The Mystery of - Cornell Universitymaxim/talks/CIPT_Fall13_DarkMatter.pdfMaxim Perelstein,...

Maxim Perelstein, LEPP/Cornell U.CIPT Fall Workshop, Ithaca NY, September 28 2013

The Mystery of Dark Matter

WIMP'Direct'Detec,on'Technologies'

•  DualEphase'Ar'(DarkSide,'ArDM):'''''''''Excellent'electron'recoil'rejec,on,'''''''''posi,on'resolu,on.''•  DualEphase'Xe'(XENON,'LUX,'PandaEX):'''''''''Suitable'target'for'both'SI'and'SD,'low'''''''''energy'threshold,'excellent'posi,on'''''''''resolu,on,'selfEshielding.'''•  Scin,lla,ng'crystals'(DAMA/LIBRA,'KIMS):''''''''Annual'modula,on'with'large'target'mass.''•  Ioniza,on'detectors'(CoGeNT,'DAMIC):''''''''Very'low'energy'threshold,'good'energy''''''''resolu,on.'

D.'McKinsey''''''''Direct'Detec,on'

Friday, September 27, 13

• Last Fall workshop focused on physics of the very small - elementary particles

• This time, we’ll talk about very large - astronomical - distance scales

• ... and some interesting connections between the two!

Introduction


Distances in the Universe

Earth10^7 m

Galaxy10^21 mSolar

System10^12 m

Cluster ofGalaxies10^23 m

“Visible Universe”10^26 m

Evidence for Dark Matter comes from these scales


Measuring Distances


Doppler Effect in Astronomy

• Analyze spectra of light from distant stars/galaxies

• Identify absorption (or emission) line patterns of familiar elements observed on Earth

• Overall shift of lines - Doppler effect - allows to determine relative velocity of the star/galaxy with respect to Earth


Expanding Universe• Light from all distant galaxies is

redshifted they are running away from us! (Hubble, 1930’s)

• Picture: Universe is like an expanding gas of galaxies

• Note: Uniformly expanding gas has no “center” - any observer (far away from the walls) would see the same picture!

Extrapolate back in time: there was a time when density was “infinite” - BIG BANG!


Universe: Infinite or Finite?

Big Bang Theory:Age = 14 billion years

“horizon”: signals sent from here 14 bln years ago are just reaching us now

(R ~ 10^26 m)

Light: c=3*10^8 m/sec

You Are Here

“visible universe”:inside the horizon

“Inaccessible universe”: outside the horizon. Finite? Not? We have no way to tell.


Evidence for DM on the Galactic Scale

Most galaxies (including ours) are orbited by “satellites”, much like

Sun is orbited by planets.

Satellites are just baby galaxies.


“Rotation Curves” Predicted

Newton’s law of gravitation


Rotation Curves Observed

Kuzio de Naray et al, The Astrophysical Journal Letters, Volume 710, L161-L166 (2010)

Kuzio de Naray et al, The Astrophysical Journal Supplement Series, 165, 461-479 (2006)

The plateau in rotation speed as the distance from the center increases is the evidence for dark matter in spiral galaxies. The fact that spiral galaxies don’t show a decline in rotation speed became widely accepted in the early 80’s.

To the right, velocity field and rotation curve of F583-1; this galaxy is 32 Mpc away and has low surface brightness (dark matter dominates).

The Case Against Warm Dark Matter 3

Fig. 1.— Observed LSB galaxy rotation curves with the best-fitting early decay dark matter (! = 3: solid red, ! = 4: dotted orange)and thermal WDM (! = 1: short-dash blue; ! = 2: long-dash green) halo fits overlaid. (A color version of this figure is available in theonline journal.)

