ElementaryPar,clePhysics attheHighestEnergieswith the...

Elementary Par,cle Physics at the Highest Energies with

the ATLAS Experiment Jason Nielsen

Department of Physics Santa Cruz Ins,tute for Par,cle Physics University of California, Santa Cruz

UCSC Physics 205 January 7, 2013

High-‐Energy Collider Physics •  Addressing the big ques,ons of par,cle physics

–  Is the Standard Model of electroweak symmetry breaking and quantum chromodynamics complete?

– What is the nature of the unknown dark maEer? •  Studying proton-‐proton collisions at 0.9-‐14 TeV energies

– UCSC group was one of the first US groups to begin involvement in ATLAS aQer SSC cancellaRon in 1994

•  Research in this field requires –  Electronics skills for experimental apparatus –  Knowledge of reconstrucRon and analyis soQware – Good grasp of current results in underlying theory – Ability to work in internaRonal collaboraRon

J.Nielsen 2 Physics 205

Large Hadron Collider at CERN

J.Nielsen Physics 205 3

ATLAS Experiment at the LHC


Why is the Detector Apparatus So Big?


In fact, it is just big enough to measure par,cle kinema,cs accurately!

Calorimeter Spectrometer (Tracker)

B

Charged parRcle moves along helix under influence of strong B field

L s

Measuring sagiEa of 1 TeV muon requires large L and large B

ParRcle deposits energy by showering in dense absorber medium

Remaining energy (X0 is measure of energy loss in medium)

ATLAS Collaborators at UCSC


Hartmut Sadrozinski Bruce Schumm Abe Seiden Vitaliy Fadeyev Forest MarRnez-‐McKinney Ned Spencer Max Wilder

Marco BaEaglia Alex Grillo Andrew Kuhl Alexander Law Alan Litke Bill Lockman Peter Manning Jovan Mitrevski

Discovery of a New Boson in ATLAS •  Announcement on July 4, 2012 of a new boson found in the Higgs search, but is it the Higgs boson?

•  Also seen by CMS experiment in the same decay modes J.Nielsen Physics 205 7

100 110 120 130 140 150 160

wei

ghts

/ 2

GeV

Σ

20

40

60

80

100

γγ→H

Data S/B WeightedSig+Bkg Fit

Bkg (4th order polynomial)

ATLAS

-1Ldt=4.8fb∫=7 TeV, s-1Ldt=5.9fb∫=8 TeV, s

=126.5 GeV)H

(m

[GeV]γγm100 110 120 130 140 150 160

wei

ghts

- Bk

gΣ

-8-4048

)µSignal strength (

-1 0 1

Combined

4l→ (*) ZZ→H

γγ →H

νlν l→ (*) WW→H

ττ →H

bb→W,Z H

-1Ldt = 4.6 - 4.8 fb∫ = 7 TeV: s-1Ldt = 5.8 - 5.9 fb∫ = 8 TeV: s

-1Ldt = 4.8 fb∫ = 7 TeV: s-1Ldt = 5.8 fb∫ = 8 TeV: s



-1Ldt = 4.7 fb∫ = 7 TeV: s

-1Ldt = 4.6-4.7 fb∫ = 7 TeV: s

= 126.0 GeVHm

0.3± = 1.4 µ

ATLAS 2011 - 2012

Current ATLAS Physics Topics at UCSC •  Searching for new physics predicted in Beyond SM

– New parRcles in theories of supersymmetry – Universal extra dimensions

•  Measuring newly-‐discovered scalar (“Higgs”) boson •  Measuring SM physics processes to test detailed calculaRons in established models of proton interacRons

•  These topics rely on development of –  Precision parRcle detector technology –  Robust parRcle reconstrucRon algorithms –  CompuRng infrastructure for “big data” analysis


ATLAS Semi-‐Conductor Tracker •  Segmented strips; p-‐n juncRon; depleRon region •  RelaRvely cheap way to cover large cylindrical area

–  SegmentaRon in z (giving “pixels”) can improve resoluRon

•  CollaboraRon with Japan, UK, and others


e h

e e

e

e

h

h

h

h

Searches for Supersymmetry


•  Non-‐resonant diphoton producRon with non-‐interacRng graviRnos (dark)

