Cosners House Forum on LHC startup April 07 1 Minimum bias studies etc…. Craig Buttar University...

Cosners House Forum on LHC startup April 07

1

Minimum bias studies etc….

Craig Buttar

University of Glasgow


2

Outline

• LHC start up• Minimum bias events

– Why study them?– What are they?

• Triggering minimum bias– Minimum bias trigger scintilators (MBTS)– Random trigger and track trigger

• Tracking– Reconstructing low pT tracks– Vertex reconstruction– Using pixel tracklets

• Underlying event– What is it and why measure it– Measurement with ATLAS

• Summary


3

1.6 10136.2 10121.7 10128.6 1011intensity per beam

1.1.45.12.06beam energy (MJ)

65102.80.7event rate 1 1 5 (kHz)

701130.8W rate 2 1 5 (per 24h)

71.10.30.08Z rate 3 1 5 (per 24h)

1.6 10302.6 10297 10282 1028Luminosity 1 5

11111111* 1 5 (m)

10442ib (1010)

1561564343Kb

1.6 10136.2 10121.7 10128.6 1011intensity per beam

1.1.45.12.06beam energy (MJ)

65102.80.7event rate 1 1 5 (kHz)

701130.8W rate 2 1 5 (per 24h)

71.10.30.08Z rate 3 1 5 (per 24h)

1.6 10302.6 10297 10282 1028Luminosity 1 5

11111111* 1 5 (m)

10442ib (1010)

1561564343Kb

Installation

Hardware CommissioningShutdown

Engineering Run

450GeV

Hardware Commissioning

450GeV

Installation

Hardware CommissioningShutdown

Engineering Run

450GeV

Hardware Commissioning

450GeV

Collisions 450GeV

Ramp commissioning

Beam commissioningBeam commissioning

450GeV450GeV

Machine checkoutMachine checkout

450GeV450GeV

Collisions 450GeV

Ramp commissioning

Beam commissioningBeam commissioning

450GeV450GeV

Machine checkoutMachine checkout

450GeV450GeV

Events/xing<<1

LHC Pilot run: 2007

S. MyersAt L=1029, can get ~10M MB events in 1 day with 30% eff


4

0.240.241.2 101.2 1032322.12.11.1 101.1 1033331571571.4 101.4 101414115 105 10101028082808

0.150.157.9 107.9 1031310.720.723.8 103.8 1032321261261.1 101.1 101414224 104 10101028082808

0.240.241.2 101.2 1032321.11.15.9 105.9 1032321571571.4 101.4 1014142255 1010101028082808

0.150.152.6 102.6 103131<< 1<< 12.4 102.4 10313142423.7 103.7 10131311114 104 101010936936

0.150.152.6 102.6 1031310.730.731.3 101.3 10323242423.7 103.7 101313224 104 101010936936

0.150.154.4 104.4 1030300.760.762.2 102.2 103131776.2 106.2 101212224 104 101010156156

0.150.151.2 101.2 103030<< 1<< 11.1 101.1 103030221.7 101.7 10121211114 104 1010104343

Rates in 2 (and 8)Rates in 2 (and 8)Rates in 1 and 5Rates in 1 and 5Beam levelsBeam levelsParametersParameters

0.150.15

Events/Events/

crossingcrossing

1.2 101.2 1030300.760.766.1 106.1 103030221.7 101.7 101212224 104 1010104343

LuminosityLuminosity

(cm(cm--22ss--11))

Events/Events/

crossingcrossing


(cm(cm--22ss--11))

EEbeambeam

(MJ)(MJ)

IIbeambeam

protonproton* 1,5* 1,5

(m)(m)

NNkkbb

0.240.241.2 101.2 1032322.12.11.1 101.1 1033331571571.4 101.4 101414115 105 10101028082808

0.150.157.9 107.9 1031310.720.723.8 103.8 1032321261261.1 101.1 101414224 104 10101028082808

0.240.241.2 101.2 1032321.11.15.9 105.9 1032321571571.4 101.4 1014142255 1010101028082808

0.150.152.6 102.6 103131<< 1<< 12.4 102.4 10313142423.7 103.7 10131311114 104 101010936936

0.150.152.6 102.6 1031310.730.731.3 101.3 10323242423.7 103.7 101313224 104 101010936936

0.150.154.4 104.4 1030300.760.762.2 102.2 103131776.2 106.2 101212224 104 101010156156

0.150.151.2 101.2 103030<< 1<< 11.1 101.1 103030221.7 101.7 10121211114 104 1010104343

Rates in 2 (and 8)Rates in 2 (and 8)Rates in 1 and 5Rates in 1 and 5Beam levelsBeam levelsParametersParameters

0.150.15

Events/Events/

crossingcrossing

1.2 101.2 1030300.760.766.1 106.1 103030221.7 101.7 101212224 104 1010104343


(cm(cm--22ss--11))

Events/Events/

crossingcrossing


(cm(cm--22ss--11))

EEbeambeam

(MJ)(MJ)

IIbeambeam

protonproton* 1,5* 1,5

(m)(m)

NNkkbb

Possible Beam Parameter Evolution at 7TeV/beam

S. Myers


5

Why measure min bias?

