New physics hiding in low energy QCD

Sean Tulin University of Michigan

Outline

Some thoughts on sensitivities of h physics decays to new Two parts to this talk: • CP violation beyond the standard model ( h – How do h decays compare to EDM limits?

 pp ) • New weakly-coupled light forces – Are there new gauge forces “hiding” under QCD?

Part 1

CP violation and

h  pp

CP violation (CPV): motivation

Cosmology (baryon asymmetry): Sakharov conditions for baryogenesis 1. Baryon number violation

(Sakharov 1967)

2. C- and CP-violation 3. Departure from equilibrium or CPT violation CP violation in the Standard Model (SM) insufficient to explain baryon asymmetry

(Gavela et al 1993, Huet & Sather 1994)

Particle physics CPV is a generic feature of particle physics theories beyond the SM e.g. Supersymmetry or neutrino see-saw models: theories have new phases that can give successful baryogenesis

CPV decay

h  pp • Current limit: BR( h  p 0 p 0 ) < 3.4 x 10 -4 (GAMS-4 p ) • Standard model

(Jarlskog & Shabalin 1995)

CKM phase: q QCD phase: BR( h  BR( h  p p 0 0 p p 0 0 ) < 10 ) < 10 -27 -18 x ( q QCD /10 -10 ) 2 Neutron electric dipole moment (EDM) constraint:

(Crewther et al 1979, Pospelov & Ritz 1999; Baker et al 2006)

d n = 2.4 x 10 -16 e cm x q QCD < 2.9 x 10 -26 e cm [90% limit] Otherwise BR( h  p 0 p 0 ) could have been sizable in SM!

CPV decay

h  pp • BR( h  p 0 p 0 ) unambiguous probe for new CPV • Caveat: Any contribution to BR( h  p 0 p 0 ) also generates a nonzero neutron EDM. Can use neutron EDM to limit BR( h  p 0 p 0 ).

• Gorchtein bound:

(Gorchtein 2008)

BR( h  p 0 p 0 ) < 3.5 x 10 -14

for d n < 2.9 x 10 -26 e cm

Gorchtein bound

CP-odd hpp coupling = CPV vertex h h CP-odd h NN coupling Integrate out pions p N g hpp p p p N CP-odd NN g coupling Integrate out h, r/w N d n ~ 2.5 x 10 -17 e cm x (g hpp /GeV) Order-of-magnitude estimate only h g g N N r/w h

(Gorchstein 2008)

N

Gorchtein bound (revisited?)

Can this bound be made more rigorous? Some ideas… CP-odd hpp coupling h g hpp = CPV vertex p CP-odd p NN coupling Match onto p -N EFT by integrating out h. Generate CP-odd (isoscalar) coupling.

N h p p p N g CP-odd NN g coupling

(Crewther et al 1979)

Match onto g -N EFT by integrating out p.

n EDM N N p

Conclusions: CPV decay

h  pp BR( h  pp ) must be far below experimental sensitivities due to stringent n EDM limit: – – Current limit: d n < 2.9 x 10 Gorchtein bound: BR( h  -26 p 0 e cm p 0 ) <

(Baker et al 2006)

3.5 x 10 -14 – Independent of particle physics model for new CPV Caveat: Bound is approximate (order of magnitude only) – Worthwhile to revisit this bound to make it more precise – BUT cannot avoid generating d n at two loop order: d n ~ e g hpp / ((4 p ) 4 M QCD 2 ) ~ 10 -18 e cm x (g hpp /GeV) Very naïve estimate

Conclusions: CPV decay

h  pp Another caveat: n EDM and BR( h  pp ) sensitive to different linear combinations of new physics CPV phases Can have fine-tuned cancellations between phases contributing to d n but not BR( h  pp ) • 10 -5 cancellation in d n  BR < 3.5 x 10 -4 • 10 -4 cancellation in d n  BR < 3.5 x 10 -6 What is the constraint on BR( – h  pp ) from d Hg ?

