Development of polarized HD target for LEPS experiments RCNP Osaka University Japan Hideki Kohri

Contents (1) LEPS (SPring-8) experiments (2) Physics motivation of introducing polarized target (3) Development of polarized HD target (4) Summary and future plan

Contents (1) LEPS (SPring-8) experiments (2) Physics motivation of introducing polarized target (3) Development of polarized HD target (4) Summary and future plan

Electron storage ring 8GeV electron beam Diameter ≈457 m RF 508 MHz 1 ‐ bunch spread is within σ ＝ 12 psec ． Beam Current = 100 mA 120 km distant from Osaka Super Photon ring ‐ ８ GeV

SPring-8 beam-line map LEPS beam-line

SPring-8 SR ring Inverse Compton  - ray Laser light 8 GeV electron Recoil electron Electron tagging Collision LEPS facility constructed in 2000 Experiment hutch 0 10m 20m Laser hutch Photon beam Energy E  = GeV Intensity ~10 6  /s Polarization linearly and circularly polarized beams. P~90% at the maximum photon energy.

 LEPS detector 1m1m TOF wall MWDC 2 MWDC 3 MWDC 1 Dipole Magnet (0.7 T) Target LH 2, LD 2 Silicon Vertex Detector Aerogel Cerenkov (n=1.03) Start counter

Mass(GeV/c 2 ) Momentum (GeV/c) K/  separation (positive charge) K+K+ ++ Charged particle identification by forward spectrometer Mass/Charge (GeV/c 2 ) Events Reconstructed mass d p K+K+ K-K- ++ --  (mass) = 30 MeV (typ.) for 1 GeV/c Kaon

LEPS physics results (A)  meson photoproduction  meson production on Li, C, Al, Cu T. Ishikawa et al. Phys. Lett. B 608 (2005) 215  p  p T. Mibe et al. Phys. Rev. Lett. 95 (2005)  d ->  d W.C. Chang et al. Phys. Lett. B 658 (2008) 209   n ->  n W.C. Chang et al. Phys. Lett. B 684 (2010) 6   p ->  p,  n ->  n W.C. Chang et al. Phys Rev. C 82 (2010) (B) Strangeness photoproduction  p -> K + ,  p -> K +  0 R.G.T. Zegers et al. Phys. Rev. Lett. 91 (2003)  p -> K + ,  p -> K +  0 M. Sumihama et al. Phys. Rev. C 73 (2006)  n -> K +  - H. Kohri et al. Phys. Rev. Lett. 97 (2006)  p -> K +  K. Hicks et al. Phys. Rev. C 76 (2007) (R)  p -> K +  - (1385) K. Hicks et al. Phys. Rev. Lett. 102 (2009)   p -> K +  (1405),   (1385) M. Niiyama et al. Phys. Rev. C 78 (2008)  p -> K +  (1520) N. Muramatsu et al. Phys. Rev. Lett. 103 (2009)  p -> K +  (1520) H. Kohri et al. Phys. Rev. Lett. 104 (2010) (C) Pseudoscaler meson photoproduction  p ->  0 p M. Sumihama et al. Phys. Lett B 657 (2007) 32  p ->  p M. Sumihama et al. Phys. Rev. C 80 (2009) (R) (D) Search for exotic resonance state Pentaquark search T. Nakano et al. Phys. Rev. Lett. 91 (2003) Pentaquark search T. Nakano et al. Phys. Rev. C 79 (2009)

Contents (1) LEPS (SPring-8) experiments (2) Physics motivation of introducing polarized target (3) Development of polarized HD target (4) Summary and future plan

(A)  meson photoproduction on proton Invariant mass of K + K - (GeV/c 2 ) Counts LEPS detector was optimized to detect  meson decaying to K + and K -.

(A)  meson photoproduction on proton Reaction mechanism Diffractive production within the vector-meson-dominance model through Pomeron exchange One-pion-exchange ss-knockoutuud-knockout The meson exchange is suppressed by OZI rule. We study the pomeron exchange, ss-knockout, and other effects near the threshold.

