Improving the YY ratio and other signals with the dHLT

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Improving the Y/Y ratio (and other
signals)with the dHLT

• Bruce Becker
• Research Centre

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Outline

• Mostly said already...
• Some interesting physics signals
• What can the dHLT bring to the game ?
• Work in progress
• outlook

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Physics introduction

• Quarkonium suppression well-established signal of
  QGP.
• Although suppression could be from other effects
• Normal nuclear suppression
• wrong description of initial state (CGC) etc
• Use ratio eliminates nuclear effects
• BUT
• Have to study many signals simulatneously
• pT dependace of ratios of resonances
• Centrality / ET / Temp dependance of resonance
  production
• etc...

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Why Upsilon family ratio?

• Large production cross section at LHC
• Clear suppression patterns for different QPG's
• Studies show that it's possible to make a
  measurement within 1 month of running. (Eric,
  Rachid Philippe)
• Even pT integrated yield gives a nontrivial
  measurement.
• Fairly detailed study already done (Erics
  talk some extensions possible)
• DAY (YEAR) ONE OBSERVABLE !

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Reminder...

• Vogt Gunion (and refs therein)
• Predict suppression patterns dependant on nature
  of plasma

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What can we measure in one (ALICE heavy ion
running) year ?

• Most important results of previous work (Eric
  Philippe)
• Given nominal
• Reaction rate
• Cross sec.
• Bkgnd level
• Feed-down contr
• Centr bins
• Can estimate
• PT spectra
• PT integrated yield

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ASSUMING L0 TRIGGERING WE CAN DISCRIMINATE
QGP/NON-QGPBut what about the dHLT ?Can we
determine the nature of the plasma ?
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What can the HLT bring to the game (I)
Reminder.

• Mandate of the dHLT is to
• Retrieve more signal (at high pT)
• Reduce background (at low pT)
• This may translate into
• Smaller errorbars
• More measurements as function of pT
• But this has to be MEASURED !

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What can the dHLT bring to the game (II)

• This requires an extended study
• real efficiency of detector (updated eff.)
• Full understanding of limitations of dHLT
• Limitations of algorithm
• Fundamental limitations from hardware
• Limitations due to current algorithm
• Both under investigation (Szostak, Becker)
• Requires offline and online implementation

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Improved trigger efficiency (I)

• The dHLT has higher efficiency than L0

To be updated !
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Improved trigger efficiency (II)

• Nothing existed in AliRoot yet to measure dHLT
  performance
• Nothing to link particles, hits to other data
  containers (digits, clusters, etc)
• dHLT needs input from digits (not hits) in order
  to be realistic
• Links added to AliRoot by Artur to overcome
  problem
• Next step dHLT into offline code
• Allow realistic efficiency determination
• See effect on various simulated signals

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Improved signal to background ratio
Tracker rejects unvalidated tracks
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Other signals of interest

• Not only interested in signals that vary with PT
  but also
• With centrality, T/Tc (Model dependant ! )
• Partial suppression case to be studied as
  function of centrality
• Remains to be seen exactly what dHLT brings to
  that measurement

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Work in progress

• Full simulation necessary
• To check dHLT efficiency
• And biasies (with multiplicity, PT)
• Map out the efficiency of the trigger in an
  interesting space
• Eff(pT (GeV),b(fm))
• Perhaps increase the
  number of cent classes
  higher statistics ?

eff
b
PT
b
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Compare dHLT triggered set with L0 triggered set

• Once simulations are complete, can compare the
  ratio of yields from dHLT and L0 to find out
• How much you gain in total yield and sig/bkgnd
• Where in phase space you gain the most
• Realistically offline simulations to be
  compared with results of dHLT prototype
• (long term goal)

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outlook

• Full study of effect of dHLT on interesting
  signals underway
• Part of larger work, integrates with other work
  at UCT
• dHLT prototype building/testing
• Offline code development and integration
• AliEn setup at UCT (use PDC04 data for
  simulations
• Physics analysis
• Results in next 3-5 months
• Will be interesting to see what dHLT can REALLY
  bring to the game !