FINUDA Status Report

1. FINUDA Status Report 30th Scientific Committee Meeting LNF, 23.05.05 A. Filippi – INFN Torino

2. Layout of the talk • Latest Issues since last Committee Report • Hardware updates • New TOFINO detector • DAQ update and performances’ improvement • Scientific production: new papers, conferences • Current activities in data analysis • Alignment campaign • Software improvements and new implementations • New Physics Results • Preparation for the next run • Choices for the new set of targets: motivations and interests • Simulation of expected signals • Conclusions & requests for next run

3. HARDWARE UPDATES:EXPECTED GOALS • New TOFINO • Purpose: improve time resolution and signal/noise ratio • Improvement of a factor of 2 expected on time resolution • Improvement of an order of magnitude expected on signal/noise ratio • DAQ Update • Implementation of new modules to increase the transfer rate of silicon detectors of a factor of 4 • Other updates: • New cabling for both TOF detectors (from constant fraction outputs to TDC’s) to reduce noise, cross-talk, attenuation, and improve rise time • Update of TOFONE f.e. electronics

4. Hardware Update: new TOFINO • New TOFINO needed because of HPDs’ aging and loss of efficiency • Completely new detector, with different spec’s • Use of Hamamatsu photomultipliers • 1.8 mm thickness vs 2.3 mm • Thoroughly built at KEK by Japanese collaborators • Building stage, as of end Apr. 05: • Support structure : in production, to be delivered in June • Delivery in Frascati foreseen in August-September • Old TOFINO overhauled, working and ready to be used, if needed The use of PM’s allows to reduce the thickness of the scintillator slabs (less energy loss) and to suitably modify the assembly geometry

5. DAQ IMPROVEMENT • Speed: • Improve VDET CRAM transfer • 66 Hz → 120 Hz • Split 2 VDET VME crates into 8 parts (8 “low cost” CAEN PCI-VME Bridges) • 120 Hz → 400 Hz • Improve global event builder (4xAMD Opteron) • Storage: • Upgrade Storage • 1.7 TB → 10 TB (daq + offline) • Reduce Raw Data size (33 kB/ev → 20 kB/ev) NEXT DATA TAKING RATES Old data taking: L = 0.71032 8 Hz Trigger Hyper New data taking: L = 1.2 1032 14 Hz Trigger Hyper expected 20 kB/event  20 Hz (Hyper + Prescaled Bhabha) = 400 kB/s STORAGE 1 fb-1  1039 cm-2s-1 / 1032 cm-2 s-1 = 107 s  400 kB/s  107 s 1 fb-1 4TB (+ analysis + simulation)  10 TB

6. SCIENTIFIC PRODUCTION Nov04 - Apr05 • Accepted Papers • Submitted Papers • Talks at International Workshops and Conferences

7. Scientific Production • Accepted papers: • Evidence for a kaon bound state in K-pp produced in K- absorption at rest • Accepted for publication in Phys. Rev. Lett. • Importance of the KNN, the lightest kaon-bound state beyond L(1405), which is considered to be a KN system. • Submitted papers • Study of 12ΛC production at DAΦNE • Submitted to Phys. Lett. B • Confirmation of observations by E369 with better resolution (1.29 MeV) and evidences for new states, even if with partial statistics and rough alignments • Talks at international conferences and Workshops: • S. Piano, @ International Workshop on “Chiral Restoration in Nuclear Medium – Chiral05”, Riken (Japan), Feb 15-17 2005: “Strange Hadrons in Nuclei, First Results From FINUDA” • P. Camerini, @ XLIII International Winter Meeting On Nuclear Physics, Bormio (Italy), Mar 13-20 2005: “Hypernuclear Physics with FINUDA at DAΦNE” • T. Bressani, Report to NUPECC General Meeting, Venice Mar 18-20, 2005 • L. Benussi, @ Int. Conf. On Nuclear Physics at Storage Rings STORI05, May 23-26 2005: “Hypernuclear physics with FINUDA”

8. CURRENT ACTIVITIES IN DATA ANALYSIS • Alignments: methods and results • On the way to better understand our data… • New Physics Selected Results • Spectroscopy • Non Mesonic Weak Decays • Mesonic Decays • KNN deeply bound states

9. ALIGMENTS: procedure and methods • Use of straight cosmic rays collected during and after the 2003-04 data taking • Iterative procedure: • First preliminary study to skim clean events for a reliable residuals estimation • Evaluation of I/OSIM and DCH residuals with respect to the straw tubes system • Global translational & rotational offsets • Finer tuning of single modules • Evaluation of outer layers residuals with respect to microvertex detectors • The two procedures should lead to equivalent results when everything is correctly aligned • Long job: good results achieved

10. Geometry starting situation: global residual distributions Inner DCH: ΔΦ= 180 µm, Δz = 1 cm Outer DCH: ΔΦ= 95 µm, Δz = 1.2 cm Straw tube system taken as reference ISIM: ΔΦ= 90 µm, Δz = 115 µm OSIM: ΔΦ= 80 µm, Δz = 177 µm

11. Alignment effects on single module geometry: fit with points on I/OSIM Example: inner drift chamber, cosmic fit from vertex detector Starting condition After fine alignment

12. A few details on residual shape improvements Example: one inner Drift Chamber (I) OLD OLD NEW NEW residual distribution along the module longitudinal coordinate (sensible to rotation effects on r-φ plane) χ2 distribution for the straight line fit (same scale!) Narrower – centered at zero!

