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LHC State of the Art and News

Arno Straessner

TU Dresden

on behalf of the ATLAS Collaboration

Vulcano Workshop 2010

Frontier Objects in Astrophysics and Particle Physics

May 24-29, 2010

FSP 101

ATLAS

Outline

• Introduction

• Status of the Large Hadron Collider and

the LHC Experiments

• First LHC Measurements

• Physics Prospects until 2011

• Conclusion

• mainly ATLAS results are shown here

• results of other experiments very similar

LHC State of the Art and News - Arno Straessner 2

The Large Hadron Collider

LHC State of the Art and News - Arno Straessner

ATLAS

CMSALICE

LHCb

• LHC design values:

• pp collisions at 14 TeV centre-of-

mass energy

• 1232 super-conducting dipole

magnets with 8.3 T field

• instantaneous luminosity of

L = 1034 cm-2s-1

• 25 ns bunch spacing

• 2808 bunches per beam

• 1.15 x 1011 protons per bunch

• stored energy of 350 MJ/beam

3

The LHC Detectors

ATLAS CMS

LHCb ALICE

Standard Model, Higgs Bosons, SUSY, and more

CP physics Heavy Ion Collisions


A Long Way Towards Regular LHC Running

• repair work after disastrous magnet incident in 2008

• new quench protection system for magnets

• sensitive to small resistance increases (nΩ)

• full repair will be carried out in LHC shutdown 2011/12

• LHC ready for pp collisions in Nov+Dec 2009:

• at 2 x 450 GeV injection energy

• integrated luminosity 20+18 μb−1 (ATLAS+CMS)

• recorded with stable beams: 12+15 μb−1 (±30% syst. uncertainty)

• 538,000 collision candidates in ATLAS during stable conditions

• collision candidates at 2.36 TeV: 34,000

• first LHC results on 0.9 TeV and 2.36 TeV collisions are now published


World Record pp Collision Energy of 7 TeV

• LHC reached 7 TeV centre-of-mass energy with 1st collision events on March 30, 2010


• very good luminosity lifetime

• longest physics fill: 30 hours

• peak luminosity continuously improved:

Lmax = 8x1028 cm-2s-1

• 2 and 3 colliding bunches

• collimator and beam dump tests

• very important:

machine studies for safe high intensity

operation → reached 1011 p per bunch

• goals for 2010/2011 run

• 7 TeV max. energy

• 768 colliding bunches

• total luminosity of 1 fb−1

• beyond 2013:

• go for 13-14 TeV ultimate energy

• 50-70 fb−1 until 2016

• 3000 fb−1 until 2030

β* squeezed to 2m

x10 improvement

6

higher beam

intensity

Integrated Luminosity


• data taking efficiency ~ 95%

• very similar for CMS, LHCb, and ALICE (>80%)

7

7 TeV Collisions in ATLAS


• largest physics cross-section at LHC: inelastic pp collisions (minimum bias)

8

7 TeV Collisions With Pile-Up


CMS

• no. of pile-up events increases with intensity per bunch

• at nominal LHC luminosity and energy:

~25 pile-up events (in-time)

ATLAS Detector Performance


|η|<2.5

|η|<4.9|η|<3.0

4 Tesla 2 Tesla

10

ATLAS Status Page on 1st Day of 7 TeV Run


• high operational fraction of all

detector components:

• Pixel 97.5% of 80 M channels

• SCT 99.8% of 6 M channels

• TRT 98% of 370 k channels

• calorimeter channels

> 97.3 % (LAr, Tile)

• muon spectrometer

> 99% (MDT, CSC)

• muon trigger chambers

> 99% (RPC, TGC)

The ATLAS Trigger System

• primary trigger in trigger commissioning phase:

• minimum bias trigger scintillators

• MBTS hit on either of the detector sides

• >99.8 % efficient

• time difference between hits on both sides

is used to estimate beam background in

collision events

• other triggers run in parallel to compare their

performance to offline analysis


Minimum Bias

Trigger Scintillator

40 MHz Collision Rate

75 kHz L1 Trigger

200 Hz EF Trigger

3 kHz L2 Trigger

~1.5

MB/evstorage

Hardware

ACTIVE

SoftwareMONITORING

MODE

12


• primary trigger in trigger commissioning phase:

• minimum bias trigger scintillators

• MBTS hit on either of the detector sides

• >99.8 % efficient

• time difference between hits on both sides

is used to estimate beam background in

collision events

• other triggers run in parallel to compare their

performance to offline analysis


Minimum Bias

Trigger Scintillator

40 MHz Collision Rate

75 kHz L1 Trigger

200 Hz EF Trigger

3 kHz L2 Trigger

~1.5

MB/evstorage

Hardware

ACTIVE

SoftwareMONITORING

MODE

13

after offline

vertex

identification



• example: turn-on curves of trigger efficiencies measured at 900 GeV

L1 jet trigger L1 e/γ trigger

• these triggers are ready to be used

• ATLAS is prepared for higher luminosities

• same holds for CMS, LHCb, and ALICE

Performance of the Inner Detector


RMS dominated by

vertex resolution of 75 μmintrinsic accuracy:

pixel 10 μm (rφ) 115 μm (z)

SCT 17 μm (rφ) 580 μm (z)

