Ideas of BigBite Tracking Monte-Carlo

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					           Ideas of BigBite Tracking
                 Monte-Carlo

                    Xin Qian
                   Duke, TUNL
                   MEP Group



2007-1-6                               1
                Outline
• BigBite Setup During Transversity
  Experiment.
• BigBite Background Issue.
• My understanding of the BigBite Tracking
  for Transversity Experiment.
• Why do we need a BigBite Tracking
  Monte-Carlo?
• Ideas of BigBite Tracking Monte-Carlo.
2007-1-6                                     2
  BigBite Setup During Transversity
                           Shower system    Wire chamber
• Three full wire
                                                              Optics
  chambers with 18                                            Slot-slit
  planes in total (6
  planes each
  chamber).
• Gas Cerenkov, pre-
  shower shower
  counter do the PID.
• Scintillator give the   Scintillator
  timing information.             Gas Cerenkov
                                                    Magnetic field
                                                    shielding
2007-1-6                                                        3
                  BigBite Background
• BigBite high rates
  background is a big
  problem to the wire
  chamber:
     –     low tracking efficiency,
     –     high dark current,
     –     short chamber life time,
     –     etc…
• High rate background is
  causing by
     – secondary particles,
     – low energy photon,
     – etc.
2007-1-6                               4
           BigBite Background
• Significant amount of
  background is coming from
  the downstream beam
  pipe.

• A thick shielding on the
  side will help reducing
  background.

• Some shielding material
  inside BigBite magnet will
  also help.

2007-1-6                        5
           From Seamus Riordan

2007-1-6                         6
  BigBite Background estimation
• GEANT3 with modified physics.
• Modified Physics:
     – Use exclusive event generator: photon-nuclear
       fragmentation package DINREG in GEANT
       substitutes old ‘PFIS’ mechanism.
     – Electron-nuclear interactions are modeled using
       equivalent photon representation of an electron.
• Geometry: target, BigBite magnet, detector,
  beam pipe, beam dump and Hall.
• Code is from Pavel Degtiarenko.
2007-1-6                                                  7
  BigBite Background estimation
• Rate estimation has been confirmed by
  comparison with:
     –     TRAN test run,
     –     N20 test run,
     –     SRC data,
     –     bare wire chamber test run
     –     and GEN data.
• The discrepancy is less than a factor of 2.
• For wire chamber, the discrepancy is less than
  20-30%.

2007-1-6                                           8
    Comparison between GEN data
       and TRANSVERSITY
   BD1(MHz)           BD2(MHz) BD3(MHz)                  current
GEN: 19.2              22.0     19.3                       9 uA
TRAN: 10.6             23.0     23.0                     10 uA
       Condition:      6 GeV, 30 degree, with thick shielding wall.
                       Cut 1 keV is a loose cut.

•   More shielding in front (collimator design, shield window etc.) can
    further decrease the background.

•   Background rate limitation:
     – Not on the dark current.
     – Limitation is on the confidence of the tracking algorithim,
     – also related to the low tracking efficiency.

2007-1-6                                                                  9
     2 chambers vs 3 chambers?
• With 15 uA beam, background rate ~ 35 MHz
     – 0.25MHz/wire for the first chamber, 0.18MHz/wire
       for the third chamber.
     – The probability of firing one wire during 200 ns ~
                              P = (1 − exp(− Riδ t ))
       4.9% and 3.4%.

     – Assuming 5/6 planes firing, the probability of having
       one faked point              Here P = 5% (for chamber 1)
                                                   1
           • in the first chamber ~ 25.5%. N ~ 140^2*8 for first chamber
           • In the third chamber ~ 8.5%. N represent all the possible regions.
                                             Here 8 is due to the U1,V1,X1 plane.


                Ptot = N i(C6 i P 5 (1 − P ) + C6 i P 6 )
                            5
                                 1        1
                                                6
                                                     1
2007-1-6                                                                    10
     – Assuming shower can reduce 1/2 phase
       space, the probability of having one track
           • for two chamber ~ 0.54%; contamination > 3%
             faked track.
            9uA, 3He
            number of events




                           250
                                    hits only

                           200
                                    13 minimum planes in reconstructing tracks

                                    hits and tracks
                           150


                           100


                               50


                               0
                                0   2    4      6       8      10       12     14     16
                                         number of planes contain hits passing shower cut
2007-1-6                                                                                    11
           2 chamber vs 3 chamber?
• If we have another chamber, we can reduce the faked
  track by
     – 0.0002% for a full chamber
     – 0.7% for a 3 planes chamber.
     – leading to negligible effect in the completely random situation.
• If there is some correlation between hits on different
  planes or even different chambers:
     – Hard to quantify.
     – Assuming a factor of 2 increasing in the probability.
           • 6 planes on second chamber: ~ 0.13% contamination.
           • 3 planes on second chamber: ~ 9% contamination.
     – Full middle chamber can significantly reduce the probability of
       faked track.
     – A Monte-Carlo may give a more accurate estimation.
2007-1-6                                                                  12
                        What else for 3 chambers?
     Plane u1                                                                             Plane u2                                                                             Plane u3                                                                             Plane u4
                  1.2                                                                                  1.2                                                                                  1.2                                                                                  1.2