Likely requires fine-tuning to evade d Hg limit also BUT BR( h  pp ) should be measured anyway

Part 2

Searching for new light forces

Motivation for new forces

SM based on SU(3)

C x SU(2) L x U(1) Y

gauge symmetry. Are there any additional gauge symmetries? Look for new gauge bosons.

Motivations: 1. Grand unified theories: Generically have additional gauge bosons, but typically very heavy (10 16 GeV).

2. Dark matter: Stability of dark matter related to new gauge symmetry?

Intensity frontier

mass

LHC

Motivation for new forces

New light (MeV–GeV) forces associated with dark matter (DM) have received much attention in the past few years.

– Sommerfeld-enhancement models of DM and indirect detection anomalies (e.g. PAMELA)

Pospelov & Ritz (2008); Arkani-Hamed et al (2008)

– Self-interacting DM and explaining small scale structure anomalies in dwarf galaxies – Asymmetric DM models

e.g. Lin et al (2011)

– – Hidden sector DM and relic density (g-2) m anomaly

Pospelov (2008) Feng et al (2009)

GeV-scale experimental searches for new weakly-coupled light vector bosons from a new force (“dark photon”)

Bjorken et al (2009), Reece and Wang (2009)

Searches for dark photons

Ongoing experimental efforts to discover new gauge bosons Largely focused on kinetic-mixing “dark photon” models (A’) Relies on A’ leptonic coupling to with strength e e

Essig et al (2013)

Mass Mass

New baryonic force

Dark photon limits are for a specific model where A’ couples to electrons. But there may be new forces that do not couple to leptons. How do we search for these types of new forces?

Simplest example: Gauge boson (B) coupled to baryon number Assume B couples to quarks only but not leptons (leptophobic Z’).

Flavor-universal vector coupling g B to all quarks Literature:

Radjoot (1989), Foot, et al (1989), He & Rajpoot (1990), Carone & Murayama (1995), Bailey & Davidson (1995), Aranda & Carone (1998), Fileviez Perez & Wise (2010), Graesser et al (2011), …

New baryonic force

B = gauge boson coupled to baryon number Discovery signals depend on the B mass Departures from inverse square law

Adelberger et al (2003)

m B Meson physics

Nelson & Tetradis (1989), Carone & Murayama (1995)

Low-energy n scattering

Barbieri & Ericson (1975); Leeb & Schmiedmayer (1991)

Colliders: hadronic Z, dijet resonances, … meV eV MeV GeV TeV Long range nuclear forces > 1/m p Is it possible to discover light weakly-coupled forces hiding in nonperturbative QCD regime?

Tests of perturbative QCD at colliders

Constraints on new baryonic force

• • Focus on m B ~ MeV – GeV range of interest for physics of light mesons Range of interest for h decays: m p < m B < m h • • How does B modify h decay properties?

What are the constraints on the coupling?

“Baryonic” fine structure constant

h

decay

New baryonic forces observed through light meson decays

(Nelson & Tetradis 1989) B

h  B g decay (m B < m h ) h u,d,s g Triangle diagram Decay rate related to h  gg rate Tr = trace over SU(3) flavors (u,d,s) l 8 ( l 0 ) = octet (singlet) SU(3) generator, q = singlet-octet mixing angle, Q = electric charge

B decay

How does B vector boson decay? Depends on mass… 3m p < m B < ~ GeV : m p < m B < 3m Why no B  pp ?

p : MeV < m B < m p :

B

 p + p p 0

B

 p 0 g

B B

 e + e , ggg p 0 u,d,s g

Decay channels of B boson

B has same quantum numbers as w vector meson Assume its decay properties are similar

Particle Data Book

Decay channels of B boson

B has same quantum numbers as w vector meson Assume its decay properties are similar

Particle Data Book

Violates G-parity

Decay channels of B boson

B has same quantum numbers as w vector meson Assume its decay properties are similar

