Transcript Particle Physics Experiments Ariel Schwartzman Stanford Student Orientation SLAC session 20-Aug-2012 Fundamental questions • Why are there three generations of elementary particles? • What is the dark matter? o Can.

Particle Physics
Experiments
Ariel Schwartzman
Stanford Student Orientation
SLAC session
20-Aug-2012
Fundamental questions
• Why are there three generations of
elementary particles?
• What is the dark matter?
o
Can we make it in the laboratory?
• Are there undiscovered principles of
nature? New physics laws? Extra
dimensions of space?
• Do all forces become one?
• What is the nature of the neutrino?
• Standard model:
o 12 matter particles, 4
force carriers
o Higgs boson (mass)
o Gravity?
2
Tools
3
Particle physics experiments at
SLAC/Stanford
• Energy frontier
o ATLAS Experiment at the
Large Hadron Collider
(LHC)
o Linear Collider (LC)
ATLAS
• Intensity frontier
o Heavy Photon Search
(HPS)
o Enriched Xenon
Observatory (EXO)
o LBNE
• Cosmic frontier
o Cryogenic Dark Matter
Search (CDMS)
HPS
EXO
CDMS
4
ATLAS Experiment at LHC
• World most powerful particle
accelerator
• Exploration of the energy frontier
(Tera-scale)
o Search for physics beyond the Standard
Model
• Super-symmetry (natural candidate
for dark matter particle)
o Origin of mass
• Understand the mechanism that gives
mass to particles
• Unprecedented detector
capabilities for a hadron collider:
o Enable novel and innovative
reconstruction and analyses techniques
• Internal structure of jets
(quark/gluons) and new jet algorithms
• New ways to interpret LHC events
5
The ATLAS detector
90M channels
40MHz
6
S weights / 2 GeV
Discovery of the Higgs particle!
100
Data S/B Weighted
Sig+Bkg Fit (mH=126.5 GeV)
Bkg (4th order polynomial)
80
4 leptons
60
40
20
S weights - Bkg
ATLAS
8
4
0
-4
-8
100
s=7 TeV, ò Ldt=4.8fb-1
s=8 TeV, ò Ldt=5.9fb-1
110
120
H®g g
130
2 photons
140
150
160
mg g [GeV]
• Higgs mechanism within the Standard Model give mass to
particles through the interaction of particles with a Higgs field
• ATLAS and CMS Detectors have discovered a new boson
consistent with the Higgs particle (excitations of the Higgs filed)
o Observed in different channels: 2-photons, 4-electrons/muons,
2-electrons/muons and 2 neutrinos
7
Discovery of the Higgs particle!
8
Higgs: next steps
• After the discovery of a Higgs-like particle at the LHC,
the major next step is to establish the nature of this
particle:
o Improve mass measurement
o Observe it in other (low cross section) final states
o Measurement of spin and CP quantum numbers
• Spin 0 or 2? CP odd or even?
o Coupling to fermions and bosons
• Observation in b - anti-b decay is key to probe whether it is the SM
Higgs boson
• Very challenging analysis, requiring novel reconstruction
techniques!
o Are there other Higgs-like resonances at higher (or lower) masses?
• Some super-symmetry models predict 5 Higgs particles! Two of
them electrically charged
• Extremely exciting program of research
o Many Higgs physics research opportunities at SLAC
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Super-symmetry searches
•
•
Extension of the Standard Model to solve the hierarchy problem by
introducing super-symmetric partners of the known bosons and fermions.
