Diffractive Structure Functions at ZEUS

Transcription

1 Graduate School of Science and High Tecnology Physics and Astrophysics XXIV cicle Diffractive Structure Functions at ZEUS and Calibration of the ECAL at CMS Candidate: V. Sola Supervisor: Prof. M. Arneodo

2 Outline ZEUS HERA Measurement of the diffractive ep cross section at high y Combination of the H1 & ZEUS diffractive cross sections CMS The ϕ symmetry method Calibration of the CMS electromagnetic calorimeter with the ϕ symmetry V. Sola II year PhD Seminar - 7//11

3 HERA Experiments.5 fb -1 collected by H1 and ZEUS experiments Final analyses of HERA data are underway V. Sola II year PhD Seminar - 7//11 3

4 Diffraction in Hadron Scattering Diffraction is a feature of hadron-hadron interactions (3% of σ tot ) IP vacuum quantum numbers IP IP LRG Elas%c Single Dissocia%on (SD) Double Dissocia%on (DD) Beam particles emerge intact or dissociated into low-mass states Very small fractional momentum losses (within a few %) Final-state systems separated by large polar angle (or pseudorapidity η = - ln[tan(θ/)] ) Large Rapidity Gap (LRG) Interaction mediated by t-channel exchange of an object with vacuum quantum numbers (no colour) Pomeron (IP) V. Sola II year PhD Seminar - 7//11 4

5 Why Diffraction at HERA? Real and virtual photons can fluctuate in hadronic states γ* vector meson, qq, qqg... γ* q ~1/x q ~ 1/Q Q = 'negative mass' of the virtual photon x = Bjorken scaling variable (as seen in the proton rest-frame) At HERA very small x are reached: long hadronic lifetime of the photon diffractive photon-proton scattering in perfect analogy with diffractive hadron-hadron scattering At HERA high Q are reached: short distances perturbative QCD V. Sola II year PhD Seminar - 7//11 5

6 Diffraction at HERA Q e Q γ* e p W X W IP X LRG Non-diffractive event ep e X p p t Diffractive event ep e Xp LRG Diffractive events contribute up to 15% of the inclusive DIS cross section V. Sola II year PhD Seminar - 7//11 6

7 Kinematics and Cross Sections Q = virtuality of exchanged photon x = Bjorken scaling variable y = inelasticity of virtual photon W = invariant mass of γ * -p system M X = invariant mass of γ * -IP system x IP = fraction of proton momentum carried by IP ß = x/x IP = fraction of IP momentum carried by struck parton t = (4-momentum exchanged at p vertex) typically: t < 1 GeV W Q x IP N = proton SD events t N = proton dissociative system DD events (background) DIS Q 1 GeV PHP Q ~ GAP where Y + = 1 + (1-y) = σ r D(4) (β,q,x IP,t) When t is not measured σ r D(3) (β, Q, x IP ) = σ r D(4) (β, Q, x IP, t) dt V. Sola II year PhD Seminar - 7//11 7

8 QCD Factorization in Hard Diffraction The QCD factorization theorem allows to write the diffractive cross section as convolution of universal diffractive parton densities f id (x,q,x IP,t) and partonic cross sections σ D ( ep exp ) ~ f id (x, Q, x IP, t) σ ei (x, Q ) Additionally, assuming Regge factorization, the diffractive parton densities are written as a term depending on x IP (Pomeron flux) times the Pomeron parton densities f id (x, Q, x IP, t) = f IP/p (x IP, t) f i/ipd (x/x IP, Q ) QCD fits to data provide sets of NLO diffractive PDF V. Sola II year PhD Seminar - 7//11 8

9 Measurement of the Diffractive Cross Section at High y

10 Samples Data 6/7 HER (E p = 9 GeV, s = 318 GeV) Luminosity = 44.5 pb -1 LER (E p = 46 GeV, s = 5 GeV) Luminosity = 13.9 pb -1 Monte Carlo (MC) - Non-Diffractive DIS DJANGOH (Q > 4 GeV ) - Photoproduction (PHP) PYTHIA (Q < 1.5 GeV ) Reweighted - DIFFRACTIVE DIS - SATRAP (Q > 4 GeV ) IP exchange Without Proton Dissociation Kinematic region Q = 13 GeV x =.3.1 y =.5.8 the high y region ( y >.5 ) is available for the first time at ZEUS V. Sola II year PhD Seminar - 7//11 9

