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B tagging meeting XX-XX-04. Fast b tagging at L2. Sascha Caron (NIKHEF). … using the Silicon Track Trigger (STT) Methods to do a very fast b tagging Some first results and a proposal for a L2 algorithm. Silicon Track Trigger. The STT is the. STT status.

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Fast b tagging at l2

B tagging meeting XX-XX-04

Fast b tagging at L2

Sascha Caron (NIKHEF)

  • … using the Silicon Track Trigger (STT)

  • Methods to do a very fast b tagging

  • Some first results

  • and a proposal for a L2 algorithm


Silicon track trigger
Silicon Track Trigger

  • The STT is the

Sascha Caron (NIKHEF)


Stt status
STT status

  • hardware installed, working and STT info is implemented in v13 test

    trigger list

  • STT simulator agrees well with hardware

  • STT output correlates well with D0 reconstruction

Time to think about using the STT improved

L2 track information for b tagging

Sascha Caron (NIKHEF)


Trigsim
Trigsim

  • STT information for Monte Carlo events gained using a modified trigsim

    t04.05.00 (with p17.01.00 STT routines)

    and trigsimcert to get the root tuple

  • Events used are the “usual” sets for b tagging

    Certification:

    QCD: pt>40 GeV file with 10000 events (id 8791)

    Z-> bb: 10000 events (id 8845)

    Z-> cc: 1000 events (id

    Top-> all jets

    Z-> bb with 12 multiple interactions : 1000 events

Sascha Caron (NIKHEF)


Comparison stt simulation code and modified trigsim trigsimcert
Comparison STT simulation code and modified trigsim/trigsimcert

Agreement

in the used variables

(chi2, impact

parameter

significance)

Sascha Caron (NIKHEF)


Elip method
ELIP method trigsim/trigsimcert

Sascha Caron (NIKHEF)


Elip method1
ELIP method trigsim/trigsimcert

Pdf derived using

Kernel estimation

Each sample point

is smeared by pulling

10000 sample points

out of a Gaussian with

a width optimized as

a function of S

Probability for a

track to come from

the vertex is just

the integral of the

pdf from S to inf.

Sascha Caron (NIKHEF)


Lm likelihood method
LM (likelihood method) trigsim/trigsimcert

  • Derive probability density function of the track significance S for signal (Z) and background (QCD) events

  • Use all “good” tracks with a scaled chi2<5

  • Idea : Store

    R(S)=pdfSignal(S)/ pdfbackground(S)

    in a lookup table for S (256 entries)

    Loop over all “good” tracks i and derive the product of R

    Derive a Likelihood as a descriminant:

Sascha Caron (NIKHEF)


Lm kernel estimation
LM: Kernel estimation trigsim/trigsimcert

pdf using kernel estimation

method with Gaussians

Sascha Caron (NIKHEF)


Mulm method
MULM method trigsim/trigsimcert

  • Significance is heavily dependent on

    the goodness of the track fit

  • Goodness the track fit given by scaled

    chi2 (less pt dependent)

    Idea: Include chi2 information in discriminator by using 2d p(S,chi2) pdfs

    This degrades tracks with large chi2 while still

    Using the full information provided by the STT.

Sascha Caron (NIKHEF)


MULM trigsim/trigsimcert

Sascha Caron (NIKHEF)


Summary
Summary trigsim/trigsimcert

High energy ep collisions at HERA are a unique testing ground for the SM

Various searches for new physics are performed (model independent and dedicated)

Some interesting events are found

… and HERA 2 has just started !

Sascha Caron (NIKHEF)


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