1. Ph.D. defense The measurement of the Lorentz angle in the BTeV pixel detectors: the new PCI based DAQ, the setup and the results Lorenzo Uplegger Milano 26/01/2004

2. BTeV main goals Study of the beauty baryons Research of new phenomena beyond the Standard Model Definitively the measurement of the elements of the Cabibbo-Kobayashi-Maskawa matrix The BTeV experiment will investigate one of the most fundamental problems of elementary particle physic, the CP violation. Some of the most important aspects of this kind of physics are: CP violation in b and c quark sector Measurement of the mixing phenomena of the B 0 s meson

3. BTeV main goals BTeV detector layout

4. Pixel dimensions50  m x 400  m Plane dimensions 10 cm x 10 cm Gap between stations4.25 cm Total number of stations30 Total number of planes 60 Pixel dimensions50  m x 400  m Plane dimensions 10 cm x 10 cm Gap between stations4.25 cm Total number of stations30 Total number of planes 60 Pixel vertex detector

5. The pixel detector will operate in a high magnetic field, so the position reconstructed by the pixels is shifted by the effect of the Lorentz force acting on the charge carriers in the silicon. Pixel vertex detector Thus I worked on the development of a setup which allowed me to measure the Lorentz angle. The effect on the carriers depends upon the different irradiation doses absorbed by the detector. Since the irradiation dose is greater close to the beam than in the outer regions of the pixel plane, different corrections must be applied in order to keep a good track resolution.

6. I covered many aspects of the design and implementation of this new PCI based DAQ and I will first discuss all the features required by the test-beam needs. DAQ for pixels Since the pixel detectors will be tested in a 120 GeV beam this year, the work was mainly directed to build a complete read-out system for test-beam studies but flexible enough to allow laboratory bench-test studies and in particular the Lorentz angle measurement. Furthermore the DAQ system has been designed with enough flexibility to accommodate the  strip readout chip as well. ( I would recall that my group is responsible for the construction of the  strip forward tracker )

7. 1.Measure the spatial resolution of the sensors before and after irradiation 2.Time-Walk studies 3.Test the read-out chip (ROC) in the real BTeV working conditions data-driven mode 4.Build events using only the temporal information (time-stamp) associated to pixel cells without the aim of an external trigger Test-beam main goals

8. Experimental setup

9. FPIX0 FPIX1 preFPIX2Tb telescope detectors under test

10. DAQ dedicated PC DAQ dedicated PC Detector Mezzanine-card PCI card Detector Mezzanine-card PCI card Detector Mezzanine-card PCI card Readout & processes monitor Readout & processes monitor PCI extender Read-out architecture

11. Experimental setup DATA BCO CLOCK, READ CLOCK… DATA BCO CLOCK, READ CLOCK …

12. Experimental setup DATA

13. Experimental setup DATA

14. Experimental setup DATA PCI BUS

15. Readout process DAQ main features Data 1 Data 2 Data 3 Data 5 Data 4 Data 6 Data 7 Data 8 Data 11 Data 10 Data 9 Data 12 EVENT

16. Readout process DAQ main features noise

17. Readout process DAQ main features noise Data 1 Data 4 Data 6 Data 11 Data 10 Data 7 Data 8

18. Readout process DAQ main features noise Data 1 Data 4 Data 6 Data 11 Data 10 Data 7 Data 8 noise Data 1 Data 4 Data 10 Data 7 Data 1 Data 2 Data 3 Data 5 Data 4 Data 7 Data 10 Data 9 Data 12 ?????

