LHC State of the Art and News - · PDF file•1232 super-conducting dipole ... •example: energy of photon candidates ... LHC State of the Art and News - Arno Straessner 31

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


Documents

LHC State of the Art and News - · PDF file•1232 super-conducting dipole ... •example: energy of photon candidates ... LHC State of the Art and News - Arno Straessner 31