www lnf infn itesperimentirog INFN Frascati Labs Genova

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INFN • Frascati Labs • Genova • Gran Sasso Labs • L’Aquila • Roma 1 • Roma 2 • INAF - IFSI • CNR- IFN • CERN • Geneva Leiden CERN RE 5 Mini. Grail 50 persone (39 ricercatori e tecnologi + 11 tecnici) 28. 3 FTE (22. 5 ricercatori e tecnologi + 5. 8 tecnici) LNF INFN

Summary • Explorer e Nautilus prendono dati ovvero: le curve di sensibilità non sono tutto • Risultati con duty cycle > 90% del run Explorer- Nautilus 2003 ovvero: le stiamo già vedendo? • Upgrades Explorer- Nautilus ovvero: si può ulteriormente migliorare • Strategia futura: SFERA ovvero: il primo vero telescopio di onde gravitazionali

Data taking during the last 14 years largest data base of GW data worldwide EXPLORER 1990 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 h from 10 -18 to 3· 10 -19 IGEC search 1990 91 92 NAUTILUS = upgrade 95 96 97 98 99 00 S 01 01 S 03 02 h from 10 -18 to 2· 10 -19 03 S 04/05 04 05

Pubblicazioni recenti • P. Astone et al. (ROG Collaboration): “The 2003 run of the Explorer and Nautilus gravitational wave experiments”, submitted to Class. Quantum Grav. (2005). • P. Astone et al. (ROG Collaboration): “Cumulative analysis of the association between the data of the gravitational wave detectors NAUTILUS and EXPLORER and the gamma ray bursts detected by BATSE and Beppo. SAX”, Phys. Rev. D 71 (2005). • A. de Waard, Y. Benzaim, G. Frossati, L. Gottardi, H. van der Mark, J. Flokstra, M. Podt, M. Bassan, Y. Minenkov, A. Moleti, A. Rocchi, V. Fafone, G. V. Pallottino: “Mini. GRAIL, progress report 2004”, Class. Quantum Grav. 22 (2005). • E. Coccia, F. Dubath, M. Maggiore: “On the possible sources of gravitational wave bursts detectable today”, Phys. Rev D 70 (2004). • P. Astone et al (ROG Collaboration): “Searching for counterpart of gamma-ray bursts with resonant gravitational wave detectors”, Class. Quantum Grav. 21 (2004). • A. de Waard et al (ROG and Mini. Grail Coll. ): ”Cooling down Mini. GRAIL to milli-Kelvin temperature”, Class. Quantum Grav. 21 (2004). • P. Astone: “Seven years of data taking and analysis of data from the Explorer and Nautilus gravitational wave detectors”, Class. Quantum Grav. 21 (2004). • V. Fafone: “Resonant-mass detectors: status and perspectives”, Class. Quantum Grav. 21 (2004).

Strain sensitivity (Hz-1/2) 2005

Noise budget is well understood Present Status of EXPLORER reference signal • Present limit from amplifier noise Teff~ 2 m. K h ~ 3 10 -19

DATA TAKING DURING 2003 NAUTILUS EXPLORER 4 · 10 -22 4· 10 -22 Data used for S 03

DATA TAKING DURING 2004 NAUTILUS EXPLORER 5 3· 10 -22 No veto applied • The data from May will be used for IGEC 2 analysis

DATA TAKING DURING 2005 NAUTILUS EXPLORER Up-grade 3 3· 10 -22 No veto applied

NAUTILUS OPERATIONS DURING April 2005 Duty Cycle 85 % Liquid Helium Refillings Days of April 2005

NAUTILUS - 5 April 2005 1 h starting 1 am night 1 h starting 11 am day

EXPLORER - 5 April 2005 1 h starting 1 am night 1 h starting 11 am day

Science Run 03 Coincidence measurement time 148. 7 days Data selection Accepted periods: Hourly averaged Noise Temp. < 12 m. K Accepted events: Noise Temp. before the event < 8 m. K SNRE = Event energy / Noise Temp. > 19. 5 Coincidence time window 30 ms

EXPLORER has been on the air since May 2000 with: -new, 10 µm gap transducer -new, high coupling SQUID Bandwidth: the detector has a sensitivity better than 10 -20 Hz-1/2 on a band larger than 50 Hz The noise temperature is < 3 m. K (h=4. 4 10 -19) for 84% of the time. 1998 2001 Increasing the Bandwidth of Resonant Gravitational Antennas: The Case of Explorer 2003 P. Astone et al. (ROG Collaboration) Phys. Rev. Lett. 91, 11 (2003)