19. Data1 Ts 2 Data2 Ts 2 Data5 Ts 2 Data6 Ts 2 Data7 Ts 2 Data8 Ts 2 Data9 Ts 2 Data3 Ts 2 Data4 Ts 2 BCO time-stamp DAQ main features 132 ns 123456 Data1 Ts 2 Data2 Ts 2 Data6 Ts 2 Data7 Ts 2 Data8 Ts 2 Data4 Ts 2 Data1 Ts 5 Data2 Ts 5 Data6 Ts 5 Data7 Ts 5 Data8 Ts 5 Data9 Ts 5 Data4 Ts 5 Data3 Ts 5 Data5 Ts 5 Data1 Ts 5 Data2 Ts 5 Data6 Ts 5 Data7 Ts 5 Data8 Ts 5 Data9 Ts 5 Data4 Ts 5 Data3 Ts 5 Data5 Ts 5 Data1 Ts 2 Data2 Ts 2 Data6 Ts 2 Data7 Ts 2 Data8 Ts 2 Data4 Ts 2 Data9 Ts 2 Data3 Ts 2 Data5 Ts 2

20. The read out system works in absence of an external trigger The data collection from the different pixel detectors is therefore asynchronous The DAQ must assemble the events in asynchronous mode Events are built using the time-stamp information DAQ main features

21. It is important that the data flux from pixels to PCI is not hampered by the read-out system, which transfers data to the PC. ALTERA FPGA Firmware This read-out is data driven: data are collected as soon as there is a hit above threshold in the detector 1.FPGA firmware 2.PC Read-out software In order to balance the different acquisition rates between the detectors, PCI cards and the PC, we took particular care in the design of the

22. ALTERA FPGA Firmware

23. Readout process Bank0Bank1 FPGA Shared memory Shared memory Consumer Disk writer Time Interrupt handler Reset interrupt PCI card working mechanism

24. Readout process Bank0Bank1 FPGA Shared memory Shared memory Consumer Disk writer Time Interrupt handler Reset interrupt PCI card working mechanism

25. Readout process Bank0Bank1 FPGA Shared memory Shared memory Consumer Disk writer Time Interrupt handler Reset interrupt PCI card working mechanism

26. Readout process Bank0Bank1 FPGA Shared memory Shared memory Consumer Disk writer Time Interrupt handler Reset interrupt PCI card working mechanism

27. Readout process Bank0Bank1 FPGA Shared memory Shared memory Consumer Disk writer Time Interrupt handler Reset interrupt PCI card working mechanism

28. Readout process Bank0Bank1 FPGA Shared memory Shared memory Consumer Disk writer Time Interrupt handler Reset interrupt PCI card working mechanism

29. Readout process Bank0Bank1 FPGA Interrupt handler Reset interrupt Shared memory Shared memory Consumer Disk writer Time PCI card working mechanism

30. Readout process Bank0Bank1 FPGA Shared memory Shared memory Consumer Disk writer Time Interrupt handler Reset interrupt PCI card working mechanism

31. Readout process Bank0Bank1 FPGA Shared memory Shared memory Consumer Disk writer Time Interrupt handler Reset interrupt PCI card working mechanism

32. Readout process Bank0Bank1 FPGA Shared memory Shared memory Consumer Disk writer Time Interrupt handler Reset interrupt PCI card working mechanism

33. Readout process Bank0Bank1 FPGA Shared memory Shared memory Consumer Disk writer Time Interrupt handler Reset interrupt PCI card working mechanism

34. Readout process Bank0Bank1 FPGA Shared memory Shared memory Consumer Disk writer Time Interrupt handler Reset interrupt PCI card working mechanism

35. Readout process Bank0Bank1 FPGA Shared memory Shared memory Consumer Disk writer Time Interrupt handler Reset interrupt PCI card working mechanism

36. This process of periodic memory swap and transfer to a shared memory continues indefinetely. We have several PCI cards playing this swap game in parallel: in order to be able to build events at a later stage, we needed a syncronization mechanism to keep the event builder as simple as possible. By synchronizing the swapping of all the memories we can build events in a very simple and immediate way. PCI card working mechanism

37. Interrupt handler A Interrupt handler A Interrupt handler B Interrupt handler B Interrupt handler C Interrupt handler C Interrupt handler n Interrupt handler n 01 Banks 1.The PCI card C redirect immediately the data flux to the other empty memory Readout working mechanism 2.The interrupt handler of the PCI card C forces the other cards to swap and then starts flushing its content to the host PC Each PCI card has its own interrupt-handler process listening for the memory-full signal Let’s suppose, for instance, that the PCI card C is the first being filled up.