Not exactly what the LHC was built for!But….. • Physics: measure dN/d|=0

– Compare to NSD data from SppS and Tevatron

• MB samples for pile-up studies– Calorimeter– Physics analyses– Benchmark for sLHC

• Overlap with underlying events– analyses eg VBF, Jets…

• Demonstrate that ATLAS is operational• Inter-calibration of detector elements

– Uniform events• Alignment • Baseline for heavy ions


6

What are minimum bias events?

pp collisions at

√s = 14TeV

PYTHIA6.323 PHOJET1.12

σtot

σelas

σsingle dif (AB→XB)

σ single dif (AB→AX)

σdouble dif

σnon-dif

101.5 mb

22.2 mb

7.2 mb

7.2 mb

10.3 mb

54.7 mb

119.1 mb

34.5 mb

5.5 mb

5.5 mb

4.1 mb

69.5 mbine

last

ic e

ven

ts

Trigger bias:Typically select non-single diffractive

(NSD) events


7

What are minimum bias events?

• Minimum bias are inelastic collisions of two protons– Includes very rare high-pt scatters and very common low-pt scatters

• Minimum bias is an experimental definition– Defined by experimental trigger and analysis

• Relation between experiment and physics is:

inelasticndinelasticndddddsdsdmeasuredfff

fi are acceptances for different physics processes determined by the trigger


8

Event characteristics

• Event characteristics– Non-single diffractive~non-diffractive

inelastic

– Soft tracks pTpeak~250MeV

– Approx flat distribution in to ||~3 and in

– Nch~30; ||<2.5

• Trigger rates ~70mb (NSD!)

– R~700kHz @ L=1031cm-2s-1

M. Leyton


9

Triggering minimum bias

• Use forward scintillators (MBTS)• Random trigger

– inefficient where there are <<1 events/xing– Validate at L2/EF to reduce inefficiency

• Other triggers: jet, lepton triggers– High pt thresholds bias


10

MBTS

• Trigger scintillation counters mounted on end of LAr calorimeter covering same radii as ID

ηη=2.0=2.0

ηη=3.8=3.8interactiointeraction pointn point

Beam-pipeBeam-pipe

++ηη

pan

nel

pan

nel

MBTMBTSS

UA5• To compare to UA5 and CDF data

need to understand composition of the sample trigger bias

• Currently generate inelastic and diffractive parts using PYTHIA

– Need to investigate other simulations-PHOJET


11

• Noise spectrum fits well to a Gaussian with σ=2.52pC

• Beyond 9pC (almost 4σ), non-Gaussian behavior is possible

Accidental rate must be suppressed to ~Hz, limited by EF output-rate of 100Hz

suppression required of 10-6-10-7 at 900GeV and 14TeV

Noise and Accidental Suppression – Lab testsEric Feng


12

Trigger Efficiencies and Bias

• Shown below for each coincidence logic:- Required counter threshold to suppress accidental rate to 1Hz- Corresponding trigger efficiency for each type of event

Coincidence Logic Counter Threshold [pC]

Trigger Efficiency

900 GeV 14 TeV

Non-Diff Single/

Double Diff.

Non-Diff Single/

Double Diff.

1+1 10.75 98% 35% 99% 42%

2+2 7.75 97% 27% 98% 36%

3+3 6.25 94% 20% 97% 30%

4+4 5.25 90% 15% 95% 24%

5+5 4.50 85% 10% 92% 19%

6+6 4.00 79% 7% 89% 14%

Eric Feng


13

Track Trigger

L2 track trigger to validate random trigger when <<1 events/xing

LVL 1

LVL 2

Event-Filter

1 kHz eventrate

100 Hz eventrate

13 MHz eventrate

reduction by a factor 10

storage

pass-through

random trigger

R. Kwee


14

Selecting MinBias Events• At L2 can use

– no. of spacepoints from pixel and SCT little bias

– no. of reconstructed tracks, needed to reject beamgas, halos pt-track > ~1GeV biased

