preparation for physics: the compact muon solenoid (cms) detector greg rakness university of...

Preparation for Physics:The Compact Muon Solenoid

(CMS) Detector

Greg Rakness

University of California, Los Angeles

RNC Seminar

3 August 2009

Lawrence Berkeley National Lab

3 Aug 2009 G. Rakness (UCLA) 2/62

Outline• Description of CMS• Cosmic rays

– Running the experiment– Detector Performance:

Interaction Region Out

• CMS trigger and its synchronization

• What CMS saw during 10 minutes of beam in September 2008

… and how these things tell us that CMS is ready for physics…


CMS is an experiment in the Large Hadron Collider

LHC parameters: • Proton + proton

collisions with center-of-mass energy 14TeV

• Peak Luminosity ~ 1034/cm2/sec

~109 inelastic collisions/sec

~20 events per crossing (40MHz)

CMS

ATLAS

LHC-B

ALICE


CMS Design: Discover New Physics

SIMULATION

CMS Collab. 2007, J. Phys. G: Nucl. Part. Phys. 34 995–1579.

Some observables which must be detectable…– H Z + Z 4?– t + t b-jet + b-jet + 2

– Z e+ + e–?– H + ?– H + l + jet?

– Missing ET

– Di-jets– Heavy Ions– … and more…


How large is CMS? Compare its physical size with

other detectors…HERMES detector at HERA

(stopped taking data in 2007)

e+


STAR Detector at RHICCurrently taking data…

Au,p,d,Cu Au,p,d,Cu


CMS Detector at LHCCMS is the biggest detector that I have personally worked on…

p,Pbp,Pb


ATLAS Detector at LHC

Of course, there are bigger detectors out there…

p,Pb


The CMS Collaboration

2310 Scientific Authors 38 Countries 175 Institutions

CERN

France

Italy

UK

Switzerland

USA

Austria

Finland

GreeceHungary

Belgium

Poland

Portugal

SpainPakistan

Georgia

Armenia

Ukraine

Uzbekistan

CyprusCroatia

China, PR

Turkey

Belarus

EstoniaIndia

Germany

Korea

Russia

Bulgaria

China (Taiwan)

Iran

Serbia

New-Zealand

Brazil

Ireland

1084

503

723

2310

Member States

Non-Member States

Total

USA

# Scientific Authors

59

49

175

Member States

Total

USA

67Non-Member States

Number ofLaboratories

Associated Institutes

Number of ScientistsNumber of Laboratories

629

As of 3 Oct 2007

Mexico ColombiaLithuania


Yet another way to think of the magnitude of the CMS detector

• 468 chambers• >17,000 electronics boards

16 different types with firmware• ~400,000 readout channels• ~9000 High Voltage channels• 60 remote electronics crates• ~5,500 skew-clear cables

over a million shielded conductors• 1,400 gigabit optical fibers

All of these electronics must be operated and maintained in order just for the CSC’s to deliver physics…

Some numbers describing the CMS Cathode Strip Chambers (CSC)


Compact Muon Solenoid

Detector requirements to extract the desired physics are specified in the Technical Design Report: CERN-LHCC-2006-001

It’s been built. Does it meet the specifications?

From the Interaction Point out:

• Pixel detector

• Silicon strip tracker

• Electromagnetic calorimeter

• Hadronic calorimeter

• 4T superconducting magnet• Muon detectors interleaved with

magnet yokes: • Drift tubes• Resistive plate chambers• Cathode strip chambers

(exploded view)p

p


Accumulation of Cosmic Ray Data

(Summer 2006 – now…)


Cosmic Rays 100m Below GroundThe LHC (and CMS) is located under ~100m of rock

Muon spectra underground addressed in

L.N. Bogdanova, et al., Phys. Atom.