38. 3.The other cards start flushing their (partially) filled memory banks to the host PC. 01 Banks Readout working mechanism 1.The PCI card C redirect immediately the data flux to the other empty memory 2.The interrupt handler of the PCI card C forces the other cards to swap and then starts flushing its content to the host PC Each PCI card has its own interrupt-handler process listening for the memory-full signal Let’s suppose, for instance, that the PCI card C is the first being filled up. Interrupt handler A Interrupt handler A Interrupt handler B Interrupt handler B Interrupt handler C Interrupt handler C Interrupt handler n Interrupt handler n

39. 01 Banks Readout working mechanism A0C0… n0B0 This architecture guarantees that events with contiguous time-stamps belong to buffers which are also contiguous in the read-out process. Interrupt handler A Interrupt handler A Interrupt handler B Interrupt handler B Interrupt handler C Interrupt handler C Interrupt handler n Interrupt handler n

40. 01 Banks A0C0… n0B0 Readout working mechanism A1C1… n1B1 This architecture guarantees that events with contiguous time-stamps belong to buffers which are also contiguous in the read-out process. Interrupt handler A Interrupt handler A Interrupt handler B Interrupt handler B Interrupt handler C Interrupt handler C Interrupt handler n Interrupt handler n

41. 01 Banks BUF i BUF i+1 A0C0… n0B0A1C1… n1B1 Readout working mechanism This architecture guarantees that events with contiguous time-stamps belong to buffers which are also contiguous in the read-out process. Events with the same time-stamp are contained within the boundaries of this overall buffer (BUF i ), or at least in the next one, BUF i+1, but not in BUF i+2, making the event-builder an implementation of a sorting algorithm. Interrupt handler A Interrupt handler A Interrupt handler B Interrupt handler B Interrupt handler C Interrupt handler C Interrupt handler n Interrupt handler n

42. Event Builder Shared Memory (unordered data) Event buffer (ordered data) Timestamps: Event Every hit with a new timestamp starts a new event (column) in a buffer Other hits with the same time-stamp are appended to the right column in the buffer When the analysis of the BUFFER i+1 is over, it is reasonable to assume that there are no more data related to an event that begun in BUFFER i. Event builder

43. DAQ conclusion We built a DAQ system that will be used for the upcoming test-beam I covered many aspects in the design and implementation of this DAQ: 1.I collaborated on the software development 2.I personally took care of the FPGA programming I was then able to use this read-out system to measure the Lorentz angle in the silicon pixel detector I will show now the measurement and the results that I obtained…

44. E LL XX  Z 280  m  L effective =  X/  Z Optical Fiber Focusing Lens Blue LED Light ~2m~2m B X0X0 XLXL Pixel detector Lorentz angle

45. Experimental setup

46. Optical Fiber Focusing Lens E Blue Light B Experimental setup

47. X Y Bias E(V) B(KGauss) Lorentz displacement 400  m 50  m Pixel size in the Y direction= 400  m Pixel size in the X direction= 50  m B  parallel to the Y direction Bias E along the Z direction Lorentz displacement mainly in the X direction  Experimental setup

48. The blue light illuminated several cells in two different columns. With a threshold scan I was able to know the charge collected in each cell. Knowing the charge, I could calculate the Center of Gravity of the cluster: a bidimensional point, X and Y. Y X 50  m 400  m Measurements C.o.G. =

49. B > 0 B < 0 We expect displacements linearly proportional to the magnetic field and symmetric respect to the sign of the B field. Instead here is what I measured X-measurements B KGauss  x [  m]

50. Displacements are present even with B  0. Also in this case they are in the same direction reversing the magnetic field. B > 0 B < 0 Y-measurements B KGauss  x [  m]

