1. Some ideas and possibilities for nuclear target measurements with new generation electron beams Dan Watts University of Edinburgh

2. Outline Many proton knockout Nuclear tagging using nuclear gamma decay photons Recoil nucleon spin polarimetry – first crude look at possibilities

3. Many nucleon knockout from nuclei We have carried out some initial studies of many proton knockout from nuclei (up to >6 protons) Central physics motivation - test transport models for proton/nucleon production in nuclei (e.g. GiBUU). These models are also used for neutrino detection using heavy nuclei - neutrino interaction and energy is reconstructed from hadronic final state Assess if exotic isotopes could be produced and at what rate.

4. Many proton knockout at JLAB Use data from e2 run. Utilising Data Mining Framework. 5 GeV electron beam on 208 Pb target. Reconstruct mass of recoiling system from scattered electron and proton Good test of theoretical models – can look for events where residual nucleus near it’s ground state

5. Path of r-process P. Seeger, W. Fowler & D. Clayton, Astrophys. J. Suppl. 26, 231-312 (1965) Path of r-process below closed shell – waiting points in neutron capture Kink starts ~8 protons south of 208 Pb.

6. Terra incognita No knowledge of existence/mass of nuclei 3 protons south of 208 Pb http://www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html

7. Likely a range of mechanisms can contribute. Earler work on ( ,3N) in light nuclei indicated the main mechanism for 3N knockout is Meson production from a nucleon plus reabsorption (meson,NN) (meson,NNN) Smaller contribution of direct 3N knockout (photon coupling to 3N current) and 2N + final state interaction (e.g D.P. W et. al. Phys.Lett. B553 (2003) 25-30) At higher energies of CLAS data initial 2-meson and 3-meson production may contribute leading to possibilities for high multiplicity emission What are the mechanisms of many-proton knockout? meson

8. 12 C( ,ppn) reaction at Mainz Dominant mechanisms giving strength at low missing energy 2N+FSI, direct 3N, N  +ABSORPTION Clear peak from intermediate exchange pion (close to mass shell) D.P.W et. al. Phys.Lett. B553 (2003) 25-30)

9. CLAS analysis – study of low missing mass fragments 208 Pb(e,e’p) Reconstruct mass of recoiling system using detected electron and proton(s) 4-vectors Low missing mass fragment particularly interesting First crude analysis – fit near threshold using gaussian having width of CLAS resolution Simple guess for background shape

10. Mass (GeV) 208 Pb(e,e’pp) 208 Pb(e,e’ppp) Mass (GeV) 208 Pb(e,e’pppp) 208 Pb(e,e’ppppp)

11. low missing masshigh missing mass CLAS analysis - Relative yield for different multiplicities Not detector acceptance corrected

12. CLAS analysis – study of low missing mass fragments Assuming centroid of gaussian gives the mass of daughter system – compare with ground state masses. reasonable agreement with exp/theory Will calibrate using proton knockout from 56Fe – masses measured up to 8 protons south

13. Next steps Analyse data from wide range of targets Pass theoretical models through the detector acceptance and compare Preliminary GiBUU result

14. Recoil nucleon spin polarimetry Coupling of large acceptance nucleon spin polarimetry to large acceptance detectors would provide important new data to the future nucleon/deuteron physics programmes (e.g meson spectroscopy, DVCS? What (if anything) is possible/feasible?

15. Large acceptance spin polarimetry It is possible to get spin information on recoiling nucleons from study of their scattering in an analysing medium Recent work at MAMI has shown that good results can be obtained using a kinematic reconstruction of this scatter – without the need for large acceptance nucleon tracking systems

16. Data G4 total G4 no nuclear int Proton scattering angle in graphite Analysing power of scatterer Unpolarised polar angle distributiion x and y (transverse) components of nucleon polarisation No. nucleons scattered In the direction  n(  ) =n o (  ){1+A(  )[P y cos(  )–P x sin(  )] Large acceptance spin polarimetry at MAMI

17. C x * for p( ,  0 ) from CB@MAMI polarimeter Sikora, DPW, Glazier PRL12 022501 (2014 )

18. Fit B Juelich PWA Changes in P 11 partial wave and P 11 (1710) pole positions with new fit New fit shows features more consistent with SAID PWA using only  N scattering Only for one PWA framework – but Illustrates utility of new observables – even when poorer stat accuracy C x * for p( ,  ) from CB@MAMI polarimeter Fit to world data ( including beam-target) Forced fit to Cx* data Harder Forced fit to Cx* data PRELIMINARY

19. Ongoing work using CLAS data Have large dataset of D( ,pn) from g13 run period – can we obtain information on nucleon spin polarization from nucleon scatters in the start counter? First study – look at (n,p) charge exchange reactions. Get first info on final state neutron polarizations. Check HHC,.. models. Further constraints on proposed d* state Reconstruct incident neutron track kinematically - track proton in CLAS Measured (n,p) analyzing powers on light nuclei close to (established) free nucleon N. Zachoriou (Edinburgh) Scintillator Target cell

