# Presentation: 710196

## Marcello Lunardon 

**HOT QUARKS 2006**
**Villasimius, May 15-20/2006**
**Study of the ALICE performance for the measurement of beauty via the**
**electron decay channel **
*Marcello Lunardon*** **
*for the ALICE collaboration*

## Contents

** ****Description of the strategy for detecting the beauty-originated electrons**
** ****Evaluation of uncertainties and measurement performance**
** ****Conclusions**

***Study of the ALICE performance for the measurement of beauty via the electron decay channel***

## Open Beauty detection in p-p and Pb-Pb at LHC with ALICE

***	******in p-p 14 @ TeV***		  			***charm*****	****	*****0.16***
***	******	******	******	******	******	******	******	******beauty******	******	******0.007***
***	******in Pb-Pb @ 5.5 TeV (5%****** ************tot******)*** 		***charm******	*****	*****115***
***	******	******	******	******	******	******	******	******beauty******	******	******4.6***

***high uncertainty: 1.8 - 7.3***

**Baseline predictions on beauty production at LHC:**
**NLO (MNR code, 1992) in pp + binary scaling (shadowing included for PDFs in the Pb) **

**Open Beauty detection in p-p and Pb-Pb ****at LHC with ALICE**

***How much signal?***

**Expected number of electrons:**
**	****Semi-electronic channel B.R.:  ~ 10 %  for both b ******** e and b ******** c ******** e**
**	****ALICE acceptance for b/c  electrons:  ~ 24 %**
**	******** ****in p-p****	****  ****~ 0.0007 beauty electrons / event**
**	******** ****in Pb-Pb ****~ 0.5 beauty electrons / event**
**Number of electrons for reference statistics:**
**	****10****9**** events (1 year p-p at nominal luminosity):** **~ 0.7 M beauty electrons**
**	****10****7**** Pb-Pb central events (1 Pb-Pb year):** **~ 5 M beauty electrons**

-    MNR code: Mangano, Nason, Ridolfi, NPB373 (1992) 295.

## How much background?

**Open Beauty detection in p-p and Pb-Pb ****at LHC with ALICE**

**Expected number of ****charm**** electrons:**
**	****Semi-electronic channel B.R.:  ~ 10 % for c ******** e**
**	****ALICE acceptance for b/c  electrons:  ~ 24 %**
**	******** ****in p-p****	****  ****~ 0.008 charm electrons / event**
**	******** ****in Pb-Pb ****~ 6 charm electrons / event**

*13 times more!*

*... need a very efficient detection strategy! *

**Expected number of electrons from** **other sources ****:**
**	*****- Dalitz and strange particles decays***
***	******- ************ conversions***
***	******- hadrons  misidentified as electrons***
***	********* ****both p-p and Pb-Pb  ****~ a lot / event**

## How to detect them?

**1) tracking in ITS+TPC+TRD**

**2) electron identification in TRD+TPC**

*electron track*

**Detection strategy**

## ITS

-  Track position resolution mainly provided by the 2 layers of silicon pixels

**Detection strategy**

**ITS**

**SPD**

- track position resolution

## Intermezzo: SPD assembly in Padova

***Drawing ...***

***... assembling ...***

***... testing ...***

***... relax!***

- CHESSADDAFA’
- PECCAMPA’ !!!

*“**What I have to do to survive!”*

## Combined info from TRD (trans. rad.) and TPC (dE/dx)
TRD rejects 99% of the  and ALL heavier hadrons (pt > 1 GeV/c)
TPC further rejects residual pions (up to 99% at low p) 
About 20% of electrons rejected

- TRD rejects 99% of the  and ALL heavier hadrons (*p*t > 1 GeV/c)
- TPC further rejects residual pions (up to 99% at low p)
- About 20% of electrons rejected

**Detection strategy**

## Detection strategy

**Detection strategy**

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

- d0 distributions for “electrons”  from different sources:

-  b quark has c 500 m
-      decay electrons d0 ~ few-100 m (B = 0.4 T)

***The heavy-flavors detection key point: ******	******	******	******	******	******the track impact parameter cut***

## Detection strategy

**Detection strategy**

***p-p vs. Pb-Pb : primary vertex reconstruction***

-  Track position resolution determined both by track parameters precision and vertex position precision.
-  In Pb-Pb: several tousands of primary tracks  very good and easy determination of the primary vertex (***x,y* ~ 15 m)

