estimating the material in the detector using hadronic...

ATLAS: Collisions!

Vivek Jain Indiana UniversityApr 5, 2010

Wednesday, April 7, 2010

Vivek Jain 2

Outline

Introduction A brief tour of the detector

Detector Performance – 900 GeV data Tracking, jets, e/mu, b-tagging, …

Physics result - 900 GeV data Inclusive charged-particle multiplicities

Future Plans Conclusion


Vivek Jain 3

The Large Hadron Collider

Proton-proton collider 7-14 TeV c.m energy

27 km circumference

At 4 interaction points,detectors measure theoutcome of the collisions: Alice, LHCb ATLAS, CMS

• Multi-purpose detectors to study high energy collisions:• Standard Model Physics – top, bottom, QCD, Higgs…• Beyond Standard Model – SUSY, Extra Dimensions, Z’, W’…


Vivek Jain 4

The ATLAS detector is the result of ~20 years of activity by a worldwide community of scientists and engineers 1992 ATLAS Letter of Intent

1997 Construction starts2003 Installation at Point 1 starts2008 Installation completed (Cosmics)20 Nov 2009 Single Beam Splash23 Nov 2009 Collisions at 900 GeV


Vivek Jain 5

From last week!


Vivek Jain 6


Vivek Jain 7

ATLAS:

~7800 tonsA tour of the experimental hallis truly awe inspiring


Vivek Jain 8

Inner Detector

Tracking detector in 2 Tesla solenoid fieldID contains 3 sub-detectors (resolutions) Pixel detector: 10/115 µm in Rϕ/z Silicon strip detector: 17/580 µm Transition radiation tracker: 130µm Rϕ

The ID provides around 3 pixel, 8 SCT and ~30TRT measurements per charged track at η = 0.Coverage: |η| < 2.5 (2.0 for TRT)Allows for accurate track and vertex reconstruction.Resolution goal: σpT /pT = 0.05% pT …1%

è σ ~ 1% for 100 GeV, 25% @500 GeVWednesday, April 7, 2010

Vivek Jain 9

Calorimeters Measure energy deposit

Missing transverse energy is a very important discriminant for Beyond SM physics, e.g., SUSY

Electromagnetic (Pb/Cu/W + LAr) Precision measurements of photons, electrons & hadrons |η| coverage up to 4.9

Hadronic Barrel (Steel + Scint. Tiles) Measure energy

deposit of hadrons |η| coverage

up to 1.7

9Wednesday, April 7, 2010

Vivek Jain 10

Muon Spectrometer

Precision tracking chambers and trigger chambers Monitored drift tubes Cathode drift chambers Thin-gap chambers Resistive plate chambers

|η| coverage up to 2.7 Magnetic field produced

by 3x8 air-core toroids Barrel/End Cap toroids Complex field map B ~ 0.5T, but varies in R/Z Bend in barrel is in Z Bend in ECap is along R


Vivek Jain 11

Trigger Primary physics trigger in

2009: Beam pickup timing

devices (BPTX) Electrostatic beam

pickup located at ± 175 m from IP

Minimum Bias Trigger Scintillators (MBTS)

located at ± 3.56m in z (in front of EC calorimeters)

32 scintillating counters covering 2.09 < |η| < 3.84

Average event rate of collision trigger (MBTS + BPTX) in Dec. 2009 ~ 10 Hz

L2 and EFare software


Vivek Jain 12

Commissioning prior to Test beam data (2004)

Understand detector response, calibration procedures, tuned simulation

Cosmics (2008+2009) Preliminary calibration, alignment,

timing Single Beam splash events

Timing, trigger studies Data challenges to “stress-test”

computing & grid infrastructure Well prepared for collisions


Vivek Jain 13

Data Taking in 2009

20 Nov 2009: single beam splash 23 Nov 2009: First collisions 900 GeV 6 Dec 2009: First collisions with stable

beam. Full detector switched on! 8 Dec 2009: First collisions at 2.36 TeV 16 Dec 2009: end of 2009 data taking

