A Journey Towards Mont Blanc

The Top of Mont blanc

TJ — Sun, 14 Aug 2011 22:17:31 +0000

Finally I reached the top of Mont Blanc. It took 11 years after I saw Mont Blanc and 2 years after I failed to summit the Mont Blanc and had to stay one night at vallot hut in 2009. This time, I prepared better than before. I was able to get used to the altitude while I was staying at Zermatt where I tried to go climbing to Matterhorn. I took the morning train to go to Nid d’Aigle at July 30.

From this last station, I hiked up for 5 hours to go to Gouter hut where I was planning to stay one night. Actually I was going to go a little high up to snow area and stay one night with only my sleeping bag. But the weather was not good. (I tried to go up and waited a little for snow to stop. But it did not happen. So I came back down.) And I decided to stay inside Gouter hut and laying myself on the chair to get some sleep hopefully two or three hours at least. Around 10 pm, the weather became clear and beautiful.

View from Gouter hut after stop snowing

Then I woke up around 1:30 am (Actually I was not able to sleep at all!) and started to go for summit of Mont Blanc. It was dark and I was alone when I walked through the ridge. Around 2 am, when I turned back I saw the line of head lamps which is pretty long. After going through steep slope and sharp Bosses Ridge and 6 hours fighting alone made me standing on the top of Alps, Mont Blanc. It was cold and hard to breathe so I just took some photos and headed down as fast as I can.

Summit Mont Blanc at 6:30 am in 2011 July 31

Sunrise from the Top of Mont Blanc

But I was so exhausted. It was already around 10:30 am when I got back to Gouter hut where I got one bowl of soup. It took almost 8 hours to go back down to Nid d’Aigle station. I don’t think I will do this alone again.

SVD unfolding

TJ — Wed, 22 Jun 2011 23:23:21 +0000

Currently I am working on unfolding on ttbar system mass distribution. I decided to use Singular Value Decomposition (SVD) method for unfolding. Unfolding is basically to go back to truth level distribution taking into account the detector effects which distorts the distribution. Simple inverting matrix method has been shown not to give reasonable result due to statistical fluctuation for ttbar system mass. This fluctuation comes from the small coefficient of decomposed singular values. In order to suppress the fluctuating components, we regularize the solution assuming that truth distribution must be smooth. For this reason, the regularization can also be called smoothing procedure. The small singular value components are suppressed by multiplying Si²/(Si²+Sk²) to 1/Si. Then if Si is small and Sk is high, the component becomes suppressed. That’s the basic idea.

Recently what I found is that with k=1, the unfolded distribution is supposed to be same as the training truth distribution. I tested. I confirmed that it is true. But I failed to have right normalization. The unfolded distribution is half smaller than what it is supposed to be.

I studied more. I realized that the scale factor, Si²/(Si²+Sk²) becomes 0.5 if you set k to be 1. So this results in the unfolded distribution is half smaller than it should be. However, we are not using k=1. Setting k=1 will give useless unfolded result which is exactly the same as the training truth distribution. In order to have reasonable result, we should set k to be larger than 2 at least.

Determining k term is not easy. From original paper, the plot of log di as a function of i seems to give some idea where we can set k to be. Another way to determine the k term is to compare unfolded result with truth distribution which is not used for producing response matrix and get chi2. I was able to obtain the plot of log di as a function of i. I will have to test with another generator as well to follow the second way.

champsfromier climbing with Yuna

TJ — Sun, 10 Oct 2010 13:06:04 +0000

doing two different things

climbing on tunnel

how to do this

When I was playing with Yuna, I saw all of sudden the interestring thing which is climbing on the tunnel. Once I touched it, it is actually quite feasible. So I tried it. And Yuna seemed to find her own interesting.

Walking down with Yuna

TJ — Thu, 23 Sep 2010 19:47:16 +0000

Yuna on the way to market

She walks now. She is enjoying it. But if there is something that gets her attention on the street, she is so concentrated on the subject and trying to taste it. It takes hours to get to market. In the photo, she is looking at her mom.

cosmique ridge

TJ — Sun, 30 May 2010 17:30:02 +0000

May 24

We took the first cable car to Aiguille du Midi and started cosmique ridge under very good weather condition. I remember last year we had hard time to find the starting point due to snow storm. In this trip, we were able to see how beautiful the view is from cosmique ridge. I also realized how important it is to have good weather condition. That will determine whether you succeed your goal or not. It is good to know where to start and how it looks like. There were still full of snow. For me, I would like to have snow. So next time if I go there again, I will go in winter. That will be more challenging.

Branching ratio of top quark decay

TJ — Sun, 21 Jun 2009 21:56:19 +0000

At the LHC, top quark production cross section is 10 times larger than Tevatron. At Tevatron pair production cross section is 67 pb while at LHC the cross section is 860 pb. So it is fair to say that top quark decay background is dominant in higgs searches at LHC.

Top quarks always decay to W boson and b quark. So the decay channel is depending on W boson decay. W boson decay to lepton and neutrino with 1/9. Since there are three kind of leptons, the rate of decaying to lepton is going to be 3/9. However tau decays eventually to electron or muon which are soft enough to be removed by applying transverse momentum requirement in the analysis. Experimentally total rate of decaying to lepton will be 2/9. The decay to hadron is 6/9.

Now think about 3 cases. Single lepton plus jets, dileptons and multi-jet.

1. Single lepton plus jets : one W decays leptonically and the other W decays hadronically. Then the rate is 2 x 2/9 x 6/9 = 29.6% of all top quark pair production. 2 is needed because there are two cases.

2. Dileptons : each W decays leptonically. 2/9 x 2/9 = 4.9%. It provides clean samples but there are two neutrinos which makes it hard to reconstruct top mass.

3. Multi-jet : The lagest sample of top quark pair production is 6 jets decay from fully hadronic decay. The branching ratio is 6/9 x 6/9 = 44.4%. However these events suffer from a very large background from multi-jet events.

I am posting it not to forget the branching ratio.

In March 2009, D0 and CDF reported electroweak single top decay discovery at Tevatron. The cross section of single top quark is 244 pb, 60 pb or 10 pb for W-gluon fusion(t-channel), tW-channel or s-channel at LHC. It will be also interesting to see the single top result from LHC.