GGI, Florence, 28 Oct. 2009 The Search for New States and Forces of Nature Asking for a high-p T photon in Higgs production at LHC Barbara Mele Sezione di Roma
focus on two processes : ‣ pp → H ( → bb) 2j + γ (in the SM) q q’ Gabrielli, Maltoni, B.M., M.Moretti, W � Piccinini, Pittau, NPB 781 (2007) 64 H W q’ q ‣ pp → H / A ( → ττ ) + γ (in the MSSM) γ b Gabrielli, B.M., Rathsman, b PRD 77 (2008) 015007 _ A / H b Barbara Mele 2 GGI 28/10/2009
HIGGS TOTAL CROSS SECTIONS m H (GeV) σ gg [pb] σ VBF [pb] M. Spira Fortsch. Phys. 46 (1998) 120 42 4.4 � (pp � H+X) [ pb ] 10 2 � s = 14 TeV 140 33 3.8 M t = 175 GeV gg � H 10 CTEQ4M 200 18 2.5 1 qq � Hqq _ ’ � HW -1 qq 10 300 10 1.4 -2 10 _ � Htt _ gg,qq -3 10 _ � Hbb _ _ � HZ gg,qq qq -4 10 t, b H 0 200 400 600 800 1000 W, Z H M H [ GeV ] different final states ! Barbara Mele 3 GGI 28/10/2009
but interesting σ ’ s are of the order of few fb’s ( after BR’s + cuts for enhancing signal/bckg ) GOLDEN CHANNEL ! Significance -1 CMS, 30 fb H → ZZ → 4 l 10 ) [fb] e 1 5 µ Z ( ∗ ) 4 � e + 1 H 4 H cuts (*) � � � e − 2 ZZ H opt Z ( ∗ ) � � � � 3 e + 2 Br(H H ZZ 4l � � H WW 2l2 2 � � � � NLO qqH, H WW l jj � � � 1 � qqH, H l+jet � � � � 0 qqH, H � � � 100 200 300 400 500 600 2 1 m [GeV/c ] H 100 200 300 400 500 600 σ × BR (H → 4 μ ) < 6 fb 2 M (GeV/c ) focus on H m H ~ 120 GeV Barbara Mele 4 GGI 28/10/2009 w mass:
Hbb coupling dominant in light-H decay ! [ BR(H ➞ bb) ~ 70% at m H ~ 120 GeV ] but QCD bb continuum tends to swamp any EW bb resonance at hadron colliders ! Can one constrain the Hbb coupling at all ? Barbara Mele 5 GGI 28/10/2009
Constraining Hbb coupling for light H most studied channel : pp → ttH → ttbb after including detector simulation, initial “optimistic” expectations vanished ! CMS PTDR, CERN LHCC-2006-021 Also, an expected k~1.8 factor on bckgd at NLO *** CERN-OPEN-2008-020 makes everything even worse ! (***Bredenstein, Denner, Dittmaier, Pozzorini, arXiv:0905.0110 ) Barbara Mele 6 GGI 28/10/2009
Alternatives : pp H ( bb) + 2j (VBF fusion) light Jets with large invariant mass widely separated in rapidity (forward/backward) Higgs decay products lying at intermediate rapidity q q’ µ W , Z b b H jet H W , Z q q’ jet potential difficult to assess (4-jet final state...???) Mangano, Moretti, Piccinini, Pittau, Polosa (2003) Barbara Mele 7 GGI 28/10/2009
