Multimessenger observations of neutron rich matter

Transcription

1 Multimessenger observations of neutron rich matter Brian Alder 208 Pb Introduction: neutrino and gravitational wave probes of neutron rich matter. PREX at Jefferson Laboratory uses parity violating electron scattering to accurately measure the neutron radius of 208 Pb. Description of exp. and first results. Implications of neutron radius for: Nuclear theory and three neutron forces. Astrophysics and neutron star radii. Follow on parity measurements. C. J. Horowitz, IU and MSU, WCU/Hanyang-APCTP Focus Program, Effective field theories, halos, driplines and EoS for compact stars, Pohang, Korea, Apr. 2012

2 Neutron Rich Matter Compress almost anything to g/cm 3 and electrons react with protons to make neutron rich matter. This material is at the heart of many fundamental questions in nuclear physics and astrophysics. What are the high density phases of QCD? Where did the chemical elements come from? What is the structure of many compact and energetic objects in the heavens, and what determines their electromagnetic, neutrino, and gravitational-wave radiations? Interested in neutron rich matter over a tremendous range of density and temperature were it can be a gas, liquid, solid, plasma, liquid crystal (nuclear pasta), superconductor (Tc=10 10 K!), superfluid, color superconductor... Focus on simpler liquid, solid, and gas phases. Supernova remanent Cassiopea A in X-rays MD simulation of Nuclear Pasta with 100,000 nucleons

3 Probes of Neutron Rich Matter Multi-Messenger Astronomy: seeing the same event with very different probes should lead to fundamental advances. Often photons from solid neutron star crust, supernova neutrinos from low density gas, and gravitational waves from energetic motions of liquid interior of neutron stars. Laboratory: Nuclei are liquid drops so most experiments probe liquid n rich matter. However one can also study vapor phase be evaporating nucleons. Electroweak measurements, Heavy ion collisions, Radioactive beams of neutron rich nuclei... Computational: Important theoretical and computational advances aid in study of n rich matter. Chiral effective field theory depends on important and poorly known three neutron forces. Large scale computations: molecular dynamics, monte carlo, no core shell model, coupled cluster, Review article: Multi-messenger observations of neutron rich matter, Int. J. Mod. Phys. E 20 (2011) 1.

4 It s the same stuff in the laboratory and in the heavens For Newton the stuff was mass. In 19th century it was spectral lines. Gave birth to astrophysics and the very name of the 2nd element helium. Today the stuff is neutron rich matter. In astrophysics and in the laboratory it is the same neutrons, the same strong interactions, and the same equation of state. A measurement in one domain (astronomy or the lab) has important implications in the other domain.

5 Neutrino probes of neutron-rich matter Sun in neutrinos Supernova neutrinos carry unique flavor information (some what complicated by oscillations) that may be closely related to nucleosyntheis. New underground dark matter, solar nu,... experiments will be very sensitive to nu from the next galactic supernova (SN). Example: ton scale dark matter detectors very sensitive to SN neutrinos via nu-nucleus elastic scattering. Provides info on mu/ tau nu spectra not available in Super-K. [CJH, K. Coakley, D. McKinsey, PRD68(2003)023005] Neutrinos are emitted from the low density ~10 11 g/cm 3 neutrino-sphere region. This gas phase can be described with a Virial expansion [CJH, A. Schwenk, NPA776(2006)55] and studied in the lab with HI collisions.