• Rejection of empty events, compare to cosmic runs

<sct-spacepoints>=3 <sct-spacepoints>=0

noise spacepoints from ¼ sct-barrel from cosmics data simulation of noise in whole SCT

R. Kwee


15

Rejecting beam-gas

To reject beam gas need track reconstruction

SCT-cut

at 20 sp

pixel-cut

at 900 sp

minbias 99.2 86.3

noise 0 0.4

beamgas 77.3 31.6

Diffractive (SD+DD)

50.2 15.0 R. Kwee

Beamgas Diffractive


16

CMS MB trigger: Trigger Towers

• Use Forward HCAL – Towers: N vs P

• Strongly correlated

• Trigger should cut on nTowers hit on “N” side and “P” side– e.g. N>10 and P>10

ORCA Simulation


17

Tracking in MB events

• Acceptance limited in rapidity and pt

• Rapidity coverage– Tracking covers ||<2.5

• pT problem

– Need to extrapolate by ~x2 Need to understand low pt

charge track reconstruction

1000 events1000 events

dNch/d

dNch/dpT

Black = Generated (Pythia6.2)

Blue = TrkTrack: iPatRec

Red = TrkTrack: xKalman

Reconstruct tracks with:Reconstruct tracks with: 1) pT>500MeV1) pT>500MeV 2) |d2) |d00| < 1mm| < 1mm 3) # B-layer hits >= 13) # B-layer hits >= 1 4) # precision hits >= 84) # precision hits >= 8

ppTT (MeV) (MeV)


18

Where is the Momentum Limit ?

• Tracker is in principle sensitive to soft tracks– Pt = 400 MeV - tracks reach end of TRT

– Pt = 150 MeV - tracks reach last SCT layer

– Pt = 50 MeV - tracks reach all Pixel layers

150MeV

50MeV

400MeV

A.Salzburger


19

Track reconstruction efficiencies

• MC/Track cuts: • η < 2.5, z0 < 150 mm, d0 < 1 mm• Efficiency: fraction of MC tracks with > 50%

matched hits

Pt=200MeV

Tracking efficiency >20-50% for pt>200MeV

M.Leyton

pT (MeV)


20

Dan ClemensTrack Reconstruction efficiencies by track insertion

efficiency by track insertion

reconstruction with New Tracking

Plot by M.Leyton for comparison : truth matched

•Insert a track into a minimum bias event by overlapping a simulated single track event.

•Reconstruct merged event and look for inserted single track to determine efficiency.


21

Track multiplicity

X V

erte

x R

esid

uasl

Minbias Vertex Reconstruction

I. Dawson, K. Prokofiev

• How well can we reconstruct primary vertex position of a minbias event?

– A good vertex reconstruction efficiency in multi-pp bunch crossings may allow measurement of σNSD.

– Knowledge of primary vertex position can improve signal to noise, eg, H →γγ (UE to Higgs similar to MB)

• Use VxBilloirTools package to fit vertex to minbias tracks.

• Shown here are residuals (difference between reconstructed and truth)

Typically ~250μm precision


22

Tracklet Method

Primary vertex(standard tracking)

Hits in B-layer

Hits in Layer 1

ηΦ

Each hit assigned η,Φ relative to primary vertex

Calculate Δη,ΔΦ for each pair

“Tracklet” defined (now) as Δη<0.01,ΔΦ<0.15

Peter Steinberg, BNL

Exploring methods with sensitivity at lower pTwith even fewer pixel-hits


23

Single Event

Φ

η

Hits in B-layer and L1. Black circles are Truth-primary charged hadrons.Clustered pairs of hits visible near truth hadrons.



24

“Momentum Reconstruction”

pT = 0.011/ΔΦ → Poor person’s tracking code. spatial resolution kicks in above ~2 GeV



25

Charged primary hadronsReconstructed


at low pT (down to 100 MeV) the recontructed and truth pT match well, at higher pT reconstruction gets distorted

Momentum reconstruction


26

Inclusive dNch/dη

Current parameters good for η~0, large backgrounds at |η|~2


Charged primary hadrons

Reconstructed

Focus on |η|<1, look at multiplicity distributionslinear response,good resolution


27

CMS Tracking

Similar to ATLAS pixel tracklets


28

What is the underlying event

High PT scatter

Beam remnants

ISR

Hard and soft physics• ISR• beam remnants• central particle production• colour flow/string drawing


29

VBF Signal (HWWll)