11 Event Selection F L online trigger Good DQM run z vtx < 3 cm At least one good electron Electron finder probability cut E e > 6 GeV R CTD > cm (radius cut) 4 < E - p z < 65 GeV y EL <.95 y JB >.5 p T,h /p T,e >.3 QED Compton cut ( ep eγp ) η MAX <. Hit requirement on road MVD + CTD Geometry cut for bad CAL regions X p' e' V. Sola II year PhD Seminar - 7//11

12 η MAX Distribution MAX 5 HER Data - HER Monte Carlo DJANGOH PYTHIA SATRAP MAX 4 LER Data - LER Monte Carlo DJANGOH PYTHIA SATRAP MAX Diffractive DIS sample η MAX <. Non-Diffractive DIS background is less than 5% PHP background is negligible MAX V. Sola II year PhD Seminar - 7//11 11

13 Control Plots - HER Q EL Q Data - HER Satrap Q [GeV EL ] x EL x Bj log (x ) EL y EL y y EL β x IP 3 5 x IP M X 3 5 M X log (x Agreement between data and Monte Carlo ) IP M X [GeV] V. Sola II year PhD Seminar - 7//11 1

14 Control Plots - LER Q EL 6 5 Q Data - LER Satrap x EL 8 x Bj y EL 35 3 y Q [GeV EL ] log (x ) EL y EL 3 β x IP 9 8 x IP M X M X log (x Agreement between data and Monte Carlo ) IP M X [GeV] V. Sola II year PhD Seminar - 7//11 13

15 σ r D(3) 6/7 Measurement x IP D(3) r LRG LRG 6/7 HER LRG 6/7 LER =.7 =.468 =.56 =.115 =.5 =.769 =.545 =.319 =.151 =.7 =.816 =.615 =.385 =.191 =.91 Q (GeV ) 3 4 LRG (published) LRG 6/7 HER LRG 6/7 LER σ r D(3) measured with the same binning scheme of the last ZEUS published analysis [Nuclear Physics B 816 (9) 1-61] =.847 =.667 =.439 =.8 = =.878 =.7 =.54 =.78 =.14.5 =.94 =.773 =.57 =.335 = x IP Proton dissociation not subtracted in all samples Good agreement between the measurements In the high y (= low x IP ) region a difference between HER and LER cross sections is visible F L D(3) V. Sola II year PhD Seminar - 7//11 14

16 σ r D(3) 6/7 Measurement x IP D(3) r LRG LRG 6/7 HER LRG 6/7 LER =.7 =.468 =.56 =.115 =.5.5 =.769 =.545 =.319 =.151 =.7.5 =.816 =.615 =.385 =.191 =.91.5 =.847 =.667 =.439 =.8 = =.878 =.7 =.54 =.78 =.14.5 =.94 =.773 =.57 =.335 = x IP Q (GeV ) LRG (published) LRG 6/7 HER LRG 6/7 LER σ r D(3) measured with the same binning scheme of the last ZEUS published analysis [Nuclear Physics B 816 (9) 1-61] Proton dissociation not At fixed Q subtracted in all, β, x samples IP Good agreement between the σ D r measurements = F D y/y + F D L In the high y (= low x IP ) region a difference between HER and LER cross sections is visible F L D(3) Q = s y β x IP lower s higher y V. Sola II year PhD Seminar - 7//11 14

17 Towards the Publication Many systematic studies done hadronic final state reconstruction (calorimeter cells, energy flow, tracks, triple angle method) and correction for the noise effects η MAX reconstruction (calorimeter cells, energy flow, tracks) and threshold variations checks for possible backscattering on the beam magnets (could influence the η MAX value) studies for possible backgrounds (DD, photoproduction, Compton QED) trigger studies electron energy scale studies reweighting of the diffractive Monte Carlo studies on specific analysis cut The cross section measurement is very stable with respect to all the above studies Two independent analyses give the same results Work to be done some further reweighting on the diffractive Monte Carlo modify the selection to access lower Q region detailed study for a binning scheme optimized in the high y region First ZEUS measurement of the diffractive cross section in the high y region V. Sola II year PhD Seminar - 7//11 15

18 Combination of the H1 & ZEUS Diffractive Cross Sections

19 Motivation The key assumption is that H1 and ZEUS experiments are measuring the same cross sections at the same kinematical points Averaging H1 and ZEUS diffractive data provides a model independent tool to study consistency of the data and to reduce systematic uncertainties Experiments cross calibrate each other The combination method uses an iterative χ minimization which include full error correlations (A. Glazov DIS5 & HERA-LHC WS, code available) The combined cross sections can be used as single input in a QCD analysis to extract unique and precise proton s diffractive PDFs V. Sola II year PhD Seminar - 7//11 16

