Jornadas LIP, Dez. 2005 P. Martins - CFTP-IST The NA60 Silicon Vertex Telescopes Dimuon measurements Dimuon measurements Vertex telescope used in: Vertex

Jornadas LIP, Dez. 2005 P. Martins - CFTP-IST

The NA60 Silicon Vertex The NA60 Silicon Vertex TelescopesTelescopes

Dimuon measurements Dimuon measurements Vertex telescope used in:Vertex telescope used in:

Ions runs (2003)Ions runs (2003) Protons runs (2004)Protons runs (2004)

Jornadas LIP, Dez. 2005 2P. Martins - CFTP-IST

Measuring dimuonsMeasuring dimuons Signals within reach:Signals within reach:

Vector mesons ( η, ρ, ω, ϕ, J/ψ and ψ’ )Vector mesons ( η, ρ, ω, ϕ, J/ψ and ψ’ ) Open charm simultaneous semi-leptonic Open charm simultaneous semi-leptonic

decaysdecays Drell-Yan quark anti-quark annihilation Drell-Yan quark anti-quark annihilation

BackgroundBackground Simultaneous π and K decaysSimultaneous π and K decays


• Degraded dimuon mass resolution• Large combinatorial background• Cannot distinguish prompt muons from decay muons

Measuring dimuonsMeasuring dimuons

MuonOther

Energy lossMultiple scattering

hadron absorber

muon trigger and tracking

target

beam

magnetic field

or

?


2.5 T dipole magnet

hadron absorber

• Improved dimuon mass resolution• Reduced combinatorial background• Origin of muons can be accurately determined

Matching in coordinate and momentum space

targets

beam tracker

Measuring dimuons Measuring dimuons in NA60in NA60muon trigger and tracking

magnetic field

MuonOther

or

!

vertex telescope


Requirements on the telescope

A vertex telescope for heavy-ion A vertex telescope for heavy-ion runningrunning

High-energy (nuclear) collisions

Dimuonproduction

Smallcross-section

High statistics

Selectivedimuon trigger

Radiation tolerance

Fast read-outGranularity

High multiplicityenvironment

High precision

Fixed-target

Segmented target

As a function of centrality

Radiation-hardzero degree calorimeter

High luminosity


8” read-out chip wafer

Silicon pixel detectorsSilicon pixel detectorsPixel sensorPixel sensor • 12.8 13.6 mm2 active area • 256 32 cell matrix• 50 425 µm2 cell size

Read-out chip 750 µm

Silicon sensor 300 µm

ALICEALICE1LHCB read-out 1LHCB read-out chipchip

• Operated at 10 MHz• Radiation tolerant up to ~ 30 Mrad• 32 columns parallel read-out

+5” sensor wafer (layout)

25 µm solder bump =


• 800’000 channels, 50 425 µm2 pixel size

• 12 tracking points with good acceptance• 9 X (bending plane, |B| = 2.5 T)• 3 Y (non-bending plane)

• 8 “small” 4-chip planes• 8 “big” 8-chip planes• ~ 2 – 3 % X0 per plane

The silicon pixel vertex The silicon pixel vertex telescopetelescope

B

beam tracker

targets


Vertexing performanceVertexing performance• Data collected in October 2003

with 158 GeV Indium beam

Z-vertexZ-vertexdeterminationfrom pixel telescope

σz ~ 200 µm

Beam tracker sensors

Target box windows

In targets

Transverse coordinatesTransverse coordinatesmeasuredby the vertex telescopeand the beam tracker

σbt ~ 20 µm → σvt ~ 12 µm

10

20

30

0

σ(µ

m)

VT Vertex resolution (for σBT = 20 µm)

Dispersion between BT track and VT vertex


Leakage current Leakage current vs. vs. timetime

Radiation toleranceRadiation tolerance

Hit efficiencyHit efficiency vs. vs. bias voltagebias voltage

• inner region needs increased bias voltageafter 4 weeks running

• 158 GeV SPS Indium beam in October 2003• ~ 4 1012 ions delivered over 5 weeks • Performance was closely monitored• Sensor type inversion was expected, seen and understood• The detector was re-used in 2004 for proton running

• strong temperature dependence• increase with integrated dose (and luminosity)


