Very Weak Interactions

or, what is 23% of the universe made of?

Itay Yavin

New York University

Rutgers University January 25, 2011

The Search for New Physics

How do we look for new physics?

Where should we look for it?

What is new physics ?

How do we make sure we don’t miss it?

In particle physics, we are interested in the fundamental building blocks of nature. We are not just looking to discover new particles, but new principles and symmetries as well. We often call this quest for the basic interactions “the search for new physics”.

Principle Based Searches

Many searches are based on theoretical principles

1)Top discovery – anomaly free gauge-theory

1)Unitarization of W-boson scattering - Unitarity

2)Higgs boson – Renormalizability

3)Supersymmetry – solution to the hierarchy problem

Phenomenological Searches

Other searches are more phenomenological in nature

1)The discovery of Quantum Mechanics

2)Neutrinos and their properties

3)The discovery of the tau

1)Dark matter and weakly coupled physics

Theoretical Efforts

1) Construct new models (hard, no obvious principals to follow)

2) Propose new searches

3) Suggest alternative explanations for observed anomalies

4) Critically examine and integrate all the known results

5) Calculate experimental observables

How can theorists aid phenomenological searches?

Missing ThingsNeutrinos were first noticed as missing energy-momentum in beta decays.

It took 23 years before their existence was confirmed.

It took another 50 years to discover that neutrinos have a mass.

Dark matter was first observed by Zwicky in cluster of galaxies.

Over the past 70 years observers have seen evidence for dark matter over many length scales.

But how does it interact?

SNO – neutrino observatory

Content

• Weakly Interacting Matter

• The Exposure Frontier

• Weak Interactions

• The Energy Frontier

Weakly Interacting Matter

The Exposure Frontier

Dark Matter

Rotation curves

Lensing Effect

Bullet ClusterWMAP

Indirect Detection

Direct Production

Direct Detection

Getting Pushed by Dark Matter(or Direct Detection Experiments)

Nuclear recoil event

Dark Matter entering target

Dark Matter leaves

CDMS: 0912.3592

Detection Schemes

CRESST-II

CoGeNT

From P. Salati’s review on Dark Matter

CoGeNT

CoGeNT is NOT seeing light dark matter elastically scattering against the nucleus.

Chang, Liu, Pierce, Weiner, and IY - 1004.0697

DAMA

CDMS

XENON10

CRESST

A Tale of Two Experiments

XENON100

Chang, Weiner, and IY - 1007.4200

Magnetic inelastic Dark MatterHow is DAMA different from the other experiments? Is there a dark matter candidate that would show up in DAMA, but not in other experiments? (inspired by inelastic dark matter, Tucker-Smith and Weiner hep-ph/0101138)

DAMA’s crystals are made NaI:

• Heavy target (iodide)

• Large magnetic dipole

A Magnetic dipole interaction:

Event Rate

astrophysics Particle physics

How many events do we get for a given cross-section?

Experimental Signatures

CDMSCRESST-IIXENON10KIMSZPELIN-III

Such a DM state explains the annular modulations seen by DAMA while avoiding the other null results of other experiments.

It can be searched for by other experiments and enjoys an additional unique signature. After the collision, the excited state travels some distance before it de-excites and emits a photon,

Standard cuts will likely miss these events, but with some care it may not be hard to distinguish from background.

Maybe the most important result of such scenarios is that they force us to think beyond the usual elastic scattering phenomenology. Inelastic, Exothermic, and Magnetic DM all result in unique experimental signatures.

Open Questions• Are there any bounds from experiments looking for neutrinos from the Sun? (not as strong as for the original iDM scenario – Nussinov, Wang, and IY, 0905.1333)

• Can such a scenario lead to the correct relic abundance?

• What are the bounds from collider searches?

• Are there convincing models that exhibit such a phenomenology?

• Will it be seen by the XENON100 experiment?

Elastic Scattering

Inelastic, Exothermic, Magnetic DM

Weak Forces

Energy Frontier

Probing Weak Forces

Precision measurements of atomic transitions

Lepton-Jets

Muon anomalous magnetic moment

Low-energy colliders

Holdom Boson – A Case StudyA very simple theoretical example of a weak force is illustrated through the Holdom effect (Holdom, Phys.Lett. B166),

The mixing term results in a coupling of the new boson to the electromagnetic current,

The story becomes even more intricate once supersymmetry is included and new scales can emerge – Cheung, Ruderman, Wang, and IY, 0902.3246

Example: Rare Z DecayLet’s consider the rare decay of the Z boson into a Holdom-boson and some extra scalar. New and interesting type of objects appear,

Lepton Jets - A collimated collection of energetic leptons with a small opening angle (Arkani-Hamed and Weiner, 0810.0714)

Dark Cascades

A’

A’

A’qq

Dark/Hidden SectorsThis phenomenon is very general. It occurs when we consider new light states coupled to the Standard Model,

Marginal Operators

Hidden Valleys, Strassler and Zurek, hep-ph/0604261

Irrelevant Operators

Lepton-jets are the hallmarks of an extra weakly coupled sector with a low scale.

Dark sectors phenomenology, Baumgart, Cheung, Ruderman, Wang, and IY, 0901.0283

(Motivated by recent astrophysical anomalies – Arkani-Hamed et al. 0810.0713)

Full EvolutionWe implemented the relevant physics into a Monte-Carlo based simulation,

Lepton JetsLepton Jets -

Cheung, Ruderman, Wang, and IY, 0909.0290

This definition grew out of a very fruitful exchange with the experimentalists who actually conducted the search for these objects.

Experimental SearchY. Gershtein and A. Haas have recently concluded the first search for these exotic objects at the Tevatron for D0 - Phys.Rev.Lett. 105 (2010)

More searches are planned for the LHC in both CMS and ATLAS.

Frontiers

keV

MeV

GeV

TeV

Weakly coupled physics be here

Large targets(Sun,Earth)

Exposure(CDMS,XENON)

Luminosity(CHARM,Babar)

Tevatron, LHC

Energy Frontier

Exposure Frontier

Precision Frontier

Atomic physics

Conclusions

Dark Matter23%Dark Energy

73%

“Us”4%

There is no guarantee any of the searches I described will succeed. There is no deep principle that ensures us something will definitely show up.

But, the frontiers are expanding and many promising explorations are underway. By casting a wide net we hope to catch something interesting. Keep in mind that . . .

Thank You

Muonic HydrogenThe long-waited measurement of the proton radius in muonic hydrogen was released this summer from the Paul Scherrer Institute (PSI). The surprising result is that it differs by 5 s.d. from the world’s average.

(reminder: original Lamb shift was the first observation of a QED effect – circa 1947)

Pohl et al. Nature 466:213-216,2010

A New Force?The discrepancy can be the result of a new force between the proton and the muon. It can also help explain the long standing discrepancy in the muon anomalous magnetic moment (Tucker-Smith and IY, 1011.4922).

Constraints:

•Neutron-Lead scattering

•Lamb-shift in ordinary hydrogen

•Neutrino reactions

It is yet unclear whether such a force can be obtained from a simple particle physics model.

Cannot be a Holdom boson type of force – would have been seen in ordinary Hydrogen

Measured deviation

Scalar force fit to muon g-2

Vector force fit to muon g-2

PredictionsMore measurements in muonic systems are planned in PSI and elsewhere. This framework allows for concrete predictions about these systems,

•Muonic Deuterium

•Muonic Helium

•True Muonium