# Presentation: 558937

## ALICEperspectives for the study ofc and b energy loss at LHC

*Andrea Dainese*
*INFN – LNL*
*ALICE Collaboration*

*Heavy quark energy loss **à** la BDMPS*
*Results for RHIC vs experimental data (*e* R**AA**)*
*Testing E loss with heavy-to-light ratios at LHC*
*Expected ALICE performance*

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## Radiative Energy Loss à la BDMPS

- Baier, Dokshitzer, Mueller, Peigne‘, Schiff, NPB 483 (1997) 291. Salgado, Wiedemann, PRD 68(2003) 014008.
- Dokshitzer and Kharzeev, PLB 519 (2001) 199. Armesto, Salgado, Wiedemann, PRD 69 (2004) 114003.

- Gluon energy distribution
- characterized by:

- transport coefficient

- sets scale of radiated energy

- colour coupling factor: 4/3 for q, 3 for g

***Radiative Energy Loss ******à****** la BDMPS***

**“****Dead cone” effect for heavy quarks:**** **
- in vacuum, gluon radiation suppressed at ** < *m*Q/*E*Q

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## RAA of c and b electrons at RHIC

- Model: pQCD + E loss probability + Glauber collision geometry
-                                “tuned” to match 0 *R*AA

-  C.Loizides

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## Electrons at RHIC: charm + beauty (+ DY)  -- pQCD baseline, and its uncertainties --

- FONLL calculation: Cacciari, Nason, Vogt, PRL95 (2005) 122001
- Comparison: Armesto, Cacciari, Dainese, Salgado, Wiedemann, hep-ph/0511257, PLB to appear

- FONLL:
- electron spectrum may be
- ~50% c + ~50% b
- for 3 < *p*T < 8 GeV
- (Drell-Yan: < 10% up to 10 GeV)

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## RAA of c and b electrons at RHIC

***R******AA****** of c and b electrons at RHIC***

- Armesto, Cacciari, Dainese, Salgado, Wiedemann, hep-ph/0511257, PLB to appear

- c

- b

- c+b

- Model: pQCD + E loss probability + Glauber collision geometry
-                                “tuned” to match 0 *R*AA

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## Next year we will have the LHC...(pp; Pb-Pb in 2008)

**~100 cc **and **~5 bb **per central Pb-Pb collision at 5.5 TeV
- Experiments will measure with good precision *R*AA for D and B (decay leptons)

***What can we learn from a comparative quenching study of massive and massless probes at the LHC?***

-  next slides + M.Lunardon

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## Heavy Flavour RAA at LHC

- Baseline: PYTHIA, with EKS98 shadowing, tuned to reproduce c and b *p*T distributions from NLO pQCD (MNR)
- (*m/E*)-dep. *E* loss with

- Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027.

- * EKRT Saturation model:
- Eskola, Kajantie, Ruuskanen, Tuominen,
- NPB 570 (2000) 379.

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## Colour-charge and mass dep. of E loss with Heavy-to-Light ratios at LHC

***Colour-charge and mass dep. of E loss ******with ******Heavy-to-Light ratios****** at LHC***

- Heavy-to-light ratios:
- Compare   *g **** h* ,  *c **** D  and  b **** B*

- Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## Beauty-to-Charm ratio: RB/D

***Beauty-to-Charm ratio: R******B/D***

- Compare c and b    same colour charge
- Mass effect  Enhancement of factor ~2, _independent_ of      (for                              )

- Adapted from Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## The ALICE Detector

***The ALICE Detector***

**|********| < 0.9**
**TPC + silicon tracker**
**+ PID detectors**

**-4 < ******** < -2.5**
**muons**

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## HVQ E loss: How in ALICE

***HVQ E loss: How in ALICE***

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## D0 K-+ reconstruction

- Ideal tool to study *R*AA
- Large combinatorial background **(simulated with d*****N*****ch****/d*****y*****=6000)**
- Main selection: displaced-vertex selection
-  pair of opposite-charge tracks with **large impact parameters**
** ****good pointing** of reconstructed D0 momentum to  the primary vertex

**Invariant mass analysis to “count” D****0**

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## D0 K-+: Results

- inner bars: stat. errors
- outer bars: stat.  *p*T-dep. syst.
- not shown: 9% (Pb-Pb), 5% (pp, p-Pb)
-                     normalization errors

**Down to *****p*****T**** ~ 0 in pp and p-Pb (1 GeV in Pb-Pb)**

- 1 year at nominal luminosity
- (107 central Pb-Pb events,
- 109 pp events)
- + 1 year with 1 month of p-Pb running
- (108 p-Pb events)