13. A few details on residual improvements Example: one inner Drift Chamber (II) OLD OLD NEW NEW residual distribution along the z coordinate Scatter plot of R residuals vs Z residuals (sensible to rotations on z-φ plane around r) Narrower – centered at zero! Becomes horizontal and aligned around zero!

14. After alignment: effects on physical measurementse+e- (Bhabha) momenta distributions • Bhabha events: due to the boost (12.6 MeV/c), NO monochromatic peaks for electrons and positrons must be seen • A smeared peak centered at the same value for both is expected • In case of disaligned geometry, the two components tend to separate in one case, and to squeeze the distribution in the second one • Before alignment (black histos): • electrons • Presence of a double peak! • Selecting single paths, the momentum difference due to the boost shows up clearly • Positrons • No double peaks, but one single narrower peak (as expected) • With alignments (red histos): • Electrons • The two peaks converge, a single peak appears, with central value µ= 0.509 MeV/c • Resolution, without cuts: FWHM = 3.2% • Positrons • Central value µ= 0.508 MeV/c • The peak broadens, FWHM = 3.2% • With alignments the peak mean central values are better centered now for both electron and positron to the same central value (within errors), and the “raw” width for both is the same

15. After alignment: effects on physical measurementsµ+ spectra from different targets • The central values of +momentum spectra selectedper targetmove towards the nominal value (235.6 MeV/c – an offset is possible due to the present normalization of the mapped magnetic field) • The spread around the central value for each target is reduced as compared with previous geometry versions (blue points) • Lower half target set better arranged by this 1st alignment version • The total momentum spectrum, integrated over all the targets, gets the ~20% narrower • Resolution depends on cuts and on chosen road: better resolution 0.57%

16. 261 MeV/c 273 MeV/c Tgt 1 Tgt 5 Tgt 8 After alignment: effects on physical measurementsπ- spectra from the three carbon targets • The peaks corresponding to 12C g.s. and the state at B =0 are correctly aligned, within 1 MeV/c (no severe cuts applied!), for data collected from all the three Carbon targets (one in boost direction, two in anti-boost) 261 MeV/c 273 MeV/c Tgt 1 Tgt 5 Tgt 8 1 8 5 Raw spectra, no “spectroscopy quality cuts”

17. Alignment procedures: summary • Many instrumental effects singled out by residual distributions study, and corrected • Improved description of the geometric positioning of single modules • Macroscopic rotational and translational effects corrected • Many single-module rotational and translational effects corrected • Good improvement of real data description • Bhabha e- and e+ distributions now single-peaked and centered • µ+momenta distributions from single target better centered around mean value • π- peaks for hypernuclear levels from different Carbon targets better aligned • Sum of peaks can now be performed

18. Studies for data quality improvement: Carbon targets (I) Tgt 1 Tgt 5 Tgt 8 • A good improvement of the quality of the signal/bck ratio is obtained by cutting on the distance between the K- interaction vertex and the point where the π– is supposed to emerge (extrapolated at the level of K- stop plane) • Residual inaccuracies in vtx determination inside targets? • Signals for hype formation in flight? Standard cuts Boost effect on tgt 5? cut on vertex-extrapolated π distance A third peak appears in between the ground state and the BΛ = 0 MeV level

19. Studies for data quality improvement: Carbon targets (II) • Adding to the requirement on the vertices distance a further cut on the -emission angle from the target (angle with the normal to the target plane) in-flight events should be suppressed • Sizeable reduction of the background beyond the ground state with oblique tracks, in spite of a larger amount of target material to be crossed by the particle • Interesting effects emerging: clean signal of a third peak 30o<  <80o GeV/c Tgt 5 60o<  <80o GeV/c

20. Spectroscopy: 7Li target • The 7ΛLi hypernucleus was extensively studied with γspectroscopy techniques, with a resolution as good as 2 keV • FINUDA cannot compete with this resolution, but in spite of this the levels definition is good, especially if the presence of at least one neutral particle in the reaction (neutron!) is required • ΔBΛ= 1.5 MeV • Compatible with 1+-3+ levels difference (Tamura) Requirement of at least one neutral particle in coincidence 2 very close peaks n

21. Spectroscopy: Aluminum target PRL 34(1975)683 • One very old (1975) measurement exists for 27ΛAl spectroscopy • Medium-A hypernuclei production with K- at rest: ? • Closest studied hypernucleus: 28ΛSi • Attempt to adapt the 28ΛSi level structure to a 27ΛAl excitation spectrum 6 MeV FWHM PRC 53(1996)1210 28ΛSi KEK E140

22. #6 #7 #5 #4 #2 #3 #1 Spectroscopy: Vanadium target • No measurement exists so far for 51ΛV production in (K-stop, π-) reactions • First indications for the feasibility of such a reaction to produce heavy hypernuclei Comparison with E369 B values (MeV) Ground state missing…!

