Direct di-
This presentation is the property of its rightful owner.
Sponsored Links
1 / 17

Direct di- g Production @ Tevatron PowerPoint PPT Presentation


  • 62 Views
  • Uploaded on
  • Presentation posted in: General

Direct di- g Production @ Tevatron. Liang HAN. University of Science & Technology of China (USTC). On behalf of the & Collaborations. 1 st motivation: SM Higgs [email protected] Production. 1. Gluon-gluon fusion gg H. Gluon-gluon fusion. W/Z associate.

Download Presentation

Direct di- g Production @ Tevatron

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Direct di g production tevatron

Direct di-g Production @ Tevatron

Liang HAN

University of Science & Technology of China (USTC)

On behalf of the & Collaborations


Direct di g production tevatron

1st motivation: SM Higgs [email protected]

  • Production

1. Gluon-gluon fusion ggH

Gluon-gluon fusion

W/Z associate

2. W/Z associate qqW/Z+H

W fusion (VBF)

3. W fusion (VBF) qqqq+H

  • Searching for light Higgs(~130GeV)

  • “inaccessible” ggHbb, S/B(QCD) ~ 10-9

135GeV

  • “common” qqbarW(ln)/Z(ll,nn) + H(bb)

  • “extra” ggHgg ,with Br(Hgg) ~ 0.2%

Direct photon pair production at O(1)fb

[email protected] 2010


Direct di g production tevatron

SM prediction on direct diphoton production

  • Quark annihilation:

LO (a2EM):

NLO (asa2EM): virtual + real emission  infra-safe

+

(ISR)

(Box)

  • Gluon fusion:

LO (a2sa2EM): gluon PDF density enhancement at low mass

+

  • Fragmentation: FSR collinear singularity

Suppressed by:

  • photon isolation

  • pT(gg)<M(gg)

(no theory)

[email protected] 2010


Direct di g production tevatron

2nd motivation: precise test of QCD predictions

  • RESBOS, Phys. Rev. D 76, 013009 (2007) :

+ Quark Scattering qqbarggand Gluon Fusion ggggup to NLO

+ Fragmentation at LO, with additional NLO approximation

+ Resummation of soft/collinear terms of initial gluons up to all orders, cancelling divergence at NLO as pT(gg)0

  • DIPHOX, Eur. Phys. J. C 16, 311 (2000) :

+ qqbargg up to NLO + ggggat LO

+ Fragmentation up to NLO

+ asymmetry di-photon pT(g1) > pT(g2)

  • PYTHIA, Comp. Phys. Comm. 135, 238(2001) :

+ qqbarggand ggggat LO

+ Resummation via parton shower

[email protected] 2010


Direct di g production tevatron

CDF results

DIPHOX

RESBOS

  • First di-g measurement @ Tevatron: 207pb-1, PRL 95, 022003 (2005)

PYTHIA

pT(g1)>14GeV, pT(g2)>13GeV; |h1,2|<0.9; ETiso<1GeV

Mgg (GeV)

pTgg (GeV)

Dfgg (rad)

Reasonable agreements between data and QCD predictions in different region :

  • Low pT (gg)~0GeV and Df~p, DIPHOX unstable due to the lack of resummation

  • Bump of pT(gg)~30GeV dominated by events of Df<p/2 andpT(gg)>M(gg),

  • described in DIPHOX as final state radiation + Fragmentation on the same quark

[email protected] 2010


Direct di g production tevatron

D0 di-photon measurement

  • D0 analysis based on 4.2fb-1 data:

  • pT(g1)>21GeV, pT(g2)>20GeV, |h1,2|<0.9, dR(1,2)>0.4

  • Isolation requirement(jet and Fragmentation) + track veto(electron)

  • pT(gg)<M(gg)  remove Fragmentation, reduce theoretical uncertainty

  • Neutral Network discriminator ONN to separate g from EM-like jet

Loose

[email protected] 2010


Direct di g production tevatron

Background composition

  • Electron misidentified in Drell-Yan Z/g*ee :

  • Estimated with GEANT simulation, normalized up to NNLO and 4.2fb-1

  • Jet-misidentified ing+jet and jet+jet :

  • Split data(Zee deducted) into 4 groups based on tighter ONN normalization

+ Npp : both pass

+ Npf : leading passes, trailing fails

+ Nfp : vice-versa

+ Nff : both fail

Loose

Tight

4×4 g/j ONN>0.6 efficiency matrix

  • Line shapes estimated by reversing ONN<0.1

[email protected] 2010


Direct di g production tevatron

Differential cross section

  • Theoretical predictions:

+ RESBOS and DIPHOX, with CTEQ6.6M, mR=mF=mf=Mgg

+ PYTHIA 6.420 with CTEQ5L

  • Data.vs.MC comparison:

Mgg (GeV)

pTgg (GeV)

Dfgg (rad)

cosq*=tanh[(h1-h2)/2]

  • RESBOS with resummation demonstrates better agreement with data

  • data shows harder pT(gg) and excess in low Df (gg)

[email protected] 2010


Direct di g production tevatron

  • Double-differential cross section:

  • The pT(gg) inconsistence occurs in Mgg< 50GeV region, where the gluon fusion is significant. NNLO correction to gggg at low mass?

  • distributions tell the same story

[email protected] 2010


Direct di g production tevatron

Systematic uncertainty

  • Dominated by uncertainty of di-photon purity, ~10-15%, followed by luminosity ~ 6%

  • the accuracy is around O(1)fb, statistics are close to systematic

[email protected] 2010


Direct di g production tevatron

Impact on Higgs search

  • Reducible background (Zee, g+j, jj)subtracted, sideband fitting into signal region

  • Combine all signal channels (ggH, W/Z+H, VBF) to increase sensitivity

D0:

CDF:

[email protected] 2010


Direct di g production tevatron

Summary

  • Direct di-g production at Tevatron has been studied both by CDF and D0

  • Data are compared with theoretical predictions, RESBOS, DIPHOX and PYTHIA. None of these calculations provides full description of data in all kinematic regions.

  • DIPHOX treats the Fragmentation better; impose pT(gg)<M(gg) would reduce the discrepancy to RESBOS;

  • RESBOS, with NLO gggg, gives the best agreement with data; hints the need of NNLO corrections for low mass region (<50GeV)

  • Provide extra the sensitivity to SM Higgs search in the most interested mass region ~130GeV

[email protected] 2010


Direct di g production tevatron

Backup Slides

[email protected] 2010


Direct di g production tevatron

CDF & DØ

  • Calorimeter : fine granularity and good energy resolution

Isolation requirement to suppress fragmentation

  • CDF : Dh×Df ~ 0.1 ×0.26

  • D0 : Dh×Df ~ 0.1 ×0.1

  • Preshower: to distinguish g vs. neutral jets

  • D0 : lead + scintillating strip Central Preshower (CPS)

  • CDF : Preshower detector + shower maximal CES

Shower shape difference between single g and multi-g from neutral hadron (e.g. p0gg)

[email protected] 2010


Direct di g production tevatron

+ Input : Preshower & Calorimeter shower shapes + tracker activities

+ Training : MC EM-like jet vs. g

+ Validation : data Zllg FSR

ISR

FSR

Loose

[email protected] 2010


Direct di g production tevatron

  • Double-differential cross section:

[email protected] 2010


Direct di g production tevatron

[email protected] 2010


  • Login