semileptonics at lhcb , and the prospects for v ub

Rob Lambert, CERN HQ&L, Oct 2010 1

Semileptonics at LHCb, and the prospects for Vub

Robert W. Lambert

on behalf of the LHCb Collaboration

Acknowledgements Thanks to the LHC and the rest of the LHCb collaboration

Specifically extra thanks to my colleagues: Marina Artuso, Phillip Urquijo, Kim Vervink, Liming Zhang

for direct contributions to this talk

Rob Lambert, CERN HQ&L, Oct 2010 2

Outline LHC and LHCb

Semileptonics and challenges

Progress towards Vcb and Vub

A little on afs

Rob Lambert, CERN HQ&L, Oct 2010 3

LHC The LHC is surpassing earlier predictions

We hope for 50 pb-1 by the end of the year

Rob Lambert, CERN HQ&L, Oct 2010 4

Online Luminosity Estimate

LHC now achieves>1pb-1 per fill!

LHCb LHCb is a dedicated, precision, b-physics experiment

High statistics: we’re in the forward region, and at LHC

Rob Lambert, CERN HQ&L, Oct 2010 5

Being Timely Proper Time: LHCb Velo precise down to 35 fs! (MC)

Rob Lambert, CERN HQ&L, Oct 2010 6

Being Precise Particle ID: separation handled by dedicated subdetectors

Two RICHes, Calorimetry and Muon system

Rob Lambert, CERN HQ&L, Oct 2010 7

RICH 1(Vertical)

RICH 2(Horizontal)

MA

GN

ET

TT

T1-T3

Semileptonic decays LHCb can reconstruct charmed and charmless B-decays

Backgrounds from open charm and other light mesons Since Vcb>>Vub, then the charmed are the first to be seen…

To measure the q2 we also need to reconstruct the neutrino...

Rob Lambert, CERN HQ&L, Oct 2010 8

Xcb XDb

Neutrino Reconstruction Use kinematics to calculate the neutrino momentum

Two ambiguous solutions, the lower momentum has lower error

Rob Lambert, CERN HQ&L, Oct 2010 9

Fit low

bb cross-section Second LHCb paper, L=(15.0±1.5)nb-1

sbb from semileptonic decays of the form

ln(IP) distribution used to discriminate prompt contribution

Rob Lambert, CERN HQ&L, Oct 2010 10

XDb 0

CERN-PH-EP-2010-029arxiv:1009.2731

bb cross-section Second LHCb paper, L=(15.0±1.5)nb-1

sbb from semileptonic decays of the form

Scale to full rapidity:

Rob Lambert, CERN HQ&L, Oct 2010 11

XDb 0

CERN-PH-EP-2010-029arxiv:1009.2731

b4920284 s Xbbpp

See ConorFitzpatrick’s talk

(yesterday)

Vub

Theoretically interesting: constrains UT and form factors

LHCb can also probe Vub in the Bs system

Rob Lambert, CERN HQ&L, Oct 2010 12

BABAR 2010arxiv:1005.3288B→pln

Vcb

Vcb is an early-data proxy for Vub, and is the main background Like Vub, need two external inputs: BR and/or Form Factors

Rob Lambert, CERN HQ&L, Oct 2010 13

Vcb

Vcb is an early-data proxy for Vub, and is the main background However, very little is known in this sector Form factors are expected to differ in q2 shape

Rob Lambert, CERN HQ&L, Oct 2010 14

BABAR 2010arxiv:1005.3288B→pln

?

BS->Xc(*)ln

Vcb

Vcb is an early-data proxy for Vub, and is the main background However, very little is known in this sector Form factors are expected to differ in q2 shape And The exclusive Ds

(*)(*) branching ratios are not well known

… plus one measurement from D (2009)Rob Lambert, CERN HQ&L, Oct 2010 15

(my copy ofthe PDG 2008)

21 1014.017.020.003.12536 XDB ss PRL 102, 051801

D** branching ratios

Rob Lambert, CERN HQ&L, Oct 2010 16

**sDBs Measurements of and will constrain

LHCb is investigating…

KD(*)(*)sD

Phys. Rev. D 32, 189–231 (1985)

Vcb

Choose a set of form-factors for the LHCb MC (HQET2/ISGW2)

Set the relative branching ratios from D/D*/D**, ~2.5:~6:~1

0.8 pb-1 examined so far, should become powerful in 50 pb-1

Rob Lambert, CERN HQ&L, Oct 2010 17

Ds

Ds*Ds**

Ds

Ds*Ds**PromptmKKp SB

MC

An aside: prospects for afs

Rob Lambert, CERN HQ&L, Oct 2010 18

afs

Great attention thanks to the recent D result Dominated by detector and background asymmetries

They measured:

3.2 s from SM!

