# Presentation: 351731

## Antimatter Gravity Experiment

- An Opportunity for Fermilab to (potentially) Answer Three of the Big Questions of Particle Physics

- _Outline_
- Motivation: Potentially BIG payoff
- Method: Use proven technology

**Thomas J. Phillips**
**Duke University**

## Physics Motivation

- g has never been measured!

**CPT:**

**earth**

**anti-earth**

**g**

**g**

**earth**

**?**

**CPT theorem assumes **_**flat**_** spacetime.**

**CPT does not address how an antiapple falls on the earth.**

**Notes:**
Need to finish

## 1. Are there undiscovered principles of nature:

-     New symmetries, new physical laws?
- 2. Are there extra dimensions of space?
- 3. Do all the forces become one?
- 4. Why are there so many kinds of particles?
- 5. What happened to the antimatter?
- 6. What is dark matter?                                      How can we make it in the laboratory?
- 7. How can we solve the mystery of dark energy?
- 8. How did the universe come to be?
- 9. What are neutrinos telling us?

- From “Quantum Universe” and
- “Discovering Quantum Universe”

- 1. Are there undiscovered principles of nature:
-     New symmetries, new physical laws?
- 2. Are there extra dimensions of space?
- 3. Do all the forces become one?
- 4. Why are there so many kinds of particles?
- 5. What happened to the antimatter?
- 6. What is dark matter?                                      How can we make it in the laboratory?
- 7. How can we solve the mystery of dark energy?
- 8. How did the universe come to be?
- 9. What are neutrinos telling us?

## This is a Dark EnergyExperiment!

- Suppose the gravitational force between matter and antimatter is repulsive
- This would **explain** “missing” antimatter!
- matter and antimatter domains grow, separate
- This would also **explain** dark energy!
- an equal mix of matter and antimatter domains would give a net repulsive force
- analogous to an ionic crystal where opposite charges attract giving a net attraction
- net repulsive force would lead to cosmic acceleration!
- Repulsion could power inflation!

## What About GR?

- Repulsive gravity for antimatter appears to be inconsistent with General Relativity, BUT
- antimatter can be identified with negative-mass solution in Kerr-Newman Geometry
- G. Chardin, AIP Conf. Proc. 643, 385 (2002)
- Dirac antimatter is a negative energy “hole”
- M. Kowitt, Int. J. Theoretical Phys. **35**, 605 (1996)
- new forces i.e. Gravivector and Graviscalar
- would ~ cancel for matter, add for antimatter
- limits exist; need precise matter-antimatter difference
- Nieto and Goldman, Phys. Rep. **205**, 221 (1991)
- A different theory of gravity?
- GR and QM incompatible by 10120, so we already need to revise our theories!

## Great 4 Public Relations!

- The public loves antimatter!
- CERN’s press release announcing they had made antihydrogen generated the biggest response they had ever gotten.
- Particle physics needs good press!
- Fermilab need physics results between the tevatron and Project X

## Make a low-velocity antihydrogen beam
Trap and cool antiprotons
Trap and cool positrons
Accelerate antiprotons, direct through positron plasma
Direct the beam through a transmission-grating interferometer
Measure g by observing the gravitational phase shift
Interference pattern shifts by the same amount that the atoms fall

- Trap and cool antiprotons
- Trap and cool positrons
- Accelerate antiprotons, direct through positron plasma
- Direct the beam through a transmission-grating interferometer
- Measure g by observing the gravitational phase shift
- Interference pattern shifts by the same amount that the atoms fall

- A Neutral Beam Experiment for Measuring g

## Atomic Interferometer

- A single grating makes a diffraction pattern:

- A second identical grating makes a
- Mach-Zender interferometer:

- The interference pattern
- has the same period as the
- gratings so a third identical
- grating can be used to
- analyze the phase of the
- pattern. The interference
- pattern “falls” by the same
- amount that the atoms fall
- as they traverse the inter-
- ferometer:

## Sodium Interferometer

- High contrast has been observed with the MIT interferometer using an uncollimated atomic Sodium beam

**An atomic interferometer using sodium atoms and vacuum transmission gratings**
**David W. Keith *****et al. *****PRL **66** 2693.**

## Sodium Interferometer

- High contrast has been observed with the MIT interferometer using an uncollimated atomic Sodium beam

**Slow (1050 m/s) beam (upper)**
**Fast (3000 m/s) beam (lower)**
**uncollimated beams**

**Slow (1050 m/s)**
**collimated beam**
**non-interfering diffraction**
**orders do not contribute**

**Atom Interferometry: Dispersive Index of Refraction and Rotation Induced Phase Shifts for Matter-Waves**
**Troy Douglas Hammond, Ph.D. Thesis, MIT, February 1997.**

- 104 detected atoms enough
- to get this phase measurement

- gravitational deflections: 19 m for 1050 m/s
-                                            2 m for 3000 m/s

## Making Antihydrogen

- Ingredients:

- .

- .

- .

- .

- .

- .

- .

- +.

- .

- .

- .

- Positrons

- .

- +.

- +.

- +.

- Collect antiprotons in a trap.  Add electrons to cool
- to 4 degrees K.  Collect positrons in an adjacent trap.

- -

- Antiprotons

- -

- -

- -

- Then raise potential of p ...

- ...and drop barrier:

- -

- .

- H

- p

- e+

- x

- v

## Antihydrogen Beam

- Cold Antihydrogen has been made by several groups at CERN
- The ATRAP group has made antihydrogen in a beam with a velocity distribution nearly ideal for the gravity experiment

- from Phys. Rev. Lett. 97, 143401 (2006)

- Slow component velocity determined by accelerating voltage

- Fast component from charge exchange with hot antiprotons (can be removed)

## Long-Term Goal

- A longer-term goal of the antimatter gravity experiment is to make a precision matter-antimatter difference measurement
- local g precision 1:1010
- can look for new ultra-weak forces

- from S. Chu, Rev. Mod.Phys. **70**, 685 (1998)

- A. Peters *et al*. Philos. Trans. R. Soc. London Ser A **355, **2223.

## Antiprotons

- CERN’s AD cannot accumulate antiprotons
- pulses of 3x107 every 90 seconds
- 0.1% capture efficiency (3x104 per pulse)
- Fermilab can accumulate antiprotons
- stacking rate typically exceeds 1011/hour
- no current ability to decelerate and trap

- Antiprotons are made at Fermilab and CERN

- Fermilab

- 104 detected atoms enough
- to get a phase measurement.
- ~10% transmission efficiency:
- need 105 antihydrogen in beam

## Conclusions

- The Antimatter Gravity Experiment could _Answer_ some BIG Questions:
- What happened to the Antimatter?
- What is the nature of Dark Energy?
- Are there New Laws, Principles, Symmetries?
- The Antimatter Gravity Experiment can be done using Proven Technologies:
- Atomic Interferometry
- Antihydrogen Production
- Fermilab should decelerate antiprotons!

## Hydrogen Interferometer

- Based upon MIT Design
- Transmission gratings have a larger period
- Less sensitive to vibration, misalignment

- Atomic Transmission gratings mounted on floating aluminum plates along with optical gratings for alignment.
- Floating aluminum plates are mounted on fixed plates with piezoelectric positioners.
- Metastable H beam too fast to see gravity.

## Vacuum Transmission Gratings

- Atomic gratings from Max Planck Institute for Extraterrestrial Physics
- Spares from Chandra X-ray telescope low-energy spectrometer
- 1 micron period

- The interference pattern has a period equal to the grating period because longer wavelengths diffract more and the larger crossing angle cancels the longer wavelength

- D

- 