Recorded data samples # of events Integrated Luminosity

Total 917.000 20 µb-1 (syst. uncertainty

900 GeV with Full Detector On 538.000 12 µb-1 up to 30%)

2.36 TeV 34.000

ATLAS data-taking efficiency during this time ~90%


Vivek Jain 13

Data Taking in 2009

20 Nov 2009: single beam splash 23 Nov 2009: First collisions 900 GeV 6 Dec 2009: First collisions with stable

beam. Full detector switched on! 8 Dec 2009: First collisions at 2.36 TeV 16 Dec 2009: end of 2009 data taking

Recorded data samples # of events Integrated Luminosity

Total 917.000 20 µb-1 (syst. uncertainty

900 GeV with Full Detector On 538.000 12 µb-1 up to 30%)

2.36 TeV 34.000

Max peak luminosity seen by ATLAS : ~ 7 x 1026 cm-2 s-1

ATLAS data-taking efficiency during this time ~90%


Vivek Jain 14

Detector Hardware Status in 2009

• High operational fractions of all detector systems!

•Pixels and Silicon strips (SCT) at nominal voltage only with stable beams

Now -99.5%100%


Vivek Jain 1515APS 2/13/2010 ATLAS Status & First Results - A.J. Lankford


Vivek Jain 1515

Many ATLAS detector performance results:Only show a few results

APS 2/13/2010 ATLAS Status & First Results - A.J. Lankford


Vivek Jain 16

View of the Inner Detector – all systems were ON in this run


Vivek Jain 17

Results from cosmics

Differences from MC mainly due toresidual misalignments

Divide a track to its upper and lower halfand refit both hit collections. Get 2 collision-like tracks originating from the same cosmic muon.Compare the two tracks to obtain resolutions.


Vivek Jain 18

Tracking in Collision data

Inside-out tracking. Start with tracks found in the Si detectors, and

extend them out to the TRT Outside-in tracking

Use leftover hits in the TRT, and make standalone tracks. Extend them back into the Si detectors and look for hits, and re-fit

Currently, pT threshold is 500 MeV/c, and many on-going studies to lower it


Vivek Jain 19

Tracking (I)Tracks used here have cuts on number of Pixel (≥ 1) and total number ofSilicon hits (≥ 6), these plots show that track reconstruction in data is well understood.pT>500 MeV/c and Impact Parameter cuts to select primary tracks

# hits inPixels asfunctionof η, φ

# hits inSCT asfunctionof η, φ


Vivek Jain 20

Tracking (II)Efficiency to extend a Pixel only track into the SCT.

Main source of inefficiency is interactionsin the ID material.

In general, data is well represented by MC, but some discrepancies in the high eta region. Mainly related to not knowing the material very well.

Use γ Conversions to look at material (Radiation lengths) + other studies


Vivek Jain 21

Intensity of the transition (=photon) radiation in the TRT α to the Lorentz Factor γ = E/m0c2 of the traversing particle. Use # of high threshold hits to separate e/π!

TRT and electron identification

Cross-check: the “tail” towardshigh-threshold hits is due toelectrons from conversion candidates!

conversion


Vivek Jain 22

An overall systematic uncertainty of 3.9% for η=0 was assigned Green bands include both statistical and systematic uncertainties Largest contribution comes from description of material in ID Used in result on Charged Multiplicities in pp collisions

Investigating lowering pT threshold for the future

Final Tracking Efficiency vs. pT, η – for use in Charged particle multiplicity paper

Andreas Wildauer

ATLAS Preliminary

ATLAS Preliminary


Vivek Jain 23

Pixel Detector: Energy Deposit Analogue readout of pixel

detector allows measurementof energy deposit dE/dx

Band for p, K, pions can be seen Cross-check with confirms bands

Andreas Wildauer

p

K

π


Vivek Jain 24

Primary Vertex:

Beam Spotis stablewithin run

X position: X width:


Vivek Jain 25

Flavour tagging of jets Plenty of heavy flavour jets in top events, SUSY, Higgs ( bb), Z’…

Need good efficiency to tag b-jets and high rejection of light quark/gluon jets

Use variety of algorithms that exploit the fact that b/c hadrons have detectable lifetimes and their daughters have large impact parameters In early data, use simpler algorithms - not as powerful as

more sophisticated ones. Less sensitive to systematics Tracking is the critical element in b-tagging

Only jet direction is needed


Vivek Jain 26

b-tagging basics

Ba0<0

a0>0

x

y

Secondary Vertex

Primary vertex

Jet axis

Soft lepton

Soft-lepton tagging:• Low pT e/mu from B (D)