Cross section and C BT ZZ for  photoproduction A.I. Titov et al. Phys. Rev. Lett. 79 (1997) 1634 A.I. Titov et al. Phys. Rev. C58 (1998) 2429 Cross Section at E  = 2.0 GeV Solid: Pomeron exchange Dotted: One pion exhange Dashed: ss knockout Dotted-dashed: uud knockout Beam-Target double spin asymmetry at E  = 2.0 GeV Strangeness content is assumed to be 0%(Solid), 0.25%(Dashed), and 1%(Dotted-dashed). Pomeron ss no ss 1% ss 0.25% ss 

Double spin asymmetry C BT ZZ   nucleon spin 1 spin 1/2 Cross section when total spin of photon and target is 3/2 Cross section when total spin of photon and target is 1/2

Energy dependence of double spin asymmetry C BT ZZ for  meson photoproduction Calculation by A.I. Titov Strangeness content of B 2 =0.25% is assumed. Suitable for LEPS energy We investigate ss content of proton and neutron by ss knockout process.

(B) Strangeness photoproduction Missing mass of p( ,K + )X E  = GeV

(B,C) K, ,  meson photoproduction Physics motivation Quark model predicts a lot of baryon resonances. However, most of them are not identified experimentally. These are called ‘Missing resonances’. They are expected to decay not only to  N channel but also to  N, K , K , K  * and K  * channels. Since only  N channel has been extensively studied so far, new data for the other channels are very important. Exotic baryon resonance search is also expected. N* N    Very weak Strong N* may be an exotic baryon resonance including ss.

Bump H. Kohri et al. Phys. Rev. Lett. 104 (2010) (B) Strangeness photoproduction Bump structure was found in K +  (1520) Differential cross sections Result of fit (Green curves) Bump energy 2.11 GeV width 140 MeV Observed width is narrower than that of usual N *. N* Status Mass Width N(2080) D 13 ** ~2.08GeV  ~300MeV N(2090) S 11 * ~2.09GeV  ~300MeV N(2100) P 11 * ~2.10GeV ~300MeV N(2190)G 17 **** ~2.15GeV ~500MeV This bump is not observed in  N. We will investigate the bump by using polarized beam and target.

Counts Mass (GeV/c 2 ) Counts Mass (GeV/c 2 ) (1)(2) Although the results are positive, statistics is not enough in both data. We took data with 3 times higher statistics than Data (2) in Data analysis is underway now. If the  + exists, the next job is to determine the spin-parity of the  +. The polarized photon beam and HD target play an important role. T. Nakano et al. PRL 91 (2003)  T. Nakano et al. PRC 79 (2009) 252 (D) Pentaquark (  + uudds ) search  C reaction  d reaction

Contents (1) LEPS (SPring-8) experiments (2) Physics motivation of introducing polarized target (3) Development of polarized HD target (4) Summary and future plan

Development of polarized HD target HD target cell For further spin studies, we introduced a polarized HD target. We started developing the HD target in Historically, the HD target has been developed by BNL/LEGS (USA) group and ORSAY(France) group for more than 10 years. ORSAY group finished the development in 2005 and their knowledge and some equipments were imported to RCNP, Osaka university group. To introduce the polarized HD target will upgrade the LEPS experiment to the next step.

