Measurements of the total-cross-section difference Δσ L(np) at 1.39, 1.69, 1.89, and 1.99 GeV

Abstract

New accurate results of the neutron-proton spin-dependent total cross-section difference Ds L np ( )at the neutron beam kinetic energies of 1.39, 1.69, 1.89 and 1.99 GeV are presented. In general these data complete the measurements of energy dependence of Ds L ( ) np over the Dubna Synchrophasotron energy region. The quasi-monochromatic neutron beam was produced by break-up of extracted polarized deuterons. The deuteron (and hence neutron) polarization direction was flipped every accelerator burst. The neutron vertical direction of polarization was rotated onto the neutron beam direction and longitudinally (L) polarized neutrons were transmitted through the large proton L-polarized target. The longitudinal target polarization direction was inverted after 1-2 days of measurements. Four different combinations of the beam and target parallel and antiparallel polarization directions, both oriented along the neutron beam momentum, were used at each energy. A fast decrease of -Ds L ( ) np with increasing energy above 1.1 GeV and a structure in the energy dependence around 1.8 GeV, first observed from our previous data, seem to be well revealed. The new results are also compared with model predictions and with phase shift analysis fits. The Ds L quantities for isosinglet state I =0, deduced from the measured Ds L ( ) np values and known Ds L ( ) pp data, are also given. The results of the measurements of unpolarized total cross sections s 0tot ( ) np at 1.3, 1.4 and 1.5 GeV and s 0tot ( ) nC at 1.4 and 1.5 GeV are presented as well. These data were obtained using the same apparatus and high intensity unpolarized deuteron beams extracted either from the Synchrophasotron, or from the Nuclotron.The investigation has been performed at the Veksler and Baldin Laboratory of High Energies, JINR. Ïðåäñòàâëåíû íîâûå òî÷íûå ðåçóëüòàòû èçìåðåíèé ñïèí-çàâèñèìîé ðàçíîñòè ïîëíûõ íåéòðîí-ïðîòîííûõ ñå÷åíèé Ds L ( ) np ïðè êèíåòè÷åñêèõ ýíåðãèÿõ íåéòðîíîâ 1,39; 1,69; 1,89 è 1,99 ÃýÂ.  îñíîâíîì, ýòè äàííûå çàâåðøàþò èçìåðåíèÿ ýíåðãåòè÷åñêîé çàâèñèìîñòè Ds L ( ) np â îáëàñòè ýíåðãèé äóáíåíñêîãî ñèíõðîôàçîòðîíà. Ïî÷òè ìîíîõðîìàòè÷åñêèé íåé-òðîííûé ïó÷îê ïîëó÷àëñÿ ïðè ðàçâàëå âûâåäåííûõ èç ñèíõðîôàçîòðîíà âåêòîðíî-ïîëÿðèçî-âàííûõ äåéòðîíîâ. Çíàê ïîëÿðèçàöèè äåéòðîíîâ (à ñëåäîâàòåëüíî, è íåéòðîíîâ) ìåíÿëñÿ îò öèêëà ê öèêëó. Âåðòèêàëüíàÿ îðèåíòàöèÿ ïîëÿðèçàöèè íåéòðîíîâ ïîâîðà÷èâàëàñü ïî íàïðà-âëåíèþ íåéòðîííîãî ïó÷êà, è ïðîäîëüíî-ïîëÿðèçîâàííûå íåéòðîíû ïðîïóñêàëèñü ÷åðåç áîëü-øóþ ïðîäîëüíî-ïîëÿðèçîâàííóþ ïðîòîííóþ ìèøåíü. Íàïðàâëåíèå ïðîäîëüíîé ïîëÿðèçàöèè ìèøåíè èíâåðòèðîâàëîñü ñïóñòÿ 1-2 ñóò èçìåðåíèé. Áûñòðûé ñïàä -Ds L ( ) np ñ ðîñòîì ýíåðãèè âûøå 1,1 Ãý è ñòðóêòóðà â ýíåðãåòè÷åñêîé çàâèñèìîñòè âîêðóã 1,8 ÃýÂ, âïåðâûå íàáëþäåí-íûå â áîëåå ðàííèõ èçìåðåíèÿõ, êàaeóòñÿ ÿâíî âûðàaeåííûìè. Íîâûå äàííûå ñðàâíèâàþòñÿ ñ ìîäåëüíûìè ïðåäñêàçàíèÿìè è ñ ðåøåíèÿìè ôàçîâîãî àíàëèçà. Ïðèâîäÿòñÿ çíà÷åíèÿ Ds L äëÿ èçîñèíãëåòíîãî ñîñòîÿíèÿ I =0, ïîëó÷åííûå èç èçìåðåííûõ Ds L ( ) np -âåëè÷èí è èçâåñòíûõ Ds L ( ) pp -äàííûõ. Ïðåäñòàâëåíû òàêaeå ðåçóëüòàò...

Measurement of the spin-dependent observables in elastic NN collisions at NICA

“…If we have a possibility for extrapolation of the measured differential cross section to zero CM angle, then we can obtain the spin-dependent total cross sections differences ∆σ L,T (NN) over the NICA collider beams energy region. However, with the increasing energy of the colliding nucleons T N Lab ≥ 2 GeV the value of ∆σ L (np) quickly falls to zero [16]. This is also confirmed by the results of E − 704 experiment at FermiLab [17].…”

Measurement of neutron and proton analyzing powers on $C$, $CH$, $CH_2$ and $Cu$ targets in the momentum region 3-4.2 GeV/c

“…ALPOM2 is placed at the beam line '1v' of the Nuclotron accelerator facility, at the Veksler Baldin Laboratory for High Energy Physics (VBLHEP) of the Joint Institute for Nuclear Research in Dubna. This beam line was used previously for several experiments using (polarized) neutron beams [40], such as the measurement of the ∆σ(n ↑ p ↑ ) total cross section difference [41].…”