konstantinos nikolopoulos university of athens / bnl atlas cathode strip chambers installation and...

Konstantinos NikolopoulosUniversity of Athens / BNL

ATLAS Cathode Strip ChambersInstallation and Commissioning

XXVI Workshop on Recent Developments in High Energy Physics and Cosmology

Ancient Olympia, 16-19 April 2008

©CERN

K. Nikolopoulos (University of Athens/BNL) – ATLAS Cathode Strip Chambers – HEP 2008 – April 17th, 2008 2

ATLAS

CMS

LHC

The ATLAS detector at LHC

Current LHC Plan : 1st June beam-pipe close and bake-out, 1st injection ~mid-June, 1st collisions

~end of summer, pilot physics run (10 TeV and 1.1x1032cm-2s-1) looks possible for 2008.

Muon Spectrometer

Air-core toroid, Precision drift and Trigger chambers

PT resolution:~10% at PT = 1 TeV (standalone)

~2.3% at PT = 50 GeV (combined)

Hadron Calorimetry

Fe/Sci + Cu/LAr

/E~60%/E 3%

E/M Calorimetry

Pb/LAr

/E~10%/E

Inner Detector

2 T solenoid

Si (Pixels + Strips)

Transition

Radiation Tracker

ALICE

LHCb

©CERN


SM Higgs → ZZ(*) → 4μ Acceptance

Building a high-precision spectrometer

is not enough. Good pseudorapidity (η)

coverage also important!

By extending the coverage from |η|

<2 to |η|<2.7 the acceptance for a

150 GeV SM Higgs decaying to

four muons increases by ~60%


Challenges in the high η coverageBesides muons from pp interactions, increased

occupancy in the Muon Spectrometer due toPrimary Background (e.g π/Κ decay in flight,

punch through hadrons) and Radiation Background (mainly n/γ ~1 MeV)

The Radiation Background is more severe for the forward region and especially for the Inner Station

(>200 Hz/cm2).

The CSCs are Multi-Wire Proportional Chambers with a symmetric cell:

1. High rate capability.

2. High single layer spatial accuracy.

3. Good two-track separation (~40% of read-out pitch).

4. Insensitive to moderate gain variations.

5. Short electron drift time (max ~ 45ns) and good timing resolution (~3.5ns)

6. Low sensitivity to neutrals → εn<10-4, εγ~1%


Principle of Operation

Spatial accuracy in the precision coordinate is in the 60 – 80 μm range, by measuring the

induced charge on the segmented cathode by the avalanche formed in the anode wire.

(Charge Interpolation)

Relative measurement → important to know the cathode strips’ relative response.

(Electronics Calibration)

η = 2

CSCs are present in 27% of the Muon Spectrometer’s pseudorapidity coverageη = 2.7

30720 channels in total →

80% in precision coordinate


Pulse Shaping / Signal Reconstruction

66.11;12;)(

,1

1)(

)(

21

2max

1

nnwidth

tttz

ezn

z

zf

Ampzf

samplingstart

zn

Only four samples of the bipolar waveform (20 MHz), mainly in its first

half, available to reconstruct the signal.

Bipolar signal shaping with relatively short peaking time (75ns) selected

crude approach → parabola around the peak

better approach → fit bipolar pulse using all samples

Parabola

Bipolar

in progress

Pulser input


Noise CorrelationThe electronic noise of the four samples is not totally independent

→ one amplifier shaper for whole pulse.Correlation pattern explained by bipolar shaping and peaking time.

Covariance


Cosmic data studies

relative layer rotation

cluster charge effect on resolution


Channel-to-Channel Cross-talk

Cross-talk appears in the pre-amplifiers due to parasitic capacitance

→ this affects several channels around the one with the main pulse

Effect of cross-talk ~0.4% of main pulse amplitude, opposite polarity and

higher frequency


Calibration/Electronics Linearity

Equalization of strips’ response using calibration

pulser (one for each layer) which provide 64

different pulse heights.

The relative amplitudes of the different calibration

levels, are understood at the 0.3% level.

The calibration system cannot cover the lower

part of the dynamic range

→ linearity of electronics is important

Found deviations consistent with pulser

understanding and well below the noise.

the electronics are linear


Cathode Strip Chamber Installation

The Cathode Strip Chambers are mounted on the Small Wheels,

which are 10 m in height nevertheless!

