How Do We Know Antimatter is Absent?

Transcription

1 How Do We Know Antimatter is Absent? EGRET, >100 MeV P.Coppi, Yale

2 Outline I. Why do we care about antimatter, or the lack thereof, in our universe? II. Local constraints on antimatter. III. Aside: why local secondary antimatter is still interesting IV. So not much is around today, but what about in the past: cosmological constraints on baryogenesis models V. Summary

3 Detection of Annihilation Gamma- Rays Release of energy by Matter-Antimatter annihilation very efficient Makes lots of gamma-rays Big problem: even with horrible gamma-ray detectors of the early 1970s they should have been seen Run through Steigman (1976) review, still valid today (constraints are even tighter!)

4

5

6 he Diffuse Extragalactic Background Energetic Particles! Henry 1999

7

8

9

10

11

12

13 Direct Detection of Antimatter Especially interesting is detection of Z>2 anti-nuclei: can t make by cosmic ray interactions or primordial nucleosynthesis Nothing seen yet despite lots of looking [See Bob Streitmatter s talk ] Stay tuned for AMS-02 (if it ever gets onto ISS)

14 Gal. Diffuse Emission, Accel. Sites, and CR Propagation - Interplay of CR, ISM and B-field - Escaping proton Accel. sites (SNR, pulsar) Star light (rad. field) π 0 production (direct + decay) in GMC Trapped proton Escaping electron Galactic Ridge Trapped electron Synch. rad. (radio) IC at accel site (X-γ) IC by elect (X-γ) π 0 prod (γ) Brems. (X-γ) Galactic Halo Earth

15 Selected Results (Balloons) - BESS Antideuteron upper limit 1.92 x 10-4 (m 2 s sr GeV/n) -1 measured during flights from D. Haas La Thuile, March 2004, page 41

16 Why care about secondary antimatter?

17 Significant antimatter is indeed observed in our Galaxy!

18 Prior OSSE result: the fountain of death

19 Searching for dark matter The lightest super-symmetric particle χ is a leading candidate for nonbaryonic CDM It is neutral (hence neutralino) and stable if R-parity is not violated It self-annihilates in two ways: χχ γγ where Eγ = Mχ c 2 χχ Ζγ where Eγ = Mχ c 2 (1 M z2 /4M χ2 ) Gamma-ray lines possible 30 GeV - 10 TeV X X q q or γγ or Zγ lines? GLAST EGRET Unresolved AGNs WIMPs Total

20 Thermal Relic DM Particles 1) Initially, DM is in thermal equilibrium: χχ f f 2) Universe cools: N = N EQ ~ e m/t 3) χs freeze out : N ~ const

21 Exponential drop Freeze out Final N fixed by annihilation cross section: Ω DM ~ 0.1 (σ weak /σ Α ) Remarkable! 13 Gyr later, Martha Stewart sells ImClone stock the next day, stock plummets Coincidences? Maybe, but worth serious investigation!

22 No-Lose Theorem: Loophole Assume gravitino is LSP. Early universe behaves as usual, WIMP freezes out with desired thermal relic density WIMP G M Pl2 /M W3 ~ year A year passes then all WIMPs decay to gravitinos Gravitinos naturally inherit the right density, but escape all searches they are superweakly-interacting superwimps

23 No-Lose Theorem: Loophole Assume gravitino is LSP. Early universe behaves as usual, WIMP freezes out with desired thermal relic density WIMP G M Pl2 /M W3 ~ year A year passes then all WIMPs decay to gravitinos Gravitinos naturally inherit the right density, but escape all searches they are superweakly-interacting superwimps

24 Cosmological Constraints: Depending on when excess antimatter is present still lying around (reheating, nucleosynthesis epoch, recombination epoch ), there can be significant consequences: CMB distortions BBN anomalies Excess diffuse background

25

26 WMAP: Measurement of 10-5 fluctuations on the entire sky to ~0.25

27

28

29

30

31

32

33

34

35

36 Can you separate baryons from anti - baryons in standard large scale structure formation scenarios? NO!

37 ilk Damping. No structure (voids) around ecombination at _today < 15 Mpc => w/out CDM, nly top-down alaxy formation)

38

39 What if there are a few odd antimatter domains still annihilating away today that somehow got missed? Can use CMB again: Sunyaev-Zeldovich effect!

40 Sunyaev-Zel dovich Effect Decrement Observations at 1 cm or 30 GHz» Cluster appears as a cool spot in CMB» This CMB temperature decrement has an amplitude of ~1 mk, a few parts in 10,000 of the CMB anisotropies» This cluster distortion is many times stronger than the primary anisotropies in the CMB» The decrement is independent of the distance of the cluster Change in CMB Temperature [µkelvin] Lower mass cluster Decrement Increment Massive cluster Observations made here Observing Frequency [GHz] Temperature map of the microwave background toward one of the most distant known galaxy clusters» Coolest temperatures are red» Hottest temperatures are blue» Contours are spaced by 2 sigma» Central decrement is ~1/1,000 Kelvin

41 New Galaxy Clusters from the Survey SZE Survey will provide many more distant clusters in one month than all previous work combined One year survey» 12 deg 2 mapped» if favored model correct ~500 total clusters ~400 distant clusters at lookback times corresponding to half the age of the Universe or more ~150 clusters at distances greater than today s most distant known galaxy cluster Exceedingly strong test of structure formation models Total Number of Clusters Beyond a Distance Cluster Yield from SZE Survey (Best X-ray survey to date) Distance Most distant known clusters Figure from Holder et al. in prep Age: t H t H 2 t H 3 t H 4