•forward tagging jets

•correlated isolated leptons

• low hadronic activity in central region

•central Higgs production

Tagging jet

Tagging jet

H

W

WZ/WZ/W

Important discovery channelFor Higgs in mass range120-200GeV


30

Model Parameter

Simple MSTP(82)=1

PARP(81)=1.9

Complex MSTP(82)=4

PARP(82)=1.9

Tuned MSTP(82)=4

PARP(82)=1.8

PARP(84)=0.5

Model CJV (eff) LEPACC (eff) All Vetoes (eff)

Simple 0.943 ± 0.003 0.610 ±0.001 0.084 ±0.001

Complex 0.885 ± 0.003 0.575 ±0.001 0.076 ±0.001

Tuned 0.915 ± 0.003 0.589 ±0.001 0.080 ±0.001

Uncertainty at the level of ~6% on CJV Pt>20GeV and ~3% on leptonGiving a total uncertaintly in the range ~8%


31

Average multiplicity of charged particles in the underlying event associated to a leading jet with Pt

ljet (GeV).

Average pTsum (GeV) of charged

particles in the underlying event associated to a leading jet with Pt

ljet (GeV).

Describing the region transverse to the leading jet


32

Min-Max analysis

Jet #1 Direction

“Toward”

“TransMAX” “TransMIN”

“Away”

Jet #1 Direction

“Toward”

“TransMAX” “TransMIN”

Jet #2 Direction

“Away”

“Leading Jet”

“Back-to-Back”

•TransMAX and transMIN sensitive to radiation and soft UE respectively •Back-to-back sample suppresses radiation• difference between tranMAX region and transMIN in leading jet and b-2-b jet sample


3333

EETT jet #1jet #1 = 1.63TeV = 1.63TeV

EETT jet #2jet #2 = 1.16TeV = 1.16TeV

Measuring the underlying event at ATLAS


3434

First physics studies with the underlying event

~ 15 days of data taking in 2007 enough to cover up to pT(leading jet) ~ 40 GeV

~ 15 days of data taking in 2007 enough to cover up to pT(leading jet) ~ 40 GeV

ATLAS - √s=900 GeVATLAS - √s=900 GeVATLAS - √s=14 TeVATLAS - √s=14 TeV

√√s=14TeVs=14TeV

√√s=900GeVs=900GeV

Reconstructed tracksReconstructed tracks

Multiplicity of charged particles with pT > 0.5 GeV and ||< 1 in region transverse to leading jet


35

Selecting the underlying event: |ηtrack | < 2.5, pT

track > 1.0 GeV/c

Njets > 1, |ηjet| < 2.5, ET

jet >10 GeV,

J1J1 J2J2 J3J3

J4J4J5J5

J6J6

charged particles (generator level)

J1J1 J2J2 J3J3

J4J4

J5J5

J6J6charged particles (generator level)

Measuring the underlying event in TeV jets


36

Ra

tio

<N

Tra

ckR

eco>

/<N

Tra

ckM

C>

Ra

tio

<N

Tra

ckR

eco>

/<N

Tra

ckM

C>

Leading jet ET (GeV)Leading jet ET (GeV)

Selecting the underlying event: |ηtrack | < 2.5, pT

track > 1.0 GeV/c

Njets > 1, |ηjet| < 2.5, ET

jet >10 GeV,


37

summary

• Minimum bias and underlying event are uncertain at LHC energies– Energy extrapolation for SppS and CDF not known– dN/d|=0 measurement can be done in early running

• Triggering– Both ATLAS and CMS are developing minimum bias triggers– Need to understand trigger bias to compare to UA5,CDF….

• Tracking– Low pt tracking is challenging but progress by both

ATLAS+CMS

• Underlying event can be measured with early data– Need to ensure overlap between jet and mb samples

• Waiting for data


38

Extra slides


39

We are taking REAL DATA !

• SR1 cosmics test stand– Final TRT barrel

– Final SCT barrel

– 1 sector cabled for both

Day zero start-up looks promising!


40

• Offline reconstruction worked

with little problems within hours– Debug cabling…

• First results are very positive– See residuals and pulls

– No alignment or detailed

calibration yet !

– Reflects excellent mechanical

precision…

• More for Ringberg Workshop

in 2 weeks

• I am definitely very optimistic for first data taking having seen this !– Detector is on a good way !

