ppr chapter 6.5 & d 0 detection

ALICE Physics Forum - March 11, 2003 Andrea Dainese 1

PPR chapter 6.5&

D0 detection

Andrea Dainese

University of Padova


6.5 Charm and Beauty: updateFirst part on c and b production at LHC is finalized

It will be submitted as a Note in these days

Contents:cross sections and yields in Pb-Pb and pp at NLO (Nicola)

c and b kinematical distributions and PYTHIA tuning (Nicola)

D and B meson parameterized pT distributions for Pb-Pb NEW

cross sections and yields in p-Pb at NLO NEW

Bjorken-x acceptance for ALICE in pp, Pb-Pb, p-Pb NEW

Present ALICE baseline for c and b production

To be used as an input for simulation studies


Cross sections in p-Pb

Centre of mass energy:

Rapidity shift for p-Pb (Pb-p):

Cross sections at NLO (MNR) calculated for pp w/o and w/ shadowing corrections by R. Vogt

PDF set: MRST (for pp and Pb-Pb the calculation was done with MRST and CTEQ5M, and results were averaged; MRST result were ~10% lower than the average)

shadowing: EKS98 (same as for Pb-Pb)

Extrapolation to p-Pb:no centrality selection assumed (min. bias collisions)

TeV 8.8TeV 14 AZsNN

)47.0( 47.0)ln(21 )( AZy

AshadQQpp

QQpA )( inelastic

pAQQpA

QQpAN


Charm cross sections

SystemPb-Pb (5%)

5.5 TeV

p-Pb (m.b.)

8.8 TeV

pp

14 TeV

6.64 8.57 11.18

Shadowing effect 0.65 0.81 1.00

45000 1443 11.18

115 0.76 0.16

)(mbQQNN

)(mbQQtot

eventN QQ /

5 150


Beauty cross sections

SystemPb-Pb (5%)

5.5 TeV

p-Pb (m.b.)

8.8 TeV

pp

14 TeV

0.18 0.28 0.51

Shadowing effect 0.84 0.89 1.00

1790 52 0.51

4.56 0.028 0.0072

)(mbQQNN

)(mbQQtot

eventN QQ /

4 160


Accessible x range (1)

Bjorken x = p(parton) / p(proton)

Heavy Quark prod. at LO:

The x range probed depends on:

At central rapidity x1 ~ x2

Charm has lower mass lower x values

Measurements at forward rapidity lower range in x2

....../21 BDJQQgg

QQQQNN yMs , ,

)exp(1

11 QQ

NN

QQ ys

M

Z

Ax )exp(

2

22 QQ

NN

QQ ys

M

Z

Ax

charm beauty

Pb-Pb 5.5 TeV 4.3 10-4 1.6 10-3


Accessible x range (2)

MUON ARM

MUON ARM

BARREL

BARREL

p-Pb and Pb-p allow to cover a broader x range and

reach down to x ~ 10-6 in MUON ARM

x ~ 10-4 in BARREL handle to Gluon Shadowing

same as in pp at 14 TeV!


D0 detection in pp collisions

Generation of signal and background

Tracking and Primary vertex reconstruction in pp

Particle ID in TOF

Secondary vertex selectionEffect of primary vertex resolution

Tuning of selection cuts

Results

Estimate of results for p-Pb collisions


Generation

“Signal event” = 1 Pythia pp event with a D0 K with K and in TPC acceptance

Corresponds to 1044 pp Minimum Bias events

Generated 2 106 “signal events” ( = 2.06 109 pp MB evts)

2.9 106 pp non-diffr. events generated, reconstructed, analyzed using distributed resources and AliEn (only final “ntuple” with D0 candidates copied to Padova)

Correspond to 4.1 106 pp MB events (fraction of non-diffr. events / MB events taken from Pythia: 70 %)

Signal

Background


Impact parameter measurement

Request of two tracks with large impact parameters is one the most important selection criteria

vertextrackrd )(0

in the direction to the track

SGNBKG


Interaction vertex at the LHCPosition of the beam in (x,y) given by the machine with very high precision (stable for a long time)“Nominal” size of the beam:

= 15 m in Pb-Pb = 15 m in pp (L ~ 1031 cm-2 s-1) 150 m in pp (if L is reduced at ALICE IP to ~ 1029 cm-2 s-1)

The vertex position has to be reconstructed in 3D using tracks

Feasibility study done with two scenarios:vertex position known with a resolution of 15 m vertex position reconstructed with tracks


3D reconstruction with tracksTrack reconstruction in TPC+ITS

TPC tracking parameterization

ITS Kalman filter (6/6 points)

ITS tracking uses the position of the primary vertex: (x, y) from beam position (resolution ~ 150 m)z from pixels information (resolution ~ 150 m)

