Gamma Gamma HBT Using STAR EMC an Update on 62'4A GeV data

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Gamma Gamma HBT Using STAR EMC(an Update on
62.4A GeV data)
Debasish Das VECC Kolkata Sergey Panitkin
BNL Subhasis Chattopadhyay VECC, Kolkata Tapan K
Nayak VECC, Kolkata A A P Suaide Instituto de
Fisica da USP Sao Paulo, Brazil

• Results so far with both SMD present
• (1)study on
  the relevance of cuts
• (2)study of Qinv
  distributions with cuts
• The studies of 2 EMC Points in LOW Qinv region
• Summary and Future plan

Gamma-Gamma HBT meeting , YALE
MAY 2005
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THE EMC ANALYSIS
THE 62.4 A GeV QA daywise
BEMC
SMDE
SMDP
For this analysis we have taken EMC points which
have both SMDs present 6 days of data total For
the present talk we have 2 days (88 89)
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THE EMC ANALYSIS
The Analysis with EMC StEvent
EMC Hits From MuDst
EMC Calibration
EMC Clustering
Analysis
EMC Point Maker
Study of the EMC Point Multiplicity
Combinations of points we have 4 catergory as
such (a)Points from Barrel . SMD eta and phi
plane not present.---CATEGORY-(0) (b)Points from
Barrel and SMD eta , but SMD phi not
present..---CATEGORY-(1) (c)Points from Barrel
and SMD phi , but SMD eta not present..---CATEGORY
-(2) (d)Points from Barrel and both SMD (eta and
phi) planes present..---CATEGORY-(3)
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• EMC Points have both SMD
• Proper hadron suppression

Angle(rad)

• The Energy cut Egt0.4 GeV/c (as 0.4 GeV the
  cluster "Seed" for energy in Barrel Towers from
  where energy is taken),removes the cases where 2
  showers in SMD can cause a split in the Tower
  energy(sharing).So such cases will get removed
  with Egt 0.4 GeV/c.
• The rejection of Points/Hits from same tower
  also reduces the splits to certain extent.
• But still there is a bump at lower angles.The
  fall at angle 0.02 radians seems to coincide
  with the 3 SMD strip width , below which the
  present EMC cluster finder cannot work!

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Both Points from SMD-? or SMD-? in low Qinv
Both SMD-? present
Eta-diff Phi-diff between EMC Points shows a
peak at 0.21(3 SMD strips width!)
Both SMD- ? present
Eta-diff Phi-diff between EMC Points shows a
peak at 0.21(3 SMD strips width!)
Possible hindrance in understanding overlapped
cluster!
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• EMC Points have both SMD
• Proper hadron suppression

MINV(QINV)
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Pair Alpha Modulus(E1 E2)/ (E1E2)
MIXED
REAL

• There is a structure at low Qinv for REAL, absent
  in MIXED.
• The study of this cut is motivated by WA98 Photon
  HBT studies where clusters where found to be
  splitting in disproportionate energies. Here with
  EMC clusters we have no such information, but
  this study can help us to understand whether we
  need them for this analysis or not.

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Pair Alpha Modulus(E1 E2)/ (E1E2)

• Pair Alpha RATIO for QINVlt50 MeV.
• There is a difference in the REAL and MIXED.
• After 0.2 Pair Alpha we see a rise in Ratio.

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Pair Alpha Modulus(E1 E2)/ (E1E2)

• Pair Alpha RATIO for QINVgt50 MeV.
• There is no difference in the REAL and MIXED.
• The Pair Alpha Ratio is almost close to unity.

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Pair Alpha Modulus(E1 E2)/ (E1E2)
Photon correlation
Opening Angleo

• Opening Angle RATIO and Photon Correlation
  functions with and without Pair Alpha cutslt0.1.
• There is small change and so maybe in present
  analysis or understanding of splits this cut
• may not be useful.

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• EMC Points have both SMD
• Proper hadron suppression

Angle(rad)

• The Energy cut Egt 0.8 GeV/c (as 0.4 GeV the
  cluster "Seed" for energy in Barrel Towers from
  where energy is taken),removes the further cases
  of split clusters! The change in the ratio shows
  that.
• The Alpha cuts do make a change but not quite
  significant.

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• EMC Points have both SMD
• Proper hadron suppression

MINV(QINV)
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• EMC Points have both SMD
• Proper hadron suppression
• We will require more stats
• and later extend this study for 200 GeV AuAu

MINV(QINV)
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Summary Outlook

• The rise in low Qinv below ?0 peak
• removed after the Higher energy cuts are
  applied.
• But now it needs to be studied more in detail
  from
• the detector point of view.Also with various
  energy cuts.
• So what is done so far

• Hadron suppression was implemented.
• Opening Angle cut to suppress cluster merging was
  studied.
• The splitting issues in clusters are identified
  and also removed with energy cut, which reduces
  the huge peak seen before. But these split
  clusters properties need more study.
• Opening angle cut and energy influences low Qinv
  region lt50MeV
• Initial Studies done to understand properties of
  low Qinv cluster properties from the detector
  point of view.

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BACK UP
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BARREL PARAMETERS----OVER-VIEW
(??, ??)tower (0.05, 0.05)
(??, ??)SMD (0.007, 0.007)
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Hadron Suppression or Track rejection

• To reduce the possibility of hadron contamination
  in Photon sample while analyzing the correlation
  functions of EMC Points we need to reject the
  tracks associated with EMC HITS.
• Here we follow a certain procedure to reject
  those EMC POINTS
• which exist in certain eta and phi proximity of a
  projected TPC TRACK.
• This is described in a cartoon below.