TABLE 1Best-Fit Cored Halo Parameters and Primordial Phase Space Densities

Early Decay DM ! = 3 Early Decay DM ! = 4Galaxy rcore "0 #2

rQp rcore "0 #2

rQp Mtot

UGC 4325 4.6a 106b 3.1 · · · 4.6a 106b 3.1 · · · · · ·

F563-V2 1.1±0.1 188±30 0.65 4.8 1.3±0.2 167±25 0.74 5.9 9.8F563-1 1.4±0.1 106±16 0.50 3.2 1.8±0.1 90±12 0.50 3.1 14DDO 64 2.7a 57b 3.3 · · · 2.7a 57b 3.3 · · · · · ·

F568-3 2.8±0.4 40±6 1.5 0.71 3.0±0.4 38±5 1.4 1.0 28UGC 5750 4.3±0.7 11±1 0.92 0.42 4.8±0.8 10±1 0.89 0.53 30NGC 4395 0.6±0.1 346±42 2.6 21 0.7±0.1 278±33 3.0 29 2.6F583-4 0.9±0.1 98±22 0.59 13 1.1±0.2 82±18 0.68 14 2.9F583-1 1.7±0.1 48±4 0.58 2.9 2.1±0.2 43±3 0.54 2.9 11

Thermal WDM ! = 1 Thermal WDM ! = 2Galaxy rcore "0 #2

rQp rcore "0 #2

rQp Mtot

UGC 4325 4.1±1.0 88±6 3.1 · · · 4.3±1.0 90±5 3.1 · · · · · ·

F563-V2 1.5±0.2 118±18 0.71 72 2.5±0.2 93±14 1.4 14 4.3F563-1 2.1±0.2 66±9 0.43 35 3.8±0.2 47±6 0.69 5.9 7.3DDO 64 2.7a 45b 3.1 · · · 2.7a 47b 3.1 · · · · · ·

F568-3 3.8±0.4 27±3 1.2 9.3 5.0±0.4 25±2 1.1 3.4 9.2UGC 5750 5.7±0.8 7.1±0.7 0.83 5.4 7.1±0.7 7.0±0.2 0.74 2.4 6.9NGC 4395 0.7±0.1 262±34 2.9 478 1.7±0.1 121±16 5.1 42 1.7F583-4 1.3±0.2 66±16 0.67 149 2.4±0.3 38±8 1.2 26 1.5F583-1 2.5±0.2 30±2 0.50 31 4.0±0.2 22±1 0.77 7.0 4.2

Note. — Best-fit halo parameters (rcore, !0), lower limits on the primordial phasespace densities (Qp), and the total mass of the system, Mtot. The units for rcore arekpc and the units for !0 are 10!3 M" pc!3. The units for Qp are 10!9 M" pc!3 (kms!1)!3. The units for Mtot are 1010M".a upper limitb lower limit

Bosma and van der Kruit, Astronomy and Astrophysics, vol. 79, Nov. 1979, p. 281-286

Rubin, Ford and Thonnard, Astrophysical Journal, vol. 238, June 1, 1980, p. 471-487

Rotation speed and dark matter in galaxies

Sunday, July 28, 13 Two Possible Conclusions:

Newton’s Law of Gravity is wrong

at large distances

OR...

Visible galaxy is surrounded by

gravitating“dark matter”

? NO!


Dark Matter “Halo”

v independent of R implies


Gravitational Lensing

• Einstein’s General Relativity: any gravitating mass should bend light

• Massive objects between source and observer can act as “gravitational lenses”

• Observation of lensing provides information about the mass of the lens - a way to “weigh” distant galaxies


Weak Lensing

• Distortion of shapes of distant sources

• Allows to map spatial profile, or distribution, of mass in the distant galaxy (or cluster of galaxies) that acted as the lens


Evidence for DM: Bullet Cluster

Observation: profile of gravitating mass is NOT the same as the profile of visible (luminous) mass

direct evidence for the existence of dark matter

inconsistent with modifications of Newton’s law

No. 2, 2006 DIRECT EMPIRICAL PROOF OF EXISTENCE OF DARK MATTER L111

Fig. 1.—Left panel: Color image from the Magellan images of the merging cluster 1E 0657!558, with the white bar indicating 200 kpc at the distance of thecluster. Right panel: 500 ks Chandra image of the cluster. Shown in green contours in both panels are the weak-lensing k reconstructions, with the outer contourlevels at k p 0.16 and increasing in steps of 0.07. The white contours show the errors on the positions of the k peaks and correspond to 68.3%, 95.5%, and99.7% confidence levels. The blue plus signs show the locations of the centers used to measure the masses of the plasma clouds in Table 2.

