1. Results of a MWPC TPC in CAST Berta Beltrán (University of Zaragoza, Spain) TPC Workshop Paris, 20-21 December 2004

2. Paris, TPC workshop 21/12/2004Berta Beltrán2 Outline Introduction to the CAST experiment The MWPC TPC of CAST Description of the Chamber Characterization of the Chamber in the Panter facility Passive shielding

3. Paris, TPC workshop 21/12/2004Berta Beltrán3 CAST: principle of detection X-ray detector Axion – photon conversion in the ~9 Tesla transverse magnetic field of an LHC dipole prototype a + magnet  + magnet L≈10m X-ray CAST TPC Coherence (qL<<1)→1 Axion-photon conversion probability

4. Paris, TPC workshop 21/12/2004Berta Beltrán4 CAST: experimental setting TPC Cryogenics CCD Calorimeter µMegas 80º 14º

5. Paris, TPC workshop 21/12/2004Berta Beltrán5 University of British Columbia, Department of Physics, Vancouver, Canada Michael HASINOFF Ruder Boskovic Institute, Zagreb, Croatia Milica KRCMAR, Biljana LAKIC, Ante LJUBICIC Centre d''Etudes de Saclay (CEA-Saclay), DAPNIA, Gif-Sur-Yvette, France Samuel ANDRIAMONJE, Stephan AUNE, Alain DELBART, Esther FERRER, Ioanis GIOMATARIS, Emile PASQUETTO, Jean Pierre ROBERT, Igor G. IRASTORZA Technische Universitat Darmstadt, Institut für Kernphysik, Darmstadt, Germany Theopisti DAFNI, Dieter HOFFMANN, Manfred MUTTERER, Periklis RAMMOS, Yannis SEMERTZIDIS Johann-Wolfgang-Goethe Universität Frankfurt, Institut für Kernphysik, Frankfurt Am Main, Germany Vladimir ARSOV, Joachim JACOBY Albert-Ludwigs-Universität Freiburg, Freiburg, Germany Horst FISCHER, Jurgen FRANZ, Donghwa KANG, Kay KONIGSMANN, Fritz-Herber HEINSIUS, Christian SCHILL Max-Planck-Gesellschaft (MPG) Max-Planck-Institut für Extraterrestrische Physik, Garching, Germany Heinrich BRAEUNINGER, Jakob ENGLHAEUSER, Peter FRIEDRICH, Markus KUSTER Max-Planck-Institut fur Physik Muenchen, Germany Rainer KOTTHAUS, Gerhard LUTZ, Georg RAFFELT National Center for Scientific Research "Demokritos" (NRCPS), Athens, Greece George FANOURAKIS, Theodoros GERALIS Aristotle University of Thessaloníki, Thessaloniki, Greece Spyridon DEDOUSIS, Christos ELEFTHERIADIS, Anastasios LIOLIOS, Argyrios NIKOLAIDIS, Konstantin ZIOUTAS Scuola Normale Superiore (SNS), Pisa, Italy Luigi DI LELLA Russian Academy of Sciences, Institute for Nuclear Research (INR), Moskva, Russia Alexandre BELOV, Sergei GNINENKO, Nikolai GOLUBEV Instituto de Física Nuclear y Altas Energías, Universidad de Zaragoza, Zaragoza, Spain Berta BELTRAN, Jose Manuel CARMONA, Susana CEBRIAN, Gloria LUZON, Angel MORALES, Julio MORALES, Alfonso ORTIZ DE SOLORZANO, Jaime RUZ, Jose VILLAR European Organization for Nuclear Research (CERN), Geneve, Switzerland Klaus BARTH, Enrico CHESI, Gino CIPOLLA, Martyn DAVENPORT, Michel DELATTRE, Rui DE OLIVEIRA, Fabio FORMENTI, Jean-Noel JOUX, Christian LASSEUR, Angelika LIPPITSCH, Thomas PAPAEVANGELOU, Alfredo PLACCI, Bruno VULLIERME, Louis WALCKIERS Enrico Fermi Institute, University of Chicago, Chicago, Il, United States of America David MIlLER, Juan COLLAR, Joaquin VIEIRA University of South Carolina, Department of Physics and Astronomy, Columbia, Sc, United States of America Frank AVIGNONE, Richard CRESWICK, Horacio FARACH CAST Collaboration ~75 participants from 16 institutions.

6. Paris, TPC workshop 21/12/2004Berta Beltrán6 CAST detectors requirements Signal characteristics Low intensity X-ray signal Energy range 1-10 keV, with peak in ~4 keV. Photon coming parallel to the magnet beam Detector requirements Low background, robust and stable operation. Good efficiency in this range, low threshold. Good position resolution CAST: 3 different detectors TPC (CERN/ZGZ) μMegas (Saclay/Athens/CERN) CCD (MPI/HLL)

7. Paris, TPC workshop 21/12/2004Berta Beltrán7 Let’s see how the CAST TPC fulfils this requirements… Conventional technology: robustness and stability guaranteed Built with low background materials ( mainly Plexiglas) + Passive shielding → low background 10 cm 30 cm 15 cm (1850 V) (0 V) (-7000 V)

8. Paris, TPC workshop 21/12/2004Berta Beltrán8 Efficiency of a 10-cm-long ionization chamber for different gases at normal pressure (Source: X-ray data booklet) Filled with Ar (95%)/CH 4 (5%) at atmospheric pressure Drift region: 10 cm Section 15 ×30 cm 2 Essentially total conversion of photons up to 6 keV

