DARK MATTER DIRECT DETECTION IN ELECTRON ACCELERATORS

1. DARK MATTER DIRECT DETECTION IN ELECTRON ACCELERATORS J. Hisano (ICRR, Univ. of Tokyo) 東北大学21世紀COE「物質階層融合科学の構築」 素粒子・天文合同研究会「初期宇宙の解明と新たな自然像」 2005年9月20日(火) ～ 21日 (水)  東北大学理学部キャンパス 理学総合棟 ７４５号室 This talk is based on collaboration with M.M.Nojiri, M.Nagai, and M.Senami (hep-ph/0504068).

2. Contents of my talk • Introduction DM in universe, SUSY DM, conventional DM direct detection • Dark matter detection in electron accelerator • Conclusion

3. I Introduction Non-baryonicCold Dark Matter (CDM)in the Universe • Rotation curve • CMB anisotropy (WMAP) • Structure formation New stable particle beyond the standard model

4. Structure formation in CDM model History of galaxy formation • Primordial fluctuation grows by gravitational instability. CDM assists the efficient formation. • The N-body simulation is consistent for L>~1Mpc. Unresolved problems : Galaxy • DM spatial distribution inside galaxies • Clumpy structure • Cuspy in Galactic center • DM velocity distribution • Maxellian? • Non-thermal component? If DM particles can be detected, the Dark Side in the universe can be probed more directly.

5. Neutralino DM in the SUSY Standard Model • Lightest SUSY particle (LSP) is stable due to the R parity • Lighest neutralino (Majorana fermion) • Neutralino is a “good” DM candidate. • Predictable thermal relic abundance • We can study the thermal history of the Universe. • Detectablities • 1) (Conventional) direct detection on the ground • 2) Indirect detection using anomalous cosmic rays

6. Conventional direct detection • neutralino-nuclei elastic scattering • measurement of phonon, ionization, and/or scintillation • typical recoil energy is E<~100KeV. • effective Hamitonian (neutralino is Majonara fermion.) Spin-independent (SI) interaction. Coherent process Heavy atoms More important in neutralino search Spin-dependent interaction. Non-zero spin terget. • counting rate of SI ( ) • CDMS II. 73Ge Target and the exposure 19.4kg days (52.6 live days) leads

7. spin-independent cross section for neutralino • . Neutral Higgs exchange is dominant, but, it • is highly model dependent due to neutralino • mixing and heavier Higgs mass. • O(10)% hadronic uncertainties come from mass fractions of strange quark and gluon to baryon mass. Bino-like LSP SI cross section (cm2) from light Higgs contribution

8. Experimental status • high target mass (R<1event/day/Kg) and large atomic number target (A~100). • low energy threshold (Q<100KeV) • low background (Neutron and electron recoil) • underground, hybrid-type detector, pulse shape analysis…..

9. Summary of Introduction Dark matter in the universe is established quantitatively. However, • constituent of the DM • DM spatial and velocity distributions inside galaxy. are still unresolved problems. • Collider experiments, LHC(2007~) and GLC (201?~), study • properties of the DM particle (such as neutralino), mass and • interaction. • (Conventional) direct DM detection on the ground may probe • before LHC starts, and the proposed reaches • also cover What can we do after that (>~2020 -2030) ?

10. : electron : neutralino (DM) II, Dark matter detection in electron accelerator “Fixed” target experiment. Target is neutralino DM in space. detector Electron beam pipe Scattering is induced by s-channel selectron exchange. Selectron on-pole production is possible if we can tune beam energy to since DM neutralinos are highly NR. Cross section is enhanced as selectron exchange when

11. Necessary conditons for experiment • Expected # of event • Decay width of (right-handed) selectron to Bino-like LSP. a) small mass difference at most (10~30)GeV, and it must be measured with precision O(10)MeV. b) high current electron beam, such as O(100) A. c) long detector, such as O(100) m. Merits for experiment We may measure DM velocity distribution under well control.

12. a) Small mass difference 0.2 In MSUGRA Bino and right-handed selectron masses are 0.1 One of favored regions by WMAP is . Small mass difference may be expected. Bino-stau coannihilation 0 100 200 300 400 Mass difference measurement • Collider experiments LC: ~ 50MeV (absolute value from threshold scan) ~ (Mass diff. from end point.) • DM detection in electron accelerator • measurement of daily modulation of event rate • if enough statistics (Later we will come back).

13. b) high current electron beam • KEKB(SuperKEKB): • positron (3.5 GeV) 1.861A (9.4A) • electron (8.0 GeV) 1.275A (4.1A) • Synchrotron radiation (SR) at arc sections • the beam pipe damage and the beam power loss. • →Energy Recovery Storage Ring (noticed by Oide-san in KEK.) accelerator decelerator beam energy is lowered at the arc sections energy energy The beam is accelerated decelerator detector accelerator (GEV-scale Energy recovery linac (ERL) is still under debate.)

14. c) Long detector • Signal: almost monochromatic and transverse electron • Possible BGs: expected to be highly suppressed by Pt cut. • Electron scattering with the beam gas • low Pt • pion production from photo-nucleon interactions • also low Pt, but number may be huge. (Of course, more serious BG studies is needed in the realistic set up) →measurement of Pt for recoiled electron is required. TRD (particle ID) Beam pipe Tracking chambers with solenoid magnets Mask for pile up from upper reaches Cost reduction is needed. Solenoid magnet : ~1M$/m.

15. III, what can we measure ?? Dark matter local density and velocity distribution • Spherically-symmetric isothermal distribution (at halo flame) ←Flat rotation curve is well explained. • Earth motion at halo flame generates DM wind at earth flame • from the Constellation Cygnus.

16. Daily modulation of the event rate rotation of Earth ⇒daily modulation We may measure and velocity and direction of the DM wind. DM wind 42° 1 sidereal day = 23h56m4.09s

17. What else can be measured. beam energy deviation dark matter wind dispersion • modulation phases are reverse in the positive and negative • energy deviation. • energy dependence may resolve degeneracy of and →But, total event # should be O(102-3). (under discussing). cross section (microbern) Energy dependence at peak

18. Enything else? • Spherically-symmetric isothermal distribution is right? • Sagittarius dwarf tidal stream • Sagittarius dwarf satellite galaxy being tidally disrupted. • High velocity particle stream (v~300km/s) , whose mass • density is (0.3-25)% of the local density. • spherical velocity dispersion ? • Maxellian ? Or non-thermal components ? • N-bodies’ results are contradictory. (Freese et al) (from Newton)

19. IV, Conclusion DM physics after LHC and LC experiments (20~30 years latter! ) is discussed. That is, DM direct detection in electron accelerator. Selectron on-pole production is used. In order to realize it, a) small mass difference at most (10~30)GeV b) high current electron beam, such as O(100) A. c) long detector, such as O(100) m. Requirements are severe, but, the experiment may be controlled well and, • DM local density • DM velocity distribution may be measured. They are important for galaxy formation. Neutralino astronomy will probe the Dark side of the universe.

20. Let us hope that the time is more ripe for this realization.

21. Back up slide

22. Neutralino relic density • Neutralino annihilation freezes out at and neutralino is decoupled from thermal bath. • Minimal supergravity (MSUGRA) predicts Bino-like neutralino • LSP. 1, Stau coannihilation region: 2, Funnel region: 3, Focus point region: large Higgsino-Bino mixing Stau LSP (Ellis et al)

24. The ratio of the cross sections Beam axis is Perpendicular / Parallel to the DM wind