42 Don t mess with Big Bang Nucleosynthesis! Very constrained now with WMAP

43

44

45

46

47 Blazars=EGRB? Not obvious! Unpleasant surprise for GLAST? (source count prediction too optimistic?) Integral Flux (E>100 MeV) cm -2 s -1 Pohl et al. 1997

48 Degenerate Big Bang Nucleosynthesis BBN Allowed Using the observed abundances of D, 4 He, and 7 Li alone, CMB BBN is very pliable to allow large neutrino asymmetries CMB Allowed BBN Allowed Due to cancelling effects between ν µ/τ and ν e, and baryon density, Ω b h 2 Orito et al 02 astro-ph/

49 The Death of Degenerate BBN and New Constraints Allowed CMB Allowed: BBN + LMA+Atm Allowed Allowed

50 Some further comments on the cosmological X-ray/gamma-ray background X-ray background could have been diffuse hot gas (except for CMB problems), but it is now resolved into (many!) AGN (accreting black holes) What about gamma-ray background? TBD

51 The gamma-ray background Ormes 2002, GLAST presentation

52 CDF-N/GOODS, 2Msec(!) Chandra Diffuse X-Ray Background CDF-S

53 Proposed EGRB Sources Blazar AGN (known) Cosmic Rays in Galaxies (probably not enough luminosity, caveat: starbursts) Converging Velocity Flows/Shocks in Large Scale Structure Formation (e.g., merging clusters possible evidence) Exotica (topological defects, neutralinos, cascading, matter-antimatter annihilation?)

54 ean free path or VHE photons Absorption (pair production) and Cascading important for cosmological VHE sources. Coppi & Aharonian 1997

55 he cascade pectrum from cosmological opulation of HE sources ndependent of rimary source pectrum for >10 TeV! nz ( ) (1 + z) 3 nz ( ) (1 + z) nz ( ) (1 + z) 0 6 Coppi & Aharonian 1997

56 Response to Change in IR/O Background GeV background measurement = calorimeter for VHE universe! Coppi & Aharonian 1997

57

58

59

60 [B=0]

61 on t orget ascades! Blazar Background Models, a la Stecker & Salamon 1996 Including IR/O absorption Coppi & Aharonian 1997

62 Most sources can think of, even decaying/annihilating CDM particles, trace large scale structure look for clustering signal! Bromm et al. 2003

63 Will the true extragalactic gamma-ray background please stand up? EGRET All-Sky Map, E>100 MeV

64 The problem: even looking towards the Galactic poles see evidence of energetic particles and target matter! Synchrotron Hydrogen Column (N H ) Keshet et al. 2003

65 The big unknown: Inverse Compton emission from halo cosmic ray electrons Discrepancy!

66 Strong et al., 2003, astro-ph/ So, let s make things fit by jiggling I.C. component Keshet, Loeb, & Waxman (2003) I ( E > 100 MeV) [integral flux] γ σ < ph cm sec sr (3 )!

67 An alternative (mundane particle physics) explanation GeV Excess Explained? No.1/2 Gamma-rays from π0 alone. L=(-30,30) B=(-5,5) EGRET Intensity Map Model A (MSOP02) What? Model A (LIS) The peak moves to ~800MeV Prediction of Scaling Models July 20, 2004 SLAC Experimental Seminar

68 GeV Excess Explained? No.2/2 Combined with Brems and Inverse-Compton (Galprop) L=(-30,30) B=(-5,5) EGRET Intensity Map Explains about 50% of the Excess with LIS. Explains the Excess fully with MSOP02. Model A (MOSP02) Model A (LIS) Scaling Models July 20, 2004 SLAC Experimental Seminar

69 de Boer et al Anomalies in e+ and p-bar? No.1/2 Neutralino decay to γ-ray? Neutralino decay to p-bar? July 20, 2004 SLAC Experimental Seminar

70 Anomalies in e+ and p-bar? No.2/2 Measurement by HEAT collaboration (e+ spectrum by a series of balloon exp.) de Boer et al July 20, 2004 SLAC Experimental Seminar

71 Model A Prediction on p-bar Spectrum Exp. data Model A vs. Scaling Model Scaling model with LIS July 20, 2004 SLAC Experimental Seminar

72 Model A Prediction on Positrons Spectrum Diffractive process favors e+ over e- Non-Diffractive process dominates overall spectrum e+ e- July 20, 2004 SLAC Experimental Seminar

73 1. Accurate modeling of p(α)-ism interaction is likely to explain the GeV Excess with minor modification in the cosmic proton (α) spectrum. 2. Excess in anti-proton flux will naturally be explained by the scaling violation. 3. Excess in e+ flux for E > 5 GeV may be explained by inclusion of diffractive process. 4. With much improved data from GLAST, we can turn Galaxy to a HEP and Astorphysics laboratory. July 20, 2004 SLAC Experimental Seminar

74 Summary: Like the standard model in particle physics, we have a good cosmological model (inflation + reheating & adiabatic perturbations + CDM + gravitational instability) that explains a lot of data Like the standard model, it s phenomenological and missing lots of key ingredients, e.g., baryogenesis But whatever you decide to do fix it, it has to be pretty subtle lots of constraints! Occam s razor: antimatter gone before nucleosynthesis epoch => null searches (but you never know )