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Analysis of theD+

s K+K -π+ channel in the ALICE experiment

Serhiy SenyukovUniversità & INFN di Torino

(4050 m. asl)

Open charm and QGP

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QGP

A

A

c

Ds

K

K

πD0

π

K

Primary producti

on

Interaction with QGP

Decay of D

mesons

Detection of

products

c-

Results for D0 and D+

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2<pT<3 GeV/c

p-p @ 14 TeV

Pb-Pb @ 5.5TeV

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Question: We know that D0 and D+ can be reconstructed with

high significance. Why do we need also Ds?Answer:1. To measure charm yield more precisely we need to

measure as many channels as we can2. Study of different ways of hadronization:

• String fragmentation:Ds+ (cs) / D+ (cd) ~ 0.6it should be easier to take a light meson from a vacuum than the strange one

• Recombination:Ds+ (cs) / D+ (cd) ~ N(s)/N(d) (~ 1 at

LHC?)recombination occurs inside the medium.

Why Ds?

ALICE setup

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Inner Tracking System:

Vertexing, Tracking,PID

Time Projection Chamber:Tracking,

PIDTime-of-Flight

detector:PID

Selection strategy

6

invariant-mass analysis of fully-reconstructed

topologies originating from displaced vertices

build triplets of tracks with correct combination of charge signs and large

impact parameters particle identification to tag

the decay products calculate the vertex (DCA

point) of the tracks good pointing of

reconstructed D momentum to the primary vertex

Primary Vertex

Ds flight line

Secondary vertex

K

K

DsKK

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Ds vs. D+ & D0

D0 D+ Ds

Combinations * 106 pairs 109 triplets 108 triplets

cτ 123 μm 312 μm 150 μmHadronic branching

ratio3.8% 9.2% 4.3%

Abundance** 30 9 5* - without cuts, with Ideal PID at dη/dy=6000** - PbPb (0-5% central), NLO pQCD + Binary Scaling + EKS98, in central acceptance

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Cut tuning schemeSignal events

Cuts alghoritms

Background events

Cuts alghoritms

Normalization to 107 events

Normalization to 107 events

Significance calculationSignif=S/(S+B)1/2

Significance normalized

o Signal – 2500 PYTHIA events with full simulation each containing 9100* Ds generated in the barrel acceptance (-0.9<η<0.9) forced to decay into hadronic channels:

o D+sK+K0*K+K -π+

o D+sφπ+K+K-π+

o Background – 15000 HIJING(Number of signal is negligible)

o Significance – calculated with respect to 107 central events (1 year) * Number is tuned in order to have the

same performance of the detector as in BKG event

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Single track selection3 variables:• Pt(K) – Transverse

momentum of Kaon*• Pt(π) – Transverse

momentum of Pion*• d0 – impact parameter of

track

Before cuts After cuts

Cut: Pt>0.5 GeV/cCut: Pt>0.5 GeV/cCut: d0>35 μm

* Ideal PID is assumed

Pt of Ds (GeV/c)

Pt of Ds (GeV/c)

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Combining tracks to pairs• Single tracks are combined to pairs with opposite sign (K+K- &

K+π-) or (K-K+ & K-π+)• Crossing point is found using vertexing algorithm• Two values are calculated:

– Dispersion of tracks around the cross-point:– Distance from cross-point to primary vertex

• First cut is made on dispersion: σ<300 μm• Second cut is made on the distance: d(pair)<300 μm

22 2 2 2

1

( ) ( ) ( )k o k o k ok

x x y y z z

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Triplet selection• Triplet of 3 tracks is

formed• Secondary vertex is

calculated• Dispersion of tracks

around the vertex is found• Cuts are tuned in for Pt bins:

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Resonances separation• Ds decays via resonances• Calculation of Inv Mass for KK and Kπ

pairs• Accept triplet if

|M(KK)-m(φ)|<Δm1 OR |M(Kπ)-m(K0*)|<Δm2

Inv

Mas

s (K

π)

Inv Mass (KK)

Inv

Mas

s (K

π)

Inv Mass (KK)

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Final multicutVariables considered:1. Cos Θpoint2. Cos Φopening3. Distance between primary and secondary vertex4. Sum of impact parameters squared5. Dispersion of secondary vertex (additional

tuning)

Signal Ds via φ

Signal Ds via K0* K0*-like BKG

φ-like BKG

Cos Point

Cos Opening

D+s

π+

K+

K-Φopeni

ng

Pt(Ds)

Θpoin

t

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Results for Ideal PID

φ K0*

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Conclusion and To-Do•Monte-Carlo simulation shows that reconstruction of the

DsKKπ is feasible in the range of Pt down to 3 GeV/c.

•Study of Real PID is in progress. Reduction of significance by factor of ~2 is expected

•Bigger statistics for background events is needed to reduce the error and better tuning of cuts.

•Case of pp collisions is under study. Some preliminary results without multicut are present.

3-5 GeV/c

>5 GeV/c

φ channel 5.1±0.4 19±5K0*

channel 2.0±0.7 9±3