Polarization method HD target is polarized by the static method using “brute force” at low temperature (10 mK) and high magnetic field (17 Tesla). It takes about 2-3 months to polarize the target. Advantage and disadvantage HD molecule does not contain heavy nuclei such as Carbon and Nitrogen. The HD target needs thin aluminum wires (at most 20% in weight) to insure the cooling. Polarization H : 90 % D : 60 % Relaxation Time About 1 year at 300 mK and 1 Tesla during the experiment. Characteristics of polarized HD target

N - = N exp(- E - /kT) N + = N exp(- E + /kT) N - /N + = exp((E - - E + )/kT) = exp(  E/kT) = exp(2  p B/kT) k: Boltzmann constant  p : Proton magnetic moment B: Magnetic field T: Temperature Proton polarization P = (N + - N - )/(N + + N - ) = tanh(  p B/kT) In case of B = 17 Tesla, T = 10 mK, P ~ 90% E Boltzmann law of statistical mechanics E+E+ E-E- Temperature (mK) Polarization (%) at 17 Tesla H polarization D polarization D polarization is small because  D <  p N

Principle of polarizing HD Polarization is kept for a long time. T 1 is short. T 1 becomes long.

RCNP Osaka university SPring-8 BL33LEP beamline HD target TC1 DRS SC IBC TC2 HD gas distillation system SC IBC K+K+ K-K-  Transportation of polarized HD target

Dilution refrigerator (DRS) Leiden Cryogenics DRS-3000 ( 3 He/ 4 He dilution refrigerator) Cooling power 3000 μ W at 120 mK Lowest temperature 6 mK

Dilution refrigerator (DRS) + Superconducting magnet Magnetic Field 17 Tesla Homogeneity of Magnetic Field 5×10 -4 for 15 cm Magnetic Field (Tesla) Y Position (mm) Y axisDRS Magnet Y Position (mm) HD target

Two transfer cryostats (TC) were prodived by France Orsay group in 2005 Right : used at RCNP Left : used at SPring-8 4 He cryostats Magnetic Field : ~0.2 Tesla Temperature : T ~ 4.2 K

Storage cryostat (SC) was also provided by France Orsay group 4 He cryostat Magnetic Field : 2.5 Tesla Temperature : T~1.5 K Homogeneity : for target region

3 He/ 4 He dilution refrigerator (IBC) Lowest temperature : 0.3 K Magnetic field : 1 Tesla Field homogeneity : 5 x for target region

First production of polarized HD target (2008Nov-2009Jan) Purity of HD ： about 99% Temperature ： T = 14 mK Magnetic Field ： B = 17 Tesla Aging time : 53 days Expected Polarization ： 80%(H) Measured Polarization ： 40%(H) Measured relaxation time (T 1 ) : 100 days

H NMR signals after aging HD for 53 days Dispersion function Absorption function Polarization degree for hydrogen P ~ 40 %

Results of first production of HD target Expected Polarization ： 80%(H) Measured Polarization ： 40%(H) Measured relaxation time (T 1 ) : 100 days for SPring-8 experiment condition T 1 is long enough for SPring-8 experiment. If we increase the aging time in the next production, T 1 becomes longer. We estimated some causes for the low polarization degree. (1) Calibration of target polarization might be not good. (2) Amount of o-H 2 impurity might be too small.

Results of first production of HD target Expected Polarization ： 80%(H) Measured Polarization ： 40%(H) Measured relaxation time (T 1 ) : 100 days for SPring-8 experiment condition T 1 is long enough for SPring-8 experiment. If we increase the aging time in the next production, T 1 becomes longer. We estimated some causes for the low polarization degree. (1) Calibration of target polarization might be not good. (2) Amount of o-H 2 impurity might be too small.

Improvement of NMR S/N ratio Temperature of electronics was stabilized. Input signal was canceled by double balanced mixer. S/N ratio was improved by an order-of-magnitude, which is good for calibration of polarization degree. Before improvement After improvement Hydrogen-NMR (T=1.5K) T. Ohta et al. NIM-A 633 (2011) 46

Conventional NMR system (~80 kg) Portable NMR system (~7 kg) Another development (Portable NMR system) The HD target is produced at RCNP and transported to SPring-8. The polarization should be measured at both places. But conventional NMR system is not easy to move. We developed a portable NMR system by the soft ware system with PCI eXtensions for Instrumentation (PXI). T. Ohta et al. NIM-A 633 (2011) 46

Results of first production of HD target Expected Polarization ： 80%(H) Measured Polarization ： 40%(H) Measured relaxation time (T 1 ) : 100 days for SPring-8 experiment condition T 1 is long enough for SPring-8 experiment. If we increase the aging time in the next production, T 1 becomes longer. We estimated some causes for the low polarization degree. (1) Calibration of target polarization might be not good. (2) Amount of o-H 2 impurity might be too small.

