Transcript Precision Measurements, Small Crosssections, and Non-Standard Signatures: The Learning Curve at a Hadron Collider Henry Frisch Enrico Fermi Institute and Physics Dept University of Chicago Lecture.

Precision Measurements, Small Crosssections,
and Non-Standard Signatures:
The Learning Curve at a Hadron Collider
Henry Frisch
Enrico Fermi Institute and Physics Dept
University of Chicago
Lecture 1: Introduction to Collider Physics
Lecture 2: Tevatron Jets; W,Z,g; Top, Bottom
Lecture 3:
1) Searching for the Higgs
2) Searching for Not-SM events
3) The Learning Curve at a Collider
4) Unsolved Problems
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Acknowledgements
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Thanks to many CDF and D0 colleagues whose
work I’ll show… Also SM MC generator folks
(these are the heros- we need more of them!)
Apologies to D0- I tend to show much more CDF
than D0 as I know it much better (happy for help
on this).
Opinions, errors, and some of the plots are my
own, and do not represent any official anything.
Note-These lectures are frankly pedagogicalapologies to the experts in advance..
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Some topics woven in the lectures:
(part of the hadron collider culture)
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‘Objects’ and their limitations (e.g. em clusters)
Fake rates and efficiencies (z=1 limit and I-spin)
The rationale for signature-based searches
The problem of communicating experimental
results in a model-independent way
The problem of Njets in W and Z production
Systematics-limiting variables
The doubling time: luminosity vs learning
The role of hardware in attracting/keeping
young folks..
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Some Basics- Partons, Luminosity,..
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Before 1970, folk-wisdom was that dsigma-dPt
fell like e-6pt – no interest in exploring pt axis of
the Peyrou plot. Changed with ISR and Fermilab
high Pt pion production..
Parton model was new- not clear what was
source of high-Pt pions- hard-scattering, CIM,..
Jets and fragmentation - `fans’, or `pencils’?
We know so much more now, but shouldn’t
forget the lessons we learned along the way…
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E100 at Fermilab: 1970-77
First Results- 1972- see
power-law behavior and
energy dependence at large
Pt
BUT- ISR beat us to punch
line (sadly, and barely)
Note energy-dependence
at high Pt- evidence of
hard scatters
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From Rick Field’s Lectures at UC, July 2006
Telagram (sic) from Feynman
July 1976
SAW CRONIN AM NOW CONVINCED WERE RIGHT TRACK QUICK WRITE
FEYNMAN
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1971 Berman, Bjorken, and Kogut
Seminal Paper on Hadron Collider Physics- early days
of the parton model
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1971 Berman, Bjorken, and Kogut
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Crossection and Luminosity
(This slide for string theorists- apologies to others)
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Parton Distribution Functions
Gluon
W at LHC
W at TeV
B-quark!
Up
Down
Thanks to Joey
Huston
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Parton-parton Collisions
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The Peyrou Plot: Pt vs Plong;
Rapidity, Pseudo-rapidity
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Orders of Magnitude in Lum vs time
Race of SppS
and Tevatron for
the W and Z;
then for top; now
with LHC for
….?
TeV
Now
LHC?
(note date on slide1997- 10 yrs ago)
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Fermilab (40 miles west of Chicago)
Sears Tower
Superconducting Tevatron Ring
(980 GeV)
Pbars
P’s
(downtown
Chicago)
D0 is here
CDF is here
1 km radius
Antiproton source
(creation and cooling)
Main Injector Ring
(120 GeV)
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Tevatron Startups: 1987 & 2007
(Recent interest wrt LHC- may or may not be relevant to LHC startup)
1987: In nanobarns
2007: In picobarns
LHC is a different beast, but the positive 2nd derivative vs time is deeply fundamentalThe accelerator guys continue learning and improving- lum grows faster and faster…
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The DZero Detector
Calorimeter
Tracking
Silicon
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CDF Detector (5000 Tons)
EM,
Had,
with
embedd
ed 1
plane of
MWCP
at 6X0
Tracking: 8 Layers of 12 sense wires
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Silicon: L00,5SVX,2ISL layers
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Particle Identification
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Charged Leptons- particularly the e and m are
how we trigger on the W and Z- and hence the top
(t->Wb), SUSY (charginos, neutralinos), ..
Neutral leptons- neutrinos- partially ID’s by MET
Heavy flavor- charm, bottom, is identificable by
lifetime- CDF can trigger on displaced vertices
Photons identified by no em cluster, no track
Taus identified surprisingly well
At low Pt can separate pi, K, p by TOF and
dE/dx
All else lumped into `jets’ or hadrons
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Electron Identification
Muon Identification
Credit: Sacha Kopp, undergrad
Beam Line (z axis)
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Beam Line (z axis)
widely-used jargon
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Jet Identification
Neutrino Identification
Credit: Sacha Kopp, undergrad
Note- could be any weaklyinteracting neutral particleor, multiple n’s
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A real CDF Top Quark Event
T-Tbar -> W+bW-bbar
W->charm sbar
B-quark
T-quark->W+bquark
T-quark->W+bquark
TRIDENT
B-quark
Cal. Energy
From electron
W->electron+neutrino
Beam (not at 0,0!)
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Fake Rates
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In addition to the efficiency for identifying an
`object’, need to know how often you get it wrong
(`fake rate’)- depends on definition of the object.
Examplesan isolated pizero in a jet (z=1) can fake a photon
 A low momentum (~5 GeV) K+ can decay K->mn, and
the kaon track segment and the muon track segment
can reconstruct to a straight line, giving a high-Pt m.
 A jet can fake an electron
 A jet can fake a tau
 A tau can fake a photon… etc.
