσT and ΔσL by the relations:

– ΔσT = 2 σ1tot (2)

– ΔσL = 2 (σ1tot + σ2tot) (3)

Values of σ0tot, ΔσT and ΔσL are connected with the imaginary parts of three invariant forward scattering amplitudes a + b, c and d via three optical theorems:

σ0tot = (2π/K) Im [a(0) + b(0)], (4)

– ΔσT = (4π/K) Im [c(0) + d(0)], (5)

– ΔσL = (4π/K) Im [c(0) – d(0)]. (6)

where K is the c.m. momentum of the incident nucleon. Relations (5) and (6) allow one to extract the imaginary parts of the spin-dependent invariant amplitudes c(0) and d(0) at an angle 0° from the measurement values of ΔσL

and ΔσT.

Using the measured values of ΔσL,T(np) and the existing ΔσL,T (pp) data at the same energy, one can deduce ΔσL,T (I=0) as:

ΔσL,T (I=0) = 2 ΔσL,T (np) – ΔσL,T (pp). (7)

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.

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

Measurements of the Measurements of the A00A00kkkk(np)(np) and and A00A00nnnn(np)(np) from from npnppnpn

process.process.[dσ/dΩ]pol(E, θ) = dσ/dΩ(E, θ) [1 + A00n0(E, θ) PB

n + A000n(E,θ) PTn +

+ A00nn(E,θ) PBn PT

n + A00ss(E,θ) PBs PT

s + (8) + A00kk(E,θ) PB

k PTk + A00sk(E,θ) (PB

s PTk + PB

k PTs)],

where dσ/dΩ is a cross section for unpolarized nucleons. If the scattered particles are detected at 0° angle then analyzing powers A00n0(E,0) = A000n(E,0) = 0 and parameters A00sk(E,0) = 0 and A00ss(E,0) = A00nn(E,0). Thus, only two non-vanishing spin-dependent quantities A00nn(E,0) and A00kk(E,0) remain in (8). Due to symmetries of amplitudes, which hold separately for isospins I=0 and I=1, the same relations are valid at Θc.m= π. Moreover the amplitude e(0) = e(π) for any isospin. The measurement np observables at Θc.m= π are connected with the invariant amplitudes as follows:

dσ/dΩ (π) = ½[|a|2 + |b|2 + |c|2 + |d|2], (9)

dσ/dΩ A00nn(π) = ½[|a|2 – |b|2 – |c|2 + |d|2], (10)

dσ/dΩ A00kk(π) = Re a* d + Re b* c. (11)

where all experimental quantities and amplitudes are Θc.m= π.

These equations can be transformed to:

dσ/dΩ (1 + A00kk) = |b + c|2 = A + (Re b + Re c)2, (12)

dσ/dΩ (1 – A00kk – 2A00nn) = |b – c|2 = B + (Re b – Re c)2, (13) dσ/dΩ (1 – A00kk + 2A00nn) = |b + c – 2d|2 = C + (Re b + Re c – 2Re d)2, (14) where terms A, B, C contain the imaginary parts of amplitudes only. The real parts of the amplitudes b, c and d can be determined from Eqs. (12-14) using known imaginary ones. A knowledge of I=1 system is assumed in order to use the amplitude symmetries for the transformation of I-0 amplitudes from Θ=0 to Θ=π and vice versa.

Rdp ratio for charge-exchange at t=0 andratio rnf/fl

np->pn Energy dependence of the ratio Rdp=dσ/dΩ(nd -> pnn) / dσ/dΩ(np->pn) (15)

for elastic charge exchange process nppn at 0º in Lab. (or elastic npnp backward scatteting in C.M.S.) will be measured at high intensity unpolarised neutron beam from the Nuclotron using the magnetic spectrometer and liquid hydrogen and deuterium targets. Rdp is connected with helicity NN amplitudes by:

dσ/dΩ(nd) 2 1

R = –––––––––= ––– ∙ ––––– , (16) dσ/dΩ(np) 3 (1+R')

|Φ4–Φ2|

2 R' = ––––––––––––––– , (17)

2∙|Φ 1|2+|Φ4+Φ2|

2

where Φi are the helicity NN amplitudes and R'= rnf/flnp->pn ( or RID is was used in ref. [8a]) is the ratio of 'spin non-

flip' to 'spin flip' cross sections for nppn process. For R'=0 we have dσ/dΩ(nd) = 2/3 ∙ dσ/dΩ spinflip(np). (18) Relation (18) demonstrate a using deuteron as filter for non spin-flip amplitudes at t≈0 , i.e. using the exclusive Pauli principle for nd→p(nn) quasi -elastic reaction with two nn-system with parallel spins [5,8].

The values of Rdp give an additional relation between spin-dependent NN-amplitudes and a set of such data allows to avoid an uncertainties of real parts extraction.

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

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

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.

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

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

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

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

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.

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 = 250 - 540 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.

1. In book ed. Baldin A.M. Research Program of LHE JINR (Dubna 1999) 37-43,"Delta-Sigma Experiment" Spokesmen V.I.Sharov, L.N.Strunov. 1b. R.Binz Ph.D.Thesis.Freiburg (1991).

2. A.A.Nomofilov et al.,Phys.Lett. B325(1994),p.327; Phys.Rev.Lett.v.74,N25(1995),p.4997. 3. V.I.Sharov et al.,JINR Rapid Com.,3[77]-96, (1996) 13; 4[96]-99 (1999) 5; Z.Phys.C.71,N1, (1996) 65; to be publ.Yad.Phys.8(2005);Eur.Phys.J.C37,79(2004). 4. E.L.Lomon et al. at the proper references in [3]; M.Matsuda: Nucl.Phys. A631 (1998) 436. M.Matsuda et al, Few-Body Systems Suppl.12,457(2000) 5a R.Binz Ph.D. Thesis.Frieburg University Germany (1991); 5b J.Ball et al., Eur.Phys.J.C5 (1998) 57 6. A.A. Morozov et al., Czech.Journ.of Phys. Vol.55(2005).Suppl 7. R.A. Shindin et al., Czech.Journ.of Phys. Vol.55(2005).Suppl 8a. F.Lehar, Private Comm. May 11.2005. 8b V.V.Glagolev et al. Eur.Phys.J.A15(2002),471 9. V.P. Dzhelepov et al., Nuovo Cim.Suppl.III (1956), 61 10a. V.I.Sharov et al.,Eur.Phys.J.C13,255-265(2000); 10b. V.I.Sharov et al. Czech, J, Phys. 55 (2005)

Conclusion1. New –ΔσL(np) results complete in the main the measurement of the –ΔσL(np) energy dependence at the Dubna

Synchrophasotron region. 2. Anomalys rapid decrease of –ΔσL(np) values above 1.1 GeV was observed in the first data taking runs and is confirmed

in the latest run and a minimum or a shoulder around 1.8 GeV is observed. 3. The necessity of more detailed and accurate –ΔσL(np) and simultaneously A00kk measurements around 1.8 GeV and

new –ΔσT(np) and simultaneously A00knn data in the kinetic energy region above 1.1 GeV is emphasized. 4. A number of physical and methodical results on investigation of the elastic np→pn charge-exchange process over a few

GeV region are also presented. The possibilities for A00kk(np), A00nn(np) and Rdp measurements, using prepared magnetic spectrometer, were demonstrated.

We are grateful to the JINR, JINR VBLHE and DLNP Directorates for these investigations support. The

investigations were supported in part by the Russian Foundation for Basic Research (Grant № 02–02–17129).