Provides a candidate for dark matter (LSP)
“Natural” solutions require a light 3rd generation (stop, sbottom squarks)
o One of the highest priorities at the LHC
o Major involvement by the SLAC group: analysis design, use of novel
reconstruction techniques, and optimized b-tagging selections
o Strong connection with the theory group
b/ t
b̄/ t¯
b̄/ t¯
¯
b̃/ ¯t̃
˜b̄/ ˜t¯
L SP
g̃
L SP
g̃
b̃/ t̃
b̃/ t̃
L SP
L SP
b/ t
Sbottom/stop direct production:
2 b-jets and missing ET
More additional jets (and leptons)
in the case of stop production
b̄/ t¯
b/ t
Gluino mediated sbottom/stop production:
4 b-jets and missing ET
12 or more jets in the case of
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(gluino-mediated) stop production
int
L = 4.71 fb-1, s = 7 TeV
1
SUSY
CLs Observed limit ± 1 sTheory
1000
0-lepton + b-jets, 2.0 fb
g ® bb
1
CLs Expected limit ± 1 sexp
mc~0 [GeV]
1200
~
~0, m(~
g-~
g production, ~
g ® bb+c
q) >> m(~
g)
1
mc~0 [GeV]
Super-symmetry searches
600
800
500
ATLAS Preliminary
3 b-jets channel
400
~g ®
bi
f or
~
+c 1
bb
0
700
-1
All limits at 95% CL
600
800
~
~0 , m(~
g-~
g production, ~
g ® t t +c
q) >> m(~
g)
400
dd
en
CLs Expected limit ± 1 sexp
SUSY
CLs Observed limit ± 1 sTheory
SS dilepton, 2.0 fb-1
1-lepton plus bjet, 2.0 fb -1
Multi-jets, 4.7 fb -1
g ® tt
All limits at 95% CL
ATLAS Preliminary
3 b-jets channel
300
rb
~c fo
1
+
t
idd
en
0
200
200
0
200
int
L = 4.71 fb-1, s = 7 TeV
1
~g ®
t
100
300
400
500
600
700
800
900
1000
1100 1200
m~g [GeV]
0
400
500
600
700
800
900
1000
1100
m~g [GeV]
• Exclusion limits reaching 1 TeV for gluino masses
• Extend the exploration of the Tera-scale:
o analysis of more (new) data
o use of innovative analysis ideas to enhance the discovery reach, specially
in in regions of the parameter space that are very difficult to probe:
• m(~b)~m(LSP): high backgrounds and low reconstruction efficiency
• High multiplicity final states and boosted tops
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Jet substructure
• Distinguish boosted heavy particles decaying into “single-jets” from
large mass QCD jets
o Use of novel techniques, many of them pioneered by SLAC/Stanford theorists
o Exploit excellent ATLAS detector capabilities (granularity)
o Fascinating new area of research, with major participation from the SLAC
group
• N-subjettiness, angular correlation functions, QJets, dipolarity, …
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Research opportunities
• Detector activities:
o State-of-the-art data acquisition
concept for high luminosity upgrade
o Pixel detector upgrade and sensors
o Trigger algorithms and online
infrastructure
• Physics analysis and
development of physics
tools:
o Jet substructure techniques
o Higgs>bb/Zg and beyond the
Standard Model Higgs searches
o Super-symmetry searches
o Searches for new phenomena
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SLAC ATLAS contact info
Prof. Ariel Schwartzman
[email protected]
Prof. Su Dong
[email protected]
Dr. Charlie Young
[email protected]
Detailed info on ATLAS@SLAC for students:
http://www.slac.stanford.edu/exp/atlas/students/
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Cryogenic Dark Matter Search (CDMS)
• Direct detection of dark matter
o CDMS searches for weekly-interacting massive particles (WIMPS)
o 10Kg of new “ZIP” Ge detectors at the Soudan Underground Laboratory
in Minnesota
o 200Kg experiment planned for deeper SNOLAB site in Sudbury, Canada
• Very sophisticated detector technology to
provide robust rejection of backgrounds
o State-of-the-art developments within condense matter and particle
physics
2010 CDMS Collaboration Meeting at SNOLAB
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SuperCDMS
• SuperCDMS technology: Identify dark matter by simultaneously
measuring phonons and ionization produced in Ge crystals:
o Phonons heat tungsten strips kept at transition between normal and
superconducting state - acts as a “calorimeter” in the traditional sense
o Ionization signal helps distinguish electron recoils (highly ionizing - largely
background) from nuclear recoils from Dark Matter interactions
0
Dark Matter
(mass ~ GeV – TeV)
Germanium
h
recoil energy
(tens of keV)
E ~ 3V
e
phonons
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Pictorial tour of SuperCDMS efforts
10 kg of IZIP detectors running at Soudan
100 mm IZIP layout – bonding pad detail
100 mm ionization detector
60 keV 241Am ionization test
SNOLAB neutron simulation
6 detector/month
Top view ofthroughput
towers
test
100 mm tower mechanical/wiring concept
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Research opportunities
• Simulation of interactions from neutron calibration
source
• Optical imaging of CDMS detectors for
identification of photolithography defects
• Low noise cryogenic amplifier characterization
Prof. Blas Cabrera
[email protected]
Dr. Richard Partridge
[email protected]
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Heavy Photon Search
•
Dark Matter may be part of a hidden sector
and may carry an analogue of electric
charge which couples to “heavy photons”
•
Heavy Photons (hidden sector gauge bosons,
A’) would be produced in Dark Matter
annihilations and mediate Dark Matter
interactions with regular matter
•
Heavy Photons will couple to regular electric
charge by virtue of their mixing with the
photon. Accordingly, they can be produced
by, and decay into electrons and positrons
•
The Heavy Photon Search is a search for a
massive vector gauge boson radiated by
electron beams, decaying to e+e-
HPS Experiment
• An intense electron beam impinging on a thin target
would produce heavy photons
QED
• We “see” heavy photons as mass bumps above the
large QED background, or as detached decay
vertices downstream of the target
• Heavy photons are detected in a compact silicon
microstrip spectrometer/vertex detector triggered by
a PbWO4 electromagnetic calorimeter.
