Physics opportunities with the AT-TPC D. Bazin NSCL/MSU at ReA
Reaction studies at ReA Radioactive beams are used in inverse kinematics Target is now the (usually light) probe nucleus Scattered particles have low energies Beam intensities are small (from 1 to 8 pps) High luminosity needed: large acceptances, thick targets New types of instruments needed Active Target Time Projection Chamber (AT-TPC) Gas is both target and detector medium: thick target without loss of resolution Vertex determination, virtually π angular coverage, very low energy threshold Excitation functions from beam slow down and vertex determination
AT-TPC physics program at ReA Resonant scattering for nuclear cluster structure studies Inverse kinematics proton scattering for single-particle structure studies via IAS population Fusion cross sections with neutron-rich isotopes below the Coulomb barrier Inverse kinematics transfer reactions for single-particle structure such as (d,p), (p,d), (p,t), ( 3 He,d), Excitation functions of reactions of astrophysical interest such as (α,p) for instance Exotic radioactive decays (3α decay from 12 C Hoyle state, 2p radioactivity, ) ReA3 upgrade is crucial to access the full potential of these reaction tools
Insulator gas volume (N 2 ) Principle of operation Field shaping rings Cathode: - kvdc (1kV/cm) e - e - e - e - e- e - e- e- e - e- Pad plane and electron amplifica$on device (Micromegas) Beam e - e - e - Electric field Posi%on - >(x, y) Ac$ve gas volume He, H 2, D 2 Dri1 %me - > z
AT-TPC setup Straight and tilted (7 ) configurations Yoke Tilt relative to beam axis to increase accuracy for small angles TPC Beam Placed inside 2 Tesla solenoid (increase range and measure Brho) 2 liters (1 m by cm) active volume Financed by NSF-MRI
Pad plane and electronics,2 triangular pads Central region density x for small angle scattering GET (General Electronics for TPC) Digital readout instrumentation of each pad Internal trigger generation using multiplicity signals Data filtering (partial readout, zero suppression, )
Visualization of nuclear reactions in 3D Last commissioning in December 21 Beam: He at 3 MeV/u Target: He(9%) + CO 2 (%) @ Torr Magnetic field: 2 Tesla Event displays Right: hit pattern on pad plane, orange region is trigger exclusion zone Top left: integrated time projection Bottom left: 3D reconstruction of event
Prototype AT-TPC
Prototype AT-TPC Scattering 6 He + α at Twinsol 2 pps 6 He Confirm strong α-cluster state in Be. Suzuki et al. PRC 213
Prototype AT-TPC Scattering 6 He + α at Twinsol 2 pps 6 He Confirm strong α-cluster state in Be. Fusion Be + P (Ar/Methane) Sub-barrier fusion with low-intensity RIBs. (2 cps) Suzuki et al. PRC 213 J. Kolata A. Howard (Notre Dame)
be 39.7() MeV using silicon detectors prior to the physics run. The range of Be in t about cm. The Ec.m. thus decreases from 39 /1 11 MeV to zero while traveli 1 total count ofstates 3.2. The beam in purity was about Cluster C3% with main contaminants of H gas volume. The average rate of Be that entered the volume was 3 ions per secon 8 9 Be (%) and B (3%). Scattering Tracks in Prototype AT-TPC 99 Resonant scattering of MeV/u Be beam (TWINSOL) on He Be Scattering Angle [deg] θ(be,lab) 8 9 7 8 6 7 6 3 2 3 2 E c.m. [MeV] d σ/ d Ω [mb/sr] Radius [cm] 6 Be A + B + 9 26 3 7 8 Be θ( Be) 3 θ(α) 7 + + Observed 2 and resonances 3 α 6 3 - + 2 match linear chain calculations 2+ 2-3 6 9 Time [µs] θ(α,lab) (AMD) 3 Figure.9: Angular data of events gated on the Be peak in Fig..6. Kinematics c Figure.1: Reconstructed trajectories of (A) reaction products in the prototype AT-TPC. overlay The the data: elastic scattering (B) is in black, and the first excited state (3.368 M 2 Be nucleus is seen, as are the paths of the reaction Be) path of the incoming products Beinelastic and scattering is in red. of the6latter 8 1 3 6 7 8 9 He. The ray traces two nuclei allow12 for their angles to be calculated. 