51. The reason for this effect can be due to: 1.a movement of the apparatus caused by magnetic attraction 2.a residual hysteresis in the ferromagnetic parts of the apparatus 3.a combination of the previous two I excluded residual hysteresis effects by performing a full set of measurements along a complete hysteresis cycle and checking the reproducibility of the measurements. I didn’t observe any appreciable differences between measurements at the same B value at different points of the hysteresis cycle So I tried to investigate a possible movement due to the attraction of parts of the apparatus by the magnet Investigating

52. Since the Lorentz displacement is an odd function of the magnetic field, while any movement due to magnetic attraction is an even function of it, by taking the sum of the measured positions at opposite values of the magnetic field one can cancel the contribution of the Lorentz effect, and, vice-versa, by taking the difference one can cancel the mechanical effect.  ( X B +X -B )/2 or ( Y B +Y -B )/2 = Mechanical movement  ( X B -X -B )/2 or ( Y B -Y -B )/2 = Lorentz displacement How to measure the mechanical movement?

53. This movement exists, as shown by the following histograms, and is proportional to the module of the magnetic field as expected, but it should not depend on the value of the BIAS voltage. I checked this by fitting all the movements to a common line (RED) 100 V 350 V300 V 250 V 200 V150 V 400 V Measured mechanical X-movement

54. Even in this view exists a unique movement that can fit all data with a good  ²(  ²/d.o.f = 1.14 ) even if it is not as good as in X 100 V 350 V300 V 250 V 200 V150 V 400 V Measured mechanical Y-movement

55. Taking the difference ( X B - X -B )/2 we then find the Lorentz displacement. For consistency we have to check that the Lorentz displacement be strictly linear with the magnetic field. We can easily see that now the movement is linearly proportional to the magnetic field and it decreases, as expected, increasing the Bias voltage. Lorentz X-displacement 100 V 350 V300 V 250 V 200 V150 V 400 V 6m6m7.8  m6.8  m  m5.5  m5m5m9m9m

56. In the Y direction instead we can fit the data with a straight line, within the errors, but the movement doesn’t scale as expected with the Bias voltage. Nevertheless the residual Lorentz displacement in this view is very small (B is almost parallel to Y) and practically comparable with the errors. ONLY 1  m Lorentz Y-displacement 100 V 350 V300 V 250 V 200 V150 V 400 V

57. Position finding algorithm Since the position is deduced by computing the charge cluster center of gravity from binned pixel cells, an indetermination is introduced in the measurements by the finite size of the cells. I investigated this effect by assuming a shape for the LED light given by a gaussian fit to the charge collected on the pixel cells

58. X-correction The final correction curve is given by the following plot X = Measured Center of Gravity coordinate Y = Corrected coordinate value 3389 3390

59. X-corrected mechanical movement The correction is really tiny for the mechanical movement. 100 V 350 V300 V 250 V 200 V150 V 400 V

60. Corrected Lorentz X-displacement 100 V 350 V300 V 250 V 200 V150 V 400 V While for the Lorentz displacement the correction is ~1  m at most

61. The same procedure has been applied to Y-coordinate where the effect is sizable due to the large discretization (400  m). I assumed the same LED shape as in X and I verified it rotating the optical fiber of 90 degrees Y-correction

62. Corrected Y-mechanical movement 100 V 350 V300 V 250 V 200 V150 V 400 V

63. Corrected Lorentz Y-displacement 100 V 350 V300 V 250 V 200 V150 V 400 V 1.6  m 2.6  m 1.5  m 0.8  m 1.8  m 1.2  m

64. Final Lorentz displacement at 2.8 KGauss Combined X and Y displacement at different bias voltages LL Lorentz displacement

65. Comparison with theory The Lorentz angle is proportional to the magnetic field  L =  H B where the proportionality factor,  , is the Hall mobility which is related to the drift mobility via  H = r H ·  The Hall factor, r H, is a dimensionless value determined to be r H = 1.15 for electrons, while the mobility can be well described by the empirical formula  =  ) 1 + ( E ECEC )  ( 1/  E is the electric field in the sensor  ,  E C,  are parameters determined empirically and are well measured at 300° K   = 1450  cm²/V·s E C = 7240 V/cm  = 1.30 I will compare the measured effective Lorentz angle as defined by  L effective =  X/  Z with what expected from theory

