Download Searching for the invisible at the Large Hadron Collider

Searching for the
invisible at the Large
Hadron Collider
Alan Barr
University of Oxford
Wits, August 2012
Robert Hooke, 1665
Apparatus
The truth is, the Science of
Nature has been already too
long made only a work of the
Brain and the Fancy: It is now
high time that it should return to
the plainness and soundness of
Observations on material and
obvious things.
Robert Hooke
Micrographia, 1665
Our apparatus
The microscopic world…
x5
cells: 50 µm
x 20
x 10000
cell nucleus: 10 µm
x 50000
atom: 100 pm
dna: 2 nm
x5
atom nucleus: 2 fm
proton
A hundred billion atomic nuclei lined up in a row would be the width of a human hair
The Matter Particles
Quarks
Charge
+2/3
Charge
-1/3
u
d
c
s
Leptons
t
b
Feel the strong force
e
νe
µ
νµ
τ
ντ
Charge
-1
Charge
-0
Don’t feel the strong force
The Force Particles
g
W
Z
Gluon
Strong
Nuclear
γ
Photon
Weak Nuclear
(heavy)
Electromagetism
Interactions occur via exchange of particles
Standard Model
Maxwell
Dirac
Mass
terms
9
Big scientific questions
Where do the particles get their mass from?
Where has all the anti-matter gone?
What is dark matter made of?
What else is out there?
Heavy gauge bosons
• 1964: Spontaneous symmetry breaking can give
mass to gauge bosons
– Predicts new scalar particle Higgs boson
– Higgs mass not determined by the theory
•1983: Heavy W and Z bosons discovered at CERN
– masses ~80, 91 GeV
•1989-2000: Precision measurements of W and Z
at LEP support the “Standard Model”
Implications of the theory:
Invisible scalar field pervades all of space
Excitations of that field are Higgs bosons
Page 11
Where are the Higgs bosons?
EW theory consistency
MH < 144 GeV
Searches at LEP:
MH >114 GeV
Scattering theory:
MH < 1000 GeV
No-loose theorem
Unitarity of W-W scattering requires SOME new physics
at mass scales below 1 TeV
The Large Hadron Collider
Proton-proton
Controlled environment
7 14 TeV CM energy
26.659 km circumference
9300 magnets
Lorentz factor ~7000
Commissioned: 2008 First physics run: 2010
ATLAS
Segment of
4π detector
2004-2005: assembly of the semiconductor tracker
40 MHz sample rate
6M channels of electronics
20 um resolution
10 year remote operation in radiation environment
16
Observations
[Page 18
Z boson
decay
to a pair
of muons
W and Z bosons
Z e+ e-
W υ µ-
Phys. Rev. D85 (2012) 072004
Frequent
600
per sec
Every 20s
Rare
(N)NLO calculations match precision measurements
21
Increased collision rate during 2011-2012
20-30 collisions per bunch crossing (every 25 ns)
April 2012
22
Higgs boson decays
H bb
H ZZ* 4 leptons
H WW* (l υ) (l υ)
H γγ
Mass reconstruction, sketch plot
The SM Higgs Boson
At mH=125 GeV expect to produce one Higgs Boson about every 10s
Decays rapidly to a variety of different states
arXiv:1207.7214
H Z Z (ll) (l’l’)
arXiv:1207.7214
H W W (l υ) (l υ)
Neutrinos are invisible plot best lower bound on mH:
arXiv:1207.7214
H
γγ
arXiv:1207.7214
Combined statistical significance
5.9 σ
m = 126.0 ± 0.4 (stat) ± 0.4 (sys) GeV
Britain’s most popular paper:
arXiv:1207.7214
Is it the Higgs boson?
(or even a Higgs boson?)
Consistent with Standard Model … within large uncertainties
Looking beyond…
A deeper theory?
