# Presentation: 392106

## Spin Asymmetry Measurementat RIBF

**Tomohiro Uesaka**
**CNS, University of Tokyo**

**・ ****Spin-orbit coupling in nuclei**
**・ ****Why Spin-asymmetry measurement?**
**・ ****CNS Polarized proton target for RI-beam exp.**
**・ ****Future experiments at RIBF**

**The 2****nd****  LACM-EFES-JUSTIPEN Workshop**
** ****ORNL, Jan. 23********25, 2008 **

## Spin-orbit coupling in nuclei

**“****Strong spin-orbit coupling”**** constitutes**
**  ****the basis of nuclear physics **
**	****→**** ****conventional magic numbers**
**Spin-orbit splitting (********E*****ls ******= E******j>************E******j<*****) of single particle states**
**	****can be  a good measure of the spin-orbit coupling.**
**	****	********E*****ls *****(0*****p***** in ****16****O)***** *****:  ~ 6 MeV**
**Microscopic origins of the spin-orbit coupling**
**	****       **K.Ando and H. Bando, Prog. Theor. Phys.** 66** (1981) 227.
- 	       S.C. Pieper and V.R. Pandharipande, Phys. Rev. Lett. **70** (1993) 2541.
- 	**16****O, ****40****Ca cases,**
**	****	****2N spin-orbit force****	****	****→**** ****half of  ********E*****ls ***
**	****	****2N tensor force****	****	****→**** ****20****-****30% of  ********E*****ls ***
**	****	****3N forces****	****	****	****→**** ****remaining part***** ***

## Spin-orbit splitting in n-/p-rich nuclei 

**How *********E******ls***** changes as a function of Z/N?**
**	****	****a key to understand shell regularity **
**	****	****	****far from the stability line.**
- 		  ex.  J. Dobacewski et al., Phys. Rev. Lett. **72** (1994) 981.
- 		        M.M. Sharma et al., Phys. Rev. Lett. **72** (1994) 1431.
- 		        T. Otsuka et al., Phys. Rev. Lett. **97** (2006) 162501.
**	****	****         ****. . . . . .**
**	**** **
**	**** ⇔ ****isospin-dependences of interactions**
**	****	****NN spin-orbit****	****	****weak isospin dependence**
**	****	****NN tensor****	****	****strong isospin dependence**
**	****	****3N ****	****	****	****in *****n*****-rich region **
**	****	****	****	****	****    ****T=1/2 3NF → weaker**
**	****	****	****	****	****    ****T=3/2 3NF might be dominant**
**It is stimulating to see experimentally change of *********E******ls***** as a function of Z/N. **
**	**

## Experimental determination of Els

**Population of single particle/hole states**
**	****	****transfer reactions****	****	****@ low energies**
**	****	****knockout reactions ****	****	****@ high energies**
**L and J determinations**
**	****L  ←**** ****momentum dependences of cross section**
**	****J**** ←   ****spin-asymmetry ****is needed **
**	****	****	****for “model independent” determination**
**	****	****	**
**	****	**

## Solid Polarized Proton Target at CNS

**Solid Polarized Proton Target at CNS**

**New Polarized Proton Target applicable to RI beam exp.**

**T. Wakui et al., NIM A 550 (2005) 521.**
**T. Uesaka et al.,  NIM A 526 (2004) 186.**
**M. Hatano et al., EPJ A 25 (2005) 255. **

**material:        C****10****H****8  ****(+ C****18****H****14****)**
**thickness: ****	****1 mm (120 mg/cm****2****)**
**size:****	****	********14 mm**
**polarization:  P~15%**
**temperature:  100 K**
**mag. field:      0.1 T**
**  **

## Application to RI beam experiments

**The polarized target has been **
**	****successfully applied to RI-beam experiments at RIPS**
** **
** ****spin-asymmetry in the p-****6,8****He elastic scattering at 71 MeV/A. **
**Large discrepancies between data and microscopic theory (dashed lines)**
**	****	**S. P. Weppner et al.
- 		Phys. Rev. C **61** (2000) 044601.
**Angular distributions for p-****6****He and**
** ****p-****8****He are different**