Vertex reconstruction in 2 steps:VERTEX FINDING: using DCA for track pairs

VERTEX FITTING: (inspired by CMS and ATLAS methods)give optimal estimate of the position of the vertexgive vertex covariance matrix

give a

Internal Note by A.D. and M.Masera almost ready


Tuning of the algorithmInspiration: ATLAS TRT TDR

Criterion used to reject mismeasured and secondary tracks from the fit: cut on the maximum contribution to the 2

i2 <

max

if max is too low too many tracks are rejected and we loose

resolution

if max is too high bad or secondary tracks enter the fit and we

loose resolution

This cut is tuned, as a function of event multiplicity, in order to optimize the resolution


Resolutions VS multiplicity

pp with charm

pp min. bias


Impact on impact parameter resolution

as in Pb-Pbpp with charmpp min. bias


Statistics before selections

Sample S/ev B/ev S/B (value in Pb-Pb)

A (K id in TOF) 1.1 10-4 8.3 10-3 1.3 10-2 (2.2 10-

5)

Total 2.4 10-4 1.1 10-1 2.3 10-3 (4.5 10-

6)


Displaced vertex selection


Charm w/o primary vertex reconstruction?

What if we did not reconstruct the primary vertex?

1 < pT < 2 GeV/c

1 < pT < 2 GeV/c

5 < pT < 7 GeV/c

5 < pT < 7 GeV/c


Charm with new vertexer

First attempt: all tracks in the event are used to reconstruct the vertex position, only the cut on the maximum 2 is applied 1 < pT < 2 GeV/c

1 < pT < 2 GeV/c

5 < pT < 7 GeV/c

5 < pT < 7 GeV/c


Charm with new vertexer

The tracks from the D0 tend to “pull the vertex estimate closer to them”

As a consequence both impact parameters

are underestimated

For each D0 candidate the primary vertex position

is estimated using ALL tracks in the event

BUT the two decay products of the D0

V1

V2

NEWSTRATEGY

1 < pT < 2 GeV/c 5 < pT < 7 GeV/c

1 < pT < 2 GeV/c5 < pT < 7 GeV/c


Tuning of selection cuts (1)

As in Pb-Pb, cuts are tuned as a function of pT in order to maximize the significance of the signal


Tuning of selection cuts (2)

The cut on the product of impact parameters has to be carefully studied as a function of pT

Low pT D0

poor d0 resolution

High pT D0

good d0 resolution


Results – pT integrated

S/ev B/ev S/B S/S+B

Vertex

“known”2.1 10-5 4.1 10-5 50 % 84

(for 109 evts)

Vertex

recontr.1.9 10-5 1.7 10-4 11 % 44

(for 109 evts)


Analysis of the worsening: pointing

Both SGN and BKG before this cutlower by ~ 10%(events rejected because# trks < 5)

Poorer resolution oncos p

Selected SGN after this cut lower by ~ 20 %


Analysis of the worsening: d0 d0

Both SGN and BKG have broaderdistributions

Cut at < -25000 m2

Selected SGN is the ~ same

Selected BKG largerby factor ~ 4


pT distributionFor scenario with primary vertex reconstruction

pT distribution of rec. D0 and SGNC vs pT

~ 20,000 with SGNC > 10 up to 10 GeV/c (1 GeV/c bins)~ 2,000 D0 in 0.5 < pT < 1 GeV/c with SGNC = 14


Acceptance and Efficiency

~ 15 % ~ 35 %

~ 10 %


Extrapolation of results for p-Pb

Starting point:

Assume same detector performance (tracking, PID) as in ppPrimary vertex known as in Pb-Pb ( ~ 15 m)Same values for the cuts as in pp (pessimistic)

SGNSELECTED/SGNINITIAL and BKGSELECTED/BKGINITIAL

same as in pp with primary vertex “known”

pp p-Pb

(min. bias)

Pb-Pb

(central)

dNch/dy(PYTHIA-HIJING)

6 18 6000

N(D0K)

in acceptance7.2 10-4 3.6 10-3 5 10-1

5

3


Extrapolation for p-PbSGNSELECTED larger by factor 5

BKGSELECTED prop. to (multiplicity)2 larger by factor ~10

Low pT:

High pT:

Globally:

Complete simulation will be done by R.Grosso on time for the PPR

ppPbppp

pp

NNBSBSBSS

BSBS

/10/5)/(//

)10/5()/(/

ppPbppp NNSSBSS /5)(/

421.010/585/

%25/

BSS

BS


ConclusionsFirst part of chapter 6.5:

“Charm and beauty production at LHC”

ready and soon released

The rest of the chapter is growing:

Hadronic charm in pp down to pT ~ 0

(“fat” beam won’t manage to kill charm!)

First look at D0 in pA: very promising, complete study is starting

Material from the electron and muon branches will come soon

Collaboration with HLT group started during the coffee break

It will be a very tasty heavy flavour chapter!

ppr chapter 6.5 & d 0 detection

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