-  **Beauty events: the displaced tracks (electron + X) can drive the algorithm towards a wrong vertex position ******** *****we optimized the preselection of tracks***

-  In p-p: expected *<Nch>* ~ 7  (about twice for heavy-flavor events)  need efficient vertex reconstruction algorithm (A.D. and M.Masera, ALICE-INT-2003-027)

***Effect on the d******0****** resolution***

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

**Detection strategy**

- 3) Subtract (small) residual background

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

- d0 distributions for “electrons”  from different sources:

## Cut selection and uncertainties evaluation

**Cut selection and uncertainties evaluation**

**In a given *****p*****t****-bin, *****N***** “electrons” are counted, after PID and d****0**** cut: **
**	****	*****N****** ******=****** N******b****** ******+****** ******N******c****** ******+****** ******N******bkg***

**Multiply by the inelastic pp cross section (or by **
**	****Pb-Pb overlap functions): ***d****e from b**/dy = ****pp**.**d****N******b****corr**/dy*
-        pp cross section measured at LHC (*source of error*)

**Correct for acceptance/efficiency: ***d****N******b****corr**/dy** = (****N******b**** / ****)  *       efficiency calculated with MC (*source of error*)

**Subtract the contribution from background:** ***N******b**** = (**N** – **N**c**) – N**bkg *estimated from measured pions dN/d*p*t plus MC (*source of error*)

**Subtract the contribution from charm:**  ***N******b**** + N**bkg* *=*  *N** – **N**c** *estimated from D0 measurement (*source of error*)

- beauty

- charm

- other e

## Cut selection and uncertainties evaluation

- _Error from cross section normalization_:
- 5% for pp, 9% for Pb-Pb (*p*t-independent)

- _Error from acc./effic. corrections_:
- assumed 10% (in principle *p*t-dependent)

**  ****Systematic**:
- _Error from subtractions_:
- 	- **charm**: from D0 uncertainties (1020% pt-dep)
- 	- **bkg**: from ** uncert. + MC (assumed 10%)
- 	- proportional to **c/b**, **bkg/b** fraction

**  ****Statistical**:
- depends on** ****d****0**** cut**

## Cut selection and uncertainties evaluation

- 2.5 < pt < 3 GeV/c

- 7 < pt < 9 GeV/c

- 12 < pt < 16 GeV/c

-  At low-pt the _*systematic*_ error dominates
-  At high-pt the _*statistical*_ error dominates

**Cut selection and uncertainties evaluation**

***Optimization of the d******0****** cut in bin of p******t***

## Result summary

- 109 pp events

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

**Result summary**

***statistics***

***uncertainties***

***cross section***

## pp: Sensitivity vs. pQCD

- 109 pp events

-  Using UA1 MC method (*) we can extract a minimum-pt-differential cross section for B mesons
-  From electrons in 2 < *p*t < 20 GeV/c   B mesons in 2 < *p*tmin < 30 GeV/c

- (*) C. Albajar et al., UA1 Coll., Phys Lett B213 (1988) 405  C. Albajar et al., UA1 Coll., Phys Lett B256 (1991) 121

## pp: the first months at LHC

**pp: the first months at LHC**

-  LHC operations are supposed to start on July 1st 2007

- (*) J.P. Revol, Alice Physics Week, Erice, Dec. 2005

-  5 months later, one month with stable beam at L ~ 1030cm–2s–1, interleaved with machine development, should allow ALICE to collect something about **10****8**** **pp minimum-bias events (*)

## Conclusions

***ALICE has a good potential to measure  beauty production cross section both in pp and AA (vertexing and particle identification down to low p******T******) ***
***With the statistics corresponding to about one year of LHC at nominal luminosity, we expect to get a significant measurement of beauty electrons from 2 up to 20 GeV/c***
***The expected running of LHC in the first period should allow to get some significant cross section number already during the commissioning of the accelerator***
***Coming next***
***Optimization of d******0****** cuts for Pb-Pb in bins of p******T****** and sensitivity to double ratio R******BD****** (Andrea’s talk) in progress (almost ready)***

## THE END

## BACKUP SLIDES

## Theoretical Uncertainties(HERA-LHC Workshop)

- MNR code: Mangano, Nason, Ridolfi, NPB373 (1992) 295.

