1. The LHCb Vertex detector
Physics
Goals
Properties and consequences
LHCb
Overview of the detector
Vertex
Specifications
Silicon stations
Overview
Details
Radiation hardness
Read-out chip developments
Conclusions & Prospects
Hi, my name is Sander Klous and I will be talking on behalf of the LHCb collaboration.
This is an outline of my presentation.
I will briefly discuss the physics of LHCb. Then I will show an overview of the detector and zoom in on the most important component: The Vertex detector.
Vertex2003, Sander Klous (on behalf of the LHCb collaboration)
15/9/2003

2. Physics Goals Accessible by LHCb1 r h g b
Bs DsK
Bs Dsp
Accessible by LHCb
Investigate difference between Matter and Antimatter
CP violation in standard model
Rotation between mass eigenstates and weak eigenstates (CKM matrix)
Expressed with Wolfenstein parameterization
One of the 6 Unitary Triangles
Order l or l2 for all sides
Current status
The primary goal of the LHCb experiment is to investigate the differences between matter and antimatter.
In the standard model, this CP violation is accommodated by a rotation between the mass and weak eigenstates, using a matrix.
This CKM matrix is unitary and contains a phase that allows the symmetry breaking.
The matrix can be parameterized using the Wolfenstein parameterization.
In blue I circled the elements of this matrix, accessible by LHCb.
Six of the unitarity conditions can be represented by triangles. One of them is depicted here together with the matrix elements that construct its sides and some of the decays from LHCb that provide information about its geometry.
The triangle shown here is especially interesting since the lengths of all sides are in the same order. This means the geometry can be verified on internal consistency.
Here is a summary of the current constraints on the triangle.
I want to draw your attention on the constraint coming from sin(2b), which comes from the first generation b-physics experiments, babar and belle.

3. Physics Properties and consequences
You want B decays!
B’s are heavy
Results from B – factories
LHCb offers
Bs production
Higher yield
Over constrained triangle
LHC Production channel
Gluon fusion
~ 1012 bb pairs a year
Boosted system (decay length)
Angular coverage
15–300 mrad in bending plane
mrad in non-bending plane
Now that we have established that we are interested in CP violation, I’ll explain why we want B-decays.
First of all, B’s are heavy. This means they can be treated as autonomous systems, not affected by their environment, using Heavy Quark Effective Theory.
We already saw that the results from the b-factories constraint the triangle. LHCb can provide an independent measurement of this parameter in a completely different experiment.
On top of that, LHCb will be able to produce Bs mesons, not produced by the b-factories.
Furthermore LHC will produce the same amount of B mesons per seconds as are available in total at the moment.
The production mechanism for b bbar pairs in LHC is gluon fusion. Ten to the twelfth of those pairs will be created per year and the system is highly boosted.
This means that the production angles are small and the b and bbar are either both in the forward cone or both in the backward cone.
The LHCb experiment needs a coverage of mrads in the bending plane and mrad in the none bending plane. P b

4. LHCb Overview of the experiment
Here you see an overview of the LHCb detector
It has a vertex detector, rich detectors for particle identification, a magnet and tracking stations to determine pt and calorimeters and a muon detector
It runs at a luminosity of 10^32, a factor 1000 lower than big brothers CMS and ATLAS
Luminosity: cm-2s-1

5. Vertex detector Specifications
Forward detector
Detectors only 8 mm from beam
360º coverage in f
overlapping detectors
Low number of pp interactions per event
In level-0 trigger (40 MHz)
Pile – Up detector
Trigger on high pt displaced tracks
In level-1 trigger (1 MHz)
Standalone track reconstruction
Use stray field to select high pt
Identify Bs oscillations
Vertex resolution:
17 mm + 32mm/pt  44 fs (Dsp)
5s sensitivity to Bs oscillations with:
Dms = 68 ps-1
Tight material budget
The vertex detector takes a central place in LHCb
The detectors are only 8 mm from the beam and cover 360 degrees in phi direction, which means you need overlapping detectors.
To make a clean reconstruction of the B events, we want to trigger on events that only contain a low number of pp interactions
The vertex detector contains two dedicated stations, called the pile-up detector that selects those events in the level-0 trigger
The level-1 trigger is entirely based on the vertex detector. The vertex does standalone track reconstruction and combines this information with the stray field of the magnet and the level-0 objects to identify high pt displaced tracks.
The most stringent constraints for the vertex detector resolution are coming from Bs oscillation. This plot shows the simulation of an oscillation between a b and a bbar in the bs system coming from B to Ds pi.
The current expected resolution of 17 mum+32 mum over pt results in a proper time resolution of 44 fs for the Ds pi. This means we can identify Bs oscillations with a 5 sigma sensitivity up to a mass difference of 68 inverse picoseconds. (momentum resolution is 0.3%)
These kind numbers can only be obtained by minimizing the material in the detector, especially the material before the first hit in a detector.