Particle Data Book

Dominant above 3m p Dominant between m p – 3m p Violates G-parity

m B range

h

decay

Signature

415 – 550 MeV 3m p m h h 

B

g  p + p p 0 g 130 – 415 MeV m p 3m p h 

B

g  p 0 g g 0 – 130 MeV m p h 

B

g  (e + e / ggg / invis.) + g Note: for m B < m p , constraints from p 0  (e + e / ggg / invis.) + g

m B range

h

decay

Signature

415 – 550 MeV 3m p m h 130 – 415 MeV m p 3m p h 

B

g  p + p p 0 g h 

B

g  p 0

Focus on this case

g g 0 – 130 MeV m p h 

B

g  (e + e / ggg / invis.) + g Note: for m B < m p , constraints from p 0  (e + e / ggg / invis.) + g

New physics in

h  p 0 gg Decay rate:

New physics in

h  p 0 gg Decay rate:

New physics in

h  p 0 gg Decay rate: • • Observed BR( h Constrains a B  << a p 0 em gg ) << BR( ~ 1/137 h  gg ) • • h decays provide the strongest limit on vector boson in the 130—415 MeV range New baryonic force must be much weaker than the electromagnetic interaction!

Constraints on a new baryonic force

 (1S)  hadrons b  (1S)

B

b q q Low-energy n-Pb scattering Excludes nuclear forces with range > 1/m p

Constraints on a new baryonic force

h  p 0 gg

constraint

Limit assuming new physics (NP) contribution to BR satisfies: d BR( h  p 0 gg ) < 10 -4 Approximate current limit Note: neglecting interference with SM decay in narrow width approximation

Constraints on a new baryonic force

h  p 0 gg

constraint

Limit assuming new physics (NP) contribution to BR satisfies: d BR( h  p 0 gg ) < 10 -5 Projected limit (?) Note: neglecting interference with SM decay in narrow width approximation

Constraints on a new baryonic force

Pion decay constraints for m B < m p Decay rate: • • • How does B decay? Not sure… (needs more detailed calculation) B  e + e (via B g mixing) BR( p 0  e + e g ) = (1.174 ± 0.035)% (PDG) Agrees with SM value (Joseph 1960) Take d BR (p 0  e + e g ) < 7 x 10 -4 B  ggg BR( p 0  gggg ) < 2 x 10 -8

(McDonough et al 1988) Expected to be very long-lived (Nelson & Tetradis 1989)

B  invisible (long-lived on detector timescale) Use limit from neutrino decays: BR( p 0  gnn ) < 6 x 10 -4

(PDG)

Constraints on a new baryonic force

p 0 decay constraints for m B < m p Consider either p 0 g  g ee or + inv (comparable limits) If p 0  gggg is prompt on detector timescales, limit on a B is ~10 4 times stronger

Constraints on a new baryonic force

Heavy B regime ~ 500 MeV < m B < ~ GeV h ’ 

B

g Search for: h ’ or 

B

p 0 gg g  p 0 p + p g (suppressed)

h  p 0 gg

kinematics

New physics decay is two 2-body decays while SM decay is 3-body decay. So far, only considered constraint on total rate.

Can kinematic information be used to enhance the sensitivity of h  p 0 gg to new physics?

h  p 0 gg

kinematics

Prakhov (2007)

gg invariant mass distribution m B = 150 MeV Endpoint:

h  p 0 gg

kinematics

Dalitz plot: m 2 ( p 0 g 1 ) vs m 2 ( p 0 g 2 ) Decays have either m 2 ( p 0 g 1 ) or m 2 ( p 0 g 2 ) = m B 2 if new particle B involved in h decay

Conclusions

• • CP-violating h  pp decay Strongly constrained by nEDM limit (BR < ~ 3x10 -14 ) Important to revisit this limit theoretically • • • • • New hidden forces Searches for new light forces are a hot topic with a lot of experimental interest, but all searches are focusing on the “dark photon” model h decays are a fantastic probe for a new light baryonic force that couples to quarks only. Precision tests of a new force “hidden” in nonperturbative QCD.

h  p 0 gg gives strongest limit for few*100 MeV mass Current limit: baryonic force is 2000 times weaker than electromagnetism!

Better limits from kinematic analysis of h  p 0 gg ? This has not been done!