# Presentation: 321598

## Heavy Flavour Physics in ALICE

*Massimo Masera*
*University and INFN, Torino - Italy*
*for the ****ALICE**** Collaboration*

## Contents

- Heavy Flavours at the LHC
- ALICE
- Open Flavours
- Physics motivations
- Hadronic charm
- Examples: D0  K-+, D+  K-++,  Ds+  K+K-+
- B  e+X and B  +X
- Quarkonia
- Quarkonia to dielectrons at midrapidity
- Quarkonia to dimuons at forward rapidities
- J/ and  polarization
- J/ from beauty
- Conclusions

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## Yields at LHC energies

| system, s | pp, 14 TeV | Pb-Pb (0-5%), 5.5 TeV |
| --- | --- | --- |
|  | 11.2 / 0.5 | 4.3 / 0.2 |
|  | 0.16 / 0.007 | 115 / 4.6 |

- NLO pQCD calculations [Mangano, Nason, Ridolfi, NPB373 (1992) 295.]  theoretical uncertainty: factor 2-3
- From p+p to Pb-Pb: binary scaling + shadowing (EKS98)

- Predicted yields  for charm and beauty

-  HF are abundantly produced at the LHC:
- Probe unexplored small-x region with HQs at low pT and/or forward y         down to x~10-4 with charm, already at y=0

- ALICE acceptance for charm and beauty

- muon arm

- Central barrel

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## ALICE        

- ALICE

***Inner Tracking System (ITS)***

***Time Projection Chamber (TPC)***

***Time Of Flight (TOF)***

*Muon Arm - *see
- B. Espagnon’s talk

***Transition Radiation Detector (TRD)***

- ALICE channels:
- electronic (||<0.9)
- muonic (-4<<-2.5)
- hadronic (||<0.9)
- ALICE coverage:
- Extends to low-*p*T region
- central and forward rapidity regions
- Precise vertexing  to identify D (*c*~ 100-300 m) and B (*c*~ 500 m) decays

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## Track impact parameter in Pb-Pb

- Resolution on track impact parameter thanks to the 2 layers of Silicon Pixel Detectors
- Interaction point (primary vertex)
- x and y coordinates with high precision averaging over fill. Good position stability expected for LHC beam, beam=15 m
- z coordinate measured from cluster correlation on the two layers of SPD

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## Open Flavours

## Physics motivations

- p-p
- Measurement of HF production   test of pQCD calculations
- Baseline for AA
- A-A
- Study of the hot and high density medium produced in central A-A collisions
- Initial (also in p-A) and final state effects
- Effects of the medium on fragmentation
- Important for quarkonium physics
- Normalization
- B  J/ + X
- p-A
- To disentangle initial and final state effects induced by the medium

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## From p-p to A-A

- Zero order approximation: binary scaling with Ncoll
- Initial state effects (also in p-A)
- PDFs in nucleus different from PDFs in nucleon
- Anti-shadowing and shadowing
- kT broadening (Cronin effect)
- Parton saturation (Color Glass Condensate)
- Final state effects (only in A-A)
- Energy loss in medium
- In medium hadronization
- Recombination vs. fragmentation

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## Suppression observed at RHIC

-  Radiative Eloss  CR
- CR=4/3 for q
- CR=3 for gluons
- Non photonic electrons suppressed as light hadrons at high pT large quark contribution for light flavours?
- At the LHC gluon contribution should be dominant

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## D0  K-+

- D0  K-+

- Golden channel for open charm
- S/B ≈ 10%
- Significance for 1 month Pb-Pb run: S/√(S+B) ≈ 40

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## D+K-++ and Ds+K+K-+ 

- D+K-++ and Ds+K+K-+

- Measure D0/D+ instead of relying on Pythia
- Larger c≈300 m w.r.t. D0
- Larger combinatorial background
- Smaller <pT> of the decay products
- Performance comparable with       D0K-+
- Ds+ as probe of hadronization?
- Fragmentation/recombination
- Experimentally accessible?
- Ds+ (c ~ 150 μm)  K-K++ with BR ~ 4.4 %
- but mostly resonant decays: + or K0*K+
-     favours backkground rejection