High mass mB ~ 5 GeVHard fragmentation of b quarksLifetime of B hadrons: cτ ~ 470 µm (mixture B+/B0/Bs) , ~ 390 µm (Λb) for E(B) ~ 50 GeV, flight length ~ 5 mm, d0 ~ 500 µm

Spatial tagging:• Signed impact parameter of tracks (or significance)• Secondary vertex

(limited by Br: around 20% each)

Laurent Vacavant


Vivek Jain 27

Significance of Transverse IPof tracks rel.to PrVrtx

JetProb Algorithm:(for early data)

–ve values (from MC) to make resolution functionand +ve (from data values) for tagging

Determine probability of track to come from PV Make prob. for jet to be light quark/gluon jet.Heavy Flavour jets are at low probability (also other long-lived particles)

Slight bias towards low probability values Related to tails in Significance plotsMC assumes perfectly aligned detector

Data agrees well with MC. With more statistics get Res. Func. from data


Vivek Jain 28

SV0 Tagger based on secondary vertices within jet (for early data)Since in data we expect very few b-quarks, loosen cuts to keep Ks, Λ, γ, hadronic interactions.

This event also tagged by JetProb2nd jet in event (Δφ= 3.0) has SV w/ L/σ ~ 0.9

70 SV within jets in data, ~ 63 in MC (2.4 bjets in MC)


Vivek Jain 29

Calorimeter


Vivek Jain 30

Calorimeter Performance (I)

LArLAr

LAr


Vivek Jain 31

Early Performance of Level 1 Calorimeter Trigger

Comparison of ET(L1 tower) and ∑ET (offline)(separate trigger & readout processing)

using “halo” events from single beam

Level 1 ET resolution meets requirement(<5% at high energy)

ATLAS Status & First Results - A.J. Lankford


Vivek Jain 32

Calorimeter Response to Isolated Tracks Sample of isolated hadrons

0.5<pT<10 GeV, |η|<0.8

<pT> ~ 0.8 GeV No other track withinΔR=0.4

Plot: E(ΔR<0.1)/p Test simulation of calorimeter

response to single hadrons.

π0 signal


Vivek Jain 33

Early Performance of Electron IDCheck of electron ID variables•EM cluster matched to track, E/p•Fraction of high threshold hits in TRT•calorimeter shower shape variables

Sample: EM clusters ET>2.5 GeV + track•783 candidates in 330k events•Dominated by:

• hadron “fakes” ~ 70%• electrons from γ-conversions ~ 30%

E(cluster) / p(track)

Shower shapecluster radius in η

ATLAS Status & First Results - A.J. Lankford

Transition Radiation hits(TR from electrons yield more hi-thresh hits


Vivek Jain 34

JETS


Vivek Jain 35

Missing ET is a very important discriminant in (R-parity conserving) SUSY searches

χ01

χ01

~

~

Missing ET

MC(14 TeV)

Data


Vivek Jain 36

Muons:

MuonToroidwasOFFhere


Vivek Jain 37

Combined Muon Performance: Mu Spectrometer (TOROID ON) + Inner

p > 4 GeV pt > 2.5 GeV |η| < 2.5

50 cands.

In general, ATLAS is working very well. All the pre-collision commissioning has paid off


Vivek Jain 38

First Physics result from 900 GeV data - Charged Particle Multiplicities in pp

Constrain phenomenological models of soft-hadronic interactions and to predict properties at higher centre-of-mass energies. These models include multiple-parton scattering, partonic

matter distributions, scattering between the unresolved protons and colour reconnection.

