Dark Matter and LHC. Piero Ullio SISSA & INFN (Trieste) Incontri di Fisica delle Alte Energie 2006 Pavia, April 20, 2006

Transcription

1 Dark Matter and LHC Piero Ullio SISSA & INFN (Trieste) Incontri di Fisica delle Alte Energie 2006 Pavia, April 20, 2006

2 Overwhelming evidence that non-baryonic Dark Matter is the building block of all structures in the Universe: from the first snapshot of the Universe (WMAP, 2003) down to the dynamics in today s galaxies (figure from Bergström, 2000)

3 DM: the particle physicist s perspective The input from large-scale structure (linear regime) is that DM behaves like a collision-less fluid, subject to gravity and with negligible free-streaming effects CDM paradigm preferred, HDM excluded Other info, such as the mass scale, crucial to set a strategy for detection, are not imprinted in the sky, but come in once one focuses on a given DM production scheme. The most beaten tracks have been: i) thermal production of DM ii) DM generated at the end of inflation iii) DM as a condensate in a phase transition

4 CDM particles as thermal relics Freeze-out in the nonrelativistic regime, relic density set by the coupling strength to lighter SM particles: Ω χ h cm 3 s 1 σ A v T =Tf WIMP Jungman, Kamionkowski & Griest, 1996

5 WIMP DM candidates The recipe for WIMP DM is fairly simple. You need to construct an extension to the SM with: i) a new stable massive particle; ii) coupled to SM particles, but with zero electric and color charge; 0 iii) not too strongly coupled to the Z boson (a 4-th generation ν and similar states have already been excluded by direct searches). Then solve the Boltzmann equation and find what is the mass of your LSP, braneworld or KK state, LIMP, LEF, Mirror particle, etc. etc.

6 SuperWIMPs Extend the scenario and suppose that: the WIMP decoupling from thermal equilibrium is unstable and decays to a stable dark matter species which interacts super-weakly and has a negligible (small) thermal component. Examples: gravitino, or axino, or right-handed sneutrino (or...) LSP DM from late decay of thermally produced NLSP: see, e.g., Feng, Rajaraman & Takayama, 2003; Roszkowski & Ruiz de Austri, 2004; Asaka, Ishiwata & Moroi, 2005 Ω LSP M LSP M NLSP Ω NLSP Scenario invoked to fix CDM problems(?) on small scales

7 SuperWIMP DM is undetectable by definition; WIMP DM has instead a very rich phenomenology: Direct detection of local DM WIMPs Indirect detection of DM WIMPs in the halo or center of the Sun!! annihilation into, e.g., a 2-body final state lighter SM particles fragmentation and/or decay process stable species

8 Direct detection: controversial experimental results DAMA final result, Bernabei et al., 2003: Seven years, exposure kg day, 6.3 σ C.L. for a sinusoidally modulated rate; LIBRA taking data at present, with analogous but larger setup. (Signal + background) - t const. term Residuals (cpd/kg/kev) Residuals (cpd/kg/kev) Residuals (cpd/kg/kev) kev I II III IV V VI VII kev Time (day) I II III IV V VI VII kev Time (day) I II III IV V VI VII Time (day)

9 Interpretation in terms of a spin-independent coupling: DAMA final result, Bernabei et al., 2003:!" SI (pb) If e.g. SD contribution # 0 this region goes down m W (GeV)

10 ... not confirmed by competing experiments: latest from the CDMS collaboration, ''!'*-3425%(-6. /%75216&849*:%32%3;*%5<-8*25= IF!GN IF!GJ IF!MF IF!MI IF!M. IF!MG >H#H%IJJK E:*8B*4''%.FFG C*D845!" 0>#?%7)*=%.!A2B*1 0>#?%7?4= L IF LF IFF!"#$%#&''%()*+,-. LFF / Low-mass loophole (?), P.U., Kaminokowski & Vogel, 2001, Gondolo & Gelmini, 2005

11 CDMS Interpretation in terms of a spindependent coupling shaking as well: CRESST I PICASSO CDMS SK NAIAD DAMA final result, with some caveats at several levels