- ALICE PPR Volume 2
- CERN/LHCC 2005-030

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

##  Beauty via displaced electrons 

- ALICE has excellent electron identification capabilities
- Displaced electrons from B decays can be tagged by an impact parameter cut

-  M.Lunardon

- ALICE PPR Volume 2
- CERN/LHCC 2005-030

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## Charm and Beauty E Loss : RAA 

- D0  K

- B  e + *X*

- 1 year at nominal luminosity
- (107 central Pb-Pb events, 109 pp events)

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## Heavy-to-light ratios in ALICE

- 1 year at nominal luminosity
- (107 central Pb-Pb events, 109 pp events)

- ALICE PPR Volume 2
- CERN/LHCC 2005-030

*R*D/h study looks promising
*R*B/D under study, but challenging...

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## Conclusions

- Observation of (large) heavy-quarks quenching at RHIC has boosted the interest for these studies at LHC
- ALICE at LHC in excellent position:
- large production cross sections
- dedicated detectors (ITS)
- Promising performance for *R*AA of D mesons and electrons from B mesons
- Other observables are under study:
- muons from B at forward rapidity
- use of W’s as a reference
- heavy-quark jet studies (azimuthal correlations, b-tagged jets)

-  Z.Conesa

-  M.Lunardon

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## EXTRA SLIDES

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## LHC running conditions

* ****Ldt  = 5.10**26** cm**-2** s**-1** x 10**6 **s *
*5.10**32** cm**-2** PbPb run, 5.5 TeV*
*N**PbPb collisions **= 2 .10**9** collisions  *

***Ldt dt  = 3.10**30** cm**-2** s**-1** x 10**7 **s *
*5.10**37** cm**-2**  for pp run, 14 TeV*
*N**pp collisions **= 2 .10**12** collisions  *

*Muon triggers:  *
* **~ 100% efficiency, ~ 1kHz  *

*Electron triggers:  *
*       **Bandwidth limitation*
* **N**PbPb central  **= 2 .10**8** collisions  *

**

**

*Muon triggers:  *
* **~ 100% efficiency, < 1kHz  *

*Pb-PB nominal run*

*pp nominal run*

*Electron triggers:  *
*   **~ 50% efficiency  of TRD L1*
*  **20 physics events per event  *

*Hadron triggers:  *
* **N**PbPb central  **= 2 .10**7** collisions  *

*Hadron triggers:  *
* **N**pp minb  **= 2 .10**9** collisions  *

**

**

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## Application: Parton Quenching Model

- Dainese, Loizides, Paic, EPJC 38 (2005) 461.

- QW + Glauber-based medium geometry and density profile + PYTHIA for parton generation and fragmentation
- The procedure in short:
- generate parton (q or g) with PYTHIA (or back-to-back pair)
- calculate its *L* and average         along the path
- use quenching weights to get energy loss
- quench parton and then hadronize it (independent fragm.)

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## Model vs RHIC “light” data

***Model vs RHIC “light” data***

- Model: pQCD + E loss probability (quenching weights) + Glauber collision geometry
-      “tuned” to match 0 RAA in central Au-Au at 200 GeV

- Dainese, Loizides, Paic, EPJC 38 (2005) 461.

- Similar results by
- Eskola, Honkanen,
- Salgado, Wiedemann

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## Lower E loss for heavy quarks ?

- In vacuum, gluon radiation suppressed at ** < *m*Q/*E*Q
-                 ******   “****dead cone” effect**
*Dead cone implies lower energy loss* (Dokshitzer-Kharzeev, 2001):
- energy distribution ***d****/d*** of radiated gluons suppressed by angle-dependent factor
- suppress high-** tail

- Dokshitzer, Khoze, Troyan, JPG 17 (1991) 1602.
- Dokshitzer and Kharzeev, PLB 519 (2001) 199.

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## Lower E loss for heavy quarks ?

- Detailed massive calculation shows that:

- Armesto, Salgado, Wiedemann, PRD 69 (2004) 114003.

*Medium-induced gluon radiation fills the dead cone*

*Still, k*T*-integrated radiation is suppressed, but only for quite large m/E (i.e. large m, low p*T*)**

- R = 105

**Warning: large uncertainties *

*k*T

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## Model for heavy quarks

- Initially only charm
- Baseline at RHIC: *PYTHIA*, with *EKS98 shadowing*, tuned to match *p*T-shape of D cross section measured in d-Au by STAR (QM04)
- Heavy-quark *E* loss using (*m/E*)-dependent QW
-      extracted from 0,*h* *R*AA (central)
*Thermalize charms that lose all energy*
-       d*N/*d*m*T  *m*T exp(-*m*T/*T*),  T = 300 MeV

- Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027.
- EKS98: Eskola, Kolhinen, Salgado, EPJC 9 (1999) 61.