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Status and plans
•
•
•
HPS Test Run ran this past Spring at Jefferson Laboratory.
Worked well in a parasitic run! Further running approved by Program
Committee
Presently designing and building the full experiment, HPS’, for an approved six
week commissioning run at the end of 2014. Expect an extended run in 2015
HPS will be able to search a large unexplored region of the A’ mass, coupling
constant parameter space
1.1 GeV
Commissioning Run
2.2 GeV
Commissioning Run
2.2/6.6 GeV
Data Runsx
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HPS construction and operation
Test run
at JLab
Silicon tracker assembly at SLAC
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Opportunities for students
•
Good timing for new students
2012
Help analyze test run data
2012-13
Design and Propose HPS’
2013-14
Build, install, and commission HPS’ at JLAB
2014-15
Take data with HPS’ and analyze
•
Ideal training for all aspects of HEP experimentation
Experiment design, planning, and simulation
Proposal writing and submission and defense
State of the art hardware construction and commissioning
Data taking, monitoring, and analysis
Contact: Prof John Jaros
([email protected])
Rotation Projects available on HPS this year:
https://confluence.slac.stanford.edu/display/hpsg/R
otation+Projects+in+Heavy+Photon+Search
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Enriched Xenon Observatory
• Detect neutrino-less double
beta decay of Xe-136
• 2 modes of ββdecay:
o (2νββ): allowed in SM, but
extremely rare process (halflife~1020 years)
o (0νββ): only 2 electrons are
emitted
• Lepton number violation
(not allowed in the SM)
• Only possible if neutrino
have mass and are
Majorana particles
(neutrino=anti-neutrino)
half life
neutrino mass
• EXO-200 has observed the
(2νββ) decay mode in Xe for
the first time, and established
the best limit on the (0νββ)
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decay mode
EXO-200 Experiment
• 500m underground in New Mexico
• TPC (Time Projection Chamber) measures energy (scintillation light in
photo-detectors) and longitudinal position (from drift time)
o Signal reconstructed as single-cluster events
o Gamma-ray backgrounds produce multiple clusters
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Next EXO concept
• One order of magnitude
more Xe-136 (multi-ton
detector)
• Increased sensitivity by
higher background
rejection:
o 4 times deeper (2Km
underground!) to shield
more atmospheric radiation
o larger external shielding (led
and water)
• Water shielding
instrumented with PMT
to remove cosmic ray
muon backgrounds
• Access to Xe chamber
for single Barium ion
extraction and tagging
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Opportunities for students
• Characterizing detectors of Xe
scintillation photons
(photodetectors)
• Develop detector electronics that
operate at liquid Xe temperature
(165 K)
•
o Reduced noise
Ba++ extraction
Signal pulse
fitting
and identification
o Eliminate all backgrounds to 0νsignal
• mechanical probe development
• EXO-200 event reconstruction and
calibration:
o Improve efficiency and background rejection
o Compare calibration source with simulation
• Next EXO conceptual design and
optimization:
o Study of different detector concepts with
simulations to improve physics performance
Many opportunities for
rotation students which
could lead into an EXO200 analysis thesis with a
strong background in
detector R&D
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EXO Contact info
Prof. Martin Breidenbach
[email protected]
Prof. Giorgio Gratta
[email protected]
Dr. Peter Rowson
[email protected]
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LBNE
• 7 fundamental numbers
(m1,m2,m3,q12 ,q23,q13 and dCP)
• dCP may be related to leptogenesis
and the matter imbalance of the
universe
• Global competition to build the
experiment to measure it:
o LBNE experiment sends beam
from FNAL to Homestake Mine
(1300km)
• Newly formed SLAC Group joining
LBNE and (probably) a more nearteam experiment with data in 2013
or 2014
• We will likely be looking for a
rotation student in Winter or Spring
Quarter
LBNE Far Detector:
34 kTons of Liquid Argon
Contact info:
Dr. Mark Convery
[email protected]
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Summary
• Particle physics experiments aim to answer some of the
most important questions in physics today:
o
o
o
o
Origin of mass
Dark matter
Nature of the neutrino
…
• Fascinating time, new experimental tools can
fundamentally change our understanding of the universe
• SLAC has a major role in key current particle physics
experiments and in the design of future
facilities/detectors:
o Broad and diverse program of research
o Exciting research opportunities:
• State-of-the-art detector technologies, electronics, computing, algorithms for
pattern recognition, and physics analyses
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