Time resolution vs bandwidth 2002 Larger bandwidth Df Better time resolution Dt 1998 Event triggered by cosmic ray shower

Effect of cosmic rays EXPLORER is equipped with 3 layers (2 above the cryostat - area 13 m 2 - and 1 below -area 6 m 2) of Plastic Scintillators. NAUTILUS is equipped with 7 layers (3 above the cryostat - area 36 m 2/each - and 4 below -area 16. 5 m 2/each) of Streamer tubes. The cosmic ray effect on the bar is measured by an offline correlation, driven by the arrival time of the cosmic rays, between the observed multiplicity in the CR detector (saturation for M≥ 103 particles/m 2) and the data of the antenna, sampled each 4. 54 ms and processed by a filter matched to signals E = 1 m. K = 0. 15 me. V

Events are characterized by • time: time of the maximum of the filtered output • energy: energy of the maximum energy threshold time

ROG S 03 N events Explorer 72086; Nautilus 114911 Accidentals Shifting 1000 times, dt = 1 s Result Nc = 24 Background = 18. 8 P (Poisson) = 14 %

GWDAW Kyoto 2002 • Classical and Quantum Gravity 19, 5449 (2002) 3 points: • Unprecedented sensitivity • Two powerful tools in the same analysis: - amplitude (energy) consistency - sidereal time analysis • Defined analysis procedure for the next run

DIRECTIONALITY INTERFEROMETER BAR DETECTOR

G. Paturel, Yu. V. Barishev Sidereal time analysis as a tool for study of the space distribution of gw sources. Astro-ph/0211604 v 1, A&A 398, 377 (2003) The expected rate of events on EXPLORER for sources on the galactic disc and on the GC *= coincidences _______=

Number of events 2001 RUN (S 01) Sidereal hours

2001 suggestion

S 03

Conclusion • EXPLORER NAUTILUS Science run 03: - data validated by cosmic ray effect - new upper limit with bars. To be done • Use cosmic ray data to reduce calibration uncertainty • ROG data available for correlation studies with IGEC and all the other detectors.

…Therefore, to improve sensitivity: We need to improve the peak spectral sensitivity - Increase M : large and/or multimode detectors - Reduce T/Q : ultracryogenics. Low-loss materials We need to increase the bandwidth Df - Increase b : transducer w/ tighter coupling - Reduce Tn : better amplifier (double SQUIDs)

WIDENING THE BAND… ALLEGRO EXPLORER S 2 1998 S 4 2001 10 -20 NAUTILUS 880 950 AURIGA 2001 1999 10 -20 2003

IMPROVING Tn : Better Amplifiers A SQUID is so good an amplifier that noise from the second stage is usually dominant. The only suitable second stage is another d. c. SQUID. Several efforts underway to produce a reliable amplifier for antenna readouts

ROG double SQUID amplifier Energy resolution vs temperature performances improves when temperature is decreased @ T=2. 0 K, the flux noise is 0. 21 F 0/√Hz corresponding to 70 h

Double-gap transducer Actual gap on NAUTILUS transducer ≈ 9 mm @ T=4. 2 K, Q = 1. 5· 106, Vpol ≈ 200 V gap ≈ 10 mm

Parametric transducer Nb cavities with different characterisctics and sensitivities are about to be tested with the resonator. Integration of cavity with resonant mass foreseen by the end of 2006 Top view of the superconducting, bulk niobium cavity, realized by our group. In this picture, the reference surface has been removed to expose the cavity sensitive spot. The sensitive spot is a circular surface, 1 mm Ø, which is only 15 mm away from the transducer oscillating mass (gap distance). The RF antenna enters the cavity through the choke The surface shown here has not been chemically etched yet.

NAUTILUS upgrades Sh for NAUTILUS @ 0. 12 K, double gap transducer (11 mm and Q=1. 5· 106) and double SQUID (L 0=2. 5 H, k=0. 7). Teff ≈ 7 m. K (corresponding to h=2. 1· 10 -20), sensitivity < 1· 10 -21 /√Hz over about 40 Hz. Sh for NAUTILUS @ 0. 1 K, parametric transducer (m = 1 kg) Teff ≈ 3 m. K (corresponding to h=1. 4· 10 -20), sensitivity < 1· 10 -21 /√Hz over about 50 Hz.

Where can all these developments lead in the medium term?

