b and onia prodution in atlas

B and onia prodution in ATLAS

Else Lytken (CERN)

On behalf of the ATLAS collaboration

HERA-LHC workshop May 2008

E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008 2

B and onia production in ATLAS

Measure cross sections at new energy , d/dpT, d/d(), d/d

B physics a window for new discoveries Observe rare decays, measure CP violation

parameters Detailed understanding of the bb

spectrum as background to other processes.

Commissioning/early physics: calibration, alignment, trigger efficiencies etc.

¯

¯

Take advantage of copious bb production at 14 TeV: (bb) ~500 b

_

Overlap


Early physics with b’s and onia Focus of this talk is on the measurements during

commissioning phase/early physics: Linst = 1031 – 1032 cm-2s-1

Production of B’s and the quarkonia narrow resonances gives us a handle for first performance measurements complementary to and extending other SM “standard candles” such as W’s and Z’s. For instance crucial for Higgs and SUSY searches to

understand our performance with lower pT leptons Lower luminosities means lower pT trigger thresholds possible,

both for electrons and muons Given the high rates our trigger menus have the flexibility

to account for different luminosity scenarios


~200 Hz

~1-2 kHz

Initial triggers: relevant examples

L2: confirm L1 signal + additional search in regions of interestEF: offline algorithms for final selection

2.5 s

40 ms

PS Rate (kHz) PS Rate (kHz)

Electrons

EM3 60 ~0.7 600 ~0.7

2EM3 1 ~6.5 10 ~6.5

Muons

MU6 1 ~0.6 1 ~6.4

MU10 1 ~0.3 1 ~3.6

2MU4 1 ~0.1 1 ~0.7

MU6JET10 10 ~1 100 ~1

L=1031 L=1032

For initial low luminosities can trigger on both low pT electrons and muons.Expected L1 rates and prescale factors:

4 s


Inclusive b production cross section: +b-jet

fb found from fitting transverse relative pT to templates:

Transverse relative pT (GeV)

btrig =13.5%

brec = 85%

With 15 pb-1 such a fit gives us:

fbackgr = 77 ± 4 % (c; ,K )

fb = 23 ± 2 % (b ; bc )

ATLAS


Inclusive cross section: dimuonsTo distinguish bb J/ X (indirect J/) from ppJ/ (prompt J/’s, ~ 2 ) Useful variable: the (pseudo-) proper time:

cJp

MLt

T

Jxy

)/(/

Lxy = transverse

decay length

_


B measurements using excl. channels Due to high cross sections and dedicated triggers we can

reconstruct exclusive channels in early data Reconstruction of the mass and lifetime of the B± meson from B± J/ K± decay very useful for calibration and alignment performance.

Results with 10 pb-1: (mB+) = 42.2 ± 1.3 MeV (total) = 29.8 ± 0.84 %

Requirements: - dimuon trigger- displaced vertex (100 μm) - add. track with pT 1.5 GeV- track and μμ fit to same vertex- m(μμ,track) within 120 MeV of B+ mass.

ATLAS

T

xy

p

mL


B cross section with excl. channels

Channel N (100 pb-1)

B+ J/ K+ 17000

B0 J/ K0* 8700

Bs J/ 900

b J/ 260

Available statisitics with 100 pb-1:

Measurement of dB/pT using B+J/ K+ after 10 pb-1:

10<pT<18 18<pT<26 26<pT<34 34<pT<42 10<pT<42

7.7 6.9 10.5 13.9 4.3

16.1 15.8 17.6 19.8 14.8Total uncertainty (%)

(GeV)

Acceptance + stat. (%)


Quarkonia Among first measurements

+ theoretical interest: What is the production mechanism?

The Color Octet Mechanism agrees well with measured shape from Tevatron Polarization measurements:CDF sees no sign of pol. for J/, and DØ (1S) measurements not consistent with predictions.

More data with high-pT needed!

