SPSC 19 January 2010 J.S. Hangst THE ALPHA COLLABORATION University of Aarhus, Denmark Auburn...

SPSC 19 January 2010 J.S. Hangst

THE ALPHA COLLABORATION

University of Aarhus, Denmark

Auburn University, USA University of British Columbia, Canada

University of California Berkeley, USA

Simon Fraser University,Canada

University of Calgary,Canada University of Liverpool, UK NRCN - Nucl. Res.

Center Negev, Israel

Federal University ofRio de Janeiro, Brazil

RIKEN, Japan

University of Wales Swansea, UK

University of Tokyo,Japan

TRIUMF,Canada


Motivations in Brief

•Tests of fundamental symmetries by applying precision atomic physics techniques to anti-atoms:

•CPT violation?•Lorentz invariance violation? Physics beyond the Standard Model?

•(Anti)-Gravity - no current experimental effort in ALPHA, but success in ALPHA likely a prerequisite for this work (AEGIS experiment starting in 2011)

The initial physics goal of ALPHA is to TRAP antihydrogen atoms,so that they can be studied in detail.


MixingMixing

0 2 4 6 8 10 12-50

-100

-75

-125

Length (cm)

antiprotons

108 104

104 antiprotons are mixed with 106 – 108 positrons in a double trap configuration


Trapping Neutral Anti-atoms?

quadrupole winding mirror coils

€

U = −μ ⋅B

Solenoid field is the minimum in B

Well depth ~ 0.7 K/T

Ioffe-Pritchard Geometry

ALPHA octupole-based trap is 0.5 K deep


The ALPHA Approach: higher-order multipole

quadrupole

octupole


Octupole Fabrication at BNL

•Magnets wound directly on vacuum chamber (1.5 mm wall)•No metals in support structure: epoxy/fiber•High SC/copper ratio cable


ALPHA Schematic


Hbar production in neutral trap - 2008No neutral trap Full neutral trap

(in process at PLB)


ALPHA Silicon Detector


•Full detector installed and commissioned in 2009•Pbar annihilation topology well-studied during antihydrogen production (“mixing”)•Accumulated approx. 15K pbar vertices in baselines•Cosmics studied off-line; ~50K events in sample•Use mixing and cosmic data to establish cuts to apply totrapping data•Then use detector to discriminate pbar annihilations due to release of trapped antihydrogen from cosmic background •Using various cuts, can essentially eliminate cosmics as background; 25 % of signal survives (e.g., requireNtracks>2); optimisation continues•Extensively studied effect of fast magnet shut-down on detector behaviour

ALPHA Silicon Detector


Temperature Diagnostic for Antiprotons•Release antiprotons by lowering the confining well, measure the loss with scintillators•High energy tail should be a Boltzmann exponential•Same technique works for electrons and positrons using MCP for counting


Evaporative Cooling of Pbars (2009)Evaporative Cooling of Pbars (2009)

•Pulsed-field removal of electrons from electron-cooled pbars does not result in 4 K pbars•Antiprotons cooled by allowing hot ones to escape from a gradually lowered potential well•Direct measurement of antiproton temperatures as low as 10 K


Evaporative Cooling of Pbars (2009)Evaporative Cooling of Pbars (2009)

(manuscript in preparation)

ALPHA PRELIMINARY

•Antiprotons cooled by allowing hot ones to escape from a gradually lowered potential well•Direct measurement of antiproton temperatures as low as 10 K

Note: ELENA would really help here


Evaporative Cooling of Pbars (2009)Evaporative Cooling of Pbars (2009)ALPHA PRELIMINARY

(Solid lines are model calculations)


Trapping Experiments1) Accumulate pbars from AD (one or two

stacks)2) Transfer antiprotons and positrons to

adjacent wells in mixing region, ramp up octupole (900 A in 25 s)

3) Gradually and gently change potentials to bring particles into contact

4) After some mixing time, dump the charged particles using electric fields

5) Dump the magnetic trap using fast (IGBT) switch

6) Look for annihilation events from escaping neutrals

7) Use vertex topology to distinguish from cosmics


“Series 2”

•1 Stack (30x103 pbars)•4M Positrons (7x107 cm‐3)•e+ temperature 170K •Initial pbar temperature ~300K •2700 annihilation triggers in 1s•Valid runs: 212•Total pbars mixed: 6.4x106

•Annihilation triggers during mixing: 5.7x105

“Series 1”

•2 Stacks (60x103 pbars) •8M Positrons (1.3x108 cm‐3)•e+ temperature 300K •Initial pbar temperature ~300K •5000 annihilation triggers in 10s•Valid runs: 59•Total pbars mixed: 3.5x106

•Annihilation triggers during mixing: 3.5x105

Antihydrogen Trapping Experiments

In addition, we have performed dozens of “control experiments”: e.g., no octopole, no positrons, no particles at all, etc.


Mixing Potentials


Preliminary Results of Trapping Runs

•212 total runs (series 2)•Total of 107 pbars and 1.3x109 positrons mixed•Observed four vertex events consistent with trapped hbar being released during the fast magnet shutdown•A rough theoretical estimate says that we should have trapped and detected about nine under the measured conditions of the experiment•Survival time of antihydrogen in the neutral trap is unknown

Possible background of mirror-trapped antiprotons:•Preliminary simulations of charged particle clearing and trap shutdown indicate mirror trapping is very unlikely to be consistent with the observed events (time, positionof events can be used to discriminate); working to quantify this•Energetics help to rule out mirror trapping (need KE>>well depths employed)•Analysis and simulation continuing•Other unidentified backgrounds?


Candidate Trapped Hbar Event in the ALPHA detector


Summary (2009 Run)

•All systems now commissioned, systematic trapping attempts well underway

•No significant downtime during run; some helium limitations

•New temperature diagnostic for all particle species

•New cooling and manipulation techniques achieve reproducible temperatures down to 10 K for antiprotons: evaporative cooling of antiprotons (not yet used for trapping); lowest measured pbar plasma temperatures

•More than 200 trapping runs looking for trapped antihydrogen

•Have four candidate trapping events, working on background, simulations consistency checks, and systematics.

•Mirror-trapped antiprotons a possible false signal


For 2010

•Completely new electronics chain to minimize noise on electrodes – lower temperatures

•Continue development of low temperature preparation and mixing techniques

•Refine clearing of charged particles based on improved understanding of mirroring

•Improve 2009 result; accumulate more statistics

•Refine control experiments

•Begin design of ALPHA Phase II device – allows laser, microwave access

SPSC 19 January 2010 J.S. Hangst THE ALPHA COLLABORATION University of Aarhus, Denmark Auburn...

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