23. Spectroscopy Results: summary • 12C: new alignment allows to sum up spectra from all the three targets • Increased available statistics • Possibility to apply stricter cuts • Improved definition of hypernuclear levels and background reduction • Study of finer effects possible (boost, in-flight hypernuclei production) • 7Li: good hypernuclear levels identification • 51V: indications for the existence of several structures already observed in (π+,K+) experiments • Exploratory run for medium-heavy targets • Good performance of FINUDA: first hints for the production of hypernuclei in a (K-, π-) reaction at rest even from heavy targets Preliminary! 12C 27Al 51V 7Li Hypernuclear capture rate/K-stop (integrated over the bound region) as a function of the mass number

24. Non-mesonic weak decays: detection of neutrons with FINUDA • TOFONE’s features: • efficiency: about 10% • Resolution: 10 MeV for 80 MeVneutrons • Lower threshold: 6 MeVee • Lower detectable energy: 11 MeV • Upper threshold: 200 MeV • Inclusive neutron energy spectrum with µ+ coincidence (no ’s from 0 decay etc.), all targets

25. NMWD: coincidence spectra from Carbon target: protons Inclusive proton spectrum, bound region ground state region, proton spectrum Not acceptance corrected bound region, coincidence pions

26. NMWD: coincidence spectra from Carbon target: neutrons Inclusive neutron spectra in the bound and g.s. region Neutron spectra in coincidence with p, in the bound region Neutron spectra in coincidence with n, in the bound region

27. NMWD: total energies from coincidence spectra: pn, nn To be compared with the best results obtained so far for NMWDs (KEK E462-E508) Preliminary!

28. NMWD coincidence spectra from 7Li targets: protons & neutrons Inclusive spectra Not acceptance corrected protons Pions (p coincidence) neutrons

29. Mesonic weak decays: first hints with FINUDA • Improved pattern recognition for short tracks, using three points instead of four • Higher acceptance • Higher statistics • Lower resolution • Opens the possibility to: • Study reactions with low momentum stubs • Study reactions with secondary vertices (Λ decays in flight, Σdecays, etc) • Preliminary results, on the way to implement it fully in the reconstruction code

30. Mesonic weak decays: coincidence spectra from Carbon targets π- from the mesonic Λdecay Further quality cuts on hypernucleus production Selection in the bound region

31. Mesonic weak decays: coincidence spectra from 6Li targets π- from the mesonic Λdecay Very clean peak of Λin the reconstructed invariant mass of π– and p for events in the bound region (of 5 ΛHe)

32. Mesonic weak decays from medium-heavy targets • Probability of mesonic decay suppressed with mass number increase

33. Search for kaon bound states • Missing mass spectroscopy • (K-stop,n/p) → KEK-PS E471/E549, FINUDA • 4He(K-stop,n)S+(3140) → K-ppn (169 MeV bound) • 4He(K-stop,p)S0(3115) → K-pnn (193 MeV bound) • Invariant mass spectroscopy • K- absorption at rest in nuclei FINUDA • K-pp →Λ+p (Λ → p+π-) • K-pn →Λ+n, Σ-+p • K-ppn →Λ+d • Study of Λp coincidence events, with a back-to-back correlation (about 5% of the Λ events are associated with a proton) FWHM = 6 MeV mΛ± 5 MeV

34. L p Cos(Lp) < - 0.86 Improvement of K-pp bound state analysis with the new p.r. including short tracks K-pp →Λ+p Background contributions: The contribution of the quasi-free reactions on two protons sits on the peak at high invariant mass: K-pp →Σ0+p

35. π-pp invariant mass from 6Li, background subtracted To be compared with our first, published, experimental result: S0p Lp mp+mp+mK- The improved p.r. with the inclusion of short tracks puts in evidence a possible decay into Σ0p

36. PREPARATION FOR NEXT RUN: SIMULATIONS, EXPECTED RATES • New set of targets: motivation, interests • Expected signals with the new targets’ set: 9Be, 16O • Expected improvements in the accuracy of the definition of Kpp-bound states from the lightest targets