Nucl. 69 (2006) 1293;

arXiv:nucl-ex/0601019v1

Angular distribution of cosmic

ray muons is similar beneath

100m solid rock to that on the

surface…

Rate is smaller by factor of ~100

Cosmics are asynchronous

Many features of cosmic rays make them dissimilar to particles coming from the Interaction Point


Regarding Cosmic Ray Runs

… we are not collecting millions of cosmic ray triggers for their own sake…

Cosmic ray running prepares us to collect physics data when protons collide in the LHC later this year

Greater exposure to operation before beam, greater chance of finding problems before beam

Some CMS subdetectors have been operating 24/7 for months…


Chain of Command

• Shifters– Monitor all CSC activity from control room– If problems arise, call…

• CSC Expert Operators (CEOs)– Weekly rotating duty between proven experts– Mostly graduate students– If necessary, direct shifters’ questions to the appropriate…

• System experts – Experts on-call 24/7 available for each system involved in CSCs – For example, Slow Controls, Run Control, Data Quality

Monitoring, etc.

• CSC Operations Manager– Responsible for any shift logistical issues

Maintain high level of operation while avoiding personnel burnout

Flow chart for the Cathode Strip Chambers (CSC):


Dedicated run with Magnetic Field• Operated CMS for 3 weeks continuously

with magnetic field at 3.8T– October – November 2008

Num

ber

of t

rigge

rs (

x106 )

Day

Note: Months of cosmic ray running is

equivalent to a few minutes of

LHC collisions…


Event Display of Cosmic Ray with Magnetic Field OFF

+y

+x

+z

Cosmic ray enters CMS from

the top (+y), passes near the Interaction Point

(IP), exits CMS at the bottom (–y)

View of CMS looking down the beampipe

IP


Event Display of Cosmic Ray with Magnetic Field ON (3.8T)

+y

+x

+z

View of CMS looking down the beampipe

CMS Magnet: • 6m diameter• 13m long• 4T max field• Stored energy

= 2.5GJ

Solenoidal field in the z-

direction bends the cosmic ray in the r- plane

IP


Response of CMS to Cosmic Rays

Some morsels of detector performance, in the order that particles will see them when

they come from the IP


CMS Pixel Detector

66M pixels

>99% operational

At full luminosity the pixel occupancy will be

<10–4/crossing

Will be able to resolve individual tracks in a

high multiplicity environment

pp

beam pipe

Physics example: find displaced vertices from t + t bbWW 2 jet + 2

Hitmap of cosmic ray data in the pixel detector (B = 3.8T): ~75k events


Response of CMS Pixel Detector to Cosmic Rays

Data calibrated for gains

Simulation uses ideal gain calibration without charge smearing

Cluster charge associated with cosmic ray tracks:

Pixel response to muons well described by a Monte Carlo simulation


CMS Silicon Tracker

Silicon strip detectors surround the pixels

Pixels: ~ 1 m2 of silicon sensors, 65 M pixels Si strips: 223 m2 of silicon sensors; 10 M strips

r = 120 cm

z = 300 cm

Physics example: accurately measure the large momentum of muons from Z + + –

Quarter r-z view of tracker:

pixels

IP


CMS Silicon Tracker Alignment

not aligned

B=0 T

B=3.8T

Cosmic rays: median of residuals for Tracker Outer Barrel…

The quality of this cosmic ray alignment is comparable to what will be obtained with 10–50/pb of collision data

RMS = 10m


CMS Electromagnetic CalorimeterPhysics example: H + …

Energy loss per unit length for muons is well described by

Particle Data Group’s description of

stopping power in PbWO4

TotalCollision LossBremsstrahlung

Demonstrates reasonable understanding of…• Momentum scale of tracker • Energy scale of electromagnetic calorimeter


CMS Hadronic Calorimeter

Hadronic calorimeter response to muons well described by a

Monte Carlo simulation

Physics example: accurately measureSUSY particles jets + “missing” transverse energy


CMS Muon Systems (Barrel):Drift Tubes and Resistive Plate Chambers

Physics example: trigger on W (+ ) Measure efficiency with cosmic ray data (at 3.8T)…