_*Evaluation of theoretical uncertainties*_

- beauty

- charm

- CERN/LHCC 2005-014
- hep-ph/0601164

## Model Comparisons(HERA-LHC Workshop)

**Model Comparisons****(HERA-LHC Workshop)**

_*Compare predictions by several different models*_

- Good agreement between collinear-factorization-based
- calculations: FO NLO and FONLL
*k*T factorization (CASCADE) higher at large *p*T

- beauty

- charm

- CERN/LHCC 2005-014
- hep-ph/0601164

## Statistics in pp

| pt bin [GeV/c] | |d0| cut [mm] |
| --- | --- |
| 1 – 1.5 | 400 |
| 1.5 – 2 | 400 |
| 2 – 2.5 | 300 |
| 2.5 – 3 | 200 |
| 3 – 4 | 150 |
| 4 – 5 | 150 |
| 5 – 7 | 100 |
| 7 – 9 | 100 |
| 9 – 12 | 100 |
| 12 – 16 | 50 |
| 16 – 20 | 50 |

- Statistics (in 109 events)

**Statistics in pp**

## Statistical: 

**Statistical**:
**Systematic**:
- _Error from subtractions_:
- _Error from acc./effic. corrections_:
- 10% (in principle *p*t-dependent)
- _Error from cross section normalization_:
- 5% for pp, 9% for Pb-Pb (*p*t-independent)

## Statistics summary

- 109 pp events

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

**Statistics summary**

## Uncertainties summary

- 109 pp events

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

*fixed d**0** cut [200-600] ****m*

## Cross section of electrons from B

- inner bars: stat. errors
- outer bars: stat.  pt-dep. syst. errors
- not shown: norm. error (5% pp, 9% Pb-Pb)

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

## Extraction of a minimum-pt-differential cross section for B mesons

***Using UA1 MC method (*), also adopted by ALICE *********

**(*) C. Albajar et al., UA1 Coll., Phys Lett B213 (1988) 405 **** C. Albajar et al., UA1 Coll., Phys Lett B256 (1991) 121 **

-        The B meson cross section per unit of rapidity at midrapidity for *p*t*B** > p*t*min* is obtained from a scaling of the electron-level cross section measured within a given electron parameters space e

-          The semi-electronic B.R. is included here

- We use			     , where *p**T* are the previously used bins,
-  = [-0.9, 0.9] and d0 = [d0 MIN, +] m

- (thanks to R.Guernane for useful discussions)

## Extraction of a minimum-pt-differential cross section for B mesons

***Robusteness of the procedure***

**Extraction of a minimum-p****t****-differential cross section for B mesons**

- For ***p*****t****e**** > 2 GeV/c,** can
- find an “optimal” *p*tmin,
- for which the additional
- systematic error is negligible

## Beauty Energy Loss : RAA 

**Beauty Energy Loss : R****AA**** **

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

## Slide 31

## 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  *

- 

- 

## Semi-electronic beauty detection:

***simulation details***

***Magnetic field: 0.4 T***

## Semi-electronic beauty detection

*	**- can assume **complete rejection of K,p and heavier particles from TRD and TOF*
*	**- **80% electron reduction** factor for identification efficiencies of TRD (0.9) and TPC (0.9)*
*	**- **pion contamination less than 0.01%** at low momentum*

**Semi-electronic beauty detection**
***background analysis: misidentified pions***

- Effect of the PID on the pion backgound

**Number of pions much greater than number of electrons **
**good rejection using combined PID technique**

- pT > 1 GeV/c

## Semi-electronic beauty detection

***	******Semi-electronic charm measurement  at RHIC from PHENIX: photon conversions are a ***_***large part of the  background***_*** ( have to use a removable converter )***

**Semi-electronic beauty detection**
***background analysis: ************ conversions***

**Similar situation expected at**
**ALICE for electrons entering the**
**TPC, but: **
***a) request of 1******st****** SPD layer***
***b) select positive d******0 ******electrons***

## Semi-electronic beauty detection

**Semi-electronic beauty detection**
***background analysis: ************ conversions***

*b) More reduction with d**0** positive cut *

## Semi-electronic Beauty detection

***simulation results***

- Expected statistics (107 Pb-Pb events)

***Signal-to-total ratio and expected statistics in 10******7****** Pb-Pb events***

## Why beauty?

**Why beauty?**

** ****normalization for**** ** **studies**

-  B J/ **important background**

*** ******probe of the medium ( ******e. g.: ***_***energy loss***_*** of beauty in the medium  ***
***  ******to be compared with charm energy loss ************ study of ***_***dead-cone***_*** ***
***  ******effect ******);***

*** ******discovery potential (******new physics window******) ! ***

** ****interesting in its own right:**