1/α
+SUSY
Log10 (µ / GeV)
(S)particles
SM
Spin-1/2
Spin-1
Spin-0
SUSY
squarks (L&R)
quarks (L&R)
sleptons (L&R)
leptons (L&R)
neutrinos (L&?) sneutrinos (L&?)
γ
Z0
W±
gluon
h0
H0
A0
H±
Extended higgs sector
(2 doublets)
B
W0
Bino
Wino0
Wino±
gluino
~
H0
~
H±
Spin-0
After
Mixing
4 x neutralino
Spin-1/2
gluino
2 x chargino
Producing exotics?
standard
exotic
exotic
Time
standard
• If exotics can
be produced
standard
singly they can
decay
Time
exotics
exotics
Time
• If they can only
be pairproduced they
standard
are stable
Time
Require an even number of exotic legs to/from blobs
(Conserved multiplicative quantum number)
– No good for
Dark Matter
candidate
– Only
disappear on
collision
(rare)
Decays of exotics
Production part
Complete event
standard
2 exotics
Time
Decay part
heavy
exotic
Time
lighter
exotic
standard
• Events build from blobs with
2 “exotic legs”
• A pair of cascade decays
results
• Complicated end result
Time
= exotic
= standard
An event with a large momentum imbalance
Seeing the invisible
From collisions
Jets
Jets
PTmiss
JETS
From collisions
Jets:
Had. Calorimeter
E.M. Calorimeter
Tracks from vertex
In-time
b,c quark jets
can decay
to neutrinos
JETS + MISSING MOMENTUM
Measurements
Jets:
∆φ cut
Reduce:
Had. Calorimeter
E.M. Calorimeter
Tracks from vertex
Measure remainder
at small ∆φ
JETS + MISSING MOMENTUM
From cosmics
Reduce by:
(a) requiring tracks
with jets
(b) look for muon hits
Measure remainder:
(a) no beam
(b) timing
JETS + MISSING MOMENTUM
From beam halo
Reduce by requiring tracks with jets
Measure remainder with single beam / timing
JETS + MISSING MOMENTUM
Calorimeter noise
Reduce by requiring
tracks with jets
Measure remainder
(a) no beam
(b) timing
Neutrinos
Z ( υυ) + jets
(+ jets)
W ( lυ) + jets
Careful control of SM backgrounds required
Final results depend largely on
measurements from control regions
Jets
Jets
Z
υυ + jets
Calculations checked with
measurements from control regions
Jets
Jets
Z
μμ + jets
JHEP07(2012)167
Boson + multi-jet backgrounds
Leading order multi-leg calculations match data very well
JHEP07(2012)167
ETmiss tail
Expect SUSY signal in the tail
Results of the multi-jet + ETmiss search
• Agreement between Standard Model prediction and data
• No evidence for supersymmetry in this search (yet)
• Data constrain possible mass of new particles
JHEP07(2012)167
Alan Barr
[Page 49
Interpretations of results
Stop mass
Simplifed
gluino/stop
model
Bound
line
Gluino mass
Alan Barr
[Page 50
Search for squarks and gluinos
Simplifed
gluino/stop
model
Excluded
below this
line
ATLAS-CONF-2012-033
Alan Barr
[Page 51
Gluinos
Stop Squarks
[Page 52
M(H) and direct searches
constrain allowed SUSY space
Example of a consistent pMSSM point
Cahill-Rowley et. al. arXiv:1206.5800
Direct searches for stop squarks
A long way to go…
14 TeV
3000 fb-1
Alan Barr
[Page 55
[Page 56
Reach of a 33 TeV machine
Conclusions
ATLAS and CMS have found a (scalar?) boson
consistent with the SM Higgs
Detailed properties yet to be determined
Fine tuning problem for m(H) very much alive
Pressure on supersymmetry from all sides
A lot of the micro-world still to be explored
Alan Barr
[Page 58
FIN
Alan Barr
[Page 59
Alan Barr
Alan Barr
Alan Barr