6 Neutrinos and r-process Nucleosynthesis Half of heavy elements (including gold) are believed made in the rapid neutron capture process. Here seed nuclei rapidly capture many neutrons. The present best site for the r-process is the neutrino driven wind in core collapse SN. Nucleosynthesis depends on ratio of neutrons to protons, this is set by capture rates that depend on neutrino / anti-neutrino energies ν e + n p + e ν e + p n + e + Measure ΔE, difference in average energy for antineutrinos and neutrinos. If ΔE is large, wind will be neutron rich. If ΔE is small, wind will be proton rich and likely a problem for r-process. Hint of problem from SN1987a -- PRD65 (2002) SN is best site but simulations find too few neutrons, entropy is too low, time scale is wrong. Very interesting work on neutron star mergers as alternative r-process site. Searching for El Dorado with supernova neutrinos

7 Recreating Neutrinosphere on Earth Neutrinos from neutrinosphere: warm, low density gas (T~4 MeV, ~10 11 g/cm 3 ) Neutron rich system with some light nuclei 4 He, 3 He, 3 H... Light nuclei reduce anti-nu-e, but not nu-e, opacity--> important for ΔE. Can study neutrinosphere like conditions with heavy ion collisions in lab. and measure composition of light nuclei. [example J. Natowitz, Texas A&M] Neutron-neutron scattering length is very long--> nearly universal unitary gas. Can simulate neutrinosphere like systems with trapped cold atoms. Probe spin response important for neutrino interactions. Composition of intermediate velocity fragments in HI collisions: Data (blue squares) Kowalski et al, PRC 75, (2007). Our virial EOS is black. Target Projectile In a peripheral HI collision, intermediate velocity fragments from warm low density region. Intermediate velocity fragments

8 Gravitational waves and neutron rich matter We anticipate the historic detection of gravitational waves (osc. of space-time) in ~ 2016 with operation of Advanced LIGO. Gravitational waves provide info on n rich matter: Neutron star mergers --> Eq. of state. Collective r-mode osc of rotating NS --> dissipation from shear and bulk viscosity. Mountains on rotating NS depend on shear modulus/ breaking strain of NS crust. First detection likely from NS mergers. Advanced LIGO has ~10 times sensitivity of LIGO, sensitive to 1000 times volume. Rate very likely more than few/yr. LIGO Hanford

9 Gravitational Waves from NS mergers and EOS Merger of two 1.35 Msun NS MIT60 LS180 LS220 FSU2.1 LS375 NL3 HShen H Frequency of peak GW signal correlated with radius of max. mass star. A. Bauswein + H. T. Janka

10 Gravitational Waves from NS mergers and EOS Merger of two 1.35 Msun NS MIT60 LS180 LS220 FSU2.1 LS375 NL3 HShen H Frequency of peak GW signal correlated with radius of max. mass star. A. Bauswein + H. T. Janka

11 Gravitational Waves from NS mergers and EOS Merger of two 1.35 Msun NS MIT60 LS180 LS220 New full astrophysical equation of state tables by G. Shen + CJH based on large scale relativistic mean field calculations at high density and a virial expansion with light clusters + thousands of heavy Hnuclei at low densities: PRC 83, (2011). FSU2.1 LS375 NL3 HShen Frequency of peak GW signal correlated with radius of max. mass star. A. Bauswein + H. T. Janka

12 Gravitational Waves from NS mergers and EOS Merger of two 1.35 Msun NS MIT60 LS180 LS220 New full astrophysical equation of state tables by G. Shen + CJH based on large scale relativistic mean field calculations at high density and a virial expansion with light clusters + thousands of heavy Hnuclei at low densities: PRC 83, (2011). FSU2.1 LS375 NL3 HShen Frequency of peak GW signal correlated with radius of max. mass star. A. Bauswein + H. T. Janka

13 Gravitational Waves from NS mergers and EOS Merger of two 1.35 Msun NS MIT60 LS180 LS220 New full astrophysical equation of state tables by G. Shen + CJH based on large scale relativistic mean field calculations at high density and a virial expansion with light clusters + thousands of heavy Hnuclei at low densities: PRC 83, (2011). FSU2.1 LS375 NL3 HShen Frequency of peak GW signal correlated with radius of max. mass star. A. Bauswein + H. T. Janka

14 Continuous Gravitational Wave Sources and Neutron Star Crust Consider a large mountain (red) on a rapidly rotating neutron star. Gravity from the mountain causes space-time to oscillate, radiating gravitational waves. Fundamental question: how do you support the mountain? Strong GW source (at LIGO, VIRGO frequencies) places extraordinary demands on neutron rich matter, and stress matter to limit. -- Put a mass on a stick and shake vigorously. -- May need both a large mass and a strong stick. -- Let me talk about the strong stick. General Relativity asks fundamental (astro-)material science questions! Not just how strong is this material but what is the strongest possible material. Mountain involves large mass undergoing large accelerations. Source can t be much larger and still radiate at 10+ Hz.