recent proposal : Butterworth, Davison, Rubin and Salam, 2008 new strategy for pp → H ( → bb) W,Z ( → ℓℓ ’) ❄ increase ( tiny ) S/B for pp → HW(Z) → bb ℓℓ ’ by looking to events with very high-p T H and W(Z) (p T >200,300 GeV) → S/B improves ( but σ drops ...) ! challenge : high-p T H → bb quite collimated → may give a single jet → using a (QCD-motivated) subjet analysis could help ! R 200GeV R = 1.2 Eff = 70% (1%) (b) R filt b b R bb 7 300GeV R = 0.7 Eff = 70% (1%) 200GeV R = 1.2 Eff = 60% (2%) R bb g mass drop filter 300GeV R = 0.7 Eff = 60% (2%) 6 Significance values. 5 p ������������ � S = fb � B = fb S= B � fb Jet definition 4 CA, R � 1 : 2 , MD-F 0.57 0.51 0.80 K ? , R � 1 : 0 , y cut 0.19 0.74 0.22 3 L=30 fb -1 SISCONE , R � 0 : 8 0.49 1.33 0.42 2 Cross section for signal and the Z � jets back- TABLE I. 114 116 118 120 122 124 126 128 130 ground in the leptonic Z channel for 200 < p TZ = GeV < 600 Higgs Mass (GeV) and 110 < m J = GeV < 125 , with perfect b -tagging; shown for to be validated by complete our jet definition, and other standard ones at near optimal R detector simulation ! values. Barbara Mele 8 GGI 28/10/2009
γγ collisions in p Pb → p H ( → bb) Pb In the followin d ʼ Enterria and Lansberg arXiv:0909.3047 γ γ γ γ p Pb → X H Pb e p Pb → p H Pb ( − − − − given E p ~ 7 TeV (B~8.3 T) p p X p → E N(Z,A) ~ Ep x Z/A u , d , ¯ u , ¯ d , . . . ¯ b γ ¯ → p-Pb b γ at √ s NN = 8.8 TeV. H H pp collisions. First, com γ b γ b r: L pPb ∼ 10 31 cm − 2 s − 1 v γ γ A A A A (b) Semielastic case (a) Elastic case ] ] 2 2 -1 pPb @ s =8.8 TeV, 300 pb yield/[7 GeV/c yield/[7 GeV/c o Pb increases γ flux (~Z 2 ), and kills 18 18 2 m = 120 GeV/c H H b b � 16 16 pile-up (low lumi) b b � � � 14 14 o p increases γ -flux end-point and lumi 12 12 10 10 8 8 m H =120 GeV Higgs observed with 6 6 4 4 S/ √ B ~ 3 after 3-year run 2 2 0 0 100 105 110 115 120 125 130 135 140 100 105 110 115 120 125 130 135 140 Barbara Mele 9 GGI 28/10/2009 2 2 m m (GeV/c (GeV/c ) ) b b b b
summing up measurement of g Hbb challenging at LHC ! LHC potential not yet really established ! Barbara Mele GGI 28/10/2009 10
New Channel : (Gabrielli, Maltoni, B.M., M. Moretti, Piccinini, Pittau, 2007) require a further central photon from VBF pp H ( bb) + 2j + γ γ b increases triggering J efficiency ! J m H (GeV) 110 120 130 140 σ ( H γ jj ) [ fb ] 67.4 64.0 60.4 56.1 b BR ( H → b ¯ b ) 0.770 0.678 0.525 0.341 d ( ∆ R γ j > 0 . 4, p γ T ≥ 20 GeV, and m jj > 100 GeV). Barbara Mele 11 GGI 28/10/2009
qq qq H + γ � q’ q q’ q’ q q W � W,Z W,Z H H H W,Z W,Z W q’ q q’ q q q’ � � q q’ q q’ q q’ W,Z W W,Z H H H � W,Z W,Z W q’ q’ q’ q q q � from naive QED scaling : √ √ √ B ) | H γ jj ∼ √ α ( S/ B ) | H jj < ( S/ ∼ 1 / 10 ( S/ B ) | H jj Actual S/ √ B much better than this !!!! Barbara Mele 12 GGI 28/10/2009
IRREDUCIBLE BCKGD add a photon to (gluons are idle !) (q , g) (q , g) (q , g) (q , g) (q , g) (q , g) b g g g � b b b g g � � b b g g (q , g) (q , g) (q , g) (q , g) (q , g) (q , g) t,u -channel (most relevant !) (q , g) b � � (q , g) b (q , g) (q , g) (q , g) (q , g) (q , g) b b (q , g) g g (q , g) b g g � . b g � g � (q , g) g g g g (q , g) � � � � � � � b (q , g) (q , g) (q , g) (q , g) b (q , g) s-channel (suppressed at M jj ~ 1TeV) Barbara Mele 13 GGI 28/10/2009