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‘Understanding Objects’ and their limitations
Example- electro-magnetic (em) cluster
Identify an em
cluster as one of 3
objects: (CDF)
Electron-
E/p < 2: Electron
E/p> 2: Jet
P <1: Photon
Where p is from track, E
is from cal
Electron+
E/p measures
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Fund. Physicszoo
bremstrahlung
fractionXXXVRecent
Photon
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event (only an example)
‘Understanding Objects’ and their limitations
Example- Muons becomingElectrons
CDF has a cut on
EM energy for
muons- not more
than ~2 GeV
(minI
E< ~2 GeV: Muon
E> 12, E/p<2:
Electron
E<12, or E/p>2
Jet
p is from track, E is
from calorimeter
Muon Chamber Hits
Electron-
Muon Track
Electron+
Muon Tracks
Photon
Muon Chamber Hits
This is a ``Z->em’ event: Mem(2trks+cluster)=91.4
GeV
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‘Understanding Objects’ and their limitations
Example- Muons becomingElectrons
Look inside
`wedge’ at
calorimeter
towers- see a
25 GeV
colinear
brem off of
muon track
Muon Chamber Hits
EM Towers
ElectronEM Towers
ShowerMax
wiress
Muon Track
Track Extrapolation
Electron+
ShowerMax
strips Muon Tracks
Photon
Muon Chamber Hits
This is a ``Z->em’ event: Mem=91.4 GeV
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It’s not just partons inside hadronswe need hadrons inside partons!
‘Raw Fake’
rate for a jet
faking a
photon- jets
are ordered in
Et
Highest Pt
jet fakes
photon
much more
often…
Note log scale
Z=1 limit of jet fragmentation determines fake rates
for isolated photons- really different for q,g,b,c,…!
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Tevatron LHC comparisons
Mention
Trigger Bias
Tevatron aspects complementary to LHC
Bad
Good
2.8 already
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Tevatron LHC comparisons
Tevatron LHC comparisons
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Tevatron strengths compared to LHC
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Obvious ones (pbar-p,..)
Electron, photon, tau ID
has much less materialultimate MW, H->taus,?
Tau-ID; photon/pizero
separation (shower max)
Triggering at met~20GeV
Triggering on b, c quarks
(SVT)- also (?)
hyperons,…
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Fraction of a radiation length
traversed by leptons from W decay
(CDF Wmass analysis)- << 1 X0
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Calibration Techniques
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Triggering on Low Mass Dimuon
Bumps- SVT
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Muon Efficiency vs h in CDF
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h
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Calibrating the momentum scale
CDF Data from Feb. 02-Sept 03
218 pb-1 for e; 191 pb-1 for m
N.B.
First, Calibrate the spectrometer momentum
scale on the J/Psi and UpsilonMaterial traversed by muons really matters in
calibration (e.g. for Wmass measurement.)
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Calibration of E and P
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Calibration of E and P
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Calibration of E and P
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Calibration of E and P
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Calibration of E and P
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Calibration of E and P
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Calibration of Jet E
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Calibration of Jet E
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Calibration of Jet E
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Z+jet Production- THE Standard Candle
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Use Met in Zee events
to measure Met resolution
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Z+jet Production- THE Standard Candle
M(e+e-)- note low side is ok
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MT(enu)- note low side QCD bkd
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The Importance of SM Predictions!
Next 2 slides show pratfalls due to not
knowing what was `old’ (SM in these 3
cases charm, W+jets, and Z+jets )
physics and hence what was new .
 However, getting it wrong didn’t stop
these guys: Lederman and Rubbia …
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An historical aside: Lederman (Dir, Fermilab), Richter
(Dir, SLAC), and Rubbia (Director, CERN)were on a
panel at Aspen on the Future of HEP. Richter spoke
first about how SLAC would explore the Z with SLC ;
Rubbia spoke 2nd on how CERN would explore the Z
and beyond with LEP; and for Leon?................
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Two cases of non-understanding
of ‘What’s Beneath’
Carlo and the 1984 Top
Leon Lederman and 1971 J/Psi
‘Discovery’
Non-discovery
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Classic example of the importance of
thorough SM predictions of what you expect
Original
transparency of
1986 UA1
SUSY
‘Discovery’!
(Steve Ellis
showed it was a
`cocktail’ of SM
processes- e.g.
Z+jets)
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The End of
st
1
Lecture
“You could be up to your belly-buttons in (SUSY) and not know it..”- C. Prescott
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Credits
I would especially like to thank Florencia Canelli, Frank
Chlebana, Rick Field, Ashutosh Kotwal, Mario MartinezPerez, among many others.
Referemces:
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TheThe
Quarks
Quarks
BACKUP SLIDES
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High PT Jet Production and PDF’s
Note log scale
Really remarkable agreement with CTEQ PDF’s in Mass
(JJ)- note # of decades, systematic uncertainty bands
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Z+jet Production- THE Standard
Candle(SC) and PDF’s
Note log scale
Really remarkable agreement with CTEQ PDF’s - note
# of decades, systematic uncertainty bands
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Z+jet Production- THE Standard Candle
(SC) and PDF’s
Note log scale
Jet Shape in eta-phi space (R)
Energy flow in |Delta-y|=0.7
Really remarkable agreement with CTEQ PDF’s - note
# of decades, systematic uncertainty bands
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A real CDF Top Quark Event
T-Tbar -> W+bW-bbar
Measure transit time here
(stop)
W->charm sbar
B-quark
T-quark->W+bquark
T-quark->W+bquark
TRIDENT
B-quark
Cal. Energy
From electron
W->electron+neutrino
Fit t0 (start) from all tracks
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Can we follow the color flow through kaons, charm, bottom? TOF!
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