15 Neutron Star Quadrupole Moments and Gravitational Waves Mountain on a rotating NS very efficiently radiate GW. Maximum size of mountain depends on strength of NS crust. We perform large scale MD simulations of the crust breaking including effects of defects, impurities, and grain boundaries... We find neutron star crust is strongest material known:10 10 times stronger than steel. Can support few cm tall mountains! Ongoing and near future searches for weak continuous GW signals by coherently integrating for long times. This is very computationally intensive! Einstein@home uses thousands of volunteer computers. Our strong crust can support ellipticities ϵ=(i1-i2)/i3 up to 10-5, best observational upper limits now 10-7 so mountains are detectable! CJH, Kai Kadau, Phys Rev Let. 102, (2009) Movie of breaking of 1.7 million ion crystal with defect in center. Red indicates deformation.

16 Neutron Star Quadrupole Moments and Gravitational Waves Mountain on a rotating NS very efficiently radiate GW. Maximum size of mountain depends on strength of NS crust. We perform large scale MD simulations of the crust breaking including effects of defects, impurities, and grain boundaries... We find neutron star crust is strongest material known:10 10 times stronger than steel. Can support few cm tall mountains! Ongoing and near future searches for weak continuous GW signals by coherently integrating for long times. This is very computationally intensive! Einstein@home uses thousands of volunteer computers. Our strong crust can support ellipticities ϵ=(i1-i2)/i3 up to 10-5, best observational upper limits now 10-7 so mountains are detectable! CJH, Kai Kadau, Phys Rev Let. 102, (2009) Movie of breaking of 1.7 million ion crystal with defect in center. Red indicates deformation.

17 Magnetars --Bryan Gaensler Soft Gamma Repeaters (SGRs) and Anomalous X-ray Pulsars (AXPs) - occasional X-ray/γ-ray bursts - very rare giant γ-ray flares - slow X-ray periods (P ~ 5 12 sec) - rapid spin-down, sudden changes in torque - low Galactic latitude, some in SNRs - not seen in radio, no companions young neutron stars, but not ordinary pulsars, not accreting binaries Robert S. Mallozzi, UAH / NASA MSFC magnetars, isolated neutron stars with B surface ~ G (Duncan & Thompson 1992; Kouveliotou et al 1998) Rare objects: only ~12 magnetars known - active lifetimes ~10 kyr - ~10% of neutron star population? E. L. Wright (UCLA), COBE Project, Courtesy MSFC, NASA

18 The 2004 Giant Flare 27 Dec 2004 from SGR (Borkowski et al. 2004) 0.2 sec spike of γ-rays - L peak ~ 2 x erg/s ~ 1000 x L MW - E bol ~ 4 x erg/s ~ 300 kyr x L - fluence at Earth ~ 1 erg cm -2 - saturated all but particle detectors - created detectable disturbance in ionosphere (Campbell et al. 2005) - echo detected off Moon (Mazets et al. 2005) Fading 6-min tail with 7.6 sec pulsations (= known rotation period of star), similar intensity to tails in previous two giant flares Strength of spike reflects degree of reconnection; strength of tail indicates ability to trap particles Terasawa et al. (2005) Mereghetti et al. (2005) --Bryan Gaensler

19 Curst Breaking Mechanism for Magnetar Twisted magnetic field diffuses and stresses crust. Crust breaks and moves allowing magnetic field to reconnect, releasing huge energy observed in giant flares. Giant Flares We find the crust is very strong and can control large energy in the magnetic field. Helps explain large10 46 erg energy of 2004 flare from SGR1806. Thompson + Duncan