20 χ Definition [M i,true (M i + j M i α j α j )] ( α j ) χ exp(m i,true, α j )= i for a single data set M i M i,true σ i σ αj M i α j α j measured central values fitted combined H1 ZEUS values i = measured data point j = correlated systematic error source statistical and uncorrelated systematic uncertainties correlated systematic uncertainties sensitivity of datum i to systematic j fitted shift of correlated uncertainties Cross calibration of the correlated systematics between different data sets If all Δα j = standard weighted average Full χ is the sum over all χ exp V. Sola II year PhD Seminar - 7//11 17 σ i + j σ α j

21 Uncertainties Statistical uncertainties are uncorrelated Systematic uncertainties - point-to-point uncorrelated errors, added in quadrature to statistical errors giving total point-to-point uncorrelated uncertainties (additive) - point-to-point correlated errors (e.g. energy scales), often common for different measurements (e.g. PS, LRG) of a given experiment and run period (multiplicative or additive?) - overall normalization uncertainty (multiplicative) Further systematic uncertainties correlated between H1 and ZEUS (e.g. MC simulation, calibration methods,... ) are possible and need to be carefully studied V. Sola II year PhD Seminar - 7//11 18

22 Binning H1 and ZEUS binning are different both in structure (fixed β / fixed M X ) and in kinematic coverage Diffractive binning is a 3-dim binning (difficult to be visualized) In the following -dim distributions of the H1 [1] and ZEUS [] binning coverage are shown [1] Eur. Phys. J. C48 (6) [] Nuclear Physics B 816 (9) 1-61 V. Sola II year PhD Seminar - 7//11 19

23 Q H1 & ZEUS bins H1 ZEUS V. Sola II year PhD Seminar - 7//11

24 1-1 - H1 & ZEUS bins H1 ZEUS log (x ) IP V. Sola II year PhD Seminar - 7//11 1

25 Measurement Strategy Samples for the combination -> public results available at the moment - ZEUS LRG - H1 preliminary HERA II -> discussion ongoing to include also Proton Spectrometer samples, which can give complementary information through the phase space, with different precision Binning strategy -> use the H1 binning Issue: check that nothing is lost from the ZEUS kinematic coverage Issue: full decomposition of correlated systematics is not yet available for ZEUS with this binning need to check if this is feasible -> alternative solution (not favoured one): swimming of H1 & ZEUS to a common (new) grid Normalization -> 13% difference between H1 and ZEUS, compatible within (large) errors -> leaving it free in the fit (preferred) would favoured the ZEUS normalization as the ZEUS error is smaller -> difference in size of error not yet understood use all the available tagged proton data to fix the normalization V. Sola II year PhD Seminar - 7//11

26 Weighted Average D(3) * x IP r i 3 x IP 1 =.3 x = 5E-5 (i = 3) x = 8E-5 (i = ) HERA H1 ZEUS D(3) * x IP r i 3 x IP =.1 x = 5E-5 (i = 6) x = 8E-5 (i = 5) x = β x IP HERA H1 ZEUS -1 x =.13 (i = 1) x =. (i = ) 1 x =.13 (i = 4) x =. (i = 3) x =.3 (i = ) - Q [GeV H1 and ZEUS cross sections are combined using an official code available within the Collaborations and modified for the diffractive case As a first step a weighted average between H1 [1] and ZEUS [] measurements is performed ] -1 - Q x =.5 (i = 1) x =.8 (i = ) [GeV ] V. Sola II year PhD Seminar - 7//11 3

27 D(3) * x IP r i 3 x IP =.3 x = 5E-5 x = 8E-5 x =.13 HERA H1 ZEUS D(3) * x IP r i 3 x4 =.1 IP 3 x = 5E-5 x = 8E-5 x =.13 HERA H1 ZEUS x =. x =. x =.3 x =.3 1 x =.5 x =.8 x =.5 x =.8 x =.13-1 x =.13 1 x =. - x =. Q [GeV χ / ndf =.79 / 154 [Same indexing philosophy as in the previous slide] ] -1 - V. Sola II year PhD Seminar - 7//11 Q x =.3 x =.5 x =.8 [GeV ] 4