6. Vertex detector Silicon stationsy x z R
Vertex has standalone track and vertex reconstruction (Projection in R-z plane)
pitch from 40 to 103 mm
Highest x-y resolution naturally closest to interaction region
Stereo -20° and 10°
Second metal
layer
45º segments
Temperature -5 ºC
CO2 Cooling system
Thickness 220 mm
1meter
Pile - Up
stations
250 mrad
15 mrad AA
Interaction region
s = 5.3cm
42 mm
8 mm
As explained the silicon stations have full phi coverage, the red area is the overlap between two stations.
Schematically the detectors are arranged as show in the cross-section AA.
The acceptance is shown as well as the interaction region of about 5 cm.
The two Pile – Up stations are outside the acceptance.
The silicon stations are using strip detectors with R phi geometry.
The choice for strip detectors directly follow from the occupancy which is low enough because of the reduced luminosity and the selection of events with a low number of pp interactions.
The minimum active radius is 8 mm and the outside radius is 42. The thickness is 220 mum.
The R detectors are divided in 45 degree segments.
The hits in those 45 degree segments can be projected on the R-z plane and then be used for the standalone track and vertex reconstruction.
The blue line was successfully identified as a high pt displaced track, which is the key ingredient for the level-1 trigger.
I will continue with some details about the silicon.
The signal is read out over a double metal layer, allowing the chips to be outside the acceptance region.
The pitch ranges from 40 to 103 mum for the R stations and the highest x-y resolution is naturally closest to the interaction region because of the phi strips.
The phi strips have stereo angles of -20 degrees to 10 degrees.
The detectors are maintained at a temperature of -5 degrees C and a CO2 cooling system is installed to do just that. A
21 + 2

7. Vertex detector Overview
Retractable detector halves for beam injection
Silicon stations in vacuum
Beam
Detector on
X-Y tables
R detector
Phi detector
The left lower corner show the R Phi stations again. They are back to back: blue is R and yellow is phi (or vice versa).
Two other stations are mounted on the other side in the same manner.
The silicon stations are mounted inside the vacuum and the beam is located over here.
For beam injection the detector halves need to be retracted, since we need a 30 mm aperture to allow for displacements during injection.
The complete detector is on X-Y tables. The detector will be adjusted dynamically to the location of the beam before the detector halves are moved in.
There is a thin exit foil between the vertex detector and the rest of the experiment.
Thin exit foil

8. Vertex detector Details
Bellows to accommodate retractable detector halves
Thin separation between silicon stations and beam
Secondary vacuum
RF shield
Wakefield guide
Controlled pressure
250 mm thick
Complex shape (overlapping detectors)
Super plastic, hot gas formation
Here I show the thin separation between the silicon stations and the beam vacuum.
So the detectors are actually in a secondary vacuum and the box functions both as an RF shield and a Wakefield guide.
The creation of a secondary vacuum means you need to monitor and control the pressure at all times.
This is especially critical when the system goes from ambient pressure to a vacuum situation and the other way around.
In this detailed picture we can also clearly see the custom made bellows to accommodate the retraction of the detector halves.
The foil is only 250 mum thick and it has a complex shape to accommodate the overlapping detectors and to make sure forward particle tracks are perpendicularly traversing the foil.
This means the deformations in the foil are extreme. A vacuum tight foil of this shape needs to be created using special techniques. In this case super plastic, hot gas formation.

9. Vertex detector Radiation hardness
Replace detectors every 4 years
Maximum irradiation per station
5 x 1012 to 1.3 x 1014 neq/cm2/year
Detector could have undepleted layer after irradiation
Resolution of p on n detector degrades fast
Undepleted layer insulates strips from bulk
n on n ~100% efficient for only 60% depletion depth
Middle station
Far station
Being so close to the LHC beam, means that we need to pay attention to radiation hardness.
The maximum irradiation is … to … per year and the detectors are replaced every 3-4 years.
After irradiation the detector has an undepleted layer. For p on n detectors this layer insulates the strips from the bulk and the resolution degrades fast. This, in turn results in a lower efficiency.
For an n on n detector, the efficiency is still 100% for only 60% depletion depth.

