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Accelerator Based Particle Physics Experiments . Su Dong Stanford Student Orientation SLAC session Sep/16/2010. The Fundamental Questions. Are there undiscovered principles of nature: new symmetries, new physical laws ? How can we solve the mystery of dark energy ?

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Accelerator Based Particle Physics Experiments

Su Dong

Stanford Student Orientation

SLAC session


The Fundamental Questions

  • Are there undiscovered principles of nature: new symmetries, new physical laws ?

  • How can we solve the mystery of dark energy ?

  • Are there extra dimensions of space ?

  • Do all forces become one ?

  • Why are there so many kinds of particles ?

  • What is dark matter ?

    How can we make it in the laboratory ?

  • What are neutrinos telling us ?

  • How did the universe come to be ?

  • What happened to antimatter ?

Accelerator Based Particle Physics Programs




Physics Road map and Detector Evolution

Stage 2: 2020

Stage 1: 2015-6

Stage 0: 2012


Physics Opportunities

  • SLAC physics strategy:

  • Initial emphasis on physics signature tools (b-tag,jet/missingEt) and trigger. Use Standard Model measurements with early data to validate these tools to prepare for searches of new physics beyond Standard Model.

  • Current SLAC physics analyses

  • New physics search and top cross section measurement with b-tag and missing Et

  • Search for long lived new particles

  • Lepton jets

  • Heavy fermions->same sign dileptons

  • Boosted W

  • Close collaboration with SLAC theory group

  • Higgs particle

  • SuperSymmetry

  • Large extra-dimensions

  • The unexpected…

SLAC Involvement in ATLAS

2 Faculty + 1 Panofsky fellow

17+ Staff physicists & professionals

7 Postdocs

6 Grad students

& Tier2 computing center staff

  • Experimental Involvement

  • Pixel vertex detector and tracking

  • High Level Trigger and DAQ

  • Simulation

  • Tier-2 computing center

  • ATLAS Detector Upgrades

  • Opportunities to develop wide variety of experimental skills

Contact Info

Dr. Charlie Young

Prof. Su Dong

Prof. Ariel Schwartzman

(resident at CERN)

Dr. Andy Haas

Detailed info on ATLAS@SLAC for students:

BaBar @ PEP-II

& superB @ Frascati

BaBar Physics

CP violation in B0 decays

BaBar Analysis Opportunities

  • Analysis topics:

  • ISR->hadronic final states

  • B/D decay Dalitz analysis

  • Radiative B decays

  • fDs

  • Charmonium like resonances

  • Data taking ended Apr/08.

  • 465M BB events

  • 630M cc events

  • 460M tt events

  • Largest sample of Upsilon resonance data

  • 2-photon, ISR

Prof. David Leith

Dr. Blair Ratcliff

Focusing DIRC prototype now in Research Yard

  • Radiator:

    • 1.7 cm thick, 3.5 cm wide, 3.7 m long fused silica bar (the same used in the BaBar DIRC).

  • Optical expansion region:

    • filled with mineral oil to match the fused silica refraction index (KamLand oil).

    • include optical fiber for the electronics calibration.

  • Focusing optics:

    • spherical mirror with 49cm focal length focuses photons onto a detector plane.

  • Now being tested with new electronics:

snarrow ≈70ps

time (ns)

snarrow ≈220ps

time (ns)

snarrow ≈140ps

time (ns)

Focusing DIRC prototype photon detectorsNucl.Inst.&Meth., A 553 (2005) 96

  • 1) Burle 85011-501 MCP-PMT (64 pixels, 6x6mm pad, sTTS ~50-70ps)

  • Timing resolutions were obtained using a fast laser diode in bench tests with single photons on pad center.

  • 2) Hamamatsu H-8500 MaPMT (64 pixels, 6x6mm pad, sTTS ~140ps)

3) Hamamatsu H-9500 Flat Panel MaPMT (256 pixels, 3x12mm pad, sTTS ~220ps)

Cherenkov light: tagging color by time

Chromatic growth rate:

s ~ 40ps/m

Cherenkov angle production controlled by nphase:

cos c = 1/(nphaseb),nphase(red) < nphase(blue) => c< c

Propagation of photons is controlled by ngroup (≠ nphase):

vgroup =c0 /ngroup = c0 /[nphase - phase

vgroup(red) > vgroup (blue)

Analytical calculation:

dTOP/Lpath [ns/m] = TOP/Lpath(l) - TOP/Lpath (410nm)

Data from the prototype:

Geant 4 - without and with pixilization:

dTOP/Lpath [ns/m]

dTOP/Lpath [ns/m]


  • We are building a new full size prototype for Super B with new fused silica focusing elements

  • Will be starting tests in Cosmic Ray Telescope in the SLAC Research Yard this year

  • Excellent opportunity for hands-on R&D with a innovative new detector.

HPS is a new, small experiment which offers the thesis student

exposure to all aspects of experimental particle physics, from

experiment design and optimization, to hardware construction, installation and commissioning, and data analysis.Rotation Projects:

John Jaros

What is a “Heavy Photon”?

  • A heavy photon (A’) is a new, ~100 MeV spin one, force-carrying particle that couples to an analogue of electric charge. Because it will mix with “our” photon, it couples to electrons, albeit weakly:

  • Heavy photons can be produced by electron bremstrahlung off heavy targets and they decay to e+e –

  • A heavy photon appears as an e+e- resonance on a large background of QED tridents.

  • Heavy photons can travel detectabledistances before decaying, providing a unique signature.

g’ =  e

Why Consider Heavy Photons?

  • Are there are additional U(1)’s in Nature? If so, they’ll show up by mixing with “our” photon, inducing weak couplings to electric charge.

  • Heavy Photons could mediate Dark Matter annihilations. Their decays may explain excess high energy electrons and positrons in the cosmic rays; their interactions may account for the DAMA dark matter “detection”.

Pamela Positron Excess

SLAC Activities on HPS and APEX

SLAC Heavy Photon Group is engaged in two projects:

HPS (Heavy Photon Search) has just submitted a proposal to JLab

  • Review next week at JLab workshop; approval this Fall?

  • Hope to engineer, construct, test, install by Spring 2012

  • Building Si tracker/vertexer, targets, and SVT data acquisition systemGOOD PROJECTS FOR ROTATION STUDENTS

    APEX (A Prime Experiment) utilizes two large existing spectrometers in Jlab’s Hall A to search for heavy photons

  • SLAC built targets, helped with test run, and is developing analysis

  • SLAC will continue helping run and analyze APEX

    Contact: John Jaros

Si Tracker

APV25 Readout

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