                                0.942 + 0.002 - 0.002                                                                0.964 + 0.002 - 0.002                                                                0.935 + 0.002 - 0.002                                                                0.987 + 0.002 - 0.002
                    1                                                                                    1                                                                                    1                                                                                    1


                  0.8                                                                                  0.8                                                                                  0.8                                                                                  0.8
     Efficiency




                                                                                          Efficiency




                                                                                                                                                                               Efficiency




                                                                                                                                                                                                                                                                    Efficiency
                  0.6                                                                                  0.6                                                                                  0.6                                                                                  0.6


                  0.4                                                                                  0.4                                                                                  0.4                                                                                  0.4


                  0.2                                                                                  0.2                                                                                  0.2                                                                                  0.2


                   0                                                                                    0                                                                                    0                                                                                    0
                   0        2       4       6      8        10        12        14                      0        2       4       6      8        10        12        14                      0    2       4   6     8    10    12    14    16        18   20   22                 0    2       4   6     8    10    12    14    16        18   20   22
                                        Wire Number for Plane u1                                                             Wire Number for Plane u2                                                             Wire Number for Plane u3                                                             Wire Number for Plane u4



     Plane u5                                                                             Plane x1                                                                             Plane x2                                                                             Plane x3
                  1.2                                                                                  1.2                                                                                  1.2                                                                                  1.2

                                0.981 + 0.002 - 0.002                                                                0.954 + 0.002 - 0.002                                                                0.988 + 0.002 - 0.002                                                                0.952 + 0.002 - 0.002
                    1                                                                                    1                                                                                    1                                                                                    1


                  0.8                                                                                  0.8                                                                                  0.8                                                                                  0.8
     Efficiency




                                                                                          Efficiency




                                                                                                                                                                               Efficiency




                                                                                                                                                                                                                                                                    Efficiency
                  0.6                                                                                  0.6                                                                                  0.6                                                                                  0.6


                  0.4                                                                                  0.4                                                                                  0.4                                                                                  0.4


                  0.2                                                                                  0.2                                                                                  0.2                                                                                  0.2


                   0                                                                                    0                                                                                    0                                                                                    0
                   0    2       4   6     8    10    12    14    16        18   20   22                 0        2       4      6      8         10        12        14                      0        2       4       6      8        10        12        14                      0    2       4   6     8    10    12    14    16        18   20   22
                                        Wire Number for Plane u5                                                             Wire Number for Plane x1                                                             Wire Number for Plane x2                                                             Wire Number for Plane x3



     Plane x4                                                                             Plane x5                                                                             Plane v1                                                                             Plane v2
                  1.2                                                                                  1.2                                                                                  1.2                                                                                  1.2

                                0.993 + 0.002 - 0.002                                                                0.983 + 0.002 - 0.002                                                                0.968 + 0.002 - 0.002                                                                0.974 + 0.002 - 0.002
                    1                                                                                    1                                                                                    1                                                                                    1


                  0.8                                                                                  0.8                                                                                  0.8                                                                                  0.8
     Efficiency




                                                                                          Efficiency




                                                                                                                                                                               Efficiency




                                                                                                                                                                                                                                                                    Efficiency
                  0.6                                                                                  0.6                                                                                  0.6                                                                                  0.6


                  0.4                                                                                  0.4                                                                                  0.4                                                                                  0.4


                  0.2                                                                                  0.2                                                                                  0.2                                                                                  0.2


                   0                                                                                    0                                                                                    0                                                                                    0
                   0    2       4   6     8    10    12    14    16        18   20   22                 0    2       4   6     8    10    12    14    16        18   20   22                 0        2       4      6      8         10        12        14                      0        2       4       6      8        10        12        14
                                        Wire Number for Plane x4                                                             Wire Number for Plane x5                                                             Wire Number for Plane v1                                                             Wire Number for Plane v2



     Plane v3                                                                             Plane v4                                                                             Plane v5
                  1.2                                                                                  1.2                                                                                  1.2

                                0.943 + 0.002 - 0.002                                                                0.980 + 0.002 - 0.002                                                                0.979 + 0.002 - 0.002
                    1                                                                                    1                                                                                    1


                  0.8                                                                                  0.8                                                                                  0.8
     Efficiency




                                                                                          Efficiency




                                                                                                                                                                               Efficiency




                  0.6                                                                                  0.6                                                                                  0.6