Resistive Plate Chambers:

x (cm)

y (c

m)

Conclusion: overlap of technologies efficiency > 99%

Drift Tubes:

Efficiency (%

)


CMS Muon Systems (Endcap):Cathode Strip Chambers

Physics example: trigger on H + + + Use cosmic ray data to measure residuals…

Wid

th o

f ga

ussi

an c

ore

(cm

)

Resolution is better at the edges of the strips because the charge is shared between strips


CSC Residuals Distributions

position within the strip position within the strip

= 322 m 2= 566 m

Near the edges: |strip coordinate| > 0.25 Near the center: |strip coordinate| < 0.25

With the strip-staggering, the resolution of a chamber can be estimated by1/2 (chamber) = 3/1

2 + 3/22

= 161m

(c.f. value required in Technical Design Report = 150m)

per layer per layer


CMS Level-1 Trigger

It’s not a “detector,” it selects what physics we get out of the

detector…


Functionality of the trigger

Inelastic rate of 109 interactions/sec

Readout 105 events/sec

Write to disk 102 events/sec

Level-1 Trigger

High Level

Trigger

Detectors readout data when a Level-1 Accept (L1A) signal is sent by the trigger system


Level-1 Trigger

µ

e

n

p

Use prompt data (calorimetry and muons) to identify: High p

t electron, muon, jets,

missing ET

CALORIMETERs Cluster finding and energy deposition evaluation

MUON System Segment and track finding

New data every 25 ns Decision latency ~ µs


CMS Level-1 Trigger

On-detector

Calorimeter path Muon path

Final L1A decision L1A received at detectors 3.2sec after collision data readout

Off-detector


CMS Level-1 Trigger

Focus on the trigger of the Cathode Strip Chambers as an example of the detail in the

CMS L1 trigger…


Schematic of CSC Trigger Data Flow

Cathode Strip Front End Boards

Anode Wire Front End

Boards

FE

FE

Trigger Motherboard

Wire Local Charged

Track Board

ALCTTMB

CLCTCSC Track Finder

In counting house

In Peripheral Crate

On Chamber

Muon Port

Card

CSC TF

The CSC trigger is a complicated, fast tracking system


CSC Trigger Stubs Generated in Front End

Trigger stubs are formed by comparing hits to patterns…

Cathode Stub from strips• Comparator network rapidly determines hits

to ½-strip resolution per layer• Measures • Pattern Radius of curvature momentum

Anode Stub from wire groups • Defines trigger timing• Measures , bx• Pattern envelope pointing to Interaction

Point


CSC Trigger Stub Envelopes

oxxxxxxxxxxxoooooxxxxxooooooooooxooooooooooxxxxxooooooxxxxxxxxxoooxxxxxxxxxxxo

layers (z)

half strips (x)

OXXXOOOOOXXOOOOOOXOOOOOOXXOOOOOXXXOOOOXXXO

Anode collision pattern points at the Interaction Point:

wire groups (y)

layers (z)

A CSC trigger stub satisfies a local pattern of hits consistent with a high momentum track from the Interaction Point

x B-field

IP

Cathode envelope of patterns (see next slide):

Typical wiregroup width ~ 20mm Typical half-strip width ~ 10mm

Total chamber depth ~ 15cm


Cathode Trigger Stub Patterns

x B-field

Muon stubs which match patterns with higher momentum have higher priority to be passed to the CSC Track Finder

Some example patterns:

oooooxxxoooooooooooxooooooooooooxooooooooooooxoooooooooooxxxooooooooooxxxooooo

layers (z)

half strips (x)

ooooooxxxooooooooooxxoooooooooooxoooooooooooxxooooooooooxxxooooooooooxxxoooooo

oooooooxxxoooooooooxxoooooooooooxoooooooooooxxooooooooooxxooooooooooxxxooooooo

ooooooooxxxoooooooooxxooooooooooxooooooooooxxoooooooooxxxooooooooooxxxoooooooo

Increasing order of priority…

Increasing momentum…


CSC Trigger Stub Efficiency

CSC trigger primitive efficiency is >99.5% for high momentum muons (i.e., straight in dX/dZ) which point at

the Interaction Point (i.e., –1 < dY/dZ < 0)


