s. gascon-shotkin moriond qcd march 15 20121 photon production at e cm = 7 tev suzanne...

S. Gascon-Shotkin Moriond QCD March 15 2012 1

Photon Production at Ecm= 7 TeV

Suzanne Gascon-Shotkin Institut de Physique Nucléaire de Lyon

Université Claude Bernard Lyon 1IN2P3-CNRS

Suzanne Gascon-Shotkin Institut de Physique Nucléaire de Lyon

Université Claude Bernard Lyon 1IN2P3-CNRS

on behalf of the CMS and ATLAS Collaborations

Rencontres de Moriond QCD/High-Energy InteractionsRencontres de Moriond QCD/High-Energy InteractionsMarch 10-17 2012 La Thuile Valle d’AostaMarch 10-17 2012 La Thuile Valle d’Aosta


OutlineOutline

What direct photon measurements at the LHC can tell us Anatomy of a differential direct photon cross section

measurement Signal fraction measurement techniques Differential cross sections, isolated inclusive photons Comparison with Tevatron measurements Differential cross sections, isolated photon + jets (ATLAS) Differential cross sections, isolated inclusive diphoton pairs Comparison with theoretical predictions and open questions Conclusions and perspectives

Diphoton

Inclusive Photon/Photon + Jet

BornBorn BoxBoxBoxBox

HOHOBoxBoxHOHOBoxBox

2-Frag2-Frag 1-Frag1-Frag

ComptonCompton

AnnihilationAnnihilation

FragFrag


D.d'Enterria & J.Rojo, arXiv:1202.1762D.d'Enterria & J.Rojo, arXiv:1202.1762

D.d'Enterria & J.Rojo, arXiv:1202.1762D.d'Enterria & J.Rojo, arXiv:1202.1762

What direct photon measurements at the LHC can tell usWhat direct photon measurements at the LHC can tell us

R.Ichou & D.d'Enterria, PRD82 (2010) 014015

Compared to the Tevatron, fraction of Compton Compared to the Tevatron, fraction of Compton scattering remains ~80% with increasingscattering remains ~80% with increasingEt_gamma (isolated photons) [Ichou, d’Enterria 10]Et_gamma (isolated photons) [Ichou, d’Enterria 10] Can probe gluon PDF at unprecedented EtCan probe gluon PDF at unprecedented Et Can reduce gluon NLO PDF error by ~20%Can reduce gluon NLO PDF error by ~20% Leads to ~20% reduction in Leads to ~20% reduction in (gg → H) PDF (gg → H) PDF

uncertainty (D’Enterria & Rojo 12)uncertainty (D’Enterria & Rojo 12) Direct measurement of background processes to Direct measurement of background processes to

Higgs boson productionHiggs boson production


Anatomy of a differential direct photon cross section measurementAnatomy of a differential direct photon cross section measurement

LUqdq

d N

i

n

ii

n

i

n

11

Isolated 1

Experimental measurement: We measure the differential isolated cross section in bins of observables q i of width qi From a set of identified isolated photon candidates we estimate N, the number of signal photons or photon pairs in each bin To arrive at the true value of N in each bin:

We account for bin-to-bin migrations arising from detector resolution (unfolding factors U) We correct N for for =Trigger, reconstruction and photon identification efficiencies

Comparison with (usually parton-level) theoretical predictions: Impose a parton-level isolation Correct for effect on isolation efficiency due to underlying event and hadronisation (or assign a systematic error)

All measurements presented here were performed on the 2010 dataset with ~36 pb-1

of integrated luminosity


Signal Fraction Measurement techniques: + X Signal Fraction Measurement techniques: + X

Phys. Rev. D 84, 052011 Phys. Rev. D 84, 052011

Phys. Lett. B 706 (2011) 150-167Phys. Lett. B 706 (2011) 150-167

ATLAS: 'ABCD' double-sideband counting method in EM shape and Isolation energy sum (cross-checked with calorimeter isolation template) :

CMS: Combined photon Isolation and Converted photon Et/pt templates (MC w/ data validation), 2-comp. (un)binned EML fit, final results combined with Best Linear Unbiased Estimator method (Lyons et al)

Correlation between 2 variables, set to 1 andsystematic assigned

Signal Leakage


CMS: Electromagnetic Calorimeter Isolation template, CMS: Electromagnetic Calorimeter Isolation template, signal sample (random cones) and background sample signal sample (random cones) and background sample (photon candidates with a single clean track in the isolation (photon candidates with a single clean track in the isolation cone) entirely from data, validated with additional data cone) entirely from data, validated with additional data samples (W, Z and 2 clean-track sample [shown]). Binned samples (W, Z and 2 clean-track sample [shown]). Binned maximum likelihood fit to the isolation distributions of the two maximum likelihood fit to the isolation distributions of the two photons photons

Signal Fraction Measurement techniques: + XSignal Fraction Measurement techniques: + X

