j/ ψ simulations: background studies and first results using a compact rich detector

J/J/ψψ simulations: simulations: background studies and background studies and

first results using a first results using a compact RICH detectorcompact RICH detectorAlla MaevskayaAlla Maevskaya

INR RAS MoscowINR RAS Moscow

CBM Collaboration meeting CBM Collaboration meeting

September 2007September 2007

OutlineOutline

Simulation environmentSimulation environment

J/J/ψψ electrons identification by compact electrons identification by compact

RICHRICH

J/J/ψψ electrons identification by TRD electrons identification by TRD

Background suppression by compact RICH Background suppression by compact RICH

& TRD& TRD

J/J/ψψ reconstruction reconstruction

Background analysisBackground analysis

J/J/ψψ with target 25 with target 25µµm m

ΨΨ' simulation' simulationAlla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

Simulation&reconstruction Simulation&reconstruction environmentenvironment

CBMROOT Release Aug07CBMROOT Release Aug07Gold target 250Gold target 250µmµmMagnetic field: "ActiveField"Magnetic field: "ActiveField"Full reconstruction STS & MVD Full reconstruction STS & MVD

CA track finderCA track finder KF track fitterKF track fitter Primary tracks only (χPrimary tracks only (χ22 at primary vertex < 3) at primary vertex < 3)

Compact RICH: ring finding, fitting, fake rejection, track Compact RICH: ring finding, fitting, fake rejection, track matchingmatchingTRD 3 different routines for e-π separationTRD 3 different routines for e-π separationPID by RICH and TRDPID by RICH and TRD

Signal: J/Signal: J/ψψ decayed to e decayed to e++ee-- by PLUTO by PLUTO HSD multiplicity: for central Au+Au@25GeV collision HSD multiplicity: for central Au+Au@25GeV collision 1.92x101.92x10-5-5

Background: superevent of 24K central Au+Au@25GeVBackground: superevent of 24K central Au+Au@25GeV UrQMD events UrQMD events Alla Maevskaya INR RAS CBM Collaboration meeting

27 September 2007

Comparison of standard and Comparison of standard and compact RICH for J/compact RICH for J/ψψ

reconstructionreconstruction

Standard RICHStandard RICH Compact richCompact rich

Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

Electron identification by TRDElectron identification by TRD

Neural net methodNeural net method

Output value (ann) >0.9Output value (ann) >0.9

methodmethod

Output value (wkn) Output value (wkn) >11>11

LikelihoodLikelihood

Output value (like) Output value (like) >0.9>0.9


kn

π ee

π

π

ee

ee

pion suppression by compact pion suppression by compact RICH & TRDRICH & TRD

all pions in CBM acceptanceall pions in CBM acceptancesurveyed after cuts :surveyed after cuts :•Pt>1GeV/cPt>1GeV/c•RICH ring radius between 4.5 and 7 cmRICH ring radius between 4.5 and 7 cm•satisfied all TRD PID criterion: wkn>11 & like>0.9 & satisfied all TRD PID criterion: wkn>11 & like>0.9 & ann>0.9 ann>0.9 •mismatched electron's ring with wrong trackmismatched electron's ring with wrong track

24000 Au+Au@25GeV


J/J/ψψ's e's electron’s identification lectron’s identification efficiencyefficiency

•all J/ψ's electrons accepted by CBM•after cuts P<11GeV/c and Pt>1GeV/c•identified by compact RICH: neural network ring selection NN>-0.5 Nhit per ring > 15 Ring radius 4.5 – 6 cm Distance between ring center and track<1cm•identified by TRD wkn>11 & like>0.9 & ann>0.9


produced by produced by PLUTOPLUTO

Identified by Identified by “standard” “standard” RICH&TRDRICH&TRD

Identified by Identified by compact compact RICH&TRDRICH&TRD

J/J/ψψ phase space distribution phase space distribution


Invariant mass spectrum J/Invariant mass spectrum J/ψψ + + combinatorial backgroundcombinatorial background


Superevent 6x10Superevent 6x1088

central central Au+Au@25GeVAu+Au@25GeV

primary particles primary particles

identified as electronsidentified as electrons((p < 11 GeV/c, pt > 1 p < 11 GeV/c, pt > 1

GeV)GeV)

Signal/background =1.67Signal/background =1.67

Summary about using compact Summary about using compact RICH for J/RICH for J/ψψ reconstruction reconstruction

