Que es FNAL?

Fermilab:
Fermi National Accelerator
Laboratory
¿qué hacemos?
www.fnal.gov
Tevatron collider in Run II
• The Tevatron is a
proton-antiproton
s = 1.96TeV with
in RunII980
(1.8TeV RunI)
collider
GeV/beam
• 36 p and p bunches
!396 ns between
bunch crossing
– Increased from 6x6
bunches with 3.5µs in
Run I
• Increased
D0
MINOS
MINiBOON
CDF
E815
Descubrimientos
• Descubrimiento del quark Top (1995, D0 y CDF):
– Ultimo quark de los 6 predichos por la teoría del modelo
estándar. Tan pesado como el átomo de oro
• Descubrimiento del quark bottom (1977, E288):
– Descubrieron una nueva partícula, Upsilon, estado resonante
de quark b y de su antiquark. (comienza la 3rd generación)
• Determinación mas precisa de los bosones W,Z:
– Permite confirmación del modelo estándar y junto con la
medida de la masa del top => masa Higgs
•
Observación de violación CP directa (1999, Ktev)
– Tiene implicaciones en el entendimiento de la asimetría
materia-antimateria
• Medida precisa de la vida media de las partículas con
charm
– Entendimiento de las fuerzas entre quarks y de cómo
combinan los quarks para formar partículas
Descubrimientos
• Evidencia experimental del neutrino del tau (2000,DONUT)
– Ultima partícula de la tercera generación. Casi sin masa. Completa el
modelo estándar de partículas
• Estructura del protón y del neutron usando haces de neutrino
– Determinación de la división de quarks y gluones dentro de estas
partículas y su energía
• Medida del momento magnético de partículas con charm
(hiperones)
– Pequeños imanes que viven menos de un billon de segundo.
• Calculo de la constante de acoplamiento fuerte, !s, usando
superordenadores (grupo teórico, lattice QCD)
– Describe la intensidad de la fuerza fuerte. Una medida precisa de esta
constante solo se puede hacer usando cálculos numéricos de “ lattice
QCD” y gran poder de calculo.
• Descubrimiento de un quasar a 27 billones de años luz(2000,
SDSS)
– Estudian un cuarto del cielo (10000 grados2 o 200 millones de objetos
celestiales). Este es el segundo quarsar mas lejano
¿Como se
hace?
Tools from Physics Research
" Medical imaging tools – Magnetic
Resonance Imaging (MRI), PET scan
detectors, tracer nuclides, CAT scans are
derived from techniques invented for
research.
" Parallel computing – the use of many
computers to attack different parts of a
problem simultaneously – was invented by
scientists who needed faster real-time
processing of data. Such techniques are
now the mainstay of weather forecasting
and market trend analyses.
Accelerators for Society
Particle accelerators were devised to produce high energy
probes for studying the atom.
Now they are used for medical therapy, medical
diagnostics, materials research, making electronic circuits,
nuclear waste disposal and food sterilization.
CATEGORY OF ACCELERATORS
NUCLEAR AND PARTICLE PHYSICS
High energy accelerators
BIOMEDICAL ACCELERATORS
Radiotherapy
(Biomedical) research
Medical radioisotope production
INDUSTRIAL ACCELERATORS
Industrial electron accelerators
Ion implanters
Surface modification centers and research
SYNCHROTRON RADIATION SOURCES
Estimated total
NUMBERS
IN USE
112
>4000
800
~200
~1500
>2000
~1000
~50
~10000
Introduction
• Top quark was expected in the Standard Model
(SM) of electroweak interactions as a partner
of b-quark in SU(2) doublet of weak isospin for
the third family of quarks
– Evidence for top in 1994 (CDF)
– Observation in 1995 (CDF&D0)
• In Run I statistical uncertainties dominated:
– Overall consistency with the SM picture
– but…still a few loose ends
• In anticipation of much increased statistics in
Run II:
– Rich physics menu
– Increased luminosity ! increased precision
– Surprises?
• Preliminary results on: cross section, mass, W helicity
and single top
Top quark production
•Difficult
to produce
1 in 10000
Millions
Events is
a top
Top Quarks at the Tevatron
Pair production
B(t_Wb) =
100%
W’s decay
modes used to
classify the
final states
85%
15%
•Dilepton (e,m)
BR=5%
•Lepton (e,m) +jets
BR=30%
•All jets
BR=44%
• thad+X
BR=21%
Ejemplo: Masa del Top
• Un suceso top:
Identifying
particles
The quarks (and gluons) are seen as jets –
sprays of particles travelling in similar
directions
particles in a jet
quark
Jets from b-quarks are of particular interest; they have
some particles that live for a long time and their decays
are separated from the primary interaction point by a
millimeter or so, and sensed in the inner silicon
tracking detector
Neutrinos do not interact at all, but can be sensed by
the imbalance in momentum of all the observed
particles. We ‘observe’ them in the sense of Sherlock
Holmes’ dog that did not bark in the night.
Methodology & tools
Full characterization of the chosen final state
signature in terms of SM background processes (control
region)
– Optimize signal region for best measurement precision
• How to separate signal from background:
– Top events have very distinctive signatures
• Decay products (leptons, neutrinos, jets) have large pT’s
• Event topology: central and spherical
• Heavy flavor content: always 2 b jets in the final state!
