lhcb physics reach

Marco Musy Fermilab 3th May 2003 (1)

LHCb Physics LHCb Physics reachreach

Marco MusyMarco MusyUniversità di Milano Bicocca

and INFN Milano

LHC2003 International Symposium

Fermilab, 3th May 2003


Ambitious physics goals of LHCbAmbitious physics goals of LHCb

Precision CPV measurements, using also pure hadronic and multi-body final states(Bd , Bd D

Exploit CPV in new decay channels as in Bs

(BsKK, BsDsK, BsJ/ Rare b-decays

(BdKBdKBsNew particles may show up in loop diagrams,

overconstrain will allow to disentangle SMcomponents from the new-physics ones

Overconstrain the unitarity triangles Search for New Physics beyond SM

NP?NP?b

d d

b

t

t

High statistics is a requirement


CPV from CPV from LHCb in one LHCb in one

yearyear

sin

|Vtd/Vts|

|Vub/Vcs|

now

2007

2008

LHCb

and not well known

Bs mixing

BdJ/KS Bd D*

|Vub/Vcs|

• If New Physics is there

LHCb experiment can spot it in 2008 !LHCb experiment can spot it in 2008 !

BdJ/KS Bd

BsJ/ Bs DsK


Experimental Experimental challengechallenge

• LHCb has to deal with a large variety of final states with different LHCb has to deal with a large variety of final states with different topologiestopologies• Hot pp environment needs a robust trigger Hot pp environment needs a robust trigger bb inel.~ 0.01 (bb~ 500 b),

many particles are not associated to b-hadronsmany particles are not associated to b-hadrons• b-hadrons do not evolve coherentlyb-hadrons do not evolve coherently

• High bb yield, High bb yield, 1012/year of Bd, Bs , baryons, Bc with c7mm

HIGH STATISTICSBd K*

BdJ/


Detector has undergone a reduction of material in front of RICH2

(60% 40% for X0, 20% 12% for I) Less interactions in detector, Level-1 Trigger includes momentum measurement Technologies have not changed September 2003: “Detector Reoptimization TDR” and “Trigger TDR” Construction phase is in good shape ( T. Nakada talk)

LHCb LHCb detectordetector


• MC Pythia 6.2 tuned on CDF and UA5 data• Multiple pp interactions and spill-over effects included

• Complete description of material from TDRs• Individual detector responses tuned on test beam results

• Complete pattern recognition in reconstruction: MC true information is never used

• 1M inclusive bb events produced in Summer 2002• New “Spring” production ready: 10M events for September

TDRs• Sensitivities quoted here are obtained by rescaling earlier

studies to the new yields

Fully simulated bb event in Fully simulated bb event in Geant3Geant3


VELO

Bs mixing

Measure ms

at 5

up to 48 ps-1

VELO

PV ~

47m SV

~170m

Main Main performancesperformances

see dedicated talks!see dedicated talks!

Tracking

• <Ntracks>= 27 “physics” tracks

track ~ 95% p>5 GeV/c

“ghost” rate ~ 8% @pT>0.5GeV

2<p<100 GeV/c

<(KK)>= 88%

<(K )>=2.7%

RICH

e PID

<()>= 86%

<(ee )>= 78%

<( e,)>=1%

RICH-1


Efficiency includes:

Geometrical acceptance, acc

including detection efficiency, material

Trigger efficiency: Level-0 && Level-1, L0,1

including expected Pile-up rate veto

Reconstruction efficiency (tracking, calorimeters, PID), track

Selection cuts efficiency to reconstruct the final state and reject background, cut

Event Event yieldyield

untaggedChannel tot Yield

B0 0.78 % 27 k

B0 K 0.85 % 115 k

Bs KK 0.94 % 35 k

Bs Ds 0.26 % 72 k

Bs Ds-K+ 0.34 % 8 k

Bs J/ 1.66 % 109 k

Bs J/e-e 0.29 % 19 k

B0 J/KS 0.76 % 119 k

B0K0 0.09 % 20 k

1 year = 2 fb 1 year = 2 fb -1-1

LL = 2x10= 2x103232 cm cm–2–2ss--

11

yield L(t)dtyear bb 2 Prob(b bhadron) BRi

i tot

norm. to 4

acc* track* cut* L0* L1= 13% * (96%)2 * 22% * 61% *

51%


Flavour Flavour taggingtagging Knowledge of flavour at birth is

essential for the majority of CPV measurements

Opposite side lepton tag ( b l ) Opposite side kaon tag ( b c s ) - unique to LHCb, BTeV - correlated to hadron trigger