““standard” standard” RICH&TRDRICH&TRD

““compact” compact” RICH&TRDRICH&TRD

efficiencyefficiency 14%14% 14%14%

S/BS/B 1.71.7 1.671.67

compact RICH is good for J/compact RICH is good for J/ψψ:: reconstruction efficiency and reconstruction efficiency and signal/background signal/background not worse than with “standard” RICHnot worse than with “standard” RICH


Background analysis Background analysis of superevent 10of superevent 109 9 centralcentral

Au+Au@25GeVAu+Au@25GeV target 250µmtarget 25 µm

Background sourcesBackground sources::~ ~ 350350 ππ00 per per central Au+Au@25GeVcentral Au+Au@25GeV decayed indecayed in

γ γγ γ conversionconversion on the target 98.8% on the target 98.8%

Dalitz decayDalitz decay : e : e+ + ee - - γγ misidentified pions misidentified pions

Target 25µm thicknessTarget 25µm thickness!!!!!!!!!!!!!!!!!!!!!!


number of -conversions number of -conversions vs target thicknessvs target thickness

γγ

ππ0 0 DalitzDalitz

ππ++ππ--

PDG code of mother particles PDG code of mother particles produced background in mass produced background in mass

region >2.9 GeVregion >2.9 GeV

Charmonium simulation Charmonium simulation with 25with 25µm gold targetµm gold target


Simulation environmentSimulation environment

cbmroot FEB07 cbmroot FEB07

standard TRD and RICH on the end of standard TRD and RICH on the end of May07May07

fast tracking private versionfast tracking private version

superevent of 155000 Au+Au@25GeV superevent of 155000 Au+Au@25GeV central events (2.4x10central events (2.4x101010events), events), maximum possible statistics nowmaximum possible statistics now

primary particles identified as electrons primary particles identified as electrons by RICH & TRD participated in by RICH & TRD participated in combinatorial backgroundcombinatorial background


J/J/ψ invariant mass spectraψ invariant mass spectraparticles identified as electrons particles identified as electrons

with P<11GeV/c for perfect RICH &TRD with P<11GeV/c for perfect RICH &TRD

identificationidentification

Pt>1GeV/Pt>1GeV/cc

multiplicity 1.92x10-5 / central Au+Au@25GeV eventmultiplicity 1.92x10-5 / central Au+Au@25GeV eventdielectron branching ratio 0.06dielectron branching ratio 0.0632334 J/ψ correspond to superevent 2.4x1032334 J/ψ correspond to superevent 2.4x101010


ΨΨ' simulation' simulation

momentum and rapidity distribution momentum and rapidity distribution

from PLUTO from PLUTO

multiplicity according CBM TSR 2.56x10multiplicity according CBM TSR 2.56x10--

77;;

dielectron branching ratio 7.35x10dielectron branching ratio 7.35x10-3-3


ΨΨ’ ’ Pt & Y distributionsPt & Y distributions

black histogram from PLUTOblack histogram from PLUTO

blue accepted by STS(5pionts) & TRD & blue accepted by STS(5pionts) & TRD & RICHRICH

red "reconstructable" (P<11GeV/c)red "reconstructable" (P<11GeV/c)Alla Maevskaya INR RAS CBM Collaboration meeting 27 September 2007

ΨΨ' phase space ' phase space distributiondistribution

all from PLUTOall from PLUTOaccepted by accepted by CBMCBM

reconstructablreconstructablee


ΨΨ' electron daughters :' electron daughters :

momentum PtPt


Invariant mass spectraInvariant mass spectra ' + ' + backgroundbackground

2.4x102.4x1010 10 Au+Au@25GeVAu+Au@25GeV centralcentral events, 45events, 45 's's

all particles identified as all particles identified as electrons electrons

"expo" background fit "expo" background fit

+cut Pt>1GeV/c+cut Pt>1GeV/c

"Gaussian" background fit"Gaussian" background fit


J/J/ψψ & & ΨΨ‘ & combinatorial ‘ & combinatorial backgroundbackground 2.4x102.4x1010 10

Au+Au@25GeVAu+Au@25GeV

all particles identified as electrons by RICH & TRD (P<11GeV/c) + cut Pt>1GeV/c

S/B J/ψ 178; S/B J/ψ 178; ΨΨ' 1' 1 S/B J/ψ 205; Ψ' 1.5


SummarySummary

J/→e+e- 1.92 ∙10-5 14% 200 2.1 ∙ 105

'→ e+e- 2.56 ∙10-7 15% (visible!) (3.4 ∙ 102)

Additional Additional investigations investigations should be doneshould be done


multiplicimultiplicityty

total total efficiencyefficiency

S/BS/B yield/10 yield/10 weeksweeks

j/ ψ simulations: background studies and first results using a compact rich detector

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