66. Comparison with Theory P+ implant n+ E z The electric field in the sensor can be well approximated by the following formula  L = d X/ d Z =   B dX =   B dZ  …so it’s easy to calculate the trajectory of the carriers in the silicon d n

67. Lorentz displacement at 2.8 KGauss Results  ² = 1.22 LL

68. Effective Lorentz angle extrapolated at 1.6 Tesla Bias: 100Angle: 11.9 ±0.14 ± 0.3 Theory: 11.92 Bias: 150Angle: 10.6 ±0.16 ± 0.3 Theory: 10.4 Bias: 200Angle: 9.19 ±0.15 ± 0.3 Theory: 9.13 Bias: 250Angle: 8.02 ±0.15 ± 0.3 Theory: 8.1 Bias: 300Angle: 7.23 ±0.14 ± 0.3 Theory: 7.25 Bias: 350Angle: 6.83 ±0.16 ± 0.3 Theory: 6.56 Bias: 400Angle: 6.21 ±0.15 ± 0.3 Theory: 5.97 Bias: 100Angle: 11.9 ±0.14 ± 0.3 Theory: 11.92 Bias: 150Angle: 10.6 ±0.16 ± 0.3 Theory: 10.4 Bias: 200Angle: 9.19 ±0.15 ± 0.3 Theory: 9.13 Bias: 250Angle: 8.02 ±0.15 ± 0.3 Theory: 8.1 Bias: 300Angle: 7.23 ±0.14 ± 0.3 Theory: 7.25 Bias: 350Angle: 6.83 ±0.16 ± 0.3 Theory: 6.56 Bias: 400Angle: 6.21 ±0.15 ± 0.3 Theory: 5.97 Results LL

69. I can even measure the three parameters, ,  0 and E c, by fitting my measurements with the theory model. The fit is reported in the plot and the returned parameters are  0 = 1486 ± 123  = 1.19 ± 0.24 E C = 7706 ± 550 Results (  0 = 1450 ) (  = 1.30 ) ( E C = 7240 )

70. Conclusions The measured Lorentz angle agrees very well with the previous measurements. -For instance, I obtain 9.3º ± 0.14º± 0.3º at 1.4 T and 150 V, to be compared with 9º ± 0.4º ± 0.5º measured by ATLAS I was able to measure the theory parameters which are in good agreement with those reported in literature. The scaling of the Lorentz angle with the bias voltage (i.e. mobility) follows the expectations The next step will be the measurement with irradiated detectors In the end, with a relatively simple apparatus, I was able to accurately measure the Lorentz angle.

71. BACK UP SLIDES

72. In order to improve the determination of the X displacement I add a correction in the X-direction performing a MonteCarlo simulation that takes into account this effect. Data analysis 2.The mean value of these gaussians has been plotted in (a) (a) 1.I generated a sample of 10,000 gaussians with fixed width and amplitude taken from the data sample shown in figure 3.For each chosen gaussian, the shape as been superimposed on a grid of pixels at fixed positions, and the fraction of gaussian area overlapping each bin has been computed. The mean values of these redistributed charges (C.o.G) have been computed and plotted in (b) (b)

73. Data analysis 4.For each generated gaussian, the difference betweeen the input value (peak position of the gaussian) and the computed mean value after discretization is plotted in (c). The spread turns out to be of the order of 1  m 5.Finally I obtained the correlation curve between continuous beam spot and the corresponding computed values from discretized quantities. See (d) 3389 3390

74. 474 = 23,4%1548 = 76,6%  To improve the determination of the center of gravity in Y I verified, rotating the optical fiber of 90 degrees, that the distribution of the light was almost the same in X and Y. So I could learn from the more precise determination of the X position also a correction to apply to the Y. Data analysis 130344483504378183

75. Beam Axis 50  m 400  m X Plane Y Plane 50  m 400  m Pixel vertex detector