                  0.4                                                                                  0.4                                                                                  0.4


                  0.2                                                                                  0.2                                                                                  0.2


                   0                                                                                    0                                                                                    0
                   0    2       4   6     8    10    12    14    16        18   20   22                 0    2       4   6     8    10    12    14    16        18   20   22                 0    2       4   6     8    10    12    14    16        18   20   22

2007-1-6                                Wire Number for Plane v3                                                             Wire Number for Plane v4                                                             Wire Number for Plane v5
                                                                                                                                                                                                                                                                                                                                                         13
           What else for 3 chamber?
• Improvement on naïve tracking efficiency:
     – Assuming an average 95% hitting efficiency,
       the naïve tracking efficiency (neglect software
       part) is:
           • 96.4 % for 13 out of 15 planes.
           • 98.9 % for 15 out of 18 planes.
     – Middle chamber will be able to fix a point by
      itself.
• Position of middle chamber
     – Monte Carlo will help
2007-1-6                                               14
                       BigBite tracking
• The BigBite tracking code made by
  Seamus Riordan is quite successful in
  treating GEN data.
     – Brute force method which goes through all the
       possible combination within the shower-
       counter cut.
     – The least Chi2 method is used to select the
       real track.
     – The advantage:
           • in principle will find all the real tracks.
     – The disadvantage:
           • slow in the high rates situation.
2007-1-6                                                   15
                        BigBite tracking
• How slow? 10 Hz level
     – GEN:
           • Average 3 hits per plane in 200 ns window. (15 planes)
     – TRAN worst scenario:
           • Average 7 hits per plane in 200 ns window. (18 planes)
     – The ratio is (1+7/2)^18/(1+3/10)^15 ~ 1E10.
           • In TRAN case, the trigger rates is lower (half Hz level), which
             can help reducing the computing time.
           • Faked contamination is ~ 0.13%. Most combination are not
             useful.
           • Tree searching can reduce O(n) to O(log(n)).
     – In this case, a much faster tracking algorithm is
       possible and necessary for transversity experiment.

2007-1-6                                                                  16
           Why do we need a BigBite
            Tracking Monte-Carlo
•   Tracking Monte-Carlo can help in studying the software tracking
    efficiencies:

     – During GEN, the tracking efficiency can be studied in hydrogen elastic
       run by using Neutron arm information.
     – Hard to study tracking efficiency in production run
     – Equally hard to study during TRANSVERSITY production run.

•   Tracking Monte-Carlo can help evaluating/improving new tracking
    algorithm.
     – Balancing speed and tracking efficiencies?

•   Tracking Monte-Carlo can help in fixing the maxima luminosity and
    the number of planes used in the tracking.

•   Understanding Optics?
2007-1-6                                                                        17
     Some ideas on tracking Monte-
                Carlo
•   Tracking Monte-Carlo can be made based on Comgeant (From
    Eugene Chudakov)
     – GEANT3 with updated BigBite detector geometry

     – Digitization already exists in the comgeant
           • Multi-wire proportional chamber
           • Shower counter

     – Need to make a code to convert output of Comgeant into the format
       which can be read by analyzer: ADC and TDC value. (VDCsim can be
       used as a reference code)

     – In this code, we also need to add background as well
           •  Merging method for wire chamber TDC and shower counter ADC in case of
             pile up and adding background.
           • Modified digitization inside comgeant, non-linear drift time etc.



2007-1-6                                                                         18
           Acknowledgement
• Eugene Chudakov
• Ole Hanse
• Robert Feuerbach, Seamus Riordan and
  Brandon Craver.
• Xiaodong Jiang and Kalyan Allada




2007-1-6                                 19
• BACK UP slides




2007-1-6           20
                          Plan
• Check the geometry:
     – The geometry need to be consistent between
       comgeant and analyzer.
• Comgeant side:
     – Be familiar with the running and decoding
     – Adding background
     – Develop merging method for additional background.
• Analyzer side:
     – Create a code which can convert comgeant output
       into raw TDC and ADC values which can then be
       read into Analyzer.
     – Be familiar with Analyzer (BigBite).
• Expected to be finished in a couple months.

2007-1-6                                                   21
Position of the middle chamber?
• Middle chamber can be placed in front of Gas
  Cerenkov or on the back of Gas Cerenkov.
     – Chamber on the back will have less rate per wire
       which lead to less probability to have a faked track.
     – Chamber in the front will have more rate per wire, but
       it can help to reduce the multiplicity of the hitting point
       on the first chamber.
     – Naïve study shows the chamber in the front can help
       more.
     – Again, it is hard to quantify without a Monte-Carlo
       simulation. It is almost impossible to gain information
       from GEN data, since the middle chamber is fixed in
       the middle.
2007-1-6                                                        22

				
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