TABLE 2Component Masses

ComponentR.A.(J2000)

Decl.(J2000)

MX(1012 M,)

M!(1012 M,) k̄

Main cluster BCG . . . . . . . . 06 58 35.3 !55 56 56.3 5.5 ! 0.6 0.54 ! 0.08 0.36 ! 0.06Main cluster plasma . . . . . . 06 58 30.2 !55 56 35.9 6.6 ! 0.7 0.23 ! 0.02 0.05 ! 0.06Subcluster BCG . . . . . . . . . . 06 58 16.0 !55 56 35.1 2.7 ! 0.3 0.58 ! 0.09 0.20 ! 0.05Subcluster plasma . . . . . . . . 06 58 21.2 !55 56 30.0 5.8 ! 0.6 0.12 ! 0.01 0.02 ! 0.06

Notes.—Units of right ascension are hours, minutes, and seconds, and units of declination are degrees,arcminutes, and arcseconds. All values are calculated by averaging over an aperture of 100 kpc radiusaround the given position (marked with blue plus signs for the centers of the plasma clouds in Fig. 1);measurements for the plasma clouds are the residuals left over after the subtraction of the circularlyk̄

symmetric profiles centered on the BCGs.

Both peaks are offset from their respective BCGs by "2 j but arewithin 1 j of the luminosity centroid of the respective component’sgalaxies (both BCGs are slightly offset from the center of galaxyconcentrations). Both peaks are also offset at "8 j from the centerof mass of their respective plasma clouds. They are skewed towardthe plasma clouds, and this is expected because the plasma con-tributes about one-tenth of the total cluster mass (Allen et al. 2002;Vikhlinin et al. 2006) and a higher fraction in nonstandard gravitymodels without dark matter. The skew in each k peak toward theX-ray plasma is significant even after correcting for the overlap-ping wings of the other peak, and the degree of skewness isconsistent with the X-ray plasma contributing of the ob-"9%14%!8%served k in the main cluster and in the subcluster (see"12%10%!10%Table 2). Because of the large size of the reconstruction (34! or9Mpc on a side), the change in k due to themass-sheet degeneracyshould be less than 1%, and any systematic effects on the centroidand skewness of the peaks are much smaller than the measurederror bars.The projected cluster galaxy stellar mass and plasma mass

within 100 kpc apertures centered on the BCGs and X-rayplasma peaks are shown in Table 2. This aperture size waschosen because smaller apertures had significantly higher kmeasurement errors and because larger apertures resulted in asignificant overlap of the apertures. Plasma masses were com-puted from a multicomponent three-dimensional cluster modelfit to the Chandra X-ray image (details of this fit will be givenelsewhere). The emission in the Chandra energy band (mostlyoptically thin thermal bremsstrahlung) is proportional to thesquare of the plasma density, with a small correction for the

plasma temperature (also measured from the X-ray spectra),which gives the plasma mass. Because of the simplicity of thiscluster’s geometry, especially at the location of the subcluster,this mass estimate is quite robust (to a 10% accuracy).Stellar masses are calculated from the I-band luminosity of

all galaxies equal in brightness or fainter than the componentBCG. The luminosities were converted into mass by assuming(Kauffmann et al. 2003) . The assumed mass-to-lightM/L p 2Iratio is highly uncertain (and can vary between 0.5 and 3) anddepends on the history of the recent star formation of the gal-axies in the apertures; however, even in the case of an extremedeviation, the X-ray plasma is still the dominant baryonic com-ponent in all of the apertures. The quoted errors are only theerrors on measuring the luminosity and do not include theuncertainty in the assumed mass-to-light ratio. Because we didnot apply a color selection to the galaxies, these measurementsare an upper limit on the stellar mass since they include con-tributions from galaxies not affiliated with the cluster.The mean k at each BCG was calculated by fitting a two-

peak model, each peak circularly symmetric, to the reconstruc-tion and subtracting the contribution of the other peak at thatdistance. The mean k for each plasma cloud is the excess kafter subtracting off the values for both peaks.The total of the two visible mass components of the sub-

cluster is greater by a factor of 2 at the plasma peak than atthe BCG; however, the center of the lensing mass is locatednear the BCG. The difference in the baryonic mass betweenthese two positions would be even greater if we excluded thecontribution of the nonpeaked plasma component between the


Summary So Far• Motion of galactic satellites breakdown of Newton’s law OR extra

matter, gravitating but invisible (“dark”)

• Gravitational lensing must be dark matter

• Some possibilities: Huge hydrogen clouds? Non-luminous star remnants? Black holes? Sub-stellar mass objects (e.g. “MACHOs”)?

