12 March 2006, LCWS06, BangaloreS. Bhattacharya 1 Satyaki Bhattacharya The Standard Model Higgs Search at the LHC University of Delhi

12 March 2006, LCWS06, BangaloreS. Bhattacharya 2 * numbers are for barrel data taking starts 2007 Startup Luminosity 2X10 33 cm -2 /s that is: 20 fb -1 per year Silicon Tracker PbWO 4 ECAL sampling brass HCAL solenoid 4Tesla field MUON Chambers

12 March 2006, LCWS06, BangaloreS. Bhattacharya 3 Rates at the LHC Bunch crossing at 40MHz (~ 40 TBps) Leve-1 rate capability 100KHz (100 GBps) HLT capability ~ 100 Hz, gg  H < 1Hz bb almost 10 7 X gg  H Makes Higgs search (especially at low mass) difficult –Look for sharp peaks (e.g. H   ) –Complex signatures (e.g. additional jets)

12 March 2006, LCWS06, BangaloreS. Bhattacharya 4 Higgs production at the LHC gg  H High gluon flux – dominant although loop process Vector Boson Fusion (VBF) 10% at M H =100GeV Comparable to gg->H at M H =1 TeV ttH, bbH,HW,HZ

12 March 2006, LCWS06, BangaloreS. Bhattacharya 5 Decays and Search Strategy M H < ~140 GeV H  bb dominant gg  H  bb : background too large ttH  ttbb possible H   –  small BR but very clean M H < ~500 GeV GeV H  WW*/WW  l l  (serious tt,Wtb background) GeV H  ZZ  4l gives highest sensitivity between GeV M H > ~500 GeV  H large, use channels with large BR, H  ZZ/WW VBF x-sec large and can be used search channels

12 March 2006, LCWS06, BangaloreS. Bhattacharya 6 Low mass (<140 GeV): H     =646MeV Two clean electromagnetic clusters For unconverted photons Backgrounds: gg,qq  ,qg  q  5  discovery in ~15 fb -1 events/50MeV m  for 130 GeV Higgs

12 March 2006, LCWS06, BangaloreS. Bhattacharya 7 H  ZZ  4  Clean, resolution better than 1GeV Discovery Luminosity:

12 March 2006, LCWS06, BangaloreS. Bhattacharya 8 Interm. Mass: H  WW  ll'X Isolated leptons + E T miss tt serious background  Require central jet veto

12 March 2006, LCWS06, BangaloreS. Bhattacharya 9 High Mass: ZZ  lljj H  ZZ  lljj has large branching fraction at higher masses. Mass reconstruction possible but  H is large

12 March 2006, LCWS06, BangaloreS. Bhattacharya 10 Vector Boson Fusion H decay Features: Forward tagged jets Relatively high pT Higgs Important at very high mass (10% at low mass, total at very high mass) Very useful for WW*, also used for  at lower mass Ref: sn-ATLAS

12 March 2006, LCWS06, BangaloreS. Bhattacharya 11 Higgs Couplings All Higgs decays and production x-section depend on g W, g Z, g t, g b, g  Determine relative partial widths from measured rates in different channels ATLAS has used a global maximum likelyhood fit method to extract relative couplings.   /  W,  /  W,  Z /  W can be determined within 15-60% accuracy (L = 30 fb -1, m H >120 GeV.) g  2 /g W 2, g  2 /g W 2, g z 2 /g W (L = 30 fb -1, m H >125 GeV.) g t 2 /g W 2 within 30% (L = 300fb -1 ) Ref: ATLAS-phys

12 March 2006, LCWS06, BangaloreS. Bhattacharya 12 Higgs Couplings (contd.)

12 March 2006, LCWS06, BangaloreS. Bhattacharya 13 Discovery reach of CMS CMS can probe the entire “allowed” mass range 5  discovery possible in few months in many channels Total H   H  ZZ  l + l - l + l - H  WW  ll

12 March 2006, LCWS06, BangaloreS. Bhattacharya 14 Discovery Reach of the ATLAS

12 March 2006, LCWS06, BangaloreS. Bhattacharya 15 Summary CMS+ATLAS are capable of searching SM Higgs over the entire allowed mass range between LEP M H limit and ~ TeV (perturbative bound) Detailed simulation studies have been done for all major discovery channels (full detector simulation, pileup, systematics…) Optimistic: 5  discovery possible in few months Few hundred MeV mass resolution from H  , H  ZZ  4l for low-intermediate mass Higgs Also –Properties of Higgs (coupling,CP) can be measured with 100fb -1

12 March 2006, LCWS06, BangaloreS. Bhattacharya 16 Extras

12 March 2006, LCWS06, BangaloreS. Bhattacharya 17 ATLAS Detector

12 March 2006, LCWS06, BangaloreS. Bhattacharya 18 CMS Trigger Rates CMS total level1 rate is 16 kHz at startup Total High Level Trigger (HLT) is 100 Hz.

12 March 2006, LCWS06, BangaloreS. Bhattacharya 19 h 30fb -1 Decay BRs and searches for h are like SM Higgs

12 March 2006, LCWS06, BangaloreS. Bhattacharya 20 H ± 30 fb -1 For charged higgs associated production with top is dominant

12 March 2006, LCWS06, BangaloreS. Bhattacharya 21 A/H 30 fb -1 At large tan  A/H coupling to down type fermion is strong and H production with bb and H decay to  become important

12 March 2006, LCWS06, BangaloreS. Bhattacharya 22 MSSM Higgs Production gg  H most important at low mass and low tanb light higgs production x-sections similar to SM higgs at high tan  gg/qq  Hbb dominant for heavy Higgs for H ± tt  tH - b is most important

12 March 2006, LCWS06, BangaloreS. Bhattacharya 23 MSSM Higgs Production (ii)

12 March 2006, LCWS06, BangaloreS. Bhattacharya 24 MSSM Discovery reach Ref: Paris Sphicas, Physics at LHC,Vienna,2004

12 March 2006, LCWS06, BangaloreS. Bhattacharya 25 MSSM discovery reach (ii)