• Tools (need multipurpose detectors!):
– Lepton ID: detector coverage and robust tracking
– Calorimetry: hermetic and well calibrated
– B identification: algorithms pure and efficient
– Simulation: essential to reach precision goals
How to tag a high pT B-jet
Soft Lepton Tag
! Exploits the b quarks semileptonic decays
Silicon Vertex Tag
• Signature of a b decay is
a displaced vertex:
– Long lifetime of b hadrons
(c" ~ 450 µm)+ boost
– B hadrons travel Lxy~3mm
before decay with large
charged track multiplicity
# These leptons have a softer
pT spectrum than W/Z
leptons
# They are less isolated
B-tagging at hadron machines
established:
•crucial for top discovery in RunI
•essential for RunII physics program
Double b-tagged
dilepton event @ CDF
69.7
backgrounds
"=
N signal # N background
$•L
Production cross section
• Test of QCD
– discrepancies from QCD
might imply non SM
physics
Run II Summary
• SUSY processes
• Top-color objects
– Current uncertainty is
statistics dominated
• Experimental handles for
RunII:
– Larger overall efficiency
(lepton ID, trigger,
btagging) w/ better
background rejection
– Main data driven
systematics (jet energy
~
scale, ISR, $btag) scale
with 1/%N
RunII(2fb-1) &'tt/'tt <10%
Top Mass
• Top Mass: Fundamental
SM parameter
– needed to determine ttH
coupling
– important in radiative
corrections:
constrain (Mh/Mh to 35%
in RunII
• Experimental handles:
– B tagging: reduce
background & combinatorial
– Data driven systematics scale
with
1/%N (energy scale, gluon
radiation)
CDF/D0
2 fb-1goal!
Top Mass Measurement
• Template method:
– Kinematic fit under the
tt hypotesis
– Combinatorial issues
–
best )2 combination
chosen
– Likelihood fit
• Dynamical methods:
– Event probability of
being signal or
background as a
function of m(t)
– Better use of event
information ! increase
statistical power
– Well measured events
contribute more
Handles for a precision measurement
• Jet energy scale
L/L(max)
A precise measurement of the
top mass combines cutting
edge theoretical knowledge
with state of the art detector
calibration
L/L(max)
D0 preliminary
Top mass (GeV)
W mass (GeV)
–
gamma-jet balancing: basic in situ calibration tool
–
–
Z+jet balancing: interesting with large statistics
Hadronic W mass: calibration tool in tt double tagged events
–
Z!bb mass: calibration line for b-jets, dedicated trigger
• Theory/MC Generators: understand ISR/FSR, PDF’s
• Simulation: accurate detector modeling
• Fit methodology: how to optimally use event information
• Event selection: large statistic will allow to pick best
measured events
Mass measurement
•Event Selection
•Background
•Systematic Errors
Top Mass Calculation using D0 data
•Three computer-generated views of one event, Run 92704 Event 14022,
that you will analyze.
CAL+TKS R-Z VIEW CAL+TKS END VIEW
DST LEGO
•4 jets:
large blasts of particles – (red and blue towers). One of the jets
•Muon:
green tower
will often contain a low energy or "s o f t" muon (dotted green line).
•Neutrino : undetected
Top Mass Calculation using D0 data
•Mass: The mass is determined from the magnitude of the
momenta. While the momentum of the total system is zero, the
momenta of the various particles are very different.
2
2
E "p =m
2
2
2
E " p = (2m t )
•Momentum conservation
2
•Transverse momentum is cero
E 2 = (2m t ) 2
!
•Momentum: The data plot shows the direction of the
momenta and the magnitude reported in GeV/c for all
particle seen by the detector.
Top Mass Calculation using D0 data
•Because almost all of the energy of the collision is the result
of top and antitop decay, simply add the energies of the four
jets, the lepton and the neutrino before dividing by the two
tops (actually a top and an antitop quark) to obtain the
mass of the most recently discovered quark.
•Neutrino almost does not interact with the material leaving
no track in the detector
•you need to infer the momentum of the neutrino
• Doing this for many events,
•you plot the result for each of them obtaining a Top mass
distribution => improve the measurement by fitting the
distribution
•This is a very simplyfied version
•First order to undertand the idea is OK
Top Mass Calculation using D0 data
Adding up all
objects:
61.2 GeV + 7.3 GeV +
95.5 GeV + 58.6 GeV +
54.8 GeV + 17.0 GeV +
42 GeV = 336.3 GeV
Masa del top:
336.3 GeV/2 = 168 GeV
•If use the computer to calculate
the momentum of neutrino
P = 53.0 GeV
•Top mass = 174.2 GeV
• Como el ejemplo del top se hacen los analisis de datos
– Produccion debil, produccion fuerte, nueva fisica, etc..
• Se necesita:
– Conocimiento teórico del proceso elegido para estudiar
• Probabilidad de producción, productos de desintegración,
Cinemática del suceso,
– Concimiento de los fondos que falsean tu señal
– Aceleradores que produzcan las colisiones a la energía
adecuada y suficiente luminosidad para tener estadistica
– Detectores muy precisos capaces de recoger todo lo que salen de
las colisiones
– Triggers que selecciones solo sucesos interesantes para nuestro
analisis
– Medida de la eficiencia de los requisitos que piden
– Un grupo de trabajo que te ayude con todo
– Se hace en colaboraciones grandes