**2<p****T****<3 GeV/c**

- p-p @ 14 TeV

- MK (GeV/c2)

- MKK (GeV/c2)

- D+K-++

- Ds+K+K-+

***Under study***

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## Beauty to e/

- Beauty to e/

- B  e + X
- e± identification from TRD and dE/dx in TPC
- impact parameter from ITS
- Subtraction of charm contribution

- B   + X
- Muon spectrometer
- b contribution dominant at high pT
-  measurement of c contribution at low pT difficult due to high background
- Crosscheck: muon pairs from B decays
- See B. Espagnon’s talk

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## Performance for D and B quenching

- Statistical error corresponding to 107 Pb-Pb  and 109 p-p events

- Colour charge dependence

- Mass dependence

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## Quarkonia

## Quarkonia detection in ALICE

- Quarkonia detected via
- e+e- channel: electrons tracked in the central barrel, identified with the Transition Radiation Detector and the Time Projection Chamber
- +- channel: forward rapidities with the Muon Spectrometer

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## Acceptances

- J/

- 

- J/

- 

- Dielectron trigger: pT cut=3 GeV/c on individual electrons

- Dimuon trigger. pT cut = 1 GeV/c (2) for J/ ()

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## Quarkonia to dielectrons: Pb-Pb

- Dielectron invariant mass spectrum in top 10% central collisions after one “ALICE-year” of Pb-Pb data taking

- Zoom in the J/ region

- Zoom in the  region

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## Quarkonia to dimuons

- Pb-Pb @ 5.5 TeV
- One year of data taking
- J/: excellent (670.000)
-  ’: marginal
-   : ok (7000)
-  ’: low (2000)
-  ’’: very low (1000)

- p-p @ 14 TeV
- One year of data taking
- J/: 2.8106
-  : 2.7104

**Invariant mass resolution:**
** ****J/******** peak: ****~ 70 MeV/c****2**
** ********  ****peak: ****~ 100 MeV/c****2**** **

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## J/ and  polarization

- J/ and  polarization

- p-p collisions:
- Polarization measurements are a test for different quarkonia production mechanisms, since different models predict different polarizations
- A-A collisions:
- A significant J/ polarization in heavy-ion collisions is expected in case of QGP formation (Phys. Rev. C68 061902 (2003))
- See poster by E. Scomparin

- meas-gen

- polariz. pp@ 14 TeV
- vs pT

- J/ polariz. AA@ 5.5 TeV
- vs 

- Without backgorund subtraction (S/B=0.2)

- With backgorund subtraction

- meas-gen

- One year data taking

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## B  J/ + X

- B  J/ + X

- More “exclusive” than B  e/μ + X
- better handle on B momentum distribution
- _Preliminary_ pp study: pseudoproper decay time
- 	(à la CDF)

**CDF (data)**

**ALICE                        ****(prelim. simulation)**

- pT>0

- 9 Feb 2008

## Conclusions

- HF are a powerful tool to study the strongly interacting medium produced in Heavy Ion Collisions at the LHC
- High rates of Heavy Flavours are expected at LHC
- ALICE is well suited for HF physics:
- Excellent vertexing and tracking capabilities
- Exploits both electron and muon channels in different rapidity regions
- PID with several complementary techniques (dE/dx, TOF, TRD)
- Present simulations focused on the effects of realistic calibration and alignment (*see **poster P174 by S. Moretto*)

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## BACKUP

## LHC

-  Other collision systems foreseen:  p-A, lighter ions and energies
-  Running time: 4 weeks/year  integrated luminosity in one year: 0.7 nb-1 for Pb-Pb
-  One Heavy Ion dedicated experiment: ALICE.  Both CMS and ATLAS have also a Heavy Ion programme
-  Initial condition different w.r.t. RHIC
-  greater energy density, temperature, size and lifetime of the fireball
-  Significant contribution of hard processes to the total AA cross section:

| System | sNN
(TeV) | L0 (*)
(cm-2s-1) | Run time (s/year) | geom (b) |
| --- | --- | --- | --- | --- |
| p-p | 14 | 1034 | 107 | 0.07 |
| Pb-Pb | 5.5 | 1027 | 106 | 7.7 |