20 Laboratory probe of neutron rich matter PREX uses parity violating electron scattering to accurately measure the neutron radius of 208 Pb. - Electroweak reaction is free from most strong interaction uncertainties. - Description of exp. and first results. 208 Pb - Implications of neutron radius. - Follow on parity measurements. Brian Alder

21 Parity Violation Isolates Neutrons In Standard Model Z 0 boson couples to the weak charge. Proton weak charge is small: Q p W =1 4sin2 Θ W 0.05 Neutron weak charge is big: Q n W = 1 Weak interactions, at low Q 2, probe neutrons. Parity violating asymmetry Apv is cross section difference for positive and negative helicity electrons A pv = dσ/dω + dσ/dω dσ/dω + + dσ/dω Apv from interference of photon and Z 0 exchange. In Born approximation A pv = G F Q 2 2πα 2 F W (Q 2 )= F W (Q 2 ) F ch (Q 2 ) d 3 r sin(qr) Qr ρ W (r) PREX aims to measure Apv for 1.05 GeV electrons scattering from 208 Pb at 5 degrees to 3%. This gives neutron radius to 1% (+/ fm). Note Apv ~ 0.5 ppm. Donnelly, Dubach, Sick first suggested PV to measure neutrons.

22 208 Pb PREX results for RW, Rn PREX measures how much neutrons stick out past protons (neutron skin).

23 PREX in Hall A at JLab Spectometers Lead Foil Target Pol. Source Hall A CEBAF MSU Seminar, Nov 2008 R. Michaels 18

24 Hall$$$A$$$at$$$Jefferson$$Lab$ Hall A R. Michaels, JLAB 19

25 20

26 Systematic Errors Any helicity correlated beam property is possible systematic error. Example if position of beam depends on electron spin, and detector acceptance is asymmetric, this could mimic parity signal. (care about nm shifts) In general monitor, make big and measure, and control various effects. Collaboration has long experience from 5+ previous parity experiments but PREX is very challenging because of part in 10 8 error goal. 21

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28 Statistical Errors 23

29 Downtime from Radiation Problems Intense radiation from ~75 microamp beam on thick (0.55 mm) 208 Pb target caused O-ring seal to fail and interfered with some spectrometer electronics etc. Only managed to get a fraction of designed statistics. Final statistical error 0.06 ppm (9%) is three times planed 0.02 ppm (3%) error. Final physics result: Apv = ± 0.060(stat) ± 0.014(sys) ppm 24

30 Analysis 1: Fit to Mean Field Models Consider set of seven mean field models that give good charge densities and binding energies, and span a large range of neutron radius Rn. Calculate weak charge density from model ρn and ρp, ρw(r)=qpρch(r)+qn d 3 r [GE p ρn +GE n ρp] Solve Dirac Eq. to calculate APV(θ) given ρw and experimental ρch. Integrate APV(θ) over angular acceptance --> <APV> Compare least squares fit of model Rn vs predicted <APV> to measured APV = Rp ±0.060(stat) ±0.014(sym) ppm Phys Rev Let. 108, (2012) Analysis I Result: Rn - Rp = fm

31 Analysis II: Helm model weak form factor Solve Dirac eq. for wood saxon ρw and experimental ρch. Integrate over acceptance. Adjust ρw until <APV> agrees with PREX measurement. Calculate weak form factor FW(q)= d 3 r sinqr/qr ρw(r) / QW. FW(q)=0.204 ± at q=0.475 fm -1 Helm model for FW(q)=3/qR0 j1(qr0) exp[-q 2 σ 2 /2] with diffraction radius R0. Use surface thickness σ=1.02±0.09 fm from least sqs. fit to mean field models. Weak radius: RW=[3/5(R0 2 +5σ 2 )] 1/2 RW=5.83±0.18(exp)±0.03(model) fm Helm model weak charge density for 208 Pb (red) Gray band includes exp. and model errors. Blue dots is a typical mean field model (FSU). Black dashes is (E+M) charge density.