Another cause of low polarization degree Amount of o-H 2 impurity Small amount of o-H 2 (~0.01%) plays an important role in polarizing HD. Room temperature Low temperature Although amount of o-H 2 impurity might be very small because of gas distillation, we could not measure it correctly. We need a gas analyzer system for correctly measuring the o-H 2 impurity. 1 : 3

HD gas analyzer system was developed Gas chromatograph (T~110 K) Quadrupole Mass Spectrometer T. Ohta et al. NIM-A 640 (2011) 241

HD is clearly distinguished from other gases by Time and Mass/Charge Elapsed Time in Gas Chromatograph(min) Mass/Charge (u/e) o-H 2 p-H 2 HD D2D2 T. Ohta et al. NIM-A 640 (2011) 241

o-H 2 impurity decreasing during distillation Result of gas analysis Mass/Charge = 2 (u/e) Before distillation 1 week after starting distillation 2 weeks after starting distillation We can monitor o-H 2 impurity. We can optimize the amount of o-H 2 in the next production. If needed, o-H 2 can be added. o -H 2

New gas distillation system was constructed in 2009 HD is liquefied in this part.

Many(100 k) Heli-packs are filled. Stainless steel packing, called Heli-pack, is filled in cold pot Heli-pack T~18 K T~20 K T~21 K Large temperature difference is made for good separation of HD from other gases.

Good purification of HD gas H 2 concentration (p-H 2 + o-H 2 ) during gas distillation HD purity ~99.99% T. Ohta et al. arXiv: (2011) New HD gas distillation system has enough ability for purifying HD up to 99.99%. We can optimize an amount of o-H 2 in future productions. HD purity before distillation is about 95%.

Contents (1) LEPS (SPring-8) experiments (2) Physics motivation of introducing polarized target (3) Development of polarized HD target (4) Summary and future plan

Summary and future plan We are developing a polarized HD target. We tried to produce the polarized HD target in Although the polarization degree was small(40%), the relaxation time was long enough for LEPS experiments. We developed new NMR system, gas analyzer system, and gas distillation system for future production of polarized HD target. These systems are working well. We plan to carry out an experiment using polarized HD target in the next year. We constructed a new beam-line (LEPS2) at SPring-8. The BNL/E949 spectrometer will be transported to SPring-8 in this year.

We started a construction of LEPS2 new beam-line at SPring-8 in this year LEPS beam-line LEPS2 new beam-line

LEPS2 experiment hutch was constructed by RIKEN in this year August LEPS2 experiment hutch Large detector can be installed. Experiment hall of SPring-8

BNL/E949 spectrometer will be transported to SPring-8 in this year BNL/E949 spectrometer

Summary and future plan We are developing a polarized HD target. We tried to produce the polarized HD target in Although the polarization degree was small(40%), the relaxation time was long enough for LEPS experiments. We developed new NMR system, gas analyzer system, and gas distillation system for future production of polarized HD target. These systems are working well. We plan to carry out an experiment using polarized HD target in the next year. We constructed a new beam-line (LEPS2) at SPring-8. The BNL/E949 spectrometer will be transported to SPring-8 in this year.