**p-****6****He elastic**
**E/A=71 MeV/A**

**p-****8****He elastic**
**E/A=71 MeV/A**

**Spin asymmetry (*****A******y*****)**

******CM**** [deg]**

## Future experiments at RIBF

**Spin-asymmetry measurement for the (p,pN) knockout reactions**
**	****→**** ****L and J  of hole states**
**	****	****   ⇔ ****j****>**** and j****<**** distributions**
**	****→**** “****model independent” *********E******ls***** determination**
**	**

**16****O(p,pp) @ 200MeV**

- P. Kinching et al., Nucl. Phys. A **340** (1980) 423.

**p****1/2**

**spin asymmetry**

**p****3/2**

***n*****-rich oxygen isotopes**
***n*****-rich silicon isotopes**
** ****and heavier (Ni, Sn. . .)**

## (p,pN) at RIBF

**(p,pN) at RIBF**

**E/A = 200********300MeV: **
** ****	****best energy for the study**
**	****1) weak distortion for incoming and **
**	****      ****scattered proton**
**	****	*****E******p*****=150****-****250MeV**
**	****2) modest absorption for recoiled nucleon**
**	****	*****E******N*****=50****-****100MeV**
**	****3) large spin-correlation parameter**
**	****    ****in N-N scattering**
**	****	*****C******y,y***** ~ 0.8**
**	****4) reaction theory established **
**	****	****relativistic DWIA**
**	****	****   ****G.C. Hillhouse et al. **

***E******p***** [MeV]**

** ******** ****[deg]**

***C******y,y***** for *****p*****-*****p***** scattering**

## (possible) Experimental Setup

**Large spin correlation coeff.**
**	****→**** ****E****p****=200 MeV**
**Large figure of merit (d********/d********×*****C******y,y*****2****)**
**	****→****	********lab**** ~ 30 deg**

***E******p*****~60MeV**

***E******p*****~140MeV**

## Summary

**N/Z-dependences of spin-orbit splitting **
**	****	****are of critical importance in understanding**
**	****	****	****shell regularity at far from the stability line**
**	****	****	****microscopic origins of SO coupling in nuclei**
**“****Model independent” determination of *********E******ls***** is made possible**
**	****      ****by ****spin-asymmetry measurements with polarized target****.**
**	****	**
**Polarized proton solid target developed at CNS has brought into a practical usage in RI beam experiments.**
** ****(*****p,pN*****) measurements at RIBF will provide a unique opportunity to investigate SO coupling in n-/p-rich nuclei.**

## SHARAQ Spectrometer

**SHARAQ is a high resolution magnetic spectrometer**
**	****under construction at the RIBF experimental hall.**
**	****	****University of Tokyo (CNS, Sakai-g) - RIKEN collaboration**

## Design Spec. and Configuration

**SDQ**

**D1**

**D2**

**Q3**

**Maximum rigidity****	****	**
**	****	****6.8 Tm****	**
**Momentum resolution****	**
**	****	****d*****p*****/*****p***** ~ 1/15000**
**Angular resolution****	****	**
**	****	****~ 1 mrad**
**Momentum acceptance****	**
**	****	****± 1%**
**Angular acceptance****	****	**
**	****	****~ 5 msr**

## What we can learn from (p,pN)

***how p***** (*****n*****) spin-orbit splitting**
**	****	****depends on *****n***** (*****p*****) number?**
**	****→**** ****Shell regularity in the region **
**	****	****far from the stability line**
**	****	**
**    ****(p,pN) measurements at RIBF **
**    ****extend our understanding on**
**    ****nuclear structure in the region**
**    ****far from the stability-line.**

- J. P. Schiffer et al., PRL **92** (2004) 162501.