37. New targets’ setup for next data-taking • Choice: 2x6Li, 2x7Li, 2x H2O, 2x9Be • Target type better localization still to be studied (depending mainly on the boost and physical target features – stiffness, …) • Lighter targets better in anti-boost direction • Thicknesses evaluation, in the hypothesis of a 1.8 mm thick TOFINO: • 7Li, 6Li as in the previous run (+cover) • 9Be: 2 mm • H2O: 3 mm + cover (e.g. 100 µm mylar) • First simulations of expected signals/background contributions, rough evaluation of expected rates from new targets

38. 16ΛO production with FINUDA - studies • 16O is a doubly magic nucleus • 16ΛO production in (K-stop,π-) reaction at rest already studied (Tamura) • Capture rate: ≤10-3/K-stop • Four levels: • D: g.s. @ 279.3 MeV/c: R = 0.13x10-3 • C: p(3/2)-1n,sΛ @ 272.3 MeV/c: R = 0.30x10-3 • B: p(1/2)-1n,pΛ @ 267.4 MeV/c: R = 0.56x10-3 • A: p(3/2)-1n,pΛ @ 260.4 MeV/c: R = 1.12x10-3 • First simulation of the apparatus response with: • Background reactions as in 12C: • QF Λ production • K-NN interaction with Σ±,0conversion • π rescattering

39. 9 ΛBe production with FINUDA - studies • Core: 8Be nucleus, highly symmetric • Production of Λ-hypernuclei with high spatial symmetry (no from 9Be, Pauli principle) • Limited data quality in (π+,K+) production • Expected rates: some 10-4 • Observed states in (K-stop,π-) (doublets): • g.s. @ 280+284 MeV/c: R=0.34x10-3 • αα-pΛ @ 277+274 MeV/c: R=0.39x10-3 • αα-sΛ @ 270-265 MeV/c: R=0.7x10-3

40. NP A691(2001)123c 2 MeV FWHM 7ΛLi production evaluation • 7ΛLi is one of the most studied hypernuclei with γspectroscopy • The level structure is well known • Many interesting effects still to be studied: • NMWD’s • Study of nuclear density related effects • Source for the production of neutron-rich hypernuclei • K- + 7Li  7LH + p+(N/Z= 6) • Study of KNN bound states • Measured production rate of 7ΛLi in (K-stop, π-) by FINUDA: ~8.5x10-4 • 8-10 times more statistics can be expected collecting 1 fb-1

41. Hyperfragments production from 6Li • The 6ΛLi hypernucleus is unstable but several hyperfragments (ΛHe, ΛH) can be produced from its decay • Study of NMWD’s • Study of rare decays • Source of neutron-rich hypernuclei • K- + 6Li  6LH + p+(N/Z= 5) • Source of deeply bound KNN states • (Preliminary) capture rate value in the region of 5ΛHe production: 6 x10-4/K-stop • With 1 fb-1 5 times more statistics than that presently available is expected • K-+ 6Li  -+ X • X: 5He + p • X: 4He + p + n • 4He  d + d • 4He  p + 3H • 4He ++n+3H • X: 4H + p + p • 4H 4He + -

42. MC simulations of K-pp bound states for the next run I • INPUTS: • existence of a bound K-pp state • B =115 MeV, G= 67 MeV • Formation rate determined from last data taking data • Interaction in 7Li targets (typical light target) • ASSUMPTIONS: • Five times more data will be collected in the run, (hypothesis: 1 fb-1) • Decay branching ratio : Lp / S0p = 1 / 2 • Detector efficiencies = 1 • Magnetic field: B = 1 T (as in the previous data taking)

43. MC simulations of K-pp bound states for the next run II • RESULTS: • ~20 times more K-pp events can be obtained if the integrated luminosity reaches 1 fb-1 • The mass and width of the K-pp state can be determined with much better accuracy • The background (caused by fake neutrons) can be reduced by tagging m+ from K+ decays, which can be done having one order of magnitude more statistics From the simulation: B = 119 ± 2 MeV Γ= 60 ± 4 MeV

44. Conclusions • A wealth of interesting and brand new results have been extracted from the data collected in 2003-04, about • hypernuclear spectroscopy with increased statistics and better tuning • non-mesonic and (new!) mesonic decays • Measurement of first coincidence proton spectra (down to the lowest momentum ever), and (new!) neutron ones • formation of kaon bound states • other topics already mentioned in past meetings (rare decays, neutron rich hypernuclei, searches for hypernuclei, etc) • Big effort to achieve a better apparatus alignment in order to systematically spot the drawbacks spoiling the resolution • Detailed simulations of expectations from next data taking are currently underway • Hardware upgrades have been programmed in order to improve the apparatus’ performances • We just need… data! 1 fb-1 only would make us happy… and able to study a lot of new physics • By the way, at KEK the activity is quickly going on… and, of course, they are not waiting for us!