12 For SUSY WIMPs, the coherent term look promising because of interactions mediated by Higgs particles (SD effects are usually negligible): "!-p [ cm 2 ] tan # = 53 EDELWEISS 2002 XENON (projected) ! " 0! # m! [ GeV ] CMSSM, Edsjo, Schelke & P.U., 2004 nmssm, Cerdeño et al., 2004

13 ... but there can be cases in which this pattern is reversed, see, e.g., a model with large Yukawas introduced in EW baryogenesis context: Spin Independent Spin Dependent CDMS II EDELWEISS SuperCDMS -36 CDMS II Log 10 (σ Spin-Ind. /cm 2 ) Log 10 (σ Spin-Dep. /cm 2 ) SuperCDMS m LN (GeV) m LN (GeV) Provenza, Quiros & P.U., 2005

14 ...and when the SD term is large, life for neutrino telescopes becomes easier Induced muon flux (y -1 Km -2 ) Ice-Cube Super-K m LN (GeV) Tightest limits on the model, contrary to the standard lore that direct detection is always better than indirect searches Provenza, Quiros & P.U., 2005

15 Complementarity is the keyword in DM searches! Indirect detection through halo signals may be an option as well: - In general, the largest signal over background is for antiprotons, although in this case the signature is weak; - In principle, antideuterons are very promising (but the required sensitivity is very demanding, far in the future); - The search for gamma-rays (or through lower frequency radiation) is essentially at zero cost and plenty of targets. Note: big steps are being made on the experimental side!

16 for antimatter searches the next step is around the corner: positron charge fraction e+/(e- + e+) MASS 91 CAPRICE 98 CAPRICE 94 HEAT AESOP 94 TRAMP-Si 93 MASS 89 Mueller and Tang 87 Golden et al. 87 Hartman and Pellerin 76 Buffington et al. 75 HEAT 2000 Daugherty et al. 75 Fanselow et al. 69 Agrinier et al. 69 PAMELA 3y kinetic energy (GeV) HEAT excess, fitted by a WIMP DM component, Baltz et al., 2002 Much better statistics with the launch of PAMELA in autumn 2006! Lionetto, Morselli & Zdravković, 2005

17 The next-generation of space-based gamma-ray telescopes is being built: SLAC GLAST, launch in august 2007 Picture from Morselli, /16 Towers in the GRID on 7/10/05 + Agile, AMS, ect.

18 while the next-generation era for ground based instruments has already started: HESS telescope in Namibia, fully operative since Magic, Veritas, Stacee, Cangaroo, etc. ect. Tens of new TeV sources reported in last two years, compared to the 12 sources known up to 2003

19 First VHE map of the Galactic Center by HESS: A source at the position of the central BH, Sgr A* A new plerion discovered HESS map of GC, diffuse emission from the GC region

20 Spectral features of central source/excess: Single power law (Γ 2.2) from 150 GeV to 30 TeV Aharonian et al, 2006 Tentatively: the central source is a Sn remnant and the diffuse emission from in the central region is due to protons injected in the explosion

21 the GC is not any more the best bet for indirect dark matter detection! it is very hard to support the hypothesis that the central source is due to pair annihilation of dark particles, see also, e.g., Bergström, Bringmann, Eriksson & Gustafsson, 2005 E 2 dn/de [TeV m 2 s 1 ] 1e 07 1e 08 H.E.S.S neutralino annihilation fit KK annihilation fit 1e E [TeV] Ripken et al., 2005

22 it might still be that a DM component could be singled out, e.g. the EGRET GC source (?): a DM source can fit the EGRET data; GLAST would detect its spectral and angular signatures and identify without ambiguity such DM source! Aldo Morselli, INFN, Sezione di Roma 2 & Università di Roma Tor Vergata, aldo.morselli@roma2.infn.it Morselli 2005; analysis in Cesarini, Fucito, Lionetto, Morselli & P.U., 2004

23 ... or we may have to rely on alternative targets; recent proposals include: Intermediate-mass BHs, carrying mini-spikes Tens of sources with identical spectrum! Bertone, Zenter & Silk, 2005