Also, destructive interf.s in central γ emissions off q in and q fin in a t-channel gluon diagram (“coherence” effect) � � q q q { q g g b b bckg suppressed by � � b b g g (q , g) (q , g) (q , g) (q , g) requiring a central photon by O(1/10) compared to (q , g) (q , g) (q , g) (q , g) { naive QED scaling! g g b b � � b b g g q q q q (c) � (q , g) (q , g) (q , g) (q , g) (q , g) (q , g) dominant contribut. � g g g � b b (suppressed by b-quark b � � � � b b electric charge) b g g g (q , g) (q , g) (q , g) (q , g) (q , g) (q , g) Barbara Mele 14 GGI 28/10/2009
switching off the γ bb coupling in irred. bckg photon rapidity distr.s (optimized cuts) Barbara Mele 15 GGI 28/10/2009
what about signal ? W charged current spoils destructive interference at large angle ! σ ( C ) ( H γ jj ) σ ( C ) ( H jj ) = 0 . 013 , (WW → H) but Z neutral current follows BCKG pattern !!! σ ( N ) ( H γ jj ) (ZZ → H) σ ( N ) ( H jj ) = 0 . 0016 s p γ T ≥ 20 GeV, , | η γ | < central photon singles out WW over ZZ fusion !!! ∼ 2 . 5, d ∆ R j γ ≥ 0 . 7, Barbara Mele 16 GGI 28/10/2009
basic cuts : EVENT SELECTION p j p b T ≥ 30 GeV , T ≥ 30 GeV , ∆ R ik ≥ 0 . 7 , | η γ | ≤ 2 . 5 , | η b | ≤ 2 . 5 , | η j | ≤ 5 , m jj > 400 GeV , m H (1 − 10%) ≤ m b ¯ b ≤ m H (1 + 10%) , { 1) p γ T ≥ 20 GeV , then, look at distrib’s : 2) p γ T ≥ 30 GeV , d σ d σ d σ d σ d σ , , , , | ∆ η jj | , dp j 1 dp b 1 dm jj dm γ H T T add optimized cuts : p j 1 p b 1 m jj ≥ 800 GeV , T ≥ 60 GeV , T ≥ 60 GeV , | ∆ η jj | > 4 , m γ H ≥ 160 GeV , ∆ R γ b/ γ j ≥ 1 . 2 . well isolated photon Barbara Mele 17 GGI 28/10/2009
m jj distribution critical to enhance S/B ( even more than in plain VBF !!! ) S B Barbara Mele 18 GGI 28/10/2009
p T (b1) p T (j1) m( γ H) Δ η (jj) Barbara Mele 19 GGI 28/10/2009
irreducible bckgr σ ’s (optimized cuts) s p γ T ≥ 20 GeV, sub-processes σ i (pb) σ i / σ σ γ (fb) σ γ i / σ γ i gq → b ¯ b gq ( γ ) 57.2(1) 55.3 % 17.3(1) 51.6 % gg → b ¯ b gg ( γ ) 25.2(1) 24.4 % 3.93(3) 11.7 % b qq � ( γ ) qq � → b ¯ 7.76(3) 7.5 % 4.04(2) 12.1 % qq → b ¯ b qq ( γ ) 6.52(2) 6.3 % 4.49(3) 13.4 % q � ( γ ) q � → b ¯ q ¯ b q ¯ 4.60(2) 4.4 % 2.28(2) 6.8 % q → b ¯ q ¯ b q ¯ q ( γ ) 2.13(2) 2.1 % 1.21(2) 3.6 % gg → b ¯ b q ¯ q ( γ ) 0.0332(7) 0.03 % 0.124(3) 0.37 % q → b ¯ q ¯ b gg ( γ ) 0.0137(2) 0.01 % 0.094(2) 0.28 % q � ( γ ) q → b ¯ q ¯ b q � ¯ 0.000080(3) 0.00007 % 0.00080(8) 0.002 % ( m H =120 GeV ) bckg ( γ ) / bckg ~ 33 fb / 103 pb ~ 1/3000 cf. signal( γ ) / signal ~ 1/100 note : conservative choice of QCD scales in the bckg evaluation ! Barbara Mele 20 GGI 28/10/2009
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