Rob Lambert, CERN HQ&L, Oct 2010 19

hep-ex 1005.2757

fs

fs

-310 (syst)]46.12.51(stat) 57.9[ bA

2

dfs

sfsb aa

A

Xpp

Xpp vs. See Peter

Ratoff’s talk(tomorrow)

afs

At LHCb systematics will dominate exclusive measurements Particularly detector and production asymmetries

We can measure:

Since the detector asym.cancels for the same final states

Rob Lambert, CERN HQ&L, Oct 2010 20

2,

dfs

sfsds

fs

aaA

45.06.0 105.2

SMfs

fs

XDB ss

XDBd vs.

MC

afs

We have already collected thousands of relevant decays We expect to have sufficient statistics after 100 pb-1

Rob Lambert, CERN HQ&L, Oct 2010 21

~100k Ds in 5 fb-1 Estimate 100k Ds in 0.1 fb-1

Conclusions LHCb has a broad but precise physics program

We expect 50 pb-1 this year, which makes us competitive with the b-factories and TeVatron

Good prospects for the near future: Vcb, form factors, D**/D*/D ratios Gs, Gd, Gs/Gd

Hopefully also: ms, md

fs&fd

Next year: Afs and Vub

Rob Lambert, CERN HQ&L, Oct 2010 22

Theory input encouraged!

End Backups are often required

Rob Lambert, CERN HQ&L, Oct 2010 23

Semileptonic Prospects

Rob Lambert, CERN HQ&L, Oct 2010 24

50 pb-1

<0.1 pb-1

1 pb-1

10 pb-1

100 pb-1

bb cross-section

ms md

Afs

[D, D*, D**]Branching

Ratios

Form factors

Vub

CERN-PH-EP-2010-029

ratiosfs fd

Gs/Gd

Gs, Gd

Being Timely Proper Time: LHCb Velo precise down to 35 fs! (MC)

Rob Lambert, CERN HQ&L, Oct 2010 25

Being Exclusive Our forte: exclusive, reconstructed, b-decays

In particular, time-dependent measurements

Rob Lambert, CERN HQ&L, Oct 2010 26

~100k Ds in 5 fb-1 Estimate 100k Ds in 0.1 fb-1

Rob Lambert, CERN HQ&L, Oct 2010 27

The simple formula

qqb

q

qqp

qfs

qc

qfsq

fs SB

ttmaa

tA

G

22/coshcos

2222)(

10-3 -> 10 -5

ff

fftAqfs GGGG

)(

Rob Lambert, CERN HQ&L, Oct 2010 28

The simple formula

Polluting asymmetries are much larger than afs

Detector asymmetry c ~(10-2) Production asymmetry p ~(10-2) Background asymmetry b ~(10-3)

qqb

q

qqp

qfs

qc

qfsq

fs SB

ttmaa

tA

G

22/coshcos

2222)(

1//

1)()(

1)()(

0

0

SBSB

ININ

ff

b

p

i

ic

10 -2 10 -2 10 -310-3 -> 10 -5

Very Complicated

ff

fftAqfs GGGG

)(

Detector Asymmetry, c

Magnet divides +/- charge, allowing +/- asymmetry

by reversing magnet in D0: c reduced from 3% -> ~0.1%

Rob Lambert, CERN HQ&L, Oct 2010 29

-1

Asymmetry from Long Muon Tracks Reconstructed in MC

Left Right

+ve -ve

Left Right

-ve +ve

Detector Asymmetry, c

Matter detector hadronic interactions are asymmetric

Dominant systematic at order 1%

Rob Lambert, CERN HQ&L, Oct 2010 30

Kaon PDG cross-section

PDG

0

20

40

60

80

100

120

0.1 1 10 100 1000

momentum in lab frame Plab / GeV c

hadr

onic

cro

ss-s

ectio

n / m

b. K-, pK+, p

-1

Kaon interaction cross-section

K- pK+ p

Resultant charge asymmetry (MC)

Monte Carlo

Production Asymmetry, p

LHC is a proton-proton collider: not CP-symmetric

LHCb is at high rapidity where production asymm. are largest

There is never a simple control channel to measure p

Rob Lambert, CERN HQ&L, Oct 2010 31

-0.020

-0.015

-0.010

-0.005

0.000

0.005

0.010

0.015

0 50 100 150 200 250 300 350

Energy, E / GeVPr

oduc

tion

Asy

mm

etry

, p

p (B0 and B0)

Valence QuarkScattering

Monte Carlo

Explicitly asymmetric at LHC

The clever method Take Bs/Bd with the same final states ( =KKp )

All production asymmetry is in x2/x3, just throw it away

Measure the difference between Bs and Bd

Rob Lambert, CERN HQ&L, Oct 2010 32

f

2211,

dfs

sfs

dsdsfs

aaxxA

45.06.0 105.2

SM