• The answer turns out to be much more exciting - stay tuned!


More Evidence for DM:Echoes from the Early Universe

“Nucleosynthesis”: protons+neutrons

combined to form He, Li, B, ...

“Recombination”: protons+electrons

combined to form atoms


Cosmic Microwave Background

• In the early universe, photons are part of “charged plasma” - a hot gas, at a temperature of about 4000 K at recombination

• After recombination, photons no longer interact - “decouple” - and they come straight to us and can be observed! Provide direct information about conditions in the Universe “just” 400,000 yrs after Big Bang.

Light: c=3*10^8 m/sec

You Are Here


CMB:Observations• Observing CMB: see Michael Niemack’s talk and lab tour later today

• Photon energy can be measured, and is simply related to the temperature of the gas at the time when it decoupled, in the place where it comes from

• First conclusion: Universe at 400,000 years of age was remarkably homogeneous - no big lumps!

• But subtle variations in energy (at the level of 1 part in 100,000) exist, indicating tiny inhomogeneities in the primordial plasma


CMB:Observations• Details of CMB inhomogeneities contain a wealth of information about

properties of the Universe (average on very large distance scales)

• Since their discovery in 1992 by the COBE satellite, measuring and interpreting the CMB inhomogeneities has been a major research program

• Now we know (among other things): the total (average) density of the Universe, and the total (average) density of ordinary matter (protons, neutrons, electrons).

1992 2003 2013


Weighing the Universe • Space can be “curved”: e.g. a 2D world on a

sphere

• In curved space, parallel lines can meet, and triangle angles do not add up to 180

• What about our 3D space? On everyday distance scales, experience suggests it is flat

• At cosmological scales (~10^26 m), this is an experimental question, which was only answered recently, by studying CMB

• Einstein’s General Relativity connects the average density of energy (or mass) in the Universe to the curvature:

FLATCLOSED

OPEN


CMB:Curvature Determination

• Need an object of a known size, at a known distance from us

• Measure its apparent size infer bending of light rays infer curvature

• The size of hot/cold spots in the primordial gas at recombination time provides just such an object!


CMB:Curvature Determination

• Need an object of a known size, at a known distance from us

• Measure its apparent size infer bending of light rays infer curvature

• The size of hot/cold spots in the primordial gas at recombination time provides just such an object!

The Universe Is Flat:Friday, September 27, 13

“Normal” Matter Density

• All matter on Earth consists of: protons, neutrons, electrons, photons, neutrinos

• Almost all mass is contained in protons and neutrons:

• CMB hot/cold spot pattern provides information about the density of these particles at recombination time

• Independent verification is provided by measurements of abundances of He, Li, B, etc., which are related to proton and neutron densities by the theory of nucleosynthesis




“Normal” Matter Density

• All matter on Earth consists of: protons, neutrons, electrons, photons, neutrinos

• Almost all mass is contained in protons and neutrons:

• CMB hot/cold spot pattern provides information about the density of these particles at recombination time

• Independent verification is provided by measurements of abundances of He, Li, B, etc., which are related to proton and neutron densities by the theory of nucleosynthesis



Normal Matter is 4% of the TotalFriday, September 27, 13

What Is the Universe Made Of?

• 96% of the Universe is “Dark”: Dark Matter and Dark Energy (DE is topic for another day!)

• Dark matter CANNOT be gas, small stars, MACHOs, etc. - all those things are made of protons, neutrons, and electrons, while DM is NOT!