Pythia incorporates many of these models: parameters have been tuned to describe charged-hadron production and the underlying event in pp and p¯p data at CM energies between 200 GeV and 1.96 TeV


Vivek Jain 39

A specific set of optimised parameters, the ATLASMC09 PYTHIA tune [18], which employs the MRST LO* parton density functions [19] and the pT-ordered parton shower, is the reference tune throughout this paper. These parameters were derived by tuning to underlying event and minimum bias data from Tevatron at 630 GeV and 1.8 TeV. The MC samples generated with this tune were used to determine detector acceptances and efficiencies and to correct the data. For the purpose of comparing the present measurement to different phenomenological models describing minimum-bias events, the following additional MC samples were generated: the ATLAS MC09c [18] PYTHIA tune, which is an extension of the ATLAS MC09 tune optimising the strength of the colour reconnection to describe the hpTi distributions as a function of nch, as measured by CDF in p¯p collisions [3]; the Perugia0 [20] PYTHIA tune, in which the soft-QCD part is tuned using only minimum-bias data from the Tevatron and CERN p¯p colliders; the DW [21] PYTHIA tune, which uses the virtuality-ordered showers and was derived to describe the CDF Run II underlying event and Drell-Yan data. Finally, the PHOJET generator [22] was used as an alternative model. It describes low-pT physics using the two-component Dual Parton Model [23, 24], which includes soft hadronic processes described by Pomeron exchange and semi-hard processes described by perturbative parton scattering. PHOJET relies on PYTHIA for the frag mentation of partons. The versions used for this study were shown to agree with previous measurements


Vivek Jain 40

At higher luminosities will get many such events/beam crossing (at design parameters ~ 23/crossing)

At hi

Our approach is to measure distributions of primary charged particles in events with ≥ 1 charged particle (pt > 500 MeV and |η| < 2.5)

Single arm, minimum bias trigger

Single/Double Diffractive+ Non Diffractive

In general, past experimentsdetected only the ND part (mainly due to trigger effects)thus requiring many model-dependent corrections


Vivek Jain 41

Minimum Bias Trigger

Min. Bias Trigger Scintillators Mounted in front of the EC calorimeters Require at least 1 hit on either side

Measure trigger efficiency from data with orthogonal trigger which requires

colliding proton bunches in ATLAS require > 6 hits in Pixel/SCT & “loose”

track with pT > 200 MeV (L2 & EF) Trigger Efficiency wrt. the analysis

selection is extremely high

MBTS


Vivek Jain 42

Analysis Overview Use all data taken at 900 GeV with stable beams and where trigger,

tracking detectors, and solenoid were operational Measure fully inclusive inelastic distributions to avoid any model

dependence Study events with

a reconstructed primary vertex and ≥ 1 reconstructed track with pT > 500 MeV, |η| < 2.5 ≥ 1 hit in pixel, ≥ 6 hits in SCT |d0

PV| < 1.5 mm, |z0PV|sin(θ) < 1.5 mm

Correct for trigger, vertex & track efficiency But do not extrapolate outside our phase space

This leaves ~326k events for analysis Beam background estimated from unpaired bunches is < 10-4


Vivek Jain 43

Primary Vertex Reco & Secondaries The reconstructed primary vertex must

contain ≥ 3 tracks with pT > 150 MeV, |d0

BS| < 4 mm

Vertex reconstruction efficiency isderived entirely from data

~100% for events with 4 or more tracks η dependence for (n>1) is ~ flat Systematic uncertainty < 0.1%

Cut on d0 and z0 removes secondaries Estimate remaining secondaries from

the impact parameter distribution 2.20% ± 0.05 (stat) ± 0.11 (syst)

of selected tracks

ATLAS Preliminary


Vivek Jain 44

Charged particle density versus η and pT

(left) ATLAS data shows higher values than all MC tunes But: MCs are tuned in different region of phase space

(right) data/MC agrees well only for pt < 0.7 GeV

Nch: number of primarycharged particles corr.to hadron level

Normalized to # of selected events Nev

pT > 500 MeV|η| < 2.5Nch ≥ 1

ATLASPreliminary


Vivek Jain 45

Results (II)

(left) MC excess of events at Nch = 1 but always lower for Nch ≥ 10

(right) increase of <pT> with higher Nch

Change in slope around Nch = 10 as seen by CDF (used in MC09c tune)

Nch: number of primarycharged particles corr.to hadron level

Normalized to # of selected events Nev

pT > 500 MeV|η| < 2.5Nch ≥ 1


Vivek Jain 46

Comparison of Results

Andreas Wildauer

Compared to CMS:Nch consistently lower than measured by ATLAS.This is expected because of CMS definition of NSD, where events with nch=0 enter the normalization, and a subtraction of SD events

Compared to UA1:Nch ≈20% higher than ATLASUA1 used a “double arm” trigger which rejects events with low charged particle multiplicities