- (*) L0 (ALICE)= 1031

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## HF: general Physics motivations

- Goal: study the properties of the medium
- Charm and beauty are abundantly  produced at LHC
- Heavy flavours are produced (early) in the initial collisions mainly via gluon fusion  they are hard probes
- Production yield in p-p from pQCD:
- Naive expectation. Binary scaling to A-A
- They travel in the medium  experience the full collision history

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## Heavy Flavours in ALICE

- ALICE channels:
- electronic (||<0.9)
- muonic (-4<<-2.5)
- hadronic (||<0.9)
- ALICE coverage:
- Extends to low-*p*T region
- central and forward rapidity regions
- Precise vertexing  to identify D (*c*~ 100-300 m) and B (*c*~ 500 m) decays

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## Baseline: p+p collisions

- Hard  processes (q-qbar annihilation, gluon fusion) occurring at short space-time scale (~1/2mq)

- Cross section evaluation  factorized pQCD:

- B or D mesons

- b or c
- quarks

- Cross section to produce hadron M

- Parton Distribution Functions – xa and xb are parton momentun fractions in the colliding hadrons

- Cross section at parton level: pQCD. Currently NLO used as a baseline for ALICE.  FONLL  better description at high pT

- Fragmentation function (non perturbative)

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## p+p: charm cross section

- CDF, PRL91 (2003) 241804
- FONLL: Cacciari, Nason

- FONLL:
-  beauty production well described at Tevatron (J/ψ from b decay)
- charm production underpredicted at Tevatron
- RHIC p+p data underpredicted
- Discrepancy between Phenix and Star

- Cacciari, Frixione, Mangano, Nason and Ridolfi, JHEP0407 (2004) 033

- PRL98, 192301 (2007)

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## D/B Mesons

- Total yield for Pb-Pb central interactions (5% inel) at 5.5 TeV

- D mesons:
-  c ~ 100 – 300 m
-  Significant BR for

- B mesons:
-  c ~ 500 m
- large BR in semileptonic decay channels (20%)
- inclusive single electron measurement of  *B**** e ****e** X *
- inclusive muon/dimuon measurement of  *B**** **** ******  **X *

- Main selection tool for D/B mesons: displaced secondary vertices

- Total yield for Pb-Pb central interactions (5% inel) at 5.5 TeV

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## D+K-++

- D+K-++

- Measure D0/D+ instead of relying on Pythia
- Larger c≈300 m w.r.t. D0
- Larger combinatorial background
- Smaller <pT> of the decay products
- Performance comparable with       D0K-+

**2<p****T****<3 GeV/c**

**d**** ****CUT****(********m)**

**cos********point****CUT**

***Significance S/************(S+B) for 2<p******T******<3 GeV/c***
***(normalized to 10******7****** PbPb events)***

**p****T**** D****+**

******point**

- p-p @ 14 TeV

- Dist prim. Sec. (m)

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## Ds+K+K-+

- MK (GeV/c2)

- MKK (GeV/c2)

- Ds+ as probe of hadronization?
- from string fragmentation: cs / cd ~ 1/3
- after decays: Ds+ (cs) / D+ (cd) ~ 0.6
- from recombination: cs / cd ~ N(s) / N(d)
- How large at LHC?
- experimentally accessible?
- Ds+ (c ~ 150 μm)  K-K++ with BR ~ 4.4 %
- but mostly resonant decays: + or K0*K+
-     favours bkgnd rejection

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## B mesons via B e e X  (I)

*Distributions normalized to the same integral in order to compare their shapes*

- d0 distributions for “electrons”  from different sources:

***	******Inclusive measurement of electrons coming from semi-electronic decay of beauty hadrons***

**need good electron identification**: combined PID in TPC (dE/dx) + TRD

**key selection point**: again good measurement of the track impact parameter

- B mesons via *B**** e ****e** X*  (I)

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## 1) Electron PID: reject most of the hadrons

- 3) Subtract (small) residual background

- 2) Impact parameter cut: reduce charm and bkg electrons

- |d0| distributions for “electrons”  from different sources:

- B mesons via *B**** e ****e** X*  (II)

***	******Selection of the beauty electron candidates in 3 steps***

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## B mesons via B e e X  (III)

***expected statistics and systematic uncertainties***

***p******T******-differential electron cross section reconstructed from ~ 1 to 20 GeV/c***

- B mesons via *B**** e ****e** X*  (III)

***Results for beauty in Pb-Pb***

- 107 central (0-5%) Pb-Pb events

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## HF to muons 

- HF to muons

- Single muons from beauty are dominant at high pT  fit on distribution tail
- Muons from charms are dominant at low pT  difficult measurement due to large background
- Muon pairs from B:

- BDsame

- BBdiff

- BDsame

- BBdiff

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## HF to single muon in p-p

- Signal:  from b/c decays
- Background:
-  from /K decays
- Can be extracted from data
-  from the absorber
- Subtraction: tracks do not point to the vertex, no FMD hits
- Good preliminary results: high statistics needed

- Slices in pT. Correct for diamond shape

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## Quarkonia to dimuons

- Centrality dependence of J/ and  normalized to unlike sign dimuon rates from beauty

- Shadowing + 2 different suppression scenarii:
- High dissociation temeperature
- Low dissociation temperature

- Error bars  1 month data taking
- _Assumptions_
- Perfect subtraction of combinatorial background
- Zero nuclear absorption cross section

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## Quarkonia to dielectrons: Pb-Pb

- Dielectron invariant mass spectrum in central collisions after one “ALICE-year” of Pb-Pb data taking

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## GOAL: Evaluate the statistical error bars for measurements of v2 for D± mesons reconstructed from their K decay in Pb-Pb collisions
v2 vs. centrality (b=collision impact parameter)
v2 vs. pT in different centrality bins
HOW: fast simulation to generate:
ND+ (pT,b) with an angular distribution 
                  dND/d = v2D,in cos [2(-RP)]
For each D+: an event made of Ntracks is superimposed 
                  dN/d = v2ev,in cos [2(-RP)]
Inputs of the simulation: ND+ (pT,b) , v2D,in, Ntracks ,v2ev,in
Outputs: v2D measured.

- Perspectives for D± elliptic flow

**GOAL**: Evaluate the statistical error bars for measurements of v2 for D± mesons reconstructed from their K decay in Pb-Pb collisions
- v2 vs. centrality (b=collision impact parameter)
- v2 vs. pT in different centrality bins
**HOW**: fast simulation to generate:
**N****D+**** (********p****T****,********b)** with an angular distribution
-                   dND/d = **v****2****D,in** cos [2(-RP)]
- For each D+: an event made of **N****tracks** is superimposed
-                   dN/d = **v****2****ev,in** cos [2(-RP)]
- Inputs of the simulation: **N****D+**** (********p****T****,********b)** , **v****2****D,in****, N****tracks**** ,v****2****ev,in**
- Outputs: **v****2****D**** **measured.

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

##  Large stat. errors on v2  of          D± → K in 2·107 MB events

- v2 vs. pT

-  Large stat. errors on v2  of          D± → K in 2·107 MB events

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## B elliptic flow 

- B elliptic flow

- v2 evaluated from Be+X
-  Pb-Pb centrality: 20-60%

- 1 year at nominal luminosity

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## Kinematical distributions: prompt J/ versus secondary J/

- Kinematical distributions: prompt J/ versus secondary J/

- “pseudo proper
- decay time”

- Primary J/

- Secondary J/

- x

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008

## In order to extract the fraction fB of J/ from b-hadron decays, one should fit simultaneously 
the invariant mass spectrum 
one distribution which can discriminate prompt from detached J/(e.g. x or d0e+·d0e-)
the tails of the M(e+e-) distribution measures the percentage of background 

- the invariant mass spectrum
- one distribution which can discriminate prompt from detached J/(e.g. x or d0e+·d0e-)
- the tails of the M(e+e-) distribution measures the percentage of background

- How to measure the fraction of secondary J/

- M. Masera   Heavy Flavour in ALICE

- 9 Feb 2008