Same side pion and kaon tag (with coming either from B** or

fragm. successfully used by CDF already)

Vertex charge tagging

l

B0

B0

D

K-

•Only single particle tagging (e, , K) from opposite side B decay used

in this presentation = 0.40,D = 0.40 DD22 = 6.4% = 6.4%

•The new MC data give similar results

b

b

d

u

d

u

B0

+


Flavour taggingFlavour tagging

Work is in progress to update and improve the efficiencies

Method tag ωtag eff

12.4 35.5 1.0 ±0.1

e 7.7 43.3 0.14 ±0.07

K (OS) 26.3 36.2 2.1 ±0.3

K (SS) 17.3 29.7 2.9 ±0.3

Vtx Charge 23.9 40.0 0.9 ±0.2

TOTAL 65.8 34.8 6.1 ±0.4

Typical tagging efficiencies:

in Bs K, KK, Ds channels (after L0*L1 trigger, any nr of collisions)

Bs Same Side

IP/

Bs Opposite Sideeff

K-tag

K-tag


BB(s)(s) KKK K KK

Selection cuts on Signal charged tracks, PID

Reconstructed B

max pT min IP/

pT(B) L/L

incl. bb

signal

Proper time = 41 fs

=18 MeV/c2

92% purity

Combinatorial bb bckgr, can be fully rejected even relaxing mass cut S/B S/B ~~ 1 1


from Bfrom B(s)(s) K KK K

(proposed by R. Fleischer )

• Relies on “U-spin” symmetry assumption (ds) which is the

only source of theoretical uncertainty

• Clean measurement of

assuming from Bs J/ and from B J/Ks

• Sensitive to New Physics contribution which can be

pointed out

by comparing with obtained from DsK



dirCPA mix

CPA Evaluation of and sensitivity

from time-dependent measured asymmetry

B0 + - BS K+ K-

yield 27k 35k

B/S 0.8 0.55

xq 0.755 20

D2 0.064 0.064

-0.30 0.16

0.58 -0.17

0.0 0.0

dirCPAmixCPA

input values

BB0 0 ++ -- BBSS K K++ K K--

02

sinh2

cosh

)sin()cos()(

A

xAxAA

mixCP

dirCPth

CP


tagging efficiency

BBSS K K++ K K--

BB0 0 ++ --

BBSS K K++ K K--

53.0),(

054.0)()(

mixCP

dirCP

mixCP

dirCP

AACorr

AA

200@

0),(

043.0)()(

ss

mixCP

dirCP

mixCP

dirCP

x

AACorr

AA BBSS K K++ K K--

increasing xs


In one year:

CP asymmetry can be measured in Bs KK up to xs=40 with an error increase of a factor 1.6

For xs=20 ~ 3o New

!


Decay is polluted by penguin diagrams

Penguin/Tree might be as high as 0.2

RICH PID and hadron trigger are fundamental

If |P/T| will be known to ±0.1 then

55°< °< 1010°° (depending on parameter value)

from Bfrom B00


BBss DDssDDssKK Bs K

K

, K

Ds

When selecting Bs Ds K

BR(Ds K)/BR(Ds

) = 1/15 while

(Ds K)/ (Ds

) = 70 thanks to the RICH PID

Dsmass (GeV)

~ 6.5 MeV/c2= 168 m

= 418 m

72k Ds

8k Ds K

Bs vtx resolution (mm)

Ds vtx resolution (mm)


Needed:

Hadronic trigger

K/separation

Good proper time resolution

Sensitivity depends upon

• relative amplitudes

• strong phase difference• values of , ms s s

For ms=20 ps–1:

1010oo

For ms=30 ps–1:

1212ooIn one year: 8k BsDsK reconstructed

events

fromfrom BBss D D--s s KK+ + , D, D++

s s

KK--

From the measurement of 4 time-dependent asymmetries one gets (with from BsJ/

same order tree level amplitudes (3) : large asymmetries, NP contributes unlikely

Same principle holds for B0 D*, (study at the time of TP gives similar precision on , a new evaluation is under way)


fromfrom BBss J/J/

In SM S 10-

2 Sensitive to New Physics effects

in the Bs-Bs system In one year:

109 k events Bs J/

19 k events Bs J/e+e

Determination of s

ssss 0.03 0.03

for ss = 0.15

J/is not CP eigenstate:

needs fit to angular distributions of decay final states as a function of

proper time

Assuming ms=20 ps–1:

22oo 36±1 fs

will be

updated

for TDR


fromfrom BB00 J/J/KKss

The ‘gold plated’ channel at B-factories

Precision measurement of this parameter is very important:

=0 in SM =sin 2

LHCb will bring a lot of statistics to this channel, which can be used to look into higher order effects, and fit Adir

In one year with 119k events: sin sin 0.02 0.02

Comparing with other channels may indicate NP in penguin diagrams

will be

updated

for TDR


BR( B K ) = (4.30.4) 105

Direct CP violation in SM <2%

Sensitive to New Physics effects

Rare decays:Rare decays:BB K K

In one year:

20k events B K(K)

triggered and reconstructed

Mass resolution ~72 MeV

Background from BKcan be rejected using K helicity

W

b u,c,t s


LHCb preliminary study

(ppBc) ~300 nb 109 Bc/ year

Bc J/BR ~10-2)

~ 2% 12k events/year

Background from B J/X and prompt

J/reduced cutting on the distance between primary vertex and Bc vertex

BBc c mesons mesons

CDF: mBc= 6.4 0.4 GeV, Bc ~ 0.5 ps

LHCb acceptance ~30%

M( J/GeV/c2

Possible CPV with Bc J/D, Bc DsD, DD, ...

Precision measurement of mass, life-time

p (GeV)


Current status of LHCbCurrent status of LHCb Physics Reach in 1 year Physics Reach in 1 year (2fb(2fb–1–1))

ChannelChannel Yield Yield PrecisionPrecision**

Bd J/Ks 119 k 0.6o

Bs DsK

Bd , Bs KK

8 k 27 k, 35 k

10o

3o

Bd 27 k 5o- 10o

Bs J/ 128 k 2o

|V|Vtdtd/V/Vtsts Bs Ds 72 k ms up to 58 ps

rare rare decaysdecays

Bd K 20 k

*Precisions obtained by scaling old results with the new yields All numbers will be updated together with more channels in the re-optimization TDR (September 2003)


Possible sources of systematic uncertainty:• Asymmetry of b vs b production• Detector efficiencies which depend on charge can bias tagging efficiencies

can fake CP asymmetries• CP asymmetry also in background processes

Systematics in CPV measurements

Alternate runs, swapping the orientation of magnetic field

Use control samples available with high statistics: Bs Ds72k events/year

B0 J/ K* 600k events/year B J/ K600k events/year

Study CP asymmetries in the B mass side bands

(from Technical Proposal)


ConclusionConclusion

LHCb is a dedicated detector for B physics measurements in many channels from the beginning

of LHC

A very precise determination of CKM unitarity triangle will be possible

Detector performances are being evaluated with a realistic and complete Monte Carlo simulation

LHCb offers an excellent opportunity to spot New Physics signals beyond Standard Model very soon at

LHC


back-up slides


00 reconstruction reconstruction•PreShower (scintillator+Pb+scintillator) 2X0

•ECAL (Pb+ “shashlik” scintillator) 25X0 (E)/E=10% /E 1.5%

•HCAL (Fe+scintillator) 5.6 I (E)/E=80% /E 10%

Purity ~20% in range 0.1<m <0.17 GeV/c2

pT>200 MeV

lhcb physics reach

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