toward the unknown: first physics from atlas

Toward the Unknown: First Physics from Atlas

J. Hobbs, SBU Colloquium 2

Outline

• Introduction• Why the LHC?• Atlas Experiment

– Won’t discuss CMS, LHCB, …• 1st results• Summary

Oct. 5, 2010

Thanks to my Atlas colleagues….


IntroductionThe Standard Model (SM) provides an

excellent description of experiments and is predictive

Oct. 5, 2010|c| contributions to fits assuming SM

a prio

ri “SM

”

predic

tions


But there are still issues…• Some pieces of SM to work on

– Electroweak symmetry breaking unproven

– Precision flavor studies– Stability: fine tuning issues?

• SM doesn’t answer some big questions– Fermion mass spectrum?– Dark matter?– Matter/antimatter asymmetry?

Including D0 results described 2 weeks ago– Ultimately EW + strong unification

Oct. 5, 2010


EW Symmetry Breaking• Simplest form of (Local) gauge

invariance requires massless force carriers– Photon (and gluon), m=0. OK…– MW = 80 and MZ = 91 GeV

• SM and the Higgs mechanism– Permits non-zero boson mass & gauge

invariance together– Requires a Higgs boson (thus “the Higgs

search”)

Oct. 5, 2010

Is this correct? We don’t know…


EWSB: Current state

Oct. 5, 2010

Indirect constraints on Higgs from SM consistency…

… mW and mt precision are current limiting factors


Fine Tuning / Dark Matter• SM has far too little dark matter (n’s).• Fine tuning: SM values must be within a

part in 1032 for stability. May be unnerving?Supersymmetry (e.g,) is a possible solution to both:

Includes a dark matter candidate. Removes fine-tuning by cancellation and leads to mH < 135 GeV? Predicts new particles whose multiplicity is determined by SM particle content

But no direct experimental evidence, only bounds if it exists M > 100 – 300 GeV Is it right?

Oct. 5, 2010


LHC Motivation• Tests of posited solutions to SM

shortcomings have led to lower mass bounds for new physics, but no direct observation– The space of new physics possibilities is

large. Won’t discuss specifics further…• How to proceed?

– Indirect tests (ala Higgs constraints and CP violation of 2 weeks ago and others)

– Direct searches for higher mass.

Oct. 5, 2010

High mass means higher energy, thus the LHC

Large Hadron Collider (LHC)• In general, rate for

reaction X is – NX = sX* L

• LHC: pp collider design– Ecm = 14 TeV (7x FNAL)– L = 1034/cm2/s (30x FNAL)– Beam

Stored energy 360 MJ (!)

Current 0.58 AOct. 5, 2010 J. Hobbs, SBU Colloquium 9

Most significant increase in Ecm since 1981 (ISR -> SppS)

acceleratornature, ECM


Jet rate vs. jet ET

Tevatron

This is background! unknown

LHC

Oct. 5, 2010

Other processes, s(LHC)/s(TeV) W ttbar gg(400 GeV) Z’(1 TeV) 10x 100x 20000x 300x (but mass dependent)

~~

Large Hadron ColliderRate vs. Ecm

Z

H (500)H (150)

Jet E T>100

b quark

t quark

Jet ET > ECM/4


LHC: Is 14 TeV enough?• For WW scattering to remain bounded

– Requires *something* with M<1 TeV• MH (including SUSY)…

– In SM *something* = Higgs, so MH<O(1 TeV)

– In “SUSY”, MH < 135 GeV, and more particles

• Alternatives must leave WW OK.

Oct. 5, 2010

Encouraging… (some say “guaranteed”)


LHC: What’s the situation now?• Restart in Sept. 2009 after year delay for

magnet connection induced problems• ECM = 7 TeV.

– A safety factor for magnet connections– (Also lower energies during start up)

• Beyond ECM, performing very well– Already at design protons/bunch– Long beam lifetimes, good emittance– Stored energy, 5 MJ – 10 MJ (FNAL, 2 MJ)

Oct. 5, 2010


LHC Performance

Oct. 5, 2010

For past two weeks, injecting more bunches While writing this talk, the record instantaneous luminosity increased 4x with possibly another >2x coming this month…

Bunch trainscommissioned !!

4/pb/day: 400,000 W/day 400 top pairs/day


Atlas Experiment• Higher energies means more particles

and particles with more energy. – Drives experimental design: energy

containment, particle density

Oct. 5, 2010

“jet”

Charged particle trajectories EM energy

Hadronic energy

m

Beam perp to screen

g

e

p

n


Atlas Experiment

Oct. 5, 2010

O(107) read out channels operating efficiency 98%

J. Hobbs, SBU Colloquium 16Oct. 5, 2010

Dijet Event: MJJ = 2.55 TeV ET

J1 = 420 GeV ET

J2 = 320 GeV

(plus others…)

J. Hobbs, SBU Colloquium 1920% of the Atlas collaborators

Can you find Caputo, McCarthy or Hobbs?

Atlas Experimeters

Oct. 5, 2010

SBU Atlas @ SBUSBU Atlas @ CERN + a few missing


1st Science• Can we see the things we expect?