ATLAS Preliminary <Nch>ATLAS Preliminary <Nch>|η| < 2.5 1.333 ± 0.003(stat.) ±

0.040(syst.)NSD |η| < 2.4 1.241 ± 0.040 NSD obtained using the Pythia DW tune (Tevatron) NSD obtained using the Pythia DW tune (Tevatron)

CMS NSD (pt > 0.5 GeV) 1.202 ± 0.043


Vivek Jain 47

Physics Prospects for 2010 - 2011•We are scheduled for a long data-taking run at Ecm = 7 TeV in 2010 – 2011: ~ 1 fb-1

•Physics reach is less than at Ecm=14 TeV,

• ~0.2x rate for ttbar; ~0.1x rate for W-prime (1.5 TeV)

•But more than at 2 TeV for high mass objects

~20x rate for ttbar; ~200x rate for W-prime (1.5 TeV)

47


Vivek Jain 48

LHC planning and scenario for the coming 8 years

Note: - Long shutdown in 2012 for preparing design-energy running - 6 months shutdown in 2015 to bring in LINAC4 - Nominal LHC design performance aimed at 2016 - Likely a long shutdown in 2017 (or around that time)

4

This scenario is based on the outcome of the recent ‘Chamonix’ meeting (one month ago) where the machine experts, the experiments and the CERN Management have reviewed the current LHC situation

(integrated luminosities in fb-1)(cm-2s-1)

Moriond EW, 7-March-2010 Peter Jenni (CERN)

48Discoveries at Hadron Colliders


Vivek Jain 49

Three steps in physics program:

Understand detector & reconstruction: using physics samples: Z→ee, µµ (σ~ 0(20 nb)), ttbar (0(100 pb)), …

“Re-discover” Standard Model measure at LHC energies Minbias, W/Z + jets/γ, Drell-Yan, W mass, Dibosons Understand as background to BSM searches

Search for new physics

Most of the plots shown in the next few slides used fast simulation studies to go from 14/10 TeV to lower c.m. energies


Vivek Jain 50

Some of the projections shown here are from Chamonix 2009, whichassume a very well-understood detector and use fast simulation to go from 14 to lower energies

Projections assume similar S/BATLAS can trigger and reconstructleptons up to |η|<2.5Signal cross-section rises fasterthan W+ n-jets background

Ecm (TeV)W’


Vivek Jain 51

Standard Model Higgs at the LHC

GF WBF/VBF

WH / ZH (Tevatron)

ttH

SM Higgs branching ratios

√s=14 TeVM. Duehrssen, La Thuile


Vivek Jain 52

Combined 1 fb-1 H→WW significance extrapolated from the 14 TeV studies – simple cut analyses – will improve over time

~4σ discovery potential possible with 1 fb-1 at 7 TeV

Systematicsstill uncertain

•Combination of gg (0-jets), VBF (2-jets)

•Tevatron currently excludes 162-166 GeV @95%. Will improve with more data and analysis ideas

• Limits on ZZ will be weaker with the same dataset

• Other modes, e.g., ττ, γγ, bb will need more data

7 TeV


Vivek Jain 53

SupersymmetryR-parity conserving SUSY could be found rather quickly if it is at ~1 TeV mass scale Large cross-section for

e.g. expect ~ 100 evts for 1000 pb-1 (√s=7 TeV) in the spectacular golden dilepton channel (for benchmark SU3 mSUGRA point)

χ01

χ01

~

~

Missing ET

Dark matter candidate


Vivek Jain 54

SUSY reach with 200-250 pb-1@ 10 TeV ≈ 1 fb-1 @7 TeV ?

Discovery up to m ~ 750 GeV discovery reach beyond Tevatron expected exclusion (~400 GeV) for √s ≥ 7 TeV

Requires very good understanding of backgrounds, in particular fake missing Et coming from instrumental effects (noise, cracks, …)

SU4

SU3

Many channels (n jets + m leptons) being investigated:• Jets + ET

miss channel: highest reach•1-lepton + jets + ET

miss channel: more robust against Background uncertainties


Vivek Jain 55

Summary

ATLAS is performing very well All sub-systems are operational

Started collecting data at 7 TeV on Mar 30 Data collection efficiency is close to 100%

Start of a “long marathon”!