- baseline d*N*/d*p*T

- baseline *R*AA

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## Charm RAA at RHIC (Au-Au 200 GeV)

***effect of the mass***

*thermalized component*

**Small effect of mass for charm** (~50% for D, ~30% for e) at low *p*T [large uncertainties!]
**Basically no effect in “safe” *****p*****T****-region**

- Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027.

- Model: pQCD + E loss probability + Glauber collision geometry
-                                “tuned” to match 0 *R*AA

-  C.Loizides

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## Electrons at RHIC: charm + beauty + DY  (pQCD baseline, and its uncertainties)

- FONLL calculation: Cacciari, Nason, Vogt, PRL95 (2005) 122001
- Drell-Yan at NLO adapted from: Gavin et al., hep-ph/9502372
- Comparison: Armesto, Cacciari, Dainese, Salgado, Wiedemann, hep-ph/0511257, PLB to appear

- FONLL:
- electron spectrum may be
- ~50% c + ~50% b
- for 3 < *p*T < 8 GeV
- We investigated the DY component:
- < 10% up to 10 GeV

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## Azimuthal asymmetry (v2)

- The azimuthal asymmetry --v2 or RAA()-- of D and B mesons in *non-central* collisions tests:
- at low/moderate *p*T: recombination scenario, v2 of c/b quarks, hence degree of thermalization of medium
- at higher *p*T: path-length dependence of E loss (almond-shaped medium => v2 ~ 0.05--0.10)

**PHENIX ********0**** v****2**

- Cole @ Quark Matter 05

- v2 from E loss: Dainese, Loizides, Paic, EPJC 38 (2005) 461

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## Vertexing: track d0 resolution

***Vertexing: track d******0****** resolution***

-  Resolution mainly provided by the 2 layers of silicon pixels

-  9.8 M

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## ALICE baseline for HVQ production

| system :
sNN : | Pb-Pb (0-5% centr.)
5.5 TeV | p-Pb (min. bias) 
8.8 TeV | pp
14 TeV |
| --- | --- | --- | --- |
|  | 4.3 / 0.2 | 7.2 / 0.3 | 11.2 / 0.5 |
|  | 115 / 4.6 | 0.8 / 0.03 | 0.16 / 0.007 |
|  | 0.65 / 0.80 | 0.84 / 0.90 | --  |

-                  Theoretical uncertainty of a factor 2—3

- Cross section from MNR code (NLO): Mangano, Nason, Ridolfi, NPB373 (1992) 295.

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## D0 K-+: Selection of D0 candidates

***D******0************ K******-************+******: ****Selection of D**0** candidates*

- increase S/B
- by factor ~103!

- central Pb-Pb events

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## Cross section of electrons from B

- inner bars: stat. errors
- outer bars: stat.  pt-dep. syst. errors
- not shown: 9% normalization error

- 1 year at nominal luminosity
- (107 central Pb-Pb events, 109 pp events)

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## Comparison to pQCD predictions

***Comparison to pQCD predictions***

**charm (D****0 ******** K********)**

**beauty (B ******** e**+***X*****)**

- 1 year at nominal luminosity
- (109 pp events)

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## Role of pp reference for RAA (at LHC)

- _Exclusive_ measurements at _different energy_ in AA and in pp
-   Need to “calibrate the probe”: “translate” the pp reference   from 14 to 5.5 TeV*        *

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## Expected Sensitivity to RAA

- D0  K

- B  e + *X*

| 15% | systematic from efficiency corrections | 15% |
| --- | --- | --- |
| 12% | theory uncertainty in energy extrapolation | 8% |
| -- | charm electron subtraction | ~5% |
| 8% | normalization error (<Ncoll>) | 8% |

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

## Di-muons invariant mass

- Single muon cut: *p*t > 2 GeV/*c*
- Di-muon combinatorial bkgd subtracted with evt-mixing

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese

##  Beauty via single and di- muons in central Pb-Pb collisions

*** ******Beauty via single and di- muons ******in central Pb-Pb collisions***

- Muons “identified” in the forward spectrometer (-4<  <-2.5)
- 15 interaction lengths, but..
- muon *p*t threshold as low as 1-1.5 GeV/c

-  single muons in the spectrometer:
- beauty dominates for *p*t > 2-3 GeV/c

- Combined fit of low-mass, high-mass dimuons and single muons with shapes from MC to extract muons from B

- Hot Quarks 2006, 17.05.2006                                  Andrea Dainese