– Reconstruct charged particles– p0, hadronic jets, J/y– W*, Z bosons– Top quark?– Aggregations: multiplicities, W+jets*

• Or the unexpected? Early (proto)searches– q* high rate, low S/B– W’ lower rate, excellent S/B– Early SUSY*, LQ*

Oct. 5, 2010

Every measurement at the LHC is new territory…

*SBU involved


Low Masses: p0->gg

Oct. 5, 2010

Azimuthal angle

Pseudorapidity, h (polar angle) Diphoton mass

Mass vs. h

Are the material and calorimeter understood for the inner “1/2” of the detector?

OK at O(1%)…

ECM = 900 GeV


Dijet Production

Oct. 5, 2010

High-rate process

Differential cross section (pT) for |y| < 2.8

Measures shape, but not absolute rate.

NLOJET++ 4.1.2, CTEQ6.6


Low Masses: J/y -> mm

Somewhat different samples and selections

Do we understand the material in the outer detector?


High Mass: Z and W Bosons

Oct. 5, 2010

Reconstruct Z->ll (l=e,m), This is a critical standard candle. But low rate…

Low mass resonances indicated OK understanding of material, but here resolution mismatch indicates better stats for (probably) alignment and channel-to-channel calibration


W->ln

Oct. 5, 2010

Loose Selection

Final Selection primarily adds MET requirement

Tests understanding of hadronic calib

SBU involvement…

MT= √2pTlpT

v(1-cosdf)


W Cross Section

Oct. 5, 2010

W cross section

Why is W+ different than W-


Correlations: W and Z with jets

• Intrinsically interesting because– Hard to calculate rates with precision.– Dominant background to many new

physics scenariosOct. 5, 2010

SBU works on this

More gluons give more jets. (Each gluon is one more factor of as)


W+Jets

Oct. 5, 2010

Jet multiplicity distribution

jet pT distribution

Stony Brook group working on this topic. Cross sections in internal review now…


Top Quarks? Well, maybeExpect a few top pairs in summer data

sample

Oct. 5, 2010

Analyses ready, and and a few events…


Charged particle multiplicities in pp Collisions at ECM = 900 GeV (Phys Lett B 68, Issue 1, 21-42)And updated for 7 TeV data

1st Physics Publications

Oct. 5, 2010

Early bread & butter science which requires low Linst


Excited quark search• Highest rate visible process is pp ->

jet+jet. Can be enhanced by direct production of new

particles or indirect effects (high mass states)

Oct. 5, 2010

Signal e.g. excited quarks,Excluded over region

0.3 TeV < mq* < 1.26 TeV

(Prev. excl. mq*<0.76 TeV)

Accepted by Phys. Rev. Lett.

Jul. 23 (preliminary)


But it’s already been updated…

Oct. 5, 2010 Preliminary, 9/26

Signal e.g. excited quarks,Excluded over region

0.5 TeV < mq* < 1.53 TeV

Sep. 26


Near Term: W’ search

Oct. 5, 2010

Heavy vector bosons (W’, Z’) features of many new physics models

Clean channel, but yield falls quickly as a function of mass

Existing FNAL bounds roughly 1 TeV, so wait < 1 yr.


And down the road, e.g. SUSY

Oct. 5, 2010

Start with a basic selection and then specific requirements. Early days…


Future• Continue running at 7 TeV until end 2011

– Accumulate 1 fb-1 data (increase 100x)– Already significant room for discovery

Not Higgs, though…• LHC shutdown for 1 yr. Finish magnet

fixes, maybe modest Atlas changes• After restart, move to 14 TeV• Longer term

– Atlas upgrades (2 stages at least)– LHC luminosity growth to design

Oct. 5, 2010


• After a long wait, the LHC/Atlas program is really underway– LHC & experiments working well– Established 1st signals and initial

calibrations– Early search results already new mass

range

• Will explore significant new territory with the current data. What’s there? – Dark Matter? EWSB explained? It really

is unknown territory Oct. 5, 2010

Summary


Where to?

Oct. 5, 2010


(Simulated) H->ZZ->eejj(Simulated )SUSY event


BACKUP

Oct. 5, 2010


Gauge Unification

Oct. 5, 201040

g3

g1

g2

g3

g1

g2SM SUSY

The SM couplings do not intersect at one point.

SUSY does…


Composition of the Universe

Oct. 5, 2010

(0.4% stars)


Atlas good beam efficiency

Oct. 5, 2010


Z cross section


Trigger rates crossing at 40 MHz -> L1 then at 10 kHz -> L2 then at 1 kHz -> HLT (10 GB/s) then at 100 Hz -> tape (1 GB/s)

In a year at 50% duty cycle: 15 PB


Magnet Problem

Oct. 5, 2010

During ramp tests, a solder joint in the cold region failed with 1 V at 9 kA. 1. current ramp (10 A/s) auto stopped 2. relief circuit automatically turned on to dump magnet current ==> All functioned correctly to this pt 3. An arc developed causing failure of He (1.9K) containment 4. He boiled catastrophically causing high pressure…

toward the unknown: first physics from atlas

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