Contrary to ATLAS practice,

the Small Wheels were

fully assembled and

commissioned on the

surface

©CERN


Noise Levels are at the nominal valuesLarge-Small Chamber Periodicity observedStructure within sectors also as expected

Noise Performance

Most Probable muon signal ~350 ADC counts


Calibration Pulser Runs

Pulser runs used to test in detail the response of the precision strips to different pulse amplitudes and verify that the calibration system is fully operational.

Only two sample distributions presented here.

Bipolar Pulse Peaking Time Width of Bipolar Pulse


Cosmic RunsStrip response, HV connection and stability, gas and water circulation and the overall chamber condition.

UnfortunatelyCSC’s preferred direction not favored by the setup + Trigger on cosmic ray induced particle showers

(efficiency ~10%)= Low Rate + Low Data Quality

SW – A : 10 days of cosmic runs. 24 h runs per sector pair.SW – C : 6 days of cosmic runs. Few hours of data taking per sector pair.

Trigger ScintillatorsThe chambers were found to be in good shape!


Hit Distribution : Precision Strips

All layers have approximately the same number of hits, as expected

Layer average


Lowering the Small Wheels to the cavern

Small Wheel Side-C lowered in the cavern on 15th of February.

Small Wheel Side-A lowered in the cavern on 29th of February.

The last A

TLAS pieces

lowere

d in th

e cavern.

©CERN


CSCs at the ATLAS cavern

Noise ratio with respect to surface tests.

Work in progress!

Small Wheels currently at the “Open” position,

7m of additional unshielded cable present

→ Not present during ATLAS data taking.

Almost all services connected. Noise studies on-going. High Voltage tests to follow


Cooling system stability

Due to high heat dissipation

(~280W/chamber) cooling is needed

→ three water loops/chamber.

Final leak-less cooling system functional for

several weeks, without any problems.

One sector switched off

Controlled shut-down of two sectors

ΔPedestal/ΔΤ ~-0.03 ADC/°C

No cooling No cooling Cooling

SW-C


Summary

Detector/electronics level performance

studies performed using final CSC

electronics and data acquisition

In parallel

pre-commissioning of CSCs at the laboratory (Jul–Nov)

installation/commissioning on Small Wheels (Sep–Jan).

CSCs lowered at the cavern end of February

→ almost all services connected.

Noise studies to understand new grounding configuration

/ interferences on-going.

Preliminary results encouraging

Looking forward to pp interactions!


Additional S

lides


Muon Spectrometry in ATLAS

The ATLAS Muon Spectrometer is designed to perform precise muon reconstruction up to PT =1 TeV.

In order to achieve this goal, high spatial accuracy in the bending plane is required.

This is implemented in a cost-effective way with the usage of Drift Chambers in most

of Muon Spectrometer’s coverage.Oct 2005


Signal Reconstruction / Timing

Totally 30720 channels in the CSCs → 80% in precision coordinate

Implemented in the ATLAS softwareBipolar fit has been implemented in the ATLAS software

(currently under validation), taking into account reconstruction time issues → Don’t waste reconstruction time

Data decoding only

Bipolar Fit + Data decoding


X-Y strip charge correlation in cosmics

Line FitQy = 0.51 + 0.979*Qx


ASM-I ASM-II

CSC On-Chamber Electronics


CSC Commissioning

Data taking and testing for SW-C finished end of November 2007, for SW-A just before CERN’s annual closure.

The cathode strip chamber operation exhibits several levels of organization. Each one of them should be tested :1) Chamber Level : LV, Gas, Water, Calibration Pulser2) Layer Level : HV, Calibration Pulser3) Groups of 24 channels4) Groups of 12 channels5) Single channel level : Disconnected or noisy channels

Too complicated to intervene now, will have to live with them!

The CSC chambers have been tested several times. The latest one was Jul – Nov at the laboratory (blg. 184), both using the calibration pulser and cosmic rays.


Hit Distribution : Transverse Strips


Induced Charge Distribution

konstantinos nikolopoulos university of athens / bnl atlas cathode strip chambers installation and...

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