CSC Track FinderCombine trigger stubs from 2, 3 or 4 stations to select

high pT muons

Efficiency: trigger matching a tracker track within |Δφ|<0.3

resolution: well reconstructed muons pointing at the Interaction Region

CSC Trigger selects muons with:

• High efficiency

• Good resolution


Trigger Synchronization


Trigger Synchronization is Critical

• CMS detectors store data in a pipelined readout architecture Data are selected from a position in the

pipeline according to the timing of the trigger

Unsynchronized trigger could turn…

… into…

Need both intra-detector and inter-detector synchronization


CSC Synchronization Problem

• 468 chambers, all with different cable lengths– 1 < < 2.4– - < <

…arranged to point at the Interaction Region…

• Cosmic rays are…– Asynchronous– Not coming from the Interaction

Region

Hit map of 1 station of CSC’s (there are 8 stations in total)


CSC Synchronization Solution

• Open up the coincidence windows

• Look at average timing differences for muons hitting multiple chambers

• Make a (big) matrix of pairwise differences for pairs with sufficient statistics

• Solve

Synchronizes simultaneous cosmic ray muons which ~point at the IP on average…


Relative Synchronization of CSC Trigger Stubs

0th order: cable lengths only… Triggers lined up within 1bx

Fine delay changes implemented Triggers lined up within 0.1bx

… the timing shift for each chamber is obtained by an analysis of the matrix of centroids of bx…

Before After


Electromagnetic Calorimeter Timing with respect to CSC Trigger

CSC

ECAL

• CSC timing muons passing simultaneously through any CSC are synchronous through trigger system

• Two peaks in ECAL distribution consistent with muons traversing:

1. CSC ECAL

2. ECAL CSC

• Timing difference approximately consistent with time-of-flight

Timing distribution of Electromagnetic Calorimeter (ECAL) data:


Trigger Synchronization with CosmicsTiming differences between different muon detectors in the barrel: Drift Tubes (DT) and Resistive Plate Chambers (RPC)

DT(Top) – DT(Bot) RPC(Top) – RPC(Bot) RPC – DT

CMSTriggers from different detectors are

well-synchronized to cosmic ray muons (on average)


The response of CMS to cosmic rays looks good.

How about something more substantial?


CMS response to LHC “Beam Splash” events

Beam splash = ~2 x 109 protons at 450 GeV/c incident on collimators ~150m upstream of CMS

CMSCMS

~150 m

p

(9 Sept. 2008)


Reconstructed segments in Cathode Strip Chambers…

BEAM SPLASH in CMS

Energy in Hadronic Calorimeter: Energy in Electromagnetic Calorimeter:


Significant Energy Deposition in CMS Calorimetry

Correlation between hadronic and electromagnetic energy

deposited in CMS from Beam Splash events

~106 GeV in the Hadronic Calorimeter…

(c.f. cosmic rays ~ 1 GeV)


Synchronization of the CMS Hadronic Calorimeter

Timing corrections from synchronous “Splash” events

Before corrections… After corrections…

Tre

cons

truc

ted

– T

pred

icte

d (n

sec)

Nanosecond-scale synchronization will be achieved with collision events


100 150 200 250 300 350 400 450 500

Bunch Crossing Number

Different CMS Detectors Triggering on LHC Beam Splash

Detector synchronization much easier with synchronous beam

“Beam Splash” events:

Hadronic Calorimeter

Cathode Strip Chambers

(Three pulses caused by

afterpulsing in photodiodes

filtered by CMS trigger rules)

Eve

nts

First synchronous signals ever seen from LHC


CMS response to LHC beam without collisions:

“Beam Halo”

pCMS

(11 Sept. 2008)