32 Analysis II: Weak form factor Compare Rw to well measured Rch=5.503 fm implies weak charge skin Rw-Rch=0.32±0.18(exp)±0.03(model) fm. Experimental milestone: direct evidence that weak charge density is more extended than E+M charge density. Rch slightly larger than point proton radius, Rch 2 =Rp 2 +<rp 2 >+N/Z<rn 2 > (neglecting small spin-orbit and meson exchange currents). Proton size <rp 2 >=0.769 fm 2, neutron <rn 2 >= fm 2 --> Rp=5.45 fm. (Qw/qnN)Rw 2 =Rn 2 +(qpz/qnn)rch 2 +<rp 2 >+Z/N<rn 2 >-(A/qnN)<rs 2 > Total weak charge Qw=Nqn+Zqp= Radiative corrected neutron weak charge is qn= , proton qp= Nucleon strangeness radius <rs 2 > ±0.04 fm 2 from HAPPEX, G0, A4... From Rw deduce Rn=5.751 ±0.175(exp) ±0.026(model) ±0.005(strange) fm. Neutron skin: Rn-Rp=0.302 ±0.175 ±0.026 fm, consistent with Analysis I, Rn-Rp= fm, within limitations of Helm model ( ± model error). -- Phys. Rev. C 85 (2012)

33 PREX and Nuclear 208 Pb Structure Brian Alder Experimental charge densities from electron scattering

34 Neutron Skin and Symmetry E 208 Pb has Z=82 protons and N=126 neutrons. Where do the N-Z=44 extra neutrons go? In the center of the nucleus? At the surface? Relevant microphysics: A pn pair in bound 3 S1 state has more attractive interaction than pp or nn pair in unbound 1 S0 state. The symmetry energy S(n) describes how E of nuclear matter rises when one goes away from N=Z. E(n, δ) E(n, δ =0)+δ 2 S(n) δ =(N Z)/A PREX constrains density dependance of sym. E, ds/dn. Symmetry E very important to extrapolate to neutron rich systems in astrophysics. 29

35 Pb Radius Measurement Pressure forces neutrons out against surface tension. Large pressure gives large neutron radius. Pressure depends on derivative of energy with respect to density. Energy of neutron matter is E of nuc. matter plus symmetry energy. Rn-Rp (fm) for 208 Pb Alex Brown et al. Neutron radius determines P of neutron matter at ¼ 0.1 fm -3 and the density dependence of the symmetry energy ds/dρ. Neutron minus proton rms radius of Pb versus pressure of pure neutron matter at ρ=0.1 fm -3.

36 Chiral Effective Field Theory Calculations of Pressure of Neutron Matter vs Density Chiral EFT calc. of pressure P of neutron matter by Hebeler et al. including three neutron forces (blue band) PRL105, (2010) 0.31 fm Rn-Rp=0.23 fm PREX nn+3n forces Their calculated P and Typel-Brown correlation --> Rn-Rp=0.14 to 0.2 fm PREX agrees with results including 3n forces. Three neutron forces are very interesting, unconstrained. Some information on 3 nucleon forces in 3 H, 3 He fm 0.07 fm nn forces only

37 PREX and Neutron Stars 208 Pb Brian Alder 32 Casey Reed

38 Neutron Star radius versus 208 Pb Radius 2Rn 2RNS

39 Pb Radius vs Neutron Star Radius The 208 Pb radius constrains the pressure of neutron matter at subnuclear densities. The NS radius depends on the pressure at nuclear density and above. Central density of NS few to 10 x nuclear density. Also, observations of massive neutron stars constrain the maximum mass the EOS can support before collapse to a black hole. This is sensitive to the EOS at high densities. Pb radius probes low density, NS radius medium density, and maximum NS mass probes high density equation of state. An observed softening of EOS with density (smaller increase in pressure) could strongly suggest a transition to an exotic high density phase such as quark matter, strange matter, or a color superconductor J. Piekarewicz, CJH