10. Read-out (Beetle) Introduction
Beetle was selected in January 2003
Used in Vertex Detector and Silicon Trackers
0.25 mm CMOS technology
Intrinsically radiation hard
Single Event Upsets
Triple redundant logic
Analogue and digital output
Digital output used in level-0
Analogue output used in level-1
Pipeline
cells
Front-ends
Vpre
The silicon stations are read-out using the Beetle front end chip.
The Beetle was selected in January during a shoot out between the two candidates.
The Beetle is a 0.25 mum CMOS chip, which means it is intrinsically radiation hard (when special layout techniques are used).
It suffers from single event upsets, which are solved using triple redundant logic with majority voting.
The Beetle is both used by the normal vertex stations and by the Pile – Up stations.
For the Pile – Up detector it needs a prompt digital output at 40 MHz that is used in level-0
For the normal vertex stations it needs an analogue output that matches the level-0 latency
Here is a schematic overview of the Beetle chip.
The front-end has various parameters to tune the performance. The preamplifier current and feedback resistance, the shaper current and feedback resistance are the most important ones.
After the front-end the signals either go the comparator for the digital output or are stored in a 186 cells deep pipeline to wait for the level-0 trigger decision.
The appropriate events are read-out by sending multiplexed information from 128 channels to the ADC.
Here you see an overview of the Beetle with the 128 front-ends arranged top down and the 186 cells deep pipeline from left to right.
Vsha
to comparator (digital out)
Readout
x 186
Out In
Mux
Ipre
Isha
Ibuf
x 128
Front-end
Pipeline

11. Read-out (Beetle) Analogue specifications
40 MHz clock frequency
1 MHz read-out
Signal / Noise > 14
Rise time < 25 ns
Spill over < 30 %
Beetle1.1
Tested in SPS beam
16 chips on 1 hybrid
PR02-R p-on-n detector
90%
10%
Rise time
Spill over
25 ns
I will now zoom in on the analogue part of the chip.
Of course it needs to match with the 40 MHz clock frequency of LHC.
It needs a 1 MHz read-out for the level-1 trigger
The signal/noise should be larger than 14,
the Rise time should be smaller than 25 ns (in accordance with the 40 MHz clock frequency)
and the spill over should be smaller than 30%
The definitions of Rise time and spill over are shown here.
Rise time is the time for the pulse to rise from 10% to 90% of its peak height.
Spill over is the remainder after 25 ns.
The Beetle1.1 was extensively tested in the SPS beam, using 16 chips on 1 hybrid.
The 16 chips were connected to a 300 mum thick PR02-R p-on-n detector

12. Read-out (Beetle) Analysis
Peak
Convolution of
Landau and Gaussian
Goal
Optimize performance
Check chip behavior
16 chips on 1 hybrid
Test beam environment
Mimic LHCb operation
Sampling mode
Sampling rate
Took 10 million events
3 ns
Spill over point
The goal of this test was to optimize the performance of the chip for the LHCb vertex detector and to check for interference effects from either 16 chips on 1 hybrid or from the test beam environment.
We also investigated specific aspects of LHCb operation, specifically the sampling mode and the sampling rate.
The analysed data looks like this.
The baseline is located here and the width of the noise can be extracted from this part of the pulse.
The signal height can be determined in the peak.
We divided the pulse into slices of 3 ns. The projection of this 3 ns slice in the peak looks like this.
The histogram can be fitted with a convolution of a Landau and a Gaussian.
This can be done for all slices and it is also shown for the 3 ns around the spill over point. Of course the convolution will take a more Gaussian shape in this point
Signal
snoise
Baseline
3 ns

13. Read-out (Beetle) Resultsm
Average capacitance: 10 pF
Signal/Noise = 17.4  0.2
Spill over = 36.1 %  1
Rise time = 23.5 ns  0.5
ENC = e-/pF
Detector capacitance : pF
Resulting S/N range:
enc (e-)
Threshold = 14
Efficiency
Hits from previous
bunch crossing
As I mentioned before there are various settings that can be used to tune the performance of the Beetle and as a result we scanned a lot of settings.
In the end, the best result we found was a Signal to Noise of 17.4 a spill over of 36.1% and a rise time of 23.5 ns, for the regions with an average capacity of 10 pF.
The LHCb detector will have strips with a capacitance between 6 and 14 pF.
Combined with our ENC measurements, this results in a S/N range between 14.5 and 21.5 (for a 300 mum detector).