DM and Particle Physics

• Particle physicists love their “Standard Model”, considered a great triumph of physics [see my Fall’12 CIPT talk]

• Most particles in the SM are highly unstable - cannot account for DM

• Only stable particle that’s not constrained by 4% is neutrino, but they are too light to be DM

• Conclusion: DM must be made out of NEW, as yet undiscovered particles!!!

• DM particle must be electrically neutral, and interact only weakly with ordinary matterDM?


Example: Supersymmetry

• Supersymmetry is the idea that each SM particle has a new, much heavier (but still tiny) particle associated with it - “superpartner”

• In simple models, the lightest supersymmetric particle - LSP - is stable

• If electrically neutral, it can be dark matter!

“DM Candidates”


Dark Matter and Colliders

• High-energy colliders, such as the Large Hadron Collider (LHC), can produce new dark matter particles!

• Signature in the detector: “missing momentum”

• Not observed so far - another chance in the next LHC run, in 2015-18

Large Hadron Collider (LHC) at CERN (Geneva, Switzerland)

Saturday, October 27, 2012

Detectors at the LHC

ATLAS Detector

Saturday, October 27, 2012

collider detector

“event”: DM production(computer simulation)


Dark Matter Underground• There’s dark matter all around us!

• Density depends on the mass of the DM particle: e.g. for SUSY dark matter, expect about 1 per coffee cup

• DM particles can scatter on ordinary nuclei, deposit (small) energy

• Detecting requires going deep underground (to shield from cosmic rays), low temperatures (to suppress thermal noise), and large detectors (to increase signal rates)

• Many experiments around the world - the hunt is on!

WIMP'Direct'Detec,on'Technologies'

•  DualEphase'Ar'(DarkSide,'ArDM):'''''''''Excellent'electron'recoil'rejec,on,'''''''''posi,on'resolu,on.''•  DualEphase'Xe'(XENON,'LUX,'PandaEX):'''''''''Suitable'target'for'both'SI'and'SD,'low'''''''''energy'threshold,'excellent'posi,on'''''''''resolu,on,'selfEshielding.'''•  Scin,lla,ng'crystals'(DAMA/LIBRA,'KIMS):''''''''Annual'modula,on'with'large'target'mass.''•  Ioniza,on'detectors'(CoGeNT,'DAMIC):''''''''Very'low'energy'threshold,'good'energy''''''''resolu,on.'



Direct DM Searches

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WIMP-NucleonsSI@cm

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Ê Cryogenic Detectors

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…'and'this'progress'is'expected'to'con,nue.'



Dark Matter in the Sky! !

1

Snowmass 2013 CF2: Indirect Detection James Buckley

Indirect Detection Fermi VERITAS

Super K

AMSPAMELA

Super-K ICECUBE

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e�, e+, p, p̄

! !

1


Indirect Detection Fermi VERITAS

Super K

AMSPAMELA

Super-K ICECUBE

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Cosmic Positrons! !

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Positron Results

• Pamela results on positron excess are now confirmation by Fermi (using geomagnetic field) and AMS result.

• Signal may also be explained by some cosmic-ray propagation models, or by astrophysical sources such as pulsars.

• A DM interpretation requires a combined astrophysical/particle physics boost of 100 or more.

New dark sector force carrier giving a Sommerfeld enhancement, hadronic channels kinematically inaccessible (e.g., Arkani-Hamed, Finkbeiner, Slayter and Weiner, 1999, PRD 79, 015014)

“standard astrophysics” prediction

data

data consistent with DM origin of the excess,

although more prosaic explanations (e.g. pulsars)

are also possible


Conclusions• Evidence for dark matter comes from dynamics of

galaxies, gravitational lensing, and cosmic microwave background

• The scientific case for existence of dark matter is rock-solid. It makes ~25% of mass in the Universe

• It cannot be made of known elementary particles

• Theories of new elementary particles often have dark matter candidates, e.g. supersymmetry

• The hunt is on for the DM particle: at colliders, underground, and in the sky

• Stay Tuned!Friday, September 27, 13

The Mystery of - Cornell Universitymaxim/talks/CIPT_Fall13_DarkMatter.pdfMaxim Perelstein,...

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