L

N

qmdddqdm

d unfolded

TT**

Isolated4

cos)(

1

cos

ATLAS: ‘Event-weighting’ method (generalisation of that ATLAS: ‘Event-weighting’ method (generalisation of that used at Tevatron, see for example used at Tevatron, see for example Phys. Rev. Lett.107, Phys. Rev. Lett.107, 102003 (2011).102003 (2011).) Signal fraction :) Signal fraction :where j={PP,PF,FP,FF} wrt where j={PP,PF,FP,FF} wrt selection criterion on Etselection criterion on EtIso. Iso. , n, ni i the observed outcome of the ith the observed outcome of the ith

event, event, a matrix expressing efficiency for an event in true a matrix expressing efficiency for an event in true state j’state j’j, jj, jjjjj to yield observed state j to yield observed state j Matrix coefficients obtained Matrix coefficients obtained

from data-driven isolation PDFsfrom data-driven isolation PDFs Xcheck: ABCD + 2d templateXcheck: ABCD + 2d templatePhys. Rev. D 85 (2012) 012003

http://dx.doi.org/10.1103/PhysRevD.85.012003



Comparison to pQCD fixed-order calculation: JETPHOX (Aurenche, Belghobsi, Catani, Fontannaz, Guillet, Heinrich, Pilon, Werlen) d/dET for ||<2.5 (CMS) 2.37 (ATLAS), 15(ATLAS) 25(CMS) GeV<ET<400 GeV Correction to theory prediction from underlying event/hadronisation: ~2.5% (CMS) Systematics-limited for ET<120 GeV, exp: ~7-20%

theoretical: dominated by scale (~10%)

Inclusive Differential Cross Sections: + X Inclusive Differential Cross Sections: + X


Phys. Lett. B 706 (2011) 150-167,Phys. Lett. B 706 (2011) 150-167, ATL-PHYS-PUB-2011-013ATL-PHYS-PUB-2011-013

S. Gascon-Shotkin Moriond QCD March 15 2012 8Phys. Rev. D 84, 052011 Phys. Rev. D 84, 052011

Slight overprediction at ET<50 GeV for both experiments




Opposite trends at low ET values (<~50 GeV), possible explanations?

Different regimes of xT=2pT/xT=2pT/√√s ~0.003 s ~0.003 (Tevatron)(Tevatron) ~0.0015 ~0.0015 (LHC)(LHC)

Different maximum parton-level Isolation ET : 2GeV CDF, 4-5 GeV LHC

Regime dominated by fragmentation

Reasonable for such a rapid ET dependence to come from physics?

An open question for theorists and experimentalists

Comparison with Tevatron MeasurementsComparison with Tevatron Measurements




World data summary, obtain power slope of n=4.5 when scale by xT, supports pQCD hypothesis (similar plot shown by K. Okada Tuesday)


D.d'Enterria & R.Ichou, HEP-EPS'11 Proceeds.

xT=2pT/xT=2pT/√√ss


Differential Cross Sections: ATLAS + Jets Differential Cross Sections: ATLAS + Jets

Motivation: Different photon-jet angular configurations correspond to regions with different relative fragmentation contribution, also different values of {x,Q2} Comparison to pQCD fixed-order calculation: JETPHOX, PYTHIA (Sjostrand et al)

SHERPA (Krauss et al) d/dET for three different rapidity ranges of the leading-pT jet (anti-kt, radius parameter=

0.4), in same- and opposite-sign configurations of X yjet, ||<1.37, ET>25 GeV, |yjet|<4.4, pTjet>20 GeV, R,jet > 1.0

http://arxiv.org/abs/1203.3161 http://arxiv.org/abs/1203.3161 New!New!New!New!


Same 'ABCD' double-sideband method for signal fraction extraction as for + X Correction to theory prediction from underlying event/pileup/hadronisation: ~0.85-0.92, 1

for high ET Systematics-limited, typical errors, exp: ~3-40% , depending on rapidity/configuration,

highest for lowest- ET photons; theoretical: dominated by scale (~20-40%) Results consistent with those for + X (data overprediction for ET<~40 GeV). Important test

of pQCD: Good data-theory agreement even in high-fragmentation (opp-sign) configurations

Differential Cross Sections: ATLAS + Jets Differential Cross Sections: ATLAS + Jetshttp://arxiv.org/abs/1203.3161 http://arxiv.org/abs/1203.3161


Comparison to pQCD predictions to order s: DIPHOX (Binoth, Guillet, Pilon, Werlen) with gamma2MC (Bern,Dixon, Schmidt) [CMS], DIPHOX and ResBos (Balazs, Berger, Mrenna, Nadolsky, Schmidt, Yuan) [ATLAS]. Correction for UE/hadronisation: ~5% (CMS) d/dQ for Q={mpt, , cos* (CMS)}, ET >{20, 23 GeV}, ||<1.44 and ||<2.5, R()>0.45 (CMS), ET >{16, 16 GeV}, ||<1.37 and ||<2.37, R()>0.4 m : Slight underprediction for ATLAS at lowest values (low 24 NNLO [see later]…

