L c + Status Report

08-Mar-0508-Mar-05

STAR

cc++ Status Report Status Report

Heavy Flavor Working GroupHeavy Flavor Working Group

Manuel Calderon de la BarcaManuel Calderon de la Barca

Indiana UniversityIndiana University

08-Mar-0508-Mar-05 Manuel Calderon de la BarcaManuel Calderon de la Barca

STAR Why? How?Why? How?

cc++ : lightest charmed baryon. : lightest charmed baryon.

Never measured in heavy ion collisions before.Never measured in heavy ion collisions before. ~15 – 20% of charm production goes into ~15 – 20% of charm production goes into cc

++.. If (signal) then {yield? spectra? Centrality dep?}If (signal) then {yield? spectra? Centrality dep?}

Does recombination work for charm as well?Does recombination work for charm as well?

cc++p Kp K-- ++ (+ c.c. mode for (+ c.c. mode for cc

--)) M = 2.285 GeV, BR (5 M = 2.285 GeV, BR (5 ± ± 1.3) %, c1.3) %, c=60 =60 m, (udc)m, (udc)

3-body decay: large combinatorical background3-body decay: large combinatorical background Momenta of daughters in good PID regionMomenta of daughters in good PID region

Maybe there’s a chance?Maybe there’s a chance?


STAR GEANT SimulationsGEANT SimulationsOverall acceptance = 17%Overall acceptance = 17%Acc == (all 3 daughters leave 10 hits in TPC)Acc == (all 3 daughters leave 10 hits in TPC)

Thrown

Accepted


STAR GEANT AcceptanceGEANT Acceptancevs. pvs. pTT (~20% at 1 GeV/c), vs. y (~40% at y=0) (~20% at 1 GeV/c), vs. y (~40% at y=0)


STAR Where are the daughters?Where are the daughters?

Pion Kaon Proton

Original <pt>Original <pt> Accepted <pt>Accepted <pt>

0.3760.376 0.3850.385

KK 0.4950.495 0.5830.583

pp 0.5970.597 0.6770.677


STAR Rough Yield EstimateRough Yield Estimate cc/(D/(D00+D+D++) = 0.3, D) = 0.3, Dss/(D/(D00+D+D++) = 0.2) = 0.2 If If cccc==DDDD + + cc + + DsDs then then

cc//cccc = 0.2 = 0.2 If If cccc=600 =600 b and :b and :

TTaaaa=23 mb=23 mb-1-1 for 10% central for 10% central TTaaaa=5.5 mb=5.5 mb-1-1 for minbias for minbias i.e. assuming binary collision scalingi.e. assuming binary collision scaling

ccbar yield per 10% central = .023 x 600 = 14 ccbar yield per 10% central = .023 x 600 = 14 ccbar yield per minbias = .0055 x 600 = 3.3 ccbar yield per minbias = .0055 x 600 = 3.3

cc++ yield per 10% central = 14x0.2x0.5 = 1.4 yield per 10% central = 14x0.2x0.5 = 1.4

cc++ yield per minbias = 3.3x0.2x0.5 = 0.33 yield per minbias = 3.3x0.2x0.5 = 0.33

Branching ratio 5%: 1.4x0.05=0.07 central, 0.33x0.05=1.65 e-2Branching ratio 5%: 1.4x0.05=0.07 central, 0.33x0.05=1.65 e-2 Accepted Accepted cc

++ = 0.07 x 0.17 = 0.012 central, 2.8 e-3 minbias = 0.07 x 0.17 = 0.012 central, 2.8 e-3 minbias Efficiency 0.8 (single track) : .012x(0.8Efficiency 0.8 (single track) : .012x(0.833) = .006 central, 1.44 e-3) = .006 central, 1.44 e-3 1 1 cc

++ in the right decay mode in our acceptance per 200 10% central events. in the right decay mode in our acceptance per 200 10% central events. 1 1 cc

++ in 1000 minbias events. in 1000 minbias events.


STAR Analysis CutsAnalysis Cuts

Fit points >=24Fit points >=24dE/dx points >=20dE/dx points >=20Dca < 1.5 cmDca < 1.5 cm |h|<1.0|h|<1.0PID cuts:PID cuts: |nSigma_X|<1 && |nSigma_Y|>3 && |nSigma_Z|>3|nSigma_X|<1 && |nSigma_Y|>3 && |nSigma_Z|>3

Where x,y,z == pion,kaon,protonWhere x,y,z == pion,kaon,proton


STAR PID ChecksPID Checks

Few events

Hey, what’s all this stuff??

Deuterons visible, other tracksare possible merged tracks, but theircontribution is small.

More events!


STAR Data: pt of candidate daughtersData: pt of candidate daughters

This is the right kinematic range for the This is the right kinematic range for the cc++..

Can we beat the background?Can we beat the background?


STAR Invariant mass plots central.Invariant mass plots central.

Background estimate from 3.2 M central events.Background estimate from 3.2 M central events. 23 counts per event: S/B = 0.006/23 = 2.6x1023 counts per event: S/B = 0.006/23 = 2.6x10-4-4

For a 3For a 3 signal, need : 9 x 2(3833) = 69K signal, need : 9 x 2(3833) = 69K cc++

NNeventsevents = 69K/0.006 = 11.5 M central events = 69K/0.006 = 11.5 M central events (sufficient in Run IV)(sufficient in Run IV)

(Signal) (Signal)


STAR Invariant mass plots (minbias).Invariant mass plots (minbias).

Background estimate from 118K minbias events.Background estimate from 118K minbias events. 12 counts per event: S/B = 0.00144/23 = 6.2x1012 counts per event: S/B = 0.00144/23 = 6.2x10-5-5

For a 3For a 3 signal, need : 9 x 2(16014) = 288K signal, need : 9 x 2(16014) = 288K cc++

NNeventsevents = 288K/0.006 = 48 M minbias events = 288K/0.006 = 48 M minbias events (not sufficient in Run IV)(not sufficient in Run IV)

(Signal) (Signal)


STAR Background subtractionBackground subtraction If we flip the sign of the pion, can that give us a If we flip the sign of the pion, can that give us a

background histogram if background histogram if +/+/- = 1 ?- = 1 ?

Doesn’t work!


STAR Why doesn’t it work?Why doesn’t it work?Ratio is not exactly 1.Ratio is not exactly 1.


STAR +/+/- expanded scale- expanded scale

Ratio not flat and not =1 to few per mil.Ratio not flat and not =1 to few per mil. Important when need to model background in millons of events!Important when need to model background in millons of events!

Contamination above 0.6 GeV plays a role.Contamination above 0.6 GeV plays a role.


STAR Fitting the shape.Fitting the shape.

Approach: Approach: polinomial fit in 2.1 < M < 2.5polinomial fit in 2.1 < M < 2.5Add a gaussian and see if chi2 improves.Add a gaussian and see if chi2 improves.

(for later, i.e. no signal there, statistics is still too low.)(for later, i.e. no signal there, statistics is still too low.)


STAR

In pT bins, does subtraction work?In pT bins, does subtraction work?

pK+- (c+)

0<pt<0.53.6 M Central Events

pK-+ (c-)

1<pt<1.53.6 M Central Events

Subtraction of pol6 fit.Invariant mass.

2/dof=0.99

2/dof=0.79


STAR ConclusionsConclusions

From rough signal and background numbers, From rough signal and background numbers, possible signal in Run 4possible signal in Run 415 M events for ~315 M events for ~3 signal in central events. signal in central events.

To do:To do:Process data as it comes, check for pt dependence.Process data as it comes, check for pt dependence.Will process minbias, central events.Will process minbias, central events.

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