Coloroctet

Color singlet

Tevatron data

NRQCD

(1s)

J/

kT factorization model


Quarkonia in ATLAS: J/ e+e-

Min bias ppJ/(ee)pp(ee)(1S)ppDrell-Yan(ee)

@ L1 trigger

L1 (trig) ~ 27%L2, EF under optimization

Initial data: take advantage of electron trigger paths as wellCurrent studies using 2EM3 Single-e triggers under investigationLater data (“low luminosity”, L=1033cm-2s-1) has to rely on single-μ b trigger also for J/(ee)X, (ee)X

N(J/) after L1: 4.2 M events

N() after L1: 1.2 M events

1031 cm-2s-1


J/ e+e-

Two electron id methods explored: Low pT version of standard ATLAS

isolated electron cut based on shower shapes, associated to high quality tracks with E/p >0.7, conversion veto, and transition radiation hits

Less efficient for electrons from b’s

2nd method (pT 2 GeV/c) extrapolates in narrow window to calorimeter and uses likelihood ratio (similar variables)

After offline selection 100 pb-1: ~230k J/’s and ~43k ’s Expect to measure m(J/) to ~0.6%

N = # good pion tracks

Ne = same + misid. as e’s

R = N / Ne

“b-electrons”

L1 + offline selection

Mee (GeV)

d/

dm

(n

b/0

.5G

eV

)


J/ μ+μ-

Current studies use a combination dimuon trigger, (trig) = 87% L1, 97% L2, with analysis cuts of 6 and 4 GeV

Rate 1 Hz expected at EF for all quarkonium μμ (incl ’, (2,3S) )

L1 combined L2 combined

J/ J/

10


Dimuons: ResultsRequire: muons from same vertex and proper time < 0.2 ps

With pT1 6 GeV, pT2 4 GeV:

15k J/’s per 1 pb-1

2.5k ’s (1S) 1-2 days with L = 1031cm-2s-1

Bkg w/overtex cuts

With 10 pb-1: S/B = 60 for J/ and 10 for d/dpT ~ 1 % for J/ , ~5 % for

10 pb-1: also measurement of c J/()

~ 1 fb-1: b ()


Polarization P(J/)P(-)

P(+)

*

Dimuon triggers: little or no information for high cos*Single-: combined with 0.5 GeV track gives access to these values (~ pT range but larger pT(+,-) )Single-u trigger => larger background Still: S/B = 1.2 (J/) and 0.05 (Upsilon)

6410+t

Measure high-pT polarization to distinguish production models

*2*

cos1cos

d

dN

x103

Combine and fit to measured distribution in slices of pT

Shown: 12 pT 13 GeV

Long. pol.( = -1)

Trvs. pol.( = +1)

ATLAS


J/* = ATLAS~10 pb-1

* *** *

0.8 fb-1

Polarization resultsAlready with 10 pb-1: measure J/ pol. to same precision as TeV with 1.3 fb-1 - but with interesting high pT data!Same precision for polarization studies can be reached after ~100 pb-1

Crude superimpose of ATLAS stat uncertainties with 10 pb-1 assuming =0 :

NRQCD

*

*

*

*

* = ATLAS~10 pb-1

*


Quarkonia as a monitoring tool Offline and online monitoring with

J/’s and ’s important to have a low pT data point in addition to Z’s

Given the large statistics expected should be able to use this already in the beginning

Check mass shift as a function of pT:

momentum scale, energy loss curvature diff:

detector misalignments and :

magnetic field, material effects

6 pb-1

1 week w. L=1031

Perfect alignment

Example of identifying a problem


Summary and outlook

ATLAS well prepared for B and quarkonia cross section measurements in initial low luminosity period

Early data studies will also help us during commissioning For cross section measurements already enough statistics with

the early data! (10 pb-1 or less) Key measurements based on muon triggers but in initial period

will also have electron channels for comparison Stay tuned for the next chapter in J/ and Upsilon high-pT

polarization measurements!

Backup


Single-muon trigger: S/BMost relevant for J/ studies …


Polarization measurement


More on polarization

Resolution of reconstructed cos* is ~0.0015

Combined measurement Unpolarized 17<pT <21 GeV

J/


AcceptancepT cuts (trigger and offline) means pT(J/) 10 GeV, whereas non-zero A for Upsilons also at ~0RoI’s based on trigger towers of

x ~ 0.1 x 0.1 R separation between leptons also

affects sensitivity to material effects

J/

Upsilon(6,4)-cuts


Electron efficiencies

“standard cuts”“b electrons”

Efficiency of single electronsbased on MC truth

(EM3:e5;e5)


Inclusive b productionAfter fit


The 3 production mechanisms

NLO: Gluon splitting

NLO: Flavour excitation, sensitive to PDF’s

LO: Flavour creation

b and onia prodution in atlas

Documents

b measurements

b cross section

b meson

mev of b mass

b bc atlase

s measurements

low pt electrons

onia production