24 Multiwalength detection of DM: E.g., the Coma radio halo can be fitted in spectrum and angular surface brightness by a DM induced component: S synch (!) [ Jy ] M " = 81 GeV I synch ("=1.4 GHz) [ mjy ] smooth subhalos M # = 40 GeV B! = B! (r) 10-2 M " = 40 GeV 1 HPBW ! [ MHz ] ! [ arcmin ] Colafrancesco, Profumo & P.U., 2005

25 and in these given setups we predict also:! S(!) [ erg cm -2 s -1 ] M # = 40 GeV synch. EUVE IC SAX GLAST EGRET " brems log (! [ Hz ] ) i) there may be an associated gamma-ray flux within the sensitivity of GLAST ii) the induced SZ shift in the CMB temperature may be within the sensitivity of future experiments

26 Detecting DM WIMPs at LHC? Key point: does the new physics framework we have invoked for a WIMP DM candidate need to contain new particles carrying QCD color as well as the quantum number forcing the WIMP to be stable? In some scenario they exist and they are actually the states supporting a WIMP pair annihilation rate of the order needed at freeze out in the early Universe! At LHC colored states would be produced in pairs, decay to quark or gluon jets plus a WIMP that escapes from the detector: missing energy signature.

27 Example: in a SUSY framework, a squark or gluino with mass < 1 TeV, would be discovered at 1% of the first year LHC luminosity Analogously for any framework with strongly interacting state(s) at 1 TeV appearing together a WIMP state < 1 TeV Gaugino mass g gluino, q squark Scalar mass Tovey, 2002

28 Hard to address the problem LHC versus WIMP DM in a model independent fashion, even at qualitative level: Numerous counterexamples in which no strongly interacting particle is playing a role for the WIMP relic density: possible that dark matter is made of WIMPs but LHC will not find any new heavy colored state. Stage I, no panic: take some guideline for the WIMP framework, such as naturalness for the Higgs, and realize that a weak scale spectrum for additional particles is likely: most often a signature at LHC is recovered. Stage II, panic: maybe the additional guideline for the WIMP framework is manifest just at heavier scale, such as for gauge coupling unification, and life at LHC might be hard (e.g., love and hate for Split SUSY).

29 Unavoidable strategy: focus on a given scenario and discuss its phenomenology Example: CSSM Thin slices in the parameter space selected by the relic density constraint. In any regime check the accuracy in retracing spectrum and relic density of other DM observables. Scalar mass m 0 Bulk Focus point m h, b!s" g-2 m 1/2 Funnel Gaugino mass Stau coann. Battaglia et al. 2001

30 More favorable cases: e.g., bulk region Most superpartners are light and detected at LHC (only heaviest stop, stau and neutralino are not seen in example displayed): fairly accurate prediction for the relic density Relic density Nojiri, Polesello & Tovey, 2006

31 as well as for quantities setting DM WIMPs direct/indirect detection prospects Baltz, Battaglia, Peskin & Wizansky, 2006 Annihilation rate (today) SI scatt. cross section Note: cleaner picture at a LC with 1 TeV c.m.e.

32 less favorable cases: e.g., FP region Even assuming a light M 1/2 (300 GeV), LHC finds only the gluino and 3 neutralinos: the relic density value is poorly reconstructed Relic density Baltz, Battaglia, Peskin & Wizansky, 2006

33 Going to heavier M 1/2, i.e. heavier gluinos, LHC loses sensitivity and the framework might be probed at DM searches only: Baer, Krupovnickas, Profumo & P.U., 2005 LHC sens. limit LC sens. limit Conservative halo profile

34 Even more promising for a less conservative halo profile In the Split SUSY framework detection prospects are analogous, Masiero, Profumo & P.U., 2005

35 Summary The identification of dark matter is one of the most pressing targets in Science today. In a (large) subset of the viable DM scenarios, direct/indirect detection look feasible in the near future. LHC will decisive in discriminating among the scenarios on the market, as well as (possibly) in testing the properties of DM particles. Attacking the problem on the two sides may be the key to solve it!