• Pixels are recovering from cooling problem delay– Finish 3 layer system in time

First Results


41

Tracking: Startup-Initial Alignment

• Very first alignment will be based on:– Mechanical precision

– Detailed survey data

– Cosmics data (SR1/Pit)

– Minimum bias events and inclusive bb

• Studies indicate good

efficiencies after initial alignment– Example taken from T.Golling

– Precision will need Zs and

resonances to fix energy scales,

constrain twists, etc…

M.Elsing Talk in SM meeting


42

Non-diffractive+SD+DD

Non-diffractive only

Diffractive events

Coincidences in MBTSPYTHIA charged-particle level


43

MBTS response

Non-diffractive inelastic events (sample 005001)

Non-diffractive Non-diffractive inelastic events: inelastic events: energy is deposited energy is deposited on both sides on both sides (typically)(typically)

Single and double diffractive inelastic events (sample 005002)

Single diffractive Single diffractive events: energy is events: energy is deposited on deposited on either sideeither side

Double diffractive Double diffractive eventsevents

A.Moraes


44

How many events?

• For dN/d require ~10k• For UE need ~20M MB events to get some with leading jets

PT~30GeV• Need to overlap with jet triggers

– Prescaled PT>25GeV• ~40M events gives ~10 hits/strip in barrel SCT• CMS quote ~18M to intercalibrate their calorimeter with MB


45

Performance goals


46

Machine considerations


47

LHC operational cycle

0

14000

-3000 -2000 -1000 0 1000 2000 3000

Time [s]

MB

cu

rre

nt

0

1

2

3

4

5

6

7

8

9

B [

T]

RAMP DOWNSTART RAMP

PHYSICS

PREPAREPHYSICS

BEAM DUMP

PREINJECTIONPLATEAU

INJECTION

T0 Tinj

SQUEEZE

PHYSICS

Ramp down 18 Mins

Pre-I njection Plateau 15 Mins

I njection 15 Mins

Ramp 28 MinsSqueeze 5 Mins

Prepare Physics 10 MinsPhysics 10 - 20 Hrs


48

Stage I physics runStage I physics run

Start as simple as possibleStart as simple as possible

Change 1 parameter Change 1 parameter (k(kbb N N **1 , 51 , 5)) at a timeat a time

All values for All values for nominal nominal emittanceemittance

7TeV7TeV

10m 10m * in point 2 (luminosity looks fine)* in point 2 (luminosity looks fine)

Rates in 2Rates in 2Rates in 1 and 5Rates in 1 and 5Beam levelsBeam levelsParametersParameters

0.770.77

0.150.15

0.150.15

0.150.15

<< 1<< 1

<< 1<< 1

Events/Events/

crossingcrossing

2.2 102.2 1031313.93.91.1 101.1 10323216161.4 101.4 1013132299 10101010156156

4.4 104.4 1030300.760.762.2 102.2 103131776.2 106.2 101212224 104 101010156156

1.2 101.2 1030300.760.766.1 106.1 103030221.7 101.7 101212224 104 1010104343

1.2 101.2 103030<< 1<< 16.8 106.8 102929221.7 101.7 10121218184 104 1010104343

7.7 107.7 102828<< 1<< 14.2 104.2 1028280.50.54.3 104.3 1011111818101010104343

1.8 101.8 102727<< 1<< 1101027271010--221 101 10101018181010101011


(cm(cm--22ss--11))

Events/Events/

crossingcrossing


(cm(cm--22ss--11))

EEbeambeam

(MJ)(MJ)

IIbeambeam

protonproton

* 1,5* 1,5

(m)(m)

NNkkbb

FfkN

Ln

b*

2

4

fk

LCrossEventrate

b

TOT/

Protons/beam ? 1013

(LEP beam currents)

Stored energy/beam ? 10MJ(SPS fixed target beam)


49

Physics inefficiencies

• What fraction of primary particles reach the various detector layers, versus pT?

• Charged particle component of MB events dominated by +-, with ~10% K+-. First look at -

1) Pixel system should provide 3 space points down to ~100MeV/c.

2) Down to ~150MeV/c, particles can traverse SCT magnetic field, but reduced efficiency below 300MeV/c due to inelastic interactions in ID material.

2


50

Physics inefficiencies

What about the charged kaons?

1) Much larger inefficiencies evident, due to increased material interactions and decays.

2) For pT=300MeV/c, ~10% of K do not reach final Pixel layer.

→ For pT=100MeV/c, K do not even make it into the Pixel system!

3) In the SCT system, 15% of 500MeV/c K do not reach last SCT layer.

→ Below 300MeV/c no spacepoints in outer SCT.

3

Cosners House Forum on LHC startup April 07 1 Minimum bias studies etc…. Craig Buttar University...

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Transcript of Cosners House Forum on LHC startup April 07 1 Minimum bias studies etc…. Craig Buttar University...