9. Paris, TPC workshop 21/12/2004Berta Beltrán9 5.9 keV Argon escape peak (3keV) Low threshold → ~0.7 keV Energy resolution ~13% 55 Fe calibration (10/11/2004)

10. Paris, TPC workshop 21/12/2004Berta Beltrán10 γ The axion-conversion photons will come straight from this two bores of the magnet Only this two areas of 18 cm 2 each are sensible to this photons TPC With a wire spacing of 3 mm we can distinguish easily this kind of events from the ones that fall in the rest of the chamber → Position resolution

11. Paris, TPC workshop 21/12/2004Berta Beltrán11 TPC front view

12. Paris, TPC workshop 21/12/2004Berta Beltrán12 TPC up view

13. Paris, TPC workshop 21/12/2004Berta Beltrán13 The TPC in the magnet

14. Paris, TPC workshop 21/12/2004Berta Beltrán14 CAST TPC acquisition electronics Charge pulse Trigger built by independent card adding all anode signals Wire in TPC Preamp Integrated amplified pulse FlashADC ALTRO chip (ALICE TPC electronics) Sampling rate 10MHz Time window of 7  s 3×48 = 144 channels Pedestal subtraction Threshold

15. Paris, TPC workshop 21/12/2004Berta Beltrán15 June 2002 PANTER facility, Munich Precise calibration with different energies at the Panter Facility in Munich Energies tested: 0.3 keV 0.9 keV 1.5 keV 2.3 keV 3 keV 4.5 keV 6.4 keV 8 keV View of both TPC windows in the data from PANTER TPC characterization Anode wire number Cathode wire number

16. Paris, TPC workshop 21/12/2004Berta Beltrán16 Linearity Linear response of the gas vs. energy Experimental check of the linearity of the TPC gain. White & black dots: runs taken in two different days.

17. Paris, TPC workshop 21/12/2004Berta Beltrán17 Efficiency Efficiency of the chamber measured experimentally Green curve → windows transmission. Black dots → Experimental efficiency measured at the Panter Facility. Red line → TPC efficiency after the offline cuts.

18. Paris, TPC workshop 21/12/2004Berta Beltrán18 time (0.1  s bins) Example of X-ray hitting one only anode X-rays can hit up to 3 anode wires depending on how far from the wires they interact (diffusion of the e - cloud) TPC: Raw Data

19. Paris, TPC workshop 21/12/2004Berta Beltrán19 Background event TPC: Raw Data time (0.1  s bins)

20. Paris, TPC workshop 21/12/2004Berta Beltrán20 200 mm POLYETHYLENE 25 mm LEAD 5 mm COPPER 2 mm CADMIUM N 2 FLUX 200 l/h TPC passive shielding Designed by the Zaragoza (Spain) group In the experiment since may 2004

21. Paris, TPC workshop 21/12/2004Berta Beltrán21 View of the TPC inside the shielding

22. Paris, TPC workshop 21/12/2004Berta Beltrán22 Shielding: main tasks Reduce the level of the background Homogenize the background of the experimental area Germanium measurements of the activity in the CAST area

23. Paris, TPC workshop 21/12/2004Berta Beltrán23 Background homogenization in the experimental area

24. Paris, TPC workshop 21/12/2004Berta Beltrán24 Reduction of the background level with the shielding 4.13×10 -5 counts/KeV/sec/cm2 1.85×10 counts/KeV/sec/cm2 Reduction by a factor ~4.5

25. Paris, TPC workshop 21/12/2004Berta Beltrán25 g aγγ (95% C.L)= 1.51×10 -10 GeV -1 χ 2 /d.o.f = 31.64/27 χ 2 null /d.o.f = 27.39/28 2003 data: TPC Final result CAST(TPC+CCD+μM) 2003 data → gaγγ(95% C.L)= 1.16×10 -10 GeV -1 hep-ex/0411033

26. Paris, TPC workshop 21/12/2004Berta Beltrán26 Summary The TPC achieves the CAST signal requirements: Stable and robust, low background. Good efficiency in the region of interests, low threshold. Position sensitivity. The passive shielding works properly: Reduction of the background level by a factor ~4.5. Homogenization of the background of the area. The TPC has been taken data properly for two years, and it is giving good results inside the experiment!!

27. Paris, TPC workshop 21/12/2004Berta Beltrán27 Why Axions ?: Strong CP problem In the 70’s a new term which violates CP is included in the QCD Lagrangian. From the experimental bound on the neutron electric dipole moment,|θ|≤ 10 -9 Why is this parameter so tiny ?→ STRONG CP PROBLEM In 1977 Peccei and Queen proposed an elegant solution to this problem: Addition of a new U pq (1) symmetry in the theory such that the vacuum energy is minimized for θ =0. Weinberg and Wilczek realized that there is an additional pseudo- Goldstone boson associated with the spontaneous breaking of it: the Axion a(x). Now θ is absorbed in the definition of a(x)

28. Paris, TPC workshop 21/12/2004Berta Beltrán28 Axions : Phenomenology The AXION is: pseudoscalar neutral practically stable phenomenology driven by the breaking scale f a and the specific axion model Axion mass: Axion-photon coupling present in almost every axion model This gives rise to the Primakoff effect: axion- photon conversion (and vice versa) in the presence of electromagnetic fields. That is the only axion phenomenology on which CAST relies…

29. Paris, TPC workshop 21/12/2004Berta Beltrán29 Solar axions Thermal photon-nucleus interaction in the Sun core (T~15.6 MK)  + Z a+ Z Solar axion differential flux on Earth (K. van Bibber et al., 1989) g a γγ = 10 -10 GeV -1 Photons/(cm2 s keV)

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