“Beam Halo” Muon Traversing CMS

“Beam halo” muon ~parallel to the beampipe passes through Cathode Strip Chambers on

both endcaps


Reasonable description of beam ON data: combination of • beam halo • cosmic rays

(Separate normalization of blue and black curves not quantitative…)

Cosmic rays

Beam halo

Orientation of beam halo eventsTracks reconstructed in the cathode strip chambers


Single Beam Illumination of CMS Cathode Strip Chambers

ME4ME3ME2ME1

ME+1 ME+2 ME+3 ME+4


Cosmic rays

Initial attempts to

capture beam

1st capture of LHC beam

Automatic beam abort

First LHC Beam Capture Seen at CMSTrigger rates for “Beam-halo” (i.e., “straight-through”) muons

in one endcap of the Cathode Strip Chambers

11 Sept. 2008

LHC beam control

established within minutes of first attempt

–45<<15


First beam in 2008 was incredibly exciting

It will only get better with collisions…


Early Physics Program of CMS (I)

10/pb: Commission the detector…

Detector synchronization and alignment In-situ calibration Commission trigger Start “physics commissioning”

Jet and lepton rates; observe W, Z, top And, first look at possible extraordinary signatures…


Early Physics Program of CMS (II)

106 W l + 105 Z l + l

104 t t + X

Improve understanding of…• Physics objects• Jet energy scale • Extensive use (and

understanding) of b-tagging• Backgrounds to SUSY and

Higgs searches

Initial Higgs sensitivity Early look for excesses from

SUSY, Z, di-jet resonances…

100/pb: (Re-)Measure the Standard Model…


Early Physics Program of CMS (III)

SIMULATION

CMS Collab. 2007, J. Phys. G: Nucl. Part. Phys. 34 995–1579.

1000/pb: Higgs discovery era?

In addition: explore large part of SUSY and resonances at ~few TeV…

L dt = 30/fb


Summary

CMS is ready for beam

We are eagerly anticipating proton collisions in the LHC...


Backup slides


High Level Trigger Boundary conditions:

Code runs in a single processor, which analyzes one event at a time HLT has access to full event data (full granularity and resolution) Only limitations:

CPU time Output selection rate (~102 Hz) Precision of calibration constants

Main requirements: Satisfy physics program: high efficiency Selection must be inclusive (to discover the unpredicted as well) Must not require precise knowledge of calibration/run conditions Efficiency must be measurable from data alone All algorithms/processors must be monitored closely


Tracking at LHC

Fluence over 10 years of

LHC Operation

Need factor 10 better momentum resolution than at LEP1000 particles emerging every crossing (25ns)

CMS SS09 tsv


Data vs. Simulation Comparisons of Cosmic Muons in Endcap

Cathode Strip Chamber response to cosmic ray muons are well described by a Monte Carlo

simulation


Performance of CMS: OverviewTracking

HCAL

b-tagging CMS SS09 tsv


Before first data can be taken…Chamber-Peripheral Crate cables at Peripheral Crate:

• Chambers were checked • at assembly• upon arrival at CERN (ISR)• upon installation in SX5

• Peripheral Crate/chamber electronics were tested • at home institutions• upon arrival at CERN (ISR)• upon installation in SX5

• Low and High Voltage

• Gas

• Slow controls

• Safety systems

Only with all of this in place can we even begin to “commission” the system…


CSC ConfigurationCSC is highly configurable: ~100 parameters per CSC

Most CSC electronics are in experimental cavern (high radiation area):

• FPGAs are not radiation hard prone to single event upsets

• PROMs are radiation hard…

• FPGA program stored on one set of PROMs

• configuration parameters stored on another set of PROMs

CSC Configuration = TTC “hard reset”:

• FPGA program reloaded from PROMs

• FPGA reads its configuration from configuration PROMs

Solved issues:

1. Explicit configuration of TTCrq chip required

2. “Check configuration button” reads configuration from hardware and compares with configuration database values

preparation for physics: the compact muon solenoid (cms) detector greg rakness university of...

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