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HBD studies inRun9 200GeV p+p collisions

Jiayin Sun

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Two kinds of HBD responses

• single electron clusters (SINGLES):– One electron per cluster– Smaller HBD signal

• double electron clusters (DOUBLES):– two electrons per cluster– Larger HBD signal

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4 types of electrons in HBD

SINGLE

Signalnon-phot

FAKE SINGLEType 2

Background :One-leggeddoubles

SINGLE type 0 Background : open pairs

DOUBLE type1background

One electron is not detected. They appear to be singles but are in fact doubles.

Both electrons are detected by PHENIX

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What I did• Search an event for an electron track (normal

electron cut)– Get 1st electron – Then look for its HBD cluster ID, charge, size etc.

• Search the event again for another electron track (loose cut)– No 2nd electron single (signal + type2)– Find 2nd electron:

• Look for its HBD cluster.• Share same HBD cluster with 1st e double (type1)• Different HBD cluster single (signal + type0 + type2)

• Real singles and Type 2 are indistinguishable (both appear to be singles: 1 electron/cluster)

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Basic HBD cuts

• Distance btw track projection & cluster < 4cm• HBD cluster size > 2 pads

• Default HBD clusterizer: LBS clusterizer by Ermias.

• Ermias’s cut on minimum cluster charge: 15p.e.– To cut out scintillations

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Single electron clusters are composed of: signals background: one legged doubles (type2) background: open pairs (type0)

SINGLES HBD charge distribution

0<pT<1 1<pT<2 2<pT<3

3<pT<4 4<pT<5

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Double electron clusters are composed of:background: doubles / type 1

clean background.

DOUBLESHBD charge distribution

0<pT<1 1<pT<2 2<pT<3

3<pT<4 4<pT<5

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Background: one-legged doubles• Can be constructed from 2-legged doubles (type1),• Define:• R12 =

• To get a clean sample of doubles, choose clusters with large charge– Use arbitrary cut at charge > 60 p.e. (justified later)– Assume all clusters > 60 p.e. to be real doubles.

Type 2 Two-legged doubles (type1)

one-legged doubles (type2)

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Background: one-legged doubles

singles

Type 1

single && charge >60

Type 1 && charge >60

Singles:(Type 2 dominant)

Type 1

type

charge

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Construct one-legged doublestype 2 = type1 x (R12)-1

0<pT<1 1<pT<2 2<pT<3

3<pT<4 4<pT<5

• HBD charge

• inclusive singles• type2• type1

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Signal after subtraction0<pT<1 1<pT<2 2<pT<3

3<pT<4 4<pT<5

• HBD charge

• inclusive singles• type2• open pairs (type0)• (type1)

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Signal ( 1 < pT < 2)

Charge (p.e.)

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Results from WIS clusterizer0<pT<1 1<pT<2 2<pT<3

3<pT<4 4<pT<5

• HBD charge

• inclusive singles• type2• open pairs (type0)• (type1)

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Signal ( 1 < pT < 2) (WIS)

Charge (p.e.)

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HBD charge Cut • Design a cut on HBD cluster charge– Reject electrons with HBD charge > cut value.

• Ideally, this cut should:– cut out as many double clusters (photonic

electrons) as possible. – Keep as many signal as possible– Keep S/B ratio as high as possible

• S/B ratio is a function of the cut.– S/B = signal / (type0+type1+type2)

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S/B vs. charge cut0<pT<1 1<pT<2 2<pT<3

3<pT<4 4<pT<5

• S/B decline with cut

• lower cut:Cut out a lot of signals• higher cut:Lower S/B ratio

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Efficiency vs. charge cut0<pT<1 1<pT<2 2<pT<3

3<pT<4 4<pT<5

Efficiency = Signals left after cut Total signals

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R12 vs. pT(charge > 60 p.e.)

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R12 vs. cut at cluster charge 0<pT<1 1<pT<2 2<pT<3

3<pT<4 4<pT<5

• R12 flat from 45 p.e. to 65 p.e.

• insensitive to the cut after 45 p.e.• Stat. fluctuation at higher pT

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Background: open pairs (type0)• Distance between clusters– All– 0 < Mee < 0.14GeV– Mee > 0.14GeV

• Cut: dist < 10 cm

SINGLE type 0 Background: open pairs

dist

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Background: open pairs (type0)• A look at open pairs

SINGLE type 0 Background: open pairs

dist

mis-associated doubles