40 Observing Neutron Star Radii, Masses Deduce surface area from luminosity, temperature from X-ray spectrum. Complications: L γ = 4πR 2 σ SB T 4 Need distance (parallax for nearby isolated NS...) Non-blackbody corrections from atmosphere models can depend on composition and B field. Curvature of space: measure combination of radius and mass. Steiner, Lattimer, Brown [ArXiv: ] combine observations of 6 NS in 2 classes: X-Ray bursts and NS in globular clusters. Find EOS that is somewhat soft at medium densities so 1.4 Msun star has 12 km radius. * Predict 208 Pb neutron skin: Rn-Rp=0.15+/ fm. * F. Ozel et al. get smaller radii. Radio observations of PSR J1614 find M=1.97+/-0.04 Msun from binary with 0.5 Msun WD. Demorest et al., Nature 467 (2010) Some tension between big PREX skin and small NS radii. If PREX continues to find large Rn- Rp and 1.4 Msun NS has small radius near 10 km (Ozel et al) then EOS is stiff, soft, stiff with density --> Phase transition to exotic phase.

41 Model atmospheres determine nonblack body correction fc. This depends on luminosity and composition. Apply to 4U and find large ~15 km radius.

42 Symmetry energy review: M. B. Tsang et al, arxiv: Constraints on symmetry energy at saturation density S0 and its derivative L. 12 km neutron star radius (nstar) suggests smallish L

43 Future PREX measurements PREX-I: APV=0.66±0.06±0.014 ppm Rn - Rp = fm PREX-II (approved for 25 days) Run 208 Pb again to accumulate more statistics. Goal: Rn to 1%, ±0.06 fm. PREX-Ca (proposal for next PAC) 48 Ca smaller nucleus, measure at higher Q 2 (and beam energy) where experimental figure of merit is higher. Microscopic coupled cluster and no-core shell model calculations can directly relate Rn ( 48 Ca) to three neutron forces. Goal, sensitive to Rn to ±0.03 fm?? 48 Ca

44 Coupled cluster calculations of total binding energy of Ca isotopes. Three nucleon forces change drip line from 70 Ca to 60 Ca. Important complementarity between precise experiments on stable nuclei and less precise radioactive beam experiments on very neutron rich nuclei.

45 Conclusions

46 Conclusions Multi-messenger astronomy: Combine observations using photons, gravitational waves, and neutrinos to fundamentally advance our knowledge of the heavens.

47 Conclusions Multi-messenger astronomy: Combine observations using photons, gravitational waves, and neutrinos to fundamentally advance our knowledge of the heavens. Multi-messenger observations of neutron rich matter: Combine astronomical observations using photos, GW, and neutrinos, with laboratory experiments on nuclei, heavy ion collisions, radioactive beams... and new computational tools... to fundamentally advance our knowledge of the heavens, the dense phases of QCD, the origin of the elements, and of neutron rich matter.

48 Multi-messenger observations of neutron rich matter 208 Pb Neutron rich matter can be studied in lab. with radioactive beams and in Astrophysics with X-rays, neutrinos, gravitational waves. PREX uses parity violating electron scattering to accurately measure the neutron radius. First result: Rn-Rp( 208 Pb)= fm. Plan to get more statistics for 208 Pb, also 2nd expt. on 48 Ca very attractive. Many implications for astrophysics... Collaborators: S. Ban, M. Gorchtein, R. Michaels, J. Piekarewicz... Students: L. Caballero, H. Dussan, J. Hughto, A. Schneider, and G. Shen. Supported in part by DOE and State of Indiana. C. J. Horowitz, IU and MSU, WCU/Hanyang-APCTP Focus Program, Effective field theories, halos, driplines and EoS for compact stars, Pohang, Korea, Apr. 2012