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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:
The silicon pixel vertex The silicon pixel vertex telescopetelescope
B
beam tracker
targets
Jornadas LIP, Dez. 2005 8P. Martins - CFTP-IST
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
Jornadas LIP, Dez. 2005 9P. Martins - CFTP-IST
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)
Jornadas LIP, Dez. 2005 10P. Martins - CFTP-IST
Hit maps from a bias voltage scan after 4 weeks
Type inversionType inversionp+
n
n+
Active volume
150 V
“Brand new” pixel sensor
Jornadas LIP, Dez. 2005 11P. Martins - CFTP-IST
Hit maps from a bias voltage scan after 4 weeks
Type inversionType inversion
100 V
Jornadas LIP, Dez. 2005 12P. Martins - CFTP-IST
Hit maps from a bias voltage scan after 4 weeks
Type inversionType inversion
80 V
Jornadas LIP, Dez. 2005 13P. Martins - CFTP-IST
Hit maps from a bias voltage scan after 4 weeks
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
Jornadas LIP, Dez. 2005 14P. Martins - CFTP-IST
Hit maps from a bias voltage scan after 4 weeks
Type inversionType inversion
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)
Jornadas LIP, Dez. 2005 15P. Martins - CFTP-IST
Hit maps from a bias voltage scan after 4 weeks
Type inversionType inversion
40 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)
Jornadas LIP, Dez. 2005 16P. Martins - CFTP-IST
Hit maps from a bias voltage scan after 4 weeks
Type inversionType inversion
30 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)
Jornadas LIP, Dez. 2005 17P. Martins - CFTP-IST
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
Jornadas LIP, Dez. 2005 18P. Martins - CFTP-IST
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
Jornadas LIP, Dez. 2005 19P. Martins - CFTP-IST
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
Jornadas LIP, Dez. 2005 20P. Martins - CFTP-IST
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
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
Jornadas LIP, Dez. 2005 22P. Martins - CFTP-IST
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