TRT 130 μm

TRTSCT

Pixel

hits on reconstructed particle tracks:

overlay of many

events from one run

Reconstruction of Kaons and Lambdas


• reconstructed mass peaks in good

agreement with PDG values

• well described by MC simulation

• very good understanding of detector

PDG: mK0=497.6 MeV

PDG: mΛ=1115.7 MeV

Tagging of b-Jets• important for top physics measurements, since BR(t → Wb)=100%

• essential for particle searches, e.g. b-associated production of SUSY-Higgs-Bosons


secondary vertex

with 4 tracks

Calorimeter Performance

• e.m. shower profiles well described

• example: energy of photon candidates

in 2nd LAr calorimeter layer


π0 →γγ

• reconstruction of π0 →γγ mass peak

• very good understanding of calorimetry

Missing Transverse Energy and Jet pT

• missing transverse energy agrees well with

MC predictions over 6 orders of magnitude

• missing ET resolution as expected from MC

• important ingredient for searches for SUSY

→ look for LSP signatures

• highest jet pT of 350 GeV observed in 7 TeV

collisions


ATLAS Muon Spectrometer

• muon system with

large η coverage

• for momentum

measurement and

trigger


• J/ψ → μμ signal observed

• muon tracks reconstructed in muon

spectrometer and inner detector

• gaussian-mean mass: 3.06±0.02 GeV

• resolution: 0.08±0.02 GeV

• Nsignal = 49±12

• Nbackground = 28±4

(computed in a mass range 3σ around the peak)

√s=7 TeV

∫Ldt=320 μb-1

Ready For Some Physics – An Overview

• inelastic pp scattering dominates

→ minimum bias

• QCD processes have large cross-

sections → 2-jet events, 3-jet

events, ...

• with and w/o b-jets

• many events with W and Z bosons

• LHC is a top quark factory

• new particles searches for:

Higgs (SM and supersymmetric),

SUSY, ..

• 13 orders of magnitude


Measurement of Hadron Production


• model independent measurement of

primary charged particle multiplicity

distributions from inelastic events

• kinematic range |η|<2.5 and pT> 500 MeV,

Nch≥ 1 in this phase space

• use MBTS single-arm scintillator trigger

for high efficiency in phase space

• no removal of Single Diffractive (SD)

component.

• correct reconstructed-track distributions

back to hadron level

• trigger and vertex corrections are

measured in data

• main systematics is from track

reconstruction efficiency (4% on dNch/dη) 1st ATLAS pp physics paper

Phys Lett B 688 (2010) 21

More Hadronic Activity Then Predicted


• rate higher than modeled by PYTHIA and

PHOJET tunes, both at 0.9 TeV and 7 TeV

• similar observation by CMS

Parton Luminosities And Event Rates


Process Evts (7 TeV)

in 100 pb-1

Ratio

7 TeV/14 TeV

QCD, pT>100 GeV 32 M 0.2

Z inclusive (NLO) 3 M (3% Z→ℓℓ) 0.4

W inclusive (NLO) 10 M (11% W→ℓv) 0.5

top pairs (NLO+NNLL) 16000 0.2

H (mH=150 GeV, NNLO) 1000 0.3

• examples of dominating partonic

processes at the LHC:

• several W→μv, W→ev and

Z→ee candidates observed at

7 TeV using ~8 nb-1 of data

W/Zq(')

q

(no selection cuts)

Hg

g

t

t

t

g

g

t

t

g

g

tt

t

W→μv Candidate


Z→ee Candidate


Expectations For The 2010/2011 Run


• the goal is to collect 1 fb-1 of data per experiment at √s=7 TeV (ATLAS, CMS)

• we expect 2.5 M selected events in the channels W→ev and W→μv each

• 5 times more than Tevatron today

• measurement of W boson mass possible, but systematics are challenging:

• lepton energy scale, missing pT calibration, PDF's, W pT, backgrounds, pile-up, ...

• top physics will be very interesting:

we will overtake

Tevatron with ~150 pb-1

Top Pair Yields

• cross-section measurements of top pairs at

7 TeV centre-of-mass energy

• top quark mass measurement

• aim for mtop by ATLAS and CMS

by the end of 2010

• systematics: jet energy scale, background,

pile-up, ...

Standard Model Higgs Searches

• LEP and Tevatron today: mH <114.4 GeV and 162 GeV<mH <166 GeV excluded (95% C.L.)

• gg→H→WW is the most sensitive channels in the relevant mass range


7 TeV

• with two experiments and 1 fb-1 at √s=7 TeV:

• if no signal found: 95% CL exclusion between 140 GeV and 200 GeV possible

• evidence/discovery with 3-5 sigma for mH =160-170 GeV

SUSY Searches – mSUGRA


• no mass degeneracy of particles and sparticles → breaking of super-symmetry

• gravity mediated SUSY breaking → mSUGRA model

• R-parity is conserved in mSUGRA:

→ SUSY production in pairs

→ lightest stable SUSY particle (LSP)

is the neutralino

• typical SUSY signatures:

• multi-jets, multi-leptons, missing ET ....

• understanding the SM background

is essential

LSP escapes detection missing ET

p p

g

Lq 0

2R

0

1

qq

X q

SUSY Discovery Reach

• CMS expectation in

all-hadronic channels:

30

200 pb-1


• ATLAS estimate for

lepton + jets + missing-ET channel:

• quickly beyond Tevatron reach with 100 pb-1

• squarks and gluinos with masses above

500 GeV can be discovered with 1fb-1

at 7 TeV

• higher energies in 2013 will push the search

window wide open

Conclusion

• LHC had a very good start in 2010 at 7 TeV record centre-of-mass energy

→ continuous machine development in parallel to data taking

• ATLAS, CMS, LHCb, and ALICE detectors are in good shape

• work ongoing to further improve performance

• first measurements of charged particle production at 0.9 TeV – 7 TeV

• Standard Model physics is about to take off

• new physics signatures are in close reach

• stay tuned:

www.atlas.ch