**N********A**

**E****j<********E****j'>**

## Application to Ni isotope beams

**G. Mairle et al., Nucl. Phys.  A 543 (1992) 558.**

**spin-orbit splitting**

## Method of Effective Polarization

**16****O(p,pp) @ 200MeV**

**Method of Effective Polarization**

**p*****N***

***A******y***

***d******3************/d************1******d************2******dE***

**G. Jacob et al.,  Phys. Lett. B 45 (1973) 181.**
**P. Kinching et al., Nucl. Phys. A 340 (1980) 423.**

**polarized target for the measurement**
**possible experimental setup **

## Operation at Low magnetic field

**is crucial to achieve sufficient separation energy resolution.**
**Separation energy resolution depends primarily on **
**	**_**angular resolution**_** of **_**scattered and recoiled protons**_**. **
**	****	******** ****~ 1 mrad                   (*****B***********)****p****  ~  1****-****2 Tm**
**In the presence of magnetic field of 3 Tesla, **
**	****the proton trajectory is bended by 300 mrad before detection**
**Our polarized target working at < 0.1 T will provide**
**	****reasonable angular resolution of ~ 1mrad after correction.**

## Target Material

**Naphthalene C****10****H****8 ****with a typical thickness of 1 mm**
**	**** ****Large energy loss ( when compared with sld/liq hydrogen)**
**	****	****may spoil energy resolution of protons**
**	**** **
**	****Contribution from carbon nuclei**
**	****	****may mask the region of interest**

******E*****p***** ~2.5MeV**
******E****p****/E****p**** ~ 4%**

**Use of (high-resolution) spectrometer and beam-line**
**will be useful to solve the problems.**

## Energy correlation between p and HI

******E*****p***** ~2.5MeV**

**E****Ni**

**E****Co**

******(****E****Co********E****Ni****) ~ 30 MeV**

**120 mg/cm****2**

***E******p***

***E*****co *****-***** *****E*****Ni**

**2.5MeV**

**30MeV**

**proton separation energy from ****12****C**
**	****	*****S******p****** *****~ 16 MeV**

**16 MeV**

## Required energy resolution

**Total energy ****	****	****	****    ~ 14 GeV  (200 MeV/A × 70)**
**required energy resolution****	****    < several MeV**
**	********E/E < 1/(2000~3000)  **
**	****	****     ****or better for lighter projectile**
**Zero Degree Spectrometer (achromatic mode)**
**	********p/p = 1/ (1000****-****2000)****	****	**
**SHARAQ Spectrometer (achromatic mode)**
**	********p/p ~ 1/ 7000**

## (p,pN) measurement at SHARAQ

**D(F6) ~ 7m**

## Summary

**(*****p*****,*****pN*****) measurement with polarized protons should be**
**	****a promising method for determination of spin-parities**
**	****of single particle states.**
**RIBF energy is one of the best energy for the purpose.**
**Polarized proton target operating at low magnetic field **
**	****is a unique device for the measurement.**
**Application to Ni beams is investigated.**

## BACKUP SLIDES

**BACKUP SLIDES**

## Spin orbit coupling

**Spin orbit coupling**

**Tensor force effects T. Otsuka **

**Weakening of spin-orbit coupling**
**  ****Dobaczewski, Ring . . . .**
**  **

**3N force  B. Pudliner**

**15****N:  ********E****ls****  = 6.1 MeV**
**               ↓**
** ****7****n :  ********E****ls **** = 1.4 MeV**

## KEYS:
   ・ Large spin correlation in N-N scattering,    Cy,y ~0.8, at E/A~200 MeV
		↑↑ ≫    ↑↓
	         → incident proton interacts mostly with nucleon with the same spin
   ・ Distortion to recoiled (low energy) nucleon
		if recoiled nucleon goes into the target nucleus  → absorbed

**KEYS:**
**   ****・ ****Large spin correlation in N-N scattering,    *****C******y,y****** *****~0.8, at E/A~200 MeV**
**	****	********↑↑**** ≫   ******** ****↑↓**
**	****         ****→**** ****incident proton interacts mostly with nucleon with the same spin**
**   ****・ ****Distortion to recoiled (low energy) nucleon**
**	****	****if recoiled nucleon goes into the target nucleus  →**** ****absorbed**
**	**