)

Differential Cross Sections: + XDifferential Cross Sections: + X

JHEP 01 (2012) 133 JHEP 01 (2012) 133

Phys. Rev. D 85 (2012) 012003




: Significant underprediction for all but highest values (<~2.8), corresponds to collinear regime where no LO terms contribute, very sensitive to predictions of HO terms


Phys. Rev. D 85 (2012) 012003

JHEP 01 (2012) 133 JHEP 01 (2012) 133




pt, : Familiar ‘shoulder’ (underprediction) seen by both experiments as well as in prior Tevatron measurements, combination of Et threshholds with non-back-to back topology


Phys. Rev. D 85 (2012) 012003

JHEP 01 (2012) 133 JHEP 01 (2012) 133




+ X Uncertainties: Experimental:

Statistical error ~20% Systematics typically order of 10% dominated by knowledge of signal/background template shapes (CMS), definition of control sample (ATLAS)

Theoretical: 10-20% dominated by scale uncertainties


JHEP 01 (2012) 133 JHEP 01 (2012) 133

Underprediction for high values seen also by Tevatron experiments

JHEP 01 (2012) 133 JHEP 01 (2012) 133

cos*=tanh( y


Comparison with Theory: Open questionComparison with Theory: Open question

arXiv arXiv 1201.3084v11201.3084v1

D. de Florian, L. Cieri et al D. de Florian, L. Cieri et al arXiv:1110.2375 arXiv:1110.2375

(JHEP 01 (2012) 133) (JHEP 01 (2012) 133)

D0: PLB690 (2010) 108D0: PLB690 (2010) 108

LHC-HiggsLHC-HiggsXS WG XS WG YR2YR2

Phys. Rev. D 85 (2012) 012003

First theoretical prediction of NNLO direct contributions (de Florian, Cieri, et al 11, cf talk Sunday), to be made public (2NNLO) Remarkable improvement in CMS data-theory

comparison for , stay tuned for other observables and addition of box corrections Caveat: Smooth (Frixione) not solid cone

isolation,no frag.




Conclusion and PerspectivesConclusion and Perspectives

Direct photon measurements at the LHC performed with the 2010 dataset corresponding to ~36 pb-1 of integrated luminosity are starting to be used to constrain gluon and gluon fusion Higgs boson production PDF uncertainties Differential cross sections, isolated inclusive photons

Measurements are already systematics-limited Data in agreement with theory predictions and Tevatron measurements except for ET <~50 GeV, where there are opposite tendencies, an open question

New ATLAS photon + jet differential cross-section measurement in three different ranges of leading-pT jet y, results consistent with inclusive measurement, agreement with theory in all -jet configurations, even those with larger fragmentation contributions. Differential cross sections, isolated inclusive diphoton pairs

Measurements consistent with those of the Tevatron experiments Becoming systematics-limited New NNLO calculation of direct contributions seems to resolve a large part of collinear-regime discrepancies, need to take into account fragmentation and HO box

Perspectives: 2011 ~5fb-1 additional, 2012 ~15fb-1 at ECM =8 TeV Possible measurements: Differential cross sections: Isolated inclusive, photon + jets, inclusive diphoton pair , diphoton + jets, photon + hf, all with additional observables. Ratios between cross-sections at ECM = 7 and 8 TeV . Reexamine coherence of parton- and reconstruction-level isolation criteria, progress with theorists in understanding of isolation/fragmentation relationship. Exploit direct measurement of background processes for H search


AcknowledgementsAcknowledgements

Thanks to:

L. Carminati , V. Cerulli , V. Chetluru, L. Cieri , D. D'Enterria, D. de Florian, P. Gras , M. Grazzini, R. Ichou, J.-P. Guillet, K. Kousouris, S. Linn, D. Lopez Mateos, Y. Ma, L. Malgeri, G. Marchiori, J. Owens, E. Pilon, A. de Roeck, J. Rojo, S.-S. Yu


Generators/calculators of SM +X processes

RESBOSBalazs, Berger, Mrenna,

Yuan, hep-ph/9712471, 1997

DIPHOXBinoth, Guillet, Pilon, Werlen,

hep-ph/9911340, 2000

gamma2MC, NLOBern, Dixon, Schmidt,

hep-ph/0211216, 2002

2-frag :

DIPHOX only (NLO)

Resbos only

1-frag :

- LO, effectively in Resbos

- NLO in Diphox

BORN + FRAG (and NLO corrections)

BOX (and NLO corrections)

FIXED ORDER : NLO FIXED ORDER : NLONLO with NNLL

Resummation

BORN (up to NNLO corrections)

2gammaNNLOCatani et al,

hep-ph/11102375, 2011

qT SUB : NNLO

s. gascon-shotkin moriond qcd march 15 20121 photon production at e cm = 7 tev suzanne...

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combined photon isolation

direct photon measurements

isolated photon candidates

photon production

gasconshotkin moriond

isolation efficiency

isolation distributions

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