Session 4WBB: Polarized Ion Sources and Targets II

Polarized NH3 and ND3 Targets at FNAL-SpinQuest

SpinQuest at Fermilab is a fixed-target experiment to measure the Drell-Yan process using transversely polarized NH₃ and ND₃ targets and unpolarized 120-GeV proton beam.  In the Drell-Yan process, a quark in one scattering hadron and an anti-quark in the other hadron annihilate into a virtual photon and then decay into a muon (lepton) pair.  The angular distribution of final-state muon pairs with respect to the target polarization is sensitive to the Sivers function of light anti-quarks in the nucleon, which is one of the eight Transverse Momentum Dependent (TMD) parton distribution functions.  The Sivers function of each anti-up and anti-down quarks can be extracted by the use of the NH₃ and ND₃ targets for p+p and p+d reactions.  The intensity of the proton beam is as high as 2*10¹² protons/second, in order to accumulate the required number of Drell-Yan events.  The polarized target has been designed to accommodate this high intensity.

It is equipped with an evaporation refrigerator with a maximum cooling power of 3 W.  The target temperature is maintained at 1 K under heat loads due to the proton beam and the DNP microwave.  The polarization is higher than 80% for NH₃ and 32% for ND₃.  The commissioning of the whole target system with the beam is planned in November 2023.  The design and the performance of the polarized target will be presented.   

Polarized targets at CERN from the past to the future

Polarized solid targets had been used for a study of the nucleon spin structure in the M2 beam line at CERN SPS since 1980s.

The COMPASS experiment (NA58), which started the data taking in 2002, reveals details of the gluon polarization and transverse-momentum-dependent correlations with SIDIS and DY processes.

The COMPASS polarized target system had been playing an important role to obtain those results.

 It consists of a 50 mK dilution refrigerator, a 2.5 T solenoid magnet, and a 70 GHz microwave system.

Solid ⁶LiD beads as deuteron target and NH₃ as proton target material were contained in 130 cm long the target place.

The targets were polarized by DNP technics.

I will present the polarized target results for the COMPASS experiment.

I will also review a polarized gas target project at CERN-LHCb as well was the future planning of the AMBER experiment for the polarized GPD program.   

Development of polarized La nuclear target for T-violation search

In compound nuclear states formed by resonant absorption of a low-energy neutron to a lanthanum-139 nucleus, the parity non-conservation effect (P-violation) is amplified by a factor of 10$^6$ via mixing process of S and P wave. The time reversal asymmetry (T-violation) is also expected to be amplified in the same process. The NOPTREX collaboration has a plan of the T-violation search using a polarized lanthanum-139 and a polarized neutron as the first choice. A single crystal of LaAlO₃ doped with Neodymium ions as paramagnetic centers is a good candidate as target material since the crystal with neodymium concentration of 0.03 mol% has shown about 20% polarization at 1.5 K in 2.3 T by using the dynamic nuclear polarization (DNP) technique. The T-violation experiment requires to maintain high polarization of lanthanum in a low magnetic field (~ 0.1 T). 

Our previous studies with the 0.03mol% crystal have estimated longer relaxation time than 1 h at 0.1 K in 0.1 T, so that the DNP tests of various crystals with different neodymium concentrations are necessary. Thus, we have focused on following three issues, one is to establish the way of crystal growth for preparation, the second is to construct the new DNP system for the neodymium optimization, and the third is a heat simulation for determining a crystal dimension, which is necessary for a design of target cryogenics.

We prepared two kinds of crystals with 0.05mol% and 0.01mol% based on the floating zone method at Tohoku University and evaluated them with the simplified DNP system at Yamagata University. The 0.01mol% crystal showed an unsaturated polarization of about 20% in 1.5 K and 2.3 T. We also prepared the DNP system at RCNP, which has the 1.5 K cryogenics capable to continuous operation for a long time. This system allows us to measure a saturated polarization and a long relaxation time.

In this talk, we report the present status and future prospects based on the results of the DNP tests and test operation of the new DNP system.