Thanks to colleagues from whom I “borrowed” slides – Andi Wildauer, Andy Lankford, Claude Guyot, Michael Duehressen, Peter Jenni, Laurent Vacavant. P.A. Delsart


Vivek Jain 56

Road Map of Expected Hadron Collider Performances

Now Tevatron 2 TeV 5 fb-1 (analysed) LHC 0.9 and 2.4 TeV 10 - 20 µb-1

End 2011 Tevatron 2 TeV 10 fb-1

LHC 7 TeV 1 fb-1

End 2014 LHC 14 TeV 25 fb-1

End 2016 LHC 14 TeV 100 fb-1

Early 2020ies LHC 14 TeV 500 fb-1

2030 (s)LHC 14 TeV 3000 fb-1 (ultimately…)

(These are round numbers and estimates, just to give a rough idea…)

Many LHC simulations have been made for 10 TeV, an energy previously (before Chamonix 2010) considered as an intermediate operation point for LHC on its way to the design collision energy

Moriond EW, 7-March-2010 Peter Jenni

56


Vivek Jain 57

More information


Vivek Jain 58


Vivek Jain 59

ATLAS LAr Calorimeters

LAr Calorimeters:•EM Barrel : (|η|<1.475) [Pb-LAr]•EM End-caps : 1.375<|η|<3.2 [Pb-LAr]•Hadronic End-caps: 1.5<|η|<3.2 [Cu-LAr]•Forward: 3.2<|η|<4.9 [Cu,W-LAr]

~190K readout channels


Vivek Jain 60

EM Barrel SegmentationM

in. 22

X0Segmentation in η and depth

by etching cells on Cu electrode

Segmentation in φ by summing signals over electrodes:

16 in strips, 4 in mid, 4 in back

Basic cell: Δη×Δφ=0.025×0.025

Fine segmentation for Position/direction measurementShower shape


Vivek Jain 61

PMT

Plastic scintillatorinside steel absorberstructure

WLS fiber

Tile CalorimeterSampling calorimeter made of plastic scintillator and steel

Light signal proportional to energy deposity in plastic

Notice orientation of scintillator plates


Vivek Jain 62


Vivek Jain 63

P.A. Delsart


Vivek Jain 64

Triggering on Muons


Vivek Jain 65

Cross Sections at LHC σtot = 100 mb (huge!)

Exploration of TeV scalephysics (e.g. Higgs) requires

high beam energy, luminosity

LHC is a W, Z, t, b factory bkgd for discovery physics

Channel LHC# events for 100 fb-1

Total statistics previous expts

W µ ν ~109 ~104 LEP~106 Tevatron

Z µ µ ~108 ~106 LEP~105 Tevatron

tt W b W b µ ν X

~107 ~104 Tevatron

1 ‘year’ @ design luminosityProb

abili

ty o

f int

erac

tion

N = LσWednesday, April 7, 2010

Vivek Jain 66

Most of the previous charged-particle multiplicity measurementswere obtained by selecting data with a double-arm coincidence trigger, thusremoving large fractions of diffractive events. The data were then further corrected to remove the remaining single-diffractive component. This selectionis referred to as non-single-diffractive (NSD).

In some cases, designated as inelastic non-diffractive, the residual double-diffractive component was also subtracted. The selection of NSD or inelastic non-diffractive charged-particle spectra involves model-dependent corrections for the diffractive components and for effects of the trigger selection on events with no charged particles within the acceptance of the detector. The measurement presented in this paper implements a different strategy


Vivek Jain 67

mSUGRA is merely a convenient framework to account for SUSY breaking (only 4 free parameters + 1 sign) for assessing the discovery potential for R-conserving SUSY with χ0

1 as Lightest Super-symmetric Particle (LSP, Dark matter candidate).

The search strategy is largely motivated by the cosmological constraints on the DM relic density. Taking into account LEP and Tevatron results, define benchmark points in the (m0,m1/2 plane):

mSugra - generic searches in RG evolution of scalar and gaugino masses in a typical SUGRA

Cape Town 01/02/2010 67Beyond2010 ATLAS

SU2SU1SU3SU4

SU6

SU8

m1/

2


estimating the material in the detector using hadronic...

Documents