**Method of Effective Polarization**

**proton with spin↑**

**R**

**L**

**L**

**j****<**

**j****>**

**if *****p******N***** < 0 **
**	**
***A******y***** < 0 for j****>**
***A******y***** > 0 for j****<**

***p******N***** < 0**

## (p,pN) at RIBF

**(p,pN) at RIBF**

**E/A = 200********250MeV: **
** ****	****best energy for the study**
**	****1) weak distortion for incoming and **
**	****      ****scattered proton**
**	****	*****E******p*****=150****-****250MeV**
**	****2) modest absorption for recoiled nucleon**
**	****	*****E******N*****=50****-****100MeV**
**	****3) large spin-correlation parameter**
**	****    ****in N-N scattering**
**	****	*****C******y,y***** ~ 0.8**
**	****4) reaction theory established **
**	****	****relativistic DWIA**
**	****	****   ****G.C. Hillhouse et al. **

***E******p***** [MeV]**

** ******** ****[deg]**

***C******y,y***** for *****p*****-*****p***** scattering**

## NN spin correlation parameter

## Experiments at RIBF

**(p,pp)****	****	****Ni , Sn, Ca isotopes**
**(p,pn)****	****	****N=50, 28 isotones**

**from BigRIPS**

**SHARAQ/**
**SAMURAI**

**proton detectors**

**neutron detectors**

**Notes:**
P. Kinching et al., Nucl. Phys. A 340 (1980) 423.

## Polarized Proton Targets for RI beam

**Little has been studied for unstable nuclei**
**	****high statistics needed **
**            ****->**** ****high intensity beams is/will be available**
**	****lack of a polarized target applicable to RI beam experiments**
**	****	****->**** ****new solid polarized ****proton**** target at CNS**
**Requirements on the polarized proton target for RI beam exp.**
**     ****RI beam**** : ****Low intensity of < 10****6**** Hz**
**	****	****	****high-density solid target****      ****gas target**
**any *****p***** solid target:   compound including hydrogen atoms**
**        ****detection of ****recoiled protons: ****essential for event ID **
**	****	****            ****5 MeV proton: range < 0.2mm B******** = 0.33 Tm**
**      ****conventional *****p***** targets at ****low *****T*****(<1K)**** and at ****high *****B *****(>2.5T)***** ***
***	******	******	*****places serious difficulty in proton detection.**

## Solid Polarized Proton Target at CNS

**New polarized proton target operated **
**	****at**** low mag. field of 0.1T and high temp. of 100K**
**	****TRICK: use of electron polarization in photo-excited triplet **
**	****	****	****state of aromatic molecules**
**	****	****	****independent of temperature/field strength.**
**	****	****	****H.W. van Kesteren et al., Phys. Rev. Lett. **55** (1985) 1642.**

**T. Wakui et al., NIM A 550 (2005) 521.**
**M. Hatano et al., EPJ A 25 (2005) 255. **
**T. Uesaka et al.,  NIM A 526 (2004) 186.**

**material:        C****10****H****8  ****(+ C****18****H****14****)                +       **
**thickness: ****	****1 mm (120 mg/cm****2****)**
**size:****	****	********14 mm**
**polarization:  P~20%**
**  **

**naphthalene**

**pentacene**

## Target Apparatus

**14mm**

**1mm**

**RI beam**

**Ar-ion laser**

## Polarization during p-6He experiment

**Magnitude of polarization is limited by insufficient laser power.**
**	****development of new pumping source is now going on**
**	****	****for higher polarization (theoretical maximum = 73%).**

**small effects**
**of radiation **
**damage**

## SHARAQ Spectrometer (CNS) 

**SHARAQ Spectrometer (CNS) **

**B********= 6.8 Tm**
**   ****300MeV/A, A/Z=3**
**p/********p = 15000**
****** ****= 3********5 msr**

**to be completed in 2008**