2 A. Fritsch et al., submitted to PRC 2 3 6 7 He Scattering Angle [deg] 8 9 + 2+ 6+ + 2+ + + + 3+ + 2+ 2+ + (I) (II) (III) d σ/ d Ω [mb/sr] d σ/ d Ω [mb/sr] 8 6 2-2 - -6-8 A E c.m. [MeV] E c.m. [MeV] Ec.m. [MeV] Figure S1: (A) Trajectories of a Be + scattering event. (B) labbe vs. lab plot + + 6 kinematical curves for elastic scattering and3inelastic scattering to the Be 2 1 state. C D A B + 9 9 + 3 2 (III) triaxially deformed 8 3 7 8 ρp ρn ρp-ρn 2 33 7 7 Reaction trajectories were measured by2detecting electrons liberated from gas at 6 6 3 + 2 2 1 (IV) linear chain molecules colliding with charged ions. These 2 electrons are guided toward the Mic 1MeV/.1 in 3 3 1 2 2 (IV) through 12 1 quadrant. Figure.2: A ray pad 8 signals in time for a1 triggered The relative trace 6 68 12 2 2 3 3 6 6 77 88 99 + 2+ [1/fm3] time of each pad signal is denoted by a black diamond. The linear fit is shown in red. B + 2 C /sr] 1 d B.B. E c.m. [MeV] θ c.m. [degree] 3 + C D 9 96 3 Figure 1: Differential cross sections of Be scattering off particles: (A) elastic scatte D. Bazin, ReA3 upgrade workshop, August 2, 21 8 + ] Be α r] 8
Proton scattering to IAS resonances Evolution of neutron orbitals in A Z can be studied via the A Z(d,p) A+1 Z transfer reaction or by populating T > analog states of A+1 Z in A+1 Z+1 via the A Z(p,p ) reaction Spectroscopic factors for excited states in A+1 Z can be deduced reliably from cross sections of resonances observed in A+1 Z+1
Inverse kinematics in AT-TPC Ar beam from ReA3 at. MeV/u Gas target: 2 Torr of C H Excitation function from incident energy to (beam stopped) Next experiment: 6 Ar at.2 MeV/u from ReA3 + CCF (9/21) Higher beam energies would allow reaching higher energy states
Inverse kinematics in AT-TPC Ar beam from ReA3 at. MeV/u Gas target: 2 Torr of C H Excitation function from incident energy to (beam stopped) Next experiment: 6 Ar at.2 MeV/u from ReA3 + CCF (9/21) Higher beam energies would allow reaching higher energy states
Transfer reactions ReA3 energies too low for most cases (Q-value, momentum matching) AT-TPC can provide highest luminosity, can detect both light and heavy particles with close to π coverage and good resolution Elastic cross section of entrance channel measured simultaneously H 2 and D 2 gas targets can be made significantly thicker than CH 2 and CD 2 foils Reaction energy known for each event (vertex), allows to sum angular distributions measured at different energies
Example: 38 S(d,p) Study shell quenching between N=2 and N=28 below the Z=2 closure Simulations show 2 kev resolution achievable
Example: 38 S(d,p) Study shell quenching between N=2 and N=28 below the Z=2 closure 6 38 S(d,p) f 7/2 MeV/u Simulations show 2 kev resolution achievable Angular distributions from different energies can be cumulated Cross section (mb/sr) 3 2 f 7/2 MeV/u f 7/2 3 MeV/u f 7/2 2 MeV/u 1 9 8 7 6 2 3 Θ c.m. x E
Example: 38 S(d,p) Study shell quenching between N=2 and N=28 below the Z=2 closure 6 38 S(d,p) f 7/2 MeV/u Simulations show 2 kev resolution achievable Angular distributions from different energies can be cumulated Meaningful experiments can be achieved with only 1, pps! Cross section (mb/sr) 3 2 1 9 8 7 f 7/2 MeV/u f 7/2 3 MeV/u f 7/2 2 MeV/u 6 2 3 Θ c.m. x E
Example: 38 S(d,p) Study shell quenching between N=2 and N=28 below the Z=2 closure 6 38 S(d,p) f 7/2 MeV/u Simulations show 2 kev resolution achievable Angular distributions from different energies can be cumulated Meaningful experiments can be achieved with only 1, pps! Cross section (mb/sr) 3 2 1 9 8 7 f 7/2 MeV/u f 7/2 3 MeV/u f 7/2 2 MeV/u Energy should be -12 MeV/u! Needs ReA12! 6 2 3 Θ c.m. x E
Outlook ReA3 upgrade to energy range -1 MeV/u would open great opportunities for experiments with the AT-TPC The AT-TPC can provide high luminosity without compromising resolution This is paramount because of the low intensities of reaccelerated radioactive beams Simple transfer reactions such as (d,p), (p,d), (d, 3 He) are of particular interest
AT-TPC collaboration NSCL team D. Bazin, W. Mittig, W. Lynch, S. Beceiro-Novo, Y. Ayyad, J. Bradt, L. Carpenter, J. Manfredi, S. Rost, M. Cortesi, J. Yurkon Other institutions T. Ahn, J. Kolata, Z. Chajecki, D. Suzuki, U. Garg, R. Kanungo