14. Read-out (Beetle) Mimic sampling mode/rate
Time 1 2 3 4 5 6 7
Time sample
Test beam mode
Mimic sampling rate
Occupy read-out circuit
Send test pulses at high rate
Mix with physics triggers
Let ADC only read physics triggers
No deteriorating effects were found
Test beam mode: 19.7  0.2
Single time sample: 19.6  0.2
Test beam mode: 18.7  0.2
High trigger rate: 18.7  0.2
Note: comparison with other settings
Time 1 2 3 4 5 6 7
Time sample
Continuous beam 1
LHCb sampling mode
LHCb operation was mimicked with two special measurements.
In the beam test each trigger initiated the read out of 8 consecutive samples.
This allows the extraction of the complete pulse shape without shifting the latency between measurements.
Together with the continuous beam, the complete pulse shape can be profiled.
In LHCb sampling mode, each trigger initiated the read out of 1 sample. We did three measurements with different latencies to obtain the complete pulse shape.
We also mimicked the high sampling rate of the LHCb experiment.
At high sampling rates, the read-out is almost continuously active. This could cause additional noise from cross-talk on the shaper circuit.
To mimic this condition, we introduced test pulses at high rate and mixed them with the physics triggers.
The ADC only received the physics triggers, so only physics data was registered.
We found no deteriorating effects in those measurements. The signal/noise ratios of the measurements are shown here. Note that these measurements were done with different settings for the Beetle then our preferred result.

15. Silicon and Read-out To do
Beam test with irradiated
p on n Czochralski silicon
To do:
Analysis of beam tests
Irradiated Czochralski silicon
Single Beetle1.2 chip
Beam test with new hybrid
16 Beetle1.2 or 1.3 chips on hybrid
Thinner detectors
3D detectors ???
So both our silicon developments as well as our read-out developments are well along the way.
There is however still a lot of work to do.
We are analysing the results from a beam test with irradiated Czochralski silicon in June this year
For the read-out we have a functional Beetle1.2 chip that solves a problem with a saturation in the preamplifier of the Beetle1.1
We are constructing a hybrid equipped with 16 Beetle1.2 or 1.3 chips connected to out baseline detector to get some final numbers on performance
The baseline solution will be this 220 mum n-on-n oxygenated detector with R phi configuration,
but for upgrades we are interested in all other developments, including thinner and 3D detectors.
High resistance
High oxygen content

16. Conclusions
LHCb is a next generation experiment for CP violation measurements
The vertex detector for LHCb is a mechanically challenging project
Production has started
The silicon and hybrid developments are in their final phase
Results from the beam test with irradiated Czochralski silicon are coming
The new hybrid will be tested in the test beam with 16 Beetle1.2 chips
The Beetle read-out chip developments are in their final phase as well
Version 1.1 is extensively tested and complies almost with specifications
Version 1.2: a single chip is just tested in the test beam
Version 1.3 is the final version and is submitted on a MPW run in June
Next year, system tests will start
The construction of the LHCb vertex detector is on track

18. LHCb Vertex and Trigger
Talk on Thursday,
Thomas Schietinger
Level-0 trigger combines
High pt info from calorimeters and muon detectors
Pile - Up information from Pile – Up detector
Counts number of primary vertices per event
2 dedicated stations in the vertex detector
Digital read-out at 40 MHz
Outside acceptance
Level-1 trigger
Identify displaced tracks at 1 MHz
Low occupancy
High efficiency
R/Phi configuration
Match with high pt tracks
Vertex
Station: A B ZA ZB RA RB
RA/RB = ZA/ZB = k

19. Physics Properties and consequences
You want B decays!
B’s are heavy
Results from B – factories
LHCb offers
Bs production
Higher yield
Over constrained triangle
LHC Production channel
Gluon fusion
~ 1012 bb pairs a year
Boosted system
b + g b dg
g - 2dg P b g

20. For Bs sdecay is in the order of a few mm
LHCb Specifications
Angular coverage
15–300 mrad in bending plane
mrad in non-bending plane
Trigger on displaced vertices
Excellent vertex resolution
Single pp interactions
Particle identification
K/p separation
Flavor tagging
1 – 150 GeV
For Bs sdecay is in the order of a few mm