GWIC Scenario for future detectors in the resonant-mass field “ * In the medium-term, the realization of a spherical detector, to be proposed now to the funding agencies, * In the longer term, research toward wideband resonant detectors using Dual Detection techniques. A spherical detector can make use of the state of the art readout technology, developed for the bars and for Mini. Grail, profiting from a larger mass and from the omnidirectional nature of the spherical detectors. Such a detector could have a sensitivity competitive with VIRGO and LIGO in the 1 k. Hz region. And since it allows full sky coverage during all observation time, and determination of the source direction, it can have an important role in a coordinated coincidence search. Since the principles of operation and technology are well understood, a funding proposal could be prepared soon. ”

sensitivities in the 2006 - 2012 prospective

GW are described by a symmetric and traceless tensor hij information: h+ hx ampl. of the 2 pol. states; H source direction; A resonant mass detector is characterized by those eigenmodes having the appropriate (quadrupole) symmetry cylindrical bar only one quadrupole mode interacts strongly with GWs The cross section is dependent on the wave propagation direction. The single output is a (unknown) combination of the components (same for an interferometer) sphere five degenerate quadrupole modes (described using the basis of the five spherical harmonics Y 2 m with m=± 2, ± 1, 0; the same basis can be used to express hij in the equivalent spherical components hm)

The experimental situation 2. TIGA experiments • TIGA arrangements • TIGA experiments

To allow the detection and identification of GW signals it is useful to complement the IFO network with an advanced resonant-mass observatory Added value • Duty cycle • Sky coverage • Instruments based on different principles Strategy: Realization of a Resonant-mass GW Observatory Complementing the IFO Network VIRGO - SFERA 2 m first hybrid observatory

The proposed detector: SFERA 2 m dia, Cu. Al M = 33 tons f 1 = 1. 0 k. Hz f 2 = 1. 9 k. Hz The Collaboration INFN/ROG (I) University of Geneva (CH) University of Leiden (NL) Cost ~ 2. 1 MEURO

Pulse tubes 3 He pumping tube 80 K radiation shield 4 K radiation shield Joule-Thomson heat exchanger 700 m. K radiation shield 50 m. K radiation shield still Continuous heat exchanger 50 m. K plate Sintered heat exchanger Mixing chamber

Detectable signals Burst sources (SN explosions, final merging of a NS-NS binary system) We assume H(f) constant over the sensitive bandwidth, Sh(f) also flat in this window, Df ~ 200 Hz, tg = O(1) ms, • SN explosions From current estimates: DE = 10 -2 Moc 2 - 10 -6 Moc 2 (deviation from sphericity of the collapse). SFERA sensitivity: r = 33 Mpc - r = 330 kpc

• Starquakes, Soft Gamma Repeaters and Magnetars NS (as well as hypothetical compact objects - quark stars, NS with a core of deconfined quarks) can produce GW bursts, after a sudden rearrangements of their structure, either in the crust or in the core. Crustquakes can emit in GW an energy and even larger values in corequakes. A very interesting example: magnetars, NS with magnetic fields 1014 - 1015 G (100 -1000 x than ordinary pulsars). They are believed to explain the Soft Gamma Repeaters (X-ray sources with persistent luminosity 1535 -1036 erg/s, that occasionally emit huge bursts of soft gamma rays, with a power up to 1042 erg/s (magnetic field lines drift through the liquid interior of the NS, stressing the crust and generating strong shear strains. For high magnetic fields, the NS crust breaks and the elastic energy is suddenly released in a large starquake, which generates a burst of soft gamma rays. The radiated energy range is 10 -10 -10 -9 Moc 2, up to 10 -8 Moc 2 in giant flares. Corequakes could be more powerful (the relevant energy scale is determined by hadronic physics). For a GW burst with DErad = 10 -8 Moc 2 , r range: 33 kpc (exploring the Galaxy). While the closest observed NS is at about 100 pc, population synthesis calculation indicates that the NS closest to us should be at just 5 -10 pc and that in a sphere of radius 100 pc around the Sun, there should be O(104) NS’s.

SFERA If funded in January 2006 assembling and tests during 2007 commissioning at the beginning of 2008 Science Run at the end of 2008

Finanziamenti richiesti per il 2006 - CONTINUAZIONE EXPLORER E NAUTILUS da quanto assegnato nel 2005 640 k. Euro (di cui 150 k. Euro ME) + - INIZIO REALIZZAZIONE SFERA INFN - 20% per Criostato - 20% sfera di rame-alluminio - 20% sospensioni Leiden - refrigeratore 80 k. Euro 70 k. Euro 60 k. Euro