Hit maps from a bias voltage scan after 4 weeks

Type inversionType inversionp+

n

n+

Active volume

150 V

“Brand new” pixel sensor



Type inversionType inversion

100 V




80 V



Type inversionType inversionp+

n

n+

irradiation

n+

p

p+

Active volume

Pixels disconnected from the active volumedo not work

Less irradiated zonesare still connected

for the same bias voltage

n+

p

60 V




50 V

Pixels at small radiiPixels at small radiireceive more fluence :receive more fluence :

Lowering the bias voltage leaves an Lowering the bias voltage leaves an ever larger area not fully depleted ever larger area not fully depleted (i.e. very inefficient)(i.e. very inefficient)




40 V






30 V




Physics from the Indium runPhysics from the Indium runVery good mass Very good mass

resolutionresolution ωω and and ϕϕ perfectly perfectly

resolvedresolved ηη→→µµ++µµ-- seen for the seen for the first first

timetime in nuclear collisions in nuclear collisions

Ability to trace muon offsetsAbility to trace muon offsets Prompt dimuons (resonances) peak Prompt dimuons (resonances) peak

at low valuesat low values Displaced D meson decays have a Displaced D meson decays have a

long taillong tail

Weighted offset

DataPrompt + Charm


Measure c production in c → J/ψ+ decays

High luminosity

Radiation damage Pile-up rejection

Operate the vertex telescope at negative

temperatures

Fluences similar to the 2003 Indium run

More accurate timing

Challenges in proton-nucleus Challenges in proton-nucleus runningrunning

40 MHz average* interaction rate

Lower leakage current and depletion voltages

* Poisson statistics : 26 % of the time there are >1 interactions in 25ns

Measure single muon production time differences

Use silicon micro-strips at the start of the telescope

Thin detector

Minimizes electrons’ multiple scattering and energy loss

Reduced material budget(no readout chips, hybrids or cooling rings on the way of the particles)

Challenges met by…

Use ATLAS silicon pixel detectors

Measure peaking time in micro-strips

→ e+e- measurement


50 ns readout gate(4x shorter than the ALICE pixel planes)

From idea to running experiment in 8 months

Two planes fully cover the angular acceptance

From all charged tracks…

…we only keep those with a hit in the ATLAS planes

Bad chips outside of

acceptance

ATLAS pixel planesATLAS pixel planes


Reconstructed pulse shape

Analogue pulse shape reconstruction provides timing and amplitude.Measured the phase between the 40 MHz clock and the (random) trigger arrival time.

Dispersion of the reconstructed peaking time at low intensity

Hits in time with trigger

Hits from pile-up interactions

Low intensity

Nominal intensity

Silicon micro-strip timingSilicon micro-strip timing


7 nuclear targets at two proton beam energies: 400 and 158 GeV

Collected ~ 300’000 J/ψ events in p-A collisions at 400 GeV

At 158 GeV we should be able to determine α(J/ψ) with an error better than 1%

p-A @ 158 GeV~ 30’000 J/ψ events

3 days’ data

(before muontrack matching)

2004 proton-nucleus run2004 proton-nucleus run

z-vertex (cm)

Al U W Cu In 3 x Be Pb

Beam of ~ 4 × 109 p/burst

p beam

158 GeV


Summary and conclusionsSummary and conclusions NA60 built and operated in 2003NA60 built and operated in 2003

thethe first radiation-tolerant first radiation-tolerant silicon silicon pixel detector in the pixel detector in the worldworld Unprecedented precision measurements in heavy-ion Unprecedented precision measurements in heavy-ion

collisionscollisions Very big impact in many physics topics in dimuon productionVery big impact in many physics topics in dimuon production

Integrated radiation doses comparable to years of LHC Integrated radiation doses comparable to years of LHC operationoperation

Detector still operational and even used in the following yearDetector still operational and even used in the following year

In 2004 we In 2004 we further upgraded this telescopefurther upgraded this telescope with faster with faster detectorsdetectors Successfully operated at interaction rates in excess of the Successfully operated at interaction rates in excess of the

LHCLHC

Questions?Merry Christmas and Happy New Year

Documents

Jornadas LIP, Dez. 2005 P. Martins - CFTP-IST The NA60 Silicon Vertex Telescopes Dimuon measurements Dimuon measurements Vertex telescope used in: Vertex