Post on 16-Aug-2021
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Fermilab:Fermi National Accelerator
Laboratory
¿qué hacemos?
www.fnal.gov
• The Tevatron is aproton-antiprotoncollider with 980GeV/beam
• 36 p and p bunches!396 ns betweenbunch crossing– Increased from 6x6
bunches with 3.5µs inRun I
• Increasedinstantaneousluminosity:– Run II goal 30 x 1031
cm–2 s-1
– Current: 3÷4.5 x 1031
cm–2 s-1
Tevatron collider in Run II
RunI)(1.8TeV RunII in1.96TeV s =
D0
CDF
E815
MINOS
MINiBOON
• 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 concharm– 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, usandosuperordenadores (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 “ latticeQCD” 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
Descubrimientos
¿Como sehace?
Tools from Physics 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.
" Medical imaging tools – Magnetic
Resonance Imaging (MRI), PET scan
detectors, tracer nuclides, CAT scans are
derived from techniques invented for
research.
Accelerators for SocietyParticle 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 NUMBERSIN USE
NUCLEAR AND PARTICLE PHYSICSHigh energy accelerators 112BIOMEDICAL ACCELERATORSRadiotherapy(Biomedical) researchMedical radioisotope production
>4000800~200
INDUSTRIAL ACCELERATORSIndustrial electron acceleratorsIon implantersSurface modification centers and research
~1500>2000~1000
SYNCHROTRON RADIATION SOURCES ~50Estimated total ~10000
• Top quark was expected in the Standard Model(SM) of electroweak interactions as a partnerof b-quark in SU(2) doublet of weak isospin forthe 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 inRun II:– Rich physics menu
– Increased luminosity ! increased precision
– Surprises?• Preliminary results on: cross section, mass, W helicity
and single top
Introduction
Top quark production
•Difficult
to produce
1 in 10000
Millions
Events is
a top
Top Quarks at the Tevatron
85%
15%
W’s decaymodes used toclassify thefinal states
Pair production
B(t_Wb) =100%
•Dilepton (e,m) BR=5%
•Lepton (e,m) +jets BR=30%
•All jets BR=44%
• thad+X BR=21%
• Un suceso top:
Ejemplo: Masa del Top
Identifying particles
The quarks (and gluons) are seen as jets –sprays of particles travelling in similardirections
Jets from b-quarks are of particular interest; they havesome particles that live for a long time and their decaysare separated from the primary interaction point by amillimeter or so, and sensed in the inner silicontracking detector
Neutrinos do not interact at all, but can be sensed bythe imbalance in momentum of all the observedparticles. We ‘observe’ them in the sense of SherlockHolmes’ dog that did not bark in the night.
quark particles in a jet
Methodology & tools
Full characterization of the chosen final statesignature in terms of SM background processes (controlregion)
– 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
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~3mmbefore decay with largecharged track multiplicity
B-tagging at hadron machinesestablished:
•crucial for top discovery in RunI•essential for RunII physics program
Soft Lepton Tag
! Exploits the b quarks semi-leptonic decays
# These leptons have a softerpT spectrum than W/Zleptons
# They are less isolated
Double b-taggeddilepton event @ CDF
69.7
backgrounds
!
" =Nsignal #Nbackground
$ •L
Production cross section
• Test of QCD– discrepancies from QCD
might imply non SMphysics
• SUSY processes
• Top-color objects
– Current uncertainty isstatistics dominated
• Experimental handles forRunII:– Larger overall efficiency
(lepton ID, trigger,btagging) w/ betterbackground rejection
– Main data drivensystematics (jet energyscale, ISR, $btag) scalewith 1/%N
Run II Summary
RunII(2fb-1) &'tt/'tt <10%
~
Top Mass
• Top Mass: FundamentalSM parameter
– needed to determine ttHcoupling
– important in radiativecorrections:
constrain (Mh/Mh to 35%in RunII
• Experimental handles:– B tagging: reduce
background & combinatorial
– Data driven systematics scalewith
1/%N (energy scale, gluonradiation)
CDF/D0
2 fb-1goal!
Top Mass Measurement
• Template method:– Kinematic fit under the
tt hypotesis
– Combinatorial issues
– best )2 combinationchosen
– Likelihood fit
• Dynamical methods:– Event probability of
being signal orbackground as afunction of m(t)
– Better use of eventinformation ! increasestatistical power
– Well measured eventscontribute more
Handles for a precision measurement
• Jet energy scale– 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 bestmeasured events
A precise measurement of the
top mass combines cuttingedge theoretical knowledgewith state of the art detectorcalibration
D0 preliminary
Top mass (GeV) W mass (GeV)
L/L
(max)
L/L
(max)
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
will often contain a low energy or "soft" muon (dotted green line).
•Muon: green tower
•Neutrino : undetected
Top Mass Calculation using D0 data
•Mass: The mass is determined from the magnitude of themomenta. While the momentum of the total system is zero, themomenta of the various particles are very different.
•Momentum: The data plot shows the direction of themomenta and the magnitude reported in GeV/c for allparticle seen by the detector.
!
E2" p
2= m
2
E2" p
2= (2mt )
2
E2
= (2mt )2
•Momentum conservation
•Transverse momentum is cero
•Because almost all of the energy of the collision is the resultof top and antitop decay, simply add the energies of the fourjets, the lepton and the neutrino before dividing by the twotops (actually a top and an antitop quark) to obtain themass of the most recently discovered quark.
•Neutrino almost does not interact with the material leavingno 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 massdistribution => improve the measurement by fitting thedistribution
Top Mass Calculation using D0 data
•This is a very simplyfied version
•First order to undertand the idea is OK
Top Mass Calculation using D0 data
Adding up allobjects:
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 calculatethe 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 energíaadecuada y suficiente luminosidad para tener estadistica
– Detectores muy precisos capaces de recoger todo lo que salen delas colisiones
– Triggers que selecciones solo sucesos interesantes para nuestroanalisis
– Medida de la eficiencia de los requisitos que piden
– Un grupo de trabajo que te ayude con todo
– Se hace en colaboraciones grandes