LEPS-HD target collaboration RCNP, Osaka University, Japan M. Fujiwara, K. Fukuda, T. Hotta, T. Kunimatsu, C. Morisaki, H. Kohri, T. Ohta, S. Ono, M. Uraki, K. Ueda, M. Utsuro, and M. Yosoi Academia Sinica, Taipei, Taiwan National Kaohsiung Normal University, Kaohsiung, Taiwan S.Y. Wang IN2P3, Orsay, France S. Bouchigny, J.P. Didelez, and G. Rouille Kobe Tokiwa University, Kobe, Japan M. Tanaka If you are interested in the experiments, please contact me.

Calibration of polarization degree of HD H T = 4.2 K B = 1 Tesla T = K B = 17 Tesla Extrapolation Calibration data(P~0.024%) Calibration temperature should be lowered. For example, T ~ 1.5 K. (P~0.068%) Polarization was fixed (P~90%)

Improvements of measurement of HD polarization Calibration temperature should be decreased. from T=4.2 K to T=1.5 K. Physics reactions, such as  p ->   p,  p ->  + n, or  p ->  p may be used for calibration of HD polarization. (Bonn-ELSA group Jlab-CLAS group obtained preliminary results. ) We need to find a good method to measure the HD polarization correctly.

(A)  meson photoproduction on proton LEPS cross section data Diffractive  meson photoproduction on proton T. Mibe et al. Phys. Rev. Lett (2005) We also investigate the bump structure found in our data.

(A)  meson photoproduction on proton Decay asymmetry of  meson Reaction mechanisms are not so different between two energy regions.  =  =  >0 means that natural parity exchange is dominant T. Mibe et al. Phys. Rev. Lett (2005)

(B) Strangeness photoproduction Photon beam asymmetry  for K +  and  K +   Vertical = [ 1 + P   cos(2  ) ] Horizontal = [ 1 - P   cos(2  ) ] N = F acc = P   cos(2  ) N : K + photoproduction yield  : K + azimuthal angle P  : Polarization of photon dd dvdv dd d  unpol dd dd dhdh dd dd N v - N h N v + N h  (deg.)  >0  >0 means that K * exchange in t-channel is strong in the reaction mechanism. E  = GeV M. Sumihama et al. PRC 73 (2006)

16 observables for the  p KY reaction Observable Polarization Beam Target Hyperon Cross section & Single polarization d  /d   linear - - T - transverse - P - - y Beam-Target double polarization G linear z - H linear x - E circular z - F circular x - Beam and Recoil hyperon double polarization Ox linear - x Oz linear - z Cx circular - x Cz circular - z Target and Recoil hyperon double polarization Tx - x x Tz - x z Lx - z x Lz - z z CLAS measured for K +  and K +   CLAS and SAPHIR measured for K +  and K +  0 LEPS Many groups

16 observables for the  p KY reaction Observable Polarization Beam Target Hyperon Cross section & Single polarization d  /d   linear - - T - transverse - P - - y Beam-Target double polarization G linear z - H linear x - E circular z - F circular x - Beam and Recoil hyperon double polarization Ox linear - x Oz linear - z Cx circular - x Cz circular - z Target and Recoil hyperon double polarization Tx - x x Tz - x z Lx - z x Lz - z z Asymmetries obtained from target polarization have not been measured. We measure these asymmetries.

Background in analyzing gas components Mass(u) BG D H 2 D Molecule H 2 HD D 2 HD -> H + D + (BG for H 2 ) HD + H + -> H 2 D (BG for D 2 )

HD target TC1 DRS SC IBC TC2 SC We measured relaxation time for various condition T 1 for TC1 T 1 for SC T 1 for TC2 T 1 for IBC

Relaxation time of hydrogen polarization T 1 = 6 days TC1 (4K 0.2 Tesla) T 1 = 12 days SC (1.5K 1 Tesla) T 1 = 6 days TC2 (4K 0.2 Tesla) T 1 = 100 days IBC (0.3K 1 Tesla) If the initial polarization is assumed to be 100%, we can start a physics experiment with a polarization of 98%. Experiment Start

IBC （ In Beam Cryostat ） for BL33LEP Al wire 2.5cm