•  World’s best sensiRvity to General Gauge MediaRon models of GMSB

•  Working on improvements for the 8 TeV dataset

[GeV]missTE

0 50 100 150 200 250 300

Entri

es /

10 G

eV

-210

-110

1

10

210

310 = 7 TeV)sData 2011 (QCDW, top

γγW,Z + =190 TeVΛSPS8

-1Ldt = 4.8 fb∫SR C

ATLAS

[GeV]10χ∼

m200 400 600 800 1000 1200

[GeV

]g~

m

700

800

900

1000

1100

1200

1300

1400

1500

ATLAS∫ = 7 TeVs, -1L dt = 4.7 fb

)theorySUSYσ1 ±Observed limit (

)expσ1 ±Expected limit (-1ATLAS 1.0 fb

< 0.1mmτ =2, cβGGM: bino-like neutralino, tan

01χ∼

< m

g~m

Searches for Supersymmetry


•  Neutralino decays to Higgs bosons, followed by decay to b quarks

•  IdenRfy jets of parRcles coming from b quarks

•  First search for Higgs bosons in “cascade decays” of SUSY parRcles

0 50 100 150 200 250 300

Even

ts /

10 G

eV

-110

1

10

210

310

410

510 ATLAS-1 Ldt = 4.7 fb∫

=7 TeVs

QCD multijetW+jetstt

single topsignal m(gluino,neutralino)=(800,750) GeVsignal m(gluino,neutralino)=(500,150) GeV

SM Totaldata

ATLAS

[GeV]missTE

0 50 100 150 200 250 300Dat

a/M

C ra

tio

00.5

11.5

22.5

33.5

44.5

stat. errorsyst. error

Neutralino mass [GeV]200 300 400 500 600 700 800 900 1000

Glu

ino

mas

s [G

eV]

300

400

500

600

700

800

900

1000

1100

)theorySUSYσ1 ±Observed limit (

)expσ1 ±Expected limit (

ATLAS

-1 Ldt = 4.7 fb∫=7 TeVs

|<0µ=1.5, |βGGM: higgsino-like neutralino, tan

NLSPg~

All limits at 95% CL

Searches for Higgs Bosons •  Low-‐mass Standard Model Higgs bosons also decay most oQen to b-‐quarks, “tagged” by precision track vertexing


•  Difficult but important measurement of the most common Higgs boson decay: is it as expected?

[GeV]bbm20 40 60 80 100 120 140 160 180

Even

ts/2

0 G

eV

05

1015202530354045 ZH

WHMultijetTopWbWZbZDibosonPre FitData 2012

ATLAS Preliminary = 8 TeVs, -1 L dt=13.0 fb∫ > 200 GeVW

T1 Lepton 2 Jets, p

Universal Extra Dimensions •  All parRcles propagate through 4+2 dimensions

– Addresses weakness of gravity relaRve to other forces –  Two compacRfied dimensions give rise to tower of excited modes (new parRcles – dark maEer?)


•  Certain 2UED scenarios predict direct producRon of 4 top quarks – impressively large number of parRcles in the event

P. Manning

ATLANTIS Event Display


Proposed LHC & ATLAS Upgrade •  New high-‐mass parRcles are produced rarely, so it has been proposed to increase the LHC luminosity (sLHC) and increase the overall rate of pp collisions

•  Expect fluences of 1016 neutron equivalent / cm2 in inner detector over lifeRme of the experiment –  Requires radiaRon-‐hard detectors, fast readout of tens of thousands of important track points

•  Working on research & development for –  Inner “B-‐Layer” addiRon: pixel layer near beamline, used to improve secondary vertex idenRficaRon

–  Phase II: replace enRre tracking detector


ATLAS Tracker Upgrade R&D

•  RadiaRon-‐hard silicon sensor technology

•  SiGe low-‐power analog preamplifier design

•  ConstrucRon of prototype detector modules

•  High-‐speed data transmission on thin cables

•  SimulaRon of performance


LHC pp Run Schedule •  2010-‐2011: 7 TeV, collected 5 s-‐1 total •  2012: 8 TeV, collected 20 s-‐1 more •  2013-‐2014: 18-‐month shutdown to install silicon IBL •  2015-‐2017: 14 TeV, 50 s-‐1 at designed 1 x 1034 cm-‐2s-‐1

•  2018: 12-‐month shutdown for “Phase 1” upgrade •  2019-‐2021: 14 TeV beyond design luminosity, 300 s-‐1

•  2022: shutdown for “Phase 2” upgrade


Other high-‐energy colliders, including ILC, also in design phase Which is best for studying the proper3es of the new boson?

Summary •  UCSC ATLAS group: parRcle physics at the energy fronRer

–  Searches for new parRcles – Measurements of Higgs boson –  Precision measurements of the Standard Model

•  SCIPP laboratory hosts R&D on the proposed detector upgrades for the ATLAS experiment tracking systems


ElementaryPar,clePhysics attheHighestEnergieswith the...

Documents

Transcript of ElementaryPar,clePhysics attheHighestEnergieswith the...