20.  sc distributions as expected  sc distributions - strong acceptance effects -but cancel to first order when constructing beam asymmetry cos(2  ) fit to extract transferred polarisation A ~0.1 : Needs detailed modelling to obtain accurate value Similar analysis using start counter with CB@MAMI in progress (S. Kay Edinburgh) D( ,pn)

21. Polarimetry in new energy regime Central programmes at CLAS 12 in area of meson spectroscopy and nucleon structure (DVCS,DVMP) What is possible for these programmes (quick discussion)

22. Glue-X/MesonEx production kinematics |t| (GeV 2 ) Proton kinetic energy (GeV)  + p → X + p M X =2 GeV E  =9 GeV Proton angle (degrees) Heavy mass meson photoproduction ~ M X ~2 GeV nucleon energies for low t in similar region to previous analyses |t| GeV 2 |t| (GeV 2 ) Polar angles in region of 40 degrees

23. Glue-X/MesonEx production kinematics Proton kinetic energy (GeV) |t| (GeV 2 )  + p → X + p M X =0.78 GeV E  =9 GeV |t| (GeV 2 ) Proton angle (degrees) Light vector meson mass ~ 0.8 GeV Low t Polar angles ~45-75

24. DVCS Nucleons have low energies

25. The CND in CLAS12 – A MAKESHIFT POLARIMETER? Complicated: spin precession in B field, extracting scatter , acceptance, efficiency, analysing powers,.. Rule of thumb – error bars for beam recoil observables larger than beam target by:  factor ~8 from analysing power (0.1 – 0.3 compared with 0.8 for polarised target)  factor ~6 from reduced number of analysable events (scales as sqrt) Need theoretical steer to justify the effort – are beam-recoil observables (with poorer statistical accuracy than the beam target observables) worthwhile for the nucleon structure meson spectroscopy physics programmes ?? Calculations needed… Bars 3cm thick, 3.5 cm wide Very roughly 3% per layer probablity for (n,p) or (p,p) Acceptance for polar angles <~40 degrees Would need extensive simulation programme to establish capabilities. First test simulations to see if anything is feasible are underway (G. Smith, L.Zana, Edin

26. Thank you for your attention

29. Phoswich design - good timing properties of LaBr to be combined with high stopping power, lower cost scintillators Different timings of the scintillator output - allow  E-E ?? → Need Flash ADC or dual gated ADC readout Crystal tests with possibilities for CLAS12

30. First tests of LaBr/CsI phoswich

31. Investigate phoswich: particle ID capabilities, timing etc. (In collaboration with Univ. York (UK). Plans for portable array for use at SPIRAL - shared use at JLAB ? Explore LaBr / hybrid modules alongside other crystal possibilities for forward calorimeter Grant request (approved but pending) - additional RA support and further money for prototype crystals Future plans

32. Hybrid meson production Coherent and incoherent nuclear production processes suppress the s-channel nucleon resonance contributions → greatly simplifies the PWA for hybrid searches Could the J  of residual nuclear states provide new information? Tag by detecting nuclear decay photon in coincidence Example: 0 + to 2 + transition emphasizes tensor like exchanges in t-channel → favourable production mechanism for hybrids in flux tube model 12 C 12 C(2 + ;T=0; 4.4MeV) Also use in nuclear DVCS? e.g. select higher twist effects? Hypernuclei?

33. 12 C 12 C(2+;4.4MeV) Coherent proposal 4 He at JLAB: virtual photon tagger with TPC estimate ~60k hybrid mesons produced Incoherent → Rate not limited by TPC ~10 2 increase in  flux → No minimum limit on t → Will lose factor ~10 in cross section due to loss of coherence in amplitudes, form factor effects Incoherent hybrid meson production A. Donnachie arXiv. 0806. 3698(2008)   (1600)   (1400)   (1320) TPC detection limit 0.3 0.20.1 t(GeV/c 2 ) 1 10 100 0.1 12 C(  J/  ) 12 C Coherent Sum incoherent Incoherent 2 + level Ratio to cross section on nucleon at  =0

34. As well as the J  of the nuclear state the angular distribution of the nuclear decay photons tells you about the alignment of the residual nucleus Polar distribution wrt mom transfer gives sensitivity to the spin dependence of the production amplitude (next slide) (Tryasuchev and Kolchin Phys. At. Nuc. 70 827 (2007)) Azimuthal distribution allows information on meson-nucleon interaction to be extracted. e.g. J/  photoproduction from 12 C ( V.L. Korotkikh and N.I. Strakov, Yad. Phys. 37 1030 (1983 ) Nuclear decay photons

35. t-channel amplitudes of (Sandy Donnachie, Univ. Manchester, UK) being incorporated into model of nuclear photoproduction (Helmy Sherif, Univ. Alberta, Canada) First step - Plane wave calculations for t-channel eta production. Calculations for further channels e.g. a o, f o in progress New calculations in progress

36. Detector issues – next steps Can LaBr readout be in a region where conventional PMTS could be used? – Depend on necessary solenoid, shielding etc Edinburgh group applied for R&D funds for LaBr and SenSL avalanche PMT readout and 1 year RA Device would need upwards of ~60 crystals Crystals should be ~10cm depth to give ~80% photopeak efficiency up to 10 MeV SOLENOID Nuclear decay Photon calorimeter

37. CND possibilities