Λc

baryon reconstruction in Au+Au collisionsat √s

NN= 200 GeV

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Nuclear Physics Institute,

Czech Academy of Sciences

Faculty of Nuclear Sciences

and Physical Engineering,

Czech Technical University in Prague

Outline

December 7–11, 2015 Miroslav Simko, Zimanyi School of Heavy Ion Physics, Budapest 2/14

• Physics motivation of Λ� analysis

• STAR with Heavy Flavor Tracker

• Reconstruction of Λ�

• Simulations and cuts optimization

• Run 2016 expectation at STAR

Motivation

• Never observed in heavy-ion collisions

• Quarks: udc

• Baryon to meson ratios (such as p/�, Λ/K�) are significantly enhanced in heavy-ion collisions compared to p+p

• Similar enhancement expected in Λ�/D�

• Λ� would bring more insight into coalescence of charm quarks

• Λ�/D� enhancement is one of the signatures of quark gluon plasma

December 7–11, 2015 Miroslav Simko, Zimanyi School of Heavy Ion Physics, Budapest 3/13

[J.Phys.Conf.Ser. 50 (2006) 192]

[Phys. Rev. Lett. 108 (2012) 72302]

� baryon

• Challenging to measure, ∼ 60 �m

• Three body decay branching ratios:

• Λ� → pK�� (5.0�1.3)%

• Λ� →pK* (1.6�0.5)%

• Λ� → Λ(1520)� (1.8�0.6)%

• Λ� → K�Δ (0.86�0.3)%

• Nonresonant (2.6�0.8)%

December 7–11, 2015 Miroslav Simko, Zimanyi School of Heavy Ion Physics, Budapest 4/14

[Particle Data Group, Chin. Phys. C38 (2014) 090001]

December 7–11, 2015 Miroslav Simko, Zimanyi School of Heavy Ion Physics, Budapest 5/14

2� acceptance in azimuth

HFT:

← SSD

← IST

←PXL

Silicon vertex

detector

TPC: Tracking

dE/dx (PID)

← �1 � � � 1

→

TOF:

1/�

(PID)

STAR detector

HFT performance

December 7–11, 2015 Miroslav Simko, Zimanyi School of Heavy Ion Physics, Budapest 6/14

p [GeV/c]0.2 0.4 0.6 0.8 1 1.2 1.4

DC

A_X

Y [

cm

]

­310

­210

­110 Protons

Kaons

Pions

• New pixel detector based on MAPS technology

• Pitch: 20.7�20.7 μm�, thickness: 0.4% ��

• Pointing resolution: ∼30 μm at high !

• 1.2�109 events at 200 GeV recorded in 2014

• See Jakub Kvapil’s talk (Wednesday 10:00am)

Run14 production Au+Au @ 200 GeV

STAR Preliminary

New � measurement in run 2014

December 7–11, 2015 Miroslav Simko, Zimanyi School of Heavy Ion Physics, Budapest 7/14

Quark Matter 2015

STAR Preliminary

• Combinatorial background greatly reduced• Thanks to the HFT

• Significance rose by a factor of 4 to 51

• Much more precise measurement

• New p+p data taken in 2015 will improve uncertainties

� reconstruction

December 7–11, 2015 Miroslav Simko, Zimanyi School of Heavy Ion Physics, Budapest 8/14

• Three particle decay: BR = 5%, ∼ 60 μm

• Particle identification using TOF 1/�information and dE/dx in the TPC

• Significant background reduction with the HFT

• Cuts have to be optimized using simulations

Data driven Monte Carlo simulation for cuts optimization

December 7–11, 2015 Miroslav Simko, Zimanyi School of Heavy Ion Physics, Budapest 9/14

[Phys. Rev. Lett. 113 (2014) 142301]

• Λ� decayed in PYTHIA

• Momenta and track positions smeared according to data

• Rough estimate of Λ� behavior

• Λ� with flat rapidity

• ! distribution from published D� minimum bias Au+Auspectrum

• Λ�/D� ratio obtained from e+p data (ZEUS)

[Eur. Phys. J. C44 (2005) 351]

• Scaling with "�#$$

decay length [cm]0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04

n [­]

0

2

4

6

8

10

12

14

16

18

20

22

cΛSimulated

Background (scaled)

Decay length

Comparison: simulation and background from data

December 7–11, 2015 Miroslav Simko, Zimanyi School of Heavy Ion Physics, Budapest 10/14

• Background from run 2014 Au+Au data

• Background: Wrong charge sign combinations

• Same cuts applied on simulation and background

STAR Preliminary

Run 2014 Au+Au @ 200 GeV

)θcos(0.98 0.982 0.984 0.986 0.988 0.99 0.992 0.994 0.996 0.998 1

n [

­]

20

25

30

35

40

45cΛSimulated

Background (scaled)

)θcos(

STAR Preliminary

Run 2014 Au+Au @ 200 GeV

Daughters pair distance [cm]0 0.01 0.02 0.03 0.04 0.05 0.06

n [­]

0

2

4

6

8

10

12

14

16

18

20

cΛSimulated

Background (scaled)

Maximum distance between vertices of pairs

December 7–11, 2015 Miroslav Simko, Zimanyi School of Heavy Ion Physics, Budapest 11/14

[cm]πDCA K 0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02

n [

­]