28 Future Plans Obtain a combined cross section of H1 and ZEUS with full treatment of correlated errors -> The most precise measurement of the ep diffractive cross section (preliminary result expected for DIS 11 in April) Perform a QCD fit to the combined cross section -> Unique and precise set of diffractive PDF from HERA experiments (preliminary result expected in summer) V. Sola II year PhD Seminar - 7//11 5

29 Intercalibration of the ECAL Barrel Using the Azimuthal Symmetry Method

30 The CMS Experiment at the LHC CMS is one of the two general purpose detectors at the Large Hadron Collider In CMS recorded 43 pb -1 of data from pp s = 7 TeV V. Sola II year PhD Seminar - 7//11 6

31 The Electromagnetic Calorimeter Homogeneous and hermetic detector with high granularity ( PbWO 4 crystals ) ϕ η Barrel (EB) 36 supermodules (SM) η < 1.48 Endcaps (EE) 1.48 < η < 3 Accurate intercalibration necessary to achieve energy resolution of.5% (set by H γγ channel) V. Sola II year PhD Seminar - 7//11 7

32 Phi Symmetry The Method The method is based on the assumption that for a large number of minimum bias events the total transverse energy (E T ) deposited in all crystals in a ring at fixed pseudorapidity (η) should be the same At the first order, the crystal inter-calibration constants can be defined as IC ~ ΣE T / <ΣE T > i where <ΣE T > i is the mean transverse energy collected by crystals at the same η In the determination of ΣE T only energy deposits between a low and a high threshold are considered the lower cut remove the noise contribution the upper cut avoid a possible bias from very high E T deposits (e.g. electrons originating from W or Z decays) The ϕ inhomogeneities of the detector are taken into account introducing a data-driven correction V. Sola II year PhD Seminar - 7//11 8

33 Crystal Calibration Map of the Inter-calibration Constants (IC) for the 61 EB crystals [CMS AN AN- - 15] V. Sola II year PhD Seminar - 7//11 9

34 Crystal Calibration Map of the Inter-calibration Constants (IC) after inhomogeneities corrections [CMS AN AN- - 15] V. Sola II year PhD Seminar - 7//11 3

35 Precision of the IC Constants 5 nb -1 of data used July IC from ϕ symmetry Combined IC (beam dump, π and ϕ symmetry) [CMS PAS EGM- - 3] The systematic limit of the ϕ symmetry method is already achieved The crystal-by-crystal calibration constants obtained with the ϕ-symmetry method are combined together with constants obtained from other independent methods (π and beam dump events) For the central barrel ( crystal η index 45) the combined inter-calibration precision is found to be.6% The level of precision reached in EB is such that Z width measurement is not affected V. Sola II year PhD Seminar - 7//11 31

36 ECAL Calibration Status ECAL Calibration still ongoing Precision achieved at the end of : EB Plans for the phi symmetry calibration in 11: monitoring tool for the EB active part in the calibration of the EE V. Sola II year PhD Seminar - 7//11 36

37 References The CMS Collaboration, Electromagnetic calorimeter calibration with 7 TeV data, CMS PAS EGM--3 S. Argirò, M. Obertino, R. Paramatti, V. Sola, and T. Tabarelli de Fatis, Intercalibration of the ECAL Barrel using the azimuthal symmetry method on 9/ data, CMS AN AN--15 V. Sola II year PhD Seminar - 7//11 33

38 Schools & Conferences Fi6ng Workshop 3 March - 1 April 9 DESY Hamburg, Germany CTEQ Summer School on QCD Analysis and Phenomenology 4 June - July 9 Madison, Wisconsin USA Higgs miniworkshop 3 4 November 9 Torino, Italy European School of High- Energy Physics (CERN) June - 3 July Raseborg, Finland Poster contribu%on: Calibra'on of the CMS Electromagne'c Calorimeter with first LHC data XCV Congresso Nazionale della Società Italiana di Fisica 8 September 3 October 9 Bari, Italy Talk contribu%on: Funzioni di stru?ura e PDF del protone a HERA Rencontres de Moriond - QCD and High Energy InteracTons 13 - March La Thuile, Italy Talk + Proceedings contribu%on: Diffrac'on at HERA XVIII InternaTonal Workshop on Deep- InelasTc ScaUering and Related Subjects 19-3 April Florence, Italy ICATPP Conference on Cosmic Rays for ParTcle and AstroparTcle Physics 7-8 October Como, Italy Poster + Proceedings contribu%on: Calibra'on of the CMS Electromagne'c Calorimeter with first LHC data V. Sola II year PhD Seminar - 7//11 34