5

10

15

20

25

30 cΛSimulated

Background (scaled)

πDCA K

[GeV/c]T

p0 1 2 3 4 5 6

n [

­]

­410

­310

­210

­110

1

10

210

cΛSimulated

Background (scaled)

of piT

p

[GeV/c]T

p0 1 2 3 4 5 6

n [

­]

­210

­110

1

10

210

cΛSimulated

Background (scaled)

of KT

p

Comparison: simulation and background from data (2)

STAR Preliminary

Run 2014 Au+Au @ 200 GeV

STAR Preliminary

Run 2014 Au+Au @ 200 GeV

STAR Preliminary

Run 2014 Au+Au @ 200 GeV

STAR Preliminary

Run 2014 Au+Au @ 200 GeV

• Decay length, cos(%), and !cuts most powerful

• The variables are strongly correlated

• Multivariate analysis

Multivariate analysis for cuts optimization• Cuts variables highly correlated

• Multivariate analysis• Can create complicated cut structures in N-dimensional spaces

• Toolkit for MultiVariate Data Analysis (TMVA)[PoS ACAT 040 (2007), arXiv:physics/0703039]

• Rectangular cuts, Neural networks, Boosted decision trees,…• Ongoing work

• Preselection for TMVA:• N-dim array of cuts for N variables with small increment

• Maximizing significance: & '()*+

()*+ (,+

• Select Signal and Background• Few iterations

December 7–11, 2015 Miroslav Simko, Zimanyi School of Heavy Ion Physics, Budapest 12/14

p [GeV/c]0.2 0.4 0.6 0.8 1 1.2 1.4

DC

A_X

Y [

cm

]

­310

­210

­110 Protons

Kaons

Pions

p [GeV/c]0.2 0.4 0.6 0.8 1 1.2 1.4

DC

A_X

Y [

cm

]

­310

­210

­110 Protons

Kaons

Pions

Outlook: Run 2016 Au+Au at 200 GeV

December 7–11, 2015 Miroslav Simko, Zimanyi School of Heavy Ion Physics, Budapest 13/14

122 -m at 450 MeV protons 110 -m at 450 MeV protons

Run 2014 production Aluminum cables

• 1.2�109 events recorded in run 2014 – 2�109 are expected in Run 2016

• Pixel improvements:• Changed cable material copper→aluminum

• Replacement of non-working sensors – better efficiency

• Pointing resolution improved

STAR Preliminary STAR Preliminary

Conclusion

• STAR may be able to measure Λ� baryons for the first time in heavy-ion collisions thanks to excellent pointing resolution of the HFT

• Important probe for coalescence of c-quarks

• Cuts optimization using data driven simulation

• Multivariate analysis – a powerful tool for cuts

• 2016: More statistics with better HFT

December 7–11, 2015 Miroslav Simko, Zimanyi School of Heavy Ion Physics, Budapest 14/14

Thank you for your attention

December 7–11, 2015 Miroslav Simko, Zimanyi School of Heavy Ion Physics, Budapest 15/14

Backup

December 7–11, 2015 Miroslav Simko, Zimanyi School of Heavy Ion Physics, Budapest 16/14

Daughters .

decay length [cm]0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04

n [

-]

0

2

4

6

8

10

12

14

16

18

20

22

cΛSimulated

Background

Decay length

[GeV/c]T

p0 1 2 3 4 5 6

n [

t]

0

10

20

30

40

50

60

70cΛSimulated

Background

of KT

p

[GeV/c]T

p0 1 2 3 4 5 6

n [

-]

0

10

20

30

40

50 cΛSimulated

Background

of pT

p

[GeV/c]T

p0 1 2 3 4 5 6

n [

-]

0

10

20

30

40

50

60

70

80

90 cΛSimulated

Background

of piT

p

December 7–11, 2015 Miroslav Simko, Zimanyi School of Heavy Ion Physics, Budapest 17/14

Silicon Strip Detector (SSD)

December 7–11, 2015 Miroslav Simko, Zimanyi School of Heavy Ion Physics, Budapest 18/14

SSD readout refurbishment

December 7–11, 2015 Miroslav Simko, Zimanyi School of Heavy Ion Physics, Budapest 19/14

Fiber-to-LVDS

• Upgrade from 200 Hz to 1 kHz

• New• 40 ladder cards on detector

• 5 RDO cards

• 5 Fiber-to-LVDS boards

RDO board – adapted from PXL Ladder cards

Intermediate Silicon Tracker (IST)

December 7–11, 2015 Miroslav Simko, Zimanyi School of Heavy Ion Physics, Budapest20/14

Pixel detector (PXL)

DCA pointing resolution (12⊕ 24 GeV/ .)

Radii Layer 1 at 2.8 cm

Layer 2 at 8 cm

Pixel size 20.7μm � 20.7μm

Hit resolution 3.7 μm

Position stability 6 μm RMS (20 μm envelope)

Radiation length Layer 1:�/�� � 0.4%

Layer 2: �/�� � 0.5%

Number of pixels ∼ 356 M

Integration time (affects pileup) 185.6 ms

Radiation environment 20 – 90 kRad/year

2 � 1066to106� 1 MeV n eq/cm�

Installation time ∼ 1 day

December 7